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Difference Between PAM and IBM – Plasma Arc Machining and Ion Beam Machining

Pintu — Mon, 11 May 2020 12:45:51 +0000

Different forms of energy (such as mechanical, thermal, electrical, chemical, electro-chemical, light, etc.) are directly utilized in advanced machining processes to realize material removal from the workpiece for fabricating intended 3-D feature following the subtractive manufacturing approach. Plasma Arc Machining (PAM) is one such advanced machining process where thermal energy (heat) is primarily used to melt down and vaporize material from the workpiece. A high temperature jet of thermal plasma is first obtained by intensely heating a suitable gas (such as air, helium, nitrogen, argon) with the help of an electric arc. This high velocity plasma jet is then directed towards the workpiece using a nozzle. PAM plasma temperature can reach 20,000°C or even more. When the plasma jet having such a high temperature strikes the work surface, the workpiece material at that spot quickly melts down and vaporizes owing to this extreme temperature of the plasma. While a smaller fraction of the material is removed in the form of vapour of the concerned workpiece material, majority of the material in molten state is blown away by the high velocity plasma jet. Thus material removal for plasma cutting or machining occurs in both the ways. PAM can be applied to electrically conductive as well as non-conductive materials; however, the electric arcing fashion will be different (transferred plasma arc and non-transferred plasma arc). Although PAM offers a relatively higher material removal rate, its cut quality is affected by wider kerf, wider heat-affected zone, stray cutting, and deformation. The PAM process is incessantly noisy, but it does not require a vacuum chamber for its operation.

The Ion Beam Machining (IBM) process is another advanced machining process; however, its working principle is not based on thermal energy. Rather, it is one mechanical energy based process where momentum transfer takes place in atomic level. In IBM, ample ions are first generated by glow-discharge across two electrodes having very high potential difference (around 100 kV). Such ions are then constricted in the form of a beam and accelerated towards the workpiece. When the narrow beam of high velocity ions strikes the workpiece, it can dislodge atoms from the work surface without heating or melting the substrate. The corresponding mechanism of material removal is terms as “sputtering”, where high velocity ions strike the atoms of a solid surface to knock them off by momentum transfer. Accordingly, material removal occurs in atomic form, and thus, it generates highly finished surface. Moreover, IBM process is free from thermal damages, but it requires a soft-vacuum chamber for its operation (this increases the length of mean free path, and thereby reduces the chance of collision between air molecules and ions). Several similarities and differences between PAM and IBM are given below in table format.

Similarities between PAM and IBM

Both PAM and IBM are considered as advanced machining processes (AMP) or non-traditional machining (NTM) processes.
Physical contact between a solid tool and workpiece does not exist in either of these two processes. Accordingly, these processes are free from burr formation, progressive wear, mechanical residual stress, etc. However, thermal residual stress may develop in PAM due to thermal cycle.
Process capability for both the cases is independent of mechanical and chemical properties of the workpiece material.
Both the processes can be applied to electrically conductive and non-conductive materials. Note that the arcing fashion for PAM will be different for conductive and non-conductive materials.
Both the plasma beam and ion beam are made of charged particles.
Electrodes are indirectly used in both the processes to generate plasma or ions.
These processes are commonly integrated with computer control system to facilitate precise control.

Differences between PAM and IBM

Plasma Arc Machining (PAM)	Ion Beam Machining (IBM)
PAM is one thermal energy based advanced machining process.	IBM is one mechanical or kinetic energy based advanced machining process.
Mechanism of material removal in PAM is a combination of (i) vaporization, and (ii) blowing away in molten state.	Mechanism of material removal in IBM is sputtering (dislodging by bombarding ions).
A constricted jet of intensely hot plasma is used to supply thermal energy for material removal.	A beam of high velocity ions is used to transfer momentum for dislodging atoms from the working surface.
Material removal in PAM takes place in the form of vapor of the concerned workpiece material. However, considerable fraction of the material is blown away in molten form.	In IBM process, atom (or a cluster of atoms) is removed directly from the workpiece surface. No such melting or vaporization occurs here.
Power density of the plasma jet is relatively higher (10² to 10³ W/mm²).	Power density of ion beam is significantly less (10^-2 to 10⁰ W/mm²).
Plasma forming gases (air, argon, nitrogen, hydrogen) must be continuously pumped into the high pressure gas chamber. This gas gets converted to thermal plasma when it flows coaxially with the high temperature arc, and finally comes out of the chamber in the form of a high velocity plasma jet.	A gas (argon) is introduced in a vacuum chamber at a relatively lesser flow rate. This gas is then ionized by striking with energized free electrons (electron ionization). The ionized particles are then manipulated to form a narrow but high velocity ion beam.
PAM process does not require a vacuum chamber for its operation. It can be operated in open atmosphere.	IBM process necessitates a soft vacuum chamber having pressure in the order of 10^-3 to 10^-5 atm.
PAM process is associated with excessive thermal damage of the workpiece. It produces a wide heat affected zone.	Thermal damage in IBM process is mostly neglected (a very narrow zone of atomic level may get affected by impact).
PAM tends to deform the object owing to very high temperature non-uniform heating and subsequent cooling of a wide area.	IBM process is free from deformation as heating is mostly negligible.
PAM process is usually very noisy. So personal protective equipment (such as ear muffler) are indispensably necessary.	IBM process is not noisy.
PAM can be used to cut thick objects (even up to 50 mm).	IBM is not suitable for deep cutting. It is preferred for micro-fabrication, smoothening and surface contouring.
PAM usually does not generate highly finished surface. Concerned roughness is in the order of 0.5 – 2.0 μm.	IBM is especially suitable for generating highly finished surfaces having nanometric roughness (10 nm or even lower).

References

Nonconventional Machining by P. K. Mishra (Narosa Publishing House).
Allen et al. (2009). Ion beam, focused ion beam, and plasma discharge machining. CIRP Annals. https://doi.org/10.1016/j.cirp.2009.09.007

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Difference Between Transferred Arc and Non-Transferred Arc Plasma Torch

Pintu — Sat, 09 May 2020 12:49:59 +0000

Thermal plasma is the ionic form of matter that is obtained by heating suitable gas to a very high temperature. Plasma consists of excited ions of gaseous atoms and free electrons (thus plasma can conduct electricity). Localized temperature of plasma can reach 30,000°C or even more. Such a high temperature can virtually melt and vaporize any material regardless of its physical state. An artificially created controllable jet of high temperature plasma can be utilized for several purposes including cutting or machining, welding, coating, heat treating, etc. All these processes utilize the heat of the plasma jet in different ways to fulfill the intended purpose. However, the basic requirement for such activity is a constricted jet of high temperature plasma flowing at high velocity. In order to artificially generate plasma, a plasma-forming gas (can be air, hydrogen, argon, or nitrogen) is introduced into a gas chamber at a high flow rate (1 – 5 m³/h). The gas chamber contains a tungsten electrode, which is connected with the negative terminal (cathode) of a DC power source. The positive terminal of the power source can be connected either with workpiece or with the nozzle of the gas chamber. Based on this connection, plasma torch (plasmatron) can be classified as transferred arc plasma torch and non-transferred arc plasma torch.

In transferred arc plasma torch, the workpiece is made an integral part of the electrical circuit. Therefore, the positive terminal of the DC power source is connected to the workpiece (while the electrode remains connected with the negative terminal). No need to mention that the workpiece must be electrically conductive. When sufficient voltage (around 200 V) is applied across two terminals, a long electrical arc forms between the electrode and workpiece through the small nozzle opening. As it is difficult to establish the arc directly between the electrode and workpiece (because of 5 – 10 mm gap), an auxiliary arc is established between the electrode and nozzle at the beginning of the work for a very short period. The plasma-forming gas that is pumped into the gas-chamber comes out through the small nozzle opening surrounding the electric arc. Owing to the high arc temperature, the gas automatically gets converted to plasma and emerges out of the nozzle in the form of a jet to finally strike the workpiece. The transferred arc plasma torch is also known as direct arc plasma torch as electrical connection is made directly between the electrode and workpiece. The problem with this arrangement arises when the workpiece is not electrically conductive. In such cases, the copper nozzle is connected to the positive terminal (anode) of the DC power source, while no connection is made with the workpiece. Such an arrangement is known as non-transferred arc plasma torch or indirect arc plasma torch. Here electric arc forms between the electrode and the nozzle. However, the plasma-forming gas forcefully directs the arc into the small nozzle opening, while itself gets converted to plasma and comes out of the nozzle as a high temperature high velocity jet. Various similarities and differences between transferred and non-transferred plasma torch are given below in table format.

Similarities between transferred and non-transferred arc plasma torch

In both the cases, an electrode is indispensably used to liberate electrons. This electrode is given negative polarity (cathode).
Both the arc systems are based on DC (direct current). The voltage remains around 200 V, while current can be as high as 1,000 A.
Plasma forming gas (like air, hydrogen, argon, or nitrogen) is also required to pump into the gas chamber continuously regardless of the type of plasma torch used.
In both the cases, an electric arc supplies necessary heat to form plasma.
Irrespective of the torch type, plasma beam operations are very noisy. Accordingly, proper personal protection must be used while operating plasma machines.

Differences between transferred and non-transferred arc plasma torch

Transferred Arc Plasma Torch	Non-transferred Arc Plasma Torch
The electric arc is constituted between an electrode and the workpiece. However, an auxiliary arc is established between the electrode and nozzle at the beginning of the work for a very short period.	The electric arc is constituted between an electrode and the nozzle, and the same arc is continued for the entire operation.
Here the workpiece is made anode (positive terminal of DC power source), whereas the nozzle is kept electrically neutral. Cathode is always a copper electrode.	Here the workpiece is kept electrically neutral, whereas nozzle is made anode. As usual, cathode is always a copper electrode.
Direct arc plasma torch can be applied to electrically conductive workpieces only.	Indirect arc plasma torch can be applied to every workpiece regardless of electrical conductivity. However, it is preferred for non-conducting materials.
Direct arc has relatively higher electro-thermal efficiency (85 – 95%).	Indirect arc has comparatively low electro-thermal efficiency (65 – 75%).
Direct arc is overwhelmingly used for machining (or cutting), welding, hardfacing, remelting, and spraying.	Indirect arc is preferred for flame spraying, spheroidizing heat treatment, ore processing, etc.
Transferred arc plasma torch is also known as “Direct Arc Plasma Torch” because the arc is maintained directly between the electrode and workpiece.	Non-transferred arc plasma torch is also known as “Indirect Arc Plasma Torch” because the arc is not maintained between the electrode and workpiece though the workpiece receives the heat.

References

Modern Arc Welding Technology by Ador Welding Limited (Oxford and IBH Publishing Company Pvt. Ltd.).
Nonconventional Machining by P. K. Mishra (Narosa Publishing House).

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Difference Between LBM and PAM – Laser Beam Machining and Plasma Arc Machining

Pintu — Sat, 09 May 2020 12:31:26 +0000

Non-traditional machining (NTM) processes can directly employ various forms of energy for removing material from workpiece in order to fabricate the intended 3-D feature. EDM, LBM, EBM, and PAM are four common NTM processes that use thermal energy (heat) to selectively remove material. In these processes, material removal mostly takes place in vaporized and sometimes in molten state. The source of heat is, however, different for these four processes. Laser Beam Machining (LBM) is one thermal energy based NTM process where material is removed by melting and vaporization through the action of a high energy density laser beam. First, a monochromatic and coherent beam of laser (Light Amplification by Stimulated Emission of Radiation) is generated using suitable lasing medium (Nd-YAG, Nd-Glass, Ruby, CO₂). The beam is then constricted to increase energy density, and the constricted laser beam is focused on the working surface with the help of lenses. Intense heat generation occurs at a very narrow spot where the laser beam strikes the workpiece surface leading to an instantaneous localized temperature rise of the order of 10,000°C. Such a high temperature can rapidly melt down and vaporize any solid material. Accordingly, majority of the material removal occurs in vapour state. The workpiece is usually integrated with the CNC system to move the worktable at a specified path at pre-set feed rate for cutting a particular profile.

Plasma is an extremely hot matter consisting of ionic particles. Plasma Arc Machining (PAM), also known as Plasma Arc Cutting (PAC), utilizes a high velocity jet of plasma to supply thermal energy (heat) for melting and vaporizing the workpiece. In order to artificially generate plasma, a suitable plasma forming gas (such as air, argon, nitrogen, and hydrogen) is first introduced into a gas chamber under high pressure. An electric arc is also constituted between a tungsten electrode and copper nozzle of the chamber (or workpiece, if it is conductive). The plasma forming gas is then forced to pass surrounding the electric arc through the small nozzle opening. Owing to the intense arc heating, the gas gets converted to high temperature plasma. This plasma jet is then directed towards the workpiece, where it rapidly elevates the cutting zone temperature to as high as 20,000°C leading to melting and vaporization. Although a fraction of the workpiece material is removed in vaporized form, rest of the material in molten state is blown away from the cutting zone by the high velocity plasma jet. Thus, material removal in PAM is a combination of (i) displacing the molten metal and (ii) vaporizing the material. Plasma jet is relatively wider, and thus the process is associated with broader heat affected zone and wider kerf. PAM is not suitable for precise and miniaturized feature fabrication. Rather it is preferred for thick cutting or plasma heating regardless of the mechanical, electrical and chemical properties of the sample. Various similarities and differences between LBM and PAM are given below in table format.

Similarities between LBM and PAM

Both the LBM and PAM processes are thermal energy based non-traditional machining (NTM) processes as material removal takes place by melting and vaporization of workpiece materials. However, the source of heat is different for these two processes.
No vacuum chamber is required for operation of LBM or PAM process. This is unlike EBM and IBM (FIB) where the work chamber must have low vacuum pressure.
Both the processes can be applied for electrically conductive as well as non-conductive materials. Electrical conductivity plays no role on the performance and applicability of these two processes. However, the arcing fashion in PAM is different for electrically conductive and non-conductive materials.
Both the LBM and PAM processes can create thermal damages to the workpiece. A narrow heat-affected zone (HAZ) exists on the processed samples. However, this HAZ is usually wider for PAM as compared to that for LBM.
In both the processes, several parameters and various movements are usually controlled by CNC system.

Differences between LBM and PAM

Laser Beam Machining (LBM)	Plasma Arc Machining (PAM)
A high intensity beam of laser (coherent photon particles) is used to supply heat for melting and vaporizing the workpiece material.	A high temperature plasma jet (highly excited ions and electrons) is used as the heat source for melting and vaporizing the workpiece material.
No separate gas is required to supply to generate laser beam as it is directly generated using the lasing medium (Nd-YAG, Nd-Glass, Ruby, CO₂) with the assistance of flash tube.	Suitable plasma forming gas (air, argon, nitrogen, hydrogen) is required to supply continuously to a closed gas chamber under high pressure, which ultimately comes out as high temperature plasma jet.
No electric arc is required to establish in LBM process.	An electric arc is essentially required to supply immense heat for converting the gas into plasma. This arc can be constituted between (i) a tungsten electrode and (ii) nozzle or workpiece.
Although melting and vaporization both occur simultaneously, most of the material is removed in the form of vapour. Only small percentage is removed in molten form.	Both melting and vaporization occur in PAM too; however, majority of the material is blown away by the high velocity plasma jet when the workpiece material remains in molten state. A comparatively smaller fraction of the material is removed in vaporized form.
The laser beam characteristics (such as beam diameter, energy density, incidence timing, incidence pattern, etc.) can be controlled effectively and easily. Such parameters can also be changed rapidly as per the desired level.	PAM is less flexible in terms of parameter controlling and their variation.
Laser beam can be allowed to strike the workpiece either continuously or intermittently (as in the case of femtosecond laser).	Plasma jet is usually allowed to continuously strike the workpiece.
In LBM, the kerf width can be maintained very small (even below 0.1 mm).	In PAM, kerf is relatively wider (3 – 10 mm).
A narrow localized heat-affected zone can be noticed in the specimens after cutting by LBM. So it causes very little thermal damage to the workpiece.	Specimens cut by PAM can have significantly wider heat-affected zone. The extent of thermal damage made in PAM is more.
LBM process capability is affected by optical properties of the workpiece surface (transparent, translucent and opaque). Highly reflective surface can reduce rate of heat input.	PAM process is not affected by the optical properties of the workpiece surface.
LBM process is not noisy and can be carried out without specific personal protections.	PAM process is very noisy. Thus proper hearing protection (like ear muffler) is needed for operators.

References

Unconventional Machining Processes by T. Jagadeesha (I. K. International Publishing House Pvt. Ltd.).
Advanced Machining Processes by V. K. Jain (Allied Publishers Private Limited).
Nonconventional Machining by P. K. Mishra (Narosa Publishing House).

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Difference Between EBM and IBM – Electron Beam Machining and Ion Beam Machining

Pintu — Fri, 08 May 2020 17:52:59 +0000

Non-traditional machining (NTM) processes can directly utilize different forms of energy (like mechanical, thermal, chemical, electric, light, etc.) to selectively remove material from the workpiece in order to fabricate intended 3-D feature. These processes eliminate the barrier imposed by mechanical strength and hardness of the workpiece for processing by a conventional metal cutting process. Several NTM processes have emerged over the last few decades, which include AJM, USM, CHM, ECM, LBM, PAM, EBM, IBM, etc. Each of these processes has distinct capability in terms of processable materials, feature size, achievable accuracy, extent of collateral damage, etc. Electron Beam Machining (EBM) is one thermal energy based NTM process where a concentrated beam of high velocity electrons is used to remove material by melting and vaporization. First ample free electrons are generated in a tungsten cathode, and these electrons are then accelerated in an electric field by means of high potential difference. Several lenses are used to constrict the high velocity electrons in the form of a narrow beam. This electron beam is allowed to strike the workpiece where the kinetic energy of the electrons is converted into thermal energy leading to immense heat generation. Localized temperature rise can be as high as 10,000°C, which can melt down and vaporize the workpiece material leading to material removal. The entire EBM process is carried out in a high vacuum (1 × 10^-8 atm) chamber (i) to avoid excessive collisions between the electrons and air molecules, and (ii) to protect tungsten filament from oxidation.

On the other hand, Ion Beam Machining (IBM) utilizes a concentrated beam of high velocity ions to remove material. However, material removal in IBM does not take place by melting and vaporization. Rather, the high velocity ions strike the molecules of the workpiece surface and knock them out by means of momentum transfer. The associated mechanism of material removal is termed as “sputtering” where incidental ions strike a solid surface to dislodge one or more atoms from the surface leading to material removal in atomic level. Sometimes assistance of a gaseous medium is also taken for efficient knocking of the surface atoms. Owing to atomic removal, the material removal rate in IBM is very low; however, it can produce highly finished surface. Moreover, ions don’t generate excessive heat on the workpiece surface, and thus extent of thermal damage is also negligible. Though IBM process is carried out in a soft vacuum chamber, it does not require very low pressure to be maintained as it is required in EBM. A variant of IBM process, focused ion beam (FIB) is gaining popularity in micro- and nano-fabrication domains owing to its inherent capability of manipulating atoms. Various similarities and differences between EBM and IBM processes are given below in table format.

Similarities between EBM and IBM

Both electron beam and ion beam machining processes are categorized as non-traditional machining (NTM) processes or advanced machining processes (AMP). However, the mechanism of material removal in EBM and IBM is different.
Both follow the subtractive manufacturing approach (material is removed gradually from a solid block) for fabricating intended 3-D feature.
Capability of these two processes does not depend on mechanical strength or hardness of the sample material. Chemical properties of the workpiece also have no influence on these two processes. However, IBM process relies on surface binding energy of the workpiece.
In none of these two processes, physical contact between the tool and workpiece exits. In fact, no such solid tool is employed in these processes. Thus these processes are free from burr formation, gradual tool wear, mechanical residual stress, etc. It is worth mentioning that residual stress may develop owing to thermal cycle in EBM.
Both are suitable for small components as the process must be carried out in a vacuum chamber with controlled environment.
These processes are commonly integrated with computer control system to facilitate precise control.

Differences between EBM and IBM

Electron Beam Machining (EBM)	Ion Beam Machining (IBM)
EBM is a thermal energy based advanced machining process.	IBM is one mechanical or kinetic energy (momentum transfer) based advanced machining process.
A concentrated beam of high velocity electrons is used to supply heat for removing material from workpiece.	A beam of high velocity ions is used for material removal purpose.
The mechanism of material removal in EBM is melting and vaporization.	The mechanism of material removal in IBM is sputtering (or atom dislodging by ion impact).
Material removal in EBM takes place in the form of vapour of the concerned workpiece material. However, small fraction of material is removed in molten form.	In IBM, individual atom (or a cluster of atoms) is directly dislodged from the workpiece surface. Continuous dislodging is required to realize sizeable amount of material removal. However, no melting or vaporization takes place.
Power density of the electron beam is relatively higher (10³ to 10⁶ W/mm²).	Power density of ion beam is significantly less (10^-2 to 10⁰ W/mm²).
EBM process is carried out in a vacuum chamber having very low pressure (1 × 10^-8 atm) to avoid collision of electrons with air molecules and to protect hot tungsten filament.	IBM process requires a soft vacuum chamber with comparatively higher pressure, in the order of 10^-3 to 10^-5 atm.
X-ray generation intrinsically occurs in EBM process. Thus, the process is somewhat risky to the operator.	No such X-ray generation takes place in IBM process. So, it is relatively safer to operate.
EBM process is applicable to electrically conductive materials only, as the workpiece is grounded (earthen) to dispense electrons for maintaining electrical neutrality. (The electron beam strikes the workpiece to generate thermal energy. These electrons must be continuously dispensed from workpiece to avoid accident and reduce repulsion force to the incident beam).	IBM process can be applied to electrically conductive as well as non-conductive materials.
EBM process capability depends on the thermal properties (such as conductivity, diffusivity, etc.) of the workpiece material.	IBM process is mostly independent of the thermal properties of the workpiece material.
It can cut features having high aspect ratio (up to 5:1). Deep hole drilling and thick cutting (up to 6 mm thickness) can be carried out using EBM.	It is not suitable for deep cutting or fabricating features having high aspect ratio. IBM is preferred for shallow contouring, micro-cutting, polishing, etc.
The width or area of thermal damage observed in EBM process is relatively wider.	Impact damage on the workpiece is very narrow in IBM process. Often, no palpable collateral damage is perceived.
Material removal rate (MRR) of EBM process is significantly higher (around 40 mm³/min). So it is a productive and economic process.	Material removal rate (MRR) of IBM process is very low (in the order of 2 × 10^-4 mm³/min).

References

Unconventional Machining Processes by T. Jagadeesha (I. K. International Publishing House Pvt. Ltd.).
Nonconventional Machining by P. K. Mishra (Narosa Publishing House).
Allen et al. (2009). Ion beam, focused ion beam, and plasma discharge machining. CIRP Annals. https://doi.org/10.1016/j.cirp.2009.09.007

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Difference Between LBM and IBM – Laser Beam Machining and Ion Beam Machining

Pintu — Fri, 08 May 2020 17:44:30 +0000

Several advanced machining processes have been developed over the last few decades to cater the evergrowing demand of high quality small-scale products made of a wide variety materials with highly finished surfaces and close tolerance. Laser beam machining and ion beam machining are two such processes that follow subtractive manufacturing approach to fabricate intended features with improved accuracy and tight tolerance. However, their working principle and extent of capability are different. Laser Beam Machining (LBM) is one thermal energy based non-traditional machining process where a concentrated and coherent beam of photons (laser) is used to supply thermal energy (heat) for selectively removing material from the workpiece. When the laser beam strikes the workpiece, intense heat generation takes place in a narrow localized zone that can cause an instantaneous temperature rise of the order of 10,000°C. Such a high temperature can virtually melt and vaporize any solid material. Accordingly, the material is mostly removed in the form of vapour of the concerned workpiece material. The LBM process does not require a vacuum chamber for its operation. Though LBM offers relatively high material removal rate, it leads to the formation of a narrow heat-affected zone (HAZ). The process is also affected by re-cast layer formation and taper cutting while machining thick samples.

Ion Beam Machining (IBM) is another non-traditional machining process, but here material removal occurs due to mechanical impact. Unlike LBM, here thermal energy (heat) has no direct role in removing material. In IBM, a concentrated beam of high velocity ions is allowed to strike the workpiece surface. Upon striking, momentum transfer takes place between the incidental ions and the atoms of the workpiece surface. This results in dislodging of atoms from the surface leading to material removal. Thus material removal occurs in atomic level without any melting or vaporization. Although IBM offers very low material removal rate (MRR), it generates highly finished surface with nanometric level roughness. In fact, a variant of IBM known as Focused Ion Beam (FIB) is preferred for micro- or nano-fabrication and surface smoothing. Furthermore, the process is free from collateral thermal damages and re-cast layer formation. However, the IBM process must be carried out in a soft vacuum chamber to avoid haphazard collision between the ions and air molecules. Creating vacuum chamber is time consuming, which makes the overall process less productive. Various similarities and differences between LBM and IBM processes are given below in table format.

Similarities between LBM and IBM

Both laser beam and ion beam machining processes are considered as non-conventional machining processes (NTM) or advanced machining processes (AMP).
In none of the processes, there exists physical contact between a solid tool and the workpiece. So these processes are free from burr formation, residual stress generation, negative influences of gradual wear, etc. Note that, residual stress generation may occur in LBM owing to thermal cycle.
Both the processes are independent of electrical, chemical, and mechanical properties of the workpiece material. So these processes can be applied on a wide variety of materials.
These processes are expensive, and thus are used for sophisticated works only.
These processes are commonly integrated with computer control system to facilitate precise control.

Differences between LBM and IBM

Laser Beam Machining (LBM)	Ion Beam Machining (IBM)
LBM is a thermal energy based non-traditional machining process.	IBM is essentially a mechanical or kinetic energy (momentum transfer) based non-traditional machining process.
A high intensity beam of laser (coherent photons) is used to remove material from workpiece.	A beam of high velocity ions are used to remove material from workpiece.
The mechanism of material removal in LBM is instantaneous melting and vaporization.	The mechanism of material removal in IBM is sputtering (or atom dislodging by ion impact).
In LBM, material is removed in the form of vapour of the concerned workpiece material. However, a small fraction of material is removed in molten state.	In IBM, individual atom (or a cluster of atoms) is removed or dislodged directly from the workpiece surface without any melting or vaporizing.
Power density of the laser beam is relatively higher (10⁴ to 10⁶ W/mm²).	Power density of the ion beam is significantly less (10^-2 to 10⁰ W/mm²).
LBM does not necessarily require a vacuum chamber. It can be carried out in open atmosphere. Sometimes shielding gas can be applied in machining zone to avoid high temperature oxidation of the machined surface.	IBM process is carried out in a soft vacuum chamber having pressure in the order of 10^-3 to 10^-5 atm.
Applicability of LBM process depends on the optical properties (reflectivity, absorptivity and transmittivity) of the workpiece surface.	IBM process is independent of optical properties of the workpiece surface.
Process capability and productivity depend on thermal properties (such as conductivity, diffusivity, etc.) of the workpiece material.	It is mostly independent of the thermal properties of the workpiece material.
It can cut features having high aspect ratio (up to 50:1). Deep hole drilling and thick cutting (even up to 20 mm thickness) can be carried out using LBM.	It is not suitable for deep cutting or fabricating features having high aspect ratio. IBM is preferred for micro-fabrication, shallow contouring or surface smoothening.
LBM process is affected by re-cast layer formation, especially during cutting thick specimens.	No such re-cast layer formation occurs in IBM.
The area of thermal damage on the workpiece is relatively larger in LBM process.	Impact damage on the workpiece is very narrow in IBM process. Often, no palpable collateral damage is noticed.
Material removal rate (MRR) of LBM process is significantly higher (5 – 50 mm³/min). So it is a productive and economic process.	Material removal rate (MRR) of IBM process is very low (in the order of 2 × 10^-4 mm³/min).

References

Unconventional Machining Processes by T. Jagadeesha (I. K. International Publishing House Pvt. Ltd.).
Nonconventional Machining by P. K. Mishra (Narosa Publishing House).
Allen et al. (2009). Ion beam, focused ion beam, and plasma discharge machining. CIRP Annals. https://doi.org/10.1016/j.cirp.2009.09.007

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Difference Between WJM and AWJM – Water Jet and Abrasive Water Jet Machining

Pintu — Sat, 15 Jun 2019 06:18:32 +0000

Among the mechanical energy based non-traditional machining processes, water jet machining (WJM) and abrasive water jet machining (AWJM) are two common processes that have wide variety of applications, starting from metallic industry to textile and lather industries. In water jet machining, clean water is pumped to a high pressure (2500 – 4000 bar) with the help of intensifier and the pressurized water is delivered to the work surface in the form of a jet using a small diameter nozzle. The nozzle converts the pressure energy of the water into the kinetic energy and thus high velocity (1000 m/s) jet is obtained. Apart from delivering the water jet, the nozzle also maintains the desired delivery angle and nozzle-tip distance (NTD). In order to avoid flaring of the water jet after discharge from the nozzle, suitable stabilizer is sometimes mixed with the water. In WJM, the high velocity water jet erodes material from the workpiece. It is suitable for cutting lather, textile materials, food, polymer, etc. However, the water jet does not possess enough power to slice metallic or ceramic objects.

To improve jet power, suitable abrasive (like alumina, olivine, garnet, etc.) can also be mixed with the water. Such a process where abrasive particles are mixed with the highly pressurized water before delivering onto the work surface is called abrasive water jet machining (AWJM). Here water is used to entrain the abrasives and to flush away eroded materials. Water does not directly participate in micro-cutting of the material. The abrasives only erode material. Although the abrasive-water jet velocity remains more or less same with that of pure water jet, the power and cutting ability of abrasive-water jet is significantly higher. Accordingly, AWJM can be employed for cutting metals and ceramics also. However, due to the chance of contamination because of the abrasives, AWJM is not hygienic for application in food industries. Various similarities and differences between WJM and AWJM are given below in table format.

Similarities between WJM and AWJM

A pump and an intensifier are required in both the processes to elevate pressure of the water.
Water pressure remains more or less same for both the process. Typically water pressure remains in between 2500 – 4000 bar.
For both the processes, the jet velocity when it comes out of the nozzle remains around 1000 m/s.
Catcher is desired in both the cases. Catcher is used to absorb the residual velocity of jet after machining the workpiece. It protects the work holding devices from the erosive action of jet by diminishing the residual energy.
A nozzle is desired in both the processes to convert the pressure energy of either water or water-abrasive mixture into kinetic energy. So the nozzle delivers high velocity jet in both the processes. It also directs the jet towards the work surface maintaining appropriate stand-of distance (SOD) and discharge angle.

Differences between WJM and AWJM

Water Jet Machining (WJM)	Abrasive Water Jet Machining (AWJM)
In WJM, a high velocity jet of pure water (sometimes mixed with stabilizer) is used to erode material.	In AWJM, a high velocity jet of water-abrasive mixture is used to erode the workpiece material.
Material removal from the workpiece takes place only due to the erosive action of water jet.	Material removal takes place due to the micro-cutting action of abrasives (water does not directly participate in cutting the material).
No mixing chamber is desired as abrasive is not mixed with water.	A mixing chamber (focused tube) is required for mixing abrasives with the pressurized water maintaining the pre-defined mixing ratio.
The jet of water does not possess high power, and thus it cannot be advantageously applied for cutting metals, alloys and ceramics.	The jet of abrasive-water mixture possesses enough power to slice metallic plates of thickness up to 10 mm.
No cost of abrasive is associated with WJM process.	Cost of abrasive is an additional expenditure in AWJM process.
It is free from the risk of abrasive embedment on the finished surface.	It is associated with the risk of abrasive embedment, particularly for ductile workpiece materials.
It is suitable for cutting softer materials like wood, leather, polymer and food items. It is also used for cleaning and removing coating.	It can be used for a wide variety of applications from wood and polymer to metal cutting industries.
WJM can be employed in food industries for slicing food items like frozen meat, fish, etc.	Presence of abrasive particles makes WAJM process unhygienic for application in food industries.

References

Advanced Machining Processes by V. K. Jain (Allied Publishers Private Limited).
Unconventional Machining Processes by T. Jagadeesha (I. K. International Publishing House Pvt. Ltd.).
Nonconventional Machining by P. K. Mishra (Narosa Publishing House).

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Difference Between Machining and Fabrication

Pintu — Thu, 13 Jun 2019 13:27:48 +0000

Fabrication indicates building the desired component using one or more manufacturing processes. Manufacturing is one technical term that is defined as a step by which raw material or scrap is converted to the useful product by adding substantial values. The manufacturing step consists of seven basic processes – each of these processes once again consists of many operations. Machining is just one manufacturing process; there are many others as discussed below.

1. Casting is one manufacturing process: The oldest manufacturing process where the raw material is first melted, poured into a pre-built mould and subsequently allowed to cool down. This mould is built in accordance with the desired object as the inverse profile of the mould is imparted on the object. Once solidified, the object inside the mould is taken out by breaking (or disassembling) the mould. There are several casting operations (like sand casting, permanent mould casting, investment casting, centrifugal casting, etc.), each one has unique benefits and limitations and thus is suitable for particular applications. Whatever be the case, casting process is suitable to provide a basic shape and size to the product, but mostly it cannot provide complex shapes, intricate details and smooth surfaces in mass production. Therefore, casting is one basic manufacturing process that can impart basic form to the object.

2. Joining is one manufacturing process: Joining is another manufacturing process by which two or more materials can be integrated temporarily or permanently to get a single larger unit. As usual there are various joining processes such as welding, soldering, brazing, riveting, fastening, coupling, adhesives, etc. to facilitate joining of wide variety of materials in innumerable ways.

3. Forming is one manufacturing process: In forming, work material is plastically deformed by external application of pressure (or force). The deformation is carried out in accordance with the desired product, its features and dimensions. Various forming operations include rolling, forging, extrusion, drawing, etc.

4. Machining is one manufacturing process: Machining is one secondary manufacturing process where excess material is gradually removed from the workpiece in order to impart desired shape, size and finish. There are various types of machining processes including conventional machining (like turning, milling, drilling, facing, etc.), non-traditional machining (like AJM, USM, EDM, ECM, CHM, LBM, etc.), abrasive cutting (like grinding, lapping, honing, etc.) and micro-machining (like micro-milling, precision turning, micro-drilling, etc.). However, every machining process follow the same basic principle of gradual removal of excess material from workpiece (this machining is one subtractive manufacturing process).

5. Surface working is one manufacturing process: It is also one secondary manufacturing process where surface integrity of the product is altered to obtain the desired one. Usually it does not change the shape or dimension of the component; however, various surface properties are altered. Thus surface working is also known as surface modification. It include several operations including heat treatment, coating, colouring, etc.

6. Additive manufacturing is one manufacturing process: Contrary to the subtractive manufacturing (or machining) process where layer by layer material is gradually removed from the solid 3-D workpiece, in additive manufacturing, layer by layer material is deposited one above another to build a 3-D product. Even though the manufacturing approaches are opposite in these two cases, the ultimate product may be same. This additive manufacturing process include several operations like 3-D printing, rapid prototyping, lithography, etc.

7. Powder metallurgy is another manufacturing process: It is also one manufacturing process where fine-grain (or powdered) material is poured into a mould after mixing with appropriate adhesive. The mixture is then compressed, sintered without melting, and subsequently allowed to cool down. A solid 3-D component with intricate details can be built by this process; however, it is suitable for small size objects. It is similar to casting to some extent, but here no melting takes place (although powder and adhesive mixture is heated to an elevated temperature).

What is the difference between machining and fabrication?

Fabrication is nothing but making or producing desired product using appropriate raw material. One or more of the above mentioned seven manufacturing processes are utilized to fabricate the intended product. So fabrication is carried out with the assistance of one or more manufacturing processes. Machining is just one among seven types of manufacturing processes. Therefore, machining is one gradual material removal process that may or may not be required for fabrication of a product.

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Difference Between Machine and Machine Tool

Pintu — Thu, 13 Jun 2019 10:24:04 +0000

In the field of mechanical engineering, “Machine” is defined as an assembly of mechanisms that are clustered together in such a way that it can perform certain operations by utilizing electrical, mechanical, hydraulic and/or pneumatic power, and thereby reduces the requirement of human effort and intervention in doing the task. However, “Machine Tool” is not exactly same with the machine. The term Machine includes wide variety of machinery, whereas Machine Tools are all such machines that possess the following characteristics.

Machine Tools must be power driven (human operated machines are not machine tools).
Machine Tools must be non-portable (portability is irrespective of size). So machine tools are always firmly installed with the ground.
Machine Tools must have sufficient value (value in terms of capability and performance, not on the basis of cost).
Machine Tools should be able to perform more than one type of machining or metal cutting operations. (Examples of machining operation include straight turning, taper turning, internal turning, threading, facing, drilling, boring, reaming, tapping, milling, shaping, planing, slotting, broaching, hobbing, grinding, etc.).
Machine Tools should utilize a cutting tool to shear off excess materials from workpiece in the form of chips.

If and only if all of the above five conditions are satisfied by a particular machine then it can be called a Machine Tool. Hence, all machine tools are basically machines, but not vice versa. Examples for machine tool include lathe, milling, shaping, etc. It is worth mentioning that usage of the phrase Machine Tool is confined to the metal cutting field only.

Functions of a machine tool

It transmits power from the prime mover (such as electric motor) to the required location as and when necessary for cutting or machining action.
It provides necessary motions to accomplish cutting action. Such motions include, but not limited to, cutting velocity, feed motion, depth of cut, etc.
It also manipulates power and motion, including transformation of one type of motion to another type (such as rotation to translation or oscillation), reduction or increase of speed, changing the direction of rotation, etc.
It supports and holds workpiece and other necessary devices, such as cutting tool, coolant pipeline, etc.
It also transmits cutting force and vibration to the ground.
Usually, it provides a better cutting fluid discharge facility.
Finally, it provides an ergonomic platform for human workers to carry out machining.

Why lathe is not a machine?

By the definition of machine, any kind of lathe can be called a Machine! However, in the metal-working or machining field, it is commonly (sometimes mandatorily) termed as a machine tool. Since lathe qualifies all five conditions as mentioned above, so it is one machine tool. The term ‘Machine Tool’ has special significance in metal-working field as it indicates the worth of a particular machine. Traditionally it is also believed that operation on lathe is mandatory for making any mechanical product even for making another machine tool. Due to its extreme capability, people associated with metal-working field love to designate lathe as a machine tool. Therefore, lathe is not a machine; it is a machine tool.

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Difference Between Machine Tool and Cutting Tool

Pintu — Thu, 13 Jun 2019 10:12:42 +0000

In the field of mechanical engineering, Machine is defined as an assembly of mechanisms that are clustered together to perform certain operations by utilizing electrical, mechanical, hydraulic and/or pneumatic power. Total number of mechanisms exist within a machine may vary from just few to few hundreds! Accordingly size of a machine also varies. Some machines, irrespective of their size, are portable. For example, a hand drill (small machine) and a large mining crane both are portable.

What is a Machine Tool?

The concept of machine tool is strictly restricted within the metal-working (or machining) field. By definition, a machine tool is a power operated, non-portable and valuable machine that can perform multiple machining operations by remove excess material from a pre-formed blank with the help of a suitable cutting tool. So a machine having following five characteristics can be considered as a machine tool.

It must be power driven (human operated machines are not machine tools). The form of power at input to the machine tool can be either electrical, mechanical, hydraulic, pneumatic or a non-conventional one.
It must be non-portable (portability irrespective of size). Thus machine tools are always firmly installed with the shop floor.
It must have sufficient value (value in terms of capability and performance; not on the basis of cost).
It can perform more than one machining or metal cutting operations.
It utilizes a cutting tool to shear off excess materials from workpiece.

If and only if all of the above five conditions are satisfied then a machine can be called a machine tool. In fact, machine tool is appropriate (sometime mandatory) term to designate such machines that qualify all five conditions. Examples of machine tool include Lathe machine tool, Milling machine tool, Shaping machine tool, Industrial drilling & boring machine tool, etc. Therefore, all machine tools are basically machines, but not vice versa.

What is cutting tool and how it differs from machine tool?

Machine tool is completely different from the cutting tool (also called cutter). A cutting tool is a small device having one or more wedge shaped and sharp cutting edges to facilitate shearing during metal cutting. So a cutting tool basically removes (shears off) material from workpiece. It is rigidly mounted on the machine tool in appropriate location. Shape and features of the cutting tool varies widely based on the required machining operation and intended performance.

Cutting tool cannot provide any motion required for cutting. All intended motions are provided by the machine tool. So cutting tool is mounted on a machine tool using suitable tool holding arrangements so that it can compress a thin layer of workpiece material to gradually shear it off in the form of chips for realization of material removal. For example, lathe is a machine tool, while the SPTT (single point turning tool) is a cutting tool. The following table displays several machine tools and typical cutting tools that can be mounted on corresponding machine tools.

Machine Tool	Cutting Tool
Lathe machine tool	Turning tool
	Threading tool
	Centering tool
	Drill
	Grooving and parting tool
	Knurling tool
Drill machine tool	Drill
	Boring tool
	Reamer
Milling machine tool	Peripheral mill
	Face mill
	End mill

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Difference Between AJM and WJM – Abrasive Jet & Water Jet Machining

Pintu — Wed, 12 Jun 2019 04:36:21 +0000

Mechanical energy based non-traditional machining (NTM) processes directly utilize mechanical energy to gradually remove material from the workpiece primarily by erosion. Examples of such processes include abrasive jet machining (AJM), water jet machining (WJM), abrasive water jet machining (AWJM) and ultrasonic machining (USM). In abrasive jet machining, abrasive particles are first mixed with the compressed gas at a pre-defined mixing ratio. This mixture is then directed towards the workpiece in the form of a high velocity jet by means of a nozzle. The small diameter nozzle converts the pressure energy of the air-abrasive mixture into kinetic energy, and thus high velocity jet is obtained. This nozzle also maintains appropriate stand-off distance (SOD) and discharge angle. This high velocity jet erodes material from the work surface at a controlled rate and thus material removal is obtained. Here only abrasive particles participate in erosion of workpiece material; compressed air has no role in it.

In water jet machining (WJM), a high velocity jet of water is used to remove material. Here a fluid pump is used to enormously increase water pressure (as high as 2500 – 4000 bar). This pressurized water is then discharged with the help of small diameter nozzle that converts the pressure energy into kinetic energy. The water jet that comes out of the nozzle possesses enough energy to slice polymeric or organic materials. Thus WJM is commonly used in food, polymer and leather industries. Often stabilisers (mainly long chain polymers) are mixed with water to reduce the tendency of jet flaring once it is discharged from nozzle. Sometimes smaller size solid abrasive particles are also mixed with the water to improve cutting ability. Such a process where abrasives are mixed with water is termed as Abrasive Water Jet Machining (AWJM). It can efficiently cut thin metallic sheets apart from polymer, wood and leather. However, presence of abrasive makes this process unsuitable for food slicing. Although, AJM and WJM both employ high velocity jet to cut material, they are different in several aspects. Various similarities and differences between AJM and WJM are given below in table format.

Similarities between AJM and WJM

AJM and WJM both are non-traditional machining processes (NTM). However, none of them is considered as hybrid process. A hybrid NTM process is a combination of two processes where workpiece material is removed simultaneously in two distinct ways.
Both are mechanical energy based NTM processes as they directly utilize kinetic energy to remove material. Abrasive water jet machining (AWJM) and ultrasonic machining (USM) also expand mechanical energy for material removal. There are several other NTM processes that expand other forms of energy for material removal (such as thermal energy in LBM, PAM and EBM, electro-chemical energy in ECM, etc.).
Both the processes require an appropriate nozzle for converting pressure energy of fluid (air in case of AJM, water in case of WJM) into kinetic energy (in the form of high velocity jet).
Performance of AJM or WJM does not depend on electrical and thermal conductivity and chemical inertness of the workpiece material. However, several mechanical properties like strength, hardness, etc. influence process capability.
None of these processes is associated with the burr formation, thermal damages, etc.
Both the processes can be integrated with CNC system for efficient control and precise delivery of jet. It also helps reducing environmental pollution and at the same time it offers a healthy working condition for workers.

Differences between AJM and WJM

Abrasive Jet Machining (AJM)	Water Jet Machining (WJM)
A high velocity jet of air-abrasive mixture is utilized for material removal.	A high velocity jet of pure water is utilized for material removal.
The working medium for AJM is dust-free and dehumidified air.	Working medium in WJM is clean water.
An air compressor is used to deliver pressurized air.	In place of air compressor, a liquid pump along with intensifier is used to deliver pressurized water.
Air pressure typically remains within 2 – 10 bar.	Water pressure remains very high, typically between 2500 – 4000 bar.
Velocity of the air-abrasive mixture jet when it comes out of the nozzle usually remains in the order of 100 – 300 m/s.	Velocity of water jet as it comes out of the nozzle remains around 1000 m/s.
There always exists a tendency of grit embedment on the machined surface in AJM. This may affect surface properties and appearance.	WJM is not associated with the risk of any embedment (as no abrasive is utilized here).
It cannot be employed in food processing industries due to inherent risk of abrasive contamination.	It is preferred and hygienic for slicing food items (like frozen meat, fish, etc.).
It can efficiently machine hard materials including metals. In fact, AJM is preferred for machining hard brittle metals and ceramics.	Water jet does not possess enough power for cutting metals or ceramics. It is suitable for cutting softer materials like woods, rubber, leather, etc.

References

Unconventional Machining Processes by T. Jagadeesha (I. K. International Publishing House Pvt. Ltd.).
Advanced Machining Processes by V. K. Jain (Allied Publishers Private Limited).
Nonconventional Machining by P. K. Mishra (Narosa Publishing House).

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Difference Between Shaping and Planing

Pintu — Thu, 06 Jun 2019 08:55:48 +0000

Machining is basically one material removal process where excess material is sheared off by the mutual interaction between workpiece and cutting tool. There exist several machining processes to cater the need of processing a wide variety of workpiece materials in innumerable ways. For examples, lathe operations (such as straight turning, taper turning, internal turning, threading, grooving, etc.) are primarily carried out to generate cylindrical or conical surfaces. Milling operations are carried out primarily for generating flat surfaces. Similar to the lathe and milling operations, shaping and planing are two machining processes that can generate flat surfaces at different planes or orientations. However, the rotation of workpiece or cutting tool imparts necessary cutting velocity the lathe operations and milling processes. On the contrary, both shaping and planing processes utilize only reciprocating motion to provide three necessary process parameters (cutting velocity, feed motion, and depth of cut).

Since reciprocating motion is utilized to impart cutting velocity both in shaping and planing, so either the cutting tool or the workpiece is required to reciprocate. Here, only forward stroke is utilized for removing material, while the backward stroke is kept idle. So cutter engages with the workpiece only in forward stroke. Since backward stroke does not involve in cutting, so the time of this redundant stroke can be reduced while giving more time for forward stroke. Quick-return mechanism is commonly employed to for this purpose. Although both shaping and planing utilize quick-return mechanism, their main difference lies on the point of application of cutting velocity. In shaping, the reciprocating movement of the tool provides cutting velocity; while in planing reciprocating movement of work table (workpiece) provides intended cutting velocity. Accordingly, quick-return mechanism is integrated with the cutter for shaping operation and with the worktable in planing operation. Although there are many similarities among shaping and planing, they are different in many aspects, as discussed below.

Similarities between shaping and planing

Both shaping and planing are conventional machining operations that follow subtractive manufacturing approach (layer-by-layer removal of material from a solid blank).
Both utilizes general purpose machine tools (shaping machining and planing machine).
None of them utilize any rotational motion (as in case of turning, milling or drilling). Only reciprocating motion is used to impart required cutting velocity, feed and depth of cut.
Areas of application of both the processes are also similar. This includes making straight slots, grooves, pockets, T-slots, V-blocks, etc.
None of them can produce any curved slots (like circular or parabolic slot).
In both the cases, excess material is removed from the workpiece in the form of chips (this is unlike non-traditional machining processes where material can be removed in various forms including ions, atoms, vapor, solid debris, etc.).
Both utilize single point cutting tool (shaping tool and planing tool have only one active cutting edge that participates in material removal action at a time).
Quick return mechanism is employed in both the machine tools; however, their point of application are different.

Differences between shaping and planing

Shaping	Planing
Shaping is one machining operation where workpiece is held stationary while cutting tool (ram) is reciprocated across the work.	Planing is similar machining operation but here the cutting tool remains stationary while workpiece (worktable) is reciprocated under the cutter.
Workpiece (bed) imparts feed motion, while cutting tool gives cutting motion.	Workpiece (table) imparts cutting motion, while cutting tool gives feed motion.
Shaping operation is performed in a machine tool called Shaper (also called shaping machine).	Planing operation is performed in a machine tool called Planer (also called planing machine).
Here quick-return mechanism is integrated with the ram that holds the cutter. So shaping machine uses quick return mechanism for tool movement.	Here quick-return mechanism is integrated with the worktable that holds the workpiece. SO planing machine uses quick return mechanism for worktable movement.
Shaper is traditionally a small machine and preferred for smaller jobs.	Planer is larger machine and can accommodate heavier and larger jobs.
It provides low MRR, thus shaping is less productive.	Planer has longer stroke length and can take heavy cuts, so MRR is high and the operation is productive.
Only one cutting tool can be used at a time.	Facility to accommodate multiple tools and simultaneously using all of them is also available in some planing machines.

References

Machining and Machine Tools by A. B. Chattopadhyay (Wiley).
Metal Cutting: Theory And Practice by A. Bhattacharya (New Central Book Agency).
DeGarmo’s Materials and Processes in Manufacturing by J. T. Black and R. A. Kohser (Wiley).

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Difference Between Cutting Speed and Cutting Velocity

Pintu — Wed, 05 Jun 2019 10:52:40 +0000

Conventional machining operation utilizes a wedge shaped cutting tool having one or more sharp cutting edges to facilitate shearing. To achieve material removal, three relative motions between workpiece and cutting tool are indispensably necessary. These are also called process parameters. One of such three relative motions is cutting velocity, other two being feed motion and depth of cut. In few machining processes, the cutting velocity is imparted either by rotating the workpiece or by rotating the cutter. For example, in lathe operations like turning, threading, face turning, parting, grooving, drilling, etc. the workpiece is rotated, while the cutting tool is rotated in milling processes. Such rotation (workpiece or cutter) can be expressed in two different ways, namely cutting speed and cutting velocity.

Cutting speed is basically the rotational speed of either workpiece or cutting tool (whichever is rotating, based on the machining operation). It is measured by the unit revolution per minute (rpm) and usually designated by N. On the other hand, cutting velocity is the tangential velocity of either rotating workpiece or rotating cutting tool. It is usually measured by the unit meters per minute (m/min) and designated by V_c. However, there exist few machining operations where neither workpiece nor cutting tool rotates; instead, they undergo linear reciprocating motions, for example, shaping or planing operation. For such cases, this linear velocity of workpiece or cutting tool (whichever is reciprocating) is termed as cutting velocity. Cutting speed becomes invalid in such scenario, as there is no rotational object. Various similarities and differences between cutting speed and cutting velocity are explained in the following passages.

Similarities between cutting speed and cutting velocity

Both cutting speed and cutting velocity are interrelated and one is proportional to another.
One can easily be converted to another, provided that the diameter of either cutter or workpiece (the rotating one) is known. The following formula can be employed to convert cutting speed into cutting velocity or vice versa.

Differences between cutting speed and cutting velocity

Cutting Speed	Cutting Velocity
Cutting speed indicates the rotational speed of either workpiece or cutting tool.	Cutting velocity indicates the tangential velocity of either rotating workpiece or rotating cutting tool.
It is commonly expressed in revolution per minute (rpm).	It is commonly expressed in meters per minute (m/min).
Cutting speed is a scalar quantity.	Cutting velocity is one vector quantity.
It is usually not considered as a machining process parameter.	It is considered as one crucial machining process parameter.
Cutting speed is only associated with those machining operations where either workpiece or cutting tool rotates.	Cutting velocity is associated with all conventional machining operations irrespective of presence or absence of rotation of workpiece or cutting tool.
Cutting speed is mainly useful during operating the machines (including conventional one and CNC based machine tools).	Cutting velocity is useful in various analysis, such as assessment of cutting force, temperature, vibration, machinability, economy of machining, etc.

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Difference Between Machining and Grinding

Pintu — Wed, 05 Jun 2019 09:53:12 +0000

Primary objective of any subtractive manufacturing process is to remove layer by layer material from a solid 3-D blank to achieve desired shape, size and finish. Achieving high dimensional accuracy, close tolerance and surface finish are usually not possible by conventional machining processes like turning, milling, shaping, planing, drilling, etc. Such processes are mainly applied for bulk removal (stock removal) of material with high material removal rate. In order to improve surface quality and dimensional accuracy, separate finishing operations can be carried out. Grinding, reaming, honing, lapping, etc. are classified as surface finishing processes. Such processes offer low material removal rate (MRR) but high accuracy, close tolerance and better finish.

Conventional machining (also known as metal cutting) processes utilize a sharp-edged wedge shaped cutting tool to compress and shear off material from workpiece. This cutting tool has defined geometry. Cutter material also varies widely – from age old carbon steel to modern day’s materials like cBN and diamond. On the other hand, grinding utilizes a circular wheel made of sharp, tiny and random shaped abrasive grits strongly held on suitable bonding medium. These abrasives actually remove material from work surface in the form of micro-chips to provide a smooth surface. Although grinding wheel has defined specification, the abrasive grits have no specific geometry. Moreover, only a limited types of abrasive is used, like alumina, silica, diamond, etc. Important similarities and differences between machining and grinding are discussed below.

Similarities between machining and grinding

Both machining and grinding processes follow the basic principle of subtractive manufacturing approach. Here layers of excess material are removed from a solid 3-D blank to obtain final product. On the contrary, in additive manufacturing approach, layer by layer material is added one over another to build a solid 3-D product.
In both the machining and grinding processes, material removal takes place in the form of solid chips.
In both the cases material is removed by shearing (ploughing and rubbing occur in grinding but they do not remove material).
Presence of cutter is mandatory in both the cases for realizing material removal.
Only mechanical energy is utilized for material removal in both the cases (unlike NTM processes where various forms of energy like mechanical, electrical, thermal, chemical, etc. are used to remove material).

Differences between machining and grinding

Machining	Grinding
Machining is one bulk material removal process (i.e. high MRR). Thus it is economical and suitable to give proper size and also for semi-finishing.	Grinding has low material removal rate and is preferred only for finishing.
Accuracy and tolerance achieved by conventional machining operations are not so good. Achieving tolerance below 50µm is very difficult.	It can provide better accuracy and tolerance. In grinding, achievable tolerance can be as low as 2µm.
In machining, cutting tool is usually made of metals or alloys, which is substantially harder than work material. However, ceramic, diamond and cBN tools (non-metallic) are also available, usually in the form of inserts.	Cutting tool for grinding, i.e. the wheel, is made of abrasive materials (such as alumina, silica, etc.) bonded in harder medium (like resin, metal, etc.).
Cutting tool used in machining has specific geometry. Values of the geometrical features may vary from one tool to another, but each tool has pre-defined geometry as per tool signature.	Grinding wheel may have specific pre-defined features, but the abrasive grits (which actually participate in material removal) have random geometry and orientation.
Rake angle of a cutting tool may vary from positive to negative. However, the negative rake usually does not go above (–15º) as it may severely degrade machinability.	Abrasive grits have haphazard rake angle. A much wider variation of rake angle from (+75º) to (–75º) is noticed among abrasive grits.
During machining operation, each main cutting edge of the tool actively and mostly equally participates in material removal action.	Only few (about 1%) abrasive grits actually engage in material removal action (shearing). Some grits just engage in rubbing, scratching and ploughing. A major percentage of grits do not even touch the work material in every rotation.
Generated cutting temperature is comparatively low, and only a tiny portion (5-8%) of it diffuses into the workpiece. Thus thermal damage of the machined surface is usually insignificant.	Severe heat is generated during grinding, and also a substantial amount of heat diffuses into the workpiece. This causes thermal damage of the machined (ground) surface such as changing hardness.
The maximum cutting speed (rpm) used in conventional machining is typically limited to 2000 rpm (limited by the capability of machine tool, especially gears and bearings). Thus cutting velocity (m/min) is also lower.	Rotational speed of grinding wheel is much higher (2000 – 4000 rpm). Ultra high speed grinding (speed around 20,000 rpm) is also carried out for some specific applications.
Specific energy consumption (power per unit volume of material removed in kW/mm³) is much lower.	Specific energy consumption is 5–50 times higher than that of the machining.
There exist some surface hardened and inherently hard materials that cannot be machined by conventional methods.	Such materials can be finished by grinding without appreciable problem.

References

Machining and Machine Tools by A. B. Chattopadhyay (Wiley).
Metal Cutting: Theory And Practice by A. Bhattacharya (New Central Book Agency).
Manufacturing Process for Engineering Materials by S. Kalpakjain and S. Schmid (Pearson Education India).
DeGarmo’s Materials and Processes in Manufacturing by J. T. Black and R. A. Kohser (Wiley).

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Difference Between Jig and Fixture – Special Purpose Devices

Pintu — Wed, 05 Jun 2019 07:10:44 +0000

In conventional machining, the cutting tool compresses a layer of work material to shear it off in the form of chips. Both the cutting tool and the workpiece is rigidly mounted on the machine tool maintaining appropriate orientation. All relative motions are also offered by the machine tool to smoothly accomplish material removal. In mass production of a product in conventional machine tool, same work is required to perform repeatedly for a large number of times. Several special purpose devices can be utilized in such scenario for easy, efficient, uninterrupted and productive machining. Jig and fixture are two special purpose devices that assist economic mass production requiring no additional set-up. They are meant for improving productivity, reducing human effort, reducing error due to human endurance, facilitating interchangeability, and minimizing rejection.

A jig is one special purpose device used to guide and locate the cutting tool to pre-defined position on the workpiece. Apart from guiding the cutter, it mandatorily holds, supports and locates the workpiece with respect to machine and cutter. Jigs are normally used in frilling, reaming and tapping. Basic purpose of a fixture is to securely mount the workpiece in correct position maintaining desired orientation with respect to machine and cutter. However, it cannot guide the cutting tool to move at a pre-defined location. Fixtures are commonly clamped to the machine tool and are used in reciprocating type operations like milling, shaping, slotting, planing, etc. It is to be noted that neither the jig nor the fixture is an integral part of machine. They are separate units that can be placed and temporarily clamped on the workpiece. Now-a-days, with the advent of automated or CNC (Computer Numerical Control) based machine tools, usage of such special purpose devices reduces considerably. Various similarities and differences between jig and fixture are given below.

Similarities between jig and fixture

Jig and fixture mandatorily consist of arrangements for locating and clamping and an optional arrangement for tool guiding (jig bush).
Both can eliminate individual marking and positioning. This reduces idle time during machining that ultimately improves productivity.
Both tends to reduce unpredictive human error caused by performing similar task repeatedly for large duration (human too has an endurance limit or stress).
Both can improve accuracy in machining in several ways. Thus close tolerance can be achieved easily. They also reduce production of defected items and thus rejection.
Both are used for non-automatic machines. They are not necessary for automated CNC based machines as locating task is executed by pneumatic or hydraulic system.
Both can partially automates the machining process (reduces human engagement in manufacturing).
Both can be made of similar metals, such as phosphor bronze (reduces wear during repeated usage), high carbon steel, etc.

Differences between jig and fixture

Jig	Fixture
Jig is a device primarily used to guide the cutter to repeatedly move at predefined locations on the workpiece. Jigs can also hold, support and locate the workpiece apart from guiding the cutter.	Fixture is a device used to rigidly grip, support and locate the workpiece maintaining intended orientation. It does not guide the cutter to move to a particular location.
A jig is usually lighter in weight. Sometimes jigs are hold by hand only without clamping.	Fixture is commonly heavier and robust as it is required to sustain the cutting force and vibration. So it is clamped firmly with the work table.
Jig is considered easy to use and thus less skill is required to operate this device.	Fixture is somewhat complicated to use and thus requires skill.
No additional device is required for locating the cutter with respect to job.	Additional accessories like blocks, gauges, etc. are desired to accurately move the cutter in intended location.
Jig is frequently used in drilling, boring, reaming and tapping.	Fixture is employed in milling, planing, shaping, slotting, etc.

References

Manufacturing Processes by J. P. Kaushish (PHI Learning Private Limited).
Jigs and Fixtures by P. H. Joshi (Tata McGraw-Hill Publishing Company Limited).
Manufacturing Processes–II by H. S. Bawa (Tata McGraw-Hill Publishing Company Limited).

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Difference Between Turning and Milling

Pintu — Wed, 05 Jun 2019 06:24:08 +0000

Conventional machining is one type of manufacturing process in which excess material is removed from a pre-formed blank by shearing in the form of chips using a wedge shaped cutting tool in order to get desired shape, finish and tolerance. There exist several machining processes to efficiently machine a wide variety of materials in innumerable ways. Turning and milling are just two examples of such machining processes. Others being tapering, drilling, shaping, planing, slotting, knurling, boring, reaming, sawing, chamfering, etc. Each of these processes has unique benefits and limitations, and thus is suitable for particular requirements.

Although both turning and milling follows the principles of subtractive manufacturing, their areas of application are different as they produce different geometrical surfaces. Turning is used to reduce diameter of a job, and thus provides a cylindrical surface. It is carried out in lathe with the help of a single point cutting tool (known as turning tool). Here the workpiece rotates at a fixed rpm to provide necessary cutting velocity, while the tool is moved to provide required feed. On the other hand, milling produces a flat or stepped surface. It is carried out in milling machine and it employs a multi-point cutter (milling cutter). Here the cutter rotates at fixed rpm to provide cutting velocity, while the workpiece is moved with respect to the stationary cutter to provide feed. Important similarities and differences between turning and milling are given in the following sections.

Similarities between turning and milling

Both turning and milling are conventional machining processes. Such processes utilize a specially designed cutting tool that physically compresses a thin layer of workpiece material to gradually shear it off in the form of solid chip.
Both turning and milling follow subtractive manufacturing approach. Here layer by layer material is removed from a solid 3-D block to obtain intended product. On the contrary, additive manufacturing approach follows the concept of addition of thin layer of material one over another to build a solid 3-D block.
Both turning and milling processes employ a solid cutting tool to shear off material from the workpiece; however, the shape and features of the cutters for these two processes vary widely.
Chip formation is inherent in both the cases. In fact, it is fundamental to every conventional machining process.
Both the processes can produce reasonably good surface finish; however, it depends on several other factors including cutting velocity, feed rate, depth of cut, tool geometry, cutting environment, etc.
Heat generation is inherent in both the processes. Consequent effects of high cutting temperature are also similar for both the operations.
Cutting fluid can be applied in both the processes.

Differences between turning and milling

Turning	Milling
Turning is performed to generate a cylindrical or conical surface.	Milling is performed primarily to generate a flat surface.
Machine tool that is used for turning operation is called Lathe.	Milling is carried out in Milling machine.
Turning process utilizes a single point cutting tool, called SPTT (Single Point Turning Tool).	Milling process utilizes a multi-point cutting tool, called milling cutter.
In turning, cutting tool continuously remains in contact with workpiece during the operation.	In milling, tooth continuously engages and disengages during operation (intermittent cutting).
Here the workpiece is rotated at fixed revolution per minute (RPM). This rotation provides necessary cutting velocity.	Here the cutter is rotated at fixed revolution per minute (RPM). Rotating cutter provides necessary cutting velocity.
In turning, feed motion is derived by moving the cutting tool (tool carriage).	In milling, feed motion is derived by moving the workpiece (worktable).
It can produce fragmented, discontinuous, or continuous chips (based on work and tool materials, cutting parameters, etc.).	Milling inherently produces discontinuous chips.

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Difference Between Additive and Subtractive Manufacturing

Pintu — Tue, 04 Jun 2019 13:19:27 +0000

Economic production of near-neat shape products with close tolerance and high accuracy is a challenging task for manufacturing industries. Two different approaches have evolved over the years for efficiently and economically fabricate such products. In one approach material is added layer by layer to build a 3-D component, while in other approach material is removed layer by layer to obtain desired 3-D product. As the name suggests, in additive manufacturing approach (or philosophy) thin layer of semi-solid material is deposited one over another to build a 3-D component. As an analogy you may consider building construction where layers of bricks are cemented one after another to get entire building with desired shape and features. So processing starts at nil, thickness or height increases as layers are deposited one above another and final product is obtained without any wastage. 3-D printing is the common example of a manufacturing process that follows additive manufacturing approach.

Contrary to additive approach, layer by layer material can also be removed from a solid blank to obtain a product having desired shape, size and dimension. This approach of removing layers of material from a solid blank is termed as subtractive manufacturing. As an analogy you may consider carpentry works where excess wood is removed carefully to obtain intended features. All machining processes (conventional and NTM) follow this approach. It cannot fabricate an enclosed cavity, neither it can vary volumetric density of building material. However, when component size is large, subtractive approach vehemently dominates additive approach on the basis of fabrication capability, time and productivity. Various similarities and differences between additive and subtractive manufacturing are tabulated below.

Similarities between additive and subtractive manufacturing

Primary aim of both additive and subtractive manufacturing approaches is to fabricate a solid 3-D product with better surface finish and close tolerance at minimum number of steps.
Both approaches are used in today’s manufacturing industries (none of them is obsolete); however, subtractive approach is used overwhelmingly still now.

Differences between additive and subtractive manufacturing

Additive Manufacturing	Subtractive Manufacturing
In additive manufacturing, layer by layer material is added one over another to develop desired solid 3-D product.	In subtractive manufacturing, layer by layer material is gradually removed from a solid block to fabricate 3-D product.
This manufacturing concept is usually suitable for materials having low melting point, such as plastic.	This manufacturing concept can be applied to all solid materials irrespective of melting point.
Volumetric density (thus weight) of the constructive material of final component can be controlled during operation.	Material density cannot be controlled during operation. Density of object remains same with that of the initial solid block (usually a cast product).
No material wastage takes place in these processes.	These processes are associated with material wastage in the form of chips, scraps, dissolved ions, vapors, etc.
Complex shapes can be easily fabricated using additive manufacturing techniques.	Subtractive manufacturing processes have limited capability in fabrication of complex shapes.
Structures containing fully closed internal hollow parts can be produced by these processes.	Structures containing enclosed hollow parts cannot be produced by these processes, unless joining is allowed.
These processes are applicable to a narrow range of materials.	These processes can efficiently handle a wide variety of materials.
These processes are time consuming and costly but can provide superior quality and desired property without requiring any further processing.	These processes are time efficient and economic. These are usually suitable for mass production where requirement of product quality is not so tight.

References

Additive Manufacturing Technologies by I. Gibson, D. Rosen and B. Stucker (Springer).
Additive Manufacturing of Metals: The Technology, Materials, Design and Production by L. Yang, K. Hsu, B. Baughman, D. Godfrey, F. Medina, M. Menon and S. Wiener (Springer).

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