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Difference Between Coated and Uncoated Cutting Tool in Metal Cutting

Pintu — Sun, 26 Jan 2020 06:34:35 +0000

Cutting tool is a part and parcel in every conventional machining process. Tool material and geometry are two active parameters that influence process capability and machinability. For uninterrupted material removal, the tool material should be harder than the workpiece material. In addition to the hardness, tool material should ideally possess certain common properties, such as high strength, high toughness, high fatigue strength, shape retention capability at high temperature, high thermal conductivity, good formability, etc. A single material may not offer all required properties. In order to harness most of the intended properties, tools are sometimes coated with suitable material so that the substrate material provides few properties and the coating material provides rest of the intended preparties. Sometimes multiple layers of coating are also deposited on the tool material so that each layer fulfils one desired property. Common coating materials for cutting tool include Titanium Nitride (TiN), Titanium Carbo-Nitride (TiCN), Titanium Aluminum Nitride (TiAlN), Diamond, etc.

Coating material deposition on the tool substrate is usually carried out either by Physical Vapor Deposition (PVD) method or by Chemical Vapor Deposition (CVD) method. Accordingly, coated tools become costlier as compared to uncoated tools. However, a coated tool can offer high material removal rate (MRR) and extended service life. These, in turn, reduce the frequency of tool replacement and cut down the associated cost for the machine idle time. Thus the overall production cost may reduce significantly with a coated tool. In addition, a coated tool has low wear rate and breakage tendency. This helps in machining features with tight tolerance for a prolonged period. Coating also helps in improving lubricity between flowing chips and rake surface of the tool. This can directly reduce the rate of heat generation, which helps in achieving better machinability. Despite several benefits, a worn-out tool cannot be re-used easily. In such case, an uncoated tool can be re-sharpened simply by grinding and can be re-used easily. Several similarities and differences between coated tool and uncoated tool are given below in table form.

Similarities between coated tool and uncoated tool

Irrespective of presence or absence of coating, the tool material provides necessary mechanical strength during metal cutting.
All intended geometrical features (inclinations and radius) are incorporated on the tool material only. Coating does not usually alter such features.
Heat generation, residual stress, burr formation, etc. are common problems in every conventional machining regardless of the usage of a coated or uncoated tool. However, the degree of such factors can be altered by selecting suitable coating material.

Differences between coated tool and uncoated tool

Coated Tool	Uncoated Tool
During machining with a coated tool, the coating material comes in physical contact with the workpiece material.	During machining with an uncoated tool, the tool material comes in physical contact with the workpiece material.
A coated tool typically offers extended tool life.	Uncoated tools usually have lower tool life.
Presence of coating on the tool substrate can reduce the rate of tool wear (adhesion, abrasion, oxidation, etc.)	Uncoated tools are prone to various wears.
Coated tools are usually expensive.	For same material, dimension and feature, an uncoated tool is cheaper.
Very less tool changing is required as each tool offers long life. So the idle time associated with tool replacement is also less.	As each uncoated tool has comparatively shorter tool life, so frequent tool changing is required. Accordingly, associated idle time is also high.
A coated tool cannot be re-sharpened easily once it is worn out.	The biggest benefit of uncoated tool is that it can be re-sharpened easily by grinding to re-use the worn out tools.
Some coating materials help improving lubricity (i.e. reduces sliding friction between flowing chip and rake surface of the tool).	For same workpiece material and cutting environment, coefficient of friction between chip and rake surface of the tool is usually higher.
Due to low coefficient of friction, the rate of heat generation during machining is also less.	For the same workpiece material and process parameters, the rate of heat generation is comparatively higher.
Coating can also restrict the rate of heat conduction into the tool substrate. This, in turn, discourages plastic deformation of the cutting edge caused by high cutting temperature.	Edges of the uncoated tools are susceptible to plastic deformation as the rate of heat conduction is not restricted.
Coated tools enable usage of high velocity, feed and depth of cut. So such tools offer high MRR.	High velocity, feed and depth of cut cannot be used with uncoated tool due to the inherent risk of accelerated wear and plastic deformation.
Coated tools can also offer high toughness, which restricts catastrophic breakage of the edges.	Uncoated tools usually have low toughness, and thus such tools are vulnerable to catastrophic breakage.
Coating can also improve fatigue resistance, so same tool can be used continuously for a longer duration.	Uncoated tools typically have low fatigue life.
Proper coating material also discourages built-up edge (BUE) formation on the edges of the tool.	At high temperature and mismatched compatibility, BUE formation on uncoated tool is a common incident.

References

Machining and Machine Tools by A. B. Chattopadhyay (Wiley).
Manufacturing Process for Engineering Materials by S. Kalpakjain and S. Schmid (Pearson Education India).
Saha et al. (2020); An investigation on the top burr formation during Minimum Quantity Lubrication (MQL) assisted micromilling of copper; Materials Today: Proceedings; https://doi.org/10.1016/j.matpr.2020.02.379

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Difference Between Open Belt Drive and Cross Belt Drive

Pintu — Sat, 08 Jun 2019 06:32:17 +0000

Mechanical power transmission system takes help of several drives and elements in order to transmit power, torque and motion from one shaft to another shaft. Such drives can be either engagement type (gear drive and chain drive) or friction type (belt drive and rope drive). Belt drive is one reliable mechanical power transmission system that is commonly used to transmit power and motion over considerably larger distance (even up to 15m) between driving shaft (usually a prime mover such as an electric motor) to driven shaft. Being a friction drive, belt drive is inherently associated with slip. So it cannot provide constant velocity ratio, thus it is one non-positive drive. This slip, however, can protect the driver unit from overloading in the driven part. Presence of flexible belt between two shafts also enables this drive to absorb vibrations induced in machinery. This belt many have various configurations, such as flat belt, V-belt, ribbed belt, etc. A flat belt is one jointed belt that has a rectangular cross-section. Only one surface of the belt comes in contact with the outer surface of the cylindrical pulleys.

Pulleys of the driver and driven shafts can be connected using the flat belt in two distinct ways—open belt and crossed belt. Each of them has unique benefits over the other one. In open belt drive arrangement, belt proceeds from top of one pulley to the top of other pulley without crossing. So the driver shaft and driven shaft rotate in same direction. Contrary to this, in crossed belt drive, belt proceeds from the top of one pulley to the bottom of other pulley and thus crosses itself in between two pulleys. Here driving shaft and driven shaft rotate in opposite directions. It offers higher contact angle, so power or torque transmission capacity also increases. However, due to crossing, belt continuously rubs itself, which leads to reduced belt life. Various similarities and differences between open belt drive and crossed belt drive are given below in table format.

Similarities between open belt drive and crossed belt drive

In both the cases, flat belt is used. V-belt and ribbed belt cannot be utilized in crossed configuration (they are always open).
In both the cases, driving and driven shafts must be parallel. However, a small misalignment does not possess noticeable problem.
Both can transmit power and motion for substantially large distances (even up to 15m). In comparison, trapezoidal belt or V-belt is suitable for short distance (usually within 1m).
In both the cases power transmission occurs by means of friction between the pulley and belt.
Slip can occur in both the cases. So none of them can offer constant velocity ratio. Thus they are non-positive drive.

Differences between open belt drive and crossed belt drive

Open Belt Drive	Crossed Belt Drive
In open belt drive, belt proceeds from top of one pulley to the top of other pulley without crossing.	In crossed belt drive, belt proceeds from top of one pulley to the bottom of other pulley and thus crosses itself.
In open belt drive, driving shaft and driven shaft rotate in same direction.	In crossed belt drive, driving shaft and driven shaft rotate in opposite direction.
Contact angle (or wrap angle) between the belt and pulley is comparatively small (always below 180º in smaller pulley).	Contact angle between the belt and pulley is comparatively large (always above 180º in smaller pulley).
Length of the open belt is smaller as compared to cross belt.	For the same pulley diameter and same centre distance between driver and driven shafts, longer belt is required in cross belt drive.
Here belt remains in same plane in every rotation during its operation.	Here belt bends in two different planes in every rotation during its operation.
Here belt does not rub with itself. So belt life is considerably high.	Here belt rubs with itself and thus life of the belt reduces.
Open belt drive is suitable when driving and driven shafts are in horizontal or little bit inclined.	Cross belt drive can be advantageously applied for horizontal, inclined and vertical positions of driving and driven shafts.
Power transmission capacity is small due to smaller wrap angle.	It can transmit more power as wrap angle is more.

References

Introduction to Machine Design by V. B. Bhandari (McGraw Hill Education India Private Limited).
A Textbook of Machine Design by R. S. Khurmi and J. K. Gupta (S. Chand).
Theory of Machines by R. S. Khurmi and J. K. Gupta (S. Chand).

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Difference Between Flat Belt Drive and V-Belt Drive

Pintu — Sat, 08 Jun 2019 05:54:23 +0000

Majority of mechanical machine units are driven by a prime mover, which converts mainly electrical energy into mechanical energy (usually in the form of rotation of a shaft). Power generated by the prime mover is transferred to the intended location for driving various elements of the machinery. Several power transmitting elements are used for such transmission purposes; each of them has specific advantages and disadvantages. Gear drive, belt drive, chain drive, rope drive, clutch, etc. are notable elements of mechanical power transmission system. Belt drive is one flexible drive where an endless belt (jointed or jointless) is employed to transmit power from driver shaft and driven shaft by means of friction between the belt and pulleys. It is simpler and economic as compared to gear drive or chain drive and can be used for medium to long shaft distances. It is also capable protecting the driver unit by absorbing vibrations. By means of slip, it can also keep the system safe from overloading.

Commercial belts are available in different cross-sections; among them flat belts and V-belts are frequently used. A flat bet has rectangular cross-section where width is significantly larger than thickness. It usages a cylindrical pulley where bottom surface of the belt comes in contact with the outer surface of the pulley. On the other hand, V-belt has trapezoidal cross-section with width comparable to height. It employs a pulley having corresponding V-grove to accommodate the V-belt. Both the side surfaces of the belt remains in contact with the pulley. Whereas flat belt is a jointed belt, V-belt is jointless. Although power transmission capability of flat belt is comparatively low, it can transmit power and motion to a longer distance. V-belt tends to eliminate slip but is costly and cannot be used for very long center distances. Various similarities and differences between flat belt and V-belt are given below in table format.

Similarities between flat belt drive and V-belt drive

Both flat belt and V-belt drives can transmit power and motion to a longer distance as compared to gear drive.
Both are suitable for transmitting power between parallel shafts only. Although little parallelism error does not possess any palpable problem, they are primarily not suitable for intersection shafts.
Both of them are flexible drives due to the presence of flexible element (belt). A flexible drive can isolate the prime mover from machine unit and thus restricts transmission of undesired vibrations.
Both are friction drives, which indicates power and motion are transferred from driver to driven shaft by means of friction between the pulley and belt.
Although V-belt drive eliminates slippage, both of them are categorized under non-positive drive because of creep motion. In fact, V-belt can also slip when load on driven shaft exceeds a certain limit.
Pulleys are indispensably required on both the shafts in every belt drive. However, pulley geometry varies based on belt configuration.

Differences between flat belt drive and V-belt drive

Flat Belt Drive	V-Belt Drive
Flat belts have a rectangular cross-section, where width of belt is much larger than thickness.	V-belts have a trapezoidal cross-section, where maximum width is almost same with the thickness.
The pulleys for flat belt drive are simple in construction and thus cheaper.	Here pulleys must contain V-slot to accommodate V-belts. Slot angles must match with that of the belt, otherwise power transmission capability will reduce. Thus these pulleys are costlier.
In flat belt drive, only one surface of the belt remains in contact with the pulley.	In case of V-belt drive, two inclined surfaces continuously remain in contact with the pulley.
Wide range of velocity ratio can be obtained by utilizing stepped pulleys of different diameters and easily shifting belt from one pulley to another.	Such shifting provision does not exist in V-belt drive.
Flat belts can be used for transmitting power to a long center distance (even up to 15m).	V-belt drive is suitable for power transmission in short center distance (usually below 1m).
Flat belt drive can be used either in open configuration or in crossed configuration.	V-belt is always used in open configuration.
Efficiency of the flat belt drive is comparatively higher.	Efficiency of the V-belt drive is low.
Power transmitting capability of flat belt drive is low.	V-belt drive can transmit comparatively higher power because of the increased friction force due to wedge action.
Flat belt drive is suitable when velocity ratio is up to 4:1.	Higher velocity ratio (up to 7:1) can be obtained by V-belt drive.
Slip occurs frequently in flat belt drive. Thus is not a positive drive.	Due to higher friction force for wedge action, slip does not occur at low speed in V-belt drive. However, if load exceeds the rated capacity, then slip may occur.
Flat belts are jointed (hinged), so their operation is noisy.	V-belts are endless, so their operation is quite.
Flat belt drives are usually suitable for horizontal power transmission.	V-belt drives are preferred for transmitting power in any direction, even when belt is vertical.
Flat belts are also relatively cheaper.	V-belts are costlier.
Flat belts are commonly used in belt conveyer, saw mills, food industries, etc.	V-belts are commonly used in electric pumps, compressors, machine tools, etc.

References

Design of Machine Elements by V. B. Bhandari (Tata McGraw Hill Education Private Limited).
Theory of Machines by S. S. Rattan (McGraw Hill Education India Private Limited).

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Difference Between Belt Drive and Chain Drive

Pintu — Sat, 08 Jun 2019 05:13:57 +0000

Basic purpose of mechanical drive is to transmit torque, motion and power from driving shaft (usually a prime mover like an electric motor) to driven shaft, and also to alter the intensity, direction and speed as per the requirement. There exist several mechanical drives to fulfill varying industrial and machinery requirements. Such drives can be classified into two major categories—positive drive and non-positive drive. A positive drive is free from slippage and thus provides constant velocity ratio. Contrary to this, a non-positive drive cannot provide fixed velocity ratio due to slippage or other similar issues. Each drive has unique advantages over the other one and thus is used in various applications. Gear drive and coupling are examples of positive drive. Chain drive also offers constant velocity ratio if designed and maintained properly. On the other hand, belt drive and rope drive are considered as non-positive drive as they are prone to slip and creep.

Belt drive is one type of mechanical drive where motion and power are transferred from one shaft to another by means of friction between belt and pulleys mounted on each shaft. As friction plays the primary role in power transmission, so it is also called a friction drive. Slip can occur between belt and pulley when load exceeds the rated capacity. Such slippage is not always undesirable as it can inherently protect various machine elements from overloading. On the contrary, chain drive is one engagement type power transmission system that transmits motion and power by means of successive engagement and disengagement chain with sprocket. Being a positive drive, it offers a fixed velocity ratio; however, sometimes fails to protect the system from excessive loading. Various similarities and differences between belt drive and chain drive are given below in table format.

Similarities between belt drive and chain drive

Both belt drive and chain drive are mechanical drives. Thus they utilize various mechanical elements which must be in physical contact for transmitting power. Apart from mechanical drive, other drives that are frequently used in industries include hydraulic drive, pneumatic drive and electrical drive.
Both belt drive and chain drive are suitable for transmitting power and motion for medium to larger shaft distance. For shot distance, gear drive is preferred. However, V-belt can be applied for short to medium distance also.
They can be applied for parallel driver and driven shafts only. They are not suitable for transmitting power between non-parallel shafts. It is worth mentioning that quarter-turn belt can be used for non-parallel non-intersecting shafts.
Both require frequent adjustment in tension; otherwise slip percentage increases as the belt or chain stretch out with service time.

Differences between belt drive and chain drive

Belt Drive	Chain Drive
Belt drive is one friction type mechanical drive where friction force between belt and pulley is used to transmit power and motion.	Chain drive is one engagement type mechanical drive where power and motion are transmitted by successive engagement and disengagement of chain with sprocket.
Belt drive is preferred for medium to long center distance between driver and driven shafts.	Chain drive can be used for short to medium center distances.
Although belt drive is suitable for parallel shafts, slight parallel error is tolerable and does not create noticeable problem.	In chain drive, parallelism must be maintained precisely, otherwise chain may leave sprocket without any warning.
Slippage occurs in belt drive when load exceeds frictional force.	No such slippage occurs in chain drive.
Because of slip, velocity ratio does not remain constant in belt drive. Thus it is not a positive drive.	Here velocity ratio remains fixed. So chain drive is one positive drive. However, polygonal effect may lead to non-uniformity in speed.
Efficiency of belt drive is comparatively low because of frictional loss.	Efficiency of chain drive is high, usually above 95%.
Belt tension is affected by atmospheric conditions and temperature. Thus performance of belt drive also changes with external factors.	Chain drive is usually not affected by atmospheric conditions and temperature.
Belt drive requires minimum maintenance.	Chain drive requires regular maintenance including lubrication.

References

Introduction to Machine Design by V. B. Bhandari (McGraw Hill Education India Private Limited).
A Textbook of Machine Design by R. S. Khurmi and J. K. Gupta (S. Chand).
Theory of Machines by R. S. Khurmi and J. K. Gupta (S. Chand).

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