Welding is one of the manufacturing processes by which two or more similar or dissimilar materials can be joined permanently by coalescence formation with or without the applications of external pressure, heat or filler material. When external heat is applied to fuse faying surfaces it is termed as fusion welding; otherwise it is called as solid state welding. During fusion welding, filler material can be applied externally to fill the root gap for getting a sound weld joint. However, if root gap is too small then filler may not be applied also. On the basis of whether filler material is applied or not and also the composition of filler, welding processes can be categorized into three groups – Autogenous, homogeneous, and heterogeneous.
Autogenous welding is the process of joining two components without the application of filler material. This is useful when root gap is zero or very small and base plates are thin. However, if root gap is substantially wide or edge preparation is conducted, then filler must be applied to fill the lacuna. The composition of this filler material can be either identical or substantially different from that of the parent components to be welded. Accordingly, welding with filler can be grouped into two categories—homogeneous welding (when composition of filler is same with composition of base metal) and heterogeneous welding (when compositions are different). Similarities and differences between homogeneous welding and heterogeneous welding are discussed in the following sections. For details, you may read following articles.
- Autogenous welding – Examples, Advantages and Disadvantages.
- Homogeneous welding– Examples, Advantages and Disadvantages.
- Heterogeneous welding– Examples, Advantages and Disadvantages.
Similarities between homogeneous and heterogeneous welding
- Both homogeneous welding and heterogeneous welding need filler material to be applied during process.
- Coalescence is formed in both the cases.
- Both provide permanent joints.
- Joining of more than two components is also possible by both the ways.
Differences between homogeneous and heterogeneous welding
|Homogeneous welding||Heterogeneous welding|
|Here, metallurgical composition of filler material is identical with that of the parent materials.||Here, metallurgical composition of filler material is substantially different from that of the parent materials.|
|Not possible while joining dissimilar materials.||Dissimilar metals can be joined by this process.|
|Because of same composition, compatibility (chemical, physical and mechanical) of any kind is obvious.||Selected filler material should have to be compatible with parent components to obtain a crack-free reliable joint.|
|Melting point of filler is same with that of the base plates.||Melting points of two can be substantially different and this factor should be carefully considered prior to welding.|
|Physical, chemical and mechanical properties of weld bead are roughly same with that of base metals.||Properties of weld bead can be improved to desired level by suitably selecting compatible filler.|
|Joints are susceptible to corrosion. Corrosion resistance of the joint cannot be improved by homogeneous welding.||Corrosion resistance of the joint can be enhanced by heterogeneous welding. This is advantageous for marine applications.|
|No dilution effect exists here.||During melting, dilution effect (change in composition in filler metal due to its mixing with the base metal) needs to be carefully controlled.|
|Rate of expansion or contraction is approximately same for molten filler and base metals. So chance of crack formation is also less.||Unequal rate of contraction between molten filler and base metals during solidification can lead to residual stress generation and crack formation, which are highly undesirable.|