The selection of a suitable process to manufacture a component is not a straightforward matter. There are many factors which need to be considered, for example: size of component, material to be processed and tolerance on dimensions. Whilst all processes have slightly different capabilities, there is also a large overlap - for many components there are a large number of processes which would do the job okay. So, where do we start?
Material compatibility
In product analysis (and a lot of design work), the material to be processed is often known before the process to be used has been decided. This makes life a little easier as the first thing we can do now is check what processes can be used for our chosen material - i.e. which are compatible. For convenience, processes can be split up into:
Metal shaping: e.g. forging, rolling, casting
Polymer shaping: e.g. blow moulding, vacuum forming
Composite forming: e.g. hand lay-up
Ceramic processing: e.g. sintering
Machining: e.g. grinding, drilling
Joining: e.g. soldering, gluing
We can then use a material-process compatibility table to determine which processes are suitable.
|
+ : routine ? : difficult X : unsuitable |
Polymer | Wood | ||
| ABS (thermoplastic) |
UF (thermoset) |
Pine | ||
| Polymer Shaping |
Polymer extrusion | + | X | |
| Compression moulding | + | + | ||
| Injection moulding | + | ? | ||
| Blow moulding | + | X | ||
| Machining | Milling | + | X | + |
| Grinding | X | X | + | |
| Drilling | + | ? | + | |
| Cutting | + | ? | + | |
| Joining | Fasteners | + | + | + |
| Solder / braze | X | X | X | |
| Welding | + | X | X | |
| Adhesives | + | + | + | |
Technical performance
The next stage is to assess the various technical aspects of each process to see whether they will perform well. For example:
Can we make something this size? For instance, you can't die-cast an engine block - it's too big.
Is the processes suitable for the shape we need? For example: tubes are long and thin so ideal for extrusion but not casting; and you can't blow-mould a telephone case because of all the holes in it!
Will we get the finish we want? Both dimensional tolerance (accuracy) and surface roughness (smoothness) are strongly influenced by which process is used, for instance sand casting is poor for both whilst die-casting is very good.
How good will the quality be? This is the most difficult problem to address and usually there is little that can be said without actually trying it! However, we can sometimes make rough comparisons - for instance sand castings can often be porous and so might not be very strong.
All this kind of information can only be obtained by reading descriptions of the various processes and then making informed decisions - of course experience helps!
Once all the processes that can perform well have been identified, the final step is to compare the costs of the various options...
Next: Compare the costs of competing manufacturing routes.The approach to process selection given here is, of course, not the only one possible - it is geared towards the processing information provided on the TEP CD-ROM and constitutes a reasonable approach at this level. Many processing routes involve a series of manufacturing steps (e.g. cast, machine, grind and drill), but this is beyond the scope of our discussion.