I saw a comment posted a while ago asking if it is necessary to consider Design for Manufacture when in the early stages of design ….. absolutely! The design itself and the manufacturing technique are so intertwined that to design without manufacture in mind will likely lead to parts that cannot be made within cost targets. It is inconceivable to not consider design and manufacture concurrently.
Material and geometry are to a greater extent constrained by the manufacturing process selected. The process chosen will largely determine the material, the shape and the amount of secondary machining necessary on the part. In short, the manufacturing process chosen will affect or even dictate the fit, form, function as well as cost.
Consider a machined enclosure that has a face acting as a heat sink. There is a tendency to always machine functioning prototypes from “Solid”, which will likely result in the use of Aluminium alloy 6082 or 6063. These alloys are readily available, are easy to machine and have a good coefficient of thermal conductivity so are great for housing electronics. So far, so good.
Machining can be quite a time-intensive process, depending on the geometry to be created. In this rather simplistic illustration the costs to produce a real-life enclosure base part by 3 different methods are compared:
In this particular case machining is the cheapest option for less than 45 parts, after which Sand Casting becomes more attractive. Once over around 350 units it’s Gravity Die all the way.
The problem is that these three processes necessitate the use of different materials and will require different geometry to enable them to be made cost-effectively. You simply cannot design a vanilla flavoured enclosure and then send off an RFQ to see how best to make it. For example, the machined enclosures are cheapest with orthogonal walls whereas drafts will be required for the cast versions. Sand casting requires the minimum wall thickness to be greater than those cast by die, and if it was dimensionally the same the die casting will be heavier than its sand counterpart due to the increase in density.
This will result in finished parts of different mass, strength, finish and thermal performance, so if the performance of the part is critical then it will likely need to be redesigned and re-engineered to best suit the new method of manufacture.
The solution is clear – design for the intended volume from the onset and obtain information on the likely cost (& lead-times) when in the concept stage, so that an informed decision can be made at the Concept Ready milestone. Engineering work (structural, thermal etc.) also needs to be done at this early stage – the decision on the method of manufacture will be locked-in very early in the process, so it needs to be right and the part will need to function to specification. Don’t omit the secondary operations such as machining for gasket mating faces, painting & masking – the devil is in the detail and these will amount to the lion’s share of the cost! Once the technique that will deliver the best-fit performance has been identified it’s a case of optimising the detailed designing for the chosen method of manufacture.
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