After two post on the basics and workshop structure, I can finally start to go into the details of which questions to ask for design for manufacturing (DFM). In subsequent posts I will have more questions on design for assembly (DFA), which can of course be combined into design for manufacturing and assembly (DFMA). I will also have a brief refresher on creativity techniques. Let’s start asking questions!
Design for Manufacturing Questions
Design for manufacturing looks for cost potentials during manufacturing. The details here are very part specific, but creativity can be inspired by a series of questions. Here I look in particular at design for manufacturing. This excludes the related design for assembly, which I will discuss later. Hence, manufacturing is any type of casting, forging, cutting, or similar operations that do NOT assemble the product. Although, there may be quite a bit of overlap in the questions.
Can You Use a Softer Material?
Processing cost for cutting processes may depend a lot on the hardness of the material. Using a hard material may take more time, and a softer material may be handled with increased cutting speed and/or depth, reducing processing time. The harder material may also wear out the tool faster, or even increase the wear on the machine due to the harder chips that are created. For example, can your replace hardened steel with normal steel, or normal steel with aluminum, or aluminum with plastic, etc?
Overall, a softer material may be able to reduce the machining cost, as long as the function is still adequate.
Are There Cheaper/Better Production Processes?
It may be possible to replace an expensive process with a cheaper or better production process. This is especially useful if you have not yet purchased the machines or tools. Can you change the design so a three-axis milling machine is sufficient and you don’t need the more-expensive five-axis milling machine?
Another example is to replace an expensive cast-iron part with formed sheet metal. Often, sheet-metal parts are much easier to produce than cast parts. For example, Papst Manufacturing was THE bicycle company around 1890. Their bicycle hubs were made from cast steel. They were extremely strong, but also very expensive and heavy. Its competitor Western Wheel Works designed these hubs using sheet metal, which was much more profitable and popular, and that helped them to overtake their competitor.
Especially with plastic injection molding, undercuts is a big topic. Every undercut requires an often-complex mechanism in the mold to handle this undercut. Every single undercut can easily add tens of thousands of euros to the cost of the mold. Luckily, any mold designer worth his money is already trying to avoid undercuts. But see if maybe you can reduce them even more.
Can You Reduce the Number of Process Steps?
Another big question is if you can reduce the number of process steps. Every additional process step increases handling, transport, waiting, and a lot of other factors that can cause additional cost. You may not always find potential here, but it is possible.
Can You Loosen the Tolerances?
Tolerance limits are hard to define. Make them too lose and quality suffers. Make them too tight and costs go up. The design department is measured, among other things, on product quality but not so often on product cost. Hence, in case of doubt design, departments will often go for tighter tolerances. Production, on the other hand, is more often measured on the production cost, and would like to have loser tolerances. These conflicting goals are complicated by the fact that most tolerances are not based on hard facts but rather on gut feeling and opinions. Arguing based on opinions has a lot of conflict potential. Yet, often there is also potential in loosening tolerances and therefore reducing manufacturing cost.
Can You Use Common Parts?
The use of common parts is often a big potential in design for manufacturing. This overlaps later with design for assembly where we try to reduce the number of part variants. Rather than having a custom-designed part for your product, it may be better to re-use a part that you have already designed. Or even better, can you use an off-the-shelf standard part?
The more common parts you have, the larger the production quantity for these parts. Larger quantities benefit from the economy of scale. It is usually cheaper per part to make twenty parts instead of ten. This doesn’t even include the additional benefits that we will find during assembly.
Can You Simplify or Eliminate the Set Up?
It may also be possible to change the part design to simplify the set-up or the changeover. This topic crosses into the topic of changeover optimization, also known as SMED. Can you design your parts in a way that makes it easier to change your machines from one part to another? Or generally cheaper to set up the part in a machine?
For example, in the early history of American industrialization, John Hall managed to introduce interchangeable parts to gun making around 1800. Interchangeability required precision, and to make precision manufacturing easier, Hall used a reference point that he called a bearing point to his parts. This was the starting location for any dimensions measured or gauged, simplifying the later manufacturing processes.
Maybe you can eliminate the set-up altogether? Can you design your part in a way that it is machined only from one side, eliminating machining on the other side and hence eliminating a set up altogether. There are parts out there where the machining itself takes mere minutes, but the set-up requires hours of labor and downtime of the machine.
These design for manufacturing techniques require creativity and new ways of thinking to improve your product design for better manufacturing and/or assembly. This is a good time to use creativity techniques. Probably the most common one (but also a bit boring) is brainstorming. For more on this see my post How to Do Brainstorming.
But there are more techniques out there. One of my favorites is creative provocation, where the moderator tries to figure out where some unsolved problems are based on the discussion. Next the moderator adds an artificial limitation by requiring the team to design a part that avoids this problem altogether. For example, in one of my previous workshops, the team had trouble finding a good way to bring a workpiece carrier back to the beginning of the line. I then challenged them to design a line without any workpiece carriers. The resulting solution amazed them. Again, this creative prevocation is one of my favorite creativity techniques. For more see my post on creative provocation.
This post looked at how to make manufacturing easier. My next posts will look at how to make assembly easier. This design for assembly has a lot of potential, and I have a total of three posts looking only at design for assembly. Now, go out, make your parts easier to manufacture, and optimize your industry!