I am sending this out on a Sunday because I am just too busy to do so during the week. To those who have responded and reached out to me, I thank you for having confidence in me. I will prove to you that you have made a good decision. Although I still have time available for new clients, working on a first-come first-served basis tends to push delivery times out a bit, for those who contact me later rather than sooner. “Yesterday” is all booked up, so if you call and want your design work done yesterday, I will not be able to comply. Seriously, please do not procrastinate in contacting me if you have some work you want done. I really hate to disappoint my clients and potential clients or provide delivery dates far in the future.
Last time I presented the concepts of DFM (Design For Manufacturability) and DFA (Design For Assembly) and started with a brief discussion of DFM. So, let’s take a brief look now at DFA and consider how that affects a product’s design.
Wouldn’t life be great if the only assembly we needed to do was to load balls into the tips of ball-point pens or between the inner and outer races of ball bearings? Taking only a single dimension to define a sphere, there is no consideration about left side, right side, front, back, top or bottom. What a breeze, just drop them in place – no orientation required. However, if you have components that have any other geometry, DFA is something to which you need to pay attention. Let’s look at a slightly more difficult part to assemble.
Take, for example, a cylindrical pin that needs to be inserted into a hole in a part. If it is possible to make both ends of the pin the same, say the same fillet radius or chamfer, you have made life a lot more simple. If the production volume warrants, feeding the pins from a vibratory feeder bowl and track is a breeze. For hand assembly, just pick up a pin from a box of pins, place it in the hole and just hammer it in.
Making it a little more difficult, suppose you have a pin that is 2” long, has the same fillet radius on both ends, with only half the length of the pin (1”) measuring Ø.5000” and the other half measuring Ø.5005” with a tolerance on the dimensions of ±.0001”. Now, the pin has to be inserted into a hole measuring Ø.4995” ±.0001”, such that the smaller end of the pin (Ø.5000”) protrudes. How do you error-proof this assembly operation? You need either a skilled and careful person doing this operation and/or a rather sophisticated (expensive) piece of measuring and inserting equipment. Those, apparently, are your only choices.
Although many would leave it at that point, my first thought is to ask what fits on the end of the pin that protrudes. Perhaps it’s a part that has to be removed and replaced periodically. If so, why not just open up the hole in this second part, so you can use a pin as described in the earlier example. A pin with the same diameter along its full length is definitely going to be a whole lot cheaper than a “stepped” pin. And, since you have to make the hole in the second part anyway, why not make the hole a thousandth of an inch bigger to start with?
To some this is a very obvious example, but my point is to communicate the concept. We will look at some different scenarios of how DFA concepts can be applied to make sure you get the best product at the lowest cost.
Again, I am out of space and out of time. Stay tuned.