Yurchenco and Sun on Injection Molding and Precision

Source: Interview with Jim Yurchenco and Rickson Sun, 26 April 2000.

Injection Molding

Yurchenco: And of course we were pushing in the area of molding-- Our knowledge as a company at that point of molding processes and what could be done in tooling was pretty tiny. We knew a few basic rules, and we had a few guidebooks published by General Electric, with rules of thumb that after a while you learn don't mean anything anyway, so you're always wondering, what can I get away with? You're looking at other parts, other things that are out there, and saying, "Ooh, look at this. They did this, so maybe I could do this, too."

Pang: Was it clear that you had to go with injection molding for this, or were there--

Yurchenco: There were no other viable alternatives, in terms of effectiveness for the dollar. The cost of these parts is so low: basically you rent a machine for X dollars an hour, and it'll produce Y parts per hour, and the cost of materials is a dollar a pound or something, and you're dealing with grams of material per unit. It's accurate, it's reproducible, the tooling is relatively inexpensive. There are other processes used for high-volume production, but all of them have drawbacks compared to injection molding for this type of product, where you don't have really difficult mechanical environments for things to live in-- high temperature, high forces, radiation, so forth. For normal human environments this is a great process.

Jim Yurchenco talks at greater length about the choice of injection molding in another interview.

Sun: It was amazing that when we went over the resolution requirements, given the state of the art you were willing to push injection molding, to how small you were willing to mold those slots and encoders, and it worked out.

Yurchenco: [spreads out drawing] Rickson's talking about these little wheels that have slots that open and close in front of the LED and phototransistor, which are captured inside this device. How small a piece of steel can you accurately make? This was 20-some years ago, and injection molding has come a long way particularly in tooling, and one of the reasons that mice are cheaper is that you can do things in tooling that were extremely difficult to do in those days. Almost everything was machined in those days, and EDM work-- which was burning-- was relatively new and not widespread. And there certainly was no CNC machining, everything had to be made from drawings, there was no real connection to databases that you could use to compute cutter paths and so forth.

So there was a lot more human skill in making a tool like this in some ways than there is today. A lot of this is turned over to machines. The operators get a lot more metal cut per hour, and I don't want to denigrate the toolmakers. But the guy who made this (holds up model of ribcage) was a guy named Vic Renden, in a company called Mico-Molding over in Santa Clara, and this was a really magnificent piece of work that he did on this tool.

Sun: I don't think he's around any more, but he had some interesting stories, because it was a difficult part to mold. Apple pulled the tool from him, because they found someone who said they could make it for less, but it turned out they weren't able to make it. So they had to bring the tool back to Vic Renden.

Yurchenco: The bean counters sometimes take over and shoot themselves in the foot.

Sun: How long did it take you to come up with this?

Yurchenco: I don't know, I have no recall on what the timeline was on this.... I don't remember it taking an extraordinary period of time, maybe a couple weeks. I mean, it was fun; it was really fun. So the time kind of goes right by. This wasn't drudgery, this was a real kick.

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Document created on 10 June 2000;