There’s more to CNC machining than the model

The scenario is familiar: a designer comes up with an idea for a product — a consumer device, part of a military system, a vehicle, etc. After some refinement, the next step is the detailed design and creation of a prototype. Engineers then generate CAD models for all the parts of the new product and start looking for someone to make them. And that’s where trouble can start. How do they choose a production company to make the new parts, and how do they work with that company?

One approach, says Scott Garron, Technical Sales Engineer at Protolabs, is to go to a broker that farms out each part to one or more manufacturing houses. This method works, he says, except that it makes no provision for the design engineer to work with the people who actually cut the metal. If there’s a problem, everything has to begin again —adding to the overall lead time and cost to manufacture.. And if there’s a problem in doing the machining, who will take the responsibility? And what happens to the schedule?

A better approach, Garron says, is to bypass the jobber and go directly to the contract manufacturer. If there’s a problem with the design, he explains, an application engineer from that company will get with the designer and work things out. And if brought in early enough, the application engineer can provide feedback that will help the designer avoid pitfalls that will add additional and unnecessary time and expense.

Younger engineers, he points out, may not have much experience in manufacturing processes, and may design a part that will be difficult to produce. Those of us of a certain age may remember that Toyota was known for requiring new engineers to work in production for a year before beginning their design work — solely to educate them on how things are made and what’s necessary for them to be manufacturable.

“You bring a smart young engineer,” Garron says, ”but unless you let him see what he’s actually doing out on a practical application, in a machine, understands how the tooling works, understands the different grades of metal and how they move,” he’s likely to create less-than-optimal designs. The cure? “There’s so much that goes into it,” he explains, that “even a few months of just sitting at a machine and listening to a machinist would help him understand what they’re doing.”

A common error, Garron says, is to design something overly complicated. “Get some feedback on what those actual parts look like,” he advises. “Perhaps six out of ten times they could be simplified, and when you simplify a part, and you understand it better, you can machine it faster and cheaper.”

Another is to misunderstand — or ignore — details such as wall heights and feature sizes, the need to provide relief in corner pockets, or the choice of materials (does it have to be 17-4 PH stainless or would 316L or 304 work?).

Ultimately, in all these cases and more, talking to an application engineer before finalizing the model can save a great deal of time and cost in manufacture. As Garron puts it, “Just because you can think it doesn’t mean you can manufacture it.”