I recently saw a potential demand for a product that was essentially a seamless rectangular metal cup, about 1″ x 3″ on the open end and about 4″ deep. This sounded like a job for a process called “deep drawing.” In this process, a flat sheet of metal is punched through a die to form a cup shape.
Great, all I need are a few prototypes to verify the design, then a few tens of pieces for some tentative test marketing, and finally perhaps a few thousand a year for production. One problem: for a deep drawn part, a “short run” is considered “less than 60,000 pieces.” I could find only one company that could actually deliver sample parts, but none of their standard sizes were close enough to what I needed.
Many industries and processes seem to be this way. Here are a few of the common characteristics:
- There are no standard sizes
- Every part is custom
- No parts are stocked
- The process requires expensive tooling
- The tooling is optimized for long life and a high rate of production
- There are high setup costs and minimum lot charges.
- If a company does offer any “standard” parts, it means “We made that for someone once, and we still have the tooling, so we might make more.”
Plastic injection molding used to be this way, and mostly still is. Injection molding is a great way to make thousands and thousands of parts for only pennies each. Traditionally, the molds are made from hardened tool steel. The two halves of the mold are carefully hand-finished by skilled craftsmen to fit perfectly together. They are highly polished, again by hand, so that the parts release easily and the wear to the tool is minimized. Extensive cooling channels are machined into the mold to rapidly cool the part. As the first parts are run, the process parameters for temperature, pressure and time are tweaked and optimized until the minimum cycle time is achieved.
This all makes sense, because when you’re making a million parts, shaving a second or two off the cycle time means you can finish the run weeks sooner. This might translate to hundreds of thousands of dollars saved. But what if you only need a few hundred or thousand parts?
About ten years ago, I needed a few thousand plastic parts for a one-time project. The cost of having them machined was way too high. Then I looked into injection molding. I ended up paying about $10,000 for tooling plus a few hundred dollars for about two thousand parts. Economically it worked out to only $5 per part in the end, but it seemed like such a waste. I asked the molding house, do you have to use tool steel? It takes longer to set up the machine than to run the parts, can’t you settle for a slower cycle time? The answer was “we just don’t do things that way.”
I’m not the only one to experience that frustration, and now there is at least one company that specializes in prototype and short run injection molding. They make their molds out of aluminum with a minimum of bells and whistles, they are not interested in getting the fastest cycle time and they are not picky about the finish if you’re not – but their real strength is their automated process.
To get a quote, you fill out the order page on their website and upload a solid CAD model of your part. The part is automatically analyzed for any features that might cause manufacturing issues. When you place your order, their system automatically generates the CNC programs for their machines to mill the molds. This is all done with a minimum of human intervention, interpretation or communication. There are no 2D drawings, dimensions or tolerances – you just accept their standard tolerance and they do their best to match your model.
This company has already branched off into making machined parts as well. They already had all the technology to automate the machine of molds for CAD modeled parts, so it took no work to start offering to directly machine the actual parts themselves.
The electronics industry seems to be ahead of the curve on this phenomenon. Etched printed circuit boards used to be part where only high-volumes were justified. For years now there have existed a huge number of PCB fabricators that are willing and able to produce short runs (often only a few pieces) efficiently. Once again, the key is an automated, no-touch process from the customer’s digital file to the finished product.
The next step is already being taken, with several companies offering services that assemble and solder the parts on the board. This is possible because existing PCB design software is about to export all the required data in digital form.
Given these examples, here are a few of the keys to producing prototypes and short runs of traditionally high-volume parts:
- Make tooling that is only as good as needed to do the job at hand, not optimized for long life and rapid production. Make the old-line industry insiders cringe.
- The design of the part should be available in an industry standard digital format, such as a CAD program file of a solid model.
- Alternately, the parameters of the part should be simple and unambiguous enough that they can be entered on an online order form, such as the length, width, depth, wall thickness and material of a metal box.
- Finally, the process from customer data to finished part should be as automated as possible, requiring minimal skill and no trial and error to produce.
Back to deep drawing: Is it possible to adapt these concepts to deep drawn parts? Probably not commercially as a custom deep-drawing house. I don’t think the demand is there. However, can a simple tool be used in-house by a company that needs only a small volume of parts? Originally, I didn’t think so. The die design seemed to require a lot of experience and intuitive feel for the process to get it right. That’s probably true, IF you are trying to make a large number of parts as efficiently as possible. I found a scan of an old, out of copyright book about die design on Google Books and the formulas seem to be straightforward. I’m very tempted to make a simple die out of low-carbon steel and try deep drawing some parts on a hand-operated hydraulic shop press, just to see if it can be done.