January 11, 2013 AT 3:13 pm

Updates from Bunnie’s Manufacturing Tour of China

Bunnie’s written a brief summary of his activities so far on his manufacturing tour of China with the MIT Media Lab. Our mutual friend Akiba, who’s also along on the trip, has some nice write-ups as well. He writes:

The first day of tours started and it was an amazing experience. I’ve never been really super interested in the process of injection molding but after seeing how things are done, I found the subject fascinating. We started the day off taking the van to an injection molding factory. The owner of the factory welcomed us with open arms and surprisingly allowed us to take pictures inside the facility.

Our first stop was a meeting room where the owner brought out samples of injection molded devices for us to examine. Coleman, an injection molding expert from AQS (a contract manufacturer that’s helping us organize the tours) and Bunnie were explaining how the parts were made, the materials, finish, what decisions went into making the mold, defects, and identifying the markings from the different parts of the mold. I was impressed how much information could be had just by looking at a plastic enclosure. They were able to reverse engineer the design tradeoffs that the designers had to make, some bad decisions, and were easily able to approximate the cost of the tooling and cost per part.

After we had the discussion and an intense introduction to plastic injection molding, we headed to the tool & die shop where they make the tooling for the injection molding. The tooling is the actual steel mold that you specify to the shop for the enclosure that you want. You would normally send them your design files and an engineer from either the injection molding shop or the contract manufacturer would review the files. They’d make recommendations on how to modify the design files to improve yield and make the design more robust. From there, it’d get sent to the tool and die shop to have the design cut out of steel. One thing they cautioned on was that they were able to cut the steel molds on site, but the mold blocks which hold the molds are usually custom designed and outsourced. These have a lead time and during a busy period, could extend up to a few months. So as soon as they design size is fixed, they recommended to pre order the mold blocks to make sure they’re reserved. Then have the mold and tooling made.

The tool and die shop was amazing. I had no idea how massive the tooling was just to make a simple enclosure. The tooling is cut out of steel using CNC, EDM (Electron Discharge Machining), and manual milling. Each steel mold can weigh a ton or more and requires a lot of manual and automated work. Depending on the finish, the molds also need to be hand polished. To tool and die shop consists of a lot of heavy metalworking equipment. The steel blocks are first cut on the CNC machine. The EDM machine is used to remove steel in parts that can’t be cut accurately using a CNC machine. It uses electrical current to remove steel at a rate of 5 microns per electrical burst. They can also use EDM machines to slice large blocks of steel. The one we saw was around one foot tall and six inches thick!

Looks like the folks on this tour are getting a great education in the secrets of DFM and fabrication processes — wish I was there too!


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