Following some basic design rules can help you design successful plastic injection-molded parts. You can also get the parts that you want in less time than you expected.
A lot depends on the particular process you choose, whether the rules are bent, and by how much. Some of these rules can be bent if it's absolutely necessary for the design. But that means dealing with the costs and consequences.
During the Design News Radio Show on Thursday, July 11, at noon ET (9:00 a.m. PT), participants will learn how to use the injection molding process and work within its guidelines to make the most of its flexibility and enormous potential.
One material option that I talked to a guy about is the mold. For lower production totals you can use aluminum. Produced on a CNC machine you could make a few hundred parts with it. This makes another interesting option for low rate manufacturing.
Actually, aluminum molds can easily accommodate 10's of thousands of shots – easily up to about 35k without any honing or refinishing, and are known to produce as many as 100,000 shots. So why don't more OEMs pursue the aluminum option-?
Several reasons: primarily , machining aluminum cavity blocks costs about 90% of the cost and effort of machining steel blocks (commonly used is P20 steel), and the steel lasts 10x longer in mold cycling (typically 500,000 to 1M). So for the price of Steel (about 10% more) an OEM gets about 10x the tool life. It's a bargain.
Also from the manufacturing perspectives, most tool-makers have discovered that machining carbon electrodes then using those electrodes to EDM burn the metal cavity geometry is actually more cost effective (in materials & machine time) than direct milling the cavities. EDM burning P20 steel is common, but I've never seen aluminum burned. (,,,,wonder if its lucrative, or even possible-?)
There are other Pro's and Cons, but one is BIG for Design Engineers: the part quality. Most parts will look OK in either aluminum or steel mold cavities, but for more complex, and especially thin-walled plastic parts, steel gives superior results, and holds better dimensional accuracy. I remember several programs where we prototyped using Aluminum tools and put molded parts into Environmental testing --- with terrible results. We learned we were wasted time, "Chasing Ghosts" – trying to resolve failure issues that cleared up when parts were molded with production tool steel.
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