Plastics ProcessingQ: I am investigating low volume methods of producing plastic parts for vehicles, i.e. bumpers and rear view mirror casings. Please send me information regarding methods of producing plastic parts in a quick cost-effective manner using plastics including ABS, PP and HDPE.
A: The primary method used to produce plastic parts, especially bumpers and rear view mirror casings, is injection molding. However, some bumper fascia (the exterior cover), are produced using thermoforming techniques. Vacuum thermoforming heats a sheet of plastic (generally an amorphous resin with a softening point) until it softens and conforms to the low-cost mold. You may be able to use this process with polypropylene or HDPE. The major production process for rear and side view mirror casings is also injection molding. In the past, many side view mirror housings were cast zinc. However, because of its higher weight and cost, plastic housings currently prevail. I am unaware of other processing methods used for mirror casings. One might use thermoforming plus secondary machining to produce an interior mirror housing. If you choose to use thermoforming, I would suggest using either PP or HDPE. The Society of Plastics Industries (SPI) is a trade association primarily composed of plastics processors and plastics processing equipment manufacturers. You may find consulting with them to be helpful in your research.
Q: Is it more viable financially to produce parts in small volumes using thermoforming as opposed to injection molding?
A: In general, a thermoformed part is economical for low volumes because the cost of the mold is generally lower. The trade-off is that thermoforming a part generally takes a longer cycle time than injection molding, increasing one's labor costs. When producing a limited number of parts thermoforming molds can be made of wood or other low cost materials. For a part as large as a bumper fascia, however, the cost of an injection molding production tool will be in the hundreds of thousands of dollars, and the injection molding machine is usually a 3500 ton press (very large!), your only option would be to thermoform the part.
Smaller parts, of course have different economics, because prototype tools for injection molding can be made at relatively low cost. I suggest you consult with a local plastics molder near your university for further advice.
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