It seems that plastic parts manufacturers are continually being exercised by purchasing agents to quote a lower price on a part that is already being supplied by another company. The truth is that most of the time the cost of that plastic part is not so much dependent on the supplier, as on the part’s design – which was fixed at its design inception. It’s cost has been designed-in, sometimes many years ago.
There are many factors that affect the cost of a plastic part, many of which can be optimized and controlled at the beginning, before the part is hard-tooled. So, the first step as you embark upon the design of a new plastic part is, “Stop for a moment! Before it’s too late!”
The following factors must be considered when designing-in costs (or conversely designing-out costs).
The number of mold cavities: The labor cost of a part, as well as its overhead, is largely related to the amount of time it takes for a molding machine to run through a single cycle. Running a two-cavity (or multi-cavity) mold, means that both the labor and machine overhead costs are cut roughly in half, or by a factor directly proportional to the number of cavities.
Part tolerances: Engineers and designers have a natural tendency to want to require tighter tolerances than might actually be required for a part. Double checking with the engineer to assure than no dimension is specified tighter than required, can save both scrap and mold cost.
The material selected for the part: Material costs vary over a wide range, and their selection can fall prey to the same over-engineering typical of tolerances. The ruggedness of a part, its wall thickness and thermal performance must all be considered – and not overstated.
Secondary operations: Any manufacturing work performed on a part after it is ejected from the mold is considered a secondary operation. Sometimes those activities comprise removing additional material (sometimes called flash) from the part, drilling holes or tapping holes in a part and even packing the parts for shipment. Designing the right mold tooling, selecting the right molding machine with the right pressure capacity and even installing post-molding cycle automation can eliminate the need for manual secondary operations
Manufacturing automation: The handling of material, before and after the mold cycle reduces labor costs significantly. Handling robots, stacking bins and automation for packing or the design of special packing carriers are all considerations that can reduce costs.
Scrap Management: The use of a “hot runner” system assures that the material in the gate (the channel through which the molding material flows in the mold cavity) is not scrapped between mold cycles – but rather is kept liquid to use in the next cycle. While the installation of a hot-runner system costs a little more up-front, in most cases it pays for itself quickly in reduced scrap.
Mold Retooling: Molds wear over time. Even though they are fabricated from hardened steel, today’s glass filled materials can erode a mold over time – creating a situation where a large proportion of parts coming from that mold are out-of-tolerance or simply unacceptable in some other way. Mold re-tooling not only reduces the amount of scrap produced, but should be considered as an opportunity to incorporate some other considerations for cost reduction – like a hot-runner or multi-cavity mold.
Some of the cost factors listed above are set at inception – others can be remedied after the design. Whatever the situation, it’s simply much easier to reduce the cost of a plastic part if these options are considered first.
For more information about how to achieve cost reductions of your plastic parts, please take a quick moment fill out our Inquiry Form or call us at 503-620-6950 ext.263
This blog was originally posted May 21st, 2012