PLASTICS, ANYONE?

by Chuck Umeda 00 10

 The mention of plastics has different meaning for different people.  At the supermarket, it’s “paper or plastic?”  At the mall, you’re asked, “cash, check or ‘plastic?’”  Inventors are quick-witted folks who can cope with the choices between plastic and whatever in a store.  But many also envision plastic having a major role in their product for construction or packaging or for both.  But most inventors don’t know the technical side of plastics or how to pick the best one for their idea.  The good news is that there are a dizzying number of plastics and the bad news is that there are a dizzying number of plastics.  So where does one begin?

 One sensible solution is to find a local plastics fabricator.  In Tucson, we are fortunate to have Earle Wheatley, President and owner of both First Light (Creative Engineering Services, Inc., 520-624-8497) and also Creative Plastics & Services, Inc. (520-624-3770) for 8 years.  Creative Plastics works with acrylics (Plexiglas) and other plastics by vacuum forming and welding in larger quantities.  First Light would be a better choice for inventors for help with prototyping, packing and R&D (research and development).  Earle’s business is big enough to have a good variety of production equipment, an established operation and yet responsive enough so that a customer can contact him directly.  That’s a good thing, because he has much experience and ideas to offer.  For 24 years, he has been involved in all phases of the business: distribution, engineering, research & development, prototyping, packaging, point of purchase display development and production.  For inventors, the best part is that he is willing to work with us and do so under a “non-disclosure” agreement.

 In plastics, the factors to consider are piece price and investment of tooling, usually molds and mechanization.  Basically, there are four tiers as shown in the following table based on information from Earle Wheatley. 

The complexity of the product increases cost.  Costs associated with prototyping range from $35 to $150 per hour.

Machining has low starting cost, but the labor of the machinist makes the piece price high.  However, for some prototypes or certain hard plastics this may be the only option.

 Earle says that for prototyping and product development, vacuum forming is a good method, because one can “prove things and answer questions” very quickly.  It’s a process where a mold of the product is constructed out of wood or plastic.  A sheet of plastic is heated until it “sags” and shapes itself to the mold.  Vacuum ensures that the plastic forms to every feature of the mold.  The plastic sheet is cooled, and after some trimming and finishing operations, if needed, the part is essentially complete.  By using a plastic or wood mold, changes to the mold are made quickly and another part made.  The inventor can go through several change mold/vacuum form/evaluate product cycles rapidly.  Good features can be enhanced and poor features eliminated.  Mold costs for prototypes typically range from $200 to $1,500.  Lead time is 2 – 5 weeks.  As the product is finalized, a durable aluminum vacuum-forming mold can then be made.  Typical range of costs for production molds is $900 to $5,000.  Three to eight weeks are required for an aluminum mold.  Earle says that plastic sheet up to 3/8” thick can be vacuum formed!

The next tier is “roto” (rotational) molding and blow molding.  Most plastic bottles are made by blow molding.  Tooling costs and cost of equipment required to use that tooling increase.  The advantage is lower piece price through high production rates.

Lowest piece prices are obtained through injection molding.  Molds for this purpose typically have multiple cavities and require significant investment.  Injection molding presses heat the plastic resin and under high pressure forces it into the cavities.  When the part is cooled, the mold is opened and part is removed.  Very little finishing operations are needed.  Hardened steel molds are used because of the high pressure.  An injection mold costs $25,000 to $150,000 can produce 14¢ parts.  Lead-time for a mold is 10 to 24 weeks.  Aluminum molds cost less, but have limitations.  Earle does not do injection molding, but does provide engineering consulting for that.

How can an inventor decide what plastic to use?  Consider what the temperature requirements for the product are.  Is it used indoors (“room” temperature) or outdoors?  Must it withstand high or low temperatures?  ABS, for example costs $1 - $2 per lb., and has good temperature characteristics.  Polyethylene is $0.70 to $1 per lb.  What chemicals must it withstand?  How about wear characteristics?  What thickness of material is needed?  These questions determine the mold requirements.  Make a few first samples so that the design can be evaluated, tested and refined. 

Earle pointed out the importance of packaging.  It is the last thing people think of in terms of their product, but it is the first thing the buyer sees.  Packaging plays a vital part to protect your product and show it off.  The packaged product is what the public sees and the impression buyers get.  A cheap package implies a cheap product.  Yet, by careful planning, your product can be marketed with an inexpensive package that suggests quality.

Earle’s business are located at 2570 N. Huachuca Drive, Tucson, AZ,  85745.