Trouble with Extruded and Injection Molded Parts

Skippy: Hey Buzz - here was someone who needed help – “I have developed a new product for the construction industry. All was good while in u.s. except tooling costs. We decided to outsource to china to try to resolve this problem but in doing so we set ourselves back (over a year now) from taking this to market. ... (Product includes) both extrusion and injection molding ... with tight tolerances as profile extrusion marries to injection components. Also seeking advice on injection molds as currently mold maker claims to be doing "adjustments" to molds for about three weeks now. I am leery as to the quality of molds loss of temper etc. What should I look for in pics before final payment is made to ensure I am receiving a quality mold?”

Buzz: Any serious plastics professional will tell you that there are three major considerations in assemblies of injection molded and extruded parts - particularly when they are going to be used together with other mating parts, and sold anonymously through distribution into a vague category like 'Construction' - especially with warranty related questions in the background. The inquiry didn't mention number of cavities and general mold design criteria so without specifics it would be difficult to 'direct' them on the injection molding portion at this early point.

Skippy: What is needed?

Buzz: Consistent, clear and written communication should be the watchwords. Depending on which of these following items you NEED, it will change the way one would think about design and tool up of either plastic process, and the resulting 'tweaks' needed on tooling -

1) Dimensions (critical, control, reference)
2) Aesthetics (critical, control, reference surfaces)
3) Physicals (flammability, electrical, impact, UV, reactivity with other parts etc)

Skippy: So what thinking should be included in the ' big picture '?

Buzz: Here are a few general thoughts to consider (assuming the DESIGN issues are taken care of:)

a) Photostereolithography - for $1500 or so you can have sample parts made to dimension for critical assembly fits, including undercuts, blind holes etc. Bet on the final injection molded parts being closer to print than the extrusions (caveat - a poorly or improperly packed, voided, or stress-molded-in part can 'hit the numbers' and still be a poorly performing part in application - see Aesthetics and Physicals) and then have some examples of the extrusion produced with high and low critical tolerances produced by p- as above and submitted by your extruder. In many years, we've not found more than about a half dozen with more than 3-4 CRITICAL dimensions for assembly between parts. On the other hand - a major item to think about during the contract review process would be what OTHER mating parts does your system need to match up with? It may be that one of the parts is not yet fully developed in how it relates to them . . .

b) Understand what you NEED in terms of the big three stated above - one of the three is always easy to produce at 'rate and weight'; two of three is more difficult and probably will affect production rates, all three will nearly always affect production and discard rates and therefore your final delivered price.

c) Insist that your sample parts be produced from the actual production tooling at PRODUCTION rates from PRODUCTION material - nothing creates more ' availability to market headaches ' than to submit your sample assemblies for further consideration (aka engineering evaluations - electrical, UV, or smoke/flame) only to find out that the sample parts were made from a general purpose or utility grade of material that does not include any additives addressing your special needs - self extinguishing characteristics, dielectric properties, impact or notched IZOD capability, UV characteristics, static dissipative qualities, biocides, fungicides etc.

d) Work with a house that has their own in-house wire capability for the extrusion tooling. It is much less costly to open up or remake the extrusion tooling than the injection molding tooling - probably on the order of 6-10 to one. Ask to see examples of their tooling and their tool storage area. Notice how they keep the unused tooling on the shelf - cleaned and measured, shiny and production ready or rusty, filled with plastic and unkempt against the day someone might reorder? A number of houses will quote inexpensive flat plate tooling, but be wary of the how these tools work over multiple lots of raw materials which can and do change - particularly if your spec a 'utility grade' of material.

e) Be at least a little paranoid; Trust, but Verify. For every one of the good plastic outfits out there, there are some who won't measure up beyond the sample parts. Look for a house that has some sort of quality system/policy (with or without the ISO moniker), with sample retains on less than perfect quality parts used year to year to maintain quality checks on output, and written records of past production runs including retained information back to incoming raw materials and supplier raw materials certifications if possible etc.

f) While working with your Product Manager, get it in writing; material specs, quality and production records - ask to attend and help fill out a 'Contract Review' - answering the couple dozen critical questions that a good processor needs answers to to ' help them help you ' is a critical path to success. Some sales people can actually act in this ' Product Management ' role; and unfortunately many can't.

g) Ask for and be prepared to get enough samples to have engineering testing done on the resulting samples - and do it.

A well run product development process has additional nuances of course, but these should give you a good grounding.