Part & tooling designs...design for low cost parts, not tooling! - Business

MOLDING TECH TIPS 3-17-2007, Part & tooling designs...design for low cost parts, not tooling!

At MSINC, we see it EVERY DAY! It doesn't matter if you are a corporate automotive design engineer or a person starting a new business with a great invention; designing plastic parts to keep tooling costs down instead of designing your parts with a focus on keeping part costs down and quality is the "perfect storm" for your long term success!

Lets face the ugly truth. Launching new products into the marketplace requires a significant amount of "up front" capital money and everyone wants, and needs, to get the most return (bang) for their capital investment dollar (buck). Competition is fierce. Material and production costs always go up....not down. And even if you have a great product with little competition, you are still competing for consumer sales dollars that are not easy to get and keep for the long term.

Ok, now that we agree that every company launching a new plastic product will need to spend capital investment money on tooling before they can actually produce the parts in production quantities, and we agree that they want the best financial returns they can get back from the investments they have made, lets take the next step and assume they will actually want to stay in business if the returns are what they expected. Now we are coming to the real heart of what this article is all about...staying in business by designing your products to allow you to get the greatest financial returns on your business capital!

Now, plastic product design is a tough job. The "idea" designers design to get the products into CAD very simply and speedily without much of any consideration for anything else and we often make major changes to their part designs to make them feasible for injection molding. The "beginner" designers send us designs that can be injection molded without major changes, but will require minor changes for molding. The "average" designer sends us designs that are perfectly OK for injection molding, but are usually focused on simplicity of tooling instead of the production injection molding process itself. Finally, the "advanced" designer sends us part designs that are not only free of change requirements, but have a clear focus on robust part features, uniform wall thicknesses and many other things that will lend to lower priced parts overall.

Here are a couple of "financially irresponsible design thoughts".....and the problems with them...

"Tooling side actions like slides or cores are just too expensive"....WRONG! Too expensive compared to what? It is true that a "no action" mold will be cheaper than a mold with slides or lifters, BUT, in many cases adding features to your parts that require side actions can reduce the actual number of additional components needed in total product assemblies. Therefore, a financially responsible part design may require a slightly more expensive mold for itself, but completely eliminate the need for several additional molds!

"My part design doesn't require slides so why are you quoting it with slides?"....because it will not run consistently, efficiently and defect free without slides! I see this ALL THE TIME on parts that are very deep and/or have ribs and require long ejection strokes. If your part needs to be molded deeper than about 1"-1.5" deep on the core side of the mold, you may need slides on the outside of the part to release the part effectively during part ejection. You have to understand that lower part pricing depends on robust, problem free molding cycle times! Deep parts that want to stick in the core require ultra slow part ejection to keep ejector pins from pushing through or making un-sightly pin marks and sometimes slow ejection still isn't enough. In order to help those parts eject smoothly and freely without slow cycle times and quality problems, those parts may require simple short travel slides on the outside of the part. BEWARE OF THE MOLD MAKER that says "the part is going to shrink to the core and away from the outside anyway". Those guys obviously haven't had to dig stuck plastic out of deep ribs in a mold that is already mounted in a molding machine!

In summary, FORGET ABOUT THE TOOLING when you are designing a product. Design the product with uniform wall thickness throughout, nice draft angles throughout, pick plastic materials that are readily available in the market place, remove un-needed plastic wherever you can....EVEN IF IT WILL REQUIRE SIDE ACTIONS!!! Remember, you only have to purchase the tooling once, and the tooling should be designed for MAKING PARTS quickly and problem free for your best financial returns!

Mark Schwager - MSINC,

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