By Gregory Peterson, Accumold
As medical and wearable devices become much smaller and lighter than anyone could have previously imagined, a new breed of engineers and designers are turning their focus to ultra-small thermoplastic component design. In this shift however, a pattern has emerged where micron tolerance considerations are presenting some common mistakes.
As these designers are being asked to fit more functionality into tighter spaces, they are discovering new methods to accomplish increasingly difficult design challenges. These ideas are shaping the future of product design, but their inexperience in this micro molded space has also created an alarming trend. This knowledge gap could be responsible for massive delays in the manufacturing process, and in many cases, unnecessary product design revisions.
That trend? A failure to consider gate and ejector pin locations. As surprising as it sounds, this Achilles Heel of the micro mold process is weakening strong manufacturing companies and processes. While some designers are crossing over from micro machining, others may be new into the space and simply overlook the issue this may cause.
While this may not dynamically impact the design of your average small injection molded part, consider the surface area dedicated to an ejector pin when the entire part is 800 x 360 x 380 microns. Proportionally speaking, it’s a huge deal. Luckily, there is an easy fix.
Provided the part can be molded, at best, companies see delays in their manufacturing process as designers redesign the part to include ejector pin and gate locations. At worst, (25% of the time, in fact) these revisions result in such a dynamic change, the entire product or device has to be completely redesigned.
At Accumold, redesign decisions are typically made through three to four back and forth meetings between designers and micro mold engineers. When dealing with microns, an improperly placed gate can fail to fill the entire mold making an incomplete part that lacks a robust structure, and an ejector pin placed in the wrong location can change the part geometry. Because a design is only as strong as the molding process that produces it, there are several rules of thumb to make sure the micro molded part is designed correctly.
Gate location on every part is often located on the thickest geometry of the part to make sure the entire mold fills. Ejector pin locations should always avoid thin areas, preventing the force of the ejector pin from punching through the part, or damaging it. In some cases, ejector pin locations on the part itself are impossible. But that doesn’t mean the part cannot be made.
When ejector pin or gate locations simply can’t exist anywhere on the part without compromising the design, there are work arounds to accommodate part complexity. Adding a “gate feature” to the end of a part has proven useful. The feature is an excess portion of the part that is left connected for the sole purpose of ejecting it out of the cavity. This part then goes through another process designed to trim the gate feature off, leaving the final part.
It’s a given considering gate and ejector pin locations in advance can save a lot of time and resources, but in some cases simply thinking ahead saves the entire project. Today’s micro technology has less margin for error than past projects, and it’s vital to accommodate for these micro features that perhaps in the past, part designers never had to consider.
As in any project, it’s wise to share as many details with your molder in advance, even more so in micro molding. A project you may believe is extremely unique or challenging (or impossible) may have already been tackled and conquered. When you give your micro molder a good idea of what the part is, and how it works in the overall product design, breakthroughs are made.
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