Reduced Actions through DFM
One of the important considerations during the Design for Manufacture (DFM) stage of product development for injection molded components is reducing the need for cam actions within the mold. This is because an injection mold with fewer actions is less complex, less expensive, and quicker to build.
A medical device client needed an overflow channel at a specific level to allow a substance above a certain volume to leave the chamber. The client designed the chamber and added two channels at the appropriate level which moved out and turned down at a right angle.
In this case, our client’s original design would have required a very complicated tool in order to form the channel with a right angle. The complexity stems from the horizontal portion of the channel, which leads to an enclosed area. Attempting to tool this design as was, would have increased cost, lead time, and risk. The tool might not have worked at all, or if it did work, it would hold a high risk of working for only a limited time.
The first step was to reduce the need for the secondary cam action within the mold. The inner diameter of the chamber did not need to remain constant. Knowing this was not a constraint allowed our engineers to achieve the overflow through vertical channels with no horizontal sections. The inner diameter of the chamber tapered inward about midway down to allow for vertical channels. Draft was added to the pin forming the channel for better release.
This solution removed the need for the additional cam action, allowing for a straight pull. However, the pins forming the channel and the chamber met in what is called a Bypassing Shutoff. This means the two pins would graze each other, which introduced a new risk. Unless the opposing sides met at precisely the right point along their sides, they could touch head on and bend or break.
This called for a second round of DFM. This time the engineer reduced the chamber’s lower inner diameter enough to offset the inner diameter of the channel and form the necessary opening. The A and B sides of the tool could intentionally meet head on to create the opening. This is called an Up and Down Shutoff.
This solution removed the need for the Bypassing Shutoff and maintained the straight draw with no cam actions. In this case the risk, cost, and lead time were all reduced before moving to the mold design phase, and the Natech engineers added to their list of client victories.