Locking Features On Microscopic Molding Are Often Overlooked


Devin VanDenBroeke

As microscopic injection molding experts, we constantly work under the hood of each project, ensuring clients complete their goals without compromising project integrity.

There is nothing standard or routine about a DFM Engineer’s (Design For Manufacturability) job. We constantly overcome challenges and act as the first line of defense for snags that are often overlooked. One such snag is the unpropitious ease of creating a part design without considering locking features when designing for multi-component molded projects.

Microscopic Injection Molding Locking Features Are Vital

Locking features are often essential when looking to overmold or insert mold one or more other components. It’s easy to forget, yet can cause a lot of rework if not caught up front. And because of the unique design considerations around microscopic injection molding, engineers may not realize how important this consideration is to the manufacturability and robustness of the design.

Because locking features provide an indirect benefit to the overall part function and project success, it’s unlikely another engineer will even notice until it’s too late, even if that engineer is familiar with the design process. 

parts produced by microscopic injection molding
Parts produced in-house by microscopic injection molding techniques.

Typically appearing as a rivet, hole or protrusion on a part meant to accept an over-mold or hold another part in place if left off the final project the overall function of the part may fail with part delamination. In some cases complete separation from the substrate is likely.

While it’s true keen microscopic injection molding DFM Engineers are quick to catch this kind of issue and eager to collaborate on a solution to ensure the part will adhere during the DFM stage, this isn’t truly the best solution for OEMs. 

When redesigning larger parts, locking feature challenges are quicker and easier to overcome. Complex and critical components with micron tolerances with very little geometry to work with can be a challenge, however. Because these are the kind of projects we work on at Accumold, we know a redesign at this stage can add considerable design time to the project. It’s not always such a simple fix by the time it gets to our DFM Engineers.

By the time a DFM Engineer sees the design, they may suggest the substrate be redesigned to allow for holes that can be used as locking features for the overmolded component. In other cases, the entire part design may change to accommodate the locking feature. If there is one thing every part designer must be cognizant of, it’s location, location, location. Force is also a consideration. 

Locking features are intended to hold the overmolded component to the substrate, so part designers must fully consider the forces the final part will be under in a real use scenario. Sometimes the forces are minimal, but other times the forces exceed the strength of the locking feature design — this is a critical step in determining how robust and how many locking features are needed. 

Some Cases Require Alternate Methods

In some cases, when a hole, post, rivet or protrusion can’t be accommodated, an undercut design can be the perfect solution to a very challenging design problem. But even when a locking feature cannot be added, however, there are still options.

Often relying on a chemical bond between the substrate and overmolded component is a sufficient option. A bond of this class is heavily reliant on the two substrates selected and oftentimes a complete material change is required to ensure the chemical bond between materials is strong. This process has been made easier in the past decade due to the wide availability of cutting-edge micro molding materials

Going after big projects with impossible challenges is exciting and the potential is huge, but sometimes through no fault of the designer, projects hit brick walls. Although unlikely, when part sizes or designs cannot entertain a locking feature, the materials specified cannot be changed or die locking features in the mold design can’t be accommodated there is a final resort. 

While it’s true in these cases, projects have to be completely changed or scrapped, it doesn’t have to be a total loss — there is a parachute specially made for designers or a project manager. 

One Thing To Know: Get The Right Help

With the right partners, the risk is greatly reduced by simply bringing your part to our microscopic injection molding nerds or strategic partners as soon as possible. Engineers, such as the ones at Accumold have seen millions of scenarios and have a great amount of knowledge when in this area and the best part is, they are adept at solving the problems you may not even know you have yet due to the niche they operate in. 

Locking features are vital and considering them in advance, every time will save you precious R&D, time and money being thrown down the drain.

This article originally appeared in Design News April 10, 2019.  

Devin VanDenBroeke, DFM Engineer at Accumold

Devin VanDenBroeke manages the project engineering team at Accumold, an Ankeny, IA-based micro molding company. He also holds a degree in mechanical engineering from Iowa State University.

micromolding components next to EU coins.

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