Understanding micro molded part inspection.

A pick-up operator inspects the quality of a micro molded component under a microscope

Creating a precision microscopic component is an achievement, but measuring to ensure its accuracy is an achievement in itself. This is why so many engineers want to know the process behind micro mold part inspection.

How are micro mold parts inspected?

Micro mold parts are inspected automatically or by hand. There are three main categories of inspection in the micro mold process including: 100% inspection, SPC, and fully automated. With lower volume parts it is common to screen and inspect 100% of them by hand. Automated inspection can be very convenient, but the volumes may not justify the investment, and at times the technology available is still quite limited at such small and precise sizes.  

1. Inspection by hand

When inspecting a micro molded component by hand, the process can be labor-intensive but fairly straightforward. Parts are put in a flat container and screened under a microscope at high magnification (usually 20X). Pick up operators check for any gross defects or contamination. At the same time, the operator looks for any type of flash or damage that can happen during the molding operation. 

2. Inspecting micro mold parts using statistical process control.

The second category of the micro mold part inspection process utilizes SPC, or statistical process control. This is a very common method that utilizes a set sampling of parts from a production run. Parts are pulled from production at a pre-set interval, measured, and recorded. In this way, the operations team can monitor the production quality without the added expense and delay of looking at every part. This process works well for larger production volumes with basic quality requirements.  

3. Automated visual inspection for micro molding

The third type of inspection in micro molding is automated vision inspection (AVI). This is best utilized for higher volume or parts with very complex requirements. AVI systems perform dimensional inspection, flash and non-fill detection, gate vestige verification, and contamination/foreign material (FM)detection, to name a few examples. . AVI and other automated testing allow for parts to be inspected at a very high rate to keep the production as efficient and cost-effective as possible. 

Are micro mold parts inspected by AI?  

Micro mold part inspection can be achieved by computer or by hand, depending on complexity and volume. For example, if the job has a low volume each year, it may not make sense from an ROI standpoint to build and implement sophisticated AI or automation because of the cost versus the return. If the product is going to be running hundreds of thousands or millions of parts a year, it typically makes sense to automate the system as much as possible.  

If an OEM or engineering team needs automation to take measurements and determine pass/fail, AVI is fairly easy to set up. But if we are utilizing automation to determine contamination or visual defects like sink or splay, the process can, at times, be very difficult to design. To catch visual defects, the AVI system needs a trained image or guidelines to compare to. When working at micro levels, however, micron-sized defects can be very difficult for the system to see.  

Micron-sized defects can present a challenge because the camera system looks at components in a very black and white way, or objective standard, without the ability to make judgments. A simple visual inspection of objects, even micro molded ones, look identical. But under 20x or greater magnification, everything has a degree of variability. 

AVI can also struggle when determining defects within a component that is run with a transparent material. Understanding the internal structure of a part is vital because internal bubbles and contamination can be disruptive to the functionality of the part. Micro mold part inspection using AVI is typically fixed focus and does not have the ability to scan down through the thickness for defects in the same way a person could—especially, a trained micro mold inspector. AVI can also experience distortion issues trying to look through the plastic. This is where alternative inspection plans, like adding multiple cameras, a transmission tester, by-hand inspection, or other in-line methodology, may be needed to verify the quality. 

A great degree of training is utilized on micro mold technicians to determine what is acceptable and what is not from a quality perspective. AI, robotic vision, and camera systems sometimes do not yet have the capability to process the way a human operator can. We are seeing great strides in deep learning software, but as of writing this, those systems don’t outperform the human eye and our team’s superior decision-making. That being said, with the improvements in AI software, we are continually adding new capabilities to our AVI systems, so our staff can turn their attention to new customer challenges.    

What defects are possible in micro molding? 

The kind of defects commonly found in micro mold part inspection include small dings or damage, contamination, foreign material (FM) embedded and on the surface, and non-fill/short shot parts. The reasons for these defects can be numerous. Damage can happen by the part hitting something post-ejection en route to the collection container. Damage could also happen if a robot is not perfectly aligned with the mold, scraping the part, or not picking the part properly.  

Contamination of a molded component can happen if a press had to be restarted, or if material is caught in the screw during processing. We see this more often using optics grade materials when part clarity is most important. Surface FM can result from airborne particles from a variety of environmental factors. For this reason, many of our parts are run in clean-room locations to reduce this risk. 

Because Accumold has been micro molding at this level for more than 35 years these issues are rare, therefore our production yield is extremely high. Our precision reduces waste and lowers cost. And in all cases, our production planning team schedules the right amount to produce the right quantity and quality our customers have come to expect from us.  

How is quality determined in? 

Regardless of the micro molded part inspection method, quality is determined through a joint partnership with our customers. During the very beginning of a project, our team and our customers work through all of the print’s requirements to define what success looks like after molding. This plan is then locked into the Control Plan that all Accumold production specialists utilize when producing parts.  

The type of inspection process is also determined upfront. If 100% human inspection is chosen, operators are trained, and the Control Plan is designed so operators can clearly identify quality parts. If SPC is chosen, the customer and project team determine what critical dimensions should be checked and under what quantity and interval to achieve a proper cPk. If fully automated is chosen, the automation team begins to draft an automated inspection process that best fits the need. Their plan is a combination of AVI, AI, and/or physical testing that best fits the quality demanded and cycle time speeds. This can be a complex process to develop and build, but for projects in the high millions, there is no better way. 

Zach Boyer

Zach Boyer is a production manager of micro-mold. He has worked at Accu-mold for 18 years, starting as a production machine operator, and also has experience in Processing, Material Handling, and Supervisor roles. He has a Tool and Die degree along with multiple other certifications in Lean manufacturing, GD&T, and Kaizen. He has also completed Paulson processing training.

micromolding components next to EU coins.

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