Inspection of injection molded parts


quality control for injection moldingWhen you start with injection molding project or develop a new product, it’s necessary to know some common inspection method, so that you can control the product quality by yourself.

Product inspection is a wide definition of full quality check including cosmetic, dimensional, and functional identity. And we would like to share our knowledge and experience about it below.


Firstly, when we talk about cosmetic of a injection molded parts, it normally means some visual defects which can be identified with eyes, for example, deformation, flash, sink marks, welding line, flow marks, and unfilled section. Before mass production of injection molding, these defects much be fixed or sorted out by QC and workshop technicians.


Secondly, we would like to talk dimensional inspection( also called dimension measurement), which is people use some measurement tools to check the dimension of parts. The main measuring tool can be introduced in the following.




CMM(coordinate measuring machine) is a very worldwide famous measuring machine to check 3D dimensions without damaging the target part. This tool is much convenient than any other measuring tools. CMM can measure distance, geometry, and tolerance deviation. like concentricity, perpendicularity, runout, parallelism. Normally CMM can reach a measuring accuracy of 0.01mm for distance and 0.002 for tolerance deviation.



Projector is an useful 2D dimension inspection tool. It’s made from optics with lights inflection. You can use it to check short 2D distance and geometry profile. In principle, the projector magnifies the profile of the workpiece, and displays this on a visual screen. And you can see the workpiece with 1:1 scale, On this screen there is typically a grid and a 360 rotated compass, so that the X-Y axis of the screen can be aligned with workpiece to measure. Project is not quite accurate measuring tool, because the test result is affected by many different elements. The accuracy of project is around 0.01~0.03mm





Caliper is a quicker and convenient measuring tools to check distance, holes, pillars. Most of time people use caliper to have a quick check when necessary. It’s also a very basic measuring tools for QC, engineer, and technician. And accuracy of caliper is about 0.02~0.04mm as it’s a rough device  There are two different types of caliper that are mechanical caliper and digital caliper. Each of these two types of calipers has its relative merits and faults. And you should get it calibrated yearly to ensure the caliper itself is in normal condition. Otherwise the measuring data might be fault or useless.


Pin Gauge


Pin gauge is a profile tool to check space and holes. For example, you want to check the deformed workpiece by using a pin gauge. You can choose different thickness of gauge so as to find out the how much the workpiece is actually deformed. Just put the workpiece on a platform and you will easily check out the exact data. For hole checking, people normally call it go-no-go gauge. You just need plug into the hole with pin gauge, if it passed, it means the hole is at least big than the standard pin gauge. If failed, it is absolutely smaller than the pin gauge.


After you checked the cosmetic and dimensional aspects, you might have to check the function of  injection molded parts, at this moment, you will have to get it assembled with other components. When assembly, you can easily find out where the faulty is and how the mechanical property of the part is.

Finally If you still have problem with quality control or inspection of plastic parts. or you have any injection molding project to run, please don’t hesitate to contact us for help, thank you!