X-ray Inspection of Complex Assemblies

North Star Imaging Blog

Nate DeRoo

Inspection Services Lab Technician

We scan a lot of amazing things at North Star Imaging and one of the more interesting things we scan are small electric motors. They are complex assemblies so in order to identify the root cause of failure we must identify all the components the motor is connected to.

This motor is used to pump windshield washer fluid on the windshield of your car. But it’s very similar to motors that would be used in a wide variety of industries such as, aerospace, defense, medical devices; all very critical.

Let’s take a closer look at why this particular motor is not working anymore. All we know right now is that this motor is not pumping fluid. It could be just normal wear and tear, but there are a lot of moving parts and we don’t want to speculate as to what the problem may be. We use our X-ray system to see the inside of the motor and identify the exact cause of failure. Imagine you were manufacturing millions of these motors and you have a problem on your production line causing the motors to come out defective; you would definitely want to have your samples imaged to identify the problem as soon as possible. For this particular sample we are going to do a 3D Computed Tomography scan.

This small motor is made up of a thicker material and harder to penetrate so we must use higher power on the X-ray source. Also, to get the whole field of view, we scan it at lower resolution so this scan will be at about 40 microns. We will take around 1440 images for the full rotation. If we wanted to get a higher resolution image of a localized area on the motor we could zoom in and just focus on one certain area, like the brushes or the bushes on the other side.

After scanning our small motor, we open the 3D reconstruction. We can see it is a very complex part, because of the many different pieces involved in the construction of the part. The first thing we notice is that the outside case is quite corroded and very pitted, but this most likely wouldn’t cause the motor to fail directly. As we continue our inspection, we can see the brushes of the motor and we can slice through them and verify that they are not damaged and appear to be intact. There are no visible cracks or broken pieces in them. Now we take a top down view of this motor and slice through. It’s apparent that there is some foreign material stuck in between the magnets in the rotating portion of the motor. That could potentially cause the motor to seize up. After further inspection, we believe this motor has failed due to the corrosion of the case getting stuck in the rotation portion of the motor.

A manufacturer will typically send 100s of these to verify assembly consistency and quality of their products. X-ray inspection can help in your R&D, Product Development and QA process.


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