Why are hairpins and hairpin stators being scanned?
Since the performance and reliability of an electric motor depend to a large extent on the quality of the stator fabrication, the hairpin welds, among other things, must also be inspected during production. Non-destructive industrial computed tomography is used to create three-dimensional images that can be used to determine whether the hairpin welds have been produced in accordance with the (automotive) manufacturer’s specifications. Typical defects in the manufacturing process are, for example, pores, material accumulations and bonding defects, which can affect the performance or service life of the engine.
Microvista has already scanned
hairpin welds in the automotive industry
What are the challenges of CT-scanning hairpin stators?
There are several hundred hairpin welds on a stator, which are closely spaced in several rows and nominally have no difference. The challenge lies in separating the individual welds and assigning them unambiguously. Since the hairpins are made of copper, CT scanning hairpin stators is likely to produce image artifacts that can affect image quality and accuracy. Image artifacts can be caused, for example, by scattered radiation, noise or blurring. However, this can be minimized and controlled by an optimal scanning process. This is aggravated by unavoidable position fluctuations, which are caused by the geometry of the hairpins, but also by the global position of the stator in the scanning device. Thus, no exact position of the hairpin welds can be assumed.
How does Microvista still manage to scan hairpin stators with great precision?
Our solution is: binary codes!
This is how we proceed: Each Hairpin Stator that is to be scanned by us is given a “crown”, i.e. we place an additional polymer ring on the sheet metal assembly of the stator. The positioning of the ring is always the same by using an existing groove on the stator. At the level of the hairpin welds, 12 binary codes are evenly distributed around the circumference of the ring. Each code is made up of 4 indentations, with the binary code being represented via the depth (0001 = shallow shallow deep).
What are the advantages of this innovation?
During the evaluation of the scans, the binary codes are determined in addition to the relevant stator. Based on the respective binary code, we can therefore conclude the position on the stator and thus reliably determine the individual pin IDs. The big advantage here is that we do not have to make any assumptions about the rotational position of the stator. Based on the codes, we always know where we are in the scan volume and which pin is currently in front of us — this is interesting when higher resolutions are relevant for the evaluation. In addition, we can also evaluate different partial scans of a stator with the same software, e.g. a half, quarter or eighth stator.
Thus, the binary codes provide us with a precise reference point to determine the exact position of all hairpin welds. This forms the basis for automated image processing, which enables efficient and accurate analysis of the entire hairpin stator.
Learn more about the inspection of hairpin stators here: Quality assurance for hairpin stators