Innovative Method for evaluating Hairpin Stators

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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

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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).

Krone für Haiprin Stator mit Binärcode
CT makes invi­si­ble mark visi­ble from the outside

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

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