Recently we published a paper that focused on the OEM design and validation of new automotive parts as a concerted effort among carmaker and supplier and the resulting added value of offering such parts also to the aftermarket (see Bearing News – March 2019 edition). The focus in that document was on designing and developing the right prototype part to meet the required functional behavior and performance of the part on the new car.
A next important aspect of the homologation is the validation of the manufacturing process that needs to be put in place by the supplier to make sure that the fully optimized (prototype) design can also be replicated millions of times in a serial manufacturing process at a consistent high quality level. The OEM serial manufacturing validation process according to the well-established PPAP procedure is the focus of this paper.
From part design validation to manufacturing process validation
Once the optimal part design (prototype) is validated by the car maker, the next challenge for the supplier is to reproduce the parts in a validated serial production process, before the official SOP (Start of Production) milestone is reached.
The PPAP (Product Parts Approval Process) procedure which originates from early QS9000 quality standards (introduced into the global automotive industry in the 1990s – today superseded by ISO/TS 16949) is a procedure in which the supplier proves to the carmaker that proper production (and supporting) processes are in place that are “capable” of producing the part in serial production with a stable and high quality output (in terms of consistently staying within agreed specification limits).
Typically the PPAP process validation procedure ends with the submission to – and approval by the carmaker of the following PPAP documents:
- A customer drawing showing all main dimensions and features of the parts.
- A Dimensional Report – proving that measured critical dimensions for randomly taken parts from the new serial production process, are actually within specification limits.
- A Materials Report – proving that the chosen material/chemical critical properties are actually within agreed specifications.
- A Process Flow Chart – showing the actual process steps that will be consistently followed during serial production.
- A Control Plan – showing the quality controls, starting from incoming material inspection, on to in-process checks and up until final product inspection, to assure that all dimensions and properties are within agreed specifications.
- A PFMEA (Production Failure Mode and Effects Analysis) study – demonstrating that the production organization understands possible process failure modes, their relative impact and countermeasures that can be taken beforehand to eliminate such risks.
- A Process Capability Report – demonstrating that the manufacturing process is capable of keeping any critical dimension consistently within specification limits (represented by the so called “Cp value”) and that machine settings are such that the normal distribution mean value of such critical dimensions are actually close enough to the nominal specification value (represented by the so called “Cpk value”) – See the case study for an example from the auto bearing industry.
- A Calibration Report – demonstrating that all measuring tools are sufficiently calibrated to be able to measure all critical dimensions and machine settings properly.
The final validation of the supplier manufacturing process by the carmaker before SOP is established by the signing of the so called PPAP Part Submission Warrant (PSW). Only at this stage is the supplier allowed to start mass production of the part for the carmaker.
Critical dimensions of a wheel bearing hub unit – the importance of
stable supplier manufacturing process capabilities for OEM validated products.
As can be understood from the above discussion the main characteristic to prove the suitability of the serial manufacturing process is the process capability. All critical dimensions and properties of the product design will have to be produced within well-defined limits (specifications) to make sure that the serial mass production parts have the same quality and performance as the final prototype part that was approved on the prototype car after surviving all types of bench and field tests during the development phase of the new car model.
In the attached case study we can see the importance of the capability of the manufacturing process that assures the proper dimensions between fixing holes on a wheel bearing hub unit. For automotive OEMs part mounting dimensions are very critical. In this case the position of the holes should be exactly the same as the position of the holes on the wheel knuckle to which the wheel bearing unit needs to be fixed. If the dimensions are out of specification there will be a serious risk of misalignment during the mounting of the bolts or damage to the thread (resulting in poor fixing of the wheel hub to the wheel knuckle) leading to an unacceptable risk of failure.
Designing, developing and validating a suitable automotive part and its manufacturing process is a meticulous multidisciplinary process involving both engineers and manufacturing experts from the supplier as well as from the carmaker side.
Even if a new AM parts supplier makes a perfect copy of the original OEM design, there is absolutely no guarantee that the same supplier is capable of reproducing the same part in large volumes in a capable serial process.
Following JTEKT’s Monozukuri philosophy, Koyo manufactures the highest standard OEM validated parts and supplies exactly the same parts, from the same manufacturing processes also to the AM.
Therefore using OEM validated parts is the best warranty that they will perform according to the specifications and are actually produced with capable manufacturing processes, required to assure the proper long lasting performance in the field.
JTEKT corporation has a high reputation for excellent quality mass manufacturing of systems and products for diverse industries, including automotive, aerospace, agricon, windmill and others.
Koyo Bearings, a division of JTEKT Corporation, is a major developer and supplier of automotive bearings to the global automotive industry OEMs and aftermarket. The large range of OEM validated parts that are offered to the aftermarket are actually the same parts, from the same production processes as the ones that are originally supplied to the carmaker (as OEM parts) or the carmaker dealer network (as OES parts). The only difference is the marking and the special individual packing for distribution to the independent aftermarket.