Production Machining

MAY 2016

Production Machining - Your access to the precision machining industrial buyer.

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The aim is to assess and compare the technical cleanliness of parts produced by diferent manufacturers or at diferent locations. CONTRIBUTOR Doris Schulz is a freelance journalist specializing in the feld of surface treatment, and especially parts cleaning. Contact: By Doris Schulz N o matter whether I talk to part or cleaning machine manufacturers, one topic has been an issue over the last decade and still is: residual dirt, or "technical cleanli- ness." Te good news is that the requirements for particulate cleanliness have not increased further in industries such as automotive, hydraulics and mechanical engineering. In fact, there is a rethinking of whether cleanliness, which is feasible, is necessary because the cleaner the parts have to be, the higher the costs are for cleaning. However, in the case that cleanliness specifcations are defned, they must be met, not only when the cleaning machine is put into service, but throughout its entire operational life cycle. And this is being checked by more and more companies. Overall, the number of companies that defne cleanliness values and control cleaned parts continuously has grown signifcantly. When it comes to checking particulate part cleanliness, VDA 19, or its international equivalent, ISO 16232, has become an integral part of quality management. Te aim is to objectively assess and compare the technical cleanli- ness of parts produced by diferent manufacturers or at diferent locations. A prerequisite to ensure comparability is that the defned cleanliness level is linked to a test specifca- tion. Tat is where it gets complicated, because machined parts usually have a geometrically complex design, and therefore, the detection of particulates cannot simply be done on the surface. It requires a verifying cleaning process (extraction) in which particulates are transferred into a liquid medium, which is fltered, and then the particulates on the flter medium are measured. Tus, the test specifcation must contain information on the parameters of the verifying cleaning process and particle measurement technology. Tis also includes testing and optimizing the parameters of the cleaning process for the part in question using decay measurements in order to ensure that all particulates will be removed without attacking the part material. Various methods can be used to extract the particles from the component: spraying, ultrasound, rinsing and shaking, although process parameters such as fow rate or ultrasound power are not provided for any of these procedures. Tis freedom has led to a lack of cleanliness comparability in the Measuring Technical Cleanliness According to VDA 19 analysis results. Te extraction was therefore one key point in the VDA 19 revision. Te new version, which has been available since the middle of last year, includes starting parameters for the diferent extraction procedures. For the extraction by means of spraying, the use of a certain nozzle diameter and volumetric fow is recommended. With fow- through and blowing, two new extraction methods that use air as media have been included in the new VDA 19.1. Tey are used for parts which are not exposed to liquids during manufacturing or operation. After the extraction fuid is fltered and the flter dried, the sample analysis takes place. In order to improve comparability here, too, the revised VDA version contains conventions for systems and adjustments for gravimetrical and light microscopical standard analysis. Another novelty is the abridged analysis performed, for example, with liquid particle counters or a new system. Tis is based on optical recognition and particulate measurement, adherent to a sieve placed in the media stream. Because of the diferent detection principles, the results of the light microscopical standard analysis and abridged analysis are not directly comparable. In the case that cleanliness specifcations and analysis results do not match, it is helpful to fnd the reason. First, check cleaning process parameters, the quantity of contaminants brought into the cleaning baths or if anything has changed regarding the auxiliary substances used, such as milling oils or emulsions. If everything is OK, knowing where particulates originate is key to meeting the specifcation or for targeted process optimization. Diferent analysis methods can be used for determining the particle material and performing 3D measurement. Since cleanliness has become an important quality crite- rion for parts manufacturing, checking and documenting the compliance of specifcations has become part of the production process, at least in some industries, such as automotive. And I am sure it will spread further: Te next step will be specifcations for flm-like contaminations. CLEAN SLATE 52 PRODUCTION MACHINING :: MAY 2016

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