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New approach to peening.

Normally, automotive transmission components are shot peened with compressed air. For a French car manufacturer, Rosier took a new approach by developing a shot peening system, which accelerates and throws the blast media with turbines. This resulted not only in reducing energy consumption by 30[degrees]/o but also increasing the customer's peening capacity by 50% allowing the consistent peening of 240 work pieces per hour in one single machine.

Shot peening is an indispensable step for improving the wear characteristics, and extending the service life, of automotive gear components like shafts and toothed gears. Shot peening changes the tensile stress caused by machining, forging and heat treatment into a compressive stress. Of course, all automotive manufacturers demand that the required compressive stress values are achieved consistently within narrow specified tolerances.

When Peugeot Citroen S.A. was looking for a new peening system for treating the toothed surface areas of different gear shafts, their specifications called for compressive stress values, which can normally only be safely achieved in compressed air systems. Since the requested hourly capacity of 240 work pieces would have resulted in an extremely high compressed air requirement, with very high operating costs, the customer was keen to consider an alternative, lower cost machine concept. Among other potential suppliers the project engineers at Peugeot approached Rosier Oberflachentechnik, with whom Peugeot has been cooperating with for more than 10 years in the field of shot peening.

Empirical process development based on processing trials

To prove that the specified peening results can be consistently achieved in a turbine based peening system, Rosier conducted extensive shot blast trials at the Rosier test center. Based on detailed evaluations of the trial results with the in-house x-ray diffractometer, key process parameters like blast media quantity, media impact speed and impact angle were adapted to meet Peugeot's specifications.

Custom engineered equipment concept for a high work piece throughput

Parallel to the process development Rosier also developed a concept for the custom engineered satellite table blast machine RST 200-S16. This machine is equipped with two horizontally positioned Rutten Gamma 400 high performance blast turbines, with 22 kW drive power each. The special curved "Y" design of the throwing blades allows a highly fluid, unobstructed acceleration of the blast media. This, in combination with an optimized media feeding system to the throwing blades, generates up to 30% higher throwing speed. The result is a significantly higher impact speed of the media on the work pieces. Last but not least, a blast pattern control device ensures a precise, targeted blast stream on the work pieces. The rotary speed of the Rutten Gamma high performance turbines and the satellite stations can be adjusted by way of frequency inverter controlled motors. Up to 30 work piece specific peening programs can be stored in the system PLC controller. Since the throwing blades are made from high alloy steel, they offer a 16 times higher service life compared to standard blast turbines. To ensure optimum wear protection for the peening system, the blast chamber was made from manganese steel. In addition, the areas directly exposed to the blast stream are lined with replaceable, overlapping wear plates made from tool steel. The areas around the hot spot area are protected with liners made from manganese steel.

The custom engineered RST 200-S16 peening system allows the shot peening of gear shafts with diameters of up to 250 mm, a maximum height of 300 mm and weighing up to 5 kg (11 lbs.). The raw work pieces are manually placed on the 16 satellite stations of the rotary table. Automatic masking protects surface areas, which must not be exposed to the blast stream. After two work pieces have been placed in the load/unload station at a 15 second cycle, they are passing through two blast stations. These are equipped with lift gates to prevent any media migration to neighboring machine sections. In the subsequent cleaning station, dust and residual blast media are removed with an air blow-off system. The next station is equipped with a marking system placing a color dot on all gear shafts processed with the correct parameters. Subsequently, at the load/unload station the finished parts are removed and raw parts are loaded into the system.

Numerous control systems ensure absolute process safety and stability

To guarantee the high process safety and stability required in the automotive industry, all parameters of the peening process are continuously monitored and documented. For example, special mechanical connectors continuously check the rotation of the satellite stations. To ensure that the gear shafts are peened with the specified blast media quantity and throwing speed, the turbine RPM and amperage draw are monitored. For the automatic blast media replenishment a sensor checks the fill level in the media hopper. As soon as the level is below a predefined value, the system adds media. This is done in small increments so that a consistent media grain size distribution is guaranteed.

Ease of maintenance increases equipment uptime

Rosler's engineers focused especially on easy and quick accessibility to all machine sections that require regular maintenance and service. For example, easy access to the turbines for removing and re-installing the throwing blades to use their second side, is facilitated by simply pivoting the complete turbine housing out of the blast chamber. This also allows access to the blast area for replacement of the wear plates. All components for the blast media transport and cleaning are accessible with a large inspection platform. All this helps minimize equipment downtimes and increases availability and cost efficiency. Peugeot has been working with the new system for 6 months. During this period the energy consumption was reduced by 30%, while also experiencing a 50% capacity increase. Based on the convincing performance of the RST 200-S16, the customer placed a purchase order for a second machine.
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Title Annotation:PEENING
Publication:Finishing
Date:Nov 1, 2018
Words:970
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