New grinding program for greater productivity

Many people regard Mercedes-Benz as the best brand in the world. To maintain such a supreme image, of course, can not indulge in the glorious history of the ancestors, but should be technically improved without stopping. Because only quality can generate more demand, and only with the improvement of quality can leap to a higher level. This principle also applies to every machined workpiece – and thus to the machine tool that machines the workpiece!

Located in the small town of Gaggenau, the Meisers-Eich, Daimler-Chrysler plant is the oldest existing car factory in the world.

The factory was built on the edge of the small town at the time in 1894 and was taken over by the Mercedes-Benz & Xie company in Mannheim in 1907. Although the city of Gaggenau is still not a big city, it has grown with the development of the times, so that the factory is almost in the center of the city, and it can no longer be expanded on the original site. Therefore, it was established and put into use in the adjacent gearbox factory in Rastatt in the early 1970s. Here, there is an area of ​​approximately 227,000 m2 available for production. In Gaggenau, there are about 412,000 m2 – plus a third factory in Bad Rottenfels, with a registered area of ​​approximately 190,000 m2 of net production area. In Rastatt alone, there are approximately 2,000 employees working in the DaimlerChrysler-commercial vehicle sector. About 200 of them are in-service trainees.

Production of 500,000 gearboxes per year

In the first 100 years of the Gagenau/Raststadt plant, commercial vehicle production has been at the forefront. However, this situation has changed a lot since the introduction of the second-generation A-class car to the Rastatt plant.

Since then, the drive components for personal cars are no longer considered to be a negligible share of the production of the Rastatt gearbox. In record 2005, a total of 1,085,000 transformers, 492,000 gearboxes and 81,300 external planetary axles were produced – such a large production volume barely allowed for a slightly longer downtime. Therefore, it is not only the employees of the factory, but also the machine tools and machine tool manufacturers must be absolutely reliable. This will be explained later.

For the introduction of Class A and Class B six-speed transmissions (front drive), Class V, sports cars and several Chrysler models (tail drive) plants must create new production capacity. “We started with 170,000 gearboxes a year, and by 2008 we could reach 500,000,” explains Alexander Hartz. He is responsible for the production of gearboxes and light shafts, and the demand for these products is growing significantly in his factory.

In addition, the factory has also equipped a new machine for shaft cylindrical grinding. In 2002, DaimlerChrysler's production planning department contacted the grinding machine manufacturer JUNKER and discussed their needs with them:

- new, differently defined parts
- integral grinding in one setup (planar and external surfaces, chamfering)
- Highly flexible machining process (in terms of part specifications, part modifications, batches, etc.)
- Short setup time
- Higher usability
- Grinding with cutting fluid (for example, when gear system grinding; one center unit)

Highly flexible is of paramount importance, as the new generation of gearboxes and the new “user base” (ie: the new V-Class, the new sports car, the Chrysler model) have increased the number of models of the production components by almost one Times.

Serial arrangement instead of parallel arrangement

Only two suppliers can fundamentally meet the above requirements. After testing different solutions, JUNKER's QUICKPOINT 3000/60 is the most convincing, and only JUNKER has the experience: a grinding machine with three independent grinding spindles on the B-axis and seven to Eight grinding wheels. The CNC can control the sequential machining sequence, and one workpiece can be used to grind one workpiece at a time.

Alternatively, as in the case of the grinding wheel assembly currently used for the five-speed gearbox, the two clamping operations are completed, in which multiple planes can be machined simultaneously. Although this process requires a shorter main processing time, it requires multiple times of adjustment time, resulting in lower production efficiency, especially insufficient flexibility. Although the entire adjustment time has been reduced from the hours required for the natural corundum grinding wheel used in the old process to a quarter of an hour, the current target time is nine minutes. In addition, it is required that the grinding wheel is almost no longer required to be machined between multiple part sets. In this way, multiple batches of production can be replaced effortlessly every day, thus eliminating the need for large intermediate warehouses.

Of course, these advantages only came to a "theoretical" understanding in 2002. First, various different grinding materials and grinding processes were tested by JUNKER. As a best option, the ceramic-bonded CBN wheel is best suited for machining the outer surface, while the electroplated CBN wheel is ideal for grinding the plane. Therefore, it is recognized that this process can achieve many advantages at one time, namely:

â–  Higher flexibility â–  Higher precision â–  Faster process time (processing time, setup time and parking time)
â–  More streamlined logistics

Jonker’s “guardian” can take care of everything

It is now time to optimize this process as much as possible. So at the beginning of the project people built a common test workshop. In order to successfully start the project and shorten the study time, JUNKER then provided two rental grinding machines. Almost no new process has been implemented without the initial difficulties of development. "Despite the many difficult factors, thanks to the participants' high level of commitment, the technical problems were quickly resolved." Alexander Hartz praised the JUNKER team. A similar geographical location is an advantage, but not the most important one. The most important thing is that JUNKER is an exceptionally reliable partner with well-trained employees!

For the continuity of the machine tool, of course, there are also considerations: for each machine, it is best for each user to have a “guardian”. This "guardian" will exist throughout the life of the machine.

So far, you can estimate the savings compared to competitive processes. Compared to a well-used and stable hard turning process, the use of electroplated bonded CBN grinding wheels can reduce tooling costs for machining planes by at least half. In addition, a huge contribution to the amount of work that can be processed: 20,000 axes can be continuously ground with a CBN wheel.

Usage rate reaches 99%

People are nervously looking forward to see how stable and reliable CBN grinding of the QUICKPOINT 3000/60 can be. Now, 95% of the design manual requirements have been significantly exceeded: the “Prisma” system has recorded up to 99% of its technical availability – another testament to this correct decision.

The supply of the new grinding machine is no longer an obstacle. In October 2003, the first machine arrived and the second arrived in November; the fifth and the last one arrived in April 2005.

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