Perfect prototype measurement

Small but very capable components are in great demand in the motor-vehicle industry. This doctrine of the designers leads to ever-tighter tolerances on vehicle components. And continues to throw down new challenges to quality management – also at the Robert Bosch Works, Immenstadt. The Metrology Team tackles its tasks in the prototyping department there using a high-precision Leitz Reference Xi.

Situated in the middle of the delightful Allgäu countryside, the Immenstadt factory complex produces anti-lock braking systems (ABS), electronic stability programmes (ESP), ignition coils and electronic sensors for driving safety and fuel injection systems on series production lines and as prototypes. With some of these systems, Immenstadt takes a step to the side from running the series production lines. Process development and the construction of special machines and prototypes help maintain and expand the company’s essential know-how.

Innovation-led prototyping

“Our Prototyping Department is very specialised and yet very flexible,” says Hubert Hueber, who is Group Manager of the Protoyping Department and responsible for Chassis Systems Control. “In our field of work we manufacture prototypes, such as concept, procurement and release samples of ABS and ESP systems, which have to be dimensionally accurate for our in-house development departments and for OEMs all around the world. The batches typically comprise 1 to 100 system units per order.”

Tight tolerances, accurate CMM

The call for enhanced functionality with fewer moving parts reverberates around the think tank at Immenstadt: as systems become smaller and more compact, the tolerances tighten to match. Therefore Bosch has opted for a high-precision 3D coordinate measuring machine (CMM): a Leitz Reference Xi from Hexagon Manufacturing Intelligence with a maximum permissible error of indication (MPEE ) for longitudinal measurements of 1.2 + L/350 μm and a measurement range of 1000 x 700 x 600 mm. When measuring a length of 1 m for example, this CMM achieves an accuracy deviation as low as 4 microns.

A CMM is a source of information

The metrology technicians check samples taken at random from prototype production using the measuring machine in the climate controlled room. The majority of the test pieces are prismatic machined parts. Some of them have features with tolerances of just a few microns. The CMM provides the technicians at their machining centres with important information to help them, for example, setting the machine or mounting the part correctly.

CMM with a clever twist

The integrated rotary table of the Leitz Reference Xi performs important functions during the measuring process. It enlarges the CMM’s effective measurement volume, allows all the measurements to take place with the part in just one set-up and simplifies the stylus configuration on the LSP-X3c’s probe head. Complicated star styli are not necessary to measure the features of the ABS and ESP prototypes.

Metrology Technician Alexander Baiz explains: “The previous machine supplied by another manufacturer was not only inaccurate; it also had a rotating wrist, which complicated the measurement procedure. When measuring, we either had to calibrate an angled stylus or re-clamp the part to allow us to capture all the features. With the rotary table on the Leitz Reference Xi, we can move straight in with the stylus and measure, for example, the diagonal holes in an ABS system without recalibration or re-clamping.”

Accurate and quick with HSS

A further shortcoming of the predecessor: the measured data were generated by single-point probing. The High Speed Scanning (HSS) capability of the Leitz Reference Xi allows Bosch to measure more accurately and quicker. In this mode the stylus ball is driven along the surface of the part and supplies a high number of measured points. Baiz: “Scanning means we need only half the time we used to take, for example, to measure diameters – and the results are more accurate.”

PC-DMIS is the standard

On the software side, Bosch has long-since standardised on Hexagon’s measuring software package PC-DMIS – it was also used with the previous machine in the Prototyping Department’s measuring room. The hardware and software in the measuring room now come from the same source, which is of great advantage to Bosch. As Metrology Technician Kadir Toygar confirms: “We now obtain our machine and software from one company. The two form a single module with the same contact number for advice. That is a huge advantage. When I call the Hotline, the Hexagon applications engineers can immediately relate the situation specifically to a Leitz Reference Xi. The technical people there are simply first-class and very reliable.”