Highly accurate quality assurance


The core business of the Volkswagen plant in Kassel, Germany, which has around 16,000 employees, is transmission manufacturing. About one-third of the workforce is engaged in this field and ensures that over 15,000 transmissions per day, or about 3.7 million per year, in 16 different variants, are shipped throughout the company. Because this location is a lead plant for the transmission business segment, Volkswagen has a high level of development expertise here, along with a pilot production center where prototypes of newly developed transmissions are built.

The pilot production center is part of the transmission business segment, where production processes are devised for transmissions and for hybrid and electric drives. Metrology planner Ulrich Schneider is a member of this department. His area of responsibility includes all metrological equipment, needed for manufacturing transmissions for combustion and electric engines, from plug gages to coordinate measuring machines.




As automotive drive technology changes, the requirements for metrological equipment in the pilot production center have risen in recent years, as Schneider reports: “As E-mobility takes on an increasing role, we have had to expand our equipment so that our pilot production measurement lab stays up to date.”

The lab falls within the purview of Normen Hitsch, who is the foreman responsible for the pilot production measurement lab. With his team of 15 employees, he takes on measurement tasks primarily for the development department, but also for production, quality assurance, and planning. “We mostly measure transmission components and elements for electric motors
at this time. These workpieces vary greatly, from ball bearing components in the millimeter range to axles, shafts, rotor and stator punchings, and entire transmission housings.”

This means that employees and equipment need a great deal of flexibility. To achieve this, VW is expanding the existing laboratory, adding a second lab, and investing in a large 3D multisensor coordinate measuring machine to add to the existing thirteen different measuring machines.

A project team consisting of Schneider as the planner, the measurement technicians on Hitsch’s team, and a project manager for the structural building components, has been working on the appropriate selection since 2013. “Our specification defines the three main requirements: high precision, a large measuring volume, and the ability to use a variety of sensor systems,” explains Schneider. “The details cover existing measurement tasks as well as future requirements to be met.”


Multisensor measuring technology has been proven in practice many times at VW

The project team used that specification to request bids from measuring machine manufacturers around the world. This was followed by extensive analyses of the quotations, on-site tests with challenging work piece

s, and finally a decision. “With this measuring machine from Werth Messtechnik in Giessen, Germany, we had filtered out the right one for us from the short list of six providers,” says Hitsch confidently. “The VideoCheck® DZ HA 3D coordinate measuring machine that we installed in 2015 has proven itself many times over.”



With a specified maximum permissible error MPE E of (0.5 + L/600) μm, it is highly accurate. Its measuring volume of 1130 mm x 2000 mm x 800 mm and various optical and tactile sensors, which can be used on two independent Z-axes, cover a greater range of applications than ever before. It is also possible to retrofit a third ram, if needed, in order to incorporate even more measurement options with additional sensors.

Currently four employees run the machine in doubles in a shift operation. Quality inspector Hans-Werner Scholz reports: “Traditional measurement, like we were familiar with on turned and machined parts, has changed with the new components for electromobility. We developed new measurement strategies in internal workshops as to how we can best capture the dimensions of stator and rotor packets, for example.”

Scholz and his three colleagues Markus Hartmann, Peter Rubik, and Jens Kaul – all quality inspectors certified by AUKOM (German apprenticeship program for metrologists) – appreciate the multisensor systems of the VideoCheck® machine. They apply optical and tactile sensors as needed. They use the traditional image processing optical sensor , for example, to measure stator and rotor punchings and other flat workpieces, such as sealing rings, clutch plates, and other electronic components with high accuracy and without contact, using transmitted and incident light.





Another optical sensor that is available is the Werth Laser Probe (WLP), which they use to scan the work- piece surface. This can be used to measure workpiece flatness very quickly. “We can capture the waviness of steel plates for clutch modules,” explains Scholz, “and we are much faster than if we were to use tactile sensors.” The WLP runs at a higher speed and greater point density than the tactile alternatives, with nearly the same accuracy.


Micro-stylus for ball bearing features that are difficult to access

The measurement technicians often use the patented Werth Fiber Probe® (WFP) as well, which is considered a tactile-optical sensor. It consists of a glass fiber that can have a probe sphere with a diameter as small as 20 μm mounted on its end. Unlike a tactile measurement, the deflection is not transmitted to the machine electronics via the stylus. Instead, the position of the probe sphere is captured optically by the image processing sensor itself.
This makes the fiber probe extremely accurate as well as easy to use. The user can track the position of the probe sphere on the monitor, so it can easily b

e positioned at the desired measurement point. The team uses the WFP® in the pilot production laboratory to measure steel balls from a supplier’s ball bearing. Quality inspector Scholz explains: “A single ball bearing is very difficult to clamp in a fixture. This is not even necessary for a fiber probe measurement, as it is essentially a non-contact procedure, and the ball will not roll away.”



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