The time saved on measurements helps MAPAL Dr. Kress KG develop innovative tool solutions even more quickly for trends that will play such a pivotal role in the future. Contributed by Carl Zeiss Pte Ltd.
These days, employees from the development department at MAPAL Dr. Kress KG generally know within an hour if new tools will offer the level of precision their customers require. Instead of having to wait days for a service provider to deliver the measurement results, the company started performing onsite measurements at the beginning of 2018.
With the high-precision coordinate measuring machine (CMM) ZEISS PRISMO ultra, MAPAL inspects the workpieces machined with the new tools it manufactures. The time saved on measurements helps this global company develop innovative tool solutions even more quickly for trends that will play such a pivotal role in the future like e-mobility.
How a Workpiece Ensures a Precise Tool
“We need extremely exact measurement results to develop high-precision, innovative tools and tool solutions,” says Dr. Dirk Sellmer, vice president of R&D at MAPAL. For years, the company had an external service provider measure its workpieces and tools. Seller compares MAPAL’s tools to “Lego blocks that are combined to create complex solutions.” To deliver these bespoke products to the customers more quickly, the company invested in an extremely precise CMM from ZEISS.
In January 2018, two employees began working with the ZEISS PRISMO ultra. Almost a year later, Sellmer has reached the conclusion, “The investment has paid off.” The measuring machine provided MAPAL with the necessary precision and was immediately running at full capacity. The two employees from the development department, who alternate between the measuring system and the production machines every two weeks, inspect the department’s tools on the CMM.
Most importantly, however, MAPAL employees measure workpieces that are machined in the development area with the company’s own tools, thereby determining the workpieces’ precision and stability under manufacturing conditions. Precision is on everyone’s mind because most MAPAL tools and tool solutions are used when components need to be machined with a very high level of accuracy.
The stator housing for an electric motor is one example of how MAPAL is successfully meeting its customers’ requirements. The challenge with this cast part is to create the primary, large-diameter borehole that runs through the entire component—all with an accuracy of just a few microns. For perpendicularity, the tolerance is just 30 microns (0.03mm) and, for coaxiality, 50 microns.
The Right Tool for Stator Housings
These are extremely narrow tolerances for such large boreholes. Yet, a closer look at the design of the electric motor illustrates why these stringent requirements are necessary. Take for example the permanent magnet synchronous motor, the most frequently used motor design in new energy vehicles (NEVs). The stator is the stationary component within the motor. Coils or copper wires known as hairpins are attached. These generate a current that creates a rotating magnetic field. The rotor is located within the stator and, thanks to its own constant magnetic field, follows the magnetic field of the stator. The three-phase current of the rotor causes it to rotate in synch with the magnetic field.
The rotor cannot move unless there is a gap between it and the stator. However, the rotor is subject to considerable magnetic resistance, which in turn reduces the magnetic flux density and with it the power of the motor. Thus, designers make this gap as narrow as possible.
To ensure that the manufacturing process does not compromise the component’s design, MAPAL offers its customers a high-precision tool which is also very light for its size.
First, a borehole is made in the cylinder for the stator housing. This means that a tool approximately 30cm long creates a hole in the outer die-cast layer of the housing. Then, the surface is carefully ground down. Tools for the highly precise machining of primary boreholes for stator housings have been part of MAPAL’s product portfolio for one-and-a-half years. And since not all housings are identical, these tools are customised for each customer.
On-site Measurements for Reduced Wait Times
Automotive manufacturers generally provide 10 to 30 housings that MAPAL must then machine with the corresponding tools in its testing area. The measurements performed after multiple rounds of machining serve as the basis for optimising the highly complex tool solutions in line with the customer’s needs.
Before purchasing their own CMM, MAPAL had an external service provider measure its workpieces and tools. However, the company’s measuring expenses rose significantly within the span of just 10 years. MAPAL increasingly manufactures the tools for its customers and takes on pre-series production. Numerous measurements are performed to ensure that the customer has all the information they require. The need for more measurements also increased outlay.
Yet as the company considered whether or not to invest in a CMM, it was not the costs that ultimately tilted the balance, but time.
“We used to have to wait two to three days for measuring results. This is no longer the case,” explains Sellmer. Now, these are generally available within an hour.
Since the employees performing measurements at MAPAL have also received metrology training, there are fewer artefacts. “Since our team also works with the machines used in production, they have a highly developed intuition and know, for example, where contaminants might have impacted the measurement result,” says Sellmer.
Moreover, the components are now clamped in the machining fixtures for measurements and measured on the company’s premises. This reduces potential artefacts caused by removing the workpieces from the fixtures or preclamping them. Another significant benefit for MAPAL is the ability to intermittently perform unplanned measurements, such as with thin-walled components like a stator housing. This way, the company can see how fixturing impacts machining.
Dr. Sellmer highlights yet another key advantage: the improved communication between engineers and technicians. They can now discuss the results at the measuring machine, rather than relying solely on measurement reports. And this promotes knowledge sharing. “We now achieve our goals significantly faster,” concludes Sellmer.
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