For the production of a safety-critical, high-voltage connector ordered by Hirschmann Automotive GmbH, the stamping and hybrid technology specialists at Kramski GmbH rely on Kistler Group’s force sensors and process monitoring—with the miniaturized piezoelectric force transducer directly integrated into the progressive tool.
Connectors have continually evolved in recent decades. The driving force behind this evolution has mainly been the automotive industry; performance, signals and data must be transmitted quickly, securely and as resistant to interference as possible—especially if cars are going to be self-driven in the future. This sets strict requirements for parts, components and production processes for complex connectors.
Kramski, headquartered in Pforzheim, Germany, is a leader in this field. The company operates in four locations worldwide, including Sri Lanka, the United States and India. With a team of 700 employees, Kramski produces highly complex stamped and hybrid components.
“Our top priorities are quality and innovation. Together with partners like Kistler, we’re working at the forefront of technological development,” says Felix Nussbaum, head of sales and marketing at Kramski. In addition to cutting-edge stamping and injection molding machines, this is mainly due to the company's in-house tool manufacturing.
Kramski produces about 3 billion parts worldwide every year for its customers. Important trends in the industry include digitalization and miniaturization, as well as traceability all the way down to the individual part.
“In terms of connectors in particular, the continually expanding range of variants must be considered,” Nussbaum says. “We continuously improve our processes in line with the principles of Industry 4.0 in order to offer our customers the greatest possible quality, transparency and efficiency.”
However, the complexity of the projects should not be underestimated, he adds. Depending on the task and the work required, lead times can run as long as two years.
Kistler’s MaXYmos XY monitors evaluate the quality of a production step using two measurands, e.g. force and displacement. The benefits include:
MaXYmos is available in the variants BL (basic level), TL (top level) and NC (specifically for joining process), depending on the application.
In addition to the insertion force testing integrated into the tool, Kramski worked with Kistler to implement four other test steps: feed control during conveyor belt feeding; checking for stamping waste (double-sheet control); laser marking of finished parts (marking on the fly) and optical end-of-line testing (contour, dimensions, surface).
These tests are carried out using additional technologies from Kistler, such as optical sensors that have been specialized for stamping technology, a laser marking cell and an automatic testing system that includes camera systems and industrial image processing.
Both the finished connector and the sensor must be extremely compact.
“In order to implement the testing of insertion forces in the production process, the sensor is installed directly in the progressive tool—it’s not even visible from the outside,” explains Jörg Carle, Kramski’s COO. “Thanks to its compact size of just over 10 mm, the miniaturized force transducer 9313AA1 from Kistler is ideal for this purpose. Furthermore, the square sensor body with dual-side force application via axial threaded holes is ideal for this application.”
Kistler’s piezoelectric force sensor technology offers several other favorable characteristics that have proven themselves in automated stamping applications. Examples include overload capacity, high stiffness, sensitivity and—most importantly—longevity. “Once the sensors have been installed in the stamping tool and the line is in operation, we need to be able to rely on them over the long term,” Carle adds.
With the help of this new inline process monitoring and additional test steps that have been integrated into the production line, Kramski was able to satisfy the strict requirements of Hirschmann Automotive.
“In addition to Kistler’s leading technology, we also appreciate the close working relationship and the mutual understanding we have built,” Nussbaum says. “Over the years, this has evolved into a true development partnership that benefits both sides.
“Together, we are operating at the limits of what is technically feasible and continue to push these limits further and further,” he continues. “This fits very well with the extremely high quality standards at Kramski and should be described as a win-win relationship.”
The positive experiences with the integrated force sensor technology and process monitoring from Kistler are also demonstrated by the fact that Kramski has now commissioned a second solution for an additional production line that will be implemented in the near future.
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