Optimal Processes

Ralph Hufschmied, managing director of the tool manufacturer Hufschmied Zerspanungssysteme GmbH in Bobingen, reports that his company primarily produces custom-optimized tools. “Starting with a standard design, we develop drilling and milling tools that are exactly tailored to the machining conditions, the materials to be machined, and the economic requirements of the manufacturing companies. In this way, we make a significant contribution to optimal processes,” he says, explaining the tool manufacturers’ concept. 

Thirty years ago, he and his father founded the company based on this idea. Currently, nearly 130 employees at Hufschmied produce high-quality drilling and milling tools on this basis, primarily for materials that are difficult to machine and for unusual machining operations. This includes, for example, trimming and high-precision machining of components made from glass- and carbon-fiber-reinforced plastics for the automotive industry. The tool manufacturers also develop and implement productive and efficient processes and tools for machining high-strength, tough metals, such as titanium-aluminum alloys used in medical technology.

At Hufschmied, they are always open to innovation, as Ralph Hufschmied emphasizes. That’s why, a few months ago, they welcomed ZOLLER’s offer to work with the »mμFocus« optical inspection unit. 

This measuring technology is one of the forward-looking innovations from the Pleidelsheim-based manufacturer. For ZOLLER, the collaboration offers the especially advantageous advantage of receiving feedback from Tool manufacturers with hands-on experience regarding the device’s function, use, and measurement results. 

Ralph Hufschmied adds: “Together with ZOLLER, we have consistently found suitable measurement methods for our tool production for over 20 years. For several years now, we have been working with the »genius« measuring machines. Here, too, our experience and feedback have helped optimize the measuring machines in terms of their equipment and operation for real-world use.” That is why both partners quickly agreed to jointly further develop the innovative »mμFocus« optical measuring method using insights from tool production.

Repeated measurements of different tools have resulted in previously unimagined insights for the tool manufacturer Hufschmied. Dr.-Ing. Fuentes reports: “For example, we had been measuring the surfaces on the shafts of milling tools by probing. Despite optimal values for surface roughness R_a, there were repeatedly tools that were pulled out of the hydro-expandable or shrink fit holders due to cutting forces. We then measured these visually and arrived at surprising results.” 

The tool manufacturers discovered that the measurement results from probing are highly direction-dependent. This applies above all to the tool shanks and the resulting transferable clamping forces. Furthermore, as Dr.-Ing. Fuentes explains, the measurement results obtained via probing are not always comparable with one another and cannot consistently be used to assess roughness. “There are significant differences in tool behavior, although the averaged and measured roughness depths (R_z) of several tools are in accordance. 

In our experience, optical measurement methods and ZOLLER’s »mμFocus« inspection units are sufficient to adequately assess the relationships between roughness depths and surface behavior—in terms of clamping forces and transmissible torques—in detail.

Far-Reaching Benefits 

Optical measurement with ZOLLER’s »mμFocus« inspection unit provides specialists at the tool manufacturer Hufschmied with unprecedented insights into the properties of tool surfaces. For the initial time, it is possible to measure and evaluate surface roughness over an entire area, rather than just along a single line and in a single direction, as is the case with contact measurement. The »mμFocus« inspection unit uses a light beam to enter a surface that measures 1.0 x 0.8 mm at a resolution of 1.3 million pixels. The image of the surface on the color screen displays the height profile at a resolution of 0.3 μm using different colors. This allows the operator to holistically assess the captured and measured surface. This yields previously unexpected insights. For example, on some surfaces—such as a tool shank—a clear directional orientation of the roughness can be detected. “This may be caused by the grinding of the tools,” reports Dr.-Ing. Fuentes. 

Similar results are also obtained for coated tools using the optical, microscopic measurement method. While the commonly measured arithmetic mean roughness value R_a is uniform across the coating, significant differences can be observed in the surfaces measured using the »mμFocus« inspection unit. This applies both to the nature of the height profiles and to the roughness depths. Little is currently known about the actual geometric properties of specialized coated tools. Furthermore, conventional measurement methods can only provide a general assessment of microgeometries. In contrast, the innovative optical measurement method using »mμFocus« inspection units opens up significant opportunities for evaluating surfaces with much greater exactness and in greater detail.