Stamping, punching, bending, deep drawing and other forming processes are key to the efficient production of sheet metal formed components. Precision parts are used in the automotive industry, as well as in plastics, electrical, textile and medical technology. The quality demands on these parts and their complexity are increasing year by year and the biggest influence in their manufacture is the tools, i.e., stamping, punching and bending dies.
Founded in 1965, Fritz Stepper is a stamping tool manufacturer based in Pforzheim, Germany. The company prides itself in using the latest technologies to produce tools that are of exceptional quality in terms of design and construction. It is said to be responsible for the development of the first modular stamping tool, known as the Stepper module system. This is a universal base tool that various modules can be plugged into to allow it to be customised for entire families of precision parts.
The manufacture of these individual parts is not an easy task, but the modular tool approach allows Fritz Stepper to easily produce the individual dies that, in turn, are needed to produce the required complex and very fine punch tools like the one shown in figure 1.
Figure 1: A punch tool manufactured by Fritz Stepper.
The problem
The biggest challenge in manufacturing micro-precision dies, which can have multi-directional tolerances of <0.010 mm, is there should be no deviations in shape-giving geometry in respect of a datum. This needs to be maintained in a manufacturing environment, despite potential deviations caused by vibration, a worn tool and machine performance. Traditional 2D measurement technology only provides part of the solution, meaning there is a trade-off between accuracy and resolution. Moreover, 2D measurement technology times are too long for a production environment. Fritz Stepper therefore asked the question, is there a system that can carry out these measurements automatically and also be used to measure surface finish?
The solution
Fritz Stepper approached Bruker Alicona, an Austria-based provider of 3D optical measurement solutions, regarding the development of a system that allows a CAD file to be loaded, datums added and then automatic 3D measurement of multiple punches to be carried out.
To achieve the required results, the system needed:
• to afford multiple times higher accuracy over the full volume of the die;
• to be able to measure its complete shape-giving surface with high point density;
• to feature a modern, intuitive user interface that would require almost no operator training; and
• to fully automate recurring measurement tasks, thus freeing up metrology experts for analysis.
In addition, although not essential, if product manufacturing information (PMI) data was available then it was preferable that this would be integrable.
The solution chosen was based around the Bruker Alicona µCMM, a 3D optical coordinate measuring machine (CMM) that uses one sensor for the measurement of dimensions, position, shape and surface finish, providing high accuracy over the entire measurement volume.
The µCMM is fitted with an Advanced Real3D rotation unit, which allows for 3600 measurements and tilt, and a System 3R zero-point clamping system, which accepts the dies to be automatically picked and placed from the sample rack by the Universal Robots (UR) collaborative robot (cobot) system, both of which are shown in figure 2.
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Fig 2a
Figure 2: Fritz Stepper’s Alicona µCMM, fitted with an Advanced Real3D rotation unit and a System 3R zero-point clamping system (left), and a sample mounted on the Advanced Real3D rotation unit sample holder (right).
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Fig 2b
Figure 2: Fritz Stepper’s Alicona µCMM, fitted with an Advanced Real3D rotation unit and a System 3R zero-point clamping system (left), and a sample mounted on the Advanced Real3D rotation unit sample holder (right).
Using the system is very straightforward. The operator loads the parts to be measured into the custom-built sample rack shown in figure 3, selects the required program through the MetMaX automatic 3D measurement and evaluation software, loads the appropriate CAD file, adds the datum and PMI parameters and then starts the program, as per figure 4.
Fig 3
Figure 3: The custom-built sample rack for the µCMM.
Fig 4
The Alicona MetMax measurement software showing the measurement strategy for the whole form.
The MetMax software automatically develops a strategy for measuring measure the entire form, giving shape in respect of the selected datum. Afterwards, the operator checks for deviations from the CAD file.
Conclusion
This collaboration between Fritz Stepper and Bruker Alicona has produced an effective and accurate solution that is now in daily use. Marcel Heissler, head of laser ablation and high-speed cutting at Fritz Stepper, commented, “For us, the µCMM is the ideal solution in many ways. It offers high accuracy, even for tolerances in the single-digit micron range. Additionally, we benefit from an efficient user interface; the µCMM is designed to be operated by multiple users. Further, we have experienced a noticeable reduction in measurement times.”
Fritz Stepperwww.stepper.de/en
Bruker Aliconawww.alicona.com