GOM Metrology

GOM Metrology

Oechsler: Fewer Loops for Better Tools

Fewer Loops for Better Tools with Optical Metrology

Thanks to the invention of the actuator for the Electronic Parking Brake (EPB) by the Bavarian plastics company Oechsler AG, drivers of modern cars no longer need to worry about difficult uphill starts assisted by manually pulling the parking brake. The core of the actuator is a gear unit made of plastic. The patented design uses high-tech materials to meet the demanding performance requirements while maintaining a low installation weight.
Oechsler is a single-source service provider that supports the entire process from concept design in collaboration with customers, specification and simulation, up to toolmaking and production of parts. By using GOM’s optical 3D measuring system, the plastics specialist has been able to significantly accelerate its production of injection molding tools – among other things.

Optical 3D measuring system stood out in the benchmark test

Every year, more than 400 different materials are processed at the headquarters in Ansbach, almost 80 percent of which are fiber-reinforced materials. “Such materials have a natural tendency to warp, especially in some products like a housing part with low wall thickness.”, explains Marco Wacker, Doctor of Engineering, Head of Technology and Innovation at Oechsler and a member of the managing board.

Precision is the core competence of the company since it was founded. The measurement of these housings with tactile systems kept causing problems. Changes that had been made to the tools were not always reflected in the measured data. “When we looked at the problem a little closer, we realized that tactile measurement took too much time, in addition to measuring only part of what we needed. On top of this, tactile measurement reduces a 3D measurement to an abstract representation of binary or ternary points in a table. Then the designer must implement the results into his 3D system”, explains Wacker, “It no longer made sense in the digital age.”

In 2012, the company began to search for an alternative method. After comparing the in-house tactile measuring systems with a CT scanner and with an optical measuring system, GOM’s solution stood out due to its high speed and accuracy as well as capability of measuring hybrid parts. Therefore, Oechsler opted for a 3D scanning system from GOM, which uses blue light fringe projection.

Oechsler AG is a single-source provider that supports the entire process from concept design in collaboration with customers, specification and simulation, up to the tool making and production of parts (Image: Oechsler)

Full-field measurement in less time and with fewer iterations

Instead of capturing individual points, the optical 3D scanner performs a full-field scan of the entire part geometry, generating a high-resolution point cloud. The projected fringe pattern is recorded by two cameras. A highly detailed image consisting of millions of measuring points can be recorded contactless within a few seconds. The GOM software computes three-dimensional object coordinates for each camera pixel. This calculated polygon mesh describes freeform surfaces and regular geometries that can then be aligned with the drawing or directly with the CAD data set in a shape and dimension analysis. Compared with tactile measurement technology, the entire surface of the part can be scanned very quickly without any blind spots.

Besides that, Norbert Krauß, Research & Development Project Manager at Oechsler, confirms: “The great thing about the optical system is that it shows many things at once. There is no need to think about flatness; you can see where the diameters are, and the location of connectors, contacts, and positions.” The user gets an overview of the entire part at a glance, instead of just a few abstract points as with tactile measurement. This makes it a lot easier to perform several corrections in one step, which can significantly reduce the number of iterations.

The 3D digitizer enables simple, fast, and reliable measurement workflows at Oechsler (Image: GOM)

By using the GOM measuring system, correction loops during tool production were reduced from seven to three (Image: Oechsler)

Simulation and measuring system complement each other

Before starting mass production, the tool needs to be verified and a flow simulation is carried out. Oechsler creates an internal control loop for this process. At first, the simulation expert enters process parameters into the simulation system based on his long years of experience. The operator at the injection molding machine accepts the data, modifies parameters if necessary, or makes the tool based on his own experience. In any case, he measures the plastic product using the GOM system and returns the results to the simulation, based on which he can then improve his model again to incorporate such insights into the next simulation.

Scan-based comparison of a part made from different plastics (Image: Oechsler)

 “Step by step, we are building up experience like a library. In the long run, this helps us to simplify multiple measuring tasks. GOM is a key element in this internal control loop.”, says Birgit Hauf, a member of the R&D Department and in charge of the GOM system. The measuring results are then applied to correct and resample the tool. This control loop is repeated until the desired accuracy has been achieved. According to Krauß (Head of R&D), the improved information provided by the GOM system help reduce the correction loops from seven to three for new parts. Using free GOM Inspect software, the measuring data can be visualized and evaluated across teams.

Besides that, Oechsler is also using the ATOS system to compare materials. The measuring system allows to determine quickly during the sampling stage whether a material behaves similarly to the reference material and which adjustments may be required. Several alternative materials can be sampled at an early stage during tool release bearing in mind that there can be considerable variations between manufacturers. The GOM system helps to reduce the effort required and quickly delivers results. Oechsler has developed the measuring procedure to an extent that it is easy to handle. In the next step, Marco Wacker plans to semi-automate the measurement with GOM, and maybe go fully automated at some point, and says: “This would give us considerable time and process-related benefits for the company.”

Comparison of an attachment bore before and after correction, based on GOM measuring data and evaluations (Image: Oechsler)

Oechsler AG

The Oechler Group is known for forward-looking solutions in plastics technology. The product spectrum ranges from precise individual parts to complex assemblies and systems, e. g. for the automotive and medical technology industries as well as for other selected products. Besides three sites in Germany (Ansbach, Weißenburg, Brodswinden), Oechsler has affiliated companies in six countries all over the world: China (Taicang), Romania (Lipova), Mexico (Querétaro), USA (Acworth, Georgia), Vietnam (Long AN) and Singapore.