The spring overlayed with the nominal CAD-model and measurement features
In most industries, precision is the key to quality for an end product. So it goes for the mould-making and injection-moulding market as well. Here, right pricing and narrow profit margins dictate that a product needs to be delivered on time, with no production delays, to the highest possible standard. Part variation will directly affect the production and managing variation will save time and money. In their own words, at F. & G. Hachtel GmbH & Co. KG, “we use Computed Tomography (CT) analysis to predict, measure and control variation, distortions and metallurgical faults. The software is used for in-process and final part inspection and also production automation.”
Key highlights
- Saving time and resources through automation
- Up to three minutes per item was saved by automating the inspection process for large batches
- Manual labour was reduced as a large contributor to the minutes saved
In Aalen, Germany, Hachtel runs a facility with several services, including injection-moulding, mould-making, CT and Additive Manufacturing. For the injection-moulding branch, there is an emphasis on tooling automation, as the branch specialises in complicated processes and multi-component parts for appliances, electronics and the automotive industry, meaning the part specifications are narrow.
Hacht recently garnered experience with a supplier situation that accommodated the full testing of its inspection solutions. Having received a large batch of tooling springs, the inspection system employed by Hacht immediately identified a problem that showed the batch was defective. It was then decided to use this as an opportunity. As Hacht says: “Because of the software’s ability to automate inspection, it was decided that rather than reject the entire shipment, it would be better—and a test—to use the software’s Adaptive Measurement Template function to identify and save any good parts that might remain in the production lot.”
The way it works is that adaptive measurement templates track the shape of distorted parts against a CAD model or mesh, or the ideal part profile which may be derived from a CT scan. Even heavily deformed parts can be analysed with adaptive measurement templates. In this case, the software places optimal position measurement points on the actual part and follow the distortion, which then allows for analysis followed by acceptance or rejection.
Hachtel’s explanation for the springs’ production process shows how automation is essential and how a defective spring can result in serious delays: “The springs are inlays for an injection-moulding process and receive a plastic tip on one end. Because Hachtel gets hundreds of thousands of these springs, its tool-production process by necessity is highly automated. A positioning system places each spring individually on a transfer plate from which a handling arm takes a set of springs and loads them into the moulding tool. These steps are critical moments in the process – if a spring falls out of the handling or transfer plate the machine will go on halt and production stops. In the best case, this event requires only a little human interaction to replace the spring. In the worst case, the mould requires cleaning because the plastic was pushed out of the designated shape and nest.”
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Screenshot of Volume Graphics software analysis of the spring.
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The handling system used to single out the springs and transfer them into the loading system
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The open tool with inserted springs
In the interest of reducing down-times, which can be expensive, the company made the decision to control all springs upon delivery. This inspection is then used to determine whether the springs get rejected or if they are within specification and can be used. The shipment of defective springs was a valuable learning opportunity for Hachtel, as it pushed the CT inspection software and related handling functions further than it had before.
Kamil David Szepanski, Head of Technological Development and Product Development, explains the challenge: “Normal CT inspection typically uses a classic 3D design with defined dimensions as a basis for comparison. However, even routine springs rarely match the original CAD-model perfectly, and spring shapes can fluctuate between individual batches. This made the first, set-up transfer of measurement templates from the CAD, and even from proper pre-existing springs, difficult and time-consuming to manage.
Yet, the necessary pre-alignment was easy to automate and all samples were pre-aligned per macro. The transfer of the measurement template initially needed an individual inspection of each sample and a refitting of several geometry elements. We tried to use localized coordinate measuring machines (CMM) early on to help with correct fitting – but this increased the complexity of the template process and helped only a little on deformed parts. Some springs were too distorted to allow for an easy fit.
However, with the fully automated Adaptive Measurement Template we could ignore a pre-alignment step and didn’t have to perform any re-fitting of geometry elements. Indeed, after the application of the measurement template, we could take target features and geometries and create a “registration” of accurate part shapes. Now the registration—based on a saved datum system that included the distortion of the parts—was covered within the transfer. This allowed for slimmer and less complex measurement templates.”
Automation saving time and resources
The non-automated CT inspection process that would have been used previously was slow: a two minute preparation stage, three minutes for pre-alignment calculation, 15 seconds for copying the measurement template and a few more minutes for the manual re-fit of the elements. This adds up to roughly ten minutes per part, with half of that time being a manual task, resulting in long inspection times and high labour costs.
The automated adaptive measurement template means that although the process still has a two-minute preparation stage, the automation means about three minutes is saved per part. Beyond that, however, the process does not require further adjustments or attention from an operator.
The time saved with the automation of this process meant that in a batch that was assumed to be entirely defective, some of the springs were saved and still used in production. Hacht states that “The system proved itself not for only routine production inspection but, in this situation, very efficiently for unexpected crisis moments. Automated CT inspection saves time and resources, and preserves customer satisfaction. Furthermore, it provides unmatchable insight into sources of variation and metallurgical quality.”