Case Study: Quality Control Sensor application for zero-defect production
In injection moulding, many sensors are not only installed in the machine to keep the process under control. The tools and moulds also score with high-tech. In China, German technology is now ensuring micrometer precision.
It is no secret that China has experienced an unprecedented upswing in recent decades. The country is already surpassing Western countries in some areas. Of course, the country continues to follow successful role models from Europe and overseas, especially in the areas of mechanical engineering and industrial production.
This also applies to TSP Precision Tooling from Shanghai. Due to its technological maturity and the wide range of possibilities that precision machining and manufacturing offer, TSP is one of only a few Chinese suppliers of injection moulding tools to have achieved certification according to EU-TÜV 1699.
Sensors meet high demands
TSP offers a comprehensive portfolio in the areas of mould design, development and production. TSP is also committed to a quality guarantee for manufacturing precision, thus securing competitive advantages for its customers. However, this only applies as long as the injection moulds and moulded parts meet the high demands of the customers with an accuracy in the micrometer range.
Huang Zhihua, Molding Test Supervisor at TSP, explains: “As a supplier to the world’s leading manufacturers of fastening technology, we often receive orders for injection moulds where very high demands are made. We design the corresponding moulds based on 3D models and customer specifications. Test production then follows, as this is the only way we can ensure that the injection moulded parts are free of defects.”
Cavity pressure sensors and process monitoring systems from Kistler play an important role in injection moulding production at TSP. And TSP engineers have been working with Kistler since 2012. They are therefore familiar with the function and properties of the sensors and are able to integrate them independently into various injection moulds. “Thanks to their wide measuring range and reliability, the cavity pressure sensors best meet our very high requirements,” the expert emphasises. However, they are not only used for quality control of the injection mould design process, but also in production. There, the systems monitor production around the clock and record the data generated. According to Zhihua, this has enabled the integration of remote-controlled real-time monitoring and comprehensive, traceable documentation of production data.
Optimum transition from injection to repressurisation
A characteristic challenge in injection moulding are incompletely filled parts, so-called ‘short shots’. These can be completely avoided with the Comoneo process monitoring system from Kistler. “First we determine the critical point of material shortage using the injection mould test curve and the DoE test (Design of Experiments),” explains Zhihua. Then the experts determine the pressure value of the underfill curve according to the curve pressure at the critical point. At the same time, moulded parts that are underfilled are sorted out. “We then use the digital signal to check for such parts,” he continues.
The deviations and fluctuations in the injection volume of the injection moulding machine can therefore also be compensated for with the aid of the Comoneoswitch automatic ‘switchover’ function, which enables an optimum transition from the injection to holding pressure phase. The entire moulding process can be improved during pre-series production by detecting the optimal switchover point (the transition from injection to holding pressure phase) at which the volumetric filling of the cavity is reached. “Thus we achieve a high process stability with comparatively little effort. The requirements with regard to the planned mass production can thus be reliably met — the superimposition of the cavity pressure curves in the Comoneo system and the discrepancy shown in the trend diagram for cavity pressure make our work for this enormously easier,” remarks Zhihua.
Good parts quickly after mould change
Another function of Comoneo that is very useful for TSP is the Comoneorecover restart assistant. This is because the parameters change after the injection mould has been changed from one machine to another, so that the machine-controlled curing process of the moulded part, for example, exhibits deviations. “Using the previously stored reference curves for the cavity pressure, however, the desired result can be quickly restored,” the company states. The Comoneorecover function is used to fine-tune the injection speed, holding pressure time and cooling time. “During process recovery, you have to make sure that the reference curve is as close as possible or ideally coincides with it,” Zhihang explains the procedure.
This ensures that the parts produced after the injection mould has been changed are largely identical in size and appearance to those produced previously. “In this way, we establish a standard process that is best suited for mass production. We thus ensure that the deviations are within a specified range, which minimizes the probability of errors occurring,” says Zhihua. In addition, process monitoring with Comoneo makes it possible to sort out plastic parts that are outside the tolerance interval. All the products that get onto the conveyor belt and finally into the cartons for delivery would thus meet the zero-defect requirement.
The satisfaction with Kistler products is correspondingly high. This applies not only to the solutions and service, but also to the cooperation as a whole. Zhihua sums up: “Since the beginning of our co-operation, we have been able to count on the active support of Kistler engineers in all matters. The Kistler specialists have so far been able to solve many technical problems and have also contributed not least to the training of excellent engineers.”