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Transparency and quality in production

Transparency and quality in production

A leading German manufacturer of electrical appliances has improved quality in its production of plastic parts, by monitor cavity pressure with sensors during injection molding.

To meet the growing demand for shavers and epilators, a new production hall was recently completed at a German manufacturer’s facility. Cutting-edge manufacturing technology creates ideal conditions here for the firm to step up its output, and its partnership with Kistler guarantees that the plastic parts produced in its own facility will provide no grounds for complaints.

Defective parts cause downtime on the assembly lines – and production stoppages cost vast amounts of money. Therefore, the company’s molding operation concentrates on the high quality of the parts it produces, because this is the factor that determines the functionality of the end products. The critical challenge here is the vast and diverse range of parts. Depending on its type, an appliance can consist of 200 to 300 individual parts, including 30 to 45 made of plastic. End-to-end quality monitoring is essential for these complex and often highly intricate parts.

As part of the internal process control strategy, the decision was taken to step up consistent monitoring of cavity pressure – with the help of sensors and systems by Kistler. Measures to achieve this goal have significantly reduced the number of internal complaints. And since process monitoring based on cavity pressure was introduced, the scrap rate has been slashed by 50% – as proven by statistics. About 30 Kistler process monitoring systems are now in operation, and over 90 molds are equipped with cavity pressure sensor technology. The company uses two process monitoring systems: CoMo Injection Type 2869B and ComoNeo Type 5887A. They monitor the pressure curves from two to 32 cavities.

As regards sensors, this manufacturer mostly opts for Kistler’s rugged and resilient pressure sensors with frontal diameters of 1mm, 2.5mm and 4mm. In some of the molds, sensors are installed in every cavity but in other cases, the entire mold has only one sensor. However, all the molds are prepared so that each cavity can be retrofitted with sensor technology should the need arise. This allows the process team to decide whether or not to retrofit sensors in the remaining cavities during the debugging phase.

Since Kistler’s sensors and process monitoring systems were introduced, the company has seen a vast improvement in the quality monitoring and assessment of its injection-molded parts. Cavity pressure profiles supply valuable information about the entire process of creating a part, in correlation with the machine parameters: from the injection phase and the switchover point through to the holding pressure phase in the mold.

Thanks to targeted monitoring of parameters, operators can be certain that the quality of the molded part is right, thus preventing short shots (incomplete mold/cavity filling). The pressure in the mold has to rise above a specified level, but must not exceed a maximum peak pressure. A group of in-house experts defined these evaluation objects during the validation phase.

If the pressure curve does not reach the specified minimum level, or if it exceeds the maximum, the process monitoring system assesses the part as non-quality-compliant, so it is classified as scrap. Immediate separation of bad parts is critically important here. Merely knowing that parts are flawed will yield no economic benefit. Immediate re-sponse and consistent removal of these parts from the production process are essential in order to curtail costs caused by machine outages.

The process monitoring systems installed in the plant are simple to operate. The cavity pressure profile can be tracked in real time. On the multi-touch display, users can very easily identify process fluctuations with the help of features such as trend views. Pre-defined warning thresholds also enable them to intervene in the process at an early stage.

One key advantage of quality monitoring is the possibility of reproducing processes. In many cases, an injection molding machine is used to produce five or even eight different articles, rather than just one. And even when molds are changed, the pressure profile in the cavity must still behave as defined in the validation – regardless of any external influences that may be present. The validated reference curve is the part's ‘fingerprint’.

Cavity pressure monitoring is also very important in another way: operators can use the data (visualised as a curve) to assess the condition of their molds so as to detect wear in good time. Thus, cavity pressure monitoring acts as an early warning system if a pump loses power, and also if a nonreturn valve is not functioning perfectly.

The percentage of short shots has decreased substantially since Kistler’s sensors and process monitoring systems went into operation. This gives the manufacturer a whole series of positive benefits. So it comes as no surprise that a total of 47 additional machines at the company’s high-tech facility are to be equipped with cavity pressure sensors and monitoring systems by the end of 2019.

The planned expansion of the plant’s monitoring systems simply won’t happen without the good service and on-site support offered by Kistler that is so highly appreciated by this customer. And this leading manufacturer views Kistler’s know-how, and the support of its experts in every phase, as essential factors in all its future projects.

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