The cruise control of injection moulding

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Adaptive Process Control - or APC - is bringing to injection moulding, what cruise control brought to long-distance driving.

KraussMaffei's APC system promises zero-defect injection moulding production, and targeted adaptation of the changeover point and the holding pressure profile in each cycle. How? Because APC keeps the weight of the finished part, as specified by the mould-setter, consistent during on-going production regardless of external factors. And now, KraussMaffei has developed the APC Calculator, which automatically estimates annual savings in euros by inputting shot weight and cycle time parameters and the price for new material.

Rejection rates are closely watched in the injection moulding process and could make or break a manufacturer's bottom line. External factors such as changes in room temperature, humidity and raw material properties when using recycled materials can be factors in processes with even stable configurations. To compensate for any variations in the manufacturing process, KraussMaffei's APC system configures the ideal process, detecting any deviations and making constant alterations.

Offered for all series from KraussMaffei, the system eliminates all faults, allowing the manufacturer to retain consistently high product quality - and with the calculator function, manufacturers know exactly what their efficiency gains amount to in cash terms.

Two steps to consistent component quality

Step 1: Analysis

APC analyses the current process status, enabling the machine to keep a configured process stable if the external factors such as batch fluctuation change the viscosity of the material or the flow resistance in the mould. These changes are detected by recording specific key parameters such as the melt pressure curve of the machine.

Step 2: Control

Through clever evaluation of process data gathering in Step 1, the machine can respond to the current process state within the specified limits. APC adjusts the changeover point and the holding pressure profile to the existing melt viscosity and current flow resistance in the mould. This makes it possible to compensate for deviations online and in the same shot. Among other benefits, this results in a significantly more robust production process.

APC produces uniform shot weights within a very small tolerance, leading to the consistent component quality that can already be seen in various KraussMaffei customer projects.

"Injection moulding processes are validated mostly under the premise of constant process parameters," explained KraussMaffei's Head of Machine Technology Dr Reinhard Schiffers. "An adaptive intervention in the process and a change of the relevant parameter is therefore a controversial practice and may even represent a paradigm shift. Nevertheless, products become more complex by functions integration, usage of multi components and more complex materials.

"Manufacturing becomes more prone to disturbances and machine makers are forced to meet customer needs to continue providing high quality machines, so reception in the market has been good from the beginning as the benefits were obvious. Once operators on the machines understood the mechanism behind the technology, they easily adopted it."

The new numbers game

The APC calculator function - which was launched in May 2015 - is available in five languages (English, German, Spanish, Chinese and Russian) online and automatically estimates annual savings in euros by entering data including cycle time and shot weight parameters, and material price. The function then immediately compensates for fluctuations in the injection moulding process resulting in fewer rejects. The overall substantial savings can be made in regard to time, costs and material. Higher recyclate proportions can also be processed.

Offering maximum flexibility, all data can be changed at any time, automatically adjusting the result.

"Let's take a specific practical example, i.e. tube shoulders," said Hans Malinowsky, Product and Technology Manager at KraussMaffei. "With a throughput rate of 27 kg/h, a new material price of 1.10 euro/kg, a 1.5 per cent reduction in the reject proportion and a two per cent increase in the recyclate proportion, this produces annual savings of €4,207 (£3,060)."

These savings are even more substantial with higher throughput rates during the production of pallets (throughput rate of 440 kg/h, new price 1.15 euro/kg), for example, annual savings of more than €205,000 are attained.

APC tests its automotive mettle

One application where APC has proved it is a valuable tool in the plastics processor's arsenal is in automotive.

In 2012, KTW Kunststofftechnik Weißenburg and KraussMaffei commenced a joint project aimed at reducing the rejection rate in the injection moulding process. This is because over time external factors were affecting component quality, particularly when using recycled materials.

To compensate for these fluctuations in the process, KraussMaffei brought its APC system into the production stage with KTW.

KTW is a medium-sized Tier 1 automotive supplier specialising in high-quality exterior and interior components such as finishers, panelling covers, air ducts and wheel house shells, which are manufactured using both standard injection moulding and special processes involving multi-component technology, over-moulding of film or fabric and variotherm technology.

The Weißenburg-headquartered company processes approximately 5,000 tonnes of thermoplastic per year on more than 20 injection moulding machines. Since 1998, the company has relied solely on KraussMaffei injection moulding technology, installing 14 fully-automated machines in the clamping force range of 80 to 2,300 tonnes between 1998 and 2012. In 2011, as part of a larger package, KTW acquired the MX 2300, which produces wheel house shells from recycled materials for a large German automaker. In order to gain experience with the new features during day-to-day production and to apply these experiences to the development process, KraussMaffei equipped this large machine with the APC process control system.

The polyolefin recycled material produced by KTW for wheel house shells is stored in 80-tonne silos. Depending on their origin, the recycled materials vary in terms of grain size, consistency and bulk density, leading to substantial fluctuations in viscosity. KTW uses the APC system to intervene in the production process automatically, within definable limits, so that a change in material viscosity does not lead to fluctuations in component weight.

"The use of the APC function enabled us to substantially improve continuous monitoring of melt quality, significantly reduce the subsequent rejection rate and guarantee precise traceability of the components down to the individual shot," said Albert Burghart, Plant Manager of KTW in Weißenburg.

"This project involved close collaboration between our two companies that proved to be fruitful for both parties. Our insights and wishes were successively applied to the development of the new machine function. Everything went off without a hitch."

Going mobile?

APC technology took off in Europe thanks to KraussMaffei's close relationship with a number of local industry partners but the innovation has since been adopted by injection moulders in the US and Asia - and there is still no real competition on the marketplace.

"The goal of APC development was to improve process robustness and component quality," said Schiffers. "Though, condition-based switch-over is not new to plastics, [a system like APC] has never been achieved before by a machine maker. KraussMaffei is unique with this technology on the market."

So what next for APC? Schiffers suggested there is scope for evolution but it is important to bear the traditionalist injection moulding sector mentality in mind.

"Further development regarding process robustness and process capability are absolutely essential," he remarked. " Nevertheless, the machine-making industry is recognised as being conservative, therefore [developments such as] mobile applications must give customers immediate benefits."

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