Feature article: PIM International, Vol.3 No. 4 December 2009, pages 50-52, 1482 words

Author: Hartmut Walcher, Arburg, Geramny

Powder Processing Development, Arburg GmbH + Co KG, Postfach 1109, D-72286 Lossburg, Germany

Preventative quality assurance through the testing of feedstock prior to part production runs can offer significant cost savings thanks to a lower reject rate, suggests Arburg GmbH + Co KG, Lossburg, Germany. Hartmut Walcher explains how the company’s SELOGICA control system can be used to provide essential quality data for PIM part producers

In order to quickly and reliably assess feedstock batches prior to the volume production of PIM parts, the pressure at the change-over point of injection moulding machines provides meaningful, dependable values. These values enable the reliable assessment of possible fluctuations in batch quality. This data can be collected with ease using the Selogica control system of Allrounder machines.

In principle, powder injection moulding (PIM), used for the production of metal (MIM) or ceramic (CIM) components, does not differ significantly from the injection moulding of plastic parts. With these applications, the greatest possible consistency and highest quality of production must be ensured, based on predefined setting parameters.

The main challenge here is that an assessment of part quality is only possible following debinding and sintering. Quality problems in the production process can no longer be rectified after completion of these processing steps and a preliminary assessment of feedstock quality is therefore of decisive importance.

Costly assessment of moulded part quality

A period of several days is always required for the time-consuming subsequent processing of PIM parts, which poses the following problem for feedstock processors: Should they trust that the batch is satisfactory and continue to produce green compacts? Or should they stop the machines until the results of the quality testing become available? Both options are problematic from an economical standpoint. Of course, production must run as smoothly as possible from the outset. Moreover, feedstocks, be they metal or ceramic compounds, are comparatively expensive. Copper, titanium and precious metals, for example, are processed as well as steel alloys in MIM and three digit material prices per kilo are no exception.

Added to these costs are the machine-hour rate and the hourly rates for debinding and sintering. Accordingly, the production of reject parts is always extremely problematic because of the significant costs incurred.......

Further sections of this article include:

- Costly assessment of moulded part quality
- Many influencing factors determine part quality
- Various testing methods in use
- Control-system based solution saves time and costs
- Test procedure and significance of the results
- Sample calculations reveal major savings potential

Figures and Tables:

Fig. 1 Tests were performed on an Allrounder 170 S

Fig. 2 Required injection pressure at the various injection speeds – different preparation. Feedstocks (V4 - V7) consisted of aluminium oxide powder (CT 3000 SG from Alcoa) and Clariant binder, Licomont EK 583. The four mixtures with different mixing times and mixing intensities were prepared using a Henschel mixer. The same formulation was homogenised in a shear roller extruder

Fig. 3 Required injection pressure at the various injection speeds – different binding-agent contents. The feedstocks (A1 - A4) were produced in the shear roller extruder from aluminium oxide CT 1200 SG (Alcoa) and the same binder. The binder content was varied between 14.3 and 14.6 percent by weight

Fig. 4 Required injection pressure at the various injection speeds – different charges. A Catamold metal feedstock (BASF) consisting of two different charges (C1, C2) was tested

Fig. 5 Injected green test pieces used to gather process data. Debinding and sintering of the parts is dispensed with completely and the test pieces can immediately be regranulated and the material reused during subsequent volume production

Fig. 6 In an Allrounder injection moulding machine operating under balanced temperature conditions, the maximum injection pressure at the change-over point to holding pressure can be precisely determined via the Selogica machine control system