Feature article: PIM International, Vol.4 No. 3 September 2010, pages 50-53, 1801 words

Author: Dr. Georg Schlieper, Ingenieurbüro Gammatec, Germany

 Ingenieurbüro Gammatec, Alleestr. 101, D-42853 Remscheid, Germany

Raw materials undergo several transformations during the metal injection moulding process, from powder through to feedstock, the production of the green compact, debinding and finally sintering.

In this latest part of our back-to-basics series, Dr Georg Schlieper focuses on green compacts and the methods used to characterise their properties, as well as green part processing and handling.

When we look at the stages between injection moulding and debinding, we should consider the separation of parts from runners and sprue and discharge from the moulding machine, inspection, characterisation and quality control of green parts, green parts manual processing or machining, as well as handling and transport to the debinding process.

The essential preconditions for a high product quality, and the economic efficiency of the MIM process, are set during injection moulding. The green compact is the first intermediate product in the process that has essentially the shape of the final component and that allows it to be tested for product quality. Any defects or irregularities in the green compact will still exist in the sintered product. Sintering leads to a consolidation of the powder, but it does not ‘heal’ any defects. Therefore it is important to apply as many intelligent tests as possible to eliminate defective parts in the green stage before they go through the costly debinding and sintering process. One focus of this feature will be on testing green MIM compacts.

The first issue to be solved after injection moulding is how to separate the sprue and runners from the parts, and how to remove the parts from the injection moulding machine. There are a number of options and it has to be decided which one is the best both technically, for a high product quality, and economically, for the lowest possible manufacturing costs......

Further sections of this article include:

- Intelligent mould design saves handling costs
- The characterisation of green parts
- Part weight
- Density
- The Archimedes test
- Gas pycnometry
- Radiographic inspection
- Secondary operations on green parts
- Automatic green part handling systems
- Summary

Figures and Tables:

Fig. 1 Gate options in mould design: tap gate (left), sub gate (middle), and three plate tooling (right) (courtesy Dynamic Engineering, USA)
Fig. 2 Green MIM parts being deposited on a conveyor belt (courtesy Arburg)
Fig. 3 Principle of gas pycnometry (courtesy Micromeritics)
Fig. 4 Design principle of the gamma ray densitometer (courtesy Gammatec)
Fig. 5 Densitometer used in the press and sinter industry (courtesy Gammatec)
Fig. 6 X-ray images of tensile test bars green (left) and sintered (right) (courtesy IFAM Bremen)
Fig. 7 Robotic handling systems. Left - Robot reaching into an injection moulding machine (courtesy Reis Robotics, USA Inc) Right - Overhead-mounted robot (courtesy FANUC Robotics America Inc.)
Fig. 8 XYZ pick-and-place system (courtesy Bahr Modultechnik)
Fig. 9 Sucking picker holding a sheet (courtesy MM Engineering)