EPMA award entries highlight diversity of metal injection moulding in Europe
The European Powder Metallurgy Association’s (EPMA) annual Awards for Excellence ceremony took place in Mannheim, Germany, on September 29th 2008. The two MIM components entered into the competition highlight the diversity of Europe’s PIM industry. We take a closer look at innovative high volume micro-MIM gears from Switzerland, and a contrasting low volume luxury clock casing for the automotive industry from Germany.
MicroMIM planet carrier with sun gear
Parmaco Metal Injection Molding AG, of Fischingen, Switzerland, was highly commended for its microMIM Planet Carrier with Sun Gears, manufactured for Samsung Electro Mechanics and used in mobile phone opening and closing mechanisms.
Planetary gears are widely used to reduce the rotary speed and thus increase the rotary torque of DC motors. As there is a shift to ever smaller motors, there is consequently a demand for ever smaller planetary gears.
Such gear systems contain a number of components, one of which is the Planet-Carrier with Sun Gear (See Fig. 2). Depending of the reduction ratio, a varying number of Planet-Carriers with Sun Gear are used in one gear assembly. This component is designed to have a sun gear on one side and 3 pins to take up the planetary wheels on the other side (See Fig 3). Its precision is essential for the smooth functioning and low noise level of the planetary gear assembly.
Until now there have been two widely used methods to manufacture such gears. Up to a certain torque level, plastic injection moulded planet-carriers can be used. However, if the torque level is too high for plastic gears then steel needs to be used.
Prior to MIM production, steel components had to be assembled from a precision stamped steel disc, a number of steel pins and a steel sun gear in the centre. This technique remains widely used for such components with a diameter of 10mm or more. However, with today’s demand for ever smaller gear boxes, assembly has become an increasingly difficult task.
Samsung Electro Mechanics required a cost-effective method to produce 12 million high torque Planet-Carriers with Sun Gear for its high volume requirement of planetary gear boxes with a 6.2mm outer diameter. MicroMIM proved to be the most cost effective manufacturing route, allowing the net-shape production of a single part in place of the assembly of 5 parts. Cost savings by using MIM are in the range of 40%.
Parmaco produces these parts from a mix of carbonyl iron powder, nickel powder and a 316L master alloy. After dry mixing a thermoplastic binder is added. A 4-cavity split mould is then used on a Battenfeld Microsystem 50 moulding machine with cycle times of 5.5 seconds. The parts are solvent debound and vacuum sintered with Nitrogen partial pressure to maintain a sufficient carbon level for subsequent vacuum hardening. The parts are micro-tumbled for optimal surface finish.
Such gears demand extremely high tolerance levels, so mould design and accuracy played a key role in the development of these parts. All critical cavity dimensions were manufactured to +/-0.003mm. The cavity tolerance for the dimensions of all 32 pins is even within a range of 0.003mm. Thanks to such stringent mould requirements, Parmaco claim that the tolerance of the pin diameter can now be held to 0.015mm. The weight of the finished Planet Carrier with Sun Gear is 0.076g after sintering.
The development of the MicroMIM Planet Carrier with Sun Gear took 8 months. The second related part, a MicroMIM Planet Carrier with Shaft, took 5 months.
Founded in 1992, Parmaco is a privately owned company with recent annual growth rates reported to be in the range of 20%. Parmaco has customers in a wide range of industries including medical, fire arms, power tools, textile machinery, electronics, locking systems, connector systems for electrical and fibre optic components, gear components, automotive and dental. Although the company’s largest market is within Europe, it also supplies components to Asia and other areas of the world.
Georg Breitenmoser, General Manager at Parmaco, told PIM International ‘The size of our products ranges between 0.01g up to 90g. Our main interest is however in the production of components of less than 10g, and particularly in the MicroMIM areas where typical part weights are below 0.3g. We thank Samsung for their innovative spirit which has allowed us to work on this break through project pushing the limits of MIM to new levels.’
Clock casing for luxury automotive application
OBE Ohnmacht & Baumgärtner GmbH & Co. KG, of Ispringen, Germany, has produced a MIM clock casing for use in a high-end automotive dashboard
(Fig. 5). The part, used in a Mercedes-Benz AMG vehicle, was produced by MIM in order to achieve a perceived higher value and a cool touch by replacing an original metalised plastic part.
The clock case, which is manufactured in relatively low volumes, is produced from 316L stainless steel using an Arburg injection moulding machine with a single cavity mould that was produced in-house by OBE. The feedstock used is BASF’s Catamold system which, suggests OBE, brings them advantages thanks to good reproducibility in series production. The finished case weighs 13.6g.
An unique feature of this component is the brushed surface effect which is integrated into the tool (Fig. 6). OBE has developed significant experience in the manufacture of parts with specific surface finishes, achieved either by integrating the surface into the tool or by treating the surface of MIM parts after production to achieve the necessary quality for the luxury goods industry. MIM was seen as the only possible solution for this product, which was developed over a three month period. This clock casing is an example of how MIM technology can be effectively used for low volume high value items.
OBE was founded in 1904 and today has a 15000m² production facility in Germany that employs approximately 260 people. MIM technology was first introduced to the company in 1996 with a mould and design department. Today the company manufactures small precision MIM components for a wide range of industries including optical, luxury goods, aviation and medical devices. Growth of between 5-10% is anticipated for 2009.