October 8, 2009
by Jack Jeswiet
Powder Metallurgy (P/M) is a well developed industry in Canada that plays an important role in the automotive sector. The process has been around for ages – it was first used by the Egyptians to make iron tools and by the Incas to make jewelry. One of its first modern applications was the manufacture of tungsten filaments for incandescent light bulbs.
P/M items are found in a wide variety of products, from ballpoint pens to farm machinery. Automotive components now comprise about 70% of the P/M market, and include bushings, hubs, inserts, gears, sprockets, spacers and self-lubricating bearings. Advances in P/M technology has made it attractive to other industries, where P/M has experienced rapid growth: the aerospace industry (including landing gear components, engine mount supports, engine disks, and impellers); the nuclear power industry; and the biomedical industry where it’sused to produce controlled porous structures for dental and orthopaedic surgical implants.
A wide variety of materials are used to make P/M products including iron, steel, tin, nickel, copper, aluminum and titanium. Brass, bronze and stainless steel parts can also be made. From 1960 to 1980 the consumption of iron powder for automotive parts increased dramatically. Iron and low—alloy steels now account for 85% of all P/M usage. The total weight of P/M automotive parts in a modern vehicle can reach 13 kg with the bulk concentrated in the engine transmission (12 kg), however most individual P/M parts weigh less than 2.2 kg.
A major attraction of P/M is its near net shape capability that eliminates a series of other conventional manufacturing operations—97% of the starting powders are converted to product). It can be used to manufacture complex shapes in high volumes while keeping close tolerances at low production costs with minimal waste. P/M parts are mass produced economically in quantities as small as 5000 per year to high volumes such as 100 million per year.
As in all manufacturing situations, there’s a push to refine and improve P/M processes, thereby increasing both efficiency and productivity. For this reason, modeling P/M processes has gained considerable attention during the last decade, especially in the development of simulation models that are used to predict what will happen in the P/M process, at all stages of manufacture.
Within Canada, a research team supported by the AUTO21 Network of Centres of Excellence is working on the Next Generation Compaction System project. The team includes researchers from Queen’s University, Ryerson University and the University of Victoria plus several industry partners.
The simulation of P/M compaction and its prediction requires modelling of part ejection. This also relates directly to an understanding of P/M compaction machines. To determine if machinery is actually following the pressing and ejection schedules that have been designed, it is necessary to investigate machine rigidity and machine component interactions with accurate models, at all stages of the process.
The efficient design of powder compaction processes requires accurate simulation of the process with finite element method (FEM). Because numerical simulation is a relatively new trend in the modelling of metal powder compaction processes, the technical information needed to make accurate simulations is not available. For instance, most commercial FE (finite element) codes do not have the proper material models for metal powders, hence the on-going work. These facts make numerical implementation of metal powder material models a challenging aspect of FE analysis of metal powder compaction. As a result, part of the AUTO21 project involves the development of different material models for metal powders and their algorithms and source codes, which it is believed will help simulate the P/M process. This will help give better understanding of different aspects of process design, such as friction and lubrication, cracks, parametric study and optimization. In the end the P/M process will be more efficient and allow manufacturers to be more productive.
Dr. Jack Jeswiet is a professor at Queen’s University and a project leader for the AUTO21 Network of Centres of Excellence. For more information, please visit www.auto21.ca.