The technique is mastered for a long time but has its limits

Manufacture of parts from metal powder: this technique is known the world of metallurgy for dozens of years. "It is cheaper than the machining and offer a better quality of finish that forging", insists Thien My Phan, specialist of mechanics to Anvar. This technique will become more effective with compaction at high speed the Cetim is developing to the point, which will notably allow to make a little more complex parts.

Compaction is very used in the manufacture of parts for the automotive industry. The industrial first produces a mold comprising a matrix and several punches. The metal powder is placed in the matrix, on which a press comes pressure. "The objective is to compress or compact powder, a bit like when you step on the bucket to a block of sand on the beach", says Ludovic Lazzarotto, responsible line of sintered and forging products technical centre of mechanical industries (Cetim).

The pressure is between 800 and 1,000 megapascals, either in the order of 10 tonnes per square centimetre. At the end of this shock treatment, démoulée exhibit then undergoes a heat treatment which will bring its mechanical properties. It is the "sinter", which is done through a furnace with temperature up to about 1,150 C. "Under the influence of heat, materials broadcast each other and powder grain bind relatively strong," said Ludovic Lazzarotto.

The technique is mastered for a long time, but has its limits. In terms of size and shape of parts. "To do more, should be huge presses that would take care an entire building," said Ludovic Lazzarotto. It is also reduced to make only relatively flat parts, including the design, seen in Cup, is very simple.

Compaction at high speed (AMC) is based on the same principle, if it is that it is faster and stronger. As with a conventional, often hydraulic system pressure is exerted relatively slowly (approximately one second), impact press is violently. A mass of 350 kg is powered at a speed of 11 metres per second (about 40 kilometres per hour). At the time of the shock, the kinetic energy causes a "pressure peak" up to 50 more important and especially exercised in a much shorter time: approximately 10 milliseconds.

Perfect homogeneity

A part of the energy is transformed as heat, causing a heating of a few tens of degrees which, given the speed is not the time to disperse. "This rise in temperature allows the lubricant that added in very small quantities, to play its role and further increase the compression of the powder", says Ludovic Lazzarotto.

The mixture becomes very dense with a very low porosity, the order of 2, while a derived piece of classic compaction displays a porosity of 10. "Suddenly, it approaches of mechanical characteristics of the conventional materials", insists Ludovic Lazzarotto. This can be slightly more high parts. The violence of the shock indeed to obtain a perfect homogeneity of the piece, while with the traditional method "powder near the punch is more densification," says Florence Dore, engineer studies and business to Cetim. The phase of sinter is then the same.

There remained barriers to overcome to deploy the process in the industry. If, through the AMC, known now make simple parts, those more complicated forms will still ask efforts specialists. The concerns are related to movements of the machinery during shock. If the room has two levels, it in effect two punches come compress the powder. "It must control the movement of these punches, which occurs in a few milliseconds," insists Florence Dore. Compaction at high speed are also interested in other specialists, especially Sweden. The country hosts at the same time, a global supplier of presses to impact (Hydropropulsor) and Höganäs, the number one metal powders.