Powder metallurgy
The powder metallurgy refers to a branch of metallurgy , which deals with the production of metal powders and their processing. The manufacturing processes of powder metallurgy are characterized by the mechanical compression of metal powders in molds or presses and simultaneous or subsequent sintering of the “ green body ” at high temperatures or hot rolling to form a block.
The result is solid, finely structured semi-finished or finished parts . Sintering is particularly suitable for the mass production of small, lightweight molded parts and rollers for large sintered metal blocks.
Historical
The history of powder metallurgy and the sintering of metals and ceramics are closely related. Sintering is the term used to describe the heat treatment of pre-pressed molded parts made of fine materials (powder), whereby solid metal or ceramic parts with precisely defined dimensions and properties can be produced.
It has been proven that as early as the 12th century BC Pre-pressed objects were produced with this method. At that time, the powder was extracted manually or mechanically from sponge iron using a reduction process and then sintered or melted.
Three manufacturing steps
The manufacture of powder metallurgical products essentially comprises three sub-areas:
Metal powder
Metal powders of pure metals or alloys with grain sizes below 0.6 mm are required. The type of powder production has a strong influence on the properties of the powder, which is why many different processes have been developed. Are used mechanical method, chemical reduction method or electrolytic method, and the Karbonylverfahren , spinning, atomization, and other methods. In mechanical alloying, steel and titanium carbide powder are ground together. They weld together to form agglomerates and are repeatedly broken up, so that particles of a new composition are created. This alloying method produces a very fine-grained powder. It is either formed into raw components or green parts by cold isostatic pressing and then sintered at 1200 to 1500 ° C in a vacuum or further processed by hot isostatic pressing.
Shaping
The shaping of sintered parts begins with the compression of the metal powder in a more or less complexly shaped die. Two or more vertically movable punches exert high pressure (300 - 800 N / mm²) from above and below on the powder in the die. Under the influence of this high pressure, the powder particles are pressed together so closely that they mechanically clamp together and / or cold-weld together. The pressed part produced in this way is ejected from the die and, if the pressing process was successful, has a sufficiently good strength for further processing. In order to facilitate the pressing process and to keep signs of wear and tear on the die and punches as low as possible, a lubricant is added to the powder before pressing. Mechanical, servo-electric and hydraulic powder presses are available on the market.
The powder is compacted into green compacts in press tools under high pressure between approx. 0.1 and 1 G Pa .
Further processes are compaction by vibration , the slip casting process , bulk process and processes with the addition of binders .
Sintering
During the heat treatment (the actual sintering) the powder grains are brought into a firm bond at their contact surfaces by diffusion of the metal atoms. The sintering temperature for single-phase powders, which consist of a uniform material, is between 65 and 80% of the solidus temperature . In the case of multiphase powders, on the other hand, sintering is generally carried out in the vicinity of or above the solidus temperature of the lowest melting phase. The spaces between open-pored workpieces can also be filled after sintering by dipping them into a metal melt .
Sintering takes place in continuous ovens or hood ovens under protective gas or in vacuum ovens.
All sintered metals are porous and densities of up to 99% can be achieved. Complete densification is achieved in some cases by hot rolling. After calibration , the workpieces show high dimensional accuracy and surface quality .
Work pieces
The processes are used for the production of hard metal parts and powder injection molding . Because of the expensive pressing tools, powder metallurgy is only used for large series and only for small, light parts.
The most important area of application is the automotive industry . Typical products are e.g. B. (oil-soaked) bearing shells and bearings, engine and transmission molded parts, sieves , filters and permanent magnets .
literature
- DIN German Institute for Standardization e. V .: Powder Metallurgy. Metal powder, sintered metals, hard metals. Norms. Beuth Verlag, Berlin a. a. 1991. ISBN 3-410-12378-4
- Werner Schatt , Klaus-Peter Wieters, Bernd Kieback (eds.): Powder metallurgy . Technologies and materials (= VDI book ). 2., arr. and exp. Edition. Springer-Verlag, Berlin, Heidelberg, New York 2007, ISBN 978-3-540-23652-8 ( limited preview in Google book search).
- Hans Kolaska (Hrsg.): Powder metallurgy in science and practice. Lectures and exhibitor contributions to the Hagen Symposium, organ. from the Powder Metallurgy Committee. Powder Metallurgy Association , Rheine, annually since 1985.
See also
Web links
- https://www.ifam.fraunhofer.de/de/Kernkompetenzen/Pulvertechnologie.html
- http://www.pulvermetallurgie.com/
- http://www.komage.de/de/glossar
Individual evidence
- ↑ Archived copy ( memento of the original from October 29, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
