Powder Metallurgy has been used since the 1920s for production of wide range of structural PM components, self-lubrication bearings and cutting tools.
It encompasses the production of metal components by compaction in a form and their subsequent sintering. Products are referred as sintered components, sintered parts or PM parts.
The process comprises compaction of powder in order to produce compact having sufficient cohesion and then subsequent heating of the compact usually in a protective atmosphere to a temperature below the melting point of the main constituent. Individual particles are welded together during this process. The heating step is referred as sintering.
History of sintering
Processes and technologies with characteristics of powder metallurgy (PM) were well-known in the past as they are in the present time. For example 300 B.C. powder iron was used as material in Egypt. 2500 B.C. were powder metallurgy used in Persia. 1200 B.C. were PM technologies used for production of platinum.
The beginning of the 19th century brought a significant usage of PM technologies in commercial sphere. It included introduction of platinum coins in Russian Empire. Technical blossom at the beginning of the 20th century, together with application of new production methods brought production of wolfram fibes to lightbulbs by T.A. Edison.
After the II. World War, mainly copper powders were used at the beginning of 1950s. Production increase of parts such as gearboxes and camshafts in automotive industry caused that the copper powder was preferred material of this production type. At the end of the II. World War, PM has been developed in aircraft and nuclear industry. Significant increase of production and quality improvement is connected with 1960s. The portfolio was enlarged during 1970s. In 1980s, the commercial boom of components and products made by solidification and injection shaping from metal powder arisen.
In the present time, the biggest consumer of PM parts is automotive industry. It uses about 70% of total amount of produced parts. PM parts consumption in average European and Japanese car is about 10kg/per car. It is about 250kg/car in American car. Typical parts are sprocket wheel, distributing belt pulley, crankshaft cogwheel, valve parts, components of oil pumps, centre of synchronizing clutch pedal, parts of spring silencer, wheels of power assisted steering pump, blogging insertions of brake system, parts of electro system and many others.
(Source: Bidulský R. – Bidulská J.: Technologies of Materials Processing, Based in Powder Metallurgy, pp. 1-8).
Process of PM
In general, basic powder metallurgy process contains these steps:
1) Mix of metal powder or powders with suitable lubricant is prepared.
2) The mixture is load into a die or mold, subsequently the pressure is applied. This gives compact, which requires only sufficient cohesion to enable it to be handled safely and transferred to next stage. Such compacts are referred as green, which means un-sintered and having green density and green strength.
3) Heating of the compact, usually in a protective atmosphere at temperature below the melting point, so that the powder weld together and confer sufficient strength to the object. This process is called sintering, parts are called sintered parts.
During compaction, the mixture is pressed into anticipated shape. Later on, during the sintering process, the compact gained strength and required characteristics. Powder particles are joined together, similarly as during welding, because the temperature reaches almost the melting point.
If secondary operations are necessary, GEVORKYAN offers:
- drilling of side holes,
- cutting of threads.
The company has modern Swiss lines for hardening, carburizing, carbonitriding and nitration of its products. All types of surface and heat treatment can be used on sintered parts, similarly to conventional materials.
Process of calibration increases density and precision. It also improves part surface. Machining is used for cutting of thread or to achieve exact measure, etc. PM parts can be hardened, carburized or blackened.
Another great advantage of PM parts is their porosity. Pores can be filled with oil, resin or with any other metal. Brazing is used to create one product from individual parts during sintering without additional costs for soldering. Self-lubricating bearings and silver contacts can be produced by these means. Self-lubricating bearings have lifelong resource of lubricant without any service and silver contacts are made without necessity to use silver for whole part and afterwards, the component has identical hardness as after hardening. It is possible to apply all kinds of surface treatment (Zn, Cr, Ni and their combinations) to PM parts similarly as parts made by conventional materials.
Sintering enables brazing, which is connection of different parts into one without any additional costs for soldering.
There are two principal benefits why to use powder metallurgy products:
- cost savings in comparison to alternative processes,
- unique attributes achievable only by PM processes.
Cost savings are main advantages of structural parts, porous and composite materials, magnetic components and special alloys.
Other benefits of powder metallurgy are listed below:
- huge savings,
- composition flexibility, which is not possible by other methods, e.g. metals, bimetal combinations, etc.
- in most cases no secondary operations are necessary
- raw materials are easily obtained and relatively inexpensive
- production repeatability, parts consistent properties and dimensions
- number of secondary operations for finished parts is lower in comparison to other technologies
- controlled porosity, existence of possibility to infiltrate pores with another materials
- powder metallurgy process produces almost no waste
- parts have excellent wear resistance and friction co-efficiency
- PM technology allows production of geometries, which are not possible by machining, etc.
- parts have good chemical homogeneity
- magnetic components production by powder metallurgy
Sintered components are characterized as the best utilizable raw material with the lower energy consumption.