Powder Metallurgy Process:
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Definition of Powder Metallurgy:
- Powder Metallurgy is can be defined as the process of preparation and process the powdered iron and nonferrous metals is called as powder metallurgy.
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Powder Metallurgy Process:
These factors make this process most suitable for mass production. It mainly involves four basic steps.
- Powder Preparation:
- Mixing and Blending:
Sometimes, this process accomplished with some secondary operation like sizing, coining, infiltration, hot forging etc.
1. Powder Preparation:
- This is a first and basic step for producing an object by powder metallurgy process. Any material can convert into powder.
- There are various processes of producing powder such as atomization, grinding, chemical reaction, electrolysis process etc.
2. Mixing and Blending:
- As the name implies, this step involves mixing of two or more material powder to produce a high strength alloy material according to the product requirement.
- This process ensures even distribution of powder with additives, binders etc.
- Sometime lubricants also added in the blending process to improve flow characteristic of powder.
- Compacting means compressed the prepared powder mixture into pre-defined dies.
- This step ensures to reduce voids and increase the density of the product. The powder is compacted into the mold by the application of pressure to form a product which is called green compact (the product get by compacting).
- It involves pressure range from 80 to 1600 MPa.
- This pressure depends on the properties of metal powder and binders.
For soft powder compacting pressure is about 100 – 350 MPa.
For steel, iron etc. the pressure is in between 400 – 700 MPa.
- The green compact, produced by compressing, is not very strong and can’t be used as a final product.
- This step involves heating of green compact at an elevated temperature which ensures a permanent strong bond between adjacent particles.
- This process provides strength to green compact and converts it into a final product.
- The sintering temperature is generally about 70 to 90 percent of the melting temperature of metal powder.
5. Secondary Operation
- The sintered object is more porous compared to a fully dense material. The density of the product depends upon press capacity, sintering temperature, compressing pressure etc.
- Sometimes, the product does not require high density and the sintered product is directly used as a final product. But sometimes, a highly dense product is required (for example manufacturing bearing etc.)
- Where a sintered product cannot be used as a finished product. That’s why a secondary operation required to obtain high density and high dimensional accuracy.
- The most common secondary operation used is sizing, hot forging, coining, infiltration, impregnation etc.
Advantages, Disadvantages, and Application of Powder metallurgy process:
Advantages of Powder Metallurgy:
|1.||The parts can be produced clean, bright and ready for use.|
|2.||The composition of the product can be controlled effectively.|
|3.||Articles of any intricate shape can be manufactured.|
|4.||Close dimensional tolerance can be achieved.|
|5.||The machining operation is almost eliminated.|
|6.||Parts have excellent finish and high dimensional accuracy.|
|7.||There is the overall economy as material wastage is negligible.|
|8.||Metals and non-metals can be mixed in any proportion.|
|9.||A wide range of properties such as porosity, density etc. can be achieved effectively.|
|10.||High production rate can be achieved.|
|11.||Reduced production time.|
|12.||Highly skilled labor is not required.|
|13.||Saving in the material through reduced wastage.|
|14.||Composition structure and properties can be controlled easily.|
|15.||A wide range of parts with special electrical and magnetic properties can be produced.|
Disadvantages of Powder Metallurgy:
|1.||High initial cost of metal powder.|
|2.||Size of the parts produced is limited due to large presses and needed to get required compressing pressure.|
|3.||The equipment used for the operation is costly.|
|4.||The impossibility of having a completely dense product.|
|5.||Pressure up to 100 tonnes capacity is used even for a small product.|
|6.||The metal powder is expensive and in some case difficult to store.|
|7.||Some power may present explosion hazards.|
|8.||Dies used must be of high accuracy and capable of withstanding high pressure and temperature.|
|9.||Parts produced have poor ductility.|
|10.||High tooling cost.|
|11.||The difficulty of sintering low melting powder.|
|12.||Poor plastic properties.|
|13.||The necessity of protective atmospheres.|
Application of Powder Metallurgy:
|1.||To produce a porous product.|
|2.||To produce Babbitt bearing for automobiles.|
|3.||To produce oil pump gears for automobiles.|
|4.||Used for production of cutting tools, wire drawing dies and deep drawing dies.|
|5.||To produce refractory metal composites, eg: tungsten, molybdenum, tantalum|
|6.||For manufacturing the tungsten wires for filaments in the lamp industry.|
|7.||Diamond impregnated tools are produced by the mixture of iron powder and diamond dust.|
|8.||To produced electrical contract material, eg: circuit breakers, relays and resistance welding electrodes.|
|9.||Parts of cars, aircraft, gas turbine, electric clocks etc.|
|10.||Parts of vacuum cleaners, refrigerators|
|11.||Parts of guns, sewing machines.|
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