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Powder Metallurgy Definition:
Powder Metallurgy is can be defined as the process of preparation and process the powdered iron and nonferrous metals are called as powder metallurgy.
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 operations 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 the 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.
- Sometimes 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 gets 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 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 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.
Powder Metallurgy Advantages:
- The parts can be produced clean, bright and ready for use.
- The composition of the product can be controlled effectively.
- Articles of any intricate shape can be manufactured.
- Close dimensional tolerance can be achieved.
- The machining operation is almost eliminated.
- Parts have excellent finish and high dimensional accuracy.
- There is the overall economy as material wastage is negligible.
- Metals and non-metals can be mixed in any proportion.
- A wide range of properties such as porosity, density, etc.
- can be achieved effectively.
- A high production rate can be achieved.
- Reduced production time.
- Highly skilled labor is not required.
- Saving in the material through reduced wastage.
- Composition structure and properties can be controlled easily.
- A wide range of parts with special electrical and magnetic properties can be produced.
Powder Metallurgy Disadvantages:
- The high initial cost of metal powder.
- The size of the parts produced is limited due to large presses and needed to get required compressing pressure.
- The equipment used for the operation is costly.
- The impossibility of having a completely dense product.
- Pressure up to 100 tonnes capacity is used even for a small product.
- The metal powder is expensive and in some case difficult to store.
- Some power may present explosion hazards.
- Dies used must be of high accuracy and capable of withstanding high pressure and temperature.
- Parts produced have poor ductility.
- High tooling cost.
- The difficulty of sintering low melting powder.
- Poor plastic properties.
- The necessity of protective atmospheres.
Powder Metallurgy Application:
- To produce a porous product and
- Babbitt bearing for automobiles.
- To produce oil pump gears for automobiles.
- Used for production of cutting tools, wire drawing dies and deep drawing dies.
- To produce refractory metal composites, eg: tungsten, molybdenum, tantalum For manufacturing the tungsten wires for filaments in the lamp industry.
- Diamond impregnated tools are produced by a mixture of iron powder and diamond dust.
- To produced electrical contract material, eg: circuit breakers, relays and resistance welding electrodes.
- Parts of cars, aircraft, gas turbine, electric clocks, etc.
- Parts of vacuum cleaners, refrigerators parts of guns, sewing machines.
Powder Metallurgy Necessity or Need:
Power metallurgy becomes very much in the following cases:
- The difference in the melting temperature of the two elements.
- Melting and solidification cause poor quality.
- Melting causes loss of identifying the constituents.
- Some metals do not form a liquid solution.
Powder Metallurgy Characteristic:
- Powder metallurgy should be heat resistant.
- The size of the powder particles is to pass the powder through the screen (sieves) having a definite number of meshes.
- The powder should have good plasticity.
- It should have the ability to be cold-pressed.
- The powder should have an excellent parking factor.
- It should have a good flowability.
- The powder should be free from oxides and should have a clean surface.
- The ratio of the density of the compact to the apparent density of the powder should vary between 2:1 to 3:1