Powder Metallurgy is the art and science of manufacturing fine metal powders consolidating and fabricating them into desired shape and size. The modern powder metallurgy technology commenced in the 1920s with the production of tungsten carbide and mass production porous bronze bushes for bearings. During the world war-II the many verity of ferrous and non ferrous materials was developed until the 1960s.this method expand rapidly do to economical processing, unique properties and captive processes. The alloys and multiphase components, nonequllibrium materials with wide combination of properties are easily processed by powder metallurgy techniques.

Today the automotive industrial sector is biggest consumer of powder metallurgical components. Hardware, garden equipped industries business machines and military products are another area of Powder Metallurgy. Powder Metallurgy is the choice of today and future to acquire more strength, wear resistance and high operating temperatures.

The growing demand of powder metallurgy components can be easily seen in Automobiles, house hold items and aerospace applications.

Process Steps of Powder Metallurgy

• Preparation of Metal Powder/Alloy Powder 

• Mixing and Blending

• Compacting/Briquetting                         

• Sintering        

• Hot Pressing

• Other Operations

The particle size should be in the range of 10-100 microns. The size of the particle, purity and shape of the particles depends upon the method of the manufacture. The significance methods of powder reduction may be classified as:

• Chemical reduction methods

• Physical Reduction methods

• Mechanical Reduction Methods

Figure 1:  Chemical reduction methods

Figure 2: Physical Reduction methods

Figure 3: Mechanical Reduction Methods
 

Chemical Reduction Method

That process involves oxides halide or other salt of method this process may be carry from solid state or chemical decomposition. The hoganas process typical method of such type production  in  which  the  ore  of  pure magnetite (Fe₃O₄) found in Northern Sweden reduce with the carbonaceous material. in this process the particles of ore placed in the centre of cylindrical ceramic containers and surrounded by the concentric layers of coke and limestone. Then the container pushed through a fuel fired tunnel by producing the carbon mono from coke reduces ore into iron. That process takes place at 120°C for 24 hrs. Another method producing powder by reduction with hydrogen.

Physical Reduction Method

• Electrolytic method 

• Atomization process done by three ways gas, water and centrifugal. In the gas atomization 

The atomizing media is Nitrogen, Argon and Air. The electrolytic method is comprehensively used for preparation of cupper,iron, nickel and beryllium powders. This method yields a high purity metal with good quality P/M processing.

Mechanical Reduction Method

This method not much used primarily for the metal powder  production.  The  formation  of  metal  powder  by the this method depends on four basic techniques such as materials have easy to fracture hard and brittle metal alloys & ceramics, reactive materials and common metals like iron and Aluminium.

Figure 4: Centrifugal Ball Mill

Figure 5: Compaction Press

Figure 6: Punch and Die Set for Powder Compaction

Mixing and Blending

Mixing the powders in the desired extent are homogeneously to get the best results especially when alloys are pretend. Volatalizing and lubricating agents are also mixed to meet good porosity and lubricity. The mixing time set according to experimental procedure. Sometimes mixing may be avoided due to fear of particle size reduce.

Compaction/Briquetting

Compaction   is   the   important   step   in   powder processing    for    compacting    the    loose    powder    into the   desired   shape   with   specific   strength.    That process   is   complete   without   the   application   of   heat and  loose  powder  converted  into  desired  shape.

The powder compaction pressure take place by two ways one is without pressure (loose powder sintering in mould, vibratory compression, slip casting, slurry casting, injuction moulding) and another is with pressure (cold die compaction, explosive compaction, powder extrusion, powder rolling).

Sintering

It is the process of consolidating either loose aggrigate of powder or green compact of desired composition under the controlled condition of temperature and time. 

Sintering are basically four types:

• Solid state sintering

• Liquid state sintering

• Active sintering

• Rection sintering

Secondry operations

These operations are the conventional and non conventional machining operations like turning,grinding polishing, joining coating etc.

Figure 7(a-c): (a) Particles in Contact, (b) Formation of Necks and (c) Final Sintered Geometry

Figure 8: P/M Parts Used in Automobiles

Figure 9: P/M part classification

Powder Metallurgy in India

The story of P/M started in Indian in 1950s for the production of pours components by two companies named as Siemetals Ltd., Mumbai and Flexicons Ltd., Udhana. The IIT Bombay BARC and DMRL take place very important role for in academics and research of P/M. Today 80 % of P/M parts are used in the automotive industry.

The market of P/M parts increasing in India continuously with high growth rate. According to report of Asian powder Metallurgy Association (APMA) in 2009 the market of P/M parts of Auto  sector  was 77%. India is the fourth largest market of Automotive industry including passenger, commercial, two and four wheelers. Our India is producing 31 Million vehicles per year. The demand of sintered parts also increases 22% and further chance of increasing according to the market.

Comparison with Production Methods

For the production of any required shaped body several processing methods are competing. The selection of the methods takes place on basis of certain criteria. The criterion is as:

• Material Utilization

• Weight of the Parts

• Shaping

• Tolerances

• Purity of Material

• Microstructure

• Surface Roughness

• Manufacturing Cost

Advantages of Powder Metallurgy

• Rate of the production high

• Highly complicated objects easily manufactured

• It is highly clear and quieter operation for longer life

• Mechanical operations are not required due the good accuracy and surface finish of the object

• Life of the component part is longer

• Metal and non metal parts can be mixed in any proportion

• The object produce are relatively more uniform and free from defects such as voids, blow holes

• Excellent reproducibility and improved physical properties

• Antifriction strips can be made by powder metallurgy techniques

• Porous parts can also be produce

• There is the overall economy as material wastage is negligible

• Composition structure and properties can be controlled easily

• A wide range of parts with special electrical and magnetic properties can be produce

• Highly skilled labour is not required

Disadvantages of Powder Metallurgy

• It is difficult to secure exceptionally high purity powder with satisfactory quality and it also expensive to produce such type of powders

• It is unprofitable to produce parts in low quantity due to great expense of tooling and equipments

• Heavy investment needed for press for making larger parts

• Part produce by powder metallurgy possess poor plastic properties e.g., plasticity, elongation

• Dies used must be of high accuracy and capable of withstanding high pressure and temperature

• Some power may present explosion hazards

• The impossibility of having a completely dense product

• The necessity of protective atmospheres

There is the close interaction between technological developments and societies altitude. The scientific and technological development is responsible for the today’s civilization. The technology gives the good response by its clean formula and stops the talks of society pollution, material and energy conservation.

Many manufacturing methods metal powder are recycling techniques that utilize the scrap as a raw material for producing the powder. Mostly the atomized iron powder is made from scrap iron. Hydrogen reduce iron powder is made from mill scale, a waste product of steel rolling mill. The copper powder is made from scrap copper or from wire drawing scale or from mine water. During the sintering operation one utilize clean heat either gas or electricity and generates water vapours and carbon die oxide both are essential for biological system. The powder metallurgy playing a very important role in underdeveloped and developed world in tooling as well as manufacturing world. Metallurgy has grown in the resource deficient countries like England, Japan, France, Switzerland and Sweden etc. And all have been over taken by Russian and U.S.A.

The growth of the powder metallurgy easily understood by distinct lines.

• The product or tool which cannot be made or impractical to make by any other method made up by powder metallurgy e.g., cemented carbides, porous bearings and filters etc. There is no another method or way to make the cemented carbide without powder metallurgy

• The powder metallurgical techniques give the competition to other methods of manufacturing, but this has ability of cost saving and good performance

• The merging of P/M techniques with conventional metal working system. The combination of forging and P/M powder forging is the prime example. Extrusion of Powder Metallurgy billets is another roll compacting and isocratic coasting also be considered in this category

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