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Powder Metallurgy

Powder Metallurgy

Powder Metallurgy Introductions

Powder metallurgy is a metal powder injection molding technology that can be used to manufacture parts with irregular curves or grooves that are difficult to process. The metal powder is placed under pressure and compacted in a closed mold. The compacted material is placed in an oven and sintered at high temperatures, where the metal powders combine and form a solid. Prior to sintering, a secondary pressing operation can be performed to improve compaction of powder metallurgy components and material properties.

Advantages of Powder Metallurgy

1.Very little machining

Metal powder metallurgy can eliminates or reduces machining by producing parts of final size that meet or approach the strictest tolerance requirements.

2.Minimal to no scrap or waste

There is no waste of raw materials, minimizing waste loss by using more than 97% of raw materials in finished metallurgy products.

3.Reasonably complex shapes can be made

Powder metallurgy can create complex geometries that are impossible to achieve with other metalworking processes.

4.Close dimensional tolerances

Powder metallurgy manufacturing eliminates or reduces machining by producing parts of final size that meet or approach the strictest tolerance requirements.

5.Controlled porosity for self-lubrication or filtration

Powder metallurgy technology provides properties such as porosity and self-lubrication for manufactured parts.

6.Excellent wear resistant properties and friction co-efficient

Heat treatable material to increase strength or wear resistance of products made by powder metallurgy. Provides a good surface finish between powder metallurgy parts that can be enhanced by state-of-the-art machining operations.

Characteristics of Powder Metallurgy

  • Holes, even complicated profiles, are permissible in the direction of compressing. The minimum hole diameter is 1.5 mm (0.060 in).

  • The wall thickness should be compatible with the process typically 1.5 mm (0.060 in) minimum. Length to thickness ratio can be up to 18 maximum-this is to ensure that tooling is robust. However, wall thicknesses do not have to be uniform, unlike other processes, which offers the designer a great amount of flexibility in designing the parts.

  • Undercuts are not acceptable, so designs have to be modified to work around this limitation. Threads for screws cannot be made and have to be machined later.

  • Drafts are usually not desirable except for recesses formed by a punch making a blind hole. In such a case a 2-degree draft is recommended. Note that the requirement of no draft is more relaxed compared to other forming processes such as casting, molding etc.

  • Tolerances are 0.3 % on dimensions. If repressing is done, the tolerances can be as good as 0.1 %. Repressing, however, increases the cost of the product.

Powder Metallurgy Manufacturing Process

1. Powder Preparation 

Almost all iron powder used in the production of Powder Metallurgy structural parts is manufactured using the sponge iron process or water atomization. Non-ferrous metal powders for other Powder Metallurgy applications can be produced by a variety of methods.

2. Mixing and Blending 

This step is to mix two or more materials powders to produce a high strength alloy material according to product requirements. This process ensures the uniform distribution of metal powders with additives, adhesives, etc. Pressure lubricants are sometimes added during the mixing process to improve the flow characteristics of the powder.

3. Compacting 

Compaction is the pressing of a prepared metal powder mixture into a predetermined mold. The parts of metal powder are mixed to form a compact. This step ensures reduced voids and increased product density. The powder is pressed into the mold to form a green compact.

4. Sintering 

Green compacts produced by compression are not strong enough to be used as final powder metallurgy products. This process step involves heating the material, usually in a protective atmosphere, to a temperature below the melting point of the main component. The process provides strength for green compact products and translates it into the final product.

Powder Metallurgy vs Casting

1. Quality

In die casting, when the material does not fill the mold completely, the oxide scale will drip into the liquid, causing internal defects, streamline and porosity are common. Powder metallurgy is consistency. In each cycle, even weight of powder is deposited into the mold and compacted to the same density, and internal defects are very unlikely. What's more, microstructure determined by the cooling rate in die casting, which depends on factors such as surface area and volume. Although powder metallurgy offers greater control over porosity and consistency, as well as the ability to form finer microstructure making it suitable for the production of hard components.

2. Material Implications

Die casting is most commonly used for non-ferrous materials with low melting points. Powder metallurgy technology has greater flexibility in material use and alloy selection. In particular, although standard powder metal materials are available, powders can also be mixed. This allows to create specific attributes.

3. Mechanical Properties

Compared with other processes, die casting has good forming ability. However, powder metallurgy technology has the same design possibilities, but with better mechanical properties. Materials used for die casting have no magnetism unless they are placed in another assembly made of another metal. However, powder metals are available in a wide variety of magnetic materials. Another problem with die castings is that they can break easily, even if the components are mainly made of the relatively soft metals zinc and aluminum. Powder metallurgy components, usually made of some form of steel, stand up to more use. Using high strength materials allows you to achieve the same shape with less material.

4. Cost

There is a significant difference in cost between die casting and powder metallurgy. The low scrap rate of powder metallurgy is a huge benefit when secondary processing is used with high value materials such as copper and stainless steel. Die castings almost always need trimming to remove glitter, plus some machining operations and possibly heat treatment. Most powder metallurgy components require little rework. Although sintering is energy intensive, the total cost of sintering is less than that of casting.

Application of Powder Metallurgy

1. Application of powder metallurgy in automobile industry. Manufacturing automotive porous products, Babbitt bearings and automotive oil pump gear. 

2. Powder metallurgy used for the production of cutting tools, drawing die, drawing die. 

3. Powder metal technology used to produce tungsten, molybdenum, tantalum and other refractory metal composite materials. 

4. Powder metallurgy as science used for making tungsten wire for lighting. Diamond impregnated tools are made from a mixture of iron and diamond powder. 

5. Production of electrical contract materials, such as circuit breakers, relays and resistance electrodes. Aircraft, gas turbine, electronic clock and other parts. Vacuum cleaners, parts for refrigerators parts for guns, parts for sewing machines.

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