What is Powder Metallurgy?- Definition, and Process

What Is Powder Metallurgy?

Powder metallurgy is a term covering a wide range of ways in which materials or components are made from metal powders. This process can avoid, or greatly reduce, the need to use metal removal processes, thereby drastically reducing yield losses in manufacture and often resulting in lower costs.

Powder metallurgy is a metal forming process in which compacted metal powders are heated to just below their melting point. Although the process has been around for more than 100 years, over the past quarter-century it has been widely recognized as a superior method for making high-quality parts for a variety of important applications.

This success is due, among other things, to the advantages that the process offers over other forming technologies such as forging and metal casting, advantages in material use, the complexity of the shape, and the control of the shape in the vicinity of the network shape. These in turn contribute to sustainability and make powder metallurgy a recognized green technology.

Powder Metallurgy Process

These production technologies generally involve all or most of the following process steps:

  • Production of Metal Powder
  • Mixing and Blending
  • Compaction and shaping of the powder
  • Sintering of the compact to enhance integrity and strength
Powder Metallurgy Process

Sometimes, this process accomplished with some secondary operations like sizing, coining, infiltration, hot forging, etc.

1. Powder production

Almost all iron powders for the production of PM components are produced either using the sponge iron process or by water atomization. Non-ferrous metal powders used for other PM applications can be made by a number of processes.

2. Mixing of powders

This can often include the incorporation of alloy additives in the form of an elemental powder or the incorporation of a press lubricant.

3. Forming of the mixed powder into a compact

The dominant consolidation process involves the press-fitting of a rigid tool set that includes a die, punches, and possibly mandrels or core rods. However, there are several other consolidation processes that are used in niche applications.

4. Sintering of the compact to enhance integrity and strength

This process step involves heating the material, usually in a protective atmosphere, to a temperature that is below the melting point of the major constituent.

In some cases, a minor constituent can form a liquid phase at sintering temperature; such cases are described as liquid phase sintering. The mechanisms involved in the solid phase and liquid phase sintering are discussed briefly in a later section.

5. Secondary operations

The application of finishing processes to the sintered part. In powder metallurgy, such processes are often referred to as “secondary operations”.

Advantages of the powder metallurgy process

  • Minimizes machining by producing parts at or near-final dimensions
  • Minimizes scrap losses by typically using more than 97% of the raw material in the finished part
  • Allows a variety of alloy systems
  • Produces a good surface quality
  • Provides materials that can be heat-treated to increase strength or wear resistance
  • Provides controlled porosity for self-lubrication or filtration
  • Facilitates the creation of complex or unique shapes that would be impractical or impossible with other metalworking processes
  • Is suitable for the production of medium to high volume components
  • Provides long-term performance reliability in critical applications

FAQs.

What is meant by powder metallurgy?

Powder metallurgy is a metal-forming process performed by heating compacted metal powders to just below their melting points.

What is the principle of powder metallurgy?

Powder metallurgy is a highly evolved method of manufacturing reliable net-shaped components by blending elemental or pre-alloyed powders together, compacting this blend in die, and sintering or heating the pressed part in a controlled furnace atmosphere to bond the particles.

Where is powder metallurgy used?

Bearings and various gear parts are examples of Powder Metallurgy applications in DIY power tools and domestic “white goods”. Metal-graphite carbon brushes are also used extensively in electrical motors and generators for domestic appliances, automobiles, and power tools.

What are the benefits of powder metallurgy?

Advantages of the Powder Metallurgy Process

  • Minimizes machining by producing parts at, or close to, final dimensions.
  • Minimizes scrap losses by typically using more than 97% of the starting raw material in the finished part.
  • Permits a wide variety of alloy systems.
  • Produces good surface finish.

What powders are used in powder metallurgy?

Metal powders commonly used in manufacturing products:

  • Aluminum Powder.
  • Bismuth Powder.
  • Cadmium Oxide Powder.
  • Granular Copper.
  • Iron Powder.
  • Manganese Powder.
  • Nickel Powder.
  • Red and Black Cupric Oxide.

What is powder metallurgy in ceramics?

The basic powder metallurgy (PM) technique to fabricate ceramic and metal parts involves four steps: making powders from metals or ceramics, mixing or blending, pressing or consolidation, and sintering or firing. A mechanical method of making powders from ceramic materials is milling, which refines the powder size.

What is the basic purpose of powder pressing?

Powder pressing is the compaction of powders into a geometric form. Pressing is usually performed at room temperature. This creates a solid part called a green compact. The strength of this pressed, unsintered part, (green strength), is dependent on compatibility, binders may be used to increase compatibility.

How is powdered metal made?

The metal ore is crushed and then mixed with another material, usually carbon. Once the mix is complete, it’s put through a furnace to create a reaction that lowers the oxygen and carbon levels in the powder. It requires ore of relatively high purity to get a desirable final product.

How strong is powdered metal?

Powder forged steels can deliver high strength levels (UTS up to around 950 N/mm² as forged and 2050 N/mm² heat-treated; tensile yield stress up to around 650 N/mm² as forged and 1760 N/mm² heat treated) with higher levels of ductility (5-18% Elongation).

How is powder metallurgy different from casting?

In the powder metallurgy process all the metals are in powder form. In casting the metal is heated above its melting point and poured into a die and allowed to cool. The part is then machined for an accurate part.

Is powder metallurgy an additive manufacturing?

Powder Metallurgy/Additive Manufacturing elemental analysis of metal powders and metal parts produced by AM. An integral part of industrial product development is the manufacture of prototypes and initial samples, regardless of whether the product is a simple screw or the complex part of an airplane.

What is the disadvantage of powder metallurgy *?

High cost of tooling and equipment. This is particularly a limitation when production volumes are small. Large or complex shaped parts are difficult to produce by the PM process. Parts have lower ductility and strength than those produced by forging.

What are the disadvantages of powder metallurgy?

Limitations of powder metallurgy:

  • Tooling cost is generally and can only be justified in mass production.
  • Raw material cost is very high.
  • Mechanical properties of the parts are of low quality as compared to cast or machined parts.
  • In some cases, density of different parts of final product can very due to uneven compression.

What is grading of powder in powder metallurgy?

Soft magnetic Powder Metallurgy grades include plain iron, silicon-iron, cobalt-iron, and the more recently developed soft magnetic composites, that are based on a plain iron powder with a suitable binder/insulator addition to separate the iron powder particles after a curing treatment.

Why is sintering done?

Why is Sintering done and why is it Important? Sintering is done to impart strength and integrity to a material as well as reduce porosity and enhance electrical conductivity, translucency, and thermal conductivity.

What are the four main steps in powder metallurgy?

The first step in the overall powder metallurgy (PM) process is making metal powders. There are four main processes used in powder production: solid-state reduction, atomization, electrolysis, and chemical.

What is green compact in powder metallurgy?

Powder Metallurgy (PM) deals with products and processes which use raw material in the form of powders that are compacted into the required shape and size using suitable molds. These compacted powders are called „Green Compacts‟.

Can powdered metal be welded?

Resistance Projection Welding. Projection welding is often used to weld powder metal parts due to the limited distortion produced by the process. It’s capable of welding both high-carbon powder metal parts and case-hardened parts.

What is metal powder called?

Metals that can be found in powder form include aluminum powder, nickel powder, iron powder, and many more.

What are the characteristics of powder metallurgy?

A basic attribute of powder metallurgy is the ability to combine materials in powder form that are otherwise immiscible. This unique advantage allows the production of friction materials in which copper and other metal powders are combined with solid lubricants, oxides, and other compounds.