Powder metal technology is actually quite interesting...if you can understand all the industry terms and jargon. For newcomers looking to improve new or existing part designs, an introduction to powder metallurgy and the powder metal industry can certainly be confusing and intimidating.

Let's demystify it. Here are some simple facts to help you ease into the powder metallurgy and sintering process, including some of the advantages of powder metallurgy.

The history of powder metallurgy

Powder metallurgy has a long history, with its origins dating back to ancient civilizations.

In ancient Egypt, people began to use metal powder to make jewelry and metal crafts as early as around 3000 BC. They grind metal ores such as gold, copper and silver into powder and then use sintering techniques to press the powder into the desired shape, ultimately creating metal objects. This process is called "powder metal processing."

Ancient China also made outstanding contributions in the field of metallurgy. Chinese craftsmen began using copper powder to make bronze vessels as early as 300 BC. The powders they prepared mainly included copper, tin and lead, and these bronzes played an important role in Chinese history and culture.

Although these early powder metallurgy techniques were simple, they laid the foundation for today's modern powder metallurgy techniques. Modern powder metallurgy draws on the experience of these ancient civilizations to develop more precise and efficient methods for manufacturing a variety of metal and alloy products, making it an integral part of modern manufacturing.

Powder metallurgy is a green manufacturing process

Approximately 97% of the material entering the powder metallurgy process exits as part of the final product. Good luck finding similar net shape capabilities in any other manufacturing process. This means very little waste and scrap. Powder metallurgy (PM) is a win-win for your wallet and the environment.

Other metal forming processes, especially die casting, leave behind waste at multiple stages of manufacturing. Foundries are notorious for manufacturing:

air pollution

liquid contamination

solid waste

Compression creates compactness

Powder compaction is an early step in the powder metallurgy process.

It all starts with iron powder alloys, related alloys, or completely different metal powders. Strong pressure is applied to the powder so that it holds the shape of the mold. The resulting components are called compact components.

Characteristics that affect powder metal compaction include:

particle size

shape

work

size distribution

The type of powder and how it is made also affects how it behaves under pressure.

While it may look like your final product, the compact still needs to be sintered to fully fuse the particles together.

Sintering does not melt powdered metal

The sintering process in powder metallurgy is a form of heat treatment. The traditional sintering process heats the material to just below its melting point. Precise sintering temperatures allow the metals to retain their beneficial properties while tightly fusing them together.

Think of sintering as a glass of ice water. Although the ice cubes will eventually melt, they first fuse together at every point of contact.

Density matters

The denser the ingredient, the better its physical properties. Density is directly related to yield strength, tensile strength and overall component durability. We also use porosity to represent component density.

The density of the final product depends on several factors:

Friction between particles

Compacting strength

Sintering settings

particle size

To achieve the highest performance parts, powder metal manufacturers use their expertise to minimize friction between particles and optimize the material's sintering settings.

The compaction strength depends on the manufacturer's machinery, and you can control the particle size to your specifications.

Neck: Not as weird as it sounds

Neckling is a deformation in which relatively large strains are disproportionately concentrated in specific locations in a powder material. The resulting reduction in local cross-sectional area becomes the "neck".

When the particles fuse like ice in a glass, the point of contact is called the neck. As necking between particles increases, the space between particles (porosity) decreases. As porosity decreases, density increases. In almost all applications, this is a good thing.

The goal of powder metal manufacturers is to keep the metal particles in a necked state for as long as possible to minimize porosity in the final product.

4 steps of the powder metallurgy process

Powder metallurgy (PM) processes are more sophisticated than they were 5,000 years ago. However, it can be broken down into four steps:

Powder production

mix and blend

compaction

sintering

1. Powder production

Metal powder is the raw material of powder metallurgy process and is produced by grinding, crushing, atomization or chemical reaction. The production method you choose depends on quantity, required performance and many other factors. Atomization is used for large-scale production, while grinding and crushing are used for small-batch production.

Before starting production, the metal type needs to be selected. Commonly used metals include:

iron

steel

copper

bronze

Soft metal composites

2. Mix and Stir

A blend is a combination of metal powders with different chemical properties. On the other hand, mixed

Permanent magnet rollover protection device

Is a combination of particles with the same chemical properties and size.

Mixing and blending differ in the chemical composition of the particles, but the actual combining process is the same. Metal powders are combined with binders or lubricants to determine the characteristics and performance of the final part, such as pH, viscosity and filtration levels.

Without this step of combining materials to create new alloys, powder metallurgy would be limited to production using one material at a time.

3. Compaction

After mixing, the material is pressed into shape or compacted. The fine powder is subjected to strong pressure and enters the mold to form the desired part.

Pressure compaction is carried out through several different methods –

Cold mold compaction,

Isostatic pressure

Hot compaction

Each process is unique, but the end goal is to create a dense part ready to be sintered.

Although the part may appear finished at this point, it is not. It is not finished until sintering is complete.

4. Sintering

Sintering is a heat treatment that cre ates permanent bonds between metal particles. The temperature is always below the melting point of the metal, but hot enough to cause loose particles to bond and form a strong, usable part.

From traditional powder metallurgy to other processes, the sintering process remains unchanged.

Overview of sintering process

The sintering process is a key processing method in powder metallurgy, which is used to heat metal powder to a temperature close to the melting point so that the powder particles combine into a strong solid object. The following is a detailed explanation of the sintering process:

Raw material preparation: The first step in sintering is to prepare metal powder. These powders are usually very fine because fine particles combine more easily. Raw powders usually include powders of metals or alloys, and possibly additives such as lubricants, binding agents or reinforcing agents.

Mixing and pressing: After the powders are prepared, they are usually mixed together to ensure even distribution. These mixed powders are then placed into molds and high pressure is applied. This step is called pressing, and the purpose is to compact the powder into a "green body" of the desired shape.

Sintering process: The pressed green body is usually placed in a high-temperature furnace for sintering. During the sintering process, the green body is subjected to high-temperature heat treatment, which causes the metal powder particles to combine with each other and gradually form a solid blank. Control of temperature and time is critical to ensure successful sintering and final material properties.

Cooling and Handling: Once sintering is complete, the blank is removed from the furnace and cooled. The cooling process can affect the structure and properties of the final material. Sometimes the sintered material needs to undergo additional processing steps, such as annealing or heat treatment, to improve its properties.

Surface Treatment: Finally, the sintered material may require surface treatment to improve its appearance, corrosion resistance, or other properties. This can include polishing, plating or other coating techniques.

The advantages of the sintering process include the ability to create complex three-dimensional structures and the fact that little material is wasted during processing. This makes sintering an important method for manufacturing high-performance components, ceramics, metal alloys and other materials. The sintering process is used in a wide range of applications, including automotive manufacturing, aerospace, medical devices and the electronics industry.

Applications of powder metallurgy

Powder metallurgy is a cost-effective method for producing large quantities of complex parts and assemblies across a variety of industries.

Currently, the automotive industry uses iron and stainless steel powders to produce parts from bearings to gears.

Similar to the automotive industry, the aerospace industry makes extensive use of powder metallurgy technology to manufacture high-precision, cost-effective parts.

People are always looking for environmentally friendly, low-cost alternatives, and powder metallurgy remains a tried, trusted and true method of manufacturing high-quality finished products. Parts can be manufactured more efficiently by eliminating waste through pressing technology, with 97% of raw materials used to produce the final part.

Powder metallurgy processes: not without limitations

PM is economical and widely used, but it also has its limitations. Due to the fluidity of the metal powder, the powder metallurgy process cannot produce parts larger than 2-20 kg.

While part size is limited, quantity is not. Large-scale production in PM is cost-effective. However, when producing in small batches, the cost can be very high. Other processes, such as metal additive manufacturing, enable production through rapid prototyping or series production while increasing your return on investment.

Powder metallurgy could make better magnets

One of the emerging advantages of powder metallurgy is its ability to improve the magnetic properties of electric motors. But you can't just throw any old iron powder into a powder compactor and expect results.

Sintered soft magnetic materials and soft magnetic composite materials are the development direction of rotors, stators and many other electromagnetic components. These advanced materials provide higher magnetic efficiencies compared to electrically laminated steel and other competing methods.

Want to learn more interesting facts about powder metallurgy?

These are just a few interesting facts about powder metal.

If you have questions about this article, sintering, or anything else related to powder metallurgy, check out our other learning resources.

Powder Metallurgy and Sintering Processes 101