What is Powder Metallurgy?

author: YITECH

2025-02-22

Powder metallurgy is a manufacturing process that produces precision and high-precision parts by pressing powdered metals and alloys into rigid molds under extreme pressure.

1. What is the Powder Metallurgy Process
Powder metallurgy is a manufacturing process that produces precision and high-precision parts by pressing powdered metals and alloys into rigid molds under extreme pressure.

As technological advances have been developed and implemented, powder metallurgy has become an essential process for producing bushings, bearings, gears, and various structural parts.
Sintering plays a vital role in the precision and effectiveness of powder metallurgy. The process involves heating the powdered material to a temperature just below the melting point of the metal, causing the particles to fuse together and form a solid structure.

2. History of Powder Metallurgy

Powder metallurgy is a time-honored technique used to shape and engineer ferrous and nonferrous metals. This method has been used for thousands of years to create tools and household items. Its roots can be traced back to the early stages of the Industrial Revolution when it was first used to mass-produce a variety of components.

Prior to the early 20th century, powder metallurgy was less widely used and was not considered a practical production technology. However, with the advent of electricity and subsequent technological advances, powder metallurgy has become an efficient method for producing components with precise tolerances and minimal waste.

The powder metallurgy process involves four basic stages: powder preparation, mixing, pressing and sintering. These processes have been used for hundreds of years to manufacture a wide variety of products.

Powder metallurgy includes a variety of customized methods to meet specific component requirements. These techniques have evolved with advances in technology and engineering. Notable variations include traditional methods, injection molding, isostatic pressing and metal additive manufacturing, which is the latest innovation in this field.

3. Four steps of powder metallurgy

Powder preparation

The properties of powder metallurgy products depend largely on the characteristics of the powder used. Melt atomization is a technique for producing such powders, in which the molten metal is dispersed into fine droplets, cooled and solidified into small particles.

While atomization is the most widely used method for producing powders, alternative techniques include chemical reduction, electrolytic deposition, grinding and thermal decomposition. Each method can convert a variety of metals and alloys into powder form.

Before mixing and blending, the powder needs to be evaluated to ensure that it is suitable for the powder metallurgy process. Key factors to evaluate include flow rate, density, compressibility and strength.

Mixing and blending

During the mixing and blending stage, the powder is mixed with other powders, binders, and lubricants to achieve the desired properties of the final part. This process can be done wet or dry, depending on the specific powder metallurgy method and part requirements. The four main mixing and blending techniques are the rotating drum, rotating double cone, spiral mixer in the drum, and blade mixer in the drum. The following figure shows the rotating double cone and rotating drum, as well as examples of three mixed powders.

Compression pressing

The powder mixture needs to be pressed into a specific shape or mold. Proper pressing minimizes voids and greatly increases the density of the product. The final shape formed is called a green body, indicating that the part has been formed by this process. Pressing pressures range from 80MPa to 1600MPa. The required pressure varies according to the characteristics of each metal powder. For soft powder pressing, the pressure ranges from 100 MPa to 350 MPa. Harder metals such as steel and iron require higher pressures, usually between 400 MPa and 700 MPa.

Sintering.

Sintering

Despite being pressed under high pressure, the green body is not strong enough to be used. To create a permanent bond between the metal particles, the green body needs to be sintered, that is, heated to high temperatures. Sintering ultimately forms the final usable part. The sintering atmosphere is carefully controlled, and carbon is usually added to achieve a neutral or carburizing environment that affects the properties of the finished material. Sintering is a heat treatment process in which a number of compacted parts are heated to a high enough temperature that the particles fuse together to form a solid structure. The specific temperature varies depending on the type of metal, but is always slightly below the melting point of the metal. Pressing shapes the particles in the green body, but small pores still exist. During sintering, the material is heated to high temperatures to close these pores and enhance the strength of the part.

4. Powder Metallurgy Process

Traditional powder metallurgy technology follows the basic steps of mixing, pressing and sintering powders and alloys. It is similar to ancient techniques, but benefits from modern technological advances.

Injection Molding

The unique advantage of injection molding is its ability to mass-produce products with complex shapes. The powders for injection molding are specially formulated and added with binders such as wax or thermoplastics. The mixture (called raw material) is fed into the mold cavity of a common injection molding machine. When the green body is removed from the mold, the binder is extracted by heat treatment or solvent. Any remaining binder is dissipated during the sintering process. Injection molding powder metallurgy process is similar to plastic injection molding and high-pressure die casting, and can produce complex shapes. However, it usually requires a lot of secondary finishing. Its advantage is the ability to achieve precise dimensional tolerances and accommodate a wide range of shapes and complex geometric features. Isostatic pressing Isostatic pressing involves applying uniform pressure to the entire surface of the workpiece, ensuring that the density and microstructure of each angle and curve are consistent. This method can be cold or hot, depending on the specific needs of the manufactured part.

Isostatic pressing is further divided into cold isostatic pressing and hot isostatic pressing. Cold isostatic pressing (CIP=Cold Isostatic Pressing): Metal powder is placed in a flexible rubber mold usually made of neoprene, polyurethane, polyvinyl chloride or other elastomers, and pressure is applied at room temperature.

Hot Isostatic Pressing (HIP): Powder compaction and high temperature sintering are done in one process, so it is hot pressing.

Cold isostatic pressing is suitable for large or complex parts where die pressing is not possible. This method is suitable for a wide range of materials, and the pressure starts at just below 5000 psi and can reach up to 100,000 psi. The powder is formed using a flexible mold, which can be wet or dry.

Hot isostatic pressing combines high temperature with isostatic pressing to eliminate porosity, increase density and improve mechanical properties, making the finished part easier to process. This method can also reduce micro-shrinkage in hot isostatic pressed powder metallurgy.

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DongGuan YiTai Electronic Technologies Co.,Ltd is a manufacturing service provider located in Dongguan, China.

YiTai specialized in CNC turning machining and sheet metal fabrication mainly. As a member of Hung Mou Group, we focus on the overseas marketing development. And based on our parent company’s manufacturing capability and resources, YiTai also expended machining services such as die casting, injection molding, aluminum profile extrusion, 3D printing, which are committed to providing customers with one-stop purchasing services and experience.

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