Sintering: Definition, Importance, Types, and Process

Sintering is a fundamental manufacturing process, known by several names including powder metallurgy and metal injection molding. It involves shaping metals and binders into the desired form through molds, producing parts with various mechanical properties. Due to its cost-effectiveness, it is widely used in industries such as machinery manufacturing, automotive, and aviation. Sintering plays a crucial role in producing parts with complex details and precise dimensions.

The sintering of parts involves two steps: first, pressing the metal powder into a mold, where the product is fragile, and second, sintering the part to burn out the binder and create a complete component. Sintered parts have low individual costs and high automation levels. This article will discuss sintering, its definition, main types, and operating methods.

What is sintering?

Sintering involves pressing metals and binders into the required shape through equipment and then heating to bond the metal particles together, burning off the prior metal binder. This process is suitable for materials with high melting points, such as metal powders, ceramic materials, or high-temperature-resistant composites.
The principle of this process is to use the high melting point of metal materials and the molten binder to join the unmelted metal materials together. This ensures the original pressed shape is maintained while enhancing the product’s mechanical properties.

Why is sintering important in manufacturing?

Sintering’s importance in manufacturing lies in its ability to produce complex and precise metal parts economically and efficiently. Sintering can mold products in one go, offering short manufacturing cycles and high precision. It shortens production cycles, simplifies inventory management, reduces overall operating costs, and improves both production efficiency and product quality.

How is sintering conducted in manufacturing?

Sintering in manufacturing refers to the process of pressing metal powder and binders into molds to create the desired shape. The part is then sintered to achieve the required form. There are several sintering methods, with the most common ones being:

  • Solid-state sintering: Heating powder materials (metals, ceramics, etc.) below their melting points in a specific temperature and gas environment, causing the powder particles to solid-state bond and strengthen the part.
  • Liquid-phase sintering: Utilizing the characteristics of high-melting-point materials, melting lower-melting-point materials at a certain temperature for co-sintering, accelerating densification, and increasing final density.
  • Reaction sintering: Under certain conditions, causing powder, liquid, and gas to react with each other, forming a sintered body of a specific composition. The advantage of this process is that the product’s dimensions remain virtually unchanged.

What is the sintering process?

The sintering process can produce products with high hardness and mechanical properties that traditional processing methods cannot easily produce. It can combine the characteristics of various materials to produce high-precision, high-repeatability products at a relatively low cost. The sintering steps include the following phases:

Pre-sintering phase

In this stage, the powder particles begin to form neck connections, but the overall structure of the particles does not significantly change. Initial sintering phase: As the temperature rises, the neck connections between particles increase, particles start to rearrange, porosity begins to decrease, and the material starts to densify.

Intermediate sintering phase

In this stage, the neck connections between particles further increase, porosity significantly decreases, and the material’s densification significantly improves.

Final sintering phase

Finally, as sintering continues, the material reaches its final densification state, pores are essentially eliminated, and the material’s strength and other physical properties are significantly improved.

What materials can be used for sintering?

As a versatile technique, sintering can be applied to a wide range of materials. Common sintering materials include:
Metals: Sintering is most commonly used with metal materials, including copper-based materials, iron-based materials, nickel-based materials, various stainless steels, magnetic materials, and various alloy materials.
Ceramic materials: General ceramic materials, such as alumina, aluminum nitride, zirconia, silicon nitride, boron nitride, and silicon carbide. Glass materials: Generally refers to ceramic glazes, silica glass, lead glass, and sintered glass plates made from molten silica glass powder.

The Advantages of Sintering

The sintering process boasts several significant advantages:

  • It can effortlessly produce products with complex shapes, boasting high surface smoothness.
  • Its versatility allows for the sintering of a wide range of metals and other materials.
  • The process is cost-effective, particularly for mass production, offering savings in both costs and time compared to other manufacturing methods.
  • It is suitable for materials that are challenging or impossible to machine.

The Disadvantages of Sintered Products

However, the sintering process is not without its drawbacks:

  • Reduced Toughness: After powder compaction, internal pores in the product cannot be completely eliminated, resulting in lower strength and toughness compared to cast or forged pieces.
  • Limitations on Product Size: The flowability of metal powder is inferior to that of molten metal, imposing certain restrictions on the shape and size of the products.
  • High Mold Manufacturing Costs: The process is only cost-effective for large-scale production due to the high cost of mold manufacturing, making it less viable for small batch production.
  • Sintering Defects: Hard alloy sintering may exhibit defects such as peeling, holes, and blisters, which can affect the performance and appearance of the products.
  • Disadvantages of Solid-phase Sintering: This method requires high sintering temperatures (>2000℃) and high purity of raw materials. The sintered body has low fracture toughness and is highly sensitive to crack strength, characterized by coarse grains, poor uniformity, and typically transgranular fracture.
  • Metal Meshes and Metal Sintered Nets: Insufficient rigidity can lead to deformation, adversely affecting fluid filtration and resulting in a loss of uniformity in the filtration process.

Are Sintered Products Expensive?

The cost of sintered products is influenced by a variety of factors, including the manufacturing process, material selection, product complexity, and production volume. Typically, products range from $0.1 to $10, depending on factors such as quantity.

  • Tooling Costs: The tooling costs for sintered parts can be relatively high, especially for small batch production. This is due to the high cost of mold manufacturing, which needs to be amortized over a large number of products.
  • Production Efficiency and Energy Consumption: Sintered components are cost-effective due to their high production efficiency and low energy consumption. For mass production, using the same set of tools for pressing and sintering leads to lower costs because of the high production rate and low energy consumption of the presses and sintering furnaces.
  • Material Density and Processing Technology: Different sintering techniques and material densities significantly affect costs. For example, standard press-sintering techniques are relatively inexpensive but result in lower density. On the other hand, high-temperature sintering or advanced compaction techniques can increase density but at a corresponding increase in cost.

How long does the sintering process take to complete?

The sintering process generally takes only a few seconds to complete. However, the sintering step after molding may take several hours to finish. The sintering process is relatively fast, completed in two steps involving product pressing and sintering. As a manufacturer with large-scale production equipment, we can generally deliver to our customers within 10 to 14 days.

What are the industrial applications of sintering and its products?

Sintering has a wide range of industrial applications. Here are some common applications:
Automotive industry: Sintered parts are common in automotive transmissions, engines, chassis, and exhaust systems. Powder metallurgy technology can produce various automotive structural components, such as engine connecting rods, pulleys, and cams.
Industrial ceramics: Sintering technology plays an important role in the ceramic industry, enabling high-temperature sintering of ceramic materials to obtain dense ceramic products with excellent properties. These ceramic products are used in aerospace, automotive, and electronic devices.
Water treatment industry: Sintering technology is also applied in the water treatment industry to manufacture filtering materials and components, improving water quality and treatment efficiency.
Food industry: In the food industry, sintering technology is used to manufacture equipment and parts for processing and packaging food, ensuring food safety and hygiene.
Biomedical field: Applications of sintering technology in the biomedical field include manufacturing artificial bones, teeth, and other medical implants that require high biocompatibility and mechanical strength.
Electronics and electrical industry: Sintering technology is used to manufacture electronic and electrical components, such as electromagnets, sensors, and batteries, which require high precision and reliability.

How durable are sintered products?

Sintered metal products, especially those that have been heat-treated, are durable. Depending on the metal alloy and application, their lifespan can range from a few months to several decades.

Are sintered metals stronger?

If the material selection is appropriate, sintered parts can achieve the same strength as machined parts. Properly sintered metal parts usually have most or all of the mechanical properties of the main components. For example, the fatigue strength of MIM parts is generally 80-90% of that of forged or cast parts, due to larger grain sizes and micro-pores that can create weak links.

What is the future of sintering?

With the integration of advanced technologies, the future of sintering technology holds great potential. Optical measurement systems, such as the ATOS 3D digitizer, are revolutionizing the industry by efficiently and accurately measuring complex surfaces. These systems eliminate the labor and time-consuming traditional measurement methods, providing full-field measurements and faster verification. Adopting these advanced technologies will improve the productivity, quality control, and overall efficiency of the sintering process.

Conclusion

Sintering is increasingly used in today’s industry. This article has discussed what sintering is, the steps of sintering, and its advantages, disadvantages, and applications.
As a professional manufacturer of sintered products, please contact us if needed.

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