Summary
Highlights
Sintering is a common method for manufacturing complex metal parts, including those in car engines and high-wear components, which endure continuous stress and friction. This technology is also vital for mass-produced machine elements, such as those found in percussion drills, where sintered parts like drill bits, gears, and self-lubricating bushings exhibit diverse properties.
The process begins with metallic powders as base materials. All known metals can be reduced to powder form. For instance, iron, copper, and carbon powders are mixed with a lubricant in a rotating reservoir to achieve the desired chemical composition of the alloy.
Following mixing, the powder is shaped using a press, a sturdy die, and a system of two punches. The measured powder mixture flows from a hopper into the mold and is compressed under high pressure (65 to 800 MPa). This compaction reduces the powder volume by at least half, bonding the grains like a sandcastle to form the desired shape at ambient temperature.
For specific components like bushings, a mixture of copper and zinc powders with four metallic additives is used. A lower compaction pressure is applied to create a porous material, which allows the absorption of lubricant for later use, ensuring prolonged and maintenance-free operation.
The next crucial step is sintering, which gives the parts their mechanical characteristics. This process occurs in an inert atmosphere oven, where parts are heated below their melting point for several hours. This high temperature causes a double exchange of atoms (diffusion), transforming initially separate metal particles into a permanently bonded structure. In solid-phase sintering, the metal with the lowest melting point may liquefy, as seen with copper and zinc forming bronze.
After sintering and slow cooling, the parts undergo calibration under a press to achieve precise dimensions. This step not only corrects the size but also improves surface finish and increases the part's solidity. Bushings are calibrated in a similar manner and then saturated with lubricants, which fill their porous structure, providing a long-lasting lubricant reservoir.
Sintering is also used to produce extremely hard materials, such as tungsten carbide, which is used for drill bits and cutting inserts. Tungsten carbide, combined with a lower melting point binder metal like cobalt, forms a highly durable material resistant to wear. During sintering, the binder metal melts and diffuses between the tungsten carbide grains, reducing porosity and creating a dense, strong alloy. This process leads to reduced volume in the final product but significantly enhanced cutting capacity.