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Improving Powder Metallurgy Processes with POLYOX™
Many metal parts, tools, and equipment used in the automotive, aerospace, and agriculture industries are made using powder metallurgy. Powder metallurgy is a more sustainable process that provides manufacturers advantages of accuracy, lower costs, reduced waste, and higher production speeds than other metal part forming processes like liquid metal molding.
During the process of powder metallurgy, elemental metal or metal alloy powders are combined with additives such as binders and lubricants to be consolidated into molds or dies. This is followed by a formation process to create compacts, also known as green bodies, which have the intended shape of the part but low mechanical strength. A sintering step finishes the process and metallurgically bonds the metal particles just below their melting point. The sintered particles produce a final part that increases strength and density when cooled. A simplified overview of the powder metallurgy process flow is depicted below.
While lubricant and binder additives may make up a small portion of the powder metallurgy process by weight, they play a significant role in its success. The lubricant additives are critical during compaction to ensure that metal particles easily slide into place. Lubricants also help to provide clean separation from the molds or dies after pressing. The binder additive is necessary such that the compacts have sufficient mechanical strength (referred to as green strength at this stage) to hold their shape until the subsequent sintering step.
Some parts made from powder metallurgy can be intricately shaped or thin walled. Thus, it is especially important to use high-quality lubricant and binder additives to ensure that these compacts do not deform prior to sintering. The best-performing additives will allow many types of parts to be reliably and accurately formed using powder metallurgy with excellent quality and efficiency.
POLYOX™ Additives for Powder Metallurgy
POLYOX™ are thermoplastic polyethylene oxide polymers with a high molecular weight that serve as ideal binders and lubricant additives for powder metallurgy processes. There are several key properties of POLYOX™ that make it perfect for the powder metallurgy manufacturing process:
Binding
POLYOX™ has a very high-binding efficiency for metal powders, allowing for increased green strength of compacts after compaction and fewer rejects through cracks and breakage. This property also enables more precise metal-part geometries to be formed. POLYOX™ can also help to prevent segregation that may occur while sintering alloy-based metal powders.
Lubricity
POLYOX™ polymers impart a high degree of lubricity to metal powders, allowing them to reduce adhesion and friction between powder particles and facilitating easier compaction using lower power consumption. This lubricity also provides less wear on dies and simpler ejection of the part from the die or mold. As a result, the amount of classical lubricants needed is reduced.
Thermoplasticity
Being a thermoplastic polymer, POLYOX™ has the flexibility to be used in many forming methods, such as isotactic and mechanical pressing, thermoplastic extrusion, and injection molding processes. POLYOX™ also requires relatively low temperatures (90°C–120°C) to ensure clean burn-off with little or no tendency to char and create ash.
Water Solubility
POLYOX™ is readily soluble in water and some organic solvents such as alcohol. By washing POLYOX™ out of prefired compacts, powder metallurgy manufacturers can use less energy-intensive methods to remove the binder from the compact before firing.
Several grades of POLYOX™ may be considered for powder metallurgy processes. They are listed below in addition to the recommended use rates per application. In general, molecular weight coincides with the melting temperature of POLYOX™. Therefore, if a lower burnout temperature is needed, a grade with a lower molecular weight should be chosen.
| Grade | Molecular Weight (g/mol) | Use Rate (wt%) |
| WSR N10 | 100,000 |
Injection molding binder: 10–20 Thermoplastic extrusion binder: 10 Lubricant: Less than 3 |
| WSR N80 | 200,000 | |
| WSR N750 | 300,000 | |
| WSR 301 | 4,000,000 |
Binder and lubricant additives are essential to the accuracy and efficiency of powder metallurgy processes, where they directly impact the integrity and quality of finished parts. POLYOX™ provides the necessary binding, lubricating, and rheology modifying properties to powdered metal compacts to enable highly efficient production of parts of various shapes, thicknesses, and complexity. In addition, since POLYOX™ may be burned off cleanly and at low temperatures or washed out using water or alcohol, it affords powder metallurgy manufacturers flexibility and ease for removal prior to sintering.
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