Powder Processing

powder processing essentially refers to a manufacturing process that converts raw materials from a dry powder state to a solid form. There two main dry forming processes; cold isostatic pressing and die pressing. Powders comprise particles that have varying individual sizes. The sizes may range from micrometers to nanometers. The individual particles possess physical properties like melting point and yield strength. Powder particles usually have the same physical characteristics as bulk solids of the same material. They only behave differently in terms of flowing since powder particles easily move past each other.


Little to no liquids are added during powder processing. The processing of powders often involves molds or dies. The powder is poured into the mold and subjected to intense pressure that results in a specific shape. The compacted shapes can vary from being fairly simple to complex ones. The compacted component is usually porous. It requires post-processing to obtain its final dense form. The process is referred to as sintering.

More information on powder processing


In-depth Description of Powder Processing


The process commences with the materials in its powder state. The technique can be used on an array of materials. It is especially preferred on materials with features that preclude shaping through casting and melting. Such materials are namely ceramics like silicon nitride and alumina. It also works on brittle metals that possess extremely high melting points like tungsten that is over 2300 K. One other material is polytetrafluoroethylene (PTFE). Its viscosity is too high hence this is the only applicable molding technique.


During the initial stages, the starting powder is mixed with a binder or lubricant. It is then compressed into the desired shape in a die. This results in a 'green compact'. Despite it being exceedingly porous, it is stable enough to support its weight. This allows for gentle handling. The green compact is afterward subjected to sintering. This entails heating at an extreme temperature while subjecting the compact to some pressure for a long time. The process enables the particles to coalesce. This is basically the joining of small particles resulting in large particles that occupy the pore spaces.


The compact eventually shrinks, resulting in a homogenous solid mass that has taken the mold's shape. The final part may have a varying degree of strength and porosity depending on the sintering process that was utilized. The porosity may result in defects such as cracks. Subjecting the compact to high temperature during sintering minimizes crack formation.


Powder processing often results in a considerable reduction in the final product's size. Most of the inter-particle sizes disappear as the particles fuse during sintering. Credited engineers normally consider this before processing a part. This process is considered to be more economical when compared to other shaping techniques. One shaping alternative is machining which is more costly during the mass production of complex parts. The emerging trends based on this process include hydrostatic shock forming, functionally grading of materials and additive manufacturing like 3D powder printing.


Applications of Powder Processing


An array of products can be manufactured using this technique. The production of the insulating sleeve of a spark plug and domestic ceramics like bathroom sinks are amongst its common applications. This process can also be used on metal-based materials. It is an attractive option in the production of a gearwheel. This is since it minimizes wastage of material along with modest expenditure on labor and energy. The only significant complication it faces is the need for a die and shaped punch.


Benefits


It is ideal for the mass production of ceramic and small metal parts of all manner of sizes and shapes. It also eliminates mold component reactions that result from melt forming.