Types of Processes Used in a Powder Production Line

Types of Processes Used in a Powder Production Line

Powder production line involves the process of turning metal materials into parts. These parts are designed based on client designs and have exceptional tolerances and surface finishes.

The powders are fed into a die cavity through a feed shoe that determines the basic shape of the part. Using electric current assisted sintering reduces the furnace heat time and allows near-theoretical densities for some powders.

1. Crushing

Metal powders can be produced in several ways using various types of processes, including solid-state reduction, atomization, and chemical treatments such as oxide reduction and Powder Production Line thermal decomposition. This processing reduces or eliminates subtractive fabrication steps, lowering the cost of the final product. It also allows parts to be designed to withstand a wide range of conditions and stresses, making them suitable for high-performance applications that demand precision tolerances, strong wear resistance, and a long life cycle.

Once a metal part manufacturer has received all of the design specs from its client, it will reach out to its own certified powder supplier and purchase a specific batch of material based on that performance criteria. The material will then be mixed and blended, with a variety of additives and lubricants to create the optimal mix. This mix will then be compacted and pressed. This process, called green compacting or zero pressure molding, will press and shape the powder into a form that closely resembles the part’s overall dimensions.

The next step, known as hot isostatic pressing (HIP), will heat the green compacts to their final density while removing any air present in the powder. This will produce a finished part with the correct dimensional characteristics and as-wrought mechanical properties. The PM process takes up to twice as much time as traditional manufacturing methods, but it yields a stronger and longer-lasting product with reduced waste.

2. Blending

The blending process is necessary to combine powders with binders and lubricants. Thorough blending is important for batch uniformity, which ultimately reflects in the strength and other physical properties of the finished component. The mixing process can be done wet or dry depending on the material type and engineering specifications of the part being produced.

There are several different methods of blending powders including mixing drums, rotating double cone, and Ross Double Planetary Mixers. These devices are designed to be gentle agitators and ensure that all points of the metal blend are contacted in just 36 revolutions. Typically, the metal blend is simultaneously dried during this process to drive off moisture.

Another method of mixing is diffusion, which occurs due to the random motion of the powder particles. During this process, the particles of similar characteristics tend to move closer together and form a region within the powder bed with a higher concentration of composition.

To avoid this problem, a powder can be coated in an anti-adherent substance like magnesium stearate to prevent unwanted agglomeration during mixing. However, segregation still can occur in some situations during the blending process. This can be caused by a number of factors including particle size, shape, and density. It can also be caused by transport, packing, feeding, and storage. To avoid this problem, a continuous monitoring system can be used to monitor the content uniformity of the powder blend.

3. Forming

Metal alloys are converted into powdered form through a number of processes, including solid state reduction, atomization, and electrolysis. The powdered alloys are then blended with binders and lubricants to achieve the desired properties of the final part. A common blending process involves a rotating drum or rotating double cone.

The resulting mix is then compacted using a press or similar type of equipment. The amount of pressure used is dependent on the desired density of the finished workpiece. Typical compression ratios range from 15 to 30 parts per minute filling machinery for cylindrical workpieces. The complex shapes of modern metal products necessitate multi-level tooling, which increases production rates.

A key advantage of PM is that it produces a finished product with minimal waste. This translates to lower material costs and environmental impact. It also allows manufacturers to optimize the strength, stiffness, and hardness of a product while minimizing weight.

In the final stage of the powder metallurgy process, the workpiece is sintered to produce a fully formed part. The sintering process can be done in one of several ways, depending on the requirements of the part. One method is called a laser sintering, which uses a focused laser to bind the metal powder particles together into a solid mass. This technique is guided by a computer aided design (CAD) file, which provides the directions for the laser to bind the powder.

4. Sintering

Sintering is the process of heating a compact to a temperature above its melting point and letting it sit for an extended period of time. This heat causes the powder particles to fuse together and form a solid mass of metal, ceramic or composite material. Almost any substance can be sintered using this process including metals like tungsten and molybdenum, ceramics like alumina and zirconia or even plastics like polymers.

The powders are prepared for sintering by pulverisation and sieving to remove any impurities. The powders are then pressed into dies to form a shaped part known as a green compact. Green compacts are generally weak but the bonding mechanism that occurs during sintering can strengthen them enough for handling.

Ideally the density of the pressed compact will increase evenly throughout the part. However, this is often not the case due to friction and part geometry. Lubrication is often used to mitigate friction and help the compacts flow more smoothly but over lubrication can cause the density to decrease too much during compaction reducing the strength of the finished part.

The pressed compacts are then placed in a controlled atmosphere furnace and heated to the desired sintering temperature. This atmosphere can be created using a range of gases including carbon monoxide, disassociated ammonia, hydrogen, partially combusted natural gas or inert gases such as argon and helium.