The powder metallurgy process is famous for its incredible advantages and applications over other metal-producing technologies (metal casting and forging). According to Metal Powder Industries Federation, the global manufacturing of metal powders crosses 700,000 tons yearly. It is a superior method of producing high-quality metal parts with benefits in shape complexity, material utilization, and dimensional accuracy.
Almost 50% of the Powder Metallurgy (PM) products produced by the powder metallurgy industry are used by automotive industries. However, over 70% of the components are ferrous powder metallurgy parts. Similarly, many other manufacturing industries are also massively using PM parts.
This article explains the process, advantages, and applications of powder metallurgy. Therefore, let’s read it till the end!
What is Powder Metallurgy?
Powder metallurgy is a technology that makes highly accurate parts by compacting powdered metals and other powders in a rigid die, followed by sintering in a controlled atmosphere. The powder metallurgy parts are specified for their near-net shapes and porosity.
The major applications of the powder metallurgy process include magnets, grinding wheels, filament wires, welding rods, machine cutting tools, and so on.
What Steps are Involved in the Powder Metallurgy Process?
Here are the series of steps involved in the Powder Metallurgy process:
- Production of metal powder
- Mixing and blending
- Compacting and shaping the powder
- Sintering the compact
- Secondary operations often include sizing, coining, infiltration, hot forging, etc.
Let’s have a deeper look at the functioning of each step!
1. Powder Production
Typically, all iron powders for manufacturing Powder Metallurgy components are formed either by water atomization or using a sponge iron process. However, non-ferrous metal powders can be made using endless techniques, including inert gas atomization, plasma atomization, centrifugal atomization, electrolysis, carbonyl, and chemical conversion.
● Sponge Iron Process
During this process, the mixture of magnetite ore, coke, and lime is placed in a silicon carbide retort. Heating this retort in kiln results in an iron cake and a slag. Later, the iron sponge is separated from this slag for crushing and annealing to turn it into powder form. Usually, this powder is quite irregular in particle-like shape ensuring good green strength.
Sponge iron is ideal for iron-based, self-lubricating bearings, and almost 30% of PM parts use it.
When it comes to atomization, the separated tiny droplets of molten metal are frozen instantly to avoid contact with any surface. Ultimately, by subjecting the thin stream of molten metal to the impact of high-energy fluid jets, it disintegrates. Primarily, water is used as the liquid in atomization.
Generally, this process is suitable for all the metals that can be melted and used for forming copper, iron, brass, bronze, alloy steels, and low melting point metals like lead, zinc, aluminum, tin, cadmium, etc.
2. Mixing and Blending
Once you are done with the powder formation, it’s time to produce a high-strength alloy material according to the requirements of your project. To do so, mixing two or more different material powders is best. Moreover, adding lubricants during the blending process helps to improve the flow property of the powder.
Additionally, this step offers even distribution of powder with binders, additives, etc.
As the name implies, compacting is a stage where the prepared mixture of powder is compressed into pre-defined dies. Compacting the powder into a mold can be done by applying specific pressure in order to get a product, usually known as green compact.
The applied pressure mainly depends on the properties of binders and metal powder. However, it generally ranges from 80 MPa to 1600 MPa. The suitable pressure for soft powder compacting is about 100 to 350 MPa, while for more rigid materials like steel, iron, etc., the ideal pressure lies between 400 to 700 MPa.
With the help of compacting, you can reduce the voids and increase the density of the products at the same time.
The final product produced by compressing is not that strong to be used. Therefore, by following the sintering process, we aim to enhance the integrity and strength of the material. Typically, sintering is a process in which powdered material or green compact is heated in a controlled atmosphere. During this process, the particles chemically bond to ensure a strong permanent bond.
The temperature under which the particles sintered is normally kept below the melting point of significant components of the powder. Yet, sometimes minor components lead to the formation of a liquid phase at sintering temperature. Such a situation is termed liquid phase sintering.
After sintered parts are produced, the next step is the finishing process, commonly termed as secondary operations in powder metallurgy. Primarily, the sintered components are porous instead of dense. Their density usually depends upon various factors, including sintering temperature, compressing pressure, press capacity, etc.
If you don’t require the high-density product, you can directly use the resulting sintered product as a final product. Whereas, if a highly dense part is needed, you must perform secondary operations to achieve high dimensional accuracy and density.
Advantages of Powder Metallurgy
The following are some remarkable benefits of powder metallurgy:
● Design and Composition
Powder metallurgy allows you to design products of intricate shapes. Plus, the composition of the parts is in your hands. You can make different combinations of materials, such as a mixture of ceramics and metals.
● Ease of Usage
The machining operations are limited. Therefore, you don’t need to hire highly skilled machine operators at high rates. Further, overall the process is clean and quiet.
● Production Rate
With a powder metallurgy process, you can quickly achieve a high production rate in no time.
● No Material Wastage
The most significant advantage of the powder metallurgy technique over other metal-forming methods is almost no material wastage during the operation. Hence, it benefits you by saving material costs.
● Offers Good Finishing and Durability
Another advantage of the PM process is that the resulting parts have fine finishing and high dimensional accuracy. The process also allows you to enjoy the long-term performance of products and offers close dimensional tolerances.
● Provide a Wide Range of Properties
You can experience a wide range of properties when using powder metallurgy parts, including porosity and density. In addition, the parts have reduced wear and high corrosion resistance.
Limitations of Powder Metallurgy
Despite several advantages of powder metallurgy, it also has some limitations.
- ● The cost of metal powder and equipment is high.
- ● It is impossible to get a dense product by powder metallurgy.
- ● The dies needed for the operation must be highly accurate and withstand high temperatures and pressure.
- ● The ductility of parts is not good.
- ● It isn’t easy to sinter low-melting powder.
- ● There are size limitations when dealing with powder metallurgy parts.
- ● It’s tricky to deal with complex-shaped parts.
- ● Powder metallurgy is not economical for small-scale production.
- ● Some alloy powders are difficult to deal with.
Applications of Powder Metallurgy
The application of powder metallurgy in the industrial sector is a huge blessing for many manufacturers. It has solved the issue of refractory metals production, a building block for the formation of heat-resistant materials and tough cutting tools.
Let’s see what products different manufacturing industries are making by using the powder metallurgy process:
1. Industrial Tools
The powder metallurgy process helps form several industrial tools, including gauges, wire guides, wire drawing dies, blanking and stamping tools, hammers, bits, stones, etc.
Further, tungsten powder results in the production of different machine parts. Most commonly, the mixture of titanium carbide powders and tungsten carbide powders generates high heat and wear-resistant cutting tools.
2. Automotive Parts
Powder metallurgy gives rise to most parts of the automotive’s assembly, including piston rings, rocker shaft brackets, electrical contacts, crankshaft drive, connecting rods, brake linings, welding rods, clutch facings, and so on.
3. Porous and Complex-Shaped Parts
Porous components are also formed from powder metallurgy, i.e., bearings and filters. Besides this, most complex-shaped products, such as gears, can be made by the PM process.
4. Products with Combined Properties
Powder metallurgy is applicable when combined properties of metals and non-metals or two metals are required in a product—for instance, electric motor brushes and non-porous bearings.
5. Refractory Parts
It also plays a significant role in manufacturing refractory parts. Tungsten, molybdenum, and tantalum components are used in oscillator valves, radio valves, electric bulbs, X-ray tubes, anode, cathode, electric contact points, control grids, and many others.
6. Other Applications
In addition to the products mentioned earlier, powder metallurgy components are applicable in the following areas for different purposes:
- Electric Traction Motors
- Aerospace and defense
- Power transmission
- Construction and hardware
- Home appliances
- Firearms components
- Fluid power products
Since now you are aware of the worth of the powder metallurgy process that it helps you to create intricate shapes with no or minimal scrap. In contrast, other machining parts waste almost 50% of the material.
However, to achieve perfect powder metallurgy parts, make sure the powder has excellent plasticity, parking factor, and flowability. Additionally, it must be deprived of oxides and have the ability to be cold-pressed.