Today’s post is about a modern manufacturing process that goes by the name of Powder Metallurgy.
What is Powder Metallurgy?
Powder Metallurgy is the process of blending fine powdered materials, pressing them into a desired shape or form (compacting), and then heating the compressed material in a controlled atmosphere to bond and form the material (sintering and presintering) such that the final component usually does not require further machining processes.
Powder metallurgy became widely recognized after 1945 and today, parts which cannot be formed using other processes are made using this process.
So can any material be processed by this procedure? Well, no. There are 2 main requirements of any material for it to be processed by powder metallurgy:
1.The metal in the powder form must be able to be shaped at high temperature by molecular cohesion.
2.The metal powder must be capable of sufficiently close packing under pressure to permit welding to take place and in case of alloys, be capable of being sufficiently and intimately mixed.
Here are some products that are actually made by powder metallurgy :
- Porous products like bearings and filters.
- Refractory parts made from tungsten and molybdenum used in electric bulbs and radio valves, x ray tubes ,etc
- Products of complex shapes like gears which need complex machining when made by other processes.
- Automotive components like electrical contacts , crankshafts,camshafts, piston rings , brackets, brake linings, connecting rods ,etc.
- Products from materials that are very difficult to machine like tungsten carbide , etc Components are gauges , wire drawing dies, wire guides , deep drawing, stamping and blanking tools stone hammers, rock drilling bits.
- Tungsten parts used in high temperature operations like nozzles for rockets and missiles.
- Grinding wheels, clocks and other timing devices
So here is the basic processing procedure for making products by Powder Metallurgy :
- The first step is to mix the various powders and lubricants in the required ratio and to ensure the formation of a homogenous mixture.
- The next step is to press the component into the required shape within a specially designed die or press. The component attains its final shape at this stage, but is still very brittle and can break apart at any stage. The powder pressing cycle is shown below.
- After this stage, the shaped object is sent into a oven for the sintering process.
- Sintering is done to achieve the maximum possible hardness and strength needed in the final product. Sintering is usually done at 70- 80% of the metal’s melting temperature in an inert atmosphere of hydrogen, ammonia or other hydrocarbons. The sintering time varies from thirty minutes to several hours depending on the metal used. Sintering causes the bonding of the solid particles within the component. Once cooled, the powder bonds to form a solid piece.
- The final component thus obtained from sintering is allowed to cool down gradually after which it is sent for secondary processes, if required. These may include machining, surface finishing or joining processes.
The advantages of this manufacturing process over other processes include 99% utillisation of material, cleaner and quieter operation, ease of process automation, greater accuracies and quicker manufacturing of complex objects at a high production rate.
The disadvantages of this process are over-dependency on sintering, product size constrains, material constrains, high die design/manufacturing cost and its impracticality for small scale production.
Alright guys, thanks for reading this! Hope this was helpful!
Until next time.