What is powder metallurgy?

What is powder metallurgy?
 
Powder metallurgy is the technology which made from metal powder,through compacting and sintering process to make powder metal(or metal powder with  mixture of non-metal powder) into material and products.It is a very important subdiscipline of metallurgy and material science.
 
Powder metallurgy history
 
2500 years,iron block(solid reduction method) forging method to make iron implements.
The early of 20^th. Century,make refractory metal.In 1909, making tungsten wire for bulbs promotes the development of powder metallurgy.In 1923,the emergence of powder metallurgy hard alloy is praised as the revolution of machining.
30s,successful make out oil bushing.The development of powder metallurgy iron machinery parts,give full play to the advantage of powder metallurgy which requires less machining or even without machining
40s,metal ceramic and dispersion-strengthened material.
60s,powder metallurgy HSS and the application of powder superalloy.
80s,booming development in auto industry.
 
Features of powder metallurgy
 
Material and energy saving
Low pollution
Good dimensional accuracy
Good surface condition
Close final shape
Lower production cost
Good product consistency
Special organization of many alloys
Porous organization
Complex shape
Suitable mass production
 
 
Economy aspect
 
Energy saving:The pressure requirement of powder metallurgy is greatly lower than forging,rolling etc. Traditional process;sintering temperature is also lower than main composition melting point.So the cost of energy is much lower than forging,CNC and other process.
Material saving:the material usage of powder metallurgy is up to above 95%,much higher than other process,such as CNC,which material usage is approx between 40%-50%.
Time saving:In automatic production line,the time of forming a blank only needs 0.5 seconds;and the average sintering time of each products also lower to a few seconds.The time cost is much lower than other process.
Precision:The size of powder metallurgy products achieves high accuracy,in general process,no need further machining process.
 
Property
Some products with special properties or microscopic structure,can only be made by powder metallurgy,other process will not be able to achieve .For example:
Porous material:filter,oil bushing,porous steel etc.
Composite material:dispersion strengthened or fibre reinforced composite material
Alloy system:Most of alloy system has solvus,exceed this solvus,the forging organization will produce eutectic,eutectoid and intermetallic compounds and segregation,forming uneven organization structure;However,some elements are not miscible,even under melting condition,so it is impossible to be made out by forging.The properties of powder metallurgy can easily mix out any proportions and homogeneous organization of alloy material.
Particularity
Some material may able to use other process to make,but there is difficulty in practice.For example:
High melting point metal:Tungsten(3380℃),molybdenum(2615℃),ceramic and other high melting point material which are difficult to be made by forging.
Reactive metals:The activation of Titanium,tantalum etc.is very high under molten condition,easily oxidizing or crucible erosion,it causes great difficulty in forging,therefore,most of them are made by powder metallurgy.

The standard of choosing powder metallurgy

1.Products size
The size of powder metallurgy parts is limited by the compressibility of powder and tons of compacting machine.For normal steel powder metallurgy material,can create following spec.of parts:
Projection surface area lower than 32 000ram2
Diameter less than 170mm or max 300ram(for parts with big hole)
Maxlength 150ram,minlength 1.5ram
The max ratio between length and diameter is 5:1;the max ratio between length and wall thickness is 8
If the design of products are using non-iron metal material,the projection area can increase 50%

2.Products shape
The products geometry must be suitable to make uniaxial press in in vertical.direction.Undercut,recess or thread are normally finished by post process or machining.When the cross section of parts changes a lot,it requires the tooling on molding machine has various action.These limited components can only have 5 flats,but,through tooling design,adding small alteration in the length of parts direction is possible.When the length of parts are longer than 25.4mm,the density will be different from top(max density) to middle(relatively low).

3.Products quantity
Considering the special tooling is “hardware”,so it is necessary to discuss the purchase order quantity or MOQ.

4.Mechanics/Physical property requirements
In order to help most of products to choose suitable material,spec.35 provides widely design performance.The number of medium-density steel(6．4-6．9g／cm3) can replace cast iron or plain carbon steel;high-density brand(7．0～7．4g／em3) can replace toughness ductile iron or heat-treated iron;powder forging and non-porous material can replace high-performance steel.If the key property of products design must be beyond the standard value of standard,then these requirements must be listed on the drawing.
In order to choose the best material in performance,cost and feasibility,it is very important to discuss the application of products with customer,In order to avoid concepts unclear or misunderstanding,customer and supplier should reach an agreement before producing powder metallurgy products.like min strength,brand of material,chemical composition,inspection test,standard property value and producing tech,as these factors will influence the function of products.

5.Products usage
The products tech.spec. or drawing should provide additional information as clear as possible,also provide assembling picture to supplier to let them fully understand the application of products.For choosing material and producing process,following questions are very important:
When products work under fluid pressure,are they required sealed and no leakage?
When products are required to prevent erosion,what’s the standard?
Which area are required machining?What’s the tolerance?
What kind of heat treatment required?
Are the products used in high-impact load?
If the products require anti-wear function,which face requires?
Surface roughness is a very important design,which face requires this?And how to measure?
Are the products used in magnetic applications?
Are the products used in high temperature environment ?
What kind of burrs does the product not allowed to have?Fillet radius size?
Does the product require welding?
For the usage function of product,does it has requirement for critical location?
Does product require special package?
Powder metallurgy application field
Powder metallurgy is widely used many different fields,we can see powder metallurgy from normal mechanical machine to precision equipment;from hardware tool to big machine;from electronic industry to motor manufacture;from civil industry to military industry;from average technology to highly sophisticated tech.
Powder metallurgy products application
Various mechanical products
Porous material
Hard-alloy products
High-temperature products
High-quality tool steel
Magnetic material&contact material
Friction material
Powder metal in various fields
Metal ceramic and special ceramics
Powder metallurgy process

Powder metallurgy material standard
Currently,there are three types of usual material standard:SMF series,MPIF standard and DIN standard
SMF is Japan standard:common used are SMF5030,5040,4030,4040
MPIF is America standard:common used are FC0205,FN0205
DIN is Germany standard:common used are D11,D39
MPIF sintering carbon steel
MPIF sintering copper steel