Powder Metallurgy PM Part 1 PDF

POWDER METALLURGY 1. Introduction 2. The Characterization of Engineering Powders 3. Production of Metallic Powders 4. Conventional Pressing and Sintering 5. Alternative Pressing and Sintering Techniques 6. Materials and Products for PM  INTRODUCTION ⦁ Powder metallurgy is the name gi...

POWDER METALLURGY 1. Introduction 2. The Characterization of Engineering Powders 3. Production of Metallic Powders 4. Conventional Pressing and Sintering 5. Alternative Pressing and Sintering Techniques 6. Materials and Products for PM  INTRODUCTION ⦁ Powder metallurgy is the name given to the process by which fine powdered materials are blended, pressed into the desired shape, and then heated to bond surfaces ⦁ Typically used when large amounts of small, intricate parts with high precision are required ⦁ Little material waste and unusual mixtures can be utilized ⦁ Used for parts in the automotive industry, household appliances, and recreational equipment (to name a few) Dr. Ramadan Elgamsy  Powder Metallurgy (PM) Metal processing technology in which parts are produced from metallic powders Usual PM production sequence: 1. Pressing - powders are compressed into the desired shape to produce green compact Accomplished in the press using punch-and-die 2. Sintering – green compacts are heated to bond the particles into a hard, rigid mass Temperatures are below the melting point Dr. Ramadan Elgamsy  Why Powder Metallurgy is Important PM parts can be mass-produced to net shape or near net shape, eliminating or reducing the need for subsequent machining PM process wastes very little material - ~ 97% of starting powders are converted to product PM parts can be made with a specified level of porosity, to produce porous metal parts Filters, oil-impregnated bearings and gears Dr. Ramadan Elgamsy More Reasons Why PM is Important Certain metals that are difficult to fabricate by other methods can be shaped by powder metallurgy Tungsten filaments for incandescent lamp bulbs are made by PM Certain alloy combinations and products made by PM cannot be produced in other ways PM compares favorably to most casting processes in dimensional control PM production methods can be automated for economical production Dr. Ramadan Elgamsy  PM Work Materials Largest tonnage of metals are alloys of iron, steel, and aluminum Other PM metals include copper, nickel, and refractory metals such as molybdenum and tungsten Metallic carbides such as tungsten carbide are often included within the scope of powder metallurgy Dr. Ramadan Elgamsy  PM Materials – Pre-Alloyed Powders Each particle is an alloy comprised of the desired chemical composition Common pre-alloyed powders: Stainless steels Certain copper alloys High speed steel Dr. Ramadan Elgamsy  Basic steps of the Powder Metallurgy Process. Dr. Ramadan Elgamsy Making Powder-Metallurgy Parts Dr. Ramadan Elgamsy PM Typical parts include: bearings gears motor bushings electrical contacts cutting tool inserts tool steel blanks Dr. Ramadan Elgamsy  Powder Metallurgy Dr. Ramadan Elgamsy Collection of PM Parts Dr. Ramadan Elgamsy Powder Metallurgy In Gear Box Dr. Ramadan Elgamsy Powder Metallurgy In Car Engine Dr. Ramadan Elgamsy  PM products Dr. Ramadan Elgamsy  PM Parts A collection of powder metallurgy parts. 12 Dr. Ramadan Elgamsy Dr. R.B.M Elgamsy Dr. Ramadan Elgamsy Industrial Machines Parts Dr. Ramadan Elgamsy For Electric Motors  PM vs. Other Fabrication Methods (casting, stamping, or machining) PM is the choice when requirements for strength, wear resistance or high operating temperatures exceed the capabilities of die casting alloys. PM offers greater precision, eliminating most or all of the finish machining operations required for castings. It avoids casting defects such as blowholes, shrinkage, and inclusions. Powder injection molding is coming out as a big challenge for investment casting. However the PM process is economical only when production rates are higher since the tooling cost is quite appreciable Dr. Ramadan Elgamsy  The powder metallurgy methods start with powders and the properties of the manufactured parts depend to a large extent on the properties of the initial powders. Amongst powder properties, composition, size, form, and structure of the particle, specific surface, porosity and volume characteristics, fluidity, strength, hardness, permeability regarding liquids and gases, electric conductivity, compressibility, and sinter ability are of great importance in powder metallurgy. Metal powders consist of separate small bodies—the so-called particles—from 0.1 µ up to several millimeters in size.  In most powders, the particle size varies from several microns to 0.5 mm. Particles usually have internal pores, cracks, and impurities. Dr. Ramadan Elgamsy  Particle shape is widely varied and determined by the methods of production; Particles are divided according to their shape into three basic groups:  hair or needle-shaped, the lengths of which considerably  flat (flakes or leaves) whose length and breadth are many times greater than their thickness;  equiaxed, which are roughly identical in all dimensions. Dr. Ramadan Elgamsy Dr. Ramadan Elgamsy Material and Energy Considerations Dr. Ramadan Elgamsy  Material and Energy Considerations Machining Casting Forging Powder Metallurgy These values include the energy consumption for the production of the raw materials (powder, steel, ingot) The numbers are based on public domain data (e.g. industry reports) and individual studies in literature A generally valid comparison is nearly impossible without focusing on specific components – the scatter between the processes and different operations is high Dr. Ramadan Elgamsy  Engineering Powders A powder can be defined as a finely divided particulate solid Engineering powders include metals and ceramics Geometric features of engineering powders: Particle size and distribution Particle shape and internal structure Surface area Dr. Ramadan Elgamsy  POWDER MANUFACTURE ⦁ Properties of powder metallurgy products are highly dependent on the characteristics of starting powders ⦁ Some important properties and characteristics ⦁ C hemistry and purity ⦁ Particle size ⦁ Size distribution ⦁ Particle shape ⦁ Surface texture ⦁ Useful in producing pre-alloyed powders ⦁ Each powder particle can have the desired alloy composition ⦁ The majority of commercial powder is produced by some form of melt atomization Dr. Ramadan Elgamsy  Measuring Particle Size Most common method uses screens of different mesh sizes Mesh count - refers to the number of openings per linear inch of screen A mesh count of 200 means there are 200 openings per linear inch Since the mesh is square, the count is equal in both directions, and the total number of openings per square inch is 2002 = 40,000 Higher mesh count = smaller particle size Dr. Ramadan Elgamsy  Screen Mesh for Sorting Particle Sizes Dr. Ramadan Elgamsy  Particle Shapes in PM Dr. Ramadan Elgamsy  Interparticle Friction and Powder Flow Friction between particles affects ability of a powder to flow readily and pack tightly A common test of interparticle friction is the angle of repose formed by a pile of powders poured from a narrow funnel Larger angles mean greater interparticle friction Dr. R.B.M Elgamsy Making Powder-Metallurgy Parts 3. POWDER MANUFACTURE ⦁ Properties of powder metallurgy products are highly dependent on the characteristics of starting powders ⦁ Some important properties and characteristics ⦁ C hemistry and purity ⦁ Particle size ⦁ Size distribution ⦁ Particle shape ⦁ Surface texture ⦁ Useful in producing prealloyed powders ⦁ Each powder particle can have the desired alloy composition ⦁ The majority of commercial powder is produced by some form of melt atomization 🞂 Atomization is a process where liquid metal is fragmented into small droplets that cool and solidify into particles Methods of metal-powder production by atomization ⦁ (a) melt atomization ⦁ (b) atomization with a rotating consumable electrode.  Gas Atomization Method High velocity gas stream flows through expansion nozzle, siphoning molten metal and spraying it into chamber Dr. R.B.M Elgamsy  Water Atomization Method  High velocity water streams flow through nozzles, rapidly cooling and solidifying molten metal into collection chamber Dr. R.B.M Elgamsy  Iron Powders for PM Iron powders produced by water atomization (photo courtesy of T.F.Murphy and Hoeganaes Corporation) Dr. R.B.M Elgamsy  Milling It is a mechanical method for powder production, where the initial material is pulverized without any change in chemical composition. Reduction of particle size is beneficial for sintering, which depends on diffusion of atoms. Most common milling method is ball milling - Generally balls are used for milling. Hardness of the balls must be equal or greater than the hardness of the powder will be milled. - Amount and size of the balls are critical for the final powder size. - Wet or dry milling can be applied. - From balls or barrel impurities may added to the powder (milling time and ball hardness)  Mechanical Comminution/pulverization (a) roll crushing, (b) ball mill, and (c) hammer milling. Dr. R.B.M Elgamsy  Additional Methods of Powder Manufacture ⦁ Methods ⦁ Chemical reduction of particulate compounds ⦁ Electrolytic deposition ⦁ Pulverization or grinding ⦁ Thermal decomposition of particulate hydrides ⦁ Precipitation from solution ⦁ Condensation of metal vapors ⦁ Almost any metal or alloy can be converted into powder  4- POWDER TESTING AND EVALUATION ⦁ Powders should be evaluated for their suitability for further processing ⦁ Flow rate measures the ease with which powder can be fed and distributed into a die ⦁ Apparent density is the measure of a powder’s ability to fill available space without external pressure ⦁ Compressibility is the effectiveness of applied pressure ⦁ Green strength is used to describe the strength of the pressed powder after compacting