Introduction to Powder Metallurgy

Introduction to Powder Metallurgy

• Powder metallurgy is a process where finely divided metal powders are blended, pressed into the desired shape, and then heated to bond the surfaces.
• It's often used when creating intricate small parts requiring high precision, as it minimizes material waste.
• Applications include automotive parts, household appliances, and recreational equipment.

Characterization of Engineering Powders

• Powder characteristics influence the final product's properties.
• Critical aspects include composition, size, form, structure of the particle, specific surface, porosity, volume characteristics, fluidity, strength, hardness, permeability (liquids and gases), electric conductivity, compressibility, and sinterability.

Metallic Powder Production

• Metal powders can be made through various methods including atomization, reduction, electrolytic deposition, carbonyls, comminution, and mechanical alloying.
• The production methods themselves have factors like chemical composition, size, particle shape, surface texture, etc. that make specific powders useful.

Conventional Pressing and Sintering

• Pressing compresses metal powders into a desired shape ("green compact").
• This is often done with punch-and-die presses.
• Sintering heats the "green compact" to bond particles into a rigid mass, below the melting point.

Alternative Pressing and Sintering Techniques

• Techniques like Isostatic pressing, hot pressing, hot forging, and extrusion are alternative methods for shaping and consolidating the powder.
• These methods are used depending on the specific requirements of the final product.

PM Materials and Products

• Common PM metals include iron alloys, steel, aluminum, copper, nickel, and refractory metals (molybdenum and tungsten).
• Also often included are metallic carbides like tungsten carbide.
• Pre-alloyed powders are available with desired compositions, including stainless steel, copper alloys, and high-speed steel.

Why Powder Metallurgy is Important

• PM parts can be mass-produced to net shape or near net shape, reducing the need for further machining.
• Material waste is minimal – around 97% of starting powders are converted to the final product.
• PM parts can be tailored with specific levels of porosity to make porous metal parts for applications like filters, oil-impregnated bearings, and gears.
• Suitable for metals and materials difficult to fabricate by other techniques.
• Cost-effective for high production rate.

PM Work Materials

PM Materials – Pre-Alloyed Powders

• Each particle in pre-alloyed powder is an alloy with the desired composition.
• Common pre-alloyed powders include stainless steels, specific copper alloys, and high-speed steel

The Powder Metallurgy Process

• This section outlines the basic steps involved in the PM process, along with flow charts.
• The processes include adding various additives, blending, different pressing methods (Cold/Hot Compaction/Isostatic pressing), sintering, and finishing operations (e.g., coining, forging, machining, heat treating, impregnation, infiltration plating).

Typical PM Parts

• Bearings
• Gears
• Motor Bushings
• Electrical Contacts
• Cutting Tool Inserts
• Tool Steel Blanks

Powder Characteristics

• Relevant powder characteristics for processing include Particle size and distribution, Particle agglomeration, Surface area of particles, Interparticle friction, Particle flow and packing, Crystal structure, Composition, homogeneity, and contamination.

Measuring Particle Size

• Common method uses screens of varying mesh sizes.
• Mesh count refers to openings per linear inch.
• Higher mesh count equals smaller particle size.

Particle Size Distribution

• Particle size variation is described by a distribution function.
• Key parameters include mean particle size and standard deviation.
• These parameters are determined from measured amounts for all particle sizes within the powder. Types of particle distributions like Gaussian, polydisperse, and monodisperse are included.

Interparticle Friction and Powder Flow

• Friction between particles affects the ability of the powder to flow.
• A common measure is the angle of repose, which is formed when a powder is poured from a narrow funnel.
• Larger repose angles correlate to greater interparticle friction.

Metal Powder Production Methods

• The section includes details on different types of metal powder fabrication processes, including various forms of atomization (gas, water), mechanical methods like machining, milling, and others like chemical reduction.

Powder Testing and Evaluation

• Evaluation of powders focuses on factors like flow rate, apparent density, compressibility, and green strength to ensure suitability for further processing steps.

This quiz explores the fundamentals of powder metallurgy, focusing on processes, characteristics, and production methods of metallic powders. Dive into how particle properties affect final products and their various applications in industries like automotive and household appliances.