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AMT | Definitions and Nomenclature in Powder Injection Molding

Date:2025-06-10   Views:1004

Table of Contents

Justification

Units and Conversion Factors

Nomenclature and Symbols

Definitions

Justification

Powder Injection Molding (PIM) is a rapidly evolving technology that is still seeking standardization. Consistent nomenclature is crucial to reduce confusion within the user community. This chapter provides a definitional reference for core concepts, helping users gain more confidence with PIM through standardized language.

Units and Conversion Factors

The primary units for international trade and commerce are the SI (Le Systeme International d’Unites) units, also known as metric units. This book follows international standards, with secondary English units shown parenthetically where possible. Below are some key conversion factors and relationships:

Helpful Relations

  • 1 meter is slightly longer than 1 yard (3 feet)

  • 25 millimeters (25 mm) is about 1 inch

  • A common USA dime (10 cents) is about 1 millimeter thick

  • 1 kilogram is a little more than 2 pounds

  • 1 gram (0.001 kilogram) is slightly heavier than a paper clip

  • 1 liter is a little larger than 1 quart

  • Water boils at 212°F (100°C) and freezes at 32°F (0°C)

  • 4,000 joules is about 1 kilocalorie

  • The recommended daily caloric intake for an adult human is 8,000,000 joules (8 MJ)

  • 1 hectare (10,000 square meters) is about two and a half acres

Prefixes

  • G (giga) = 10^9

  • M (mega) = 10^6

  • k (kilo) = 10^3

  • c (centi) = 10^-2

  • m (milli) = 10^-3

  • μ (micro) = 10^-6

  • n (nano) = 10^-9

Fundamental Units

  • Length = meter (m)

  • Time = second (s)

  • Mass = kilogram (kg)

  • Amount = mole (mol)

  • Current = ampere (A)

  • Temperature = kelvin (K)

  • Plane angle = radian (rad)

  • Solid angle = steradian (sr)

  • Luminous intensity = candela (cd)

Derived Units

  • Hertz (Hz) = 1/s

  • Hour (h) = 3600 s

  • Minute (min) = 60 s

  • Liter (L) = 10^-3 m³

  • Ton (t) = 1000 kg

  • Celsius (°C) = K - 273

  • Newton (N) = kg·m/s²

  • Pascal (Pa) = N/m²

  • Bar = 0.1 MPa

  • Joule (J) = N·m

  • Watt (W) = J/s

Important Constants

  • Acceleration of gravity = 9.8 m/s²

  • Atomic mass unit = 1.661×10^-24 g

  • Avogadro’s number = 6.022×10^23 molecules

  • Boltzmann’s constant = 1.381×10^-23 J/K

  • Electric permittivity of vacuum = 8.854×10^-12 C/V

  • Elementary charge = 1.602×10^-19 C

  • Gas constant = 8.314 J/(mol·K)

  • Planck’s constant = 6.626×10^-34 J·s

  • Speed of light = 2.998×10^8 m/s

Conversion Factors

  • Length: 1 m = 39.4 inches, 1 m = 3.28 feet, 1 m = 1.09 yards

  • Area and Volume: 1 cm² = 0.155 in², 1 m³ = 35.3 ft³, 1 L = 0.264 gallons

  • Temperature: To convert K to °F, multiply by 1.8 and subtract 459.4

  • Mass: 1 kg = 2.2 lb, 1 Mg = 1.1 short tons

  • Force: 1 N = 0.225 lb force

  • Pressure: 1 MPa = 145 psi, 1 bar = 0.1 MPa

  • Energy: 1 J = 0.737 ft·lb, 1 J = 0.239 cal

  • Power: 1 W = 0.737 ft·lb/s, 1 kW = 1.34 hp

Nomenclature and Symbols

Below is a list of commonly used mathematical symbols and descriptions related to PIM products, processes, or component features:

  • a = numerical constant in calculations, dimensionless

  • P = solid cone angle, degree

  • e = strain or fractional porosity (sometimes given as %)

  • η = viscosity, Pa·s

  • γ = surface energy, J/m²

  • K = thermal conductivity, W/(m·K)

  • λ = mean free path, m

  • ρ = density, g/cm³ or kg/m³

  • σ = stress or strength, Pa (typical units MPa or 10⁶ Pa)

  • τ = shear stress, Pa (typical units MPa or 10⁶ Pa)

  • μ = friction coefficient, dimensionless

  • θ = angle, degree

  • φ = solids loading, dimensionless or often given as vol.%

  • π = 3.14159

  • Q = atomic volume, m³/atom or m³/mol

  • A = area, m²

  • B = magnetic response, T

  • c = fractional molar solubility, dimensionless

  • C = microstructure parameters such as contiguity, connectivity

  • Cp = constant pressure heat capacity, J/kg or J/mol

  • d_p = pore diameter, m (usually given as μm)

  • D = particle size or particle diameter, m (usually given as μm)

  • D_L = solid phase diffusivity in liquid phase, m²/s

  • ε = strain, dimensionless

  • E = elastic modulus or elasticity, N/m² (typical units GPa or 10⁹ Pa)

  • f = fraction, solids fraction, or fractional solids loading

  • F = force, N

  • g = gravitational constant, m/s²

  • G = grain size, m (typical units μm)

  • h = height of component, m

  • H = enthalpy or heat, J/kg

  • H = coercive force, A/m

  • I = impact energy, toughness, J/cm²

  • k = Boltzmann’s constant, 1.38×10^-23 J/(K·atom)

  • K_IC = fracture toughness, MPa·√m

  • L = characteristic sample dimension, m

  • M = mass, g

  • n = work hardening exponent, dimensionless

  • P = pressure, N/m²

  • PG = gas pressure, N/m²

  • r = component radius, m

  • R = universal gas constant, 8.314 J/(mol·K)

  • Ra = average surface roughness, m (typically given as μm)

  • RA = tensile test reduction in area at fracture, dimensionless (often given as %)

  • S = fractional saturation, dimensionless

  • t = time, s

  • T = temperature, K (usually given as °C)

  • V = volume fraction, dimensionless

  • W = weight fraction, dimensionless

  • w = width

  • x = coordinate, m

  • X = sinter bond neck size, m (often given in μm)

  • y = coordinates, m

  • Y = shrinkage, dimensionless (often given as %)

  • z = coordinate, m

  • Z = tooling expansion factor, dimensionless (often given as %)

Definitions

Below are key definitions related to PIM:

  • Acicular Powder: Needle-shaped particles that are good for debinding strength but generally detrimental to the PIM forming process.

  • Adiabatic Forming: The use of a frozen powder-water feedstock that melts and flows under pressure, but refreezes when pressure is released.

  • Admixed Powder: A small, discrete powder mixed with another powder for lubrication, bonding, or alloying.

  • Agglomeration: A tendency for small PIM particles to stick together and appear as larger particles, common with nonconducting powders such as ceramics.

  • Air Classification: The most common means for separating specific size classes of PIM powders by differential settling in a high velocity air stream.

  • Alloy Powder: A powder in which each particle is composed of the same mixture of two or more constituents.

  • Alumina: The compound of aluminum and oxygen (Al₂O₃), commonly used in ceramic PIM.

  • Angle of Repose: The angle from the horizontal plane that a pile of loose powder will assume when freely poured through an orifice.

  • Apparent Density: The mass of a unit volume of powder in the loose condition, usually expressed in g/cm³.

  • Aspect Ratio: The ratio of the maximum particle dimension to the minimum dimension.

  • Atomization: The dispersion of molten material into droplets by a rapidly moving stream of gas or liquid.

  • Atomized Powder: Alloy or metal powder produced by disintegration and subsequent solidification of a molten metal stream.

  • Attrition: A mechanical milling or grinding process used for deagglomeration, partial alloying, and particle size reduction.

  • Austenite: The face-centered cubic crystal structure of pure iron, stabilized at room temperature in austenitic stainless steels.

  • Barrel: The heated portion of the feedstock flow path before the nozzle.

  • BET Surface Area: The specific surface area measured by gas adsorption according to the Brunauer, Emmett, and Teller theory.

  • Bimodal: A particle size distribution exhibiting two mode sizes.

  • Binder: The polymer mixture that provides lubrication and strength to the powder.

  • Bingham Flow: Viscous flow of a feedstock with an initial yield strength.

  • Blending: The thorough intermingling of powders of the same nominal composition.

  • Brown State: A term describing a ferrous PIM component following debinding by slow heating in air.

  • Burnoff: The removal of the polymer binder via preheating prior to sintering.

  • Capillary Rheometer: A device for measuring viscosity by applying pressure on molten feedstock.

  • Carbo-Nitride: A heat treatment in a nitrogen and methane atmosphere causing carbon and nitrogen to diffuse into the steel surface.

  • Carbon Control: A measure of the ability to remove the PIM polymer without contamination of the powder.

  • Carbonyl Powder: Predominantly iron or nickel powder prepared by thermal decomposition of a metal carbonyl molecule.

  • Carburization-Decarburization: Events related to carbon control, involving addition or removal of carbon from the material.

  • Case Carburize: A post-sintering heat treatment aimed at diffusion of carbon into the surface of a ferrous PIM compact.

  • Catalytic Debinding: Partial removal of the polymer via heating in an atmosphere containing an agent that induces depolymerization.

  • CCIM: Cemented carbide powder injection molding.

  • Cemented Carbide: A solid composite consisting of a metal carbide and a binder phase.

  • Cermet: A composite body consisting of ceramic particles bonded with a metal.

  • Centrifugal Atomization: Formation of spherical particles by combining a melt with a centrifugal force.

  • Closed-Loop Feedback Control: A molding control for precise dimensional control using pressure monitoring.

  • Closed Pore: An isolated pore not linked to the external surface, usually formed in sintering.

  • Coarsening: The progressive enlargement of particles due to diffusion, coalescence, or solution-reprecipitation processes.

  • Coefficient of Variation: The standard deviation divided by the mean value.

  • Coining: The final pressing of a sintered compact to obtain a definite surface configuration.

  • Co-Molding: Molding two materials into the same cavity to form layers or interconnections.

  • Composite: A mixture of two or more powders forming a multiple phase structure.

  • Compression: The removal of air from melting feedstock by applying heat and pressure.

  • Computer-Aided Design: Use of computer programs for stress, fit, dimensional calculations, and visualization.

  • Computer-Aided Manufacturing: Computer-controlled machines for proper fabrication and resource utilization.

  • Critical Loading: The maximum volume fraction of solid particles in a polymer binder without forming pores.

  • Cross Linking: Formation of bonds between polymer chains to give rigidity and strength.

  • Cycle Time: The time for completion of one molding cycle.

  • Debinding: Extraction of the binder used in molding by heat, solvent, catalysis, or other techniques.

  • Delamination: Cracking of a molded compact, often leading to a hairline crack oriented perpendicular to the ejection direction.

  • Densification: The change in porosity divided by the initial porosity due to pressing or sintering.

  • Density: The mass divided by the volume, usually expressed in g/cm³.

  • Dew Point: A measure of atmosphere purity based on water content.

  • Differential Scanning Calorimetry: Determination of heat flow into or out of a PIM sample.

  • Differential Thermal Analysis: Measurement of temperature and temperature difference during heating for a PIM material and a reference.

  • Dihedral Angle: A microstructure feature associated with phase boundaries in a material.

  • Dilatant Flow: Viscosity that changes with flow conditions where the mixture dilates under stress.

  • Dilatometry: Measurement of dimensional change during thermal processing.

  • Infiltration: The process of filling the pores of a compact with a lower melting temperature metal or alloy.

  • Injection Molding: A hydrostatic forming technique for shaping powders using plastic binders.

  • Interparticle Friction: Friction between powders limiting sliding, packing, and densification.

  • Invar: Low thermal expansion alloys of iron-nickel-cobalt.

  • Irregular Powder: A powder lacking shape symmetry in individual particles.

  • Jetting: A condition arising with rapid filling of an injection mold where the feedstock shoots across the mold and fills back toward the gate.

  • Knit Line: A linear defect occurring where feedstock streams merge in the cavity.

  • Kovar: A glass-to-metal sealing alloy used for microelectronic packaging.

  • Low Pressure Molding: Use of lower pressures and low viscosity binders to fill out a complex tool cavity.

  • Lamination: A layered structure or cracking in the pressed compact resulting from ejection stresses exceeding the green strength.

  • Liquid Phase Sintering: Sintering at a temperature where a liquid and solid coexist.

  • Lubricant: An organic additive mixed into the feedstock to minimize die wear and aid in ejection.

  • Maraging Steel: A high strength, high toughness class of iron-nickel-molybdenum alloys.

  • Martensite: A distorted ferrite crystal structure due to carbon supersaturation in rapidly cooled ferrite.

  • Mean Size: The average value from the particle size distribution.

  • Mechanical Alloying: Formation of an alloy powder by milling elemental powders.

  • Median Size: The centroid of the particle size distribution.

  • Melt Index: A measure of flow at low shear strain rates.

  • Metering: Controlled forward extrusion of molten feedstock past the screw tip.

  • Microminiature: Component dimensions measured in the micrometer size range.

  • Micromolding: A new class of PIM technologies for producing components in the millimeter and micrometer size range.

  • Microstructure: Detailed information on microscopic phases, pores, grains, defects, and heterogeneities.

  • MIM: Metal powder injection molding.

  • Mixing: Thorough intermingling of powders of two or more different compositions.

  • Mold Flow Simulation: Computer simulations for analysis of flow, packing, venting, sizing, cooling, and other events in PIM forming operations.

  • Mold Release: A spray or coating that reduces component sticking to the die cavity.

  • Moldability: A relative measure of the ease of filling out a tool cavity during injection molding.

  • Multimodal: A powder size distribution exhibiting several modes.

  • Nanoscale: Powders or microstructures with sizes measured in nanometers.

  • Near Net-Shape: Technologies attempting to form a discrete component without a need for final machining.

  • Net-Shape: A compact manufactured to final density and dimensions without the need for machining.

  • Newtonian Flow: An idealized viscosity situation where stress is proportional to shear strain rate.

  • Nodular Powder: Irregular particles with knotted, rounded shapes.

  • Open Pore: A pore completely through a compact from one surface to another.

  • Oxidation-Reduction: Atmosphere-powder reactions extracting or depositing oxygen in a powder compact.

  • Packing Pressure: The peak pressure encountered in the molding operation once the die is filled.

  • Particle Size: The controlling linear dimension of an individual particle.

  • Particle Size Analyzer: An automated device for determination of the particle size distribution.

  • Parting Line: The linear mark on a compact where the die halves meet.

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