MIE221-Powder+Processing

Page 1: Course Introduction

• VELUT

• ARBOR

• Mechanical & Industrial Engineering

• University of Toronto

• Manufacturing Engineering

• Powder Processing

• Winter 2025

• MIE221

Page 2: What is Powder Processing?

• Formation of discrete parts in mold/die cavities by:

  • Compacting a mass of small particles (<150 microns) under pressure,

  • Followed by sintering.

• Normal use: Mass production of materials unsuitable for fusion techniques (e.g., casting).

• Advantages:

  • Minimal waste (near-net-shape).

  • Ability to produce complex geometries.

  • Suitable for high-performance materials (e.g., tungsten carbide).

Page 3: Powder Components

• Powders used include:

  • Graphite.

  • Lubricants.

  • Alloying elements/additives (Copper, Iron, Other base powders).

• CAMES Group Manufacturing Process includes:

  • Mixing.

  • Compacting.

  • Sintering.

Page 7: Basic Steps of Powder Processing

1. Powder Production

2. Mixing

3. Compacting

4. Sintering: Heating in a controlled-atmosphere furnace below melting point to bond particles.

Page 8: Key Powder Characteristics

• Particle size distribution.

• Particle shape.

• Micro-structure.

• Surface condition.

• Elemental composition.

• Flowability.

Page 9: Powder Production - Atomization (Water Atomization)

• Process:

  • Molten metal flows into high-pressure water jets in a tundish.

  • Liquid breaks into fine droplets that solidify quickly.

• Characteristics:

  • Irregular shape; potential surface oxide film removed by reduction processes.

Page 10: Powder Production - Atomization (Gas Atomization)

• Similar to water atomization but uses gas (usually argon).

• Benefits over water atomization:

  • More uniform powder shape.

  • Better cleanliness, avoids atmosphere reactions.

Page 11: Disadvantages of Atomization

• Refractory nozzle can introduce particles into the stream.

• Gas porosity risk in gas atomization.

• Irregular shape in water atomization.

Page 12: Powder Production - Reduction of Metal Oxides

• Höganäs Process:

  • Crush magnetite, mix with coke and limestone, heat to oxidize carbon.

  • After heating: 96% reduction to iron.

  • Magnetic separation and annealing to reduce carbon level.

Page 13: Disadvantages of Metal Oxide Reduction

• Slow reaction rates and incomplete reduction risks.

• Environmental impact due to byproducts.

• Limited control of particle size and complexity of operations.

Page 14: Powder Production - Pulverization

• Comminution method effective for hard/brittle metals.

• Process:

  • Tumbler ball mill, where hardened balls impact the metal.

  • Mechanisms include impact, attrition, and shear forces.

Page 15: Disadvantages of Pulverization

• Potential contamination from milling processes.

• Coldstream process as alternative to avoid oxidation.

  • Operates at below room temperature by gas expansion.

Page 16: Additional Disadvantages of Pulverization

• High energy consumption, non-uniform particle sizes, oxidation risk.

• Safety hazards from fine dust and potential contamination.

Page 17: Compacting

• Transforms bulk powder into preforms via compacting.

• Higher pressure leads to diminished voids and particle deformation.

Page 18: Compacting Methods

• Cold Compacting:

  • Axial or isostatic methods.

  • Minimal lubricant or binder needed.

• Roll Compacting:

  • Produces strips of powder-processed products.

Page 20: Hot Compacting

• Higher technique importance for specific materials (e.g., super-alloys).

• Heating achieved through direct or indirect means.

Page 21: Sintering Process

• Application of heat to compact to improve strength.

• Driven by reduction of surface energy and diffusion processes.

Page 22: Sintering Dynamics

• Surface area decreases as density increases.

• Grain boundaries disappear, impacting sintering rate.

Page 23: Sintering - Heat Cycle

• Controlled heating to remove lubricants is vital.

• Sintering at 60-80% of melting point; gradual cooling to minimize distortion.

Page 24: Design for Powder Processing

• Parts considered net shape with minimal finishing required.

• Avoid large sizes, thinner details, and sharp edges for optimal processing.