Additive Manufacturing Practice Flashcards

Types of Manufacturing

  • Four Categories of Manufacturing:
      - Additive (3D Printing): Manufacturing technique that builds parts layer by layer based on 3D model data.
      - Subtractive (Milling): Involves removing material from a solid block to create a desired shape.
      - Formative (Injection Moulding/Casting): Shaping materials by pouring them into molds and allowing them to solidify.
      - Fabrication (Assembly/Welding): Joining parts together to create a complete product.

Additive Manufacturing Overview

  • Governing Standard: ASTM F2792 governs the additive manufacturing process.

  • Definition of Additive Manufacturing: The process of joining materials to create parts from 3D model data, typically layer upon layer, in accordance with the ASTM F2792 standards.

Benefits of Additive Manufacturing

  • Light Weighting: Reduces weight in components, leading to efficiency gains.

  • Complex/Optimal Geometry: Allows for intricate designs that are difficult or impossible to attain using traditional methods.

  • Part Consolidation: Reduces the number of individual components needed, thus simplifying assembly.

  • No Tooling Required: Utilizes digital models directly without the need for special tooling.

  • Wider Range of Materials: Facilitates the use of diverse materials in manufacturing parts.

Additive vs. Subtractive Manufacturing

Additive Manufacturing (3D Printing)

  • Process: Involves creating layers of fused material to build up a final shape.

Subtractive Manufacturing (Casting)

  • Process: Involves pouring molten material into a mold that solidifies into a shape.

  • Material Compatibility: Suited for a wide range of materials, particularly those with lower melting points and viscosity.

  • Tooling Requirements: Requires the creation of molds before the process can begin.

Additive Manufacturing Workflow

Five Steps in the AM Workflow:

  1. Material Selection: Choosing the appropriate materials for the specific AM process.

  2. Laser Tolerance: Adjusting the precision of the laser settings for better accuracy.

  3. Layer Thickness: Determining the thickness of each layer, which can affect print quality and speed.

  4. Powder Quality: Ensuring high purity and appropriate properties of the powder feedstock.

  5. Other Constraints: Considering environmental and machine-related factors that impact the process.

Types of Additive Manufacturing Processes

Seven Types of Additive Manufacturing Processes:

  1. Powder Bed Fusion: Using thermal energy to fuse layers of powder material together.

  2. Material Jetting: Depositing droplets of build material using inkjet technology.

  3. Binder Jetting: Adding a bonding agent to powder materials to create parts.

  4. Material Extrusion: Dispensing material through a nozzle to build parts.

  5. Sheet Lamination: Bonding sheets of material together to form a 3D structure.

  6. Vat Photopolymerisation: Curing layers of liquid photopolymer with light to create solid parts.

  7. Directed Energy Deposition: Fusing materials through focused thermal energy as they are deposited.

Powder Bed Fusion Technology

  • Definition of Powder Bed Fusion: A process in AM where thermal energy fuses selected regions of a powder bed to create a part.

Types of Powder Bed Fusion Technologies:

  • Laser: Utilizes laser beams to melt powder particles.

  • Heat Lamp/Electron Beam: Uses heat or electrons to achieve fusion.

Specific Processes of Powder Bed Fusion:

  • For Polymers:
      - Selective Laser Sintering (SLS).
      - High Speed Sintering (HSS).

  • For Metals:
      - Laser Powder Bed Fusion (L-PBF).
      - Electron Beam Powder Bed Fusion (EB-PBF).

Internal Defects in Metal Powder Bed Fusion

Common Internal Defects:

  1. Cracking: Failure due to thermal stresses.

  2. Key Hole Porosity: Cavities formed during the melting process.

  3. Gas Porosity: Bubbles trapped within the material, often due to incorrect processing.

  4. Lack of Fusion: Insufficient bonding between layers.

  5. Roughness: Surface imperfections affecting the finish.

  6. Distortion: Warping due to thermal stresses.

  7. Delamination: Separation of layers in the final part.

  8. Balling: Formation of small spherical particles instead of a fused layer.

Health and Safety Implications in AM

Risks When Handling Metal Powder:

  1. Static Charge: Can lead to explosive mixtures.

  2. Explosion/Ignition: Risk of fire due to fine powders becoming airborne.

  3. Dust: Fine dust particles can pose inhalation risks.

  4. Inert Gases: Risks associated with shielding gases that could displace oxygen.

Mitigating Occupational Health Risks:

  • Inhalation: Risk of aggravating asthma or causing lung disease; PPE (Personal Protective Equipment) and RPE (Respiratory Protective Equipment) should be worn.

  • Entering Bloodstream: Fines particles may penetrate skin; ATEX rated PPE is essential.

  • Electrocution Risk: Static charge may lead to serious incidents; adhere to DSEAR (Dangerous Substances and Explosive Atmospheres Regulations) and COSHH (Control of Substances Hazardous to Health) practices.

  • Eye Irritation: Appropriate PPE must be worn to protect eyes.

Legislation on Hazardous Materials

  • Regulatory Framework:
      - Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR).
      - Control of Substances Hazardous to Health 2002 (COSHH).

Workplace Exposure Limits (WELs)

  • Definitions:

  1. Short Term Exposure Limits (STELs): Limits for exposure over 15 minutes.

  2. Time Weighted Average (TWAs): Limits for exposure over 8 hours.

  • Similarities: Both WELs set time frames for exposure to hazardous materials in the AM process.

5S Methodology in the Workplace

The 5S's:

  1. Sort: Eliminate unnecessary items.

  2. Set in Order: Organize tools and materials for ease of use.

  3. Shine: Keep the workplace clean.

  4. Standardise: Establish standards for processes and organization.

  5. Sustain: Maintain and review the 5S program regularly.

Benefits of Correct Tool Placement:

  • Reduces Accidents: Minimizes slips, trips, and falls.

  • Reduces Lost Equipment: Stops time wastage looking for tools.

  • Increases Productivity: Speeds up operations, leading to better profitability.

Risk Mitigation Steps

Six Steps to Mitigate Risk:

  1. Eliminate: Remove the risk completely if possible.

  2. Reduce: Minimize risk exposure.

  3. Isolate: Keep risks away from individuals.

  4. Engineering Controls: Use technology to minimize risks.

  5. PPE: Provide personal protective equipment.

  6. Discipline: Enforce safety and compliance protocols.

Requirements for a Good Additive Manufacturing Powder

Six Requirements:

  1. Particle Size: Ensures efficient powder flow and layer formation.

  2. Particle Shape: Affects packing density and flowability.

  3. Chemical Composition: Bulk and interstitial composition should meet manufacturing requirements.

  4. Contamination: Must be kept to a minimum to maintain integrity.

  5. Flowability: The powder should flow easily through machines.

  6. Density: Higher density usually leads to better processing results.

Tests for Powder Feedstock

Six Tests:

  1. Tap Density: Measure density of powder by comparing poured powder to densified powder.

  2. Hall Flow Test: Times the flow rate of powder through a funnel.

  3. Oxygen, Nitrogen, Hydrogen (ONH) Analysis: Combust powder to measure concentrations of fundamental gases.

  4. Morphology Assessment: Evaluates the shape and sphericity of powder particles.

  5. Particle Size Distribution (PSD): Assess particle size using sieves, microscopes, or laser diffraction techniques.

  6. Contamination Testing: Inspect for unwanted substances using microscopes.

Post Processing Setup Considerations

Six Factors to Consider:

  1. Trapped Powder: Ensure efficient removal post-processing to avoid defects.

  2. Trapped Supports: Design supports wisely for efficient removal.

  3. Height/Orientation: Proper part orientation influences quality.

  4. Surface Finish: Consider finishing to prevent defects.

  5. Warping/Sagging: Implement strategies to minimize distortion.

  6. Overhang: Evaluate for support needs in complex geometries.

Post Processing Stages

Six Stages of Post Processing:

  1. Build Completion: End of manufacturing process.

  2. Powder Recovery and Recycling: Collect unused powders for reuse.

  3. Thermal Post Processing: Heat treatments to stabilize parts.

  4. Baseplate Removal: Detach part from the build platform.

  5. Support Removal: Remove any support material for the part.

  6. Finishing: Final cosmetic or functional enhancements to the part.

Technologies for Baseplate and Powder Removal

Baseplate Removal Technologies:

  1. Wire EDM: Provides precision, cleaner cuts but is slower and more expensive.

  2. Bandsaw: Faster and cheaper but may need additional sanding.

Powder Removal Technologies:

  1. Manual Powder Blasting: Hands-on removal method.

  2. Automatic Powder Blasting (CNC Machine): Automated process for efficiency.

Support Removal Technologies:

  1. Manual Removal: Physically taking off supports by hand.

  2. Automated Support Removal (Hirtisation): Automated processes that facilitate support removal.

  3. Dissolvable Metal Supports: Supports that can be chemically dissolved post-processing.

Heat Treatment in Post Processing

  • Purpose of Heat Treatment:
      - Stress Relief: Prevents distortion due to thermal stresses.
      - Microstructure Development: Maintains desired grain size and phase distribution.
      - Porosity Removal: Addresses gas porosity for integrity.

  • Materials for Thermal Post Processing: Primarily metals.

Technologies of Thermal Post Processing:

  1. Hot Isostatic Pressing (HIP): Uses gas to uniformly compress parts enhances density.

  2. Aging: Forms second phases to enhance mechanical properties.

  3. Solutioning: Dissolves unwanted phases to improve characteristics, although costly.

Surface Finishing Techniques

Four Types of Surface Finishing:

  1. Polishing: Enhances surface smoothness.

  2. Blasting: Cleaning or texturing surfaces.

  3. Machining: Precision cutting to achieve tolerances.

  4. Thermal Deburring: Removes sharp edges via heat.

Five Reasons for Surface Finishing:

  1. Mechanical Properties: Improves fatigue resistance and wear.

  2. Corrosion Resistance: Protects against degradation.

  3. Coating Adhesion: Ensures substances stick to surfaces.

  4. Mating Faces: Ensures correct assembly and functionality.

  5. Aesthetics: Provides appealing visual qualities.

Finishing Techniques in AM:

  1. Mechanical: Such as machining.

  2. Thermal: Including laser processing.

  3. Electrical: Electro polishing methods.

  4. Chemical: Using chemical processes for finishing.

Inspection After Post Processing

Inspection Methods:

  • Metrology: Measurement techniques to ensure dimensions are within specifications.

  • Non-Destructive Testing (NDT): Techniques like blue light filters, dye penetrant testing, ultrasound, and X-ray computed tomography (XCT) to evaluate part integrity without causing damage.

  • Destructive Testing: Required to gather data on mechanical properties and microstructural analysis post-production.

Common External Defects in AM Products:

  1. Porosity: Presence of voids reduces mechanical integrity.

  2. Cracking: Unsuitable processing may lead to fractures.

  3. Insufficient Layer Fusion: Poor bonding can result in weak parts.

  4. Unconsolidated Material: Areas of incomplete fusion.

  5. Geometrical Distortion and Inaccuracy: Deviations from designed specifications.

  6. Discoloration: Alteration in material color due to processing.

  7. Contamination: Inclusion of foreign materials or gas during manufacture.

Inspection Methods for AM Products:

  1. Dimensional Metrology: Evaluating measurements against specification.

  2. Non-Destructive Testing: Methods that assess condition without damage.

  3. Destructive Testing: Identifying defects by breaking down components.

  4. Surface Metrology: Evaluating surface characteristics.

Challenges Associated with AM Inspection

Four Challenges:

  1. Geometrical Complexity: Difficulty in assessing complex shapes.

  2. Surface Roughness: Challenges in achieving desired finishes.

  3. Defects of Complex Morphologies: Identifying flaws within multipart structures.

  4. No Intermediate Stage for Inspection: Limited opportunities for quality checks during buildup.

Unique Inspection Capability:

  • Non-Destructive Testing - XCT: Exclusively capable of measuring internal dimensions of AM products.