Week 8: Polymer AM
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Questions and Answers

What is the average particle size of Nylon-12?

  • 90 microns
  • 10 microns
  • 75 microns
  • 50 microns (correct)

    • Larger particles lead to better surface finish and higher density.

    False (B)

    What effect can very fine particles have in a powder bed?

    They can aid flow.

    Average particle size of Nylon-12 is approximately __________ microns.

    <p>50</p> Signup and view all the answers

    Match the following particle sizes with their effects:

    <p>Larger particles = Poorer surface finish Smaller particles = Static electricity issues Very fine particles = Aid in flow Range of particles = Assist in packing density</p> Signup and view all the answers

    What is a consequence of powder agglomeration during the build process?

    <p>Problems with deposition on the build area (C)</p> Signup and view all the answers

    Moisture absorption has no impact on the need for drying before a build.

    <p>False (B)</p> Signup and view all the answers

    What effect can an excess of filler have on material properties?

    <p>It can cause a decrease in properties.</p> Signup and view all the answers

    In gravity-fed systems, 'bridging' occurs when powder will not flow from the ______.

    <p>chute</p> Signup and view all the answers

    Match the following powder issues with their descriptions:

    <p>Static build-up = Caused often by sieving and can affect flow Moisture absorption = May require drying to reduce excess moisture Bridging = Prevents powder flow from a chute Homogeneity of mixing = Difficulty in maintaining a good distribution of filler</p> Signup and view all the answers

    What is the primary benefit of using virgin material in laser sintering?

    <p>Greater repeatability (D)</p> Signup and view all the answers

    Recycled material always yields superior mechanical properties compared to virgin material.

    <p>False (B)</p> Signup and view all the answers

    What negative effect can occur with excessive recycling of materials in laser sintering?

    <p>Orange peel effect</p> Signup and view all the answers

    Thermal conditioning can be used to improve __________.

    <p>elongation at break</p> Signup and view all the answers

    Match the terms related to selective laser sintering with their correct definitions:

    <p>Thermal conditioning = A process to improve elongation at break Recycled material = Materials reused to reduce costs Virgin material = Unused materials that provide greater repeatability Build orientation = The placement of parts during construction affecting anisotropy</p> Signup and view all the answers

    How does build orientation affect parts produced in laser sintering?

    <p>It can produce anisotropy in materials. (B)</p> Signup and view all the answers

    Anisotropy is less of an issue in laser sintering compared to FDM processes.

    <p>True (A)</p> Signup and view all the answers

    What is one method to improve elongation at break in materials used for laser sintering?

    <p>Thermal conditioning</p> Signup and view all the answers

    What is the key factor that affects the mechanical properties of laser-sintered nylon?

    <p>Volumetric Energy Density (C)</p> Signup and view all the answers

    Post-processing techniques can enhance the mechanical properties of parts created through laser sintering.

    <p>True (A)</p> Signup and view all the answers

    What must be done before removing parts from the printer after a build?

    <p>Parts must be allowed to cool below the glass transition temperature (Tg).</p> Signup and view all the answers

    Infiltration can lead to increases in __________ but adds time, cost, and complexity to the production process.

    <p>mechanical properties</p> Signup and view all the answers

    Match the post-processing techniques to their unwanted effects:

    <p>Bead-blasting = Rounding of corners Heating = Part warpage Cooling = Discoloration Infiltration = Cost increase</p> Signup and view all the answers

    Which of the following describes the simplest definition of laser sintering?

    <p>To zap powder with a laser and melt it (A)</p> Signup and view all the answers

    Leaving heaters and nitrogen on is an essential end-of-build action for Duraform EX.

    <p>True (A)</p> Signup and view all the answers

    What is one factor that might vary between different additive manufacturing processes?

    <p>Energy input method</p> Signup and view all the answers

    What does Melt Flow Indexing measure?

    <p>Material viscosity (A)</p> Signup and view all the answers

    Differential Scanning Calorimetry (DSC) measures the heat flow difference between a sample and a known reference.

    <p>True (A)</p> Signup and view all the answers

    What key thermal properties can be measured using Differential Scanning Calorimetry (DSC)?

    <p>Temperatures</p> Signup and view all the answers

    In Melt Flow Indexing, a high melt flow rate indicates a low ________ and a low molecular weight.

    <p>viscosity</p> Signup and view all the answers

    Match the following characterization methods with their primary function:

    <p>Differential Scanning Calorimetry (DSC) = Heat flow measurement Melt Flow Indexing (MFI) = Viscosity measurement Hot Stage Microscopy (HSM) = Investigate particle flow behavior Particle Size Analysis (PSA) = Analyze particle size and shape</p> Signup and view all the answers

    Which technique is known for being accurate but expensive in the analysis of particle size?

    <p>Laser Diffraction (C)</p> Signup and view all the answers

    Thermo-gravimetric Analysis measures the mass of a sample at a single temperature.

    <p>False (B)</p> Signup and view all the answers

    What type of microscopy is used in Hot Stage Microscopy?

    <p>Standard microscopy</p> Signup and view all the answers

    The technique used to analyze the flow behavior of particles, particularly the temperature at which necking begins, is called ________.

    <p>Hot Stage Microscopy</p> Signup and view all the answers

    Which method is typically characterized as slow and inaccurate for particle size analysis?

    <p>Sieving (B)</p> Signup and view all the answers

    What is the effect on Young’s Modulus when the percentage of glass in Duraform GF increases from 0% to 50%?

    <p>It increases by 157%. (D)</p> Signup and view all the answers

    Inclusion of a filler in materials does not affect their mechanical properties.

    <p>False (B)</p> Signup and view all the answers

    What is the effect on elongation at break when the percentage of glass increases from 0% to 50%?

    <p>It decreases by 84%.</p> Signup and view all the answers

    Co-extrusion followed by grinding can offer some improvements but can affect ______ shape.

    <p>particle</p> Signup and view all the answers

    Match the following properties with their changes due to increased glass percentage:

    <p>Young's Modulus = Increases by 157% Elongation at Break = Decreases by 84% Melt Flow Rate = Decreases over successive builds Molecular Weight = Increases over successive builds</p> Signup and view all the answers

    What is one health and safety consideration mentioned in relation to nano-materials?

    <p>They require special handling protocols. (C)</p> Signup and view all the answers

    The thermal history of materials does not influence their molecular weight.

    <p>False (B)</p> Signup and view all the answers

    What is the main material being sintered in the production of Duraform GF?

    <p>Nylon-12</p> Signup and view all the answers

    The resultant parts of Duraform GF are a composite of glass beads surrounded by ______.

    <p>Nylon-12</p> Signup and view all the answers

    What happens to the melt flow rate (MFR) over successive builds?

    <p>It decreases. (B)</p> Signup and view all the answers

    Co-extrusion does not provide any improvements to the process.

    <p>False (B)</p> Signup and view all the answers

    By what percentage does Young’s Modulus increase with 50% glass?

    <p>157%</p> Signup and view all the answers

    Any un-sintered material has been in a heated bed for a substantial amount of time, affecting its ______ weight.

    <p>molecular</p> Signup and view all the answers

    Match the percentage of glass with the corresponding elongation effect:

    <p>0% = 9% 50% = 1.5% 30% = 3% 10% = 6%</p> Signup and view all the answers

    Study Notes

    Additive Manufacturing - Principles and Applications

    • This course covers advanced understanding of polymer laser sintering.
    • The course will cover recapping laser sintering, factors affecting part properties (pre-process, in-process, and post-process), scientific understanding of the process, material requirements, structure of final parts, and characterisation techniques.
    • These sessions cannot cover everything; literature searches are recommended for a deeper understanding of the topic.

    Re-cap of Laser Sintering

    • Parts are built by selectively scanning and sintering cross-sections of powdered material.
    • The process involves powder supply, a powder bed, scanning mirrors, and a laser.
    • A diagram illustrates the process.

    Why are we interested?

    • Laser sintering enables complex designs without support structures (polymers).
    • Parts can be assembled in one build step.
    • Post-processing requirements are minimized.
    • The process is time-saving.
    • Down-facing surfaces have better surface finishes.
    • Parts can have relatively high mechanical properties and stability.
    • There's a full build volume.

    Factors affecting part properties

    • Pre-process factors: material choice (type and morphology), fillers (type and level), and thermal history.
    • In-process factors: build orientation and part bed temperature.
    • Post-process factors: finishing methods.

    Material choice

    • Traditionally, Nylon-12 is common, including fillers.
    • Elastomers, PEEK, and polypropylene are also used.
    • Choosing the right material is crucial for the desired properties of the part.
    • Consider the application and the required properties of the part when selecting material.
    • The properties might differ in comparison to injection molding.
    • Some materials exhibit more susceptibility to in-process variations.

    Morphology

    • Powder deposition is critical.
    • Issues to consider include low density, poor accuracy/surface finish, over-exposure of part areas, particle size, particle shape, and powder agglomeration.
    • Particle size and distribution: Size and distribution affect powder packing and porosity. Average particle size (Nylon-12) is ~50 microns, with a range from ~10-90 microns. Larger particles result in poorer surface finish and lower density, while smaller particles could be susceptible to static, leading to poor deposition. Small particles are susceptible to nitrogen flow within the chamber (affected are the laser window; larger particles less so).
    • A range of particles can assist with denser part beds and higher mechanical properties.
    • Fine particles may aid the flow. Shape varies, with grinding sometimes leading to 'cornflakes' (illustrated). Smooth, spherical shapes are usually preferred.

    Powder agglomeration

    • Powder can clump together before or during the build process.
    • Static build-up, often arising from sieving, can be an issue.
    • Additives help flow but impact properties.
    • Moisture absorption can occur.
    • Drying may be needed to reduce issues.
    • How much drying is affected by the material type.

    Fillers

    • Fillers impact mechanical properties, often with compromise.
    • Excess filler reduces properties (ratio matters).
    • Homogeneity of mixing is important.
    • Mixing is simple but maintaining good distribution is difficult.
    • Complex mixing methods (e.g., co-extrusion followed by grinding) offer improvements but can affect particle shape.
    • Inclusion impacts resultant properties (e.g., glass beads in Duraform GF).
    • Build parameters for filled materials are often similar to standards. The resultant part is a composite of filler surrounded by the base material.
    • Young's Modulus increases with glass content (e.g., by 157% between 0 and 50%).
    • Elongation at Break decreases with glass content (e.g., by 84% between 0 and 50%).

    Thermal history

    • Laser sintering is a thermal process.
    • Unsintered materials are in a heated bed for a long time, affecting molecular weight.
    • A decrease in melt flow rate and an increase in molecular weight occur over successive builds.
    • Virgin and recycled materials are often combined to reduce cost, but virgin provides greater repeatability, and recycled can give increased properties (notably in elongation at break).
    • Thermal conditioning can be used to improve elongation at break.
    • Orange peel surface is a concern post material re-use.

    In-process Factors

    • Build orientation affects anisotropy, although less so than some other processes (e.g., FDM).
    • Different orientations may produce differing mechanical properties.
    • The discussion involves planning for this influence during real-life applications.
      • Build orientation affects mechanical properties (e.g., X, Y, and Z axes have different values for tensile strength, flexural strength, and compressive strength).
      • Part bed temperature: pre-heating of the build area is important, but uneven temperature distributions exist.
      • Edge temperatures often remain cool.
      • System upgrades can mitigate these issues.
      • Uneven part bed temperatures affect density, potentially decreasing it, in part bed temperature of 178°C (at identical energy density), which differs by roughly 4%.

    Processing parameters

    • Energy density is defined as Laser Power/(Scan Spacing x Laser Scan speed).
    • It highlights energy input, but does not consider part bed temperature or layer thickness.
    • Higher ED can lead to increased ductility.
    • In some materials, scan speed affects properties differently from laser power.
    • Volumetric energy density is just beyond the energy needed to fully melt a layer of material to achieve the best properties possible.

    Characterisation methods

    • Techniques assess materials and parts, including: DSC, MFI, HSM, PSA, and TGA.
    • For example, DSC is a thermal analysis technique to measure heat flow differences between a sample and a known reference, relating to time and temperature.
    • Different samples are used to determine necessary energy input.
    • MFI is used to measure material viscosity, observing the amount of material that flows through a specific-size orifice under load in a given time. High melt flow rates correspond to low viscosities and low molecular weights.
    • HSM is a microscopy technique applied to a heated base (with variations), to measure particle flow behavior (e.g., temperature at necking, agglomeration time).
    • PSA assesses particle size and shape (e.g., sieving, optical microscopy, and laser diffraction).
    • TGA measures sample mass at various temperatures, providing insights into physical or chemical changes (e.g., oxidation, vaporisation).
    • Other techniques such as tensile and compression testing, and surface profilometry are also used.

    Scientific understanding

    • Laser sintering involves melting powder using a laser.
    • In reality, several factors are more complex.

    Material requirements

    • The majority of laser sintering materials are based on Nylon-12.
    • Nylon-12 is suited well since there is a large window between material melt and crystallisation temperatures.
    • Bed temperature must stay in a molten state for uniform stress distribution during cooling.
    • A narrow melt range allows higher bed temperatures.
    • Other (amorphous polymers) and elastomer materials have lower mechanical but good dimensional properties.

    Sintering behavior

    • Several models predict sintering and related mechanical properties.
    • The Frenkel model offers a suitable approach to many aspects.
    • Viscosity is a key parameter, but the model's complexity is a consideration.
    • Surface tension and temperature dependency also matter but are challenging to assess accurately for powders.

    Structure of parts

    • Parts have regions with varying melting proportions.
    • Some particles are fully melted, crystallised, or have un-melted cores.
    • Partial melting occurs due to insufficient energy input, differing with particle size.

    Other techniques

    • Factors in different processes (e.g., High Speed Sintering), such as energy input methods, may vary as will the presence of ink for some methods.
    • Analysis of techniques used in other areas of additive manufacturing is recommended.

    Content

    • The material, sintering behavior, structure of parts, and characterisation methods are key course topics.

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    Additive Manufacturing – principles and applications PDF

    Description

    Test your knowledge on the properties of Nylon-12 and the effects of particle size in powder bed processes. This quiz covers key concepts in additive manufacturing related to material behaviors, agglomeration, and the use of virgin versus recycled materials. Perfect for students studying materials science or engineering technology.

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