Week 9: Metal AM Quiz
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What is a key characteristic of a eutectic alloy?

  • It forms a solid solution at all temperatures.
  • It has a melting point lower than one or more of the individual metals. (correct)
  • It remains solid at the eutectic melting temperature.
  • It has a melting point higher than that of its components.

    • Anchorless Metal Additive Manufacturing involves a heated powder bed.

    False

    What advantage does lower melting point provide in the processing of alloys?

    It allows the material to remain in a liquid or mushy state for easier processing.

    In Anchorless Selective Laser Melting, the bed temperature is held at temperature ___.

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

    Match the following terms with their descriptions:

    <p>Eutectic Alloy = Alloy with a lower melting point than its components Anchorless Metal Additive Manufacturing = Method without a heated powder bed Selective Laser Melting = Process involving laser melting of metals Residual Stress = Stress remaining in a material after processing</p> Signup and view all the answers

    What is the eutectic solidification temperature for the Si 12% weight percentage?

    <p>577ºC</p> Signup and view all the answers

    The cooling rate does not affect the resultant microstructure in selective laser melting.

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

    What effect does strategic placement of heat jackets have on mechanical performance in selective laser melting?

    <p>It can modify mechanical performance.</p> Signup and view all the answers

    In selective laser melting, rapid melting and cooling of material leads to a ________ microstructure.

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

    Match the following terms related to microstructural customization in selective laser melting:

    <p>Eutectic solidification temperature = 577ºC Heat jackets = Residual stress reduction X axis = Horizontal direction in process Z axis = Vertical direction in process</p> Signup and view all the answers

    Which additive manufacturing technique is most widely used for producing metal parts?

    <p>Powder Bed Fusion</p> Signup and view all the answers

    Laser powder bed fusion can only produce low-density parts.

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

    What is one major influence on the final properties of a part in additive manufacturing?

    <p>Material and process parameters</p> Signup and view all the answers

    Post-processing operations may include removal of excess powder and ________.

    <p>thermal processing</p> Signup and view all the answers

    Match the following post-processing operations with their purposes:

    <p>Removal of excess powder = Cleaning parts Thermal processing = Improving mechanical properties Support removal = Separating parts from platforms Surface finishing operations = Enhancing surface quality</p> Signup and view all the answers

    What are the thermal energy sources commonly used in the Powder Bed Fusion process?

    <p>Laser or electron beam</p> Signup and view all the answers

    Microstructural customization is not possible with additive manufacturing techniques.

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

    Name one post-processing method that helps reduce pores in 3D printed metal parts.

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

    What happens when the liquid metal’s contact angle increases due to an oxide film?

    <p>The liquid will undergo balling</p> Signup and view all the answers

    Oxidation only occurs when the metal is heated above its melting point.

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

    What is the effect of surface tension on liquid behavior during balling?

    <p>Surface tension causes the liquid to break up into smaller entities to minimize it.</p> Signup and view all the answers

    The presence of an oxide layer makes it difficult to process _____ during melting.

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

    Match the following concepts with their descriptions:

    <p>Oxidation = Combining an element with Oxygen Capillary instabilities = Fluid breakup to reduce surface tension Melt Pool = Transient state during material processing Inert environment = Atmosphere preventing oxidation</p> Signup and view all the answers

    Which of the following factors affects the melt pool's stability?

    <p>Length to Diameter ratio</p> Signup and view all the answers

    A high-density part produced by LPBF can exceed the properties of cast metals.

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

    At what temperature does Zinc melt?

    <p>420°C</p> Signup and view all the answers

    Bismuth melts at a temperature higher than 300°C.

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

    When the laser interacts with vapor, it can create a _____ plume.

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

    What is the eutectic material composition mentioned in the content?

    <p>Bi3Zn</p> Signup and view all the answers

    Steel failed within _____ layers during the selective laser melting process.

    <p>10</p> Signup and view all the answers

    Match the following materials with their melting points:

    <p>Zinc = 420°C Bismuth = 270°C Aluminum = 660°C Silicon = 1414°C</p> Signup and view all the answers

    What allows large flat geometries to be built without supports?

    <p>Eutectic material composition</p> Signup and view all the answers

    Eutectic formation occurs with aluminum at 88% weight.

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

    What was the pre-heating temperature used in the successful build?

    <p>250°C</p> Signup and view all the answers

    What is a corrective measure for lack of fusion porosity?

    <p>Overcome with correct energy density</p> Signup and view all the answers

    Gas occluded porosity leads to irregularly shaped pores.

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

    What are two types of porosity in LPBF mentioned in the content?

    <p>Lack of fusion porosity and gas occluded porosity</p> Signup and view all the answers

    Supports are required in metal additive manufacturing due to __________ during rapid heating and cooling.

    <p>thermal warpage</p> Signup and view all the answers

    Match the types of porosity with their corrective measures:

    <p>Lack of fusion porosity = Overcome with correct energy density Gas occluded porosity = Allow more time for gas to escape Pores within powder = Improve quality of powder Solidification cracking = Reduce thermal gradient</p> Signup and view all the answers

    Which material is mentioned as having support anchors removed within the Selective Laser Process?

    <p>Ti6Al4V</p> Signup and view all the answers

    Post-processing costs are incurred due to the removal of support structures.

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

    What can be modified to reduce solidification cracking?

    <p>Modify material composition to increase lattice stress</p> Signup and view all the answers

    The overhang length suitable for test part design ranges from __________.

    <p>1mm-15mm</p> Signup and view all the answers

    The requirement for support structures limits which of the following?

    <p>Geometric freedom</p> Signup and view all the answers

    What is a defining characteristic of eutectic alloys?

    <p>They solidify at a single melting point.</p> Signup and view all the answers

    Anchorless Metal Additive Manufacturing utilizes a heated powder bed.

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

    What occurs at the eutectic melting point?

    <p>The mixture of materials A and B melts at a lower temperature than their individual melting points.</p> Signup and view all the answers

    In the process of traditional metal additive manufacturing, the bed temperature is held constant at ___ degrees.

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

    Match the metals with their melting points:

    <p>Material A = Lower melting point than the alloy Material B = Higher melting point than the alloy Eutectic alloy = Solidifies at a specific temperature Polymer-like state = Occurs during adequate pre-heating</p> Signup and view all the answers

    What causes liquid metals to exhibit poor wetting on a solid?

    <p>Presence of an oxide film</p> Signup and view all the answers

    Oxidation occurs when a metal's surface is exposed to air.

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

    What is the primary effect of variation in surface tension during melting?

    <p>Instability in the melt pool</p> Signup and view all the answers

    The process of oxidation potential increases with ________.

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

    Match the following factors with their impact on melt pool stability:

    <p>Surface tension variation = Induces instability Length to Diameter ratio = Should be minimized Oxide layer presence = Inhibits melting Temperature increases = Increases oxidation potential</p> Signup and view all the answers

    What phenomenon occurs when the liquid metal breaks into smaller entities?

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

    Laser processing can initiate melting without breaking the oxide layer first.

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

    What is generated when the laser interacts with vapor during the melting process?

    <p>Plasma plume</p> Signup and view all the answers

    What is the eutectic solidification temperature for 12% Si?

    <p>577°C</p> Signup and view all the answers

    The placement of heat jackets cannot modify the mechanical performance in selective laser melting.

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

    What effect does rapid melting and cooling have on the microstructure in selective laser melting?

    <p>Fine and uniform microstructure</p> Signup and view all the answers

    Residual stress in selective laser melting can be reduced using __________.

    <p>heat jackets</p> Signup and view all the answers

    Match the following materials with their respective melting points:

    <p>Aluminum = 660.45°C Silicon = 577°C Zinc = 419.5°C Bismuth = 156.6°C</p> Signup and view all the answers

    Which of the following best describes Powder Bed Fusion (PBF)?

    <p>A process using thermal energy, typically laser or electron beam</p> Signup and view all the answers

    Post-processing operations are unnecessary for parts made with Powder Bed Fusion.

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

    What is one major benefit of using metal additive manufacturing with regards to part properties?

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

    In additive manufacturing, proper control of the _____ is vital for achieving the desired microstructure.

    <p>process parameters</p> Signup and view all the answers

    Match the post-processing operations with their purposes:

    <p>Removal of excess powder = Ensures part functionality Thermal processing = Improves mechanical properties Support removal = Facilitates part detachment from the platform Surface finishing operations = Enhances surface quality</p> Signup and view all the answers

    What is a common source of thermal energy in the Powder Bed Fusion process?

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

    Which process can help reduce pores in 3D printed metal parts?

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

    What is the solidification temperature of the eutectic formed by bismuth and zinc?

    <p>254°C</p> Signup and view all the answers

    The melting point of Bismuth is lower than that of Zinc.

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

    What is formed when bismuth and zinc are mixed at the correct proportions?

    <p>Eutectic alloy</p> Signup and view all the answers

    The melting point of zinc is _____°C.

    <p>420</p> Signup and view all the answers

    Match the following alloys with their melting characteristics:

    <p>Bismuth = Melts at 271°C Zinc = Melts at 420°C Eutectic Alloy (Bi/Zn) = Solidifies at 254°C Eutectic Composition = Bi 97% Wt., Zn 3% Wt.</p> Signup and view all the answers

    Which phase remains semi-liquid when cooling but does not fully solidify?

    <p>Eutectic alloy</p> Signup and view all the answers

    Liquid metal's contact angle has no effect on its flow behavior during melting.

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

    What is the purpose of maintaining a bed temperature during the selective laser melting process?

    <p>To stabilize the melt pool</p> Signup and view all the answers

    How many layers failed during the selective laser melting process with steel?

    <p>10 layers</p> Signup and view all the answers

    The eutectic composition in the content allows geometries to be built without __________.

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

    Which of the following materials forms a eutectic at 88% weight in aluminum?

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

    Large flat geometries are notoriously difficult to build without __________.

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

    Study Notes

    Additive Manufacturing - MEC454

    • Metal Additive Manufacturing - Laser Powder Bed Advanced Topics, November 25th-26th 2024, taught by Prof Kamran Mumtaz.

    Overview

    • 1) Brief Metals Recap: This section will cover a brief review of metals.
    • 2) Melt Pool Dynamics, Heat Flow & Defects: This section will cover the dynamics of the melt pool, heat flow, and resulting defects.
    • 3) Residual Stresses & Support Structures: This section will focus on residual stresses and support structures used in the manufacturing process.
    • 4) Microstructural Customisation: This section will explore how to customize the microstructure of the final product.
    • 5) Multi-material: This will cover multi-material printing.
    • 6) Productivity increase: Improved manufacturing speed will be discussed.

    Part 1 of 6: Brief Metals Recap

    • This section will cover a fundamental review of metal properties.

    Metal AM Techniques

    • Powder Bed Fusion: A process using thermal energy (laser or electron beam) to fuse metal powders layer by layer. It produces high-density, functional parts in a single step, with excellent mechanical properties and a wide range of materials.
    • Powder/Wire Feed: Laser-based process that melts wire feedstock and deposits it to build a component.
    • Sheet Lamination: Method for creating products by layering and bonding sheets.
    • Binder Jetting: A technique using an inkjet print head to deposit a liquid binder onto a bed of powder, then selectively fusing the powder particles.
    • Other: Alternative techniques.

    PBF - Post-processing

    • Removal of excess powder: Using techniques like tapping, compressed air, and ultrasonic methods.
    • Thermal processing: Relieves stress and improves mechanical properties, including treatments to reduce pores and heal microcracks (e.g., furnace cycles or HIPING).
    • Support removal: Often involves wire-EDM, band saws, or hand-finishing to remove support structures.
    • Surface finishing: Operations like machining, shot-peening, tumbling, hand-benching, electro-polishing, and abrasive flow machining. Micro-machining (for fine features) and chemical reactions may also occur.

    Process Control

    • Material: Controlling material properties like morphology, particle size distribution, and layer thickness.
    • Process parameters: Adjusting scanning speed, hatch distance, exposure time/dwell, thermal energy (power), and spot size.
    • Environment: Monitoring inert gas/vacuum conditions and pressure.

    Part 2 of 6: Melt Pool Dynamics, Heat Flow, Defects

    • This focuses on the complex processes occurring during the laser melting stages.

    LPBF - Lasers

    • Materials are melted by absorbing laser energy.
    • Typically fibre lasers are used.
    • Lasers are versatile, accurate, and have a high energy density.

    LPBF - Heat Transfer

    • Portion of laser energy is reflected, absorbed, and transmitted by the material (transmission is generally negligible).
    • Materials with high reflectance (aluminum, copper) are difficult to process.
    • Surface roughness and oxides influence material reflectance.
    • Material absorbance increases with temperature.

    LPBF - Thermal Conductivity & Melt Energy

    • Energy is transformed to heat and flows by conduction, affecting particle contacts.
    • High thermal conductivity of some metals (like aluminium and copper) creates large melt pools, making control of part resolution more challenging.

    LPBF - Energy Loss

    • Heat loss is important after melt pool formation.
    • Magnesium is hard to process due to close melt/vaporization temperatures.
    • Energy losses include reflection, transmission, thermal diffusion, radiation from the melt pool, and vaporization losses.

    LPBF - Melt pool

    • The melt pool is complex, with many interacting factors like vaporization, heat radiation/convection/conduction, recoil pressure, and gravity influencing the formation, shape, and stability.

    LPBF - Thermo-capillary Flows

    • Non-uniform heating creates surface tension variations inducing fluid motion.
    • Marangoni convection dominates the melt flow, affecting the melt pool topology.
    • Surface tension decreases with increasing temperature (in pure liquid metals).

    LPBF - Melt Pool Dynamics

    • Wettability/wetting affects interlayer connection (porosity and strength).
    • Surface free energies (liquid-vapour, solid-vapour, and solid-liquid) strongly influence wetting and, in turn, part quality.
    • Oxide-film on metals often leads to poor wetting.

    Capillary instabilities

    • Liquid breakup reduces surface tension, this varies with temperature & uneven heat distribution.
    • To reduce these instabilities, the length/diameter ratio of the melt pool should be kept small.

    Melt Pool Ejection and Recoil Pressures

    • Laser interaction with the vaporized material creates plasma plumes, causing shockwaves and pushing melt out of the pool due to recoil pressure.

    Oxidation

    • Oxidation is combining an element with oxygen; a metal's surface is continually oxidized when exposed to air.
    • Metal powders have larger surface areas leading to faster oxidation.
    • Aluminum forms very thick oxide layers, making processing more difficult (the laser must break down the oxides before melting).
    • Oxidation potential increases with temperature, impacting processes needing an inert environment.

    LPBF - Part Properties

    • Complete melting produces parts at full density which allows for matching/exceeding the properties of cast and wrought approaches.
    • Lower than full density compromises fracture toughness and fatigue properties, potentially leading to premature failure.
    • The properties of toughness and fatigue are critical for aerospace industry applications, and similar implants.

    LPBF - Porosity and Cracks

    • Lack of fusion porosity involves irregular-shaped pores. Correct energy density in the system overcomes these defects.
    • Gas occluded porosity is spherical and can be corrected by allowing more time for gas to escape.
    • Pores within the powder are also typically spherical and can be addressed with improved powder quality.
    • Solidification cracking is due to thermal gradients and rapid solidification causing uneven expansion/contraction of the material, and is addressed with corrective measures to reduce thermal gradients or modify material compositions to increase lattice stress.
    • Controlling these defects is crucial for obtaining a high-quality 3D printed part.

    Part 3 of 6: Residual Stresses and Support Structures

    • Metals expand on heating, contract on cooling.
    • Uneven cooling can lead to distortion (and witness marks) requiring mitigation.
    • Standard practices include heat treatment to dissipate stresses.

    Stresses

    • Stresses and Metal Processing: Most metals expand on heating and shrink when cooled. Controlled cooling is needed to avoid distortions and witness marks in the manufactured parts. Mitigation/management systems are used for manufacturing good-quality parts.
    • Background: Massive internal tensile stresses are generated during in-built materials processing which causes these stresses to dissipate; the geometry shows the result of cutting the material in the as-built condition, without heat treatment.
    • Effects of Residual Stress: Includes part distortion, plate distortion, cracking (with or without applied load), and decreased mechanical properties (visible only when tested).

    ALM specific quality challenges

    • Distortion can occur in parts with rapid cross-sectional changes.

    Cross section change distortion

    • Peripheral steps or witness marks are commonly formed due to the non-uniform shrinking of the molten portion.
    • Solidified areas tend to shrink proportionally to their lateral spans.
    • Alternative geometries can exacerbate the distortion effects.
    • The effect is considered when larger cross-sections form/bridge smaller ones during builds—smaller regions will shrink more than the larger regions.
    • This phenomenon is consistent across similar geometries, though visual examples may show more or less significant distortion effects.

    Support Structures

    • Thermal warpage caused by rapid heating/cooling and large thermal variations may occur, necessitating supports/anchors, which limit geometric freedom and increase post-processing, cost, time, etc.
    • Supports are also needed for parts that cannot be easily stacked.
    • (Polymers vs metal-based SLM methods)

    Overhang length

    • The length of overhangs can range from 1mm to 15mm.

    Warp Measurement

    • Measuring warp height (open and closed end) and warp length.

    EBM Overhang and Effect of Thickness

    • The influence of thickness on overhang capability (measured by the height of warping) is discussed.

    LPBF Overhang

    • The influence of bed temperature on warping is presented across different thicknesses of the overhang.

    How to eliminate supports?

    • In conventional processes, reducing thermal gradients in powder beds and enhancing knowledge of processing parameters help reduce residual stress.
    • A novel approach of the Anchorless Metal Additive Manufacturing method is discussed; this is an approach to eliminate the need for supports in the build.

    Anchorless Selective Laser Melting

    • Certain combinations of metals form eutectic alloys with low melting points, allowing for liquid/mushy states that enable easier manufacturing strategies. This specific method will be a discussion point.

    ASLM

    • The method involves heating powder beds.
    • The laser melts the metals together, and the mixture is held at the temperature until full solidification, enabling better part geometries without needing anchors/supports.

    Oxidation

    • The combination of an element with oxygen.
    • Metal surfaces continuously oxidize when exposed to air.
    • Powders have a large surface area, resulting in quicker oxidation.
    • Aluminum forms a thick oxide layer, making processing difficult (laser must break down the oxides before melting).
    • Oxidation risk rises with temperature.

    Additional topics discussed in the presentation include:

    • Microstructural customisation - controlling microstructural characteristics through varied processing parameters to manufacture custom structures,

    • Multi-material integration - different materials can be incorporated in the printing process to achieve desired design and properties.

    • Productivity improvements—including the use of more lasers or other technological advancements to increase the process speed.

    ###General Summary of the Presentation Session

    • The overall presentation session dives into the detailed mechanics of laser powder bed fusion (LPBF), along with advanced approaches and techniques.
    • It explores different variables and techniques for designing, processing, controlling, and optimizing the manufacturing process itself.
    • Various troubleshooting solutions are also provided.
    • The session ultimately aims to equip students with the knowledge to perform highly-skilled additive manufacturing processes.

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    Metal Additive Manufacturing - MEC454 PDF

    Description

    Test your knowledge on the characteristics and processing of eutectic alloys in additive manufacturing. This quiz covers key concepts such as selective laser melting, microstructure, and the effects of temperature on metal properties. Perfect for students and professionals in materials science and engineering.

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