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AM Sem 1
| Question | Answer |
|---|---|
| Name 7 Types of AM | SLS, Sheet Lamination, Material Extrusion, Binder Jetting, Powder Bed Fusion, Material Jetting, Directed Energy Deposition |
| Name the pros, cons and materials used for binder jetting | Pros : Full colour parts, no supports required, high print speed Cons: Post processing required, surface quality compromised at high speeds Materials: Thermoplastics, composites |
| Name the pros, cons, materials for Directed Energy Deposition | Pros: High quality, large build volume, excellent for repairing existing parts Cons: Post processing required Materials: Metals |
| Name the pros, cons and materials for Material Extrusion | Pros: Widely used, inexpensive, clear parts can be manufactured Cons: Vertical anisotropy, fine details not possible Materials: Thermoplastics, composites |
| Name the pros, cons and materials for Sheet Lamination | Pros: High speed, low cost, ease of material handling Cons: Strength and integrity depends on material, limited material choices, post processing required Materials: Thermoplastics, ceramics, metals |
| Name the pros, cons and materials for Powder Bed Fusion | Pros: High quality, high material properties, fully dense parts Cons: Monochrome, post processing required, high power requirements Materials: Metals, ceramics, composites, thermoplastics |
| Name the pros, cons and materials for Vat Polymerisation | Pros: Large parts, high accuracy, detailed parts, good surface finish Cons: Limited to photopolymers, expensive, slow, monochrome Materials: photocurable polymers |
| Name the pros, cons and materials for Material Jetting | Pros: High accuracy, low waste, multi materials/colours, soluble supports Cons: Expensive, poor mechanical properties Materials: Photocurable resins, ceramics, composites |
| What is Topological optimisation? | A design process which optimises performance goals. For example to achieve high mechanical properties with low weight. |
| Describe Additive Manufacturing | The addition of material layer by layer to build a part using materials such as polymers, resins, filaments and metallic powders. Each layer is a thin cross section derived from CAD data. |
| Describe Subtractive Manufacturing | The removal of material from an initial workpiece using rotating tools to create a finished part. Rotating milling tools for shaping parts and turning tools for rotational features on parts. |
| Identify some pros to Additive Manufacturing | Net shape manufacturing or near net shape Complex geometries can be created Reduced need for assembly Minimal material waste Optimal buy to fly ratio Topological optimisation |
| Identify some cons to Additive Manufacturing | Poor surface quality (eg stair stepping) Component size limited by chamber size Defects often occur such as delamination, warping, stringing or cracks from residual stress Process often slow as executed layer by layer |
| Identify some pros to Subtractive Manufacturing | High surface finish High dimensional accuracy Large range of compatible materials No noticeable size limitations |
| Identify some cons to Subtractive Manufacturing | Low buy to fly ratio High material waste Often requires assembly of multiple parts Geometry limitations due to tool accessibility Costs induced by tool wear Less customisable |
| Explain the AM Process, Binder Jetting | A liquid bounding agent is selectively deposited to join powder materials. |
| Explain the AM Process, Directed Energy Deposition | Focused thermal energy is used to fuse materials by melting as soon as they are being deposited. |
| Explain the AM Process, Material Extrusion | Material is selectively dispensed through a nozzle or orifice. |
| Explain the AM Process, Material Jetting | Droplets of feedstock material are selectively deposited. |
| Explain the AM Process, Powder Bed Fusion | A thermal energy selectively fuses regions of a powder bed. |
| Explain the AM Process, Sheet Lamination | Sheets of material are bonded to form a part. |
| Explain the AM Process, Vat Polymerisation | A liquid photopolymer in a vat is selectively cured by light activated polymerisation. |
| List and describe the first 3 key steps involved in the powder bed AM process | 1/ Prepare 3D CAD model using a CAD modelling software/reverse engineering w/ laser scanning 2/ Convert CAD file into a mesh file format (stl., amf., or 3mf). 3/ Transfer file to machine considering orientation, support structure & position for build. |
| List and describe the middle 3 steps of the powder bed AM process chain. | 4/ Setup the machine - set build parameters 5/ Build - processing of the physical object on the AM machine 6/ Remove - remove metal powder surrounding the part |
| Describe the final two steps in the powder bed AM process. | 7/ Post process - heat treatment, removal of base and support structures, cleaning of part 8/ Application - additional colouring / assembly / surface finishing |
| Name the two metallic AM processes which use powder bed technology | Selective Laser Melting / Sintering (SLS/SLM). Electron Beam Melting (EBM) |
| Describe SLS/SLM | Performed in inert gas chamber with a build platform, powder hopper and powder layering system. Platform lowered after each layer completed. Magnetic lenses & deflecting coils used to control the EB (powered by heated tungsten filament) |
| Describe EBM | Performed in inert gas chamber consisting of mould supported by build station piston. Powder coater spreads delivered powder around mould. A laser scanner controls the precise application of heat to the part. |
| Discuss key comparisons between EBM and SLS/SLM | EBM limited to conductive materials. EBM requires vacuum chamber. EBM requires more power. EBM produces higher strength parts. SLS/M produces parts w higher surface finish. SLS/M has larger material range and allows for more complex part builds |
| Describe 3 factors which can increase the surface finish during the SLM process | Melt pool dynamics-laser power,spot size,scan speed,material type. Layer surface morphology-scanning strategy,hatch distance, zstep overlap ratio. Part as built surface geometry-Removal of support structures,layer thickness, layer orientation. |
| Describe the Hall Petch relationship | Used to describe how a materials strength increases as its grain size decreases. Grain boundaries act as obstacles to the movement of dislocations, hence finer particles result in more boundaries to impede this movement. |
| Name some advantages of metal AM | Part complexity, rapid prototyping, assembly manufacture (parts can be printed in one step), lightweight builds (internal lattice structure), low buy2fly ratio (material use optimised), design flexibility & optimisation, custom parts & fine feature detail |
| Name some disadvantages of metal AM | Slow build rates, poor surface finish, poor finishing operation requirements, discontinuous production process, residual stresses in part, high cost of component and equipment. |
| Provide an example of a hybrid subtractive manufacturing process and explain its benefits. | Grinding and electrochemical machining - increases surface finish and allows complex internal geometries to be machined. Laser cutting and abrasive jet cutting - increases MRR by applying a high speed abrasive jet to the laser melted pool |
| Provide an example of a hybrid transformative manufacturing process and explain its benefits. | SF and AISF - preform created using SF then shape features using AISF hence reducing process time and improving accuracy. Laser Heat Treatment and AISF - laser heating of forming zone improves form ability and hence reduces spring back. |
| How do Material Jetting and DED processes differ. | Material Jetting uses photopolymer resins or wax which are deposited in droplets and cured by UV lights, DED uses metal wire or powder melted by a high power laser/electron beam. Material Jetting is higher speed but lower accuracy and surface finish. |
| Explain vertical anisotropy and why it is particularly problematic in AM processes. | Direction-dependent differences in a materials properties, between the vertical building direction and horizontal scanning direction. During AM parts undergo rapid repeated heating and cooling which causes solidified grain growth between & within layers. |
| Explain spring back in terms of metal AM | Spring back is when a material partially returns to its original shape after a bending force has been removed, this happens as a result of elastic deformation. It must be considered to avoid dimensional inaccuracies. |
| Describe the differences between Asymetric Incremental Sheet Forming and Sheet Forming | AISF uses a CNC too, to gradually shape the metal, instead of a custom, high cost die. AISF applies localised deformation step by step, making it ideal for prototyping and small batch production. |
| Describe sheet lamination in one sentence. | Sheets are stacked, bonded layer by layer and then cut to shape. |
| Name two advantages of sheet lamination | Fast build rate, low thermal distortion, minimal supports required, can produce large parts. |
| Name two disadvantages of sheet lamination. | The bond quality limits the parts strength, accuracy depends on the alignment/cutting, waste removal can be hard. |
| Describe VAT polymerisation in one sentence. | A vat of photopolymer resin is selectively cured by light to form layers. |
| Name the key difference between SLA and DLP. | Stereolithography scans with a laser, Digital Light Processing projects whole layers at once. DLP - fast, detailed, high res. |
| Describe PBF in one sentence. | Powder bed fusion involves the spreading of powder layers followed by an energy source which selectively fuses regions layer by layer into a solid part. |
| SLM in one sentence. | A laser melts powder locally to build a near fully dense metal part layer by layer. |
| EBM in one sentence. | An electron beam in a vacuum melts metal powder layer by layer into a solid part. |
| Typical PBF issues. | Residual stress/distortion, porosity/defects, surface roughness, supports required, post processing required. |
| Binder jetting in one sentence. | Selective deposition of a liquid binder onto a bed of powder material, layer by layer, then cured or sintered in post processing to achieve final strength. |
| What is a green part? | A fragile printed part held together mainly by binder before sintering occurs. |
| Why is binder jetting often known for its low dimensional accuracy. | Shrinkage/distortion during sintering affects final dimensions. |
| What is the main difference between binder and material jetting? | Binder jetting jets glue onto powder and needs heavy post processing, material jetting builds the material itself. |
| Describe DED in one sentence | Focused thermal energy makes a melt pool while powder/wire is fed in to build material layer by layer. |
| Which AM family does WAAM fall under? | DED (arc based, wire-fed DED) |
| Describe WAAM in one sentence. | Wire is melted by an electric arc and deposited as beads layer by layer to build a part. |
| Mention some typical defects and issues with WAAM. | Start/stop height variation, uneven cooling which causes distortion, shrinkage effects. Mitigations include preheat and toolpath planning. |
| Explain what ‘DED digital systems / simulation testing’ means. | Multi axis simulation for collision and toolpath strategy and code generation. Plus thermal/stress modelling to predict warping / residual stress |
| What is CS-DED in one sentence. | Particles impact-bond at high speed without melting, depositing layer with minimal HAZ |
| What is joule printing (DED) in one sentence | Wire is fused using resistive (Joule) heating at the contact point to deposit metal without laser/arc |
| Name 4 common post processing steps in AM | Depowder/cleaning, support removal, heat treatment, surface finishing/coatings |
| Why is post processing often essential for Metal AM? | To relieve stresses, improve density (Hot.Isostatic.Pressing), meet tolerance/surface finish requirements, remove supports |
| What is the Bath style hybrid manufacturing definition? | Combining two or more manufacturing operations from different technologies on one platform, serially or simultaneously |
| Give a classic hybrid route for high surface quality metal parts | AM (PBF/DED near net shape, and finish machining (milling/turning/grinding) |
| Two common downsides of hybrid manufacturing | High capital/complexity, datum fixing, thermal distortion/residual stress. |
| Thermally enhanced machining in one sentence | A heat source (often laser) preheats the material just ahead of the cutting zone to reduce forces and improve machinability |
| Two advantages of thermally enhanced machining? | Lower cutting forces, higher tool life/less chipping, potential for higher cutting speed |
| Two disadvantages of thermally enhanced machining? | Risk of damaging microstructure/quality if heating is inconsistent, harder to implement in multi axis milling setups. |
| What is the mushy zone in alloys? | The solidification range where solid and liquid coexist. Linked to feeding difficulty and hot tearing / shrinkage porosity. |
| CET stands for? | Columnar to Equiaxed Transition - grain structure change during solidification |
| Why can mould preheating help casting? | Reduced initial thermal gradient/chill. Improves fluidity and reduces premature freezing (too much can hurt directional solidification) |
| How does rapid protyping differ from AM? | Rapid prototyping is used to generate non-structural and non functional demo pieces, or ‘batch of one’ components for proof of concept. AM uses a real, scalable process to create fully functional final components in high tech materials. |
| AM process chain in brief | 3D CAD, convert to mesh file, file transfer to machine, setup machine, build, remove, post process, application. |
| Difference between composites and alloys | Composites are materials where two of more distinct constituents are combined on a macroscopic scale. Alloys are materials with a metallic bond between a metal(s) and an element. |
| Why is SLS performed in an inert gas chamber, and EBM in a vacuum? | To prevent oxidation, and in the case of EBM to ensure the beam does not scatter by colliding with gas particles. |
| List some unconventional machining processes | Laser beam, electrical discharge machining, abrasive water jet machining |
| Name some defects induced in the composite process | Incompletely cured matrix, porosity (voids), delamination, fibre mis orientation, fibre defects |
| Name three common AM printing issues (with polymers) and how to mitigate | Underextrusion (reduce print speed), overextrusion (increase print speed), soft layers (pause between layers) |
| Name some finishing techniques for AM PBF parts | Shape adaptive grinding, thermal finishing (laser or electron beam), plasma polishing, electro polishing. |
| Name the four types of DED | Laser, wire arc, electron beam, cold spray |
| How might you optimise the WAAM process? | Rolling after every layer is deposited to eliminate the distortion and to control the heat input to control the cooling rate. Preheating. |
| Compare wire and powder DED | Powder DED uses more energy, has a lower buy to fly ratio, takes longer, and has higher material costs. Powder DED has better feature resolution. |
| What benefits can machine learning bring to AM? | Process optimisation, design optimisation, quality control, microstructure optimisation, material formulation |
| Define hybrid manufacturing (Bath definition) | An approach that combines two or more manufacturing operations which influence and interact with each other simultaneously or in a serial manner on a single platform. |
| Name two types of Additive and Subtractive Hybrid Processes | Laser Melting and CNC Milling. Plasma Arc Welding and CNC Milling. |
| Name a Joining and Subtractive Hybrid Process | Solvent Welding and Milling |
| Name an Additive and Transformative Hybrid Process | Sheet Metal Forming and Injection Moulding |
| Name four Transformative and Subtractive Hybrid Processes | Injection moulding and milling (approximate part surface made using an array of discrete and movable pins). Laser assisted turning (CNC lathe integrated with fibre lasers to increase MRR). Laser assisted electrochemical machining. Milling and forming. |
| Explain the Hybrid Subtractive and Transformative process ‘Milling and Forming’ and why it is beneficial. | Thin features are machined to the desired accuracy then bent and stretched. Meaning that parts requiring a 5-axis machine can now be made on a 3 axis machine. |
| Give some examples of sequenced Hybrid Processes | Laser PBF then CNC Milling. WAAM then Heat Treatment. DED then Ultrasonic Surface Treatment. SLM then Hot Isostatic Pressing (HIP). Cold Spray then Shot Peening. |
| Give some examples of simultaneous Hybrid Processes | Laser Cladding with CNC Machining (Real-Time). Additive and Subtractive using a single Multi Tool head. Rolling and coating. Welding with Laser Scanning (Real-Time). |
Created by:
El707