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Lecture on�Additive Manufacturing

B. Tech. Mechanical Engineering

2023-2024

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By

Mr. Vasim Maner

M. Tech. CAD/CAM/CAE

PhD Pursuing

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YSPM’s, Yashoda Technical Campus, Faculty of Engineering, Satara.

Department of Mechanical Engineering

YTC

How many days required to build drone body?

How many days required to build this watch?

How many days required to build these objects?

Introduction

• Def: Rapid prototyping is a group of techniques used to quickly fabricate a scale model of a physical part or assembly using three-dimensional computer aided design (CAD) data. Construction of the part or assembly is usually done using 3D printing or "additive layer manufacturing" technology.

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How is Rapid Prototyping different from Additive Manufacturing?

The difference is in the use and scalability, not in the technology itself:

Rapid Prototyping: used to generate non-structural and non-functional demo pieces or batch-of-one components for proof of concept.

Additive Manufacturing: used as a real, scalable manufacturing process, to generate fully functional final components in high-tech materials for low-batch, high-value manufacturing.

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Introduction

• Additive Manufacturing (AM) is an appropriate name to describe the technologies that build 3D objects by adding layer-upon-layer of material, whether the material is plastic, metal, concrete or one day…..human tissue.

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• AM application is limitless. Early use of AM in the form of Rapid Prototyping focused on preproduction visualization models. More recently, AM is being used to fabricate end-use products in aircraft, dental restorations, medical implants, automobiles, and even fashion products.

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Techniques

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Techniques:

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• Fused deposition modeling (FDM)
• Laminated object manufacturing (LOM)
• Selective laser sintering (SLS)
• Stereolitheography (SLA or SLT)
• 3D printing (3DP)

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Compromises

Another

key compromise is

among process speed, volume

and tolerances.

AM today

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Process

These processes include:

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• Subtractive - whereby a block of material is carved to produce the desired shape using milling, grinding or turning.

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• Compressive - whereby a semi-solid or liquid material is forced into the desired shape before being solidified, such as with casting, compressive sintering or moulding.

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Stl format

•CAD model prepared in the first step is converted to STL (STerioLithography) format, a common language to almost all additive manufacturing machinary.

Two types of formats are used for STL file

▫ASCII format (mostly used) ▫Binary format

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The STL format is the tessellated representation of the CAD model in which the CAD surface is approximated to a series of triangular facets.

Fused Deposition Modeling (FDM)

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1. A spool of themoplastic wire (typically acrylonitrile butadiene styrene (ABS)) with a 0.012 in (300 μm) diameter is continuously supplied to a nozzle.
2. The nozzle heats up the wire and extrudes a hot, viscos strand (like squeezing toothpaste of of a tube).
3. A computer controls the nozzle movement along the x- and y-axes, and each cross-section of the prototype is produced by melting the plastic wire that solidifies on cooling.
4. In the newest models, a second nozzle carries a support wax that can easily be removed afterward, allowing construction of more complex parts.
5. The sacrificial support material (if available) is dissolved in a heated sodium hydroxide (NaOH) solution with the assistance of ultrasonic agitation.

FDM

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FDM

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Specification

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FDM

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Advantages

• Economical (wrt material)
• Enable multiple colour
• Wide range of material can be used

Disadvantages

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• Materials suite currently limited to thermoplastics (may be resolved by loading)

Stereolitheography (SLT)

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Stereolitheography (SLT)

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• A structure support base is positioned on an elevator structure and immersed in a tank of liquid photosensitive monomer, with only a thin liquid film above it.

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• A UV laser locally cross-links the monomer on the thin liquid film above the structure support base.

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• The elevator plate is lowered by a small prescribed step, exposing a fresh layer of liquid monomer, and the process is repeated.

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• At the end of the job, the whole part is cured once more after excess resin and support structures are removed.

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Stereolitheography (SLT)

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Stereolithography (SLT)

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Advantages

• Fast
• Good resolution
• No need for support material
• Photosensitive polymers have acceptable mechanical properties

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Disadvantages

• Expensive equipment (Rs. 10000- 40000)
• Expensive materials (photosensitive resins are of Rs. 8000-15000 /kg)
• Material suite limited to resins

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3D printing (3DP)

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1. A layer of powder (plaster, ceramic) is spread across the build area

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• Inkjet-like printing of binder over the top layer densifies and compacts the powder locally

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• The platform is lowered and the next layer of dry powder is spread on top of the previous layer

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• Upon extraction from the machine, the dry powder is brushed off and recycled

3D printing (3DP)

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Specification

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3D printing (3DP)

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Advantages:

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• Can create extremely realistic multi-color parts (24-bit color) using inkjet technology

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•Can generate complex components with internal degrees of freedom

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•Economical

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•Versatile

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Disadvantages:

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• Very limited materials suite

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•Low resolution (lowest of all AM technologies)

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•Negligible mechanical properties (unusable for any structural application)

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Selective Laser Sintering (SLS)

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1.A continuous layer of powder is deposited on the fabrication platform

2.A focused laser beam is used to fuse/sinter powder particles in a small volume within the layer

3.The laser beam is scanned to define a 2D slice of the object within the layer

4.The fabrication piston is lowered, the powder delivery piston is raised and a new layer is deposited

5.After removal from the machine, the unsintereddry powder is brushed off and recycled

Selective Laser Sintering (SLS)

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Selective Laser Sintering (SLS)

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Selective Laser Sintering (SLS)

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Advantages

• Wide array of structural materials beyond polymers
• No need for support materials
• Cheaper than EBM
• One of two technologies that allow

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Disadvantages

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• Expensive relative to FDM, 3DP
• The quality of metal parts is not as high as with EBM

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Laminated Object Manufacturing (LOM)

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1. Sheets of material (paper, plastic, ceramic, or composite) are either precut or rolled.

2. A new sheet is loaded on the build platform and glued to the layer underneath.

3. A laser beam is used to cut the desired contour on the top layer.

4. The sections to be removed are diced in cross-hatched squares; the diced scrap remains in place to support the build.

5. The platform is lowered and another sheet is loaded. The process is repeated.

6. The product comes out as a rectangular block of laminated material containing the prototype and the scrap cubes. The scrap/support material is separated from the prototype part.

Laminated Object Manufacturing (LOM)

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Laminated Object Manufacturing (LOM)

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Laminated Object Manufacturing (LOM)

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Advantages

• Relatively high-speed process
• Low cost (readily available materials)
• Large builds possible (no chemical reactions)
• Parts can be used immediately after the process (no need for post-curing)
• No additional support structure is required (the part is self-supported)

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Disadvantages

• Removal of the scrap material is laborious
• The ‘z’ resolution is not as high as for other technologies
• Limited material set
• Need for sealing step to keep moisture out

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Current materials in AM today

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-Thermoplastics (FDM, SLS)

-Thermosets (SLA)

-Powder based composites (3DP)

-Metals (EBM, SLS)

-Sealant tapes, paper (LOM)

-Starch and sugar (3DP)

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•Functional/structural parts

▫FDM (ABS and Nylon)

▫SLS (thermoplastics, metals)

▫EBM (high strength alloys, Ti, stainless steel, CoCr)

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•Non-functional/structural parts

▫SLA (resins): smoothest surface, good for casting

▫LOM (paper), 3D Printing (plaster, sand): marketing and concept prototypes, sand casting molds

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•As new materials are introduced, more functional components will be manufactured (perhaps 30-40% by 2020).

•Importantly AM is one of the best approaches for complex architected materials.

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Challenges in AM materials properties predictions

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Most AM processes introduce anisotropy in mechanical properties (z different from x,y)

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•Local differences in laser/EB power (e.g., perimeter vs center) introduce heterogeneity in mechanical properties

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•Laser fluctuations might result in embedded defects that are difficult to identify

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•All existing machines are open-loop: temperature sensors have been introduced in some processes, but the readings are not used to optimize the processing parameters on the fly.

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Defects

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Density Problem

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• Scan speed has a significant effect on density .

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• At sufficiently low scan speeds, the relative density is almost independent of the layer thickness for the selected range of the layer thickness, and a maximum of 99% relative density is achievable.

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• At higher scan speed values, a higher layer thickness results in less density.

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Defects

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Residual Stress

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• Due to localized heating, complex thermal and phase transformation stresses are generated during the process.

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• In addition, frequent thermal expansion and contraction of the previously solidified layers during the process generates considerable thermal stresses and stress gradients that can exceed the yield strength of the material.

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• Residual stresses can lead to part distortion, initiate fracture and unwanted decrease in strength.

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Defects

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Surface finish

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• Parts often require post‐processing operations such as surface machining, polishing and shot peening to attain final part surface finish.

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• Surface roughness is heavily dependent on laser processing parameters..

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Defects

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OVEERALL DISADVANTAGES

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•Small features and thin walls cannot be made accurately.

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•Layers are visible and surface finish is not good.

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•The process is very slow.

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•The built part is weak in build axis direction.

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•Support structures are required for some shapes and support structure removal is a difficult process.

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Lay Pattern

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Printing of layers in FDM has different types. Each type is used for different types of loading.

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•The angle in which the layers are printed is called raster angle.

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•The raster angle has a direct bearing on the resulting structure and plays a significant role in influencing the mechanical characteristics of parts produced.

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Infill Pattern

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In FDM, the printed part will have a structure inside instead of being a solid. This is called infill pattern.

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•This infill pattern provides high strength while reducing the total weight of the part produced. Also it reduces the printing time.

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•There are many types of infill. Rectangular, triangular, wiggle and hexagonal or honeycomb are the widely used structures. Each structure offers different properties.

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Infill Pattern

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Orientation

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Spending time optimizing the 3d model before printing can greatly improve overall quality and reduce print time. It can be done by orienting the model on the print bed to minimize the amount of support needed.

Conclusion

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4 D Printing

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Using 3D printing and multi-material structures in additive manufacturing has allowed for the design and creation of what is called 4D printing.

4D printing is an additive manufacturing process in which the printed object changes shape with time, temperature, or some other type of stimulation.

4D printing allows for the creation of dynamic structures with adjustable shapes, properties or functionality. The smart/stimulus responsive materials that are created using 4D printing can be activated to create calculated responses such as self-assembly, self-repair, multi-functionality, reconfiguration and shape shifting. This allows for customized printing of shape changing and shape-memory materials.