additive manufacturing - indian institute of...

Additive Manufacturing

Prof. J. Ramkumar

Department of Mechanical EngineeringIIT Kanpur

October 3, 2017

Outline

Introduction to Additive Manufacturing

Classification of Additive Manufacturing Systems

Introduction to Reverse Engineering

Additive Manufacturing

I Additive Manufacturing (AM) refers to a process by whichdigital 3D design data is used to build up a component inlayers by depositing material.

I The term AM encompasses many technologies includingsubsets like 3D Printing, Rapid Prototyping (RP), DirectDigital Manufacturing (DDM), layered manufacturing andadditive fabrication.

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

Additive Manufacturing contd.

Basic structure of additive manufacturing and itssubcategories

Some Examples

Some Examples contd.

Additive vs Subtractive Manufacturing

Additive vs Subtractive Manufacturing contd.

Evolution of AM Technologies

Evolution of AM Technologies contd.

Current and Potential industries for AdditiveManufacturing

Pros and Cons of AM

AM Benefits: Weight Reduction

AM Benefits: Complexity for Free

AM Benefits: Customized Medical Products

Future: Home Manufacturing

Generic AM Process

Generic AM Process contd.

Data path for additive manufacturing

Generation of Geometrical Layer Information on SingleLayers

I To produce three-dimensional models by layer-orientedadditive manufacturing processes, the 3D CAD solid must bemathematically split into the same layers as those producedphysically by the AM machine. This process is known as”slicing.”

I There are two basic methods of doing this:1) Triangulation, which leads to the STL format2) Direct cutting in the CAD system, which leads to the CL(SLI) format

STL format

I STL (STereoLithography) is a file format native to thestereolithography CAD software.

I It is widely used for rapid prototyping, 3D printing andcomputer-aided manufacturing.

I The main purpose of the STL file format is to encode thesurface geometry of a 3D object.

I It encodes this information using a simple concept called”tessellation”.

Tessellation

I Tessellation is the process of tiling a surface with one or moregeometric shapes such that there are no overlaps or gaps.

I Tessellation can involve simple geometric shapes or verycomplicated (and imaginative) shapes.

Valid vs. Invalid Tessellated Models

Exploiting tessellation to encode surface geometry

I The basic idea is to tessellate the 2 dimensional outer surfaceof 3D models using tiny triangles (also called ”facets”) andstore information about the facets in a file.

I For example, if you have a simple 3D cube, this can becovered by 12 triangles and 3D model of a sphere, then it canbe covered by many small triangles, as shown in the imagebelow.

Exploiting tessellation to encode surface geometry contd.

I Here is another example of a very complicated 3D shapewhich has been tessellated with triangles.

How does an STL file store information about facets?

I The STL file format provides two different ways of storinginformation about the triangular facets that tile the objectsurface.1) ASCII encoding2) The binary encoding

I In both formats, the following information of each triangle isstored:1) The coordinates of the vertices.2) The components of the unit normal vector to the triangle.The normal vector should point outwards with respect to the3D model.

The ASCII STL file format

I The ASCII STL file starts with the mandatory line:solid < name >

I The file continues with information about the coveringtriangles. Information about the vertices and the normalvector is represented as follows:

facet normal nx ny nzouter loop

vertex v1x v1y v1zvertex v2x v2y v2zvertex v3x v3y v3z

endloopendfacet

I Here, n is the normal to the triangle and v1, v2 and v3 are thevertices of the triangle.

I The file ends with the mandatory line:endsolid < name >

The binary STL file format

I If the tessellation involves many small triangles, the ASCIISTL file can become huge. This is why a more compactbinary version exists.

I The binary STL file starts with a 80 character header.UINT8[80] - HeaderUINT32 - Number of triangles

I The information about the triangles follow subsequently. Thefile simply ends after the last triangle.

foreach triangleREAL32[3] - Normal vectorREAL32[3] - Vertex 1REAL32[3] - Vertex 2REAL32[3] - Vertex 3UINT16 - Attribute byte countend

Special rules for the STL format

I The STL specification has some special rules for tessellationand for storing information.

I The vertex rule: The vertex rule states that each trianglemust share two vertices with its neighboring triangles.

Special rules for the STL format contd.

I The orientation rule: The orientation rule says that theorientation of the facet (i.e. which way is ”in” the 3D objectand which way is ”out”) must be specified in two ways.

I The triangle sorting rule: The triangle sorting rulerecommends that the triangles appear in ascending z-valueorder.

I The all positive octant rule: The all positive octant rulesays that the coordinates of the triangle vertices must all bepositive.

Optimizing an STL file for best 3D printing performance

I The STL file format approximates the surface of a CADmodel with triangles.

I The approximation is never perfect, and the facets introducecoarseness to the model.

I It is therefore very important to find the right balancebetween file size and print quality.

Advantages and Disadvantages of STL File Format


I The Better way is to classify AM systems broadly by theinitial form of its material, all AM Systems can be easilycategorised into1) Liquid Based2) Solid Based3) Powder Based

Liquid Based Additive Manufacturing Systems

I Building material is in the liquid state.

I The following AM Systems fall into this category:1) Stereolithography Apparatus(SLA)2) PolyJet 3D printing3) Multijet Printing(MJP)4) Solid Object Ultravoilet-Laser Printer(SOUP)5) Rapid Freeze Prototyping

I 1) and 4) are widely used method.

Solid Based Additive Manufacturing Systems

I Building material is in the Solid state (except powder).

I The solid form can include the shape in the forms of wire,rolls, laminates and pellets.

I The following AM Systems fall into this category:1) Fused deposition modeling (FDM)2) Selective Deposition Lamination (SDL)3) Laminated Object Manufacturing (LOM)4) Ultrasonic Consolidation

Powder Based Additive Manufacturing Systems

I Building material is Powder(grain like form).

I All Powder Based AM Systems employ the joining/bindingmethod.

I The following AM Systems fall into this category:1) Selective Laser Sintering(SLS)2) ColorJet Printing(CJP)3) Laser Engineered Net Shaping (LENS)4) Electron Beam Melting(EBM) etc.

Important Technologies of AM

I In the next few slides, we are going to discuss these three AMtechnologies1) Stereolithography Apparatus(SLA)2) Fused deposition modeling (FDM)3) Selective Laser Sintering(SLS)

Stereolithography

I One of the most important additive manufacturingtechnologies currently available.

I The first ever commercial RP systems were resin-basedsystems commonly called stereolithography or SLA.

I The resin is a liquid photosensitive polymer that cures orhardens Stereolithography when exposed to ultravioletradiation.

I This technique involves the curing or solidification of a liquidphotosensitive polymer through the use of the irradiation lightsource.

I The source supplies the energy that is needed to induce achemical reaction (curing reaction), bonding large no of smallmolecules and forming a highly cross-linked polymer

Stereolithography contd.


I Facts About SLA1) Each layer is 0.076 mm to 0.50 mm thick2) Starting materials are liquid monomers3) Polymerization occurs on exposure to UV light produced bylaser scanning beam- Scanning speeds - 500 to 2500 mm/s

I Part Build Time in SLATime to complete a single layer :

Ti =Ai

vD+ Td (1)

where Ti = time to complete layer i; Ai = area of layer i; v =average scanning speed of the laser beam at the surface; D =diameter of the ”spot size”, assumed circular; and Td = delaytime between layers to reposition the worktable


I Time to build a part ranges from one hour for small parts ofsimple geometry up to several dozen hours for complex parts

I SLA Build Cycle Time :

Tc =

nl∑i=1

Ti (2)

where Tc = STL build cycle time; and nl = number of layersused to approximate the part

SLA 3D Printing Product

Fused deposition modeling

I Fused Deposition Modeling (FDM), produced and developedby Stratasys, USA.

I FDM uses a heating chamber to liquefy polymer that is fedinto the system as a filament.

I The filament is pushed into the chamber by a tractor wheelarrangement and it is this pushing that generates theextrusion pressure.

I The major strength of FDM is in the range of materials andthe effective mechanical properties of resulting parts madeusing this technology.

I Parts made using FDM are amongst the strongest for anypolymerbased additive manufacturing process.

Fused deposition modeling contd.

Materials for FDM

I The most popular material is the ABSplus material, which canbe used on all current Stratasys FDM machines.

I Some machines also have an option for ABS blended withPolycarbonate.

Materials for FDM contd.

I Note that FDM works best with polymers that are amorphousin nature rather than the highly crystalline polymers.

I This is because the polymers that work best are those that areextruded in a viscous paste rather than in a lower viscosityform.

I As in amorphous polymers, there is no distinct melting pointand the material increasingly softens and viscosity lowers withincreasing temperature.

I The viscosity at which these amorphous polymers can beextruded under pressure is high enough that their shape will belargely maintained after extrusion, maintaining the extrusionshape and enabling them to solidify quickly and easily.

Limitations of FDM

I Sharp features or corners not possible to get;

I Part strength is weak perpendicular to build axis;

I More area in slices requires longer build times;

I Temperature fluctuations during production could lead todelamination

FDM 3D Printing Product

Selective Laser Sintering

Selective Laser Sintering contd.

I Layer thickness: nearly 0.1 mm thick;

I The part building takes place inside an enclosed chamber filledwith nitrogen gas to minimize oxidation and degradation ofthe powdered material;

I The powder in the building platform is maintained at anelevated temperature just below the melting point and/orglass transition temperature of the powdered material;

I Infrared heaters are used to maintain an elevated temperaturearound the part being formed;

I A focused CO2 laser beam is moved on the bed in such a waythat it thermally fuses the material to form the slicecross-section;

I Surrounding powders remain loose and serve as support forsubsequent layers.

Advantages vs. disadvantages of SLS

I Advantages1) A distinct advantage of the SLS process is that because itis fully self-supporting2) Parts possess high strength and stiffness3) Good chemical resistance4) Various finishing possibilities (e.g., metallization, stoveenameling, vibratory grinding, tub coloring, bonding, powder,coating, flocking) 5) Complex parts with interior components,channels, can be built without trapping the material inside.6) Fastest additive manufacturing process

I DisadvantagesSLS printed parts have surface porosity. Such porosity can besealed by applying sealant such as cyanoacrylate.

SLS 3D Printing Product

Introduction to Reverse Engineering

I It is the processes of extracting knowledge or designinformation from anything man-made and reproducing it orreproducing anything based on the extracted information.

I The process often involves disassembling something (amechanical device, electronic component, computer program,or biological, chemical, or organic matter) and analyzing itscomponents and workings in detail.

I Product of World War II.

Motivation for Reverse Engineering

I Interfacing: Reverse engineering can be used when a systemis required to interface to another system.

I Military or commercial espionage: Learning about anenemy’s or competitor’s latest research by stealing orcapturing a prototype and dismantling it.

I Product security analysis: To examine how a productworks, what are specifications of its components, estimatecosts and identify potential patent infringement.

I Academic/learning purposes: Reverse engineering forlearning purposes may be to understand the key issues of anunsuccessful design and subsequently improve the design.

I Saving money: when one finds out what a piece ofelectronics is capable of, it can spare a user from purchase ofa separate product.

Reverse Engineering Process

I PredictionWhat is the purpose of this product?How does it work?

I ObservationHow do you think it works?How does it meet design objectives (overall)?

I DisassembleHow does it work?How is it made?How many parts and moving parts?

I AnalyzeCarefully examine and analyze subsystems (i.e. structural,mechanical, and electrical) and develop annotated sketchesthat include measurements and notes on components, systemdesign, safety, and controls.

Reverse Engineering Process contd.

I TestCarefully reassemble the product.Operate the device and record observations about itsperformance in terms of functionality (operational andergonomic) and projected durability.

I DocumentationInferred design goalsInferred constraintsDesign (functionality, form (geometry), and materials)Schematic diagramsLists (materials, components, critical components, flaws,successes, etc.)Identify any refinements that might enhance the productsusefulness.Upgrades and changes

Reverse Engineering Process contd.

Example of Reverse Engineering

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