Additive Manufacturing

Transcription

1 Additive Manufacturing Prof. J. Ramkumar Department of Mechanical Engineering IIT Kanpur March 28, 2018

2 Outline Introduction to Additive Manufacturing Classification of Additive Manufacturing Systems Introduction to Reverse Engineering

3 Additive Manufacturing Additive Manufacturing (AM) refers to a process by which digital 3D design data is used to build up a component in layers by depositing material. The term AM encompasses many technologies including subsets like 3D Printing, Rapid Prototyping (RP), Direct Digital Manufacturing (DDM), layered manufacturing and additive fabrication. 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.

4 Additive Manufacturing contd.

5 Basic structure of additive manufacturing and its subcategories

6 Some Examples

7 Some Examples contd.

8 Some Examples contd.

9 Some Examples contd.

10 Additive vs Subtractive Manufacturing

11 Additive vs Subtractive Manufacturing contd.

12 Evolution of AM Technologies

13 Evolution of AM Technologies contd.

14 Current and Potential industries for Additive Manufacturing

15 Pros and Cons of AM

16 AM Benefits: Weight Reduction

17 AM Benefits: Complexity for Free

18 AM Benefits: Customized Medical Products

19 Future: Home Manufacturing

20 Generic AM Process

21 Generic AM Process contd.

22 Data path for additive manufacturing

23 Generation of Geometrical Layer Information on Single Layers To produce three-dimensional models by layer-oriented additive manufacturing processes, the 3D CAD solid must be mathematically split into the same layers as those produced physically by the AM machine. This process is known as slicing. There are two basic methods of doing this: 1) Triangulation, which leads to the STL format 2) Direct cutting in the CAD system, which leads to the CL (SLI) format

24 STL format STL (STereoLithography) is a file format native to the stereolithography CAD software. It is widely used for rapid prototyping, 3D printing and computer-aided manufacturing. The main purpose of the STL file format is to encode the surface geometry of a 3D object. It encodes this information using a simple concept called tessellation.

25 Tessellation Tessellation is the process of tiling a surface with one or more geometric shapes such that there are no overlaps or gaps. Tessellation can involve simple geometric shapes or very complicated (and imaginative) shapes.

26 Valid vs. Invalid Tessellated Models

27 Exploiting tessellation to encode surface geometry The basic idea is to tessellate the 2 dimensional outer surface of 3D models using tiny triangles (also called facets ) and store information about the facets in a file. For example, if you have a simple 3D cube, this can be covered by 12 triangles and 3D model of a sphere, then it can be covered by many small triangles, as shown in the image below.

28 Exploiting tessellation to encode surface geometry contd. Here is another example of a very complicated 3D shape which has been tessellated with triangles.

29 How does an STL file store information about facets? The STL file format provides two different ways of storing information about the triangular facets that tile the object surface. 1) ASCII encoding 2) The binary encoding In both formats, the following information of each triangle is stored: 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 the 3D model.

30 The ASCII STL file format The ASCII STL file starts with the mandatory line: solid < name > The file continues with information about the covering triangles. Information about the vertices and the normal vector is represented as follows: facet normal nx ny nz outer loop vertex v1x v1y v1z vertex v2x v2y v2z vertex v3x v3y v3z endloop endfacet Here, n is the normal to the triangle and v1, v2 and v3 are the vertices of the triangle. The file ends with the mandatory line: endsolid < name >

31 The binary STL file format If the tessellation involves many small triangles, the ASCII STL file can become huge. This is why a more compact binary version exists. The binary STL file starts with a 80 character header. UINT8[80] - Header UINT32 - Number of triangles The information about the triangles follow subsequently. The file simply ends after the last triangle. foreach triangle REAL32[3] - Normal vector REAL32[3] - Vertex 1 REAL32[3] - Vertex 2 REAL32[3] - Vertex 3 UINT16 - Attribute byte count end

32 Special rules for the STL format The STL specification has some special rules for tessellation and for storing information. The vertex rule: The vertex rule states that each triangle must share two vertices with its neighboring triangles.

33 Special rules for the STL format contd. The orientation rule: The orientation rule says that the orientation of the facet (i.e. which way is in the 3D object and which way is out ) must be specified in two ways. The triangle sorting rule: The triangle sorting rule recommends that the triangles appear in ascending z-value order. The all positive octant rule: The all positive octant rule says that the coordinates of the triangle vertices must all be positive.

34 Optimizing an STL file for best 3D printing performance The STL file format approximates the surface of a CAD model with triangles. The approximation is never perfect, and the facets introduce coarseness to the model. It is therefore very important to find the right balance between file size and print quality.

35 Advantages and Disadvantages of STL File Format

36 Classification of Additive Manufacturing Systems The Better way is to classify AM systems broadly by the initial form of its material, all AM Systems can be easily categorised into 1) Liquid Based 2) Solid Based 3) Powder Based

37 Classification of Additive Manufacturing Systems

38 Liquid Based Additive Manufacturing Systems Building material is in the liquid state. The following AM Systems fall into this category: 1) Stereolithography Apparatus(SLA) 2) PolyJet 3D printing 3) Multijet Printing(MJP) 4) Solid Object Ultravoilet-Laser Printer(SOUP) 5) Rapid Freeze Prototyping 1) and 4) are widely used method.

39 Solid Based Additive Manufacturing Systems Building material is in the Solid state (except powder). The solid form can include the shape in the forms of wire, rolls, laminates and pellets. 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

40 Powder Based Additive Manufacturing Systems Building material is Powder(grain like form). All Powder Based AM Systems employ the joining/binding method. 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.

41 Important Technologies of AM In the next few slides, we are going to discuss these three AM technologies 1) Stereolithography Apparatus(SLA) 2) Fused deposition modeling (FDM) 3) Selective Laser Sintering(SLS)

42 Stereolithography One of the most important additive manufacturing technologies currently available. The first ever commercial RP systems were resin-based systems commonly called stereolithography or SLA. The resin is a liquid photosensitive polymer that cures or hardens Stereolithography when exposed to ultraviolet radiation. This technique involves the curing or solidification of a liquid photosensitive polymer through the use of the irradiation light source. The source supplies the energy that is needed to induce a chemical reaction (curing reaction), bonding large no of small molecules and forming a highly cross-linked polymer

43 Stereolithography contd.

44 Stereolithography contd.

45 Stereolithography contd. Facts About SLA 1) Each layer is mm to 0.50 mm thick 2) Starting materials are liquid monomers 3) Polymerization occurs on exposure to UV light produced by laser scanning beam - Scanning speeds to 2500 mm/s Part Build Time in SLA Time to complete a single layer : T i = A i vd + T d (1) where T i = time to complete layer i; A i = area of layer i; v = average scanning speed of the laser beam at the surface; D = diameter of the spot size, assumed circular; and T d = delay time between layers to reposition the worktable

46 Stereolithography contd. Time to build a part ranges from one hour for small parts of simple geometry up to several dozen hours for complex parts SLA Build Cycle Time : n l T c = T i (2) where T c = STL build cycle time; and n l = number of layers used to approximate the part i=1

47 SLA 3D Printing Product

48 Fused deposition modeling Fused Deposition Modeling (FDM), produced and developed by Stratasys, USA. FDM uses a heating chamber to liquefy polymer that is fed into the system as a filament. The filament is pushed into the chamber by a tractor wheel arrangement and it is this pushing that generates the extrusion pressure. The major strength of FDM is in the range of materials and the effective mechanical properties of resulting parts made using this technology. Parts made using FDM are amongst the strongest for any polymerbased additive manufacturing process.

49 Fused deposition modeling contd.

50 Materials for FDM The most popular material is the ABSplus material, which can be used on all current Stratasys FDM machines. Some machines also have an option for ABS blended with Polycarbonate.

51 Materials for FDM contd. Note that FDM works best with polymers that are amorphous in nature rather than the highly crystalline polymers. This is because the polymers that work best are those that are extruded in a viscous paste rather than in a lower viscosity form. As in amorphous polymers, there is no distinct melting point and the material increasingly softens and viscosity lowers with increasing temperature. The viscosity at which these amorphous polymers can be extruded under pressure is high enough that their shape will be largely maintained after extrusion, maintaining the extrusion shape and enabling them to solidify quickly and easily.

52 Limitations of FDM Sharp features or corners not possible to get; Part strength is weak perpendicular to build axis; More area in slices requires longer build times; Temperature fluctuations during production could lead to delamination

53 FDM 3D Printing Product

54 Selective Laser Sintering

55 Selective Laser Sintering contd. Layer thickness: nearly 0.1 mm thick; The part building takes place inside an enclosed chamber filled with nitrogen gas to minimize oxidation and degradation of the powdered material; The powder in the building platform is maintained at an elevated temperature just below the melting point and/or glass transition temperature of the powdered material; Infrared heaters are used to maintain an elevated temperature around the part being formed; A focused CO 2 laser beam is moved on the bed in such a way that it thermally fuses the material to form the slice cross-section; Surrounding powders remain loose and serve as support for subsequent layers.

56 Advantages vs. disadvantages of SLS Advantages 1) A distinct advantage of the SLS process is that because it is fully self-supporting 2) Parts possess high strength and stiffness 3) Good chemical resistance 4) Various finishing possibilities (e.g., metallization, stove enameling, 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 Disadvantages SLS printed parts have surface porosity. Such porosity can be sealed by applying sealant such as cyanoacrylate.

57 SLS 3D Printing Product

58 Introduction to Reverse Engineering It is the processes of extracting knowledge or design information from anything man-made and reproducing it or reproducing anything based on the extracted information. The process often involves disassembling something (a mechanical device, electronic component, computer program, or biological, chemical, or organic matter) and analyzing its components and workings in detail. Product of World War II.

59 Motivation for Reverse Engineering Interfacing: Reverse engineering can be used when a system is required to interface to another system. Military or commercial espionage: Learning about an enemy s or competitor s latest research by stealing or capturing a prototype and dismantling it. Product security analysis: To examine how a product works, what are specifications of its components, estimate costs and identify potential patent infringement. Academic/learning purposes: Reverse engineering for learning purposes may be to understand the key issues of an unsuccessful design and subsequently improve the design. Saving money: when one finds out what a piece of electronics is capable of, it can spare a user from purchase of a separate product.

60 Reverse Engineering Process Prediction What is the purpose of this product? How does it work? Observation How do you think it works? How does it meet design objectives (overall)? Disassemble How does it work? How is it made? How many parts and moving parts? Analyze Carefully examine and analyze subsystems (i.e. structural, mechanical, and electrical) and develop annotated sketches that include measurements and notes on components, system design, safety, and controls.

61 Reverse Engineering Process contd. Test Carefully reassemble the product. Operate the device and record observations about its performance in terms of functionality (operational and ergonomic) and projected durability. Documentation Inferred design goals Inferred constraints Design (functionality, form (geometry), and materials) Schematic diagrams Lists (materials, components, critical components, flaws, successes, etc.) Identify any refinements that might enhance the products usefulness. Upgrades and changes

62 Reverse Engineering Process contd.

63 Example of Reverse Engineering

64 ... Thank You