Introduction to Reverse Engineering and also data formats using in Additive Manufacturing

DEPARTMENT OF INDUSTRIAL & PRODUCTION ENGINEERING www. jssstuniv.in
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ADDITIVE MANUFACTURING
(20IP653)
Module-4
AM & Reverse Engineering
&
AM Data formats
Course Instructor
Vijay Praveen P M
Assistant Professor
Department of I&P Engg.

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SYLLABUS
AM & Reverse Engineering: Basic Concept –
Digitization techniques – Model Reconstruction –
Data Processing for Additive Manufacturing
Technology, concept of Reverse Engineering, nature
and characteristics.
AM Data formats: STL Format, STL File Problems,
Consequence of Building Valid and Invalid Tessellated
Models, STL file Repairs. AM Software‘s: Need for AM
software, Features of various AM software.

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Basic Concept
Engineering is the process of designing, manufacturing,
assembling, and maintaining products and systems. There are two
types of engineering, forward engineering and reverse
engineering.
Forward engineering is the traditional process of moving from
high-level abstractions and logical designs to the physical
implementation of a system.
Reverse engineering is the process of duplicating an existing part,
sub-assembly, or product, without drawings, documentation, or a
computer model. It is also defined as the process of obtaining a
geometric CAD model from 3-D points acquired by scanning/
digitizing existing parts/products.

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Following are some of the reasons for using reverse engineering:
➢ The original manufacturer no longer exists, but a customer
needs the product, e.g., aircraft spares required typically after
an aircraft has been in service for several years.
➢ The original product design documentation has been lost or
never existed.
➢ Creating 3-D data from an individual, model or sculpture to
create, scale, or reproduce artwork.
➢ Some bad features o a product need to be eliminated e.g.,
excessive wear might indicate where a product should be
improved.
➢ Strengthening the good features of a product based on long-
term usage.
➢ Analyzing the good and bad features of competitor's products.
➢ Generating data to create dental or surgical prosthetics, tissue
engineered body parts, or for surgical planning.

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DIGITIZATION TECHNIQUE
Contact data acquisition obtains data using a contact
measuring process.
Contact means that the measuring probe touches the
recovery surface of objects during the data acquisition. The
devices include joined arms and CMMs. Destructive and non-
destructive methods are used in contact measuring process.
Non-Contact data acquisition technology uses an energy
source, such as laser, white light, microwave, radar, and
ultrasonic sound, to obtain 3D data of an object without
touching the surface of objects in the measurement. There
are two techniques used to receive signals of the energy
source from measured surface: reflective and transmissive
methods.

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➢ Here a high energy light source is focused and
projected at a pre-specified angle(θ) onto the surface
of an object.
➢ A photosensitive device senses the reflection from the
illuminated point on the surface.
➢ Because the fixed baseline length (L) between the light
source and the camera is known from calibration,
using geometric triangulation from the known angle (θ
), the focal length of the camera (F), the image
coordinate of the illuminated point (P), and fixed
baseline length (L), the position of the illuminated
point (Pi) with respect to the camera coordinate
system can be calculated as follows ;

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Structured Light
In structured-light techniques a light pattern is
projected at a known angle onto the surface of
interest and an image of the resulting pattern,
reflected by the surface, is captured. The image is
then analyzed to calculate the coordinates of the
data point on the surface. A light pattern
can be;
(i) a single point.
(ii) a sheet of light (line)

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➢ The most commonly used pattern is a sheet of light that is
generated by fanning out a light beam. When a sheet of light
intersects an object, a line of light is formed along the contour of
the object. This line is detected and the X,Y,Z coordinates of
hundreds of points along the line are simultaneously calculated by
triangulation.
➢ The sheet of light sweeps the object as the linear slide carrying the
scanning system moves it in the X direction while a sequence of
images is taken by the camera in discrete steps. An index number k
is assigned to each of the images in the order they are taken.
Therefore, each k corresponds to the X position of the sheet of
light.
➢ To improve the capturing process, a light pattern containing
multiple strips is projected onto the surface of an object. To
distinguish between different strips, they must be coded
approximately so that the correspondence problem is solved
without ambiguity

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Non-Contact Methods - Optical
Techniques
➢ Interferometry (Moiré Effects)
➢ The interferometry technique is well known in dimensional
inspection as well as in flatness and deformation
measurements, in which structured- light patterns are
projected onto a surface to produce shadow Moiré effects.
➢ The light contours produced by moiré effects are captured in
an image and analyzed to determine distances between the
lines.
➢ This distance is proportional to the height of the surface at
the point of interest, and so the surface coordinates can be
calculated.
➢ The moiré technique gives accurate results for 3-D
reconstruction and measurement of small objects and
surfaces. However, it has limitations for larger objects because
precision is sacrificed for range.

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Time of Flight
➢ The principle behind TOF is to measure the amount of time (t)
that a light pulse (i.e., laser electromagnetic radiation) takes
to travel to the object and return. Because the speed of light
(C) is known, it is possible to determine the distance traveled.
➢ The distance (D) of the object from the laser would then be
equal to approximately one half of the distance the laser
pulse traveled.
➢ D=C * t/2
➢ For all practical purposes, the angle is very small and thus has
no effect on the accuracy of the TOF distance measurement.
The high velocity of light allows TOF scanners to make
hundreds, or even thousands of measurements per second.
The advantage of TOF techniques is that they can digitize
large, distant objects such as buildings and bridges.

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Coherent Laser Radar
➢ The system operates by using a sensor to direct a focused
invisible infrared laser beam to a point and coherently
processes the reflected light.
➢ As the laser light travels to and fro from the target, it also
travels through a reference path of calibrated optical fiber in
an environmentally controlled module.
➢ The two paths are combined to determine the absolute
range to the point.
➢ A very wide laser-modulation bandwidth (100 GHz) makes
precise measurement possible on a millisecond timescale.
The distance measurement is then combined with positional
information from two precision encoders to determine a
point on a surface in space. They can measure large-scale
geometry precisely.

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Computerized tomography
➢ CT is a powerful transmissive approach for 3-D
reconstruction. CT has revolutionized the medical diagnostic
field. It has also been called as computerized axial
tomography (CAT) or computerized transaxial tomography
(CTAT) or digital axial tomography (DAT).
➢ CT is a nondestructive method that allows three-dimensional
visualization of the internals of an object.
➢ CT provides a large series of 2-D X-ray cross-sectional images
taken around a single rotational axis. By projecting a thin X-
ray or Y-ray beam through one plane of an object from many
different angles and measuring the amount of radiation that
passes through the object along various lines of sight, a map
of attenuation coefficients (a density map or cross- sectional
image) for the scanned surface is reconstructed.

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➢Magnetic Resonance Imaging (MRI)
➢ MRI is a state-of-the-art imaging technology that uses magnetic
fields and radio waves to create high-quality, cross-sectional
images of the body without using radiation. When hydrogen
protons in the human body are placed in a strong magnetic field,
by sending in (and stopping) electromagnetic radio-frequency
pulses, these protons emit signals.
➢ These signals are collected and processed to construct cross-
sectional images. Compared to CT, MRI gives superior quality
images of soft tissues such as organs, muscle, cartilage,
ligaments, and tendons in many parts of the body.
➢ CT and MRI are powerful techniques for medical imaging and
reverse engineering applications; however, they are the most
expensive in terms of both hardware and software for data
processing.

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Model Reconstruction
The 3D model construction by reverse engineering falls into two
categories:
➢ . Surface reconstruction
➢ Solid model reconstruction
The 3D Surface reconstruction techniques are intended to
extract only the geometric information from the measured point
cloud and are commonly used in computer graphics and
computer vision.
The 3D Solid model reconstruction techniques are expected to
extract the geometric as well as the topological information
from the measured point cloud and has application in the field
of CAD/CAM.

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The primary technologies to transform a point cloud data
set obtained by scanning into a CAD modeling are based
on the formation of either a triangular polyhedral mesh
or pieces of segments that fit in the model.
The method of triangular polyhedral mesh is to first
construct a triangular mesh to capture the part
topological features based on the point cloud data.
It is an approximation presentation of surfaces and other
geometric features with triangles. Increasing the number
of triangles will yield a better presentation of the surface,
but will increase the file size at the same time. The
software file for triangulation is usually written in the
Standard Triangulation Language (STL), frequently
referred to as STL format.

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➢ The triangular mesh will subsequently be polished up to
reduce the redundant vertices (connected points) and
smooth the surface curvatures to meet the design
requirements. In the initial point cloud data collection and
intense data are often overlapped to ensure complete
coverage of the subject part.
➢ An appropriate processing of these raw data by
reorientation, realignment, removal, and addition of patch
is essential.
➢ In the segment approach, the initial point cloud data are
segmented into patches with defined boundaries. These
discrete surface patches will subsequently be smoothed by
appropriate mathematical modeling, such as parametric
modeling, quadric functions, or NURBS. Each patch will
then be fit into a region of the part surface to build the
simulated model.

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AM DATA FORMAT
STL FORMAT
➢ Representation methods used to describe CAD geometry vary from one
system to another. A standard interface is needed to convey geometric
descriptions from various CAD packages to rapid prototyping systems.
The STL (STereoLithography)
➢ The STL file [1–3], conceived by the 3D Systems, USA, is created from
the CAD database via an interface on the CAD system.
➢ This file consists of an unordered list of triangular facets representing
the outside skin of an object. There are two formats to the STL file. One
is the ASCII format and the other is the binary format. The size of the
ASCII STL file is larger than that of the binary format but is human
readable.
➢ In a STL file, triangular facets are described by a set of X, Y and Z
coordinates for each of the three vertices and a unit normal vector
with X, Y and Z to indicate which side of facet is an object.

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Because the STL file is a facet model derived from precise CAD models, it
is, therefore, an approximate model of a part. Besides, many commercial
CAD models are not robust enough to generate the facet model (STL
file) and frequently have problems.
there are several advantages of the STL file. First,
➢ it provides a simple method of representing 3D CAD data.
➢ Second, it is already a de facto standard and has been used by most
CAD systems and rapid prototyping systems. Finally, it can provide
small and accurate files for data transfer for certain shapes.
On the other hand, several disadvantages of the STL file exist.
➢ First, the STL file is many times larger than the original CAD data file
for a given accuracy parameter. The STL file carries much redundancy
information such as duplicate vertices and edges
➢ Second, the geometry flaws exist in the STL file because many
commercial tessellation algorithms used by CAD vendor today are not
robust. This gives rise to the need for a “repair software” which slows
the production cycle time.
➢ Finally, the subsequent slicing of large STL files can take many hours.

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STL FILE PROBLEMS
• The underlying problem is due, in part, to the difficulties
encountered in tessellating trimmed surfaces, surface
intersections and controlling numerical errors.

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1.Missing Facets or Gaps
Tessellation of surfaces with large curvature
can result in errors at the intersections
between such surfaces, leaving gaps or holes
along edges of the part model [8]. A surface
intersection anomaly which results in a gap
is shown in Figure

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2. Degenerate Facets
➢ A geometrical degeneracy of a facet occurs when all of the facets’ edges are
collinear even though all its vertices are distinct. This might be caused by
stitching algorithms that attempt to avoid shell punctures as shown in Figure
6.4(a)
➢ The resulting facets generated, shown in Figure 6.4(b), eliminate the shell
punctures. However, this is done at the expense of adding a degenerate facet.
While degenerate facets do not contain valid surface normals, they do represent
implicit topological information on how two surfaces mated. This important
information is consequently stored prior to discarding the degenerate facet.

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3. Overlapping Facets
Overlapping facets may be generated due to numerical
round-off errors occurring during tessellation.
The vertices are represented in 3D space as floating point
numbers instead of integers. Thus the numerical round-
off can cause facets to overlap if tolerances are set too
liberally. An example of an overlapping facet is illustrated
in Figure

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4.Non Manifold Conditions
There are three types of non-manifold conditions, namely:
(1) A non-manifold edge.
(2) A non-manifold point.
(3) A non-manifold face.
These may be generated because tessellation of the fine
features are susceptible to round-off errors. An illustration of
a non-manifold edge is shown in Figure 6.6(a).
Here, the non-manifold edge is actually shared by four
different facets as shown in Figure 6.6(b).

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A valid model would be one whose facets have only an
adjacent facet each, that is, one edge is shared by two
facets only.
Hence the non-manifold edges must be resolved such
that each facet has only one neighboring facet along
each edge, that is, by reconstructing a topologically
manifold surface [4]. In Figures 6.6(c) and 6.6(d), two
other types of non- manifold conditions are shown fig

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A valid Model

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Invalid Model

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STL file repair

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STL file repair

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STL file repair

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Additive Manufacturing software
• 1. Ansys
• 2. Autodesk Netfabb
• 3. 3dSystems
• 4. Siemens NX AM
• 5. Materialise Magics
• 6. Solid Edge
• 7. Amphyon
• 8. Genoa 3d simulation
• 9. Additive Lab
• 10. 3yourmind

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• . Ansys
• Ansys Additive Manufacturing Solutions (AMS) is a comprehensive suite of
software tools that enable engineers to design, optimize and validate parts and
assemblies for additive manufacturing.
• Using it, engineers can predict how a part will perform when printed using
various additive manufacturing processes, identify potential problems early in
the design process and make changes to avoid them.
• Features include
• Process simulation: By using process simulation for metal Powder Bed Fusions,
Directed Energy, Deposition, and Metal Binder jets, users can identify and
minimize the risk of build errors and ensure high-quality parts.
• Topology optimization: Ansys Topology Optimization produces design insights
in real-time, which drives lightweight design possibilities faster. That helps
reduce waste and increase efficiency while still meeting design requirements.
• Printability checking: The software checks for potential problems that could
occur during the additive manufacturing process, such as porosity or
delamination.
• Data acquisition and management: Ansys AMS helps manage the data
associated with additive manufacturing, including process settings, build files,
and post-processed data.
• Structural analysis: The software includes tools for analyzing the structural
integrity of additively manufactured parts.
• Directed energy deposition: Ansys AMS supports the Directed Energy
Deposition process, which builds parts with complex geometries.
•

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• 2. Autodesk Netfabb
• Autodesk Netfabb is a powerful, industrial-grade 3D printing software that
helps files get printed by automatically preparing, repairing, and optimizing
them for output.
• It provides users with various options for printing in different scales and
resolution levels, supports STL, OBJ, and AMF file formats, and can even
generate Gcode. With its easy-to-use interface and comprehensive
features, Autodesk Netfabb is an essential tool for anybody working with
3D printing.
• Features include
• Automatic file preparation: Autodesk Netfabb automatically prepares 3D
printing files for output, including repairing, cleaning, and orienting them.
• Support for multiple file formats: The software supports STL, OBJ, and AMF
file formats, as well as Gcode.
• Wide range of printing options: Autodesk Netfabb offers users a wide
range of options for printing in different scales and resolution levels.
• Selective structures: Solid volumes may be filled with custom structures to
produce distinctive material properties for your component.
• Optimization: It assures a maximal load capacity and reduces weight by
automatically verifying and modifying lattice and skin elements

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• 3. 3dSystems
• It is a suite of software tools for designing and engineering parts for
additive manufacturing (3D printing) on 3D Systems printers. It allows
users to create and edit 3D models, slice them into layers for printing,
and control the printing process.
• Its ADII is a machine designed with 3D Systems’ additive manufacturing
software. It can print parts in multiple colors and materials and has a
build volume of 10x10x10 inches.
• Features
• Rapid prototyping: helps users quickly design and prototype parts for
additive manufacturing.
• Multi-material printing: 3D Systems’ additive manufacturing solution
supports printing parts in multiple colors and materials.
• Connectivity: With an easily scalable, adaptable system, it adapts to
rapid material and printing technology progress.
• Requirement-driven orientation: It orients your part to the build
orientation that will minimize support material and build time.
• Direct metal printing: It offers outstanding build quality for direct metal
printing with a broad range of alloys, metals, and plastics.

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4. Siemens NX AM
Siemens NX, the additive manufacturing software, is a
computer-aided design and manufacturing software
that enables users to create, edit, and mill 3D models.
Companies can use the software in the aerospace,
automotive, and medical industries.
Additionally, the Siemens NX system is equipped with
powerful analysis tools, which makes it possible to
verify designs before they are sent to production.
Features
Integrated build tools: Siemens NX AM builds
preparation tools assist with efficiently placing,
orienting, and supporting components in the build tray.
Structure Validation: It allows the designer to check for
printability and then simulate the part’s performance in
the field using integrated tools to produce production-
ready components.
Quality and analytics: It allows you to keep track of the
additive manufacturing process, examine the resulting
data, and make improvements to parts and functions.

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• 6. Solid Edge
• Solid edge is a complete product development portfolio by Seimens. It is easy
to use, deploy and maintain and provides software tools for all aspects of the
product development process, such as 3D design, simulation, manufacturing,
and data management.
• Features
• 3D design – It provides many capabilities, including synchronous technology,
sheet metal design, modular plant design, CAD drawing, and assembly
modeling & management.
• Electrical design – Designs and simulates electrical systems and analyzes
models to calculate exact wire length
• Simulation – Provides capabilities like assembly design, digital validation, and
finite element analysis.
• Data management – CAD data management solution enables you to secure
and control your product data and process. Shares product information and
collaborates.
• 3D printing – Design and 3D print your products.
• 2D drafting – Generates high-quality 2D drawings, simple drawing layouts,
diagramming, and annotation.
• Computer-Aided Manufacturing – Allows manufacturers to use new
manufacturing processes like CNC machining, nesting, cutting, bending,
molding, etc.

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• 7. Amphyon
• It is especially known for metal additive manufacturing (LBM, SLM, DMLS, Metal
3D Printing). It is simulation-based process preparation software.
• Features
• Examiner – optimizes applications based on analyzing and evaluating required
support volume build time, surface accessibility, distortion sensitivity, and post-
processing effort for every orientation.
• Supports – Creates optimized support structures.
• Mechanical process simulation – Calculates the residual stress and distortion
fields on regular desktop hardware.
• Thermal process simulation – Calculates temperature history and field on regular
desktop hardware.
• Predeformation – solution to pre-compensate residual distortions
• Integration with any brand of 3d printer
• Automates all the processes such as order, material, part import, orientation,
support, nesting, and slicing,

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• 8. Additive Lab
• It is a metal additive manufacturing software and provides
simulation technology that helps to predict metal-
deposition AM processes. In addition, it offers complete
access to all its features through a Python scripting
interface.
• Features
• Mechanical analysis
• Thermal analysis
• Customization of simulations
• Powder Bed Additive Manufacturing
• Direct Energy Deposition processes
• Scanning pattern analysis
• Melt pool analysis

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• 10. 3yourmind
• 3yourmind is AM workflow software solution that provides
additive manufacturing strategies to many industries,
including oil and gas, defense, aerospace, medical,
automotive, railway, and machine & tooling.
• Features
• CAD integration
• API integration
• Inventory analysis
• Centralized data storage
• Orientation optimization
• AM part identification

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Need of AM software
• In order to modelling
• For optimization of the product
• To convert 3D to STL file format
• To simulate 3D printing process before
physical print
• To fix the error in STL file
• To monitor the printing process
• To store the database during printing

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Important Questions
1. Explain basic steps involved in Reverse Engineering
2. What is the importance of Reverse Engg.
3. What are the types of Digitization Techniques explain
contact type techniques and its types.
4. Write a note on non contact types digitization Technique
5. Explain any 3 types of optical type Digitization technique
6. Discuss concept of model Reconstruction in reverse
engineering
7. What are the errors occurred in STL file explain.
8. Write a note on Valid and Invalid model
9. Write a note on AM software

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