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A Seminar Presentation on

ABHISHEK THOTEM.Tech, CAD-CAMVNIT, NAGPUR

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What is Reverse Engineering ?

Reverse Engineering is an activity which consists of creationof a CAD model & manufacturing of a mechanical partby scanning it and obtaining it’s geometrical details.

Need of Reverse Engineering :

To provide spares for replacing broken or worn out partsfor which no technical data is available. This can be thecase if the part was originally imported (without drawings)or the drawings being misplaced or lost.

Creation of unlicensed/unapproved duplicates. Competitive technical intelligence (understand what your

competitor is actually doing, versus what they say they aredoing).

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STEP[1]• OBTAINING THE PART GEOMETRY

STEP[2]• MATERIAL IDENTIFICATION

STEP[3]• 3-D CAD MODEL GENERATION

STEP[4]• MANUFACTURING OF A PART

STEPS IN REVERSE ENGINEERING :

STEP [1] OBTAINING THE PART GEOMETRY :-

It involves ‘automatic digitizing’ of thesurface of a physically existing object i.e. 3-D image of the object is obtained by scanning the entire object.

There are two ways of digitizing:[1] Contact type digitizing.[2] Non-contact type digitizing.

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[1]Contact Type digitizing:In this method, there is physical contact

between the measuring instrument and the surface being measured to record as many dimensions as possible.

It includes following instruments.(a) Hand Tools : Micrometers, Vernier calipers and Gauges These are used to capture the critical

dimensions needed to generate a part drawing.

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(b) Co-ordinate measuring machine ( CMM ) :A CMM consists of a contact probe that can be positionedin 3-D space relative tothe surfaces of workpartand x, y & z coordinatesof the probe are accurately and preciselyrecorded to obtaindimensional dataconcerning the partgeometry.

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[2] Non-Contact Type digitizing:

Data acquisition is done without physicallytouching the part.

It uses structured lighting and reflectionfrom the object to get the 3-D image

of the object.

It consists of following techniques :-(1) 3-D Laser Scanning(2) Industrial CT Scanning

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1. Reflection of LASER

Light from object

2. Capture of light

by CCD sensor

3. Cloud of points

( COP ) generation

4. 3-D Image

formation

(1) 3-D Laser Scanning :Working Principle

Two Types ofTechniques:(a) Triangulation(b) Time-of-flight

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Functional Diagram

(a) Triangulation Technique:

Angle of LASER emitter withhorizontal = 90 degree

Angle between incident & reflected ray (α) is determined by looking at the location of the laser dot in the sensor's field of view.

Distance between emitter & receiver (d) is known.

Height = d/tan (α) Hence, location of point on

sensor’s reference frame is found out.

CCD - Charge Coupled DevicePSD - Position Sensitive Device

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A Point Cloud is a set of vertices in a 3-D coordinate system. Point clouds are most often created by 3D scanners. The point cloud represents the set of points that the device

has measured. Many no. of points detected by scanner give 3-D image

of the object. This point clouded

3-D image is convertedinto CAD modelsby Reverse engineeringsoftwares.

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A hand-held 3D laser scanner in use for 3D modeling a 1000-year-old Viking belt buckle. The scanner has a camera to accurately texture map the object.

Example (1)

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Scanning the object using Triangulation TechniqueLaser Tracking Mechanism : Infrared LEDs

Example (2)

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(b) Time-of-flight Technique : It is used for range-finding purpose. It finds the distance of a surface

by timing the round-trip timeof a pulse of light.

● c = velocity of light,● Round-trip time (t) =

2 * time required to traveldistance between scanner& surface

● distance (d) = c.t/2

Accuracy depends on how precisely we can measure the time (t). 3.3 picoseconds(approx.) is the time taken for light to travel

1 millimeter.

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(2) Industrial CT (Computed Tomography) Scanning :

Tomography refers to imaging by sections orsectioning, through the use of any kind of penetrating wave. A device used in tomography iscalled a Tomograph, while the image produced isa Tomogram.

It uses X-ray equipment to produce3-D representations of componentsboth externally and internally.

Types of scanners :(i) Fan/Line beam scanners(ii) Cone beam scanners

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(i) Fan/Line beam scanners-[Translate] :

These are Line scanners. It is the first generation of industrial CT Scanners. X-rays are produced and the beam is collimated to create a line. The X-ray line beam is then translated across the part and data

is collected by the detector in the form of 2-D image slices. The data is then reconstructed to create a 3-D Volume rendering

of the part.

Detector

Collimated beamof X-rays

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(ii) Cone beam scanners-[Rotate] :

During the CT scan, part isplaced on a rotary table.

As the part rotates the coneof X-rays produce about1300 2D images which arecollected by the detector.

The 2D images are thenprocessed to create a 3DVolume rendering of theexternal and internalgeometries of the part.

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Examples ofCT scanning :

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Advantages of using CT scanning over other techniques such as CMM or 3D laser scanners :

• A non-destructive test for inspection and metrology

• Inspection and analysis costs from first article to production are

significantly reduced

• Design requirements for both internal and external components

are validated quickly and accurately

• Product quality is improved.

• Internal complex features can be precisely measured without

destructive testing

• Parts are scanned in a free-state environment without applying

stresses which could damage delicate parts.

• For the first time, rapid prototyping of the internal components

can be completed without the daunting task of creating the CAD

file from scratch.

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STEP[2] MATERIAL IDENTIFICATION :-

Identifying the material composition of theexisting part is the second most important task.

There are several well-established non-destructiveand destructive techniques to find the compositionof part material.(1) Mass Spectrometry(2) Scanning Electron Microscope (SEM)

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(1) Mass Spectrometry :

A sample loaded on to the mass spectrometerundergoes vaporization. Hence, it is also called as Vapour Phase Chemistry.

We get spectral lines of various masses of components.Hence, it is called Mass Spectrometry.

It measures the mass-to-charge ratio[m/Q]ofcharged particles(ions) created in the process.

It is used for determining masses of particles,for determining the elemental compositionof a sample or molecule.

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Working Principle :

Newton's Second Lawof motion : F = ma

Lorentz Force Law :F = Q (E + V * B)

ma = Q (E + V * B)

Mass to Charge ratio :

E → Electric fieldm → Mass of ionQ → Charge on ionV*B → Vector cross product of ion velocity & magnetic field

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(2) Scanning Electron Microscope (SEM)

It is a type of electron microscope that producesimages of a sample by scanning over it with a highenergy focused beam of electrons.

It uses Energy Dispersive X-ray (EDX) to producean image of microscopic structure on computer.

Electron beam's positionis combined with thedetected X-ray signalto produce an image.

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Characteristic X-raysare emitted when theelectron beam removesan inner shell electronfrom sample , causing higher-energy electronto fill the shell andrelease energy.

Intensity of the BackScattered Electron(BSE)signal is strongly relatedto the atomic number (Z)of the specimen.

BSE images can provideinformation about the distribution of differentelements in the sample.

Diagram :

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STEP [3] 3-D CAD MODEL GENERATION :-

After scanning, we get 3-D image of a part. It is converted into 3-D CAD model by Reverse engineering

software such as Geomagics ,Imageware Surfacer,Magics, Pro/Scan Tools ,Rapidform and STRIMwhich are specially developed for this purpose.

STEP [4] MANUFACTURING OF A PART :-

Once the 3-D CAD model is generated, it is manufacturedby using various manufacturing techniques.

Mainly, Rapid Prototyping is used for this purpose.

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References :

(1) Defence Science Journal, DESSIDOC,DRDO, New Delhi, in print, 2005“Computer-Aided Reverse Engineeringfor Rapid Replacement Parts” : A Case Study

(2) “KBRE: A Knowledge Based Reverse Engineeringfor Mechanical Components”Troyes, University of Technology

(3) “Reverse Engineering of Automotive Parts”Masters of Science DegreeThe University of Tennessee, Knoxville

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