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Rev engg


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Rev engg

  1. 1. 1 A Seminar Presentation on ABHISHEK THOTE M.Tech, CAD-CAM VNIT, NAGPUR
  2. 2. 2 What is Reverse Engineering ?  Reverse Engineering is an activity which consists of creation of a CAD model & manufacturing of a mechanical part by scanning it and obtaining it’s geometrical details. Need of Reverse Engineering :  To provide spares for replacing broken or worn out parts for which no technical data is available. This can be the case 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 are doing).
  4. 4. STEP [1] OBTAINING THE PART GEOMETRY :-  It involves ‘automatic digitizing’ of the surface 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. 4
  5. 5. 5 [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.
  6. 6. 4 (b) Co-ordinate measuring machine ( CMM ) : A CMM consists of a contact probe that can be positioned in 3-D space relative to the surfaces of workpart and x, y & z coordinates of the probe are accurately and precisely recorded to obtain dimensional data concerning the part geometry.
  7. 7. 7 [2] Non-Contact Type digitizing:  Data acquisition is done without physically touching the part.  It uses structured lighting and reflection from 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
  8. 8. 8 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 of Techniques: (a) Triangulation (b) Time-of-flight
  9. 9. 9 Functional Diagram (a) Triangulation Technique:  Angle of LASER emitter with horizontal = 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 Device PSD - Position Sensitive Device
  10. 10. 10  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 converted into CAD models by Reverse engineering softwares.
  11. 11. 11 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)
  12. 12. 12 Scanning the object using Triangulation Technique Laser Tracking Mechanism : Infrared LEDs Example (2)
  13. 13. 13 (b) Time-of-flight Technique :  It is used for range-finding purpose.  It finds the distance of a surface by timing the round-trip time of a pulse of light. ● c = velocity of light, ● Round-trip time (t) = 2 * time required to travel distance 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.
  14. 14. 14 (2) Industrial CT (Computed Tomography) Scanning :  Tomography refers to imaging by sections or sectioning, through the use of any kind of penetrating wave. A device used in tomography is called a Tomograph, while the image produced is a Tomogram.  It uses X-ray equipment to produce 3-D representations of components both externally and internally. Types of scanners : (i) Fan/Line beam scanners (ii) Cone beam scanners
  15. 15. 15 (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 beam of X-rays
  16. 16. 16 (ii) Cone beam scanners-[Rotate] :  During the CT scan, part is placed on a rotary table.  As the part rotates the cone of X-rays produce about 1300 2D images which are collected by the detector.  The 2D images are then processed to create a 3D Volume rendering of the external and internal geometries of the part.
  17. 17. 17 Examples of CT scanning :
  18. 18. 18 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.
  19. 19. 19 STEP[2] MATERIAL IDENTIFICATION :-  Identifying the material composition of the existing part is the second most important task.  There are several well-established non-destructive and destructive techniques to find the composition of part material. (1) Mass Spectrometry (2) Scanning Electron Microscope (SEM)
  20. 20. 20 (1) Mass Spectrometry :  A sample loaded on to the mass spectrometer undergoes 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]of charged particles(ions) created in the process.  It is used for determining masses of particles, for determining the elemental composition of a sample or molecule.
  21. 21. 21 Working Principle : Newton's Second Law of motion : F = ma Lorentz Force Law : F = Q (E + V * B) ma = Q (E + V * B) Mass to Charge ratio : E → Electric field m → Mass of ion Q → Charge on ion V*B → Vector cross product of ion velocity & magnetic field
  22. 22. 22 (2) Scanning Electron Microscope (SEM)  It is a type of electron microscope that produces images of a sample by scanning over it with a high energy focused beam of electrons.  It uses Energy Dispersive X-ray (EDX) to produce an image of microscopic structure on computer.  Electron beam's position is combined with the detected X-ray signal to produce an image.
  23. 23. 23  Characteristic X-rays are emitted when the electron beam removes an inner shell electron from sample , causing higher-energy electron to fill the shell and release energy.  Intensity of the Back Scattered Electron(BSE) signal is strongly related to the atomic number (Z) of the specimen.  BSE images can provide information about the distribution of different elements in the sample. Diagram :
  24. 24. 24 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 STRIM which are specially developed for this purpose. STEP [4] MANUFACTURING OF A PART :-  Once the 3-D CAD model is generated, it is manufactured by using various manufacturing techniques.  Mainly, Rapid Prototyping is used for this purpose.
  25. 25. 25 References : (1) Defence Science Journal, DESSIDOC, DRDO, New Delhi, in print, 2005 “Computer-Aided Reverse Engineering for Rapid Replacement Parts” : A Case Study (2) “KBRE: A Knowledge Based Reverse Engineering for Mechanical Components” Troyes, University of Technology (3) “Reverse Engineering of Automotive Parts” Masters of Science Degree The University of Tennessee, Knoxville
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