COMPUTER CONTROL IN PROCESS PLANNING Unit 2 (ME CAD/CAM)
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This document provides information on part design preparation for computer control process planning (CCPP). It discusses topics like computer-aided drafting and design (CADD), basic dimensions, geometric characteristic controls, characteristics and symbols, CAD input/output devices, topology, geometric transformations, data structures, geometric modeling for process planning, GT coding principles and examples, and part classification coding systems like Opitz and MICLASS. The document is an educational reference for the concepts and methodologies used in part design preparation for computer-based process planning.
COMPUTER CONTROL IN PROCESS PLANNING Unit 2 (ME CAD/CAM)
- 1. COMPUTER CONTROL PROCESS PLANING UNIT 2 PART DESIGN PREPARATION CCPP PART DESIGN PREPARATION 1
- 2. Design Drafting Computer-Aided Drafting and Design (CADD)is the process where a drafter/designer/engineer creates drawings or models that define a given product before it is ready to be manufactured. The drafter is the key link in the design engineering process and manufacturing steps, and must possess a working knowledge of design principles, material properties, and manufacturing processes. CCPP PART DESIGN PREPARATION 2
- 3. Basic Dimension A theoretically exact size, profile, orientation, or location of a feature or datum target, therefore, a basic dimension is untoleranced. Most often used with position, angularity, and profile) Basic dimensions have a rectangle surrounding it. 1.000
- 5. GEOMETRIC CHARACTERISTIC CONTROLS 14 characteristics that may be controlled TYPE OF FEATURE TYPE OF TOLERANCE CHARACTERISTIC FLATNESS INDIVIDUAL (No Datum Reference) FORM STRAIGHTNESS CIRCULARITY CYLINDRICITY INDIVIDUAL or RELATED FEATURES PROFILE LINE PROFILE SURFACE PROFILE PERPENDICULARITY ORIENTATION RELATED FEATURES (Datum Reference Required) RUNOUT ANGULARITY PARALLELISM CIRCULAR RUNOUT TOTAL RUNOUT CONCENTRICITY LOCATION POSITION SYMMETRY SYMBOL
- 6. Characteristics & Symbols cont’d. Maximum Material Condition MMC Regardless of Feature Size RFS Least Material Condition LMC Projected Tolerance Zone Diametrical (Cylindrical) Tolerance Zone or Feature Basic, or Exact, Dimension Datum Feature Symbol Feature Control Frame
- 7. CAD-input / output devices II. Input Devices a. Keyboard,mouse,joystick,scanners,digital camera, bar code reader, touch Sreeen,Speech input device (microphone) III. Output Devices a. Monitor , Speaker, Printers ( different types) CCPP PART DESIGN PREPARATION 7
- 8. TOPOLOGY Topologydescribes how elements are bounded and connected. Geometry describes the shape of each individual element. CCPP PART DESIGN PREPARATION 8
- 9. Topological entities Topological entities comprise all the entities that are used to construct the structure or skeleton of a model January 26, 2014 PART DESIGN PREPARATION 9
- 11. Geometrical transformations Transformations are a turn, flip, or slide of any figure.
- 12. Geometrical transformations If a figure is represented by ABC, the image of this figure will be represented by A’B’C’ (ABC PRIME) Image A B C ’ A ’ Preimage C B A figure and its image will be congruent to each other. ’ They will have the same shape and the same size.
- 13. Transformations: Translations (slides) A translation is a transformation whose points are all the same relative distance from the pre-image and which is pointing in the same direction.
- 14. Transformations: Reflections (flips) A reflection is an isometry in which a figure and its image have opposite orientations 3 3 3 7 2 0 3 3 3 7 2 0 An isometry is when the distance between any two points in the pre-image must be the same as the distance between the images of the two points.
- 15. Doing reflections: easy tricks Y-Axis Tricks If the mirror line is the yaxis, just change each (x, y) into (-x, y) X-Axis If the mirror line is the xaxis, just change each (x, y) into (x, -y)
- 16. Symmetry If a line is drawn down the middle of an object, both sides would be identical.
- 17. Axial Symmetry The points on the left side of the Y-axis will be at the negative coordinates of the points on the right side: a perfect mirror image. Example: 4 4 1 0 1 0 5 5
- 18. Transformations: Rotations (turns) A rotation turns all of the points in a figure around a given point, called the center of rotation. The center of rotation is the only point that does not change during the rotation. A’ = r(A) A’B’ = r(AB) A B A’ B’
- 19. Transformations: Rotation 180-degree turn = half turn A positive angle rotation is when one figure is rotated counter-clockwise A negative angle rotation is when the figure is rotated clockwise.
- 20. Transformations: Identity If the point of the pre-image and of the image is exactly the same, this point is united. If ALL of the points of the pre-image and image are the same, the entire figure is united.
- 21. Transformations: Expansions & Contractions Produces an image that is the same shape as the original, but it is a different size. Expansion if the scale factor is greater than 1 Contraction is the scale factor is between 0 and 1
- 23. Inverse translations If a transformation maps the pre-image onto its image, then the inverse transformation maps the image back onto the pre-image. Basically, it is the same process, but backwards. A ’ A t1 B ’ B C C ’
- 24. DATA STRUCTURES Each geometric model of an object in a CAD system is represented by a set of data. The data consist of numerical values, names, codes and symbols. This data are stored in computer memory in an organized manner. This organization represents the relationship of each data element to other elements; included in this relationship is the topological relationship of surface geometry. There are also other relationship, such as names and their associated geometries. A more complete survey on the different types of data structure for computer graphics can be found in two technical papers by Williams (1971) and Grays (1967). In this section only a general data structure of CAD will be described. The first item in the edge list, therefore, represents the number of edges. In the fig, edge 1 is represented by the data “ 3,3,4,5,” where the first 3 indicates that there are three edges; 3,4 & 5. Each edge has two vertices (edge 3 has V1 & V3). Finally, a vertex may store all the coordinates of vertices. 22.10.2013 PART DESIGN PREPARATION 24
- 25. For holes, circles, and other curves and curved surfaces, a code is necessary to distinguish them for polyhedron surfaces. For manufacturing purposes technological information’s, such as dimensions, tolerances, and geometric tolerances, are essential. They must also be included in constructing the CAD data structure. Most current systems explicitly (or more approximately externally) define such information in a manner similar to the way in which a draftsman would. Dimensioning and tolerancing information is not implicit defined within the model. For a explicit dimensioning another list is added to store the dimensioning information. CCPP PART DESIGN PREPARATION 25
- 26. Sample footer 26
- 27. Data Exchange Between CAD/CAM Systems (Data structures) Why do we need Data Exchange? Why do we need Data Exchange Design projects require data to be shared between suppliers Different companies often used different CAD systems All CAD systems have their own database formats They are mostly proprietary and often confidential Data is stored in different ways e.g. 1.0,2.0,3.0 or X1.0,Y2.0,Z3.0, etc. Data conversion between systems becomes necessary CCPP PART DESIGN PREPARATION 27
- 28. Data Exchange Formats IGES (Initial Graphics Exchange Specification) 1980 US NIST, National Institute of Standards and Technology DXF VDA – German Automotive Industry SET – Airbus PDES – American fore-runner of STEP STEP STL VRML CCPP PART DESIGN PREPARATION 28
- 29. GEOMENTRIC MODELING FOR PROCESS PLANNING In the preceding section, the fundamentals of CAD were discussed. In this section a discussion 3-D representation schemes and their applications to process planning is presented. There are seven different types of graphics representation schemes: Wire frame Primitive instancing Spatial occupancy enumeration Cell decomposition Constructive solid geometry (CSG) Boundary representation Sweeping CCPP PART DESIGN PREPARATION 29
- 30. GT coding Introduction It is true that classification helps to bring like things together, but with out having a proper coding system which reflecting the classification is introduced, handling, processing families of similar data or retrieving relevant information is more cumbersome and inefficient. Most of the time, coding is thought of in its cryptological sense, meaning to restrict and suppress the dissemination of intelligence and/or information during communication. However, when we describe it in the business and industrial context, quite the reverse is true. In industries properly designed codes are used as a shorthand, as a means to compress information and improve its communication effectiveness through the business and the outside environment. CCPP PART DESIGN PREPARATION 30
- 31. Types of Coding Industrial codes can take several forms. Those, which use the alphabet and/or numerals, are called alpha or numeric codes or as combinations of the two as alphanumeric codes. But there are also special symbol codes which are not derived from either alphabetic or numeric sources. Here we can see the different types of codes as follows. Attribute code structure Hierarchical Type Hybrid Type Special Symbol codes Sample footer 31
- 32. Attribute code structure In this type of structure, the interpretation of each symbol in the sequence is fixed and represents one feature. Thus, the value of any given digits (or position) within the code does not depend on the preceding digits. Another name of this type of symbol is poly-code. The problem associated with poly-code is that the code tends to be relatively long. On the other hand, the use of poly-code allows for convenient identification of specific part attribute. This can be helpful in recognizing parts with similar processing requirements. A typical attribute code is illustrated in the table below. Sample footer 32
- 33. Hierarchical Type In this type of code structure, each code number is qualified by the preceding digits (characters). Thus if the first digits define the type of material used, such as steel, the second digits will define a feature related to steel (like carbon constraint), and the next digit will define a feature related to the feature defined in the second digit and so on. A typical hierarchical code structure is shown in Figure below. As it was shown in the diagram, each digit is directly related to the preceding digits. Thus the second digits “2” may define a power unit of the work part, the digit in the third position may then define the type of power system (i.e. weather it is mechanical, hydraulic, or electric). In the fourth position if a digit “1” is preceded by “1”, then it may define the sub unit of the driving system that is a rotational part, or if it is proceeded by “3” it might have totally different meaning. Sample footer 33
- 34. Hybrid Type: Most of the commercial parts coding system in industries are a combination of the two pure structure (i.e. poly codes and mono codes). The hybrid is an attempt to achieve the best feature of both poly-codes and mono-codes. Hybrid codes are typically constructed as a series of short poly codes. Within each of these shorter chains, the digits are independent, but one or more of symbols in the complete code number are used to classify the part population into groups, as in the hierarchical structure. This hybrid coding seems to best serve the need of both design and production. Sample footer 34
- 35. Special Symbol codes: This is a type of code that used picture or symbols of an object other than numbers or alphabets to represent an activity, event, words, etc. This special symbol codes can be hieroglyphical, which can best characterized by the symbolic therbligs, created by Frank and Lillian Gilbreths or of more recent vintage, the flow chart codes for tracking the handling of data within a system. During their study of work and time-and motion, they used an epitomized hieroglyphic code symbols to represent a fundamental motions such as reach, grasp, think, etc. The hieroglyphic code symbols described by the therbligs codes pictorially represent the action they describe. Sample footer 35
- 36. Principles of Coding As in the case of classification, an industrial coding has also its own principles. These includes: 1. No code should exceed five characters without a break in the string. That means when the code number becomes shorter it becomes easy to handle and, fewer errors committed. 2. Identity codes should of fixed length and pattern. If we use varying-length codes within a given class of materials it will proliferate error rates and require justification in handling (right or left) to the longest code in use. 3. All-numeric codes produce fewest errors. 4. Alphanumeric combination codes are acceptable if the alpha field is fixed and used to break a string of numbers. CCPP PART DESIGN PREPARATION 36
- 37. The optiz system The Opitz coding system uses the following digit sequence: 12345 6789 ABCD The basic code consists of nine digits, which can be extended by adding four more digits. The first nine digits are intended to convey both design and manufacturing data. The general interpretation of the nine digits is indicated in Fig in next slide The first five digits, 12345, are called the “form code” and describe the primary design attributes of the part. The next four digits, 6789, constitute the “supplementary code”. It indicates some of the attributes that would be of use to manufacturing (work material, raw work piece shape, and accuracy). The extra four digits, “ABCD”, are referred to as the “secondary code” and are intended to identify the production operation type and sequence. The secondary code can be designed by the firm to serve its own particular needs. CCPP PART DESIGN PREPARATION 37
- 40. EXAMPLE Given the part design of Fig. 9.7, the form code for this part is discussed below. The overall length/diameter ratio, L/D = 1.6, so the first code = 1. The part is stepped on both ends with a screw thread on one end, so the second digit code would be 5 the third digit code is 1 because of the through hole. The fourth and fifth digits are both 0, since no surface machining is required and there are no auxiliary holes or gear teeth on the part. The complete form code in the Opitz system is “15100”. To add the supplementary code, we would have to properly code the sixth through ninth digits with data on dimensions, material, starting work piece shape, and accuracy. CCPP PART DESIGN PREPARATION 40
- 41. The MICLASS system The MICLASS classification number can range from 12 to 30 digits The first 12 digits are universal code that can be applied to any part. Up to 18 additional digits can be used to code data that are specific to the particular company or industry. For example, lot size, piece time, cost data, and operation sequence might be included in the 18 supplementary digits. The component attributes coded in the first 12 digits of the MICLASS number are as follows: 1st digit Main shape 2nd and 3rd digits Shape elements 4th digit Position of shape elements 5th and 6th digits Main dimensions 7th digit Dimension ratio 8th digit Auxiliary dimension 9th and 10th digits Tolerance codes 11th and 12th digits Material codes CCPP PART DESIGN PREPARATION 41
- 42. THANK YOU January 26, 2014 PART DESIGN PREPARATION 42