CAD

1. CAD/CAM �2002 The Ohio State University �2002 The Ohio State University

2. Manufacturing Methods Manufacturing Methods Taken Mostly from Kalpakjian (Manufacturing Processes for Engineering Materials, Addison Wesley, 2nd Ed- 1991) There are many manufacturing processes used throughout industry. Some of the more common practices include the categories of net shaping, machining, and joining. Displayed are the the basic subsections of these manufacturing methods. Net shape includes (read slide), Machining includes (read slide), and joining involves (read slide) The fundamental difference between machining and net shape is that machining produces CHIPS, net shape does not Manufacturing Methods Taken Mostly from Kalpakjian (Manufacturing Processes for Engineering Materials, Addison Wesley, 2nd Ed- 1991) There are many manufacturing processes used throughout industry. Some of the more common practices include the categories of net shaping, machining, and joining. Displayed are the the basic subsections of these manufacturing methods. Net shape includes (read slide), Machining includes (read slide), and joining involves (read slide) The fundamental difference between machining and net shape is that machining produces CHIPS, net shape does not

3. Computer Aided Design Computer Aided Design (CAD)- Use of computers to assist with the design process NC Machining (�50s) introduced a need for numerical part models to drive the machines Drafting using computers became a reality when graphics were added (CAD used to mean computer aided drafting) Finite Element Analysis (FEA) became popular in late �60s Interactive Graphical User Interfaces (GUIs) made FEA programs much more productive and accessible CAD has a wide variety of applications, including system modeling and synthesis, kinematic simulation and design, and optimization Computer aided design is the use of a computer to assist in the design process, as you may infer from its name. It really began in the 1950s when NC Machining introduced a need for some numerical based part models to drive the machines. In particular, the aerospace and automotive industries used NC machines to create very complex 3-D surface. Much work was done in these areas to generate numerical models of these surfaces. The addition of graphics made computer aided drafting a reality. Drafting was the dominant use for computers in design-- for a time CAD meant computer aided drafting. Today computer aided drafting with many �simple� 2-d drafting packages is still one of the major uses of computers to aid the design process. Finite Element Analysis became popular in late 1960�s. Interactive Graphical User Interfaces or GUIs made the FEA programs much more accessible, by allowing the user to visualize the inputs and outputs. Before the output could be neatly displayed it was very hard to know if one had modeled and then meshed his piece correctly, and even harder to determine if the constraints had been correctly applied to the correct nodes. Today CAD has a huge variety of applications in addition to those already mentioned such as system modeling and synthesis, kinematic simulation and design, and optimization. Computer aided design is the use of a computer to assist in the design process, as you may infer from its name. It really began in the 1950s when NC Machining introduced a need for some numerical based part models to drive the machines. In particular, the aerospace and automotive industries used NC machines to create very complex 3-D surface. Much work was done in these areas to generate numerical models of these surfaces. The addition of graphics made computer aided drafting a reality. Drafting was the dominant use for computers in design-- for a time CAD meant computer aided drafting. Today computer aided drafting with many �simple� 2-d drafting packages is still one of the major uses of computers to aid the design process. Finite Element Analysis became popular in late 1960�s. Interactive Graphical User Interfaces or GUIs made the FEA programs much more accessible, by allowing the user to visualize the inputs and outputs. Before the output could be neatly displayed it was very hard to know if one had modeled and then meshed his piece correctly, and even harder to determine if the constraints had been correctly applied to the correct nodes. Today CAD has a huge variety of applications in addition to those already mentioned such as system modeling and synthesis, kinematic simulation and design, and optimization.

4. Modeling Methods In order to use the computer for any design purpose, we have to be able to model the objects. We are mostly looking at ways to model physical objects here. Note that virtually all of the techniques shown in the slide are still used today, but the slide does represent a progression as well. Originally things began with graphical modeling- that was used for drafting. This is the standard job of points connected by lines. First there were the 2-d packages; later, 3-d capability was added. These graphical based modelers, and even simple 2-d graphical modelers still represent a large portion of the modeling packages in use today. Another early use of computers in design was to generate numerical models for NC machining of complex 3-d surfaces in the aerospace and automotive industries. Surface modeling is another modeling method. There are two basic methods that surface modelers use. Parametric surfaces are defined by a collection of points whose coordinates are defined as functions of two parameters. Ruled surfaces are generated by drawing straight lines between parametric curves. Many other industries also have a need to model surfaces. Surface modeling is used by the industrial designers quite often to get nice, aesthetically pleasing surfaces. However, many other industries also have the ned to model surfaces. As opposed to surface modeling, we can also try to model the solid object itself. Again there are several different methods to accomplish this task, we shall look at them in more detail on the next slides. Decomposition seeks to break up the object into small pieces and model it by assembling the pieces. Constructive modelers represent objects as combinations of basic building blocks. Boundary representation models the object by defining its bounding surfaces. Finally feature based modeling is a step forward, introducing something called a feature to help the user better store and communicate design information.In order to use the computer for any design purpose, we have to be able to model the objects. We are mostly looking at ways to model physical objects here. Note that virtually all of the techniques shown in the slide are still used today, but the slide does represent a progression as well. Originally things began with graphical modeling- that was used for drafting. This is the standard job of points connected by lines. First there were the 2-d packages; later, 3-d capability was added. These graphical based modelers, and even simple 2-d graphical modelers still represent a large portion of the modeling packages in use today. Another early use of computers in design was to generate numerical models for NC machining of complex 3-d surfaces in the aerospace and automotive industries. Surface modeling is another modeling method. There are two basic methods that surface modelers use. Parametric surfaces are defined by a collection of points whose coordinates are defined as functions of two parameters. Ruled surfaces are generated by drawing straight lines between parametric curves. Many other industries also have a need to model surfaces. Surface modeling is used by the industrial designers quite often to get nice, aesthetically pleasing surfaces. However, many other industries also have the ned to model surfaces. As opposed to surface modeling, we can also try to model the solid object itself. Again there are several different methods to accomplish this task, we shall look at them in more detail on the next slides. Decomposition seeks to break up the object into small pieces and model it by assembling the pieces. Constructive modelers represent objects as combinations of basic building blocks. Boundary representation models the object by defining its bounding surfaces. Finally feature based modeling is a step forward, introducing something called a feature to help the user better store and communicate design information.

5. Solid Modeling This slide represents a detailed breakdown of solid modeling, item C on the previous slide. There are 3 basic methods that computers will use to model an object as a solid object. In decomposition, one breaks things down into tiny blocks and builds the part block by block. Exhaustive enumeration breaks all space into evenly spaced bricks. A 3-d matrix stores information on the material type (or lack of material) in each block. Cellular decomposition just blocks out the part or parts being modeled into an irregular grid. Finally, space subdivisions uses a recursive scheme to block out all space. Constructive models allow the user to build the object by combining or subtracting various base shapes. More formally, the user assembles the model by combining graphical primitives with Boolean logic. The primitives are half spaces. A half space was defined by some function of x,y, and z, which could be used to split space into two halves. One part of space would result in the function being greater than zero when evaluated there, and the other would result in the function being less than zero. These half spaces are assembled to form a model. This works nicely, but the trouble with it is that most half spaces are infinite, and users are not comfortable working with these. So CSG or constructive solid geometry allows the user to interact with bounded objects- such as finite cylinders. In truth the computer still uses half spaces and models the finite cylinder as the intersection of an infinite cylinder with the space above one plane and below another plane. However, the user can work directly with finite objects. Finally in Boundary Representation or BREP, an object is represented by dividing its surface into a series of faces. The computer �knows� the part as the area inside the faces.This slide represents a detailed breakdown of solid modeling, item C on the previous slide. There are 3 basic methods that computers will use to model an object as a solid object. In decomposition, one breaks things down into tiny blocks and builds the part block by block. Exhaustive enumeration breaks all space into evenly spaced bricks. A 3-d matrix stores information on the material type (or lack of material) in each block. Cellular decomposition just blocks out the part or parts being modeled into an irregular grid. Finally, space subdivisions uses a recursive scheme to block out all space. Constructive models allow the user to build the object by combining or subtracting various base shapes. More formally, the user assembles the model by combining graphical primitives with Boolean logic. The primitives are half spaces. A half space was defined by some function of x,y, and z, which could be used to split space into two halves. One part of space would result in the function being greater than zero when evaluated there, and the other would result in the function being less than zero. These half spaces are assembled to form a model. This works nicely, but the trouble with it is that most half spaces are infinite, and users are not comfortable working with these. So CSG or constructive solid geometry allows the user to interact with bounded objects- such as finite cylinders. In truth the computer still uses half spaces and models the finite cylinder as the intersection of an infinite cylinder with the space above one plane and below another plane. However, the user can work directly with finite objects. Finally in Boundary Representation or BREP, an object is represented by dividing its surface into a series of faces. The computer �knows� the part as the area inside the faces.

6. Exhaustive Enumeration Special case of decomposition where primitives are cubical in shape Uniformly-sized volume elements called voxels Used extensively in computer graphics and medical graphics Efficient but requires significant storage Accuracy limited unless voxels are extremely small Exhaustive enumeration is a special case of decomposition where the primitives are cubical in shape. It features uniformly-sized volume elements called voxels. This method is used extensively in computer graphics and medical graphics. It is efficient computationally but requires significant storage. However, the accuracy is limited unless the voxels are extremely small; consequently, this would result in many more voxels and much more storage space. Exhaustive enumeration is a special case of decomposition where the primitives are cubical in shape. It features uniformly-sized volume elements called voxels. This method is used extensively in computer graphics and medical graphics. It is efficient computationally but requires significant storage. However, the accuracy is limited unless the voxels are extremely small; consequently, this would result in many more voxels and much more storage space.

7. Representation of Solid by Voxels Here is a visual representation of the Voxel solid model. Here is a visual representation of the Voxel solid model.

8. Use of Voxel Representation In Casting Here is another voxel representation. One can see how voxel representation is used in engineering for design and analysis. The voxels in these figures show the volumetric dimensions of the casting. In the first picture, the red regions represent regions of high or heavy stress. In the second picture, only the heaviest region of stress is displayed. Here is another voxel representation. One can see how voxel representation is used in engineering for design and analysis. The voxels in these figures show the volumetric dimensions of the casting. In the first picture, the red regions represent regions of high or heavy stress. In the second picture, only the heaviest region of stress is displayed.

9. Cellular Decomposition Cellular Decomposition represents a solid as a combination of irregular cells that are pasted together over common faces . Here is an example of Finite Element Analysis used in satellite imaging. The colors show the activities of each cell. Cellular Decomposition represents a solid as a combination of irregular cells that are pasted together over common faces . Here is an example of Finite Element Analysis used in satellite imaging. The colors show the activities of each cell.

10. Representation of Space Subdivision The space subdivision method uses a recursive scheme to breakdown or subdivide the solid. The divisions are typically rectangular blocks. A good example of a model of this type is the octree representation where the solid is broken down into 8 subdivided blocks. Each block of the octree is further subdivided into 8 blocks called octants and so on as represented by the left picture in figure C. Each block has either one material type, no material, or is defined by smaller blocks If a block contains only 1 material type or contains no material at all, the computer records the appropriate material constant and moves on to the next block. Each block is marked as interior, exterior or partial. If the block is partial, further subdivision is needed. If a block has several types of material or contains both open space and material, the computer then subdivides the block into smaller blocks. The computer then looks at each of the smaller blocks to see if they can be assigned a unique material type or must be further subdivided. The space subdivision method uses a recursive scheme to breakdown or subdivide the solid. The divisions are typically rectangular blocks. A good example of a model of this type is the octree representation where the solid is broken down into 8 subdivided blocks. Each block of the octree is further subdivided into 8 blocks called octants and so on as represented by the left picture in figure C. Each block has either one material type, no material, or is defined by smaller blocks If a block contains only 1 material type or contains no material at all, the computer records the appropriate material constant and moves on to the next block. Each block is marked as interior, exterior or partial. If the block is partial, further subdivision is needed. If a block has several types of material or contains both open space and material, the computer then subdivides the block into smaller blocks. The computer then looks at each of the smaller blocks to see if they can be assigned a unique material type or must be further subdivided.

11. Constructive Models Constructive solid geometry (CSG) Object made up of smaller primitive objects Permit several operations to combine primitives Union (gluing) Intersection Difference Final object obtained by operations on the primitives (CSG Tree) Very efficient in terms of storing information Visualization required individual curves and surfaces to be combined and evaluated Very expensive computationally Constructive Models Constructive Models

12. Solid Modeling Methods An example of constructive model is the half space models. Here the primitives are half spaces defined by some function of x,y, and z, which could be used to split space into two halves. One part of space would result in the function being greater than zero when evaluated there, and the other would result in the function being less than zero. For example one could represent an infinite cylinder as the space in which x2+y2-r2<0or a sphere as the space in which x2+y2+z2-r2<0. These half spaces are assembled to form a model. This is not commonly used, instead constructive solid geometry is used which uses bounded primitives. An example of constructive model is the half space models. Here the primitives are half spaces defined by some function of x,y, and z, which could be used to split space into two halves. One part of space would result in the function being greater than zero when evaluated there, and the other would result in the function being less than zero. For example one could represent an infinite cylinder as the space in which x2+y2-r2<0or a sphere as the space in which x2+y2+z2-r2<0. These half spaces are assembled to form a model. This is not commonly used, instead constructive solid geometry is used which uses bounded primitives.

13. Defining Object using CSG This shows the concepts of constructive solid modeling. Basic shapes such as cylinders and rectangles are added, subtracted, translated and rotate to create the intended shape. This shows the concepts of constructive solid modeling. Basic shapes such as cylinders and rectangles are added, subtracted, translated and rotate to create the intended shape.

14. Boundary Models Object enclosed by a set of boundary surfaces Boundary surfaces enclosed by boundary curves Most solid modeling packages use the boundary representation for storing the models Solid is considered to be bounded by a set of faces Faces have a compact mathematical representation Plane Toroid Cylinder Parametric surface such as a Bezier surface Here a solid object is represented by dividing the surface into a collection of faces such that each face is easily described mathematically. Boundary modes are enclosed by a set of boundary surfaces enclosed by boundary curves. Most solid modeling packages use the boundary representation for storing the models. The solid is considered to be bounded by a set of faces. The faces have a compact mathematical representation as a plane, torioid, cylinder or some parametric surface such as a Bezier surface. Here a solid object is represented by dividing the surface into a collection of faces such that each face is easily described mathematically. Boundary modes are enclosed by a set of boundary surfaces enclosed by boundary curves. Most solid modeling packages use the boundary representation for storing the models. The solid is considered to be bounded by a set of faces. The faces have a compact mathematical representation as a plane, torioid, cylinder or some parametric surface such as a Bezier surface.

15. Boundary Representation (B Rep) Each face bounded by a set of curves; portions of Lines Circles Cubics Information storage models: Geometrical - Point coordinates, equations for edges and faces Topological - edges bounding a face, which faces are adjacent Polyhedral models have planar bounding surfaces: very common STL files have planar triangles as bounding surfaces Many solid modelers store both CSG and boundary representation models Read slide Read slide

16. Complex Elements Complex Curves Cubic splines Bezier curves B-splines NURBS Complex Surfaces Bicubic patches Coon's patches Bezier surfaces In modeling complex elements, the computer uses various curve and surface functions to describe and draw the parts. For complex curves, some functions used are cubic splines, bezier curves, B-splines, and NURBS. Complex surfaces use such models as Bicubic patches, Coon�s patches, and Bezier surfaces. Displayed is a model of a bicubic patch. In modeling complex elements, the computer uses various curve and surface functions to describe and draw the parts. For complex curves, some functions used are cubic splines, bezier curves, B-splines, and NURBS. Complex surfaces use such models as Bicubic patches, Coon�s patches, and Bezier surfaces. Displayed is a model of a bicubic patch.

17. Polyhedral Models Polyhedral models are solid objects whose face consist of planes or planar polygons. The planes represent the faces of the object; thus, one can have many little planes that can mathematically model the shape of the part. These shapes can be very complex, including holes. It only has compact representation.Polyhedral models are solid objects whose face consist of planes or planar polygons. The planes represent the faces of the object; thus, one can have many little planes that can mathematically model the shape of the part. These shapes can be very complex, including holes. It only has compact representation.

18. Sweep Representations A sweep operation involves An object often called a generator A trajectory along which it is moved Sweep representations popular because Many machine elements have axes of symmetry and are defined as 2-1/2 D objects (as opposed to 3-D) Sweep representations are often more intuitive to users than Boolean operations (CSG). Many manufacturing processes (milling, turning, ...) can be directly modeled as sweep operations Types: Extrusion, Cutout, Revolve. Another large family of surfaces are those modeled by sweep representation. Sweep operations involves a generator object in 1, 2 or 3-D and a trajectory along which it moves. The sweep representations are popular because many machine elements have axes of symmetry and are defined as 2-1/2 D objects (as opposed to 3-D), sweep representations are often more intuitive to users than Boolean operations (CSG), and many manufacturing processes (milling, turning, ...) can be directly modeled as sweep operations. Common sweep functions are extrusion, cutout and revolve. Another large family of surfaces are those modeled by sweep representation. Sweep operations involves a generator object in 1, 2 or 3-D and a trajectory along which it moves. The sweep representations are popular because many machine elements have axes of symmetry and are defined as 2-1/2 D objects (as opposed to 3-D), sweep representations are often more intuitive to users than Boolean operations (CSG), and many manufacturing processes (milling, turning, ...) can be directly modeled as sweep operations. Common sweep functions are extrusion, cutout and revolve.

19. Extrusion/Cutout Example In extrusion and cutout operations, the generating object follows a straight line trajectory perpendicular to the object. Here is an example of an extrusion process. The generating surface is the letter I. It becomes a swept or extruded object when one take that 2-d surface and follows the direction of sweep, or the trajectory line as shown in this picture. After a certain distance, the surface becomes a solid model that looks like the picture here. In extrusion and cutout operations, the generating object follows a straight line trajectory perpendicular to the object. Here is an example of an extrusion process. The generating surface is the letter I. It becomes a swept or extruded object when one take that 2-d surface and follows the direction of sweep, or the trajectory line as shown in this picture. After a certain distance, the surface becomes a solid model that looks like the picture here.

20. Revolved Solid Similar to extrusion except that the generator surface is revolved about an axis Revolved solids are similar to extrusion except that the generator surface is revolved about an axis. An example of the revolve operation is seen here. The 2-dimensional generated surface (the backwards F figure) is revolved around the axis of revolution to create this 3-D shape. Revolved solids are similar to extrusion except that the generator surface is revolved about an axis. An example of the revolve operation is seen here. The 2-dimensional generated surface (the backwards F figure) is revolved around the axis of revolution to create this 3-D shape.

21. Feature Based Modeling Solid modelers and many of the other modelers are often quite powerful, but in truth all geometric modeling has certain limitations. The basic problem is they represent only one type of information and they do so only at one (very low) level. So the user is forced to fully specify all geometric details, when often he had just a single constraint. In other words just to get a model into the system, the user has to sometimes add unnecessary constraints which can then get locked into the design and make the ultimate design more complicated than necessary. But even while this excess of information is required for geometric values, other information, such as tolerancing information, is wholly lacking. Further the raw geometric info often will NOT capture the real design intent-- it gets lost in the over specified detail. And having to do all the geometric detail sometimes makes the designer re-invent the wheel, going through painful detail to make a few minor changes to tested designs. So as an alternative, features were introduced. Features are higher level entities that try to represent the engineering meaning, NOT just the geometric meaning. There are a wide variety of feature types, geometric, tolerance, assembly (what surfaces mate, etc). To help organize the feature types, object oriented programming has been introduced. ProE was really the first large scale commercially available FEATURE based modeler, although many others (including IDEAS) are now available. The basic difference between feature and geometry can be seen by considering a counterbore and through hole. This could be one feature, you can insert the counterbore feature directly into your model. By contrast a geometric based modeler would make you remove two cylinders, with different diameters and different lengths. If a change in the screws is made, you will have to change diameters and one of the depths. Even with variational design, you may not be able to get a formula that describes the size of the screw head in terms of the major diameter, so you will have to change each value. By contrast with a feature, you just change the size screw for which the counterbore and through hole are made. Further, the feature conveys information. It is a counterbore and through hole- the machinist sees this and knows the designer�s intent. A graphics based modeler just shows two holes. A machinist might study this and ask why the designer didn�t just tell him it was to be a through hole and counterbore for a given screw. Solid modelers and many of the other modelers are often quite powerful, but in truth all geometric modeling has certain limitations. The basic problem is they represent only one type of information and they do so only at one (very low) level. So the user is forced to fully specify all geometric details, when often he had just a single constraint. In other words just to get a model into the system, the user has to sometimes add unnecessary constraints which can then get locked into the design and make the ultimate design more complicated than necessary. But even while this excess of information is required for geometric values, other information, such as tolerancing information, is wholly lacking. Further the raw geometric info often will NOT capture the real design intent-- it gets lost in the over specified detail. And having to do all the geometric detail sometimes makes the designer re-invent the wheel, going through painful detail to make a few minor changes to tested designs. So as an alternative, features were introduced. Features are higher level entities that try to represent the engineering meaning, NOT just the geometric meaning. There are a wide variety of feature types, geometric, tolerance, assembly (what surfaces mate, etc). To help organize the feature types, object oriented programming has been introduced. ProE was really the first large scale commercially available FEATURE based modeler, although many others (including IDEAS) are now available. The basic difference between feature and geometry can be seen by considering a counterbore and through hole. This could be one feature, you can insert the counterbore feature directly into your model. By contrast a geometric based modeler would make you remove two cylinders, with different diameters and different lengths. If a change in the screws is made, you will have to change diameters and one of the depths. Even with variational design, you may not be able to get a formula that describes the size of the screw head in terms of the major diameter, so you will have to change each value. By contrast with a feature, you just change the size screw for which the counterbore and through hole are made. Further, the feature conveys information. It is a counterbore and through hole- the machinist sees this and knows the designer�s intent. A graphics based modeler just shows two holes. A machinist might study this and ask why the designer didn�t just tell him it was to be a through hole and counterbore for a given screw.

22. Traditional 2-D Drafting/CAD Typical of �old� 2-D drafting programs such as the original AUTOCAD, VersaCAD, MiniCAD, ClarisCAD, etc. Data consists of points and connectivity information If a line is changed, it is necessary to redraw all lines connected to it All objects (even text) made up of line segments. No equations used! Constraints available as drawing aids but not maintained after lines are drawn. In traditional CAD, the program stored only points and information on how the points were connected together. Polygons were defined by the lines that make up the sides. The color of the polygons was an attribute that was stored. Also, the depth order of the polygons was defined so that one polygon could be put on top of another. The purpose of the 2-D drafting programs is to make it easier to produce a drawing of the part. Some kind of hard copy is required to show the design intent. No solid information is available, and it is not possible to extract manufacturing information directly. The 2-D drafting programs will provide constraint information to aid in drawing lines. For example, it is possible to draw one line perpendicular to another or parallel to another. However, the constraints are not maintained after the line is drawn. For example, if the line is changed later, the perpendicular constraint is not maintained. 2-D drafting programs have evolved today into 2-D illustration programs. Examples are Adobe Illustrator, PC Draft, MacDraft, and the 2-D version of MiniCAD. They often have a variety of file output formats (PDF, JPEG, EPS, etc), and elaborate rendering algorithms. The are used extensively for producing graphics for web applications. However, the intent is still a drawing for visual purposes, and automatic feature recognition or extraction of manufacturing information is not possible. The file structure remains primarily as a series of points, lines, polygons, and pixel coloring information. No constraint information is maintained.In traditional CAD, the program stored only points and information on how the points were connected together. Polygons were defined by the lines that make up the sides. The color of the polygons was an attribute that was stored. Also, the depth order of the polygons was defined so that one polygon could be put on top of another. The purpose of the 2-D drafting programs is to make it easier to produce a drawing of the part. Some kind of hard copy is required to show the design intent. No solid information is available, and it is not possible to extract manufacturing information directly. The 2-D drafting programs will provide constraint information to aid in drawing lines. For example, it is possible to draw one line perpendicular to another or parallel to another. However, the constraints are not maintained after the line is drawn. For example, if the line is changed later, the perpendicular constraint is not maintained. 2-D drafting programs have evolved today into 2-D illustration programs. Examples are Adobe Illustrator, PC Draft, MacDraft, and the 2-D version of MiniCAD. They often have a variety of file output formats (PDF, JPEG, EPS, etc), and elaborate rendering algorithms. The are used extensively for producing graphics for web applications. However, the intent is still a drawing for visual purposes, and automatic feature recognition or extraction of manufacturing information is not possible. The file structure remains primarily as a series of points, lines, polygons, and pixel coloring information. No constraint information is maintained.

23. Parametric/Variational Design Parametric or variational design procedures give the user still more flexibility when using a computer in the designing process. They allow the user to reuse past design with just a few changes or modifications to the current design. The user no longer has to redo everything just to change one value. How does this process work? The user must create a rough or base design, and then assign constraints. For example the user may want a line to be horizontal with length a. The machine represents this by saying the y components of the endpoints are equal while the x components differ by a. After all constraints are defined, the computer then applies some type of solution procedure to solve the system of constraints and unknowns. A good system tells the user if there are problems with the model or if it can NOT be solved. The user can create variations on his model by varying a few parameters and having the modeler evaluate the model again. Parametric or variational design procedures give the user still more flexibility when using a computer in the designing process. They allow the user to reuse past design with just a few changes or modifications to the current design. The user no longer has to redo everything just to change one value. How does this process work? The user must create a rough or base design, and then assign constraints. For example the user may want a line to be horizontal with length a. The machine represents this by saying the y components of the endpoints are equal while the x components differ by a. After all constraints are defined, the computer then applies some type of solution procedure to solve the system of constraints and unknowns. A good system tells the user if there are problems with the model or if it can NOT be solved. The user can create variations on his model by varying a few parameters and having the modeler evaluate the model again.

24. Constraint Solution Procedures Before we talked about parametric and variational design as if they were the same, but in truth they ARE NOT. Differences between the two methods (parametric and variational) are sometimes masked to the user, however they are substantial and do matter. The differences lie in how the machine solves the user�s constraints. Originally there was ONLY rigid constraint satisfaction. Sometimes it is called Procedural Parametric or Unidirectionally Parametric design. (Please note that while both these terms contain the word parametric, when one is talking of parametric design, (and not explicitly Procedural or Unidirectionally Parametric) one is NOT talking about these methods.) Here the constraints were stored and solved in the exact order in which they were entered. This fixed order severely limits the user�s freedom in reassigning and re-evaluating. Flexible Constraint Satisfaction has some general constraint algorithm which were used to solve the constraints INDEPENDENT of the order of entry. The two basic alternatives when using flexible constraint satisfaction are parametric or variational. Parametric systems solve the system by sequentially applying assignments to model variable. As opposed to rigid constraint satisfaction the order of solution is flexible, giving one much more freedom to re-evaluate constraints. However, each variable must still be explicitly defined-- implicit equations are not allowed. By contrast variational systems solve all equations simultaneously. Thus one can have implicit equations defining the variables. Because it allows for implicit equations and therefore for coupled constraints, variational methods give the user more flexibility. However variational methods can get numerically intensive. Parametric methods allow for more rapid evaluation and are much more robust. Furthermore, they have better error checking capabilities. Today hybrid models exist, which try to take advantage of the strengths of both techniques.Before we talked about parametric and variational design as if they were the same, but in truth they ARE NOT. Differences between the two methods (parametric and variational) are sometimes masked to the user, however they are substantial and do matter. The differences lie in how the machine solves the user�s constraints. Originally there was ONLY rigid constraint satisfaction. Sometimes it is called Procedural Parametric or Unidirectionally Parametric design. (Please note that while both these terms contain the word parametric, when one is talking of parametric design, (and not explicitly Procedural or Unidirectionally Parametric) one is NOT talking about these methods.) Here the constraints were stored and solved in the exact order in which they were entered. This fixed order severely limits the user�s freedom in reassigning and re-evaluating. Flexible Constraint Satisfaction has some general constraint algorithm which were used to solve the constraints INDEPENDENT of the order of entry. The two basic alternatives when using flexible constraint satisfaction are parametric or variational. Parametric systems solve the system by sequentially applying assignments to model variable. As opposed to rigid constraint satisfaction the order of solution is flexible, giving one much more freedom to re-evaluate constraints. However, each variable must still be explicitly defined-- implicit equations are not allowed. By contrast variational systems solve all equations simultaneously. Thus one can have implicit equations defining the variables. Because it allows for implicit equations and therefore for coupled constraints, variational methods give the user more flexibility. However variational methods can get numerically intensive. Parametric methods allow for more rapid evaluation and are much more robust. Furthermore, they have better error checking capabilities. Today hybrid models exist, which try to take advantage of the strengths of both techniques.

25. Parametric/Variational Systems This shows the form of the equations for parametric and variational design. Parametric design involves a series of assignment statements, and variational design involves implicit equations that must be solved simultaneously.This shows the form of the equations for parametric and variational design. Parametric design involves a series of assignment statements, and variational design involves implicit equations that must be solved simultaneously.

26. CAM After the CAD model is designed, analyzed and optimized, then one can proceed to the next process to prepare for machining operations. This process is often termed the CAM for computer aided machining. Note, this is the second part of the term CAD/CAM in engineering design. CAM is actually a very broad term that involves the computer in many different manufacturing activities from machining to factory simulation to planning analysis. For this presentation, we will mostly deal with CAM as it pertains to machining. In the old system, a drawing prepared on the computer graphics system would have to be redrawn before it could operate on a different graphic system. One of the most important feature of today engineering drawing programs is the ability to transfer the information between the different CAD/CAM, design analysis and NC/CNC programs. Thus, when transferring the model between the two programs, one must be certain to use an acceptable file format that is recognized and accepted by the CAM program. Some common file formats used are DXF, Parasolids, IGES and STL files. As stated earlier, after the design process, the design is passed to a programmer that encodes for machining the components. This process often requires redefining and reentering part geometry in the program. After the CAD model is designed, analyzed and optimized, then one can proceed to the next process to prepare for machining operations. This process is often termed the CAM for computer aided machining. Note, this is the second part of the term CAD/CAM in engineering design. CAM is actually a very broad term that involves the computer in many different manufacturing activities from machining to factory simulation to planning analysis. For this presentation, we will mostly deal with CAM as it pertains to machining. In the old system, a drawing prepared on the computer graphics system would have to be redrawn before it could operate on a different graphic system. One of the most important feature of today engineering drawing programs is the ability to transfer the information between the different CAD/CAM, design analysis and NC/CNC programs. Thus, when transferring the model between the two programs, one must be certain to use an acceptable file format that is recognized and accepted by the CAM program. Some common file formats used are DXF, Parasolids, IGES and STL files. As stated earlier, after the design process, the design is passed to a programmer that encodes for machining the components. This process often requires redefining and reentering part geometry in the program.

27. NC/CNC In traditional machining, the designer selects and programs the feature or shape to machine, the method of machining, the tool used for machining, and the path of the tool using the CAM program. Once the engineer has determine the machining activity, then he/she can process and export the activity in the appropriate code. The CAM program generates the NC or CNC part codes that controls the machining operations. NC and CNC stand for numerically controlled or computerized numerically controlled. This method refers to a method of controlling numerical control machines from a remote location by means of a link to a computer. In traditional machining, the designer selects and programs the feature or shape to machine, the method of machining, the tool used for machining, and the path of the tool using the CAM program. Once the engineer has determine the machining activity, then he/she can process and export the activity in the appropriate code. The CAM program generates the NC or CNC part codes that controls the machining operations. NC and CNC stand for numerically controlled or computerized numerically controlled. This method refers to a method of controlling numerical control machines from a remote location by means of a link to a computer.

28. CAD model of OSU Stadium Design Here is a CAD model of the OSU stadium that has been imported into a CAM program. (mouseclick) The CAM program uses the features from the CAD program to determine the entities for the machining operations. (mouseclick) Here, one can see that there are many specifications for the tooling operation which include tool type, size, path, plunge angle, allowances, z-increments, etc. (mouseclick) Next we can run a simulation of the actual machining operation. This is where the engineer verifies the machining operation. Notice the yellow tool in this process. As the machining continues, you can see the different tool types and sizes as they cut away the block. (mouseclick) Finally, when the simulation is complete, the CAM program will process the simulation program into NC codes. (mouseclick) These codes are then exported to be used on the appropriate machines. In this case, this model can be performed on a small mill. Again, there are many different CAM programs in industry today. This is just an example one particular CAM program. Here is a CAD model of the OSU stadium that has been imported into a CAM program. (mouseclick) The CAM program uses the features from the CAD program to determine the entities for the machining operations. (mouseclick) Here, one can see that there are many specifications for the tooling operation which include tool type, size, path, plunge angle, allowances, z-increments, etc. (mouseclick) Next we can run a simulation of the actual machining operation. This is where the engineer verifies the machining operation. Notice the yellow tool in this process. As the machining continues, you can see the different tool types and sizes as they cut away the block. (mouseclick) Finally, when the simulation is complete, the CAM program will process the simulation program into NC codes. (mouseclick) These codes are then exported to be used on the appropriate machines. In this case, this model can be performed on a small mill. Again, there are many different CAM programs in industry today. This is just an example one particular CAM program.

29. Summary of CAD/CAM In summary, Computer aided design and computer aided machining are integrated processes that are used by most engineers today. We have learned that there are many different types and CAD/CAM methods used in industry. To recap, this presentation discussed the different types of modeling methods in CAD. The two modeling methods are geometric and feature based. Geometric models have three subcategories: Graphical Modeling, Surface Modeling, and Solid Modeling. Feature based modeling is a step forward because it better stores and communicates design information. Then, CAM uses these features to help designers create tooling operations and codes to machine the part. In summary, Computer aided design and computer aided machining are integrated processes that are used by most engineers today. We have learned that there are many different types and CAD/CAM methods used in industry. To recap, this presentation discussed the different types of modeling methods in CAD. The two modeling methods are geometric and feature based. Geometric models have three subcategories: Graphical Modeling, Surface Modeling, and Solid Modeling. Feature based modeling is a step forward because it better stores and communicates design information. Then, CAM uses these features to help designers create tooling operations and codes to machine the part.

30. Credits

31. Disclaimer