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Chapter 1
CAD/CAM systems
Author: George Louca
Technician Engineer
Contents

1 CAD/CAM systems 
1.1 CAD systems  

1.2 CAM systems 1.3 CAD/CAM systems 1.4 CAD/CAM implementation
1.5 CIM 
 

1. CAD/CAM systems
CAD/CAM involves the use of computer systems to accomplish certain functions in both design and manufacturing. CAD systems involve the use of computers to facilitate the design function, and CAM systems in order to support manufacturing engineering activities. These two were joined into one common definition CAD/CAM because the second act as a continuum of the first and both are aiming in integrating both design and manufacturing.
 
1.1  CAD systems
Computer-aided design system (CAD) is defined as the involvement of the computer into design activities and very often is associated with the use of interactive computer graphics system. There are many advantages in using a CAD system such as:
· Increases the productivity of the designer. CAD systems aid the designer to conceptualize the product more easily thus reducing the time needed for synthesizing.
· Improves the quality of the design by enabling the designer to perform more complicate engineering analysis and consider a larger number of design alternatives.
· Improves design documentation. The graphical output of a CAD system is superior of manual drafting, fewer errors and drawings standardization results in  better documentation.
· Create a manufacturing database. During the creation of the product design documentation such as dimensions, materials etc. much of the required data base to manufacture the product is also created.
 
1.1.1 Applications of computers in design
In the design process there are six processes that must be followed in order to design a new product or even improve and old one and are given by Shigley as:
· Recognition of the problem
· Definition of the problem
· Synthesis
· Analysis and optimization
· Evaluation
· Presentation
From these six processes a CAD system can be applied in four of them as follows:
· Synthesis (geometric modeling)
· Analysis and optimization (engineering analysis)
· Evaluation (design review and evaluation)
· Presentation (automated drafting)
 
1.1.2  Geometric modeling
A geometric model is a mathematical description of the model held in the computer memory. Besides the 2D modeling of an object in all new CAD systems a 3D model can be constructed enabling the user to view the object from all kind of different views, zoom on details, perform various engineering analyses such as stress, thermal and mass properties calculations as illustrated in figure 1.1. All this analyses mentioned above can be easily undertaken by a CAD system. However, a major drawback on this 3D modeling CAD systems is there high cost.

3D geometric modeling is being divided into three main categories:
1.  Wireframe modeling
2.  Surface modeling
3.  Solid modeling
 

1.  Wireframe modeling
Wireframe modeling uses interconnecting lines to depict an object as illustrated in figure 1.2. However, a wireframe model has serious limitations as this is concerned to be the lower level of  geometric modeling due to the lack of data regarding the faces and the
 
 
 

FIGURE 1.1 FEM showing stress contours
 

inability to distinguish between inside and outside of  a solid object. Despite this it can be used for a milling tool path simulation.

Limitations of wireframe models are laid below:
1.  Ambiguity
Due to the fact that wireframe models have no perception of solid shape, visible and hidden lines cannot be distinguished causing a confusing effect of interpreting a 3D view in many ways.
2.  Inability to recognize curved profiles
Longitudinal profiles of cylindrical shapes are not fixed edges between defined points in space thus are not recognized and are omitted. This causes even more confusion in an already confusing drawing.
3.  Inability to detect interference between components
Since there is no knowledge of surfaces there is no way of detecting interference between two objects. This is a drawback in applications such as 3D kinetic analysis of mechanisms, robot simulation, design of plant layout and complex piping assemblies.
4.  Difficulty in calculating physical properties
Due to lack of surface data physical properties such as volume, mass, surface area, center of gravity etc. are difficult to calculate and very unreliable.
5.  No facility for automatic shading
Surfaces not edges are shaded therefor color tone variations and shadow effects cannot be applied.

 
 FIGURE 1.2 Wireframe model of a nozzle as this was imported from Autocad.
 
 
2.  Surface modeling
In surface modeling a model is defined in terms of points, lines and surfaces and has the following advantages over the wireframe:
i.  Ability to recognize and display complex curved profiles.
ii.  Ability to recognize faces and thus provide the facility of shaded surfaces in 3D.
iii.  Ability to display very good tool path simulation.
iv.  Improved robot simulation
Surface modeling is widely used when designing and manufacturing curved surfaces such as car bodies. There are basically five types of surface modeling:
1.  Basic geometrical
Plane surfaces are created by drawing straight lines, circles or arcs and then sweeping an identical line through a specified distance in 3D space. However, the object constructed is not a solid volume but surfaces joined together with an empty interior.
2.  Surfaces of revolution
Created by rotating  a line about a defined axis.
3.  Blends and intersections
Blending is a very useful technique and a 3D fillet can be very easily created between a square and a cylindrical surface.
4.  Analytic
Surfaces defined by mathematical expressions and the surfaces which are generated  are according to these expressions.
5.  Sculptured of free form
These are created by displaying longitudinal splines between points defined in 3D space on sections. Widely used in the design of  car bodies, blades, telephones etc.
 

3.  Solid modeling
A solid model is described in terms  of its volumetric shape thus providing a full description of the object without any ambiguities. Since the solid modeling is the most advance of all modeling systems developed by now it has a number of advantages:
1. It gives a complete definition to the object and its volumetric shape and it’s able to distinguish between the interior and the exterior of the object.
2. As a result of it’s ability to distinguish between the interior and exterior of the object it can also detect unwanted interference between objects. Due to the latter solid modeling is very much appreciated in the design of 3D kinetic mechanisms, robot simulations and complex piping systems.
3. Provides the ability of automatic 3D sections which is very helpful on complex assemblies.
4. It has the ability of using an extensive color palette and shadow effects, giving improved visualization of the components. In addition 3D models, modeled on such modelers can be used in combination with other computer programs which are specialized on models presentation and thus provide the image of an object as this will exist in real life as illustrated in fig 1.3.

 
FIGURE 1.3 Rendered image of the 3D nozzle displayed in wireframe in figure 1.2 after converting  it to a solid model and applying on it color finishes.
 

The solid modelers fall into two main categories:
1.  Constructive representation (C-Rep)
A body composed by primitive solids such as a torus, box, cone etc.
2.  Boundary representation (B-Rep)
Primitives are formed with linear or rotational sweeps and the composite shapes are used using Boolean operations.
   Furthermore in CAD systems automatic dimensioning routines exist, which determine precise distances between surfaces on the geometric model identified by the user.  On top of this, some CAD systems have kinematics routines used to test the operation of mechanical linkages. These systems usually require animation capability.
   In addition to all the above 3D modeling is used extensively in building services and buildings that are to constructed are first designed and fitted into the landscape that are going to be located on the computer screen before actually this building is built. An example is illustrated in figure 1.4.

FIGURE 1.4 Building site fitted into its landscape by 3D studio.
 
1.1.3  Rapid prototyping
 In recent years a new technology has been created as an addition to CAD modeling systems called the rapid prototyping method. It is a technology that started from a research lab in the United States and now is being used from many major industries throughout the world such as BMW, Mercedes Benz etc.
   Rapid prototyping actually builds the object being seen on the screen of a CAD system so the part can be tested and examined more carefully. Models being constructed with this method can undertake a number of real operation tests before failure.
   This method builds the object with a laser beam being shooting in a pool of liquid raisin. When the laser beam contacts the raisin surface the raisin is being solidified. A layer of less than a millimeter is being solidified on each laser pass. This process keeps going on very slowly until the complete part is formed.
   As a conclusion on rapid prototyping method it must be pointed out that, despite the fact that the cost of the prototyping machine is quite high, it will be balanced from the low cost of the prototypes being made in comparison with the cost of modeling with the traditional method.
 
1.2  CAM systems
Computer-aided manufacturing  (CAM) is defined as the effective use of computer technology in the planning, management and control of the manufacturing process. The CAM applications are divided into two categories:
1.  Manufacturing planning
2.  Manufacturing control
 
1.2.1  Manufacturing planning
CAM applications for manufacturing planning are those in which the computer is not directly interfering with the production function. The computer is used "off line" to provide information for the effective planning and management of  the production activities. Computer-aided manufacturing in this category, is being applied in the following aspects of production:
1.  Cost estimating
Cost estimating of new products has been quite simplified in many industries and is done by a computer program which takes into consideration the appropriate labor and overhead rates to the sequence of planned operations for the components of new products. The individual components cost are them summed up to determine the overall product cost.

2.  Computer-aided process planning (CAPP)
The sequence of operations and work centers needed for the production of a given product are now being prepared by the computer. This systems can prepare these route sheets, find the optimum route and make simulations.
3.  Computerized machinability data systems
Cutting conditions in metal cutting operations such as milling, drilling, facing etc. need feed rates, division of cuts, rotational speeds etc. in order to achieve optimum cutting conditions. Computer programs have been designed to calculate this values, based on experimental or theoretical values obtained either from normal practice or the factory laboratory, which relate tool life with cutting conditions, surface finish, power consumed etc.
4.  Computer-assisted NC part programming
Machine tool programming or CNC programming is rather a difficult task when performed manually and also has high risks of error when relating with complex parts. Computerized post processors have been programmed to make the job of the part programmer. The program takes for input the drawing of the part and outputs the part program needed from the CNC to cut the part. Some integrated post processors have the ability to make simulation of the cutting process and even send the program through communication cables or modem to the machine.
5.  Development of work standards
Computer systems with the appropriate software can now calculate standard time for each job by being provided with standard time data that have been developed for basic work elements that compromise any manual task.
6.  Computer-aided balancing
Balancing a factory’s workstations and machines  is a tedious and difficult task to be performed manually especially on a large assembly line. Computer programs are now available for handling this task. Computer programs currently in market are the COMSOAL and CALB
7.  Production and inventory planning
All the major functions of production and planning can very easily be now handled by a computer system. These functions include maintenance of inventory records, automatic
recording of stock items when inventory is depleted, production scheduling, material requirements planning etc.
 

1.2.2  Manufacturing control
In manufacturing control systems the computer is used "on line" with the factory’s operations. It has direct communication with all the steps of production and is being updated continuously with data incoming from the various locations in the factory. It controls all the numerically controlled machines in the factory and it drives all the automated guided vehicles in the factory. It has direct access on all robot working and is being informed for any malfunction or breakdown. The computer can handle process control, shop floor control and process monitoring.
 
1.3  CAD/CAM systems
Therefore CAD/CAM is concerned with the application of computers to the manufacture of engineering components. This application commences from the design department and goes through virtually every department of  the factory, production department, quality control, assembly lines and right through the finished parts store rooms. Thus an integrated CAD/CAM system can therefor be defined as a system where the gap between design and manufacturing has been bridged with the use of data and information accumulated in the design process directly to the CAM procedures. This link eliminates the independent generation of data for computer programs in the manufacturing area.
      A database of information is shared by a large number of computer programs which form the so called integrated CAD/CAM system as illustrated in figure 1.5. These programs work in combination in order to achieve the connection between the design and manufacturing. All design programs feed the database with information needed from the CAM programs to move forward to the manufacturing procedure.
 
 

                     CAD                                                                          CAM
 Drawing creation                                                     Part programming
           Graphics display                      Common                  Tool and fixture design
           Draughting                              Database                   Inspection
           Design analysis                                                         Inventory
                                                                                           Scheduling
                                                                                           Costing
FIGURE 1.5 The use of information from a common database both for CAD and Cam avoids the need of independent generation of data between the design and manufacturing functions.
 

1.3.1  The CAD/CAM link
The CAD/CAM link procedure relieves the operator from the burdening task of having to perform all number of tedious calculations, relating all the cutting requirements that have to be calculated, in order to compose the part program needed by the machine, and all the optimum cutting speeds to be used during cutting. All these functions are now being performed automatically such as tool paths, cutting speeds, part programs and all the relevant requirements of an NC machine are now being generated from the CAD/CAM system. The CAD/CAM link is illustrated in figure 1.5.
 
1.3.2 A typical CAD/CAM system (How it work’s)
A typical CAD/CAM system must posses the following features besides all the special design features concerning finite element analysis, stress and thermal contours etc. Above all a CAD/CAM system must be user friendly and must have the expertise to assist even an inexperienced user to make decisions to produce a component.
1.  Machine tool selection
Machine tools can be selected from the existing machine tool library, however, if a suitable machine doesn’t exist then the specifications of a new machine tool can be given.

   Upon the selection of a machine tool all the relevant information concerning it, such as number of spindles, number of turrets, number of stations per turret etc. can be extracted from the database and stored in the manufacturing file ready for use.
2.  Material of Workpiece
Material definition is essential in the cutting procedure since all the cutting conditions are related to it.
   The material selection can be done in three ways. The first is by selecting the type of material to be cut, its metallurgical structure and heat treatment from the materials property library.
   The second option is to select the material from standard materials tables stored in the database. These materials should conform with common materials specified in British, German, American standards etc.
The third option is to specify the material properties in detail. When this procedure is completed the system should be able to provide recommendations regarding the cutting conditions.
3.  Cutter definition
The cutter can be either selected from the already existing library or information upon  the cutter’s geometry and size can be supplied from the operator. In cases of tool turrets the operators should specify the turret station for each tool with an offset number.
4.  Cutting data
The cutting data is defined in three ways, the first is by selecting the cutting operation as heavy roughing, roughing, light roughing or finishing.
   The second method is concerned with the surface finish selected. The system selects the cutting data by combining the degree of finish with the geometry of the cutter.
   The third method  is based on the depth of cut and feedrate chosen by the user.
5.  Power determination
The power required for the cutting process should be calculated in order to make certain that the machine tool can handle the operation. The power determination is based upon calculations made by combining information about the material selected, the cutter geometry, the cutting data and the machine tool specification. The cutting data combined

FIGURE 1.5                                       Select drawing
The CAD/CAM link                               from CAD library
 
Display drawing

Define cutting
profile geometry

Enter general
   manufacturing parameters

Part program
generated

2D or 3D simulation
of tool paths

Post processing
software

Select machining
tool
 
VDU display                                        Final G code                                 Floppy disc
                                                     or m/c code program                     commun. cables
                                             Direct numerical
                                                   Control
CNC machine

Final component

with the material properties give the cutting speed. The spindle speed is then
determined from the knowledge of the cutting speed and the machine tool specification and the tool geometry with the cutting data derive the average cutting chip thickness. The latter combined with the information of  the material gives the cutting force.
   The cutting forces and the speeds give the power needed for the specific cut. The power calculated is then compared with the maximum power output of the machine tool and if the cutting power exceeds the maximum power output of the machine tool the operator is informed and asked to respecify some initial data.
6.  Roughing cuts
The user is asked to define the height of the billet. If the specified height is less than that of the component an error message is displayed.
   If the specified height is valid then the user is asked to define the depth of cut. The intermediate file is examined and cutter path is extracted. The cutter locations are then determined for each cutter pass. The z height of each pass is reduced by the depth of cut. If the z height reached is the minimum z value of the surface the operation is stopped and the final pass is added separately to the intermediate file. The cutter location data may be displayed and if the user is happy it is transferred to the manufacturing data file. This is very easy on 2½D components. For 3D complex surfaces a different method is used to determine the required cutter offsets.
7.  Machining 3D shapes
The procedure for machining complex surfaces such as a mould for casting a wax pattern of a centrifugal water pump vane is as follows. First the surface is selected, the external boundary defined and machining limits calculated. The surface is then divided into a number of cross sections divided into an equal number of points. The points are then joined by fitting a cubic spline through them. If the components are particularly complex having a number of definable surfaces which can be joined together then each surface can be separately specified and the relationship between surfaces defined. Tool paths are then generated based in these 3D complex surfaces modeling.
 
 

8.  Control information
During the generation of the cutter location file the user can select some control functions to be added to the process during the production of the machining data. These functions include coolant ON/OFF, spindle ON/OFF and dwell.
9.  Detection of Erroneous data
In order to avoid undercutting due to over lapping data the component is checked before the generation of the cutter path. If any is detected, the data is modified.
   Another inspection is carried out in order to test that the cutter can reach all parts of the surface without undercutting.
10.  Point to point machining
Point to point machining is available within the system for drilling operations. As previously described, checks are built into the system to avoid the production of erroneous manufacturing data. For example if the drill diameter chosen is larger than the hole it has to drill, or if the drill length is less than the depth of the hole then the system informs the user.
 

1.3.3 The product cycle and CAD/CAM
In order to visualize the scope of the CAD/CAM better, it would worth the cause to examine the various functions that have to take place, from design to production, for a given product to be manufactured. Also, to see how it was without the application of CAD/CAM and with the application of CAD/CAM and at what functions this is applied.
   A diagram showing the various steps in the product cycle is presented in figure 1.6. This cycle begins from the needs of the customers and the market in general. The idea or concept  of this new product is cultivated, refined, analyzed, improved and transferred into a plan for the product through the design engineering process. The plan is documented by a set of engineering drawings showing how the product is made and its specifications. This typically completes the engineering activities.
   As the product moves to manufacture a process plan must be composed to specify the sequence of production operations required to make the product. Sometimes new equipment and tools must be acquired to produce the new product. In addition a production scheduling must be composed to provide the quantities and the dates that the new product should be ready. When all these plans are formulated the product goes into production, followed by quality testing, and delivery to the customer.
 
 

FIGURE 1.6 Product cycle (Design and manufacture)
 

   CAD/CAM is applying to all the different activities that take place in the new product cycle as shown in figure 1.7. Computer-aided design and automated drafting are utilized in the conceptualization, design and documentation of the product. Computers are used to perform the process planning and scheduling more efficiently. Computers are used later on during production to monitor and control the manufacturing operations. In quality control, computers are used to perform inspections and performance tests on the product and its components. As illustrated in figure 1.6 CAD/CAM is overlaid on virtually all of the activities and functions of the product cycle.
 
 
 

 
FIGURE 1.7 Product cycle revised with CAD/CAM overlaid
 

1.3.4 Robots in CAD/CAM
Although robots is not in the scope of this project it would be worth it to make a small introduction on the operations performed by robots and how this aid in the production automation and CAD/CAM.
      An industrial robot is a general purpose, programmable machine possessing certain anthropomorphic characteristics. The most typical humanlike characteristic of a robot is its arm. This arm, together with the robot’s capacity to be programmed, makes it ideally suited to a variety of production tasks including machine loading, spot welding, spray painting and assembly. The robot can be programmed to perform a sequence of mechanical motions and it can repeat that motion sequence over and over again until reprogrammed to perform something else. A robot application is illustrated in figure 1.8.
 
 
 
 

FIGURE 1.8 Unimate 4000 series robots in spot welding application on automobile assembly line (Courtesy of Unimation, Inc.)
 

   There are certain general characteristics of an industrial situation which tend to make the installation of a robot economical and practical. These general characteristics include the following:
1.  Hazardous and uncomfortable working conditions
Referring to job situations where there are potential dangers or health hazards due to heat, radiation or toxicity, or where the workplace is uncomfortable and unpleasant. Examples of such situations are hot forging, die casting, spray painting and foundry operations.
2.  Repetitive tasks
Work cycles which are consisted of a sequence of elements which do not vary from cycle to cycle can be performed by a programmed robot. Examples are pick and place operations and machine loading.
3.  Difficulty handling
In cases where the workpart or tool involved in the operation is awkward or heavy, it might be possible for a robot to perform this task. There are robots capable of lifting payloads of many tons.
4.  Multishift operation
If the initial investment cost of the robot can be spread over two or three shifts, the labor savings will result in a quicker payback. Examples of such cases are plastic injection molding and other processes which must be operated continuously.
 

1.4  CAD/CAM implementation
It would have been a serious omission if a discussion upon implementation of CAD/CAM systems was not discussed in this project. Therefore in this chapter we will attempt to develop the guidelines and criteria in brief for implementing CAD/CAM. The system  would include the following features:

An interactive graphics system and associated software design. Software packages for manufacturing. Typically, these would have to be customized to the needs of the user, but would be likely to include programs such as NC part programming, automated process planning, fixture design, and various other aids for production. A common CAD/CAM database organized to serve both design and manufacturing.

There are three options in how a CAD/CAM system will be acquired from the user company, however, in this project we are limited to discuss the most common and the feasible approach to the issue. A CAD/CAM is being suggested to be purchased  from a vendor which is specialized on such systems. This approach is considered to be the best due to the fact that a vendor of CAD/CAM systems has developed the necessary personnel and possesses the expertise and the experience to handle such cases. Such a system is said to be a "turnkey system". It will be more cost and labor consuming if a company tries to develop a CAD/CAM system on its own due to the need of qualified computer personnel and programmers. Such a system is defined as an "in house development system". In addition it doesn’t occur quite often for a CAD/CAM system to be completely suited for the needs of the company and further customization is required to bring the system in complete compatibility with the production line. This customization can be done within the firm or even by the vendor who had probably dealt with such cases before.
   However, before taking the decision to purchase such a system a company should put the question whether it needs such a system. On top of this it should be noted that such systems are quite expensive and prices start from a few hundred thousands of US dollars to several million. Therefore a thorough analysis should be made prior to implementing such a system. The analysis might be based on the following general approach:
1.  Determine the size of the work load in the various applicable function of the company (e.g. design, manufacturing planning etc.)
2.  Estimate the amount of this work load that is applicable to a CAD/CAM system.
3.  Establish priorities among the different areas in item 2.
4.  Use the prioritized list of work local areas developed in item 3 to develop the features of an appropriate CAD/CAM system for the company. These features should be divided into two major categories:
 "Must" features
 "Desirable" features

   Let’s suppose now that the work load applicable to CAD/CAM is sufficient to warrant the expense of the system or the list of features ("must" features, in particular) includes a significant number of items which are available on existing CAD/CAM systems. When the company reaches the conclusion that a CAD/CAM system is needed, the following general procedure and guidelines are appropriate for implementing the system. The procedure is based on the selection of a turnkey system rather than an in house development.
1.  Develop the criteria for selecting a turnkey CAD/CAM system. The criteria should be defined with the specific needs of the user company in mind.
2.  Study and visit other companies using CAD/CAM systems with similar needs. Asses their effectiveness in similar applications.
3.  Study the CAD/CAM system vendors. Invite them in to make presentations on their companies and product lines.
4.  Reduce the list of vendors down to the three or four most attractive candidates
5.  Determine a benefit/cost ratio (a system value per cost for the specific needs of the user company) for each system under consideration.
6.  Invite the vendor with the highest ratio to run a benchmark. A benchmark consists of one or more user-specific problems which are representative  of the typical applications expected of the CAD/CAM system by the user company.
7.  If the benchmark test is successful, the vendor is officially selected. If not successful, the second choice based on benefit/cost ratio, is selected for benchmark testing and potential contract award.
 

1.5  CIM (computer integrated manufacturing)
The term computer integrated manufacturing (CIM) is often used interchangeably with CAD/CAM. However, CIM has a slight broader meaning than CAD/CAM. The CAD/CAM functions which have been discussed throughout this chapter are dealing with all the aspects of  design and manufacturing and all the production processes involved such as material planning, production scheduling etc. and CAD/CAM establishes the direct link between the design and manufacturing processes by automating all steps leading from the one function to the other.
   Computer integrated manufacturing though includes all the engineering activities included in the CAD/CAM and includes all the business functions as well. The ideal CIM system applies computer technology to all of the operational functions and information processing functions in manufacturing from order receipt, through design and production, to product shipment. The computer presence is throughout the firm, touching all activities that support manufacturing. In this integrated computer system the output of  each activity serves as the input to the next. Thus a chain of  activities is interlinked and begins with sales orders and ends with shipment of the product. The components of the integrated computer system and their relationship is illustrated in figure 1.9.
 
 
 
 

FIGURE 1.9 Computerized elements of CIM


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