01-03-2010, 08:30 PM
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ADVANCED TRENDS IN CAD/CAM
The term CAD/CAM is a shortening of Computer-Aided Design (CAD) and Computer-Aided Manufacturing (CAM). The term CAD/NC (Numerical Control) is equivalent in some industries.
CAD/CAM software uses CAD drawing tools to describe geometries used by the CAM portion of the program to define a tool path that will direct the motion of a machine tool to machine the exact shape that was drawn.
NUMERICALLY-CONTROLLED MACHINES
Well before the development of Computer-aided design, the manufacturing world adopted tools controlled by numbers and letters to fill the need for manufacturing complex shapes in an accurate and repeatable manner. During the 1950's these Numerically-Controlled machines used the existing technology of paper tapes with regularly spaced holes punched in them (think of the paper roll that makes an old-fashioned player piano work, but only one inch wide) to feed numbers into controller machines that were wired to the motors positioning the work on machine tools. The electro-mechanical nature of the controllers allowed digital technologies to be easily incorporated as they were developed.
By the late 1960's Numerically-Controlled machining centers were commercially available, incorporating a variety of machining processes and automatic tool changing. Such tools were capable of doing work on multiple surfaces of a workpiece, moving the workpiece to positions programmed in advance and using a variety of tools - all automatically. What is more, the same work could be done over and over again with extraordinary precision and very little additional human input. NC tools immediately raised automation of manufacturing to a new level once feedback loops were incorporated (the tool tells the computer where it is, while the computer tells it where it should be).
What finally made NC technology enormously successful was the development of the universal NC programming language called APT (Automatically Programmed Tools). Announced at MIT in 1962, APT allowed programmers to develop postprocessors specific to each type of NC tool so that the output from the APT program could be shared among different parties with different manufacturing capabilities.
CAD & CAM TOGETHER AT LAST
The development of Computer-aided design had little effect on CNC initially due to the different capabilities and file formats used by drawing and machining programs. However, as CAD applications such as SolidWorks and AutoCad incorporate CAM intelligence, and as CAM applications such as MasterCAM adopt sophisticated CAD tools, both designers and manufacturers are now enjoying an increasing variety of capable CAD/CAM software. Most CAD/CAM software was developed for product development and the design and manufacturing of components and molds, but they are being used by architects with greater frequency.
Today, over three-quarters of new machine tools incorporate CNC technologies. These tools are used in every conceivable manufacturing sector, including many that affect building technologies. CNC technology is related to Computer Integrated Manufacturing (CIM), Computer Aided Process Planning (CAPP) and other technologies such as Group Technology (GT) and Cellular Manufacturing. Flexible Manufacturing Systems (FMS) and Just-In-Time Production (JIT) are made possible by Numerically-Controlled Machines.
Brief History of CAD / CAM development
The roots of todayâ„¢s CAD/CAM technologies go back to the beginning of civilization when graphics communication was acknowledged by engineers in ancient Egypt. Orthographic projection practiced today was invented around 1800s. The real development of CAD/ CAM systems started in 1950s. CAD/ CAM went through four major phases of development in the last century. 1950s was known as the era of conceiving interactive computer graphics. MITâ„¢s Servo Mechanisms Laboratory demonstrated the concept of numerical control (NC) on a three axis milling machine. Development in this era was slowed down by the inadequacy of computers of that period for interactive use. During late 1950s the Automatically Programmed Tools (APT) was developed and General Motors began to explore the potential of interactive graphics.
1960s was the most critical research period for interactive computer graphics. A sketchpad system was developed by Ivan Sutherland, which demonstrated the possibility of creating drawings and altercations of objects interactively on a CRT (cathode ray tube). The term CAD started to appear with word Ëœdesignâ„¢ extending beyond basic drafting concepts. General Motors announced their DAC-1 system and Bell Technologies announced their GRAPHIC 1 remote display system.
During the 1970s, the research efforts of 1960s in computer graphics had begun to be fruitful, and important potential of interactive computer graphics in improving productivity was realized by industry, government and academia. 1970s is characterized as the golden era for computer drafting and the beginning of ad hoc instrumental design applications. National Computer Graphics Association (NCGA) was formed and Initial Graphics Exchange Specification (IGES) was initiated.
In 1980s new theories and algorithms evolved and integration of various elements of design and manufacturing was developed. The major research and development focus was to expand CAD/CAM systems beyond three-dimensional geometric designs and provide more engineering applications.
In the present day, CAD/CAM development is focused on efficient and fast integration and/or automation of various elements of design and manufacturing along with the development of new algorithms. There are many commercial CAD/CAM packages available for direct usages which are user friendly, very proficient and competent.
Some of the commercial packages in the present market are: -
¢ Autocad, Mechanical Desktop, etc. are some low end CAD software™s which are mainly used for 2D modeling and drawing.
¢ Unigraphics, Pro-E, Ideas, Mechanical Desktop, CATIA, Euclid, etc. These are higher order modeling and designing software™s which are costlier and very efficient. The other capabilities of these software™s are manufacturing and analysis.
¢ Ansys, Abaqus, Nastran, Fluent, CFX “ These packages are mainly used for analysis of structures and fluids. Different software™s are used for different proposes, like Fluent is used for fluids and Ansys is used of structures.
¢ Alibre, Cyber-Cut, CollabCAD, etc. are the latest CAD/CAM software™s which focus on collaborative design. Collaborative design is computer aided designing of multiple users working at the same time.
Definition of CAD / CAM
Computer Aided Design “ CAD
CAD is the technology concerned with the use of computer systems to assist in the creation, modification, analysis, and optimization of a design. Any computer program
that embodies computer graphics and an application program facilitating engineering functions in design process can be classified as CAD software.
The most basic role of CAD is to define the geometry of design “ a mechanical part, a product assembly, an architectural structure, an electronic circuit, a building layout, etc. The greatest benefits of CAD systems are that it can save considerable time and reduce errors caused by otherwise having to redefine the geometry of the design from scratch every time it is needed.
Advantages
¢ Speeds up design process
¢ More designs can be produced
¢ Improved design quality
¢ Greater accuracy
¢ Changes can be made quickly
¢ Information can be stored electronically and retrieved
¢ Can be sent internationally
¢ Can calculate mathematical information such as mass, volume or centre of gravity
¢ Designs can be used directly in marketing and publicity
¢ View in virtual reality
Disadvantages
¢ High Expense
¢ Requires large processor
¢ Operators need to be trained
Computer Aided Manufacturing “ CAM
CAM is the technology concerned with the use of computer systems to plan, manage, and control the manufacturing operations through computer interface with the plantâ„¢s production resources.
One of the most important areas of CAM is numerical control (NC). This is the technique of using programmed instructions to control a machine tool that cuts, mills, grinds, punches or turns raw stock into a finished part. Another significant CAM function is in the programming of robots. CIM is also a target of CAD/CAM.
Advantages
¢ Information stored electronically means batch production machines can be reset quickly for next design
¢ Small changes in design can be implemented easily
¢ Greater productivity, especially if the machine works continuously
¢ Greater consistency of quality = fewer faulty goods
¢ Machines can work with chemicals
Disadvantages
¢ High set up costs
¢ Obsolescence
¢ May require heavy or costly maintenance
Computer Integrated Manufacturing (CIM)
Definition
Computer Integrated Manufacturing, known as CIM, is the phrase used to describe the complete automation of a manufacturing plant, with all processes functioning under computer control and digital information tying them together. It was promoted by machine tool manufacturers in the 1980's and the Society for Manufacturing Engineers (CASA/SME). Quite often it was mistaken for the concept of a "lights out" factory. It includes CAD/CAM, computer-aided design/computer-aided manufacturing, CAPP, computer-aided process planning, CNC, computer numerical control machine tools, DNC, direct numerical control machine tools, FMS, flexible machining systems, ASRS, automated storage and retrieval systems, AGV, automated guided vehicles, use of robotics and automated conveyance, computerized scheduling and production control, and a business system integrated by a common data base.
The heart of computer integrated manufacturing is CAD/CAM. Computer-aided design(CAD) and computer-aided manufacturing(CAM) systems are essential to reducing cycle times in the organization. CAD/CAM is a high technology integrating tool between design and manufacturing. CAD techniques make use of group technology to create similar geometries for quick retrieval. Electronic files replace drawing rooms. CAD/CAM integrated systems provide design/drafting, planning and scheduling, and fabrication capabilities. CAD provides the electronic part images, and CAM provides the facility for toolpath cutters to take on the raw piece.
The computer graphics that CAD provides allows designers to create electronic images which can be portrayed in two dimensions, or as a three dimensional solid component or assembly which can be rotated as it is viewed. Advanced software programs can analyze and test designs before a prototype is made. Finite element analysis programs allow engineers to predict stress points on a part, and the effects of loading.
Once a part has been designed, the graphics can be used to program the tool path to machine the part. When integrated with an NC postprocessor, the NC program that can be used in a CNC machine is produced. The design graphics can also be used to design tools and fixtures, and for inspections by coordinate measuring machines. The more downstream use that is made of CAD, the more time that is saved in the overall process.
Generative process planning is an advanced generation of CAD/CAM. This uses a more powerful software program to develop a process plan based on the part geometry, the number of parts to be made, and information about facilities in the plant. It can select the best tool and fixture, and it can calculate cost and time.
Flexible machining systems (FMS) are extensions of group technology and cellular manufacturing concepts. Using integrated CAD/CAM, parts can be designed and programmed in half the time it would normally take to do the engineering. The part programs can be downloaded to a CNC machining center under the control of an FMS host computer. The FMS host can schedule the CNC and the parts needed to perform the work.
Computer integrated manufacturing can include different combinations of the tools listed above.
The Issues
One of the key issues regarding CIM is equipment incompatibility and difficulty of integration of protocols. Integrating different brand equipment controllers with robots, conveyors and supervisory controllers is a time-consuming task with a lot of pitfalls. Quite often, the large investment and time required for software, hardware, communications, and integration cannot be financially justified easily.
Another key issue is data integrity. Machines react clumsily to bad data, and the costs of data upkeep as well as general information systems departmental costs is higher than in a non-CIM facility.
Another issue is the attempt to program extensive logic to produce schedules and optimize part sequence. There is no substitute for the human mind in reacting to a dynamic day-to-day manufacturing schedule and changing priorities.
Just like anything else, computer integrated manufacturing is no panacea, nor should it be embraced as a religion. It is an operational tool that, if implemented properly, will provide a new dimension to competing: quickly introducing new customerized high quality products and delivering them with unprecedented lead times, swift decisions, and manufacturing products with high velocity.
Control System Of Computer Integrated Manufacturing
Development of an Integrated Information Model for Computer Integrated Manufacturing
Introduction
CIM provides methods and tools to integrate new and/or existing CIM components. The integration involves data exchange among these components in an efficient and effective manner. The key benefit of integration in a manufacturing system is to consistently deliver the right information to the right components at the right time, regardless of their physical location. Many concepts for integration of manufacturing systems have been published and implemented by companies like IBM [1], Siemens, DEC, and so on. They usually offer complete solutions based on their and their partners products. However, manufacturing companies often use a variety of CIM components that are not designed to communicate well with each other.
This paper discusses the problems and a method for integrating components by using three sample applications.
Sample Applications
Three applications were selected to study their databases and the data flow between the applications. All applications are primarily used for planning of manufacturing layouts and products. The first application is a facility layout planning software (QSOM - Quantitative Systems for Operations Management) that employs the CRAFT algorithm to determine the best possible layout of departments. Layouts generated by a facility layout software are frequently used in simulation programs for further optimization. A simulation software, SIMAN, was chosen. However, a simulation also might be used by other components like product and process designers, production managers. An educational version of an MRP [2] package (MRP-DSS) will also provide information for the two other applications.
All three applications do not have explicit interfaces for communication, although the MRP package offers ASCII file import and export functions.
Figure 1: Dataflow between Selected Applications.
Figure 1 shows roughly dataflow that might occur between these applications. Based on production volume information and flow costs between departments (or workstations) the facility layout program develops the optimal layout. The simulation uses the new distances (rectilinear or euclidean) together with the sequences steps from the MRP software to determine throughput time or other relevant information.
An integration of these three or any other components brings up several problems, like:
o Location of components (single or multi-platform)
o Location of data (centralized, distributed)
o Data storage (flat files, DBMS)
o Data transportation (local, network)
o Translation of data in unified format (semantic)
o Version management (up-to-date information)
Before addressing the above points we will try to come up with an appropriate representation or schema for the integration.
Federated Database Systems
The data used by each application can be represented with a data modeling technique (e.g., Entity Relationship Diagrams). Actually all applications can be treated somehow as databases, however, the data may not be accessed and maintained as easy as with a traditional database system. The collection of cooperating but autonomous database systems (DBS) is often referred to as federated database system (FDBS). An interesting and comprehensive survey of FDBS can be found in [3].
Figure 2: Federated Database System with 3 Components
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The key concepts of FDBS are autonomy of components and partial, controlled sharing of data (Figure 2). There is usually no centralized control mechanism in a federated architecture because the component databases control the access to their data. Whatever a component database wants to share goes into the federated schema and is accessible for other components.
Figure 3 exhibits an extended five-level schema architecture [3] of an FDBS used in this paper, that is derived from the ANSI/SPARC three-level data description architecture. The local schema represents the data in locally stored format. The component schema translates the local schema into an application independent form (ERD, IDEF1.X). Whatever wants to be shared from the component schema with other applications is defined in the export schema. All export schemata together become the federated schema.
Figure 3: Five-Level Schema Architecture.
Although the federated schema is not located on one particular (centralized) machine, it is still possible to visualize the federated schema by querying all connected applications for their export schemes. Each application stores locally on what other information it depends on.
Data Processing
To transform data from one schema to another as well as handling requests from other applications we need the help of four processors:
1. Access Processor Provides access to application dependent data storage (e.g., flatfile DB, relational DB)
2. Translating Processor Translates data of local application (usually output) into convenient format for other applications (e.g., final department layout into rectilinear or euclidean distance between department centroids)
3. Construction Processor Prepares data in a way that it can be transformed into another schema. The construction processor does not modify the data as the translating processor does (e.g., it makes sure that the correct syntax and semantic for the next schema is used)
4. Filter Processor Verifies queries and commands from other applications. Controls access from other components. Enforces semantic integrity. The Filter Processor maintains also information about access rights, export schema, and version history.
Figure 4: Using Construction Processor to Create the Export Schema (right) from Component Schema (left)
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The component schema of the facility layout applicationâ„¢s data is given in Figure 4 as an IDEF1.X diagram. The small arrows indicate whether the attribute is an input or output from the layout process. In this example, other
applications (e.g., SIMAN) are interested in the distances between departments.
Sample Configuration
Figure 5 provides a sample configuration with processors and schemes for the facility layout and simulation application. We wish to use the distances from the generated layout in the simulation.
Figure 5
Figure 5: Sample Configuration of Layout-Facility and Simulation Components.
It is assumed that all applications or their data can be connected. The communication adapter enables access through a network system. There are several options for network access; the connection might be realized in the TCP/IP by using the file transfer protocol (ftp).
There are two basic methods to achieve data consistency when processing and transporting data in an integrated system [4]: a pull system that requires the receiver to ask the sender for data, or a push system, in which the sender initiates the transfer. A pull system is used for this FDBS to keep the version management simple. Otherwise, a receiver will get a new edition of any modified data regardless of need.
Figure 6 shows how the communication sequences between the two applications just for transferring the distances. Since this facility layout tool does not provide any data about distances between departments, it is necessary to translate the output file. The translating processor therefore determines the x/y coordinates of the department centroids and computes the distances between all departments. The data is then transferred to the requesting application together with additional information about the dataâ„¢s version and modification date/time. The receiver verifies the syntax and semantic of the data and updates the Integration DB (IDB) accordingly. Since there may be some more data necessary for the SIMAN experimental file, we have to distinguish between the userâ„¢s and SIMANâ„¢s experimental file. The Integration DB provides the building rules for the construction processor and merges both files into SIMANâ„¢s experimental file. This mechanism enables us to disregard data from any other system.
Figure 6: Transactions between Facility Layout and Simulation Component
.
Summary
The development of an FDBS is integrate existing CIM components by using a bottom-up development process. The components used in this paper do not support any kind database management. The integration of those components into a federation may be done by using two general approaches [3]:
¢ Migration of the files to a DBMS
¢ Extend the file system to support DBMS-like features
Both migration and extension of the file system are costly solutions and actually depend on existing capabilities of the components. Problems may occur when the federated schema becomes too large. The schema might be split up into smaller federated schemes (loosely coupled FBDS).
Pragmatic Applications
It might be more prudent for a company to begin the process of computer integration with CAD/CAM and an integrated business data base. There are many reliable and proven CAD/CAM software packages available, as there are integrated business software systems. Taking small steps instead of a wholesale CIM approach is advisable.
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