MANUFACTURING INDUSTRY USES CAD AND RELATED TECHNOLOGIES IN THEIR DESIGN AND PRODUCT DEVELOPMENT PROCESS
ABSTRACT
The importance of software development in the manufacturing industry can be seen by a recent emphasis of CAD software developers on the production of high-level systems aimed at the complete automation of design processes. A recent trend by manufacturing companies has been their use of large-scale parametric software suitable for integration into existing design methods.
CAD technology has come a long way since the early, esoteric, command-driven systems, which required as much if not more of an engineer s attention as the actual process of design, and now helps manufacturers to streamline their design processes, reduce costs, and improve product quality. Today s engineering and manufacturing professionals need a design platform that complements their creativity, innovation, and engineering skills so that they can approach design and manufacturing challenges without distraction.
1. INTRODUCTION
Computer Aided Design (CAD) is a process that utilizes computers to assist the creation, modification, analysis or optimization of a produced design. It involves integration of computers in to design activities of providing a close coupling between designer and the computer. Typical design activities involving a CAD system preliminary design, drafting, modeling and simulation.
CAD/CAM has been utilized in engineering practice in many ways including drafting, design, simulation, analysis and manufacturing. Figure 1.1 shows the product life cycle of a typical product, starting from customers, demands leading towards inception to finish product, undergoes through two main processes: the design process and the manufacturing process .the CAD process is a subset of design process and the CAM is subset of the manufacturing process: the CAD process and its tool utilize three disciplines of CAD itself, manufacturing, and the automation.
There are considerable numbers of application for the various existing CAD/CAM systems. The major available modules are geometric engine module, application module, programming module, communication module and collaborative module.
Three dimensional solid models in the computer have allowed the designers to perform analyses directly on this solid model to determine its properties and reaction to applied loads. Thus the steps of drawing have been closely linked to the analysis. Analysis by sophisticated tools on a computer model has replaced analysis by hand with simplified geometry for many applications.
Finite element modeling (FEM) and analysis (FEA) is one of the most popular applications offered by existing CAD/CAM systems. It is due to the fact that the finite element method is the most popular numerical technique for solving engineering problems. Theses packages are integrated with CAD database to automate both FEA & FEM.
Fig 1.1 Product Life Cycle
Rapid prototyping (RP) by definition means the ability to generate models directly from computer-aided design (CAD) data in a very short time.
There are two distinct RP processes:
- Subtractive processes
- Additive processes
The RP processes include, amongst others, Subtractive Rapid Prototyping (SRP), Stereo Lithography (SL), Laser Sintering (LS), Fused Depositions Modelling (FDM), Laminated Object Manufacturing (LOM), Selective Laser Sintering (SLS) and 3- Dimensional Printing (3DP) (Chua et al., 2005). RP technologies have gained diversity, complexity, sophistication and popularity since their introduction in the late 1980’s [8].
These techniques allow designers to produce tangible prototypes of their designs quickly, rather than just two dimensional pictures. For small series and complex parts, these techniques are often the best manufacturing processes available. After all, CNC technology and injection molding are economical, widely understood, and available for wide material selection. [9]
The reasons of Rapid Prototyping are
- To increase effective communication.
- To decrease development time.
- To decrease costly mistakes.
- To minimize sustaining engineering changes.
- To extend product lifetime by adding necessary features and eliminating redundant features early in the design.
Rapid Prototyping decreases development time by allowing corrections to a product to be made early in the process. By giving engineering, manufacturing, marketing, and purchasing a look at the product early in the design process, mistakes can be corrected and changes can be made while they are still inexpensive. The trends in manufacturing industries continue to emphasize the following:
- Increasing number of variants of products.
- Increasing product complexity.
- Decreasing product lifetime before obsolescence.
- Decreasing delivery time.
Rapid Prototyping improves product development by enabling better communication in a concurrent engineering environment.
Rapid prototyping is mainly intended for verifying CAD data, checking the design, functional checks of prototypes, wax models for investment casting, master models for die and models making, mold making for prototypes manufacturing, casting models, and medical use CT and MRI data. Although dimensional accuracy was given little importance in the verification stage of CAD data and design, high dimensional accuracy is now demanded of the functional check of prototypes.
The roles that prototypes play in the product development process are several. They include the following:
- Experimentation and learning
- Testing and proofing
- Communication and interaction
- Synthesis and integration
- Scheduling and markers
Prototypes can also be used for testing and proofing of ideas and concepts relating to the development of the product. For example, in the early design of folding reading glasses for the elderly, concepts and ideas of folding mechanism can be tested by building rough physical prototypes to test and prove these ideas to see if they work as intended.
Motion Analysis is typically viewed as the examination of objects and/or incidents to determine a range of facts about how they are changing, moving, and/or altering across time and space. The purpose behind motion analysis includes, but is not limited to, developing improved efficiency and better understanding of what is actually taking place.
Through motion analysis of real world objects under real world conditions we can observe and measure:
- range of motion;
- performance changes under various environmental conditions;
- variation of performance over time;
- material defects;
- minute changes that may require further examination;
- performance degradation;
- external effects upon performance;
- the previously unnoticeable;
- and much more
2. METHODOLOGY
Computer-aided design (CAD) tool for manufacturing are computer programs that evaluate producibility of a product under development using computer models of the product and simulation models for manufacturing processes.
One of the first and most prominent manufacturing applications of CAD system was the automated programming of numerically controlled (NC) machine tools.
A key element of virtually all CAD tools for manufacturing is the need to interrupt the CAD data according to manufacturing, capabilities, requirements and constraints. Generally this interpretation involves determining the characteristic shapes in the CAD data related to the manufacturing process of interest and applying knowledge about the process to determine the manufacturing operation and parameters. Solid models are rigorous computer data structure that contains a complete, unambiguous of the geometry of an object.
In some cases, these systems also include an automatic rule-driven numerically-controlled (NC) code generator, which translates CAD data into suitable NC code. A similar system that is targeted toward integrating an end-product directly from the designer’s CAD system or solid modeler was presented by Mayer et al1. This system is able to generate a process plan, a tool path, and NC code. Other systems have appeared in Chen and Voleker’s work2 where the manufacturing engineer needs only to specify the process plan. The complete part program could be derived from the plan specified.
Prototyping processes have gone through three phases of development, the last two of which have emerged only in the last 20 years [10]. Like the modeling process in computer graphics [11], the prototyping of physical models is growing through its third phase. Parallels between the computer modeling process and prototyping process can be drawn as seen in Table 2.1
Table 2.1: Parallels between geometric modeling and prototyping
GEOMETRIC MODELING
|
PROTOTYPING
|
_ First Phase: 2D Wireframe
· Started in mid-1960s
· Few straight lines on display may be:
· circuit path on a PCB
· plan view of a mechanical component
|
_ First Phase: Manual Prototyping
· Traditional practice for many
· centuries
· Prototyping as a skilled crafts is:
· traditional and manual
· based on material of prototype
|
_ Second Phase: 3D Curve and Surface Modeling
· Mid-1970s
· Increasing complexity
|
_ Second Phase: Soft or Virtual Prototyping
· Mid-1970s
· Increasing complexity
|
_ Third Phase: Solid Modeling
· Early 1980s
· Edges, surfaces and holes are knitted together to form a cohesive whole Computer can determine the inside of an object from the outside.
· Perhaps, more importantly, it can trace across the object and readily find all intersecting surfaces and edges
|
_ Third Phase: Rapid Prototyping
· Mid-1980s
· Benefit of a hard prototype made in a very short turnaround time is its main strong point (relies on CAD modeling)
· Hard prototype can also be used for limited testing
|
Common to all the different techniques of RP is the basic approach they adopt, which can be described as follows:
- A model or component is modeled on a Computer-Aided Design/ Computer-Aided Manufacturing (CAD/CAM) system. The model which represents the physical part to be built must be represented as closed surfaces which unambiguously define an enclosed volume. This means that the data must specify the inside, outside and boundary of the model. This requirement will become redundant if the modeling technique used is solid modeling. This is by virtue of the technique used, as a valid solid model will automatically be an enclosed volume. This requirement ensures that all horizontal cross sections that are essential to RP are closed curves to create the solid object.
- The solid or surface model to be built is next converted into a format dubbed the “STL” (STereoLithography) file format which originates from 3D Systems. The STL file format approximates the surfaces of the model by polygons. Highly curved surfaces must employ many polygons, which means that STL files for curved parts can be very large. However, there are some rapid prototyping systems which also accept IGES (Initial Graphics Exchange Specifications) data, provided it is of the correct “flavor”.
- A computer program analyzes a STL file that defines the model to be fabricated and “slices” the model into cross sections. The cross sections are systematically recreated through the solidification of either liquids or powders and then combined to form a 3D model. Another possibility is that the cross sections are already thin, solid laminations and these thin laminations are glued together with adhesives to form a 3D model. Other similar methods may also be employed to build the model.
Fundamentally, the development of RP can be seen in four primary areas. The Rapid Prototyping Wheel in Figure 1.3 depicts these four key aspects of Rapid Prototyping. They are: Input, Method, Material and Applications.
The rapid progress of CAD technology for the design of machine parts has now made it easy to store three-dimensional shape data on computer. The application of this three-dimensional data has realized NC programming by CAD/CAM, resulting in the remarkable advance of automated production. The increase in highly functional machine parts and advance designs has let to the designs of more and more complicated surface using CAD. To reduce the lead time and costs for the development of new industrial products, “rapid prototyping “has been recognized as a unique, layered manufacturing technique for making prototypes.
Rapid Prototyping (RP) can be defined as a group of techniques used to quickly fabricate a scale model of a part or assembly using three-dimensional computer aided design (CAD) data. Rapid Prototyping has also been referred to as solid free-form manufacturing; computer automated manufacturing, and layered manufacturing. RP has obvious use as a vehicle for visualization. In addition, RP models can be used for testing, such as when an airfoil shape is put into a wind tunnel. RP models can be used to create male models for tooling, such as silicone rubber molds and investment casts. In some cases, the RP part can be the final part, but typically the RP material is not strong or accurate enough. When the RP material is suitable, highly convoluted shapes (including parts nested within parts) can be produced because of the nature of RP.
The basic methodology for all current rapid prototyping techniques can be summarized as follows:
- A CAD model is constructed, then converted to STL format. The resolution can be set to minimize stair stepping.
- The RP machine processes the .STL file by creating sliced layers of the model.
- The first layer of the physical model is created. The model is then lowered by the thickness of the next layer, and the process is repeated until completion of the model.
- The model and any supports are removed. The surface of the model is then finished and cleaned.
Finite Element Analysis (FEA) is incorporated in few engineering technology programs (Roth, 1995). This is because the complexity of FEA analysis forces most courses to focus on the theoretical aspects of generating FEA models rather than application of FEA to solve practical engineering problems. However, FEA techniques are becoming less daunting and can now be introduced into freshman EDGD courses (Boronokay, 1997). Thus students can be introduced to this tool which is becoming increasingly common in the workplace. There are still problems, however, in introducing FEA techniques into a traditional EDGD course. These problems focus around how to use this difficult software with very specific data entry requirements (Dally, 1994). At the University of California, this was overcome for engineering students by devoting six hours of class time and "substantial" student efforts outside the classroom (Lieu, 1993). In another case, a GUI front end was created for a FEA program to overcome these difficulties at the expense of generalization capability of the software (Dally, 1994).
Solid modeling overcomes this difficulty of complex software with very specific data entry requirements. Once the solid model is created, there are several programs available that can generate the mesh patterns and perform the FEA analysis on the solid model transparently.
3.CONCLUSION
The manufacturing industry has at its disposal a wide variety of processes for constructing objects, including gravity casting, injection molding, layered manufacturing, material removal via conventional (or chemical or electrical) machining, deformation (forging, rolling, extrusion, bending), composition (as in composite materials, sintered ceramics, and the like), spray deposition, etc. CAD/CAM systems of growing sophistication are presently being introduced. Geometric computation has become ubiquitous in the manufacturing industry, as more and more real-world objects begin their design life as geometric objects modeled within a computer.
Today s CAD systems have progressed a great deal toward achieving that goal, requiring less mental energy to run so that an engineer can focus more on bringing better products to market faster. CAD technology operates efficiently on affordable computing hardware. CAD packages are now integrated with more complementary design, manufacturing, and desktop productivity applications and CAD data can now automate many functions across the product development organization. In many ways, 3D solid modeling data have become both the foundation and the glue that drive today s efficient, high-quality manufacturing operations.
REFERENCES
1. R. J. Mayer, C.J. Su, and A.K. Keen, “An Integrated Manufacturing Planning Assistant-IMPA,” Journal of Intelligent Manufacturing, (v3, n2, 1992), pp109-122.
2. S.C. Chen and H.B. Voelcker, “An Introduction to MPL: a New Machining Process/Programming Language,” IEEE International Conference on Robotics and Automation, San Fransisco, v1, pp333-344, 1986.
3- Mastering CAD/CAM by Ibrahim zeid special Indian edition 2007.
4-Amirouche F.M.L. 1993 COMPUTER AIDED designs and manufacturing, prentice hall Englewood cliffs, NJ
5-Boothroyd, G 1994 .product designs for manufacture and assembly, comput aided des, 26(7), 505-520
6-Laurence, N 1994 a high level view of STEP manuf Rev, 7(1), 39-46, The national product data exchange resources centre U.S product data association (US PRO) NATIONAL institute of standard and technology
7-Howell, Steven K. (1993). Finite element analysis in a freshman graphics course. TheEngineering Design Graphics Journal,Winter, 29.
[8] Hague R., S. Mansour, N. Saleh and R. Harris,( October 28, 2004), Materials analysis of stereolithography resins for use in Rapid Manufacturing , Journal of Materials Science, ISSN0022-2461
[9] Chua C. K. , S. M. Chou and T. S. Wong, (march 31, 2005), A study of the state-of-the-art rapid prototyping technologies , The International Journal of Advanced Manufacturing Technology, ISSN0268-3768
[8] Chua, C.K., “Solid modeling — A state-of-the-art report,” Manufacturing Equipment News (September 1987): 33–34.
[9] Metelnick, J., “How today’s model/prototype shop helps designers use rapid prototyping to full advantage,” Society of Manufacturing Engineers Technical Paper (1991): MS91-475.
[10] Lee, G., “Virtual prototyping on personal computers,” Mechanical Engineering 117(7) (1995): 70–73.
[11] Kochan, D., “Solid freeform manufacturing — Possibilities and restrictions,” Computers in Industry 20 (1992): 133–140.
No comments:
Post a Comment