Computer aiaded Concurrent Engineering seamlessly integrates design, analysis, prototyping and manufacturing stages, greatly reduces the design to manufacturing time cycle.

Conventional engineering processes, commonly being referred to as Serial Engineering Processes, follows a linear path, with each step beginning only after the last is completed (Fig. 1). So the design (Conceptual design and Detail design) should be performed at first, followed by the Analysis and Prototype. Any change will result in the repeated work from design stages. After the design passes the analysis and prototype, it is sent to the shop. If any further change is required, either in the Manufacturing preparation stage, or due to a change of purchasing or suppliers, the whole design needs to be passed back to the very beginning (the design stage). In those processes, engineers and others are isolated to each other. No matter how efficient the serial approach becomes, it's still slower and more error-prone than the parallel approach of concurrent engineering.

Fig. 1: Traditional Serial Engineering Processes [245]

With a concurrent approach to engineering, teams attack all aspects of product development simultaneously (Fig. 2).

Fig. 2: Product development 1990s style [245]

With this engineering model, the Conceptual design, Detailed design, Analysis, Manufacturing preparation as well as Purchsing and Suppliers can be considered concurrently. Most changes come in the early stages. Fewer prototypes are needed. Therefore, a product takes less time to develop, has higher quality, and costs less.

Computer Aided Concurrent Engineering Processes have the potential to significantly shorten the product development cycle as has been mentioned. The technologies involved also permit a far more thorough engineering function. For instance, Solidification Simulation packages can accurately predict the presence of designrelated defects such as shrinkage so that modifications to the model can be made until a sound casting design is arrived at, even before a hard drawing has been made. Other examples are Rapid Prototyping Processes which offer the capability of producing accurate, scaled, hard models of castings in just hours, which opens a wide array of possibilities in terms of optimizing manufacturing methods.

Computer-aided engineering tools and the communications afforded by computers play key roles in the workflow of concurrent engineering. Software packages are required for most engineering stages, such as design, analysis and prototyping. Development issues often involved includes linkage for various packages to make them work as one, e.g., transforing data from design package (CAD program) to analysis tools (finite element program).

In following, several issues related to the Computer-aided Concurrent Engineering are discussed:

• Design
• Analysis
• Rapid Prototyping
• Computer Aided Pattern Making
• Casting Machining

Those issues and their significance may vary for different manufacturing processes.

Computer tools (packages) invovolved in this stages includes those for Computer Aided Design and Solid Modeling. The Computer Aided Design tools are primarily two-dimension drafting programs used to create engineering drawing, while Solid modelers are highly sophisticated computer tools that allow the "creation" on a screen, of mathematically defined solids and surfaces.

Computer Aided Design (CAD) tools permit the generation of high quality engineering drawings in considerably less time than manual drafting methods allow. Their greatest advantage rests in the ease with which drawing modifications can be implemented which allows for greater flexibility in the design process.

Although Solid modelers have the capability of producing two-dimensional engineering drawings from the solid model, this is not their main purpose, since that task can be better accomplished with inexpensive and simple to use PC drafting programs. The main advantage of solid models is that they can be manipulated as if they were actual solids. Parts can be sectioned, features added or removed, and mass properties can be instantly computed.

Several CAD programs have capabilities for drafting parts three-dimensionally. In effect, they generate an array of contour lines called a "wireframe" which can give different visual perspectives of the final part. This capability should not be confused with Solid Modeling which will be discussed next.

After design stage is done, manufacturing simulation, sometimes referred to as virtual manufacturing, is performed. Production parameters, such as product geometry, properties, defects are predicted. If the predicted results are beyond the expection, normally design work needs to be changed (assuming the analysis model is correct).

Finite element method (FEM) is an universal and a very powerful and most frequently used tool for analysis. Finite differential method (FDM) is also used, for example, for temperature prediction.

As to the analysis and its tool selection, especially of finite element method, following aspects are of primary concern:

• Accuracy. Algorithm in the program should be optimized. With programs with various applications, such as those general-purpose FEM programs, best-fitted algorithm or model-type needs to be selected. For example, when both mechanical and thermal phenomena are involved, thermo-mechanical model is better than mechanical model. Material data (specific heat, thermo-conductivity, etc.) and boundary conditions (heat transfer coefficient, friction coefficients) should be entered accurately. Most of those material data and boundary conditions are process related (e.g. temperature dependent).
• User-friendliness of program. This related to the user-friendliness of the interface, ease and speed to generate mesh, and remeshing capability. One fundamental requirement of simulation programs is their ability to accept geometry from another CAD System. Although most of the solidification programs come with their own CAD package, requirement to create solid model from blueprints nullifies the design-to-manufacturing time cycle advantages.
• Computing time. With development of computer capacity, the computing time may not be a crical problem any more for may processes in off-line situation. To be noted is that the finite element analysis has a reputation for its high computing requirement, especially for complicated processes, such as thermo-mechanical model with large and complex plastic deformation. For Computer Aided Concurrent Engineering, the computing time should be within an acceptable limit.

Simulation programs can be two-dimensional or three-dimensional. Though two dimensional programs run faster, three-dimensional ones give much accurate results. With increased computer capability, three-dimensional programs are widely used.

Analysis tools and prediction parameters may vary for different manufacturing processes. For casting process, for example, tools are needed to perform following simulation:

• Solidification Simulation, for solidification related phonomena and defects, etc.
• Fluid Flow Simulation, for mold filling, gas entrapment, mold erosion and spalling defects, slag and dross inclusions, misruns and undesirable thermal gradients, etc.
• Mechanical Design and Stress Analysis, for mechanical and thermal stresses, failure analysis, etc.

Rapid prototyping refers to a variety of technologies that are capable of automatically generating physical models using solid modeling data. These processes take place virtually unattended and complex configurations can be produced in a matter of hours, while conventional, manual fabrication methods can take weeks and even months to produce a complete model. The availability of hard models at the initial stages of product development, leads to the production of better designs and manufacturing methods since all the engineering functions are greatly facilitated by the visualization and manipulation of hard models.

This refers to the ability to use the model to generate CNC or NC machining programs that will produce complete or partial pattern tooling from solid wood or metal in automatic machining centers.

One major concurrent engineering advantage while using CAD models is that of being able to generate machining methods and programs at an early design stage. This is commonly done, for example for casting, by "merging" a rough casting model with all the machining stock, solid cast drilled areas, etc. with a "fully machined" finish part model using a CAD/CAM machining program. Stock to be removed is highlighted, and the machining programmer is guided through the definition of various operations, tool-path design, tooling selection, etc. The CAD/CAM output is then processed through software that generates the machining programs required.

Traditional Serial engineering is still used in some instances for the following reasons:

• Simple designs can be rapidly and thoroughly evaluated by foundry and manufacturing professionals without the use of expensive and elaborate CAD/CAM technologies.
• The generation of solid models can be a lengthy and involved process that requires well-trained specialists: in many cases a two-dimensional conventional blueprint is faster, more economical, and just as effective.
• The cost of Computer Aided Technologies such as Solid Modeling, Solidification Simulation and Rapid Prototyping may be high for certain applications.

One of the key issues is the ability to transfer solid models into various simulation packages (as mentioned above), and to use the models with rapid prototyping devices and pattern machining programs.

One example, Application of Concurrent Engineering in Casting, is discussed in another paper in the category "Casting".

[245] ASM: Steel Castings Handbook, 6th Ed., 1995. ISBN 0-87170-556-7. Ed. By M. Blair, T.L. Stevens.