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Design/Manufacturing Process

The totality of the design & manufacturing process is defined by implementation, and differs in detail within every manufacturing company. The following is representative of that process as viewed from within the turnkey industry.

Conceptual Design: Also sometimes called ``preliminary design'' or ``functional design,'' this stage deals not only with aesthetic issues such as styling, but with practical issues such as simulation and industrial design for manufacturability.

Paper and pencil, brush and oils, and sculptor's clay used to be the conceptual designer's tools in the automotive industry. Today, modern CAD/CAM systems provide him more and more powerful tools which free him from the necessity to create physical models.

It is here that companies such as Cognition, Aries, and Parametric Technologies have seen an opportunity to provide design engineers an entirely new way to approach the design engineering process; offering techniques which lie far beyond traditional methods and allow engineers much greater freedom to exercise their creativity.

Photorealistic rendering output is becoming an essential capability for conceptual design; it allows management to view the design as it would be manufactured, and also allows engineers to try different variations of the design without the accompanying investment in cost and time that normal prototyping techniques traditionally require.

Analysis and Refinement:

Also loosely termed CAE, or simply ``engineering,'' various high-level capabilities come under this category.

Finite Element Modeling and Analysis is performed as part of the engineering process. This stage of the process, which is intended to subject a preliminary design to real-world constraints and to iterate on that design until its behavior, given the design, is acceptable. Even within the narrow discipline of FEM/FEA, there are many specialist disciplines. These include fatigue analysis, thermal, vibration and magnetic analysis. Plastics, iso-plastics, and composites complicate the analysis. The exercise of finite-element modeling and analysis is one of the more obvious ``applications'' to which an existing design is subjected, but there are a large number of others.

Interference analysis, structure design, mass properties, adherence to safety and/or corporate standards and imposition of local codes and regulations are often all requirements for a design to be accepted, and that design generally must pass these analyses before it can be considered for manufacturing or construction.

In the design of an automobile, for example, stress analysis is an issue only for key engine or body parts. More time-consuming is the ergonomic design of windshields, instrument panels, and even seats. A new water pump must not only be efficient, and deliver so much volume of water per minute, but it must also fit comfortably within the numerous other components which comprise an engine.

Design for Manufacture:

Also termed ``design modeling,'' this is another step in ``reality design.'' Often, a so-called ``finished'' design is impractical to manufacture. Setup costs, consistency with existing manufacturing methods, or excessive complexity may preclude the consideration of an otherwise good design, causing that design to be modified.

A large number of applications exist which satisfy this requirement. The lifetime of a stamping tool, for instance, can have a significant effect on the long-term profitability of a division which manufactures press parts: this requirement alone may have an overwhelming influence on its design. In the plastic injection process, many designs are instantly made infeasible due to their inability to lend themselves to the realistic flow properties of the liquid plastic that is injected into them at high temperatures and pressures. A difference in 5% in injection and cooling time for a complex mold can make the difference between profitability and loss to an industry which works with little room to spare.

Pedestrian considerations such as the design of clamps to hold parts while they are machined, and machine-to-fit tolerances given the practical availability of real machine tools are make-or-break decisions for a manager to make.

Included within this area are assembly verification, component design, and electro/mechanical design.

Drafting and Documentation:

This is the world of AutoCAD, yet this area represents but a small part of the turnkey vendor's CAD/CAM universe.

Detail drafting represents no more than one-third of the requirement here. Technical illustration, schematics, and layout are equally important.

Before the days of geometrical models, detail drafting used to represent the ``meat'' of practical design. Due to the significant limitations of current turnkey design systems, much of detail drafting may never appear on a geometric model.

For example, fillets and chamfers may appear only as ``features'' on models and may never be represented as actual geometric constructs. As a practical issue, it is far easier to represent a fillet by a symbol on a drawing, and then to cut it with a single path of a ball-end mill, than to go through the difficult mathematics required to represent it geometrically. This is something which practical designers know and make use of.

Other aspects of the detail drafting process have to do with what we regard as ``drawing creation,'' and are intended to aid the ultimate downstream machining process. Surface finish characteristics, tolerance limits, detail magnification, and other aspects of detail drafting are not part of the geometrical model, yet become part of the total representation of the design by virtue of the fact that draftsmen, at least within the turnkey system, can access the original model and work directly upon a local representation of it, even though they are not allowed to modify it. Thus, draftsmen can be specialists in drafting and drawing creation, without having to be expert designers too.

Toolpath Creation & Machining:

Also termed ``manufacturing engineering,'' this phase of the process is one of the most complex and demanding. Composed equally of ``manufacturing preparation'' and ``manufacturing simulation,'' most companies spend the bulk of their CAD/CAM budget here.

Manufacturing preparation includes pattern nesting, tool design, fixture design, sheet metal development, manufacturing quality control analysis, and the actual NC programming itself.

Manufacturing simulation includes coordinate measuring machines, NC flame cutting, off-line robotics, NC tube bending, wire EDM, milling, drilling, routing, flame cutting, turning, and the important area of NC toolpath verification.

Although machining is essentially performed directly off the model geometry, it is by no means as ``automatic'' as the descriptions of it tend to imply. N/C is still more art than science, and even old-fashioned techniques of creating machined parts have not disappeared.

Creation of geometry is often the simplest aspect of the N/C process. Due to limitations in the algorithms which the turnkey vendors provide, ``work-arounds'' always have to be provided, including the ability of the user to directly edit the tool path which is being generated.

Toolpath simulation is intended to allow the user to see the form of the finished part that will come out of the machining process, and to correct any problems which are observed. The development and maintenance of postprocessors, which translate geometric toolpath descriptions into a language which each machine tool understands, is an industry in itself.

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Editor: John Walker