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Integrating CAD and CAM - computer-aided design; computer-aided manufacturing - Scanning the Horizon

In today's competitive environment, many shops are feeling the pressure to take on greater CAD (computer-aided design) capabilities. This is due in a large part to the growing desire among manufacturers to exchange part designs in the form of CAD files, rather than paper prints, and suppliers must be in a position to deal with the medium. With this increasing use of CAD data, and with the greater geometric part complexities which it often enables, CAM (computer-aided manufacturing) software is also becoming more a necessity than luxury, especially in the generation of CNC part programs for multiple-surface machining.

The decision on what software to buy has become more complicated as the line between CAD and CAM has blurred--some people have come to regard the terms as synonymous--even though each is intended to serve a different purpose. CAD is the science of creating a part drawing, a process usually driven by functional or aesthetic objectives, and often executed with little awareness of the problems it might create for manufacturing. CAM is the science of creating code that drives tools to remove unwanted material easily and efficiently from a solid block of stock, leaving the intended design.

In this sense, CAD and CAM are not at all the same thing, though they still must work in harmony whenever a design is to be machined. And that can be a challenge particularly when part features deemed necessary by the designer--such as sharp corners or many small surfaces--prove difficult to replicate in tool path code.

The issue gets most interesting when it comes time to put the CAD and the CAM together. Most vendors grew up on one side of the fence or the other, and then developed the additional functionality later. And though virtually everyone refers to their offering as CAD/CAM these days, more often than not the strength of the system still lies on the side of its developer's original mission.

One CAM developer, Olmsted Engineering Company (Traverse City, Michigan), took a different approach. They continued to concentrate on their strengths--CAM, IGES file translation and shop floor integration--while applying new development efforts toward integration with established CAD systems.

Olmsted's stand-alone CAM, ACU.CARV, was developed from the machinist's perspective, incorporating functions for contour milling, climb milling and so on, and outputting contouring code in form of circular and linear interpolation commands (rather than the numerous point-to-point moves typical of most CAM systems). As part of their CAD integration process, Olmsted created a new product, ACU.CARV ADS, that runs all CAM functions directly from within AutoCAD. The user gets both functions through a single interface. Olmsted contends that by integrating the system in this manner, and at the same time keeping the CAD and CAM philosophies separate, users get the benefit of both. The system supports CNC milling, turning and wire EDM.

For CAM milling functions, the system manages three of the most difficult aspects of multi-surface machining--avoiding gouges, inserting constant or variable radii between surfaces, and automatic roughing. On the CAD side, users can create a design and specify all geometry using the same interface. Moreover, all data input for machining parameters--including stock allowance, shrink factor, and cusp height--are made using the AutoCAD dialogue boxes.

One of the system's strengths is its ability to generate 3D contours by using planar machining (constant Z), which Olmsted contends allows cutters to be driven at the optimal speeds and feeds. It does this by combining any number of complex surfaces, or types of surfaces, into a composite tool path, permitting the path to proceed from surface to surface without gouging. This way, roughing can be accomplished with flat-bottomed cutters, even if islands are present, since the system knows the composite layout of the level being cut. Add the ability to automatically control the size of cusps (or scallops) to a user-specified tolerance, and the system is capable of generating efficient part programs that create very smooth 3D surfaces right on the machine tool.

This drive toward CAD/CAM integration has helped Olmsted strengthen their existing interfaces to CAD systems, such as CADKEY and AutoCAD, in addition to the fully-integrated ACU.CARV ADS product. The company also emphasizes a strong IGES translator to import files from the range of CAD systems shops must accommodate these days.

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