Computer-aided manufacturing: Difference between revisions

Computer-aided manufacturing (CAM) is the use of a wide range of Product Lifecycle Management computer-based software tools that assist engineers, in the manufacture or prototyping of product components. 3D models of components generated in CAD software are used to generate CNC code to drive numerical controled machine tools. This involves the engineer in selecting what type of tool, machining process and paths that are to be used.

Overview

Sometimes the CAM software is integrated with the CAD system, but not always. Every piece of CAM software must first solve the problem of CAD data exchange where in the CAD system which is producing the data often stores it in its own proprietary format, much as is the case with word processor software. Usually it is necessary to force the CAD operator to export the data in one of the common data formats, such as IGES or STL, that are supported by a wide variety of software. The output from the CAM software is usually a simple text file of G-code, sometimes many thousands of commands long, that is then transferred to a machine tool using a direct numerical control (DNC) program.

While it has long been the dream to make the CAM software that can run on its own, it generally requires a human operator with much knowledge and skill of machining to select the Milling cutters and define the necessary parameters and strategies that will generate an effective tool path.

History

The first commercial applications of CAM were in large companies in the automotive and aerospace industries for example UNISURF in 1971 at Renault (Bezier) for car body design and tooling.

Machining process

Most machining progresses through four stages, each of which is implemented by a variety of basic and sophisticated strategies, depending on the material and the software available. The stages are:

Roughing

This process begins with raw stock, known as billet, and cuts it very roughly to shape of the final model. In milling, the result often gives the appearance of terraces, because the strategy has taken advantage of the ability to cut the model horizontally. Common strategies are zig-zag clearing, offset clearing, plunge roughing, rest-roughing.

Semi-finishing

This process begins with a roughed part that unevenly approximates the model and cuts to within a fixed offset distance from the model. The semi-finishing pass must leave a small amount of material so the tool can cut accurately while finishing, but not so little that the tool and material deflect instead of shearing. Common strategies are raster passes, waterline passes, constant step-over passes, pencil milling.

Finishing

Finishing involves a slow pass across the material in very fine steps to produce the finished part. In finishing, the step between one pass and another is minimal. Feed rates are low and spindle speeds are raised to produce an accurate surface.

Contour Milling

In milling applications on hardware with five or more axes, a separate finishing process called contouring can be preformed. Instead of stepping down in fine-grained increments to approximate a surface, the workpiece is rotated to make the cutting surfaces of the tool tangent to the ideal part features. This produces an excellent surface finish with high dimensional tolerances.

Shortcomings

Present day CAM software has several shortcomings that necessitates skilled CNC machinists in industry. CAM software must output code for the least capable machine, as each machine tool interpreter may add on to the standard g-code set for increased flexibility. In some cases, such as improperly set up CAM software or specific tools, the CNC machine will require manual editing before the program will run properly. None of these issues are so insurmountable that a thoughtful engineer cannot overcome for prototyping or small production runs; G-Code is a simple language. In high production or high precision shops, a different set of problems are encountered where an experienced CNC machinist must both hand-code programs and run CAM software.

As CAM packages cannot reason as a machinist can, they cannot optimize toolpaths to the extent required of mass production. While an engineer may have a working knowledge of g-code programming, small optimization and wear issues compound over time. Mass-produced items that require machining are often initially created through casting or some other non-machine method. This enables hand-written, short, and highly optimized g-code that can't be produced in a CAM package.

Job Elimination Concerns

CAM demonstrates the latent drive towards computerization that is just now touching manufacturing, where in other industries it has prevailed and matured. This has lead to a concern amongst skilled workers that computers will replace future generations of machinist as engineers become versed in CAM. At least in the United States, there is a shortage of young, skilled machinists entering the workforce able to perform at the extremes of manufacturing; high precision and mass production. As CAM software and machines become more complicated, the skills required of a machinist advance to approach that of a computer programmer and engineer rather than eliminating the CNC machinist from the workforce.

Some Software has been developed that will allow optimisation of CNC tool paths based on Finite Element Analysis (FEA) of the machining tool paths. This software is expensive and at the moment tends to be only used by the aerospace industry.

Software providers today

The largest CAM software companies (by revenue 2005) are UGS Corp and Dassault Systèmes, both with over 10% of the market; PTC, Hitachi Zosen and Delcam have over 5% each; while Planit, Tebis, TopSolid, CNC (Mastercam), ESPRIT,OneCNC, and Sescoi between 2.5% and 5% each. The remaining 35% is accounted for by other niche suppliers like BobCAD-CAM, GibbsCAM, and SurfCAM.

Areas of usage

• In mechanical engineering
• In electronic design automation, CAM tools prepare printed circuit board (PCB) and integrated circuit design data for manufacturing.

See also

• CIM Computer Integrated Manufacturing
• DNC Direct Numerical Control
• FMS Flexible Manufacturing System
• ICAM Integrated Computer-Aided Manufacturing
• MPM Manufacturing Process Management
• Category:Computer-aided manufacturing software
• List of CAD companies
• List of CAM companies

External links

• CAD/CAM Overview Online Tutorial– from Tooling University, you can register and take this class for free.
• Open Source CNC Milling - GNU Computer Aided Manufacturing (GCAM)
• What is CNC? – By Mike Lynch