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Does your shop need CAD/CAM?

Answering 17 simple questions will help determine whether you can justify CADICAM for your machine shop.

CAD/CAM isn't just for large manufacturers anymore. With the growing influence of micro-based computers in small and midsized shops, simple CAD/CAM is now affordable to any shop that does CNC machining.

For example, a simple off-line programming package such as Anilam's Microcam can be purchased for under $1000. Although lacking some features of more complex software, this inexpensive package can construct part geometry; calculate arcs, angles, and tangency points; display finished tool paths; create G-coded output for various CNC controls; and download completed, coded tool paths directly to the machines.

Before even beginning to evaluate a CAD/CAM system, first take the time to evaluate your own company's needs. Many manufacturers and job shops have made the mistake of buying elaborate systems that looked good on paper, but were difficult to implement into actual operation.

Determine who is going to use the system. If you want a system primarily for the machine shop, the software must be machinist-oriented and easy to learn. It also must be easy to interface with every piece of CNC equipment on the shop floor.

On the other hand, be careful to not lock yourself into a dead-end system. Some menu-driven programs are great for beginners, but become cumbersome after a basic level of competency is achieved. Other software programs are little more than dressed-up math packages that cannot easily interface with CNC machinery or perform even simple CAD-to-CAM conversions.

Make sure the software package and supplier offer an upward path for upgrades and expansion, and that the package is highly machinist-oriented.

Once a few basic guidelines have been established, you can begin a more extensive, needs-oriented analysis. The following 17 questions will help you get started in evaluating whether or not CAD/CAM can be justified for your shop.

1. Do you machine arcs and angles?

Any time you machine arcs and angles, off-line programming is a tremendous asset. Without it, all line-segment and arc-segment lengths must be found, intersections and tangency points determined, and trig calculations repeatedly performed. Even with the simplest CAM system, however, no trig calculations are ever required. The operator simply defines a series of lines, points, and circles, and enters his tool path. The computer then calculates all line-segment and arc-segment lengths, displays the compensated tool path, and prepares the program for downloading directly to a machine.

2. Do you produce irregularly shaped cavities? In addition to featuring canned cycles for rectangular and circular pocket-milling, CAM software also offers irregular pocket clearing. The profile of the pocket is defined, and a simple POCKET command is entered. The computer can either rough out the pocket in a zig-zag pattern to optimize the path, or a contour cycle can be specified. The latter routine will optimize surface finish and reduce benching and polishing time.

Irregular pockets of virtually any configuration, including pockets with islands, can be easily defined and machined, and no trig is needed.

To ensure top accuracy during verification of the finished tool path, some CAM systems also have look-ahead cutter compensation. This feature in a CAM system is vastly superior to even the most expensive CNC controls, both in accuracy (to 10 or more decimal places) and in sophistication.

For instance, if a particular tool cannot fit in a section of a defined cavity, the computer will override the command and flag the operator. Corrections can be made before the first cut is taken, and production of scrap is virtually eliminated. 3. Do you ever use tracing attachments or pantograph machines?

Some common CAM systems have curve-fitting, a feature used to produce undefined shapes. For example, if a machinist is working from an undefined print or mylar transparency, a series of points can be entered, either through a math formula or digitizing pad. The computer will then generate a smooth curve between the points. Virtually any shape of unknown dimensions can be produced in this way. As a result, the need for tracing attachments or pantographs is greatly reduced.

Some CAM suppliers also offer a 3-D digitizing option. A probe is set up in the CNC machine's spindle, and a digitizing window is specified. As the probe touches the model or prototype, 3-D points are generated and uploaded to the off-line computer. There, all CAM features are at the operator's fingertips.

The part image can be scaled up or down, eliminating the need for shrink-models and duplicating tools. The image can be translated, rotated, or modified in any configuration.

Moreover, cutter compensation can be added, and the finished tool path can be postprocessed for any CNC control in your shop. 4. Do you ever produce families of parts?

If you machine parts that have similar shapes but different sizes or proportions, you'll find CAM programming ideal for modifying previously written programs. Once a shape has been defined, it can be manipulated in a number of ways. For example, it can be moved in X, Y, or Z, a technique perfect for creating multiple-cavity molds. Moreover, a shape can be rotated by any angle, or scaled up or down in precise proportions. Multiple zero reference points can be set up for multiple fixturing. In a word, CAM programming adds great power and flexibility to any CNC machine tool. 5. Do you have multiple CNC machines?

If you operate more than one CNC machine tool, off-line programming can become a big time-saver. CAM allows you to use only one programming language to program all your CNC controls.

With a good universal postprocessor (provided at no extra cost in some packages), the tool path shown on the screen is automatically converted into the NC-coded data necessary to run machines with different CNC controls. You simply enter the file name of a particular CNC machine, run the program through the postprocessor, and download the completed, coded program directly to the machine.

Scheduling also is improved dramatically.

Since one CAM terminal can serve several different machines, scheduling changes often can be made at a moment's notice. If, for example, a CNC machine is tied up on a production job, a portion of the program can be redirected to another machine, even if it uses a different make of control and programming format. CAM keeps your CNC spindles turning for increased productivity and profits. 6. Do you ever do production (100 to 1000 pieces) machining?

If you perform relatively long production runs, programming time seems insignificant when compared to actual cycle-time needed per part. If spending an extra hour of programming time results in saving 2 minutes a part in a 500-part run, however, more than 16 hours of expensive CNC machining will be saved in that run.

CAM is perfect for long-run production. During machining of a cavity, for instance, the most efficient machining path can be chosen quickly. To verify your choice, some software will even calculate and display the cycle time for any given cutting tool, before the first cut is taken. Editing time is minimized, but efficiency of your CNC machine is maximized.

7. Do you produce batch (12 to 100 pieces) production runs?

If you usually produce part-runs of 12 to 100 pieces, CAM can give you the best of two worlds. When you're machining long runs, the cycle-time saving benefits of CAM will save hours of machining inefficiency. During machining of short runs, CAM's savings in programming time will make your quotes more competitive.

8. Do you perform short-run (1 to 12 pieces) production? If you produce relatively short runs of, say, 12 pieces or fewer, offline programming can save a great amount of time and money. For example, if a typical job takes 4.5 hours to program manually, but only 1.2 hours to set up and run, then 82% of total production time is spent on programming.

A simple CAM system cuts programming time in half for even the most common profiles, and time-savings of 90% to 95% are often reported on complex work. Projects that would have been impractical to set up and program manually become competitive when off-line programming is used.

9. Do you still produce one-of-a-kind work manually? Because of time needed to write CNC programs manually, some operators prefer to produce one-of-akind work conventionally, instead of using CNC. With a CAM system installed, however, it is almost always more practical to use a CNC machine to produce a part. That's because programming time is generally reduced by 50% to 95%. If you can keep even one CNC machine busy an extra six hours a week, that machine will produce at least an additional $10,000 in profit during the first year.

10. Do you enter your programs into your CNC controls manually? Even if you have only one CNC machine tool on the floor, downloading programs from an off-line programmer has its advantages. Some programs may consist of many lines of information, and could take your operator hours to enter and prove-out manually. Furthermore, errors sometimes occur while the program is being entered manually. This causes the waste of even more time for proving and editing programs. Meanwhile, the CNC machine is not producing parts or making money. With off-line programming in use, though, all programming and editing can be performed away from the machine. Also, the completed tool path can be verified before the first cut is taken. Once the operator is satisfied with his program, he postprocesses it and downloads it to the machine. Then all he need do is set his tool at zero and press the START button. A recent survey estimates that with an off-line computer for part-programming, the average shop can save at least 240 hours a year in program entry time. At a shop rate of $30 an hour, that's an annual savings of $7200 per CNC machine.

11. Do you have a drafting department? if you design your own parts or fixtures, you ought to seriously consider adding a design and drafting extension to your CAM system. CAD saves a lot of time in design, dimensioning, and modification of part drawings. Moreover, once a print is finished, 90% of your CNC programming is already completed. CAD-to-CAM conversion automatically transfers line drawings on the screen into actual geometry needed to machine a part. With only a few simple modifications, tooling and machining information can be added. Complete CNC programs can then be downloaded to your CNC machine tools.

12. Do you have a Quality Control (QC) department?

CAD/CAM streamlines your QC procedures from beginning to end. Since many common CAM systems are accurate to 10 decimal places, critical dimensions on a blueprint can be found and verified before the first cut is taken. In many cases, discrepancies in the customer's blueprint specs can be found quickly and corrected. This precludes long delays and rework costs. Once a blueprint is programmed and verified, a listing of X-Y-Z coordinates can be printed out in seconds. Since these dimensions are exactly the same as those being outputted to the CNC machine tool, QC is once again made more efficient.

Easy comparisons can be made between print, program, and part, without human error playing a significant role. Any changes in tooling, feed-rates, or surface finish can be made quickly.

13. Do you have full-time CNC programmers?

If you employ one or more machinists dedicated to writing CNC programs, off-line programming is definitely for you. Anyone familiar with CNC programming knows that the most difficult part of writing a program is defining part geometry and determining the most efficient tool path. CAM programming makes such work easy, even in the hands of a relatively inexperienced programmer. On the other hand, when CAM is used by a skilled programmer, its power and flexibility are practically unlimited. Custom canned cycles can be written, and loops and variables can be employed. Even sophisticated logic commands are readily available to the operator.

14. Have leave-time or employee turnover ever presented problems to you?

When evaluating a CAM package, make sure it is designed for machinists, not for computer programmers. That way, any machinist with a solid machine-tool background and good planning habits will quickly master its simple programming format. Training and startup time will be kept to a minimum. Also, make sure the package has a flexible postprocessor, so all your programming can be done through one keyboard. Instead of trying to make every machinist memorize many different CNC G-coded languages, all your machinists can learn just one language. If a programmer takes leave, any other programmer can easily fill in, regardless of which CNC control units are involved. Downtime is thereby kept to a minimum. 15. How do you store your NC programs?

If you currently store part programs on paper tape or microcassettes, or if you require hardcopy backups of your programs, then off-line programming systems give you added benefits. For one thing, all programs are stored on hard disks for easy manipulation and data retrieval.

This is an advantage because a 10MB hard disk has the ability to store 10 million characters of information. This is equivalent to about 160,000 feet of paper tape. One 10MB disk holds literally thousands of programs and subprograms, each retrievable in seconds.

Furthermore, specialized cycles such as routines for scribing alphabet characters can be called from the disk at random, and added to any program you're running. As your part library grows, your programming power increases as well. Another benefit lies in the fact that hard-disk and floppy-disk storage are economical. A 360K floppy sells for about $3, replacing at least $300worth of microcassette tapes. A 10MB hard disk can replace as much as $10,000-worth of tapes. 16. Do any of your customers use


If "yes," off-line programming may give you extra advantages. Most CAM programs convert DXF files or are compatible with IGES. This allows the programs to interface with nearly all popular CAD software packages on the market. By using an inexpensive telephone modem, you can transfer your customers' part drawings, with all C data, to your CAM workstation, and plot them out for easy reference. The entire program can then be converted automatically to part geometry, a tool path added, and a finished program downloaded directly to a machine.

17. Have you ever thought about upgrading or expanding your

CNC controls?

CAM systems add programming features and powerful canned cycles to almost any CNC, regardless of price or complexity. Many analysts therefore see off-line programming as the way of the future for even the smallest machine shops. In fact, some experts predict that the CNC controls of the future will be little more than black boxes supported by off-line computers. These will be tailored to the user's special needs. Software updates and increased specialization will become much more cost-effective, and every control in the shop will be able to operate at the same level of sophistication.

When all the cost-saving benefits of a simple, off-line programming system are considered, a small investment in CAD/CAM may become an excellent way to modernize your machine shop and improve the efficiency of your CNCS.
COPYRIGHT 1991 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Title Annotation:machine shops, computer assisted design and manufacturing drafting systems
Author:Smith, Harley N.
Publication:Tooling & Production
Date:Apr 1, 1991
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