Certifying a Program as Proven

Many companies that use CNC seem to struggle on a daily basis with programs that have been successfully run in the past. There is no guarantee that it will run flawlessly in the future.

Columns From: 8/18/2010 Modern Machine Shop,

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Problems with previously run programs stem from variations. Something is different from the last time you ran the job. Maybe the setup person forgot to save the corrected version of the program, so the original (incorrect) version of the program must be verified again. Maybe the workholding setup is made differently. Maybe cutting tools used in the past are out of stock. Maybe different cutting tool components were used to assemble cutting tools. Maybe the workpiece material is harder. If anything varies from the last time you ran the job, it’s likely to cause problems.
Many companies strive to certify programs as proven. However, some are more successful than others. The only way to certify a program as proven is to eliminate all variations. If everything is exactly the same as the last time the job was successfully run, the job will run exactly as it did previously.
With some CNC-using companies, variations just don’t seem to occur often. Consider a company that has but one CNC machine and it is dedicated to running a few different, yet similar workpieces. This company has purchased a limited amount of cutting and workholding tools, and there isn’t much opportunity for setup people and operators to do things differently from one time a job is run to the next. It is pretty easy to certify programs as proven in this kind of company.
In another companies, variations occur in just about every aspect of the CNC environment. There are many CNC machines that share tooling components. Not enough tooling is available for all machines when certain jobs are at the same time. Setup documentation is not specific about which cutting tools and workholding components are supposed to be used. The ordering department is not up-to-snuff. When specified components are unavailable, setup people are left to their own devices to find and patch together something that will work. CNC people within the company are at varying skill levels. Certifying programs as proven in this kind of company is much more difficult. Your company is probably somewhere in the middle of these two extremes.
Some variations are obvious and easy to identify, though they may be more difficult or costly to correct. To eliminate the tooling-component variations, for example, you must confirm that there is always enough tooling to run your various jobs, regardless of which jobs are run together. It is easy to recognize this kind of variation,
but buying the additional components may be expensive — and the expense could be reason why this variation has not yet been addressed. Given this scenario, you can either live with the (expensive) downtime that having an insufficient number of tooling components causes – or you can purchase the (expensive) additional tooling components. Which expensive alternative would you choose?
Others variations may be more difficult to spot. Often a variation is initially blamed on a CNC setup person, but insufficient documentation or training may be the real culprit. If setup documentation doesn’t explicitly specify every component to be used, different setup people will use different components. You may be taking for granted that your people do things in the same manner, when in reality, they are not. To ensure consistent work habits, you must provide eithermore training or more documentation.
Yet other variations may be beyond your control. For example, if your company purchases its own raw material, you should be able to control its quality and consistency. If a different material supplier is used each time you run a given job, it may lead to inconsistencies in raw material. You can eliminate the variation by always purchasing from the same supplier and demanding consistency from them. On the other hand, if your customer is providing you with the raw material for the jobs you do for them, you’re pretty much at their mercy.
Hopefully you have a way of pricing their jobs in such a way that material variations are billable. I cannot stress this enough: If you think certifying programs as proven is important, be on the lookout for variations. Even if you cannot justify what it takes to eliminate them, be ready with a solution for the next time you are having problems with a job and a manager says: “I thought we ran that job before!” This makes a good time to list the variations you’ve identified. It should make a great spring-board for getting improvements justified and implemented.

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