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Workholder modeling

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The goal of any machine shop should be reducing setup times close to zero—load the fixture, switch programs and push cycle start. Granted, this requires lots of organization and investment, but with quick-change fixtures and toolholders, tool management systems, and off-line presetters and simulations, huge decreases in setup time are achievable.

This last part—offline simulation—is probably the most time-consuming. Simulating CNC toolpaths to check for interference and potential crashes means every part of the machine setup must be modeled, from vises and chucks to cutting tools, toolholders and machine tools. Without online or offline simulation, program verification becomes uncertain and error-prone.

Acquiring a complete library of these models is a daunting task, however. Machine shops make hundreds, even thousands of different parts, each with its own unique combination of workholding and cutting tools. Searching through paper catalogs for tooling dimensions is extremely time-consuming.

The good news is that a number of tooling manufacturers offer CAD files of their products online. Programmers can log into the manufacturer’s Web site, enter a product code and download the file. Not every manufacturer is onboard yet, and it’s possible those CAD models will need some tweaking. And once you have electronic versions of every jaw, clamp, vise, chuck, knob, insert and holder used in the shop, someone in the company has to manage that data. Is all this work really necessary?

Bill Hasenjaeger, product marketing manager for simulation software developer CGTech Inc., Irvine, Calif., thinks it is. “Accurate modeling requires a complete representation of the machine setup,” he said. “Shops with this information catch collisions and tool interference in the programming office. Those who don’t have it discover these problems on the shop floor.”

Despite this, Hasenjaeger indicated that many shops don’t bother with complete modeling until the cost of failure becomes unbearable. When you’ve scrapped a $30,000 workpiece or spent weeks waiting on replacement parts for a crashed machine, a few hours of modeling seems worthwhile. “Those who accurately model toolholders and fixtures as part of program simulation definitely realize a benefit in machine uptime,” Hasenjaeger said.

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