Tolerance-based machining for improving CNC process

Tolerance-based machining is designed to help automate the computer numeric control (CNC) programming process, speed up delivery times, improve quality and consistency, and eliminate 2-D drawings from the process.


Jim Foster, VP channel marketing and sales, Camworks, talks about how the CNC design process used to be with 2-D drawings during his presentation at IMTS 2016 on Sep. 12. Image courtesy: Chris Vavra, CFE MediaComputer numeric control (CNC), which has been around for the last 30 years, hasn't changed much, according to Jim Foster, VP channel marketing and sales, Camworks. Foster, in his presentation "Revolutionizing CNC Programming: Using PMI and MBD information to accelerate design to manufacture," at IMTS 2016 in Chicago on Sept. 12, said tolerance-based machining is designed to help automate the CNC programming process, speed up delivery times, improve quality and consistency, and eliminate 2-D drawings from the process.

Foster cited product manufacturing information (PMI) and model-based definition (MBD) are going to be crucial by giving CNC machining something it can't provide currently: knowledge. "CNCs have become more efficient and more powerful, but they don't capture knowledge,"

Foster said. "You really don't know from a drawing if you're doing something optimally or not." Foster said that's because many CNC design processes use 2-D drawings and a 3-D model, which isn't a very efficient process. It's also cost-prohibitive and users, including manufacturers, educators, and the government, are looking for a more efficient process.

"Sixty percent of the 3-D models developed from a 2-D drawing aren't accurate because it's easy to make a change to a drawing, but it's much harder in a 3-D model," Foster said.

Recent developments to use PMI and MBD to create a simulation that allows the user to have the best of both worlds: The 3-D model combined with the information and knowledge that comes from a 2-D model, or tolerance-based machining.

Programs designed to bridge the gap, Foster said, will bring a common understanding between the CNC programmer and the designer as well as provide features that will allow the user to create a variety of settings to customize the product as much as they want. They will be able to see everything thanks to the PMI and MBD and be able to make accurate adjustments before creating the model.

"Users will be able to automatically recognize the information in front of them and leverage it," Foster said.

Example of tolerance-based machining, which uses product manufacturing information (PMI) and model-based definition (MBD) to give the CNC process knowledge and create accurate 3-D models. Image courtesy: Chris Vavra, CFE MediaTolerance-based machining has an added benefit of creating a database and a framework for future machinists, which will reduce training time. Foster said that machinists welcome this development because they are getting older and want to pass on their knowledge to the next generation of workers.

That would normally take years, but tolerance-based machining allows them to create an archive that new machinists can reference and take guidance from.

From a production standpoint, tolerance-based manufacturing will create a process that will take a matter of minutes when it used to take hours, which was shown in a live demonstration.

Foster is confident these changes will have a significant impact on the manufacturing industry. "I believe there will be a renaissance in manufacturing because of the changes and the initiatives in the industry. Any CNC manufacturer that isn't doing this will be driven to do it because of the changes."

Chris Vavra, production editor, Control Engineering, CFE Media,

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