MRO Today - Grimes raises the bar for CNCs

Grimes raises the bar for CNCs

by Paul V. Arnold

Holmes had Watson. Batman had Robin. To that list of investigation teams add Richard Grimes and the Renishaw QC10 ballbar system.

Grimes, a machine maintenance technician at Smith & Nephews manufacturing facility in Memphis, Tenn., has used the British-made diagnostic tool to greatly improve the performance and profitability of 325 computer numeric control (CNC) machines at the plant.

When Grimes was put in charge of the CNC testing, repair and validation program in February 1998, the performance of four of the plants most critical machine categories was unacceptable.

Using a Six Sigma measurement system, plant quality director Marc Wheetley determined CNC grinders and thread whirling machines operated at 3.0 Sigma. Nearly 7 percent of the time, those machines failed to perform their tasks within a specified tolerance.

Vertical mills operated at 2.25 Sigma (a greater than 20 percent failure rate). Horizontal mills operated at less than 1 Sigma (at 1.0, failure occurs 69 percent of the time).

Such failures create rework, scrap and customer dissatisfaction, and cost the company money.

Today, thanks to Grimes and the ballbar, the plants grinders are a true Six Sigma (a .0003 percent failure rate), thread whirlers are 5.5 Sigma (.005 percent failure), vertical mills are 5.25 Sigma (.009 percent failure) and horizontal mills are 4.0 Sigma (.6 percent failure).

Cost savings havent been calculated, but you can imagine the impact to the bottom line.

Grimes takes pride in those numbers, but refers to the program as an ongoing process.

If a new piece of equipment comes in, I run a series of tests on the machine, he says. If we move a machine, I rerun the test. If a machine crashes or a spindle goes out, I rerun the test. Each machine also gets a yearly test.

The machine does not run until it has passed the test.

Acing the exam isnt easy.

The ballbar checks 13 items. Those 13 items combined cannot be three-thousandths of an inch off, he says. It is strict, and it tells the whole tale. There is no cheating. It either passes or it doesnt.

While the ballbar is used on 325 machines, equipment such as Swiss turn machines cannot be fitted with the device and require different tools and tests.

Grimes handles that, as well as many other tasks.

He is in charge of the plants gauge calibration program.

He is in charge of compiling and housing all the paperwork related to the calibration and validation programs. This is a major task since the orthopedic products maker is under the watchful eye of the U.S. Food and Drug Administration.

And, he is in charge of Year 2000 testing for the machine maintenance department.

My job changes just about every day, he says. Validation takes up the largest percentage of my schedule, but the rest is just as important.

This article appeared in the October/November 1999 issue of MRO Today magazine. Copyright, 1999.