Presetting enhances product quality

Manufacturing Engineering, Sep 2001 by Meyers, John

QUALITY SCAN

Process control is a critical component of every manufacturing operation. Lack of control yields excessive process variation, which is one of the most costly aspects of any process. Reducing and controlling process variation results in significant reductions in scrap and rework expenses, improved process capability indices, and overall reductions in total product processing time.

Optimizing the overall machining process requires that all process inputs be in control and capable of yielding predictable results. Using a Tool Measuring Machine (TMM) for off-line tool qualification enables manufacturers to achieve required levels of quality and productivity.

A TMM's primary use is to accurately preset, measure, and inspect cutting tools. Presetting means physically moving a tool edge to a prescribed location. For example, boring tools must be set to a specified cutting diameter prior to use. Many tools used on older CNC controls with limited offset capability must be set up to prescribed length and diameter specifications.

When measuring a tool in a TMM, the setup person determines the actual tool length and diameter. These values enable the calculation of accurate tool offsets (the differences between the nominal or programmed tool data and the actual tool measurement).

Efficient machining operations are made possible by planning and engineering all phases of the manufacturing process. The ability to inspect tools during off-line setup ensures that engineering specifications are met before installing the tool in the machining center.

For example, the condition of a cutting tool's setup, geometry, and cutting edges can be inspected using TMMs. The TMM operator can quickly inspect tools for tool run-out, chipped or broken cutting tips, edge buildup, cratering, and fracturing. These conditions will lead to tool failure or the production of nonconforming products. Drills can be inspected to ensure that the web has been ground on-center, ensuring drilled-hole straightness. Nonconforming drill angles are easily detected. The radii of cutting inserts are verified during TMM inspections. Using incorrect tool radii may result in production part diametric and geometric feature non-conformance. Multi-insert cutting tools perform effectively only when all inserts are installed and set on a common plane. Inconsistent insert height is easily detected and corrected during tool setup.

With age and repeated use, the shanks of tapered toolholders become damaged or worn. When a non-- conforming toolholder shank is installed into a machine spindle, excessive tool runout and vibration may occur. These conditions will increase the variability of the overall process output. Off-line tool inspections performed using a TMM enable the setup person to evaluate the tool's shank-to-spindle fit.

After installing a TMM, a shop supervisor selected a new toolholder assembly, set up with a cutting tool installed, and put it into the TMM spindle. The tool was inspected for runout and was found to have 0.007" (0.18 mm) TIR. He took his calculator out, did some math, and replied that if he had used the tool in that condition his process would go out of statistical control and would produce defective parts. When asked how long it would take to determine the root cause of the problem, the supervisor replied that given the assembly was a new, unused tool, it may have taken several hours to a couple of days to diagnose and correct the problem.

TMMs are configurable to communicate tool measurement and offset data directly to a machine tool's controller. On machines equipped with multiple-tool magazines, preset backup tooling is brought into the machine's spindle without manual intervention. When using preset and pre-inspected tools, variability between tool changes is minimized. Little, if any, dimensional resizing of the workpiece after a tool change is typically required.

When configured with tool-management options, TMMs reduce human data-processing errors and document-handling and control problems. Engineering personnel prepare process control, machine, and tool setup documentation off-line. Work-instruction data and tool configurations can be maintained in an electronic database, eliminating the need for manual data and document-control handling. When needed, all manufacturing and engineering personnel access TMM database information "on-line." Off-line tool management systems that use Tool Measuring Machines effectively prevent machine downtime and decrease troubleshooting time.

John Meyers

Vice President-Quality

Parlec Inc.

Fairport, NY