Employees at a Boeing tooling shop, manufacturer of assembly jigs and fixtures for complex aerospace components, know too well that part rework wastes man-hours and reduces spindle in-cut time, limiting a shop's productivity.
In the past, the company relied on coordinate measuring machines (CMMs) for an after-the-fact check against the machines. "A CMM can tell us only when there is an error on the part, but not if there is a repeatable error traceable to the machine tool," says an official from Boeing. The tool shop decided to verify its CNC machines prior to the process, catching errors in the machines before they appear in the parts.
The shop enlisted the help of Schaumburg, IL-based Renishaw, manufacturer of machine tool calibration products. Boeing used Renishaw's Model ML10 laser calibration and Model QC10 ballbar tools to measure the accuracy of each machine and flag those requiring maintenance. The shop then fingerprinted each healthy machine over time with periodic tests. By monitoring how each machine's positioning and contouring capabilities are trending, the shop avoids putting a fine-toleranced job on a loose machine.
The ballbar and laser tools complement each other, and use the same notebook PC for machine evaluation. Model QC10 measures and plots dynamic, multiaxis errors that appear only when the machine is in motion. It tracks machine movement to +/-0.5 micron, allowing calculation of circularity error, servo gain mismatch, vibration, stick-slip errors, backlash, repeatability, and scale mismatch, as well as machine geometry. Model ML10 performs straightness, linearity, angularity, squareness, and parallelism data capture and analysis to detect backlash, scaling errors, and general component wear. The system is capable of measurement to +/-1.1 ppm accuracy.
The Boeing tooling shop has since eliminated part rework on fingerprinted machines. "With fingerprinting, we know immediately when a machine's capabilities decline, meaning we can correct the problem and return the machine to its original performance level," says the Boeing official.
