How does a faulty CNC machine tool “return to life”?

Without regular inspection and maintenance, CNC machines will gradually lose positioning accuracy and introduce errors over time.

The manufacture of fuselage components for modern aircraft has stringent requirements for accuracy and quality consistency. The life expectancy of the fuselage assembly must match the life expectancy of the aircraft, so ensuring production quality and reliability is critical in the processing of metals and composites.

BAE Systems, a global defense, aviation and security company, produces a variety of key airframe components for European Typhoon fighters. Since its inception in 2003, the European typhoon fighter has been included in the air force sequence of many countries around the world.

At the state-of-the-art manufacturing facility at Somerbury Airport in the UK, more than 80 CNC machine tools from BAE Systems are operating at high speeds, producing a variety of high-value fuselage components.

In order to ensure the quality of parts, reduce material waste and improve efficiency, maintaining the performance and output of five-axis machine tools has become one of the main duties of the company's production line engineers. It is very important to conduct regular CNC machine tool inspection and calibration checks. Early BAESystems used Renishaw's first-generation QC10 ballbar machine diagnostic system. Thereafter, the second generation wireless ballbar system was started.

QC20-W ballbar system

If the positioning performance of the CNC machine tool reaches the ideal state, then in any two linear axis linkage, the circular interpolation will exactly match the set circular trajectory. The QC20-W wireless ballbar provides a way to compare actual trajectories and set trajectories to determine if there is an error.

challenge

Even the best CNC machine tools, if not maintained, the positioning accuracy may gradually decrease, resulting in machining errors. Component wear, damage from collisions, installation errors, and even changes in susceptor vibration and ambient temperature can adversely affect accuracy.

BAE Systems' manufacturing engineers have found that the machining accuracy of one machine in many machines is slowly declining, and shop operators are losing confidence in their performance. As it becomes more and more difficult to produce parts that meet the standards, the problem machine is gradually being idle.

solution

To assist in the periodic diagnostics of CNC machine tools, BAE Systems previously used Renishaw's QC10 ballbar system to identify specific machine performance errors.

Now using the QC20-W wireless ballbar, we have also started a preventive maintenance program covering the entire plant to perform regular inspections of CNC machines.

By analyzing the QC20-W diagnostic data trends for all machines, BAE Systems has developed a robust error range benchmark to quickly check the performance of all machine tools.

BAE Systems is now able to delve deeper into the problem machine that has exited the production sequence. It observed a 200 μm XY roundness error using a ball bar. Use the ballbar diagnostic software to determine that the main failure mode of the machine is caused by servo mismatch, and then the second error source is the larger backlash error. The servo mismatch problem was corrected by optimizing the X-axis drive parameters. Check again with the ballbar to quantify the improvements obtained after the adjustment.

However, the results of the re-examination show that even if the servo mismatch has been eliminated, the machine still has serious errors. It was inspected and measured using a ballbar and a conventional gauge, and it was found that the error was caused by the wear of the ball screw of the X-axis. After renovating the ball screw and resetting the backlash compensation value, the machine reached the 30μm XY roundness requirement and rejoined the production sequence.

Jim Walsh, BAE Systems' professional manufacturing engineer, commented: “Ball meter testing is an integral part of machine tool inspection, not only helping to ensure consistent part quality, but also for machine tools that were once considered to be incompetent. It can also rejuvenate."

result

In the past, long and costly machine inspections and repairs have resulted in a large number of machine downtimes that are difficult for companies to withstand; now, BAE Systems' machine error diagnosis is almost instantaneous, which reduces downtime.

Thanks to the diagnosis of the Renishaw ballbar, a faulty CNC machine tool has regained its vitality, and significant progress has been made in workshop productivity and quality compliance, which has benefited BAESystems.