Making Machining Research More Efficient

Successful advances in developing new machining methods, cutting tools and processes depend on having quality instruments and technology as well as highly trained researchers. Both these requirements are well met at Chalmers University of Technology in Gothenburg, one of Sweden’s leading research centers.

This institution’s origins date back to 1829, when Swedish merchant William Chalmers left a legacy to establish a “technical school” that has since become one of Europe’s most respected universities of technology, with more than 8,600 students and nearly 2,000 teaching and research staff at its two Gothenburg campuses. Chalmers is home to many R&D facilities, including the International Grinding Centre (IGC), where academic research and industry collaborate on developing new technologies and skills to optimize grinding applications.

Peter Krajnik is the founder of the IGC, professor of manufacturing technology at Chalmers, and an associate member of the International Academy for Production Engineering (CIRP). Krajnik and his team play a key part in the IGC’s work by developing and optimizing the efficiency of R&D tools and processes.

“High-quality research is inconceivable without high-level skills as well as high-caliber research tools,” he notes. “Research into metalcutting applications requires particularly extensive testing, analysis and reporting. Large numbers of test cycles are essential to achieve a high degree of consistency, and to enable publications of high quality.”

New Software Helps Automate Research Processes

As a member of the IGC, the Kistler Group plays its part by contributing measurement technology is says delivers high levels of performance and efficiency. The company says one example is the world’s first and thus far only wireless piezoelectric rotating cutting dynamometer (RCD). That said, another Kistler innovation that was tested recently by the IGC is the new Piezo Tool System (PTS)) app. This software can be used with all sensor systems connected to the data acquisition solutions in Kistler’s LabAmp series.

Key features of the app include:

• Automatic signal preconditioning including filters, drift compensation, feature detection, signal cuts and more
• Automatic time- and frequency-based analysis such as fast Fourier transform (FFT) and power spectrum
• Automatic value- and feature-based analysis and trend generation
• Flexible acquisition of raw and analyzed data at different stages
• Machine communication via PTS Light Box
• Future monitoring functionality for industrial verification and manufacturing.

The IGC recently tested the PTS app in a wear testing application for grinding wheels at Chalmers. “As well as automating the data acquisition process, the new PTS software platform from Kistler also automates analysis and reporting, even in real time, as proven during our metal cutting tests,” Krajnik says. “So, it really does help us to be more efficient in our machining research.”

Force and Frequency Analysis

Wear testing of grinding wheels requires a deep understanding of the forces involved. Key parameters include the force levels, the static and dynamic components and the ratios between different forces.

“In grinding applications, it’s important to measure and analyze not only the static values such as maximum and average, but also the ratios between forces, the dynamic components of the forces and certain frequencies,” explains Dr. Philipp Hoier, project leader for this endeavor at the IGC. “Thanks to the new PTS software, we can perform a variety of analyses with just a couple of clicks.”

The measurement technology setup used during testing at the IGC consists of a complete measuring chain from Kistler. This includes a stationary LabAmp 5167A dynamometer (a laboratory charge amplifier with integrated DAQ and Ethernet connection); inductive switch to start and stop measurements automatically; and the PTS software. This setup is said to have made it easy to perform the grinding wheel lifecycle tests with a high degree of efficiency. And, given the number of repetitions needed, this added up to hours or even days of saved time for the researchers.

The PTS software comes with various types of preprocessing tools which researchers can use at different levels during data acquisition and analysis. Once the settings are completed, the program will automatically take the raw data and perform the analysis with the chosen tools in the desired order for all the tests. The PTS app can cut the signals at different time intervals according to choice, perform advanced calculations (such as FFT and power spectrum), and apply different filters. Researchers can also choose an evaluation criterion such as the maximum force in a specific direction to generate trends that can be visualized and then evaluated automatically.

Live Calculations and Automated Reporting

As the grinding wheel becomes worn, the levels of certain frequencies will increase and the PTS software can automatically capture these increases. Since the tests focused on 340 Hz, this frequency was monitored continuously. A trend analysis for this frequency can be generated directly during the test, and the PTS software can even calculate and visualize the FFT and power spectrum areas for each cut.

All the results, including both raw and analyzed data, can be exported in different file formats. Reports as well as further analyses can be generated very easily. Subsequent evaluation of the ratio between the normal force (Fn) and the feed force (Ff) for all tests is just one example. Kistler also offers an optional hardware component, the PTS Light Box, to trigger machine actions when defined events or alarms occur so the machining process is stopped immediately in such cases.

Hoyer notes that the PTS app has enabled them to automate data acquisition as well as the analysis and reporting processes. “When we’re busy operating the machine and the measurement equipment, this saves us researchers considerable time that we can then use for other important tasks,” he says. “So we’re looking forward to using this new software not only for grinding but also for other machining applications here at Chalmers such as turning, drilling or milling.”