Automated threaded wheel grinding boosted by new CNC system

Based on NUM's new-generation Flexium+ CNC platform, the threaded wheel grinding system joins the company's NUMgear suite of gear production software. Originally developed for gear hobbing applications, the capability of NUMgear has been continually extended and now includes options for a broad range of gear manufacturing processes, including shaping, grinding and honing, and is used by many manufacturers of gear production machines.

NUM developed this addition to its NUMgear portfolio while helping an Asian gear manufacturing machine company to improve the performance of a prototype threaded wheel grinder. To improve grinding speed compared with current levels, NUM decided it needed to develop custom technology software. The principal aims were to reduce the time overhead of learning the teeth positions of the hardened gear prior to grinding, and improve the accuracy of the gear grinding process.

NUM's new product offers a comprehensive CNC system for gear manufacturing machines. At the heart of the system is a high-performance electronic gearbox that allows all master axes - such as the grinding, X, Y and Z axes - and the spindle (C axis) to be fully synchronised. As part of the development work on the new threaded wheel grinder, NUM has added a major new capability to the gearbox, which is now able to predict the acceleration of axes as well as their speed, in order to minimise synchronisation time. Together with the Fast Gear Alignment, it forms part of the new NUMgear threaded wheel grinding application.

Fast Gear Alignment Function

During gear production, "threading-in' - the process of bringing the grinding wheel into contact with the gear blank - involves continuously adjusting the position of the grinding wheel relative to the work piece. A similar process is employed when bringing the machine's dressing wheel into contact with the grinding wheel. Using acoustic emission sensors to learn the sound signatures of a master gear and then using them to control positioning during production runs is a common technique for automating processes like this. However, the speed and accuracy of NUM's newly developed Fast Gear Alignment Function eliminates the need for this entirely. As an example, aligning the grinding wheel with a 180mm diameter gear with 71 helical teeth takes just 0.5 of a second - without any need to acquire acoustic signatures or make manual adjustments.

A second aim of NUM's development required that the gear grinder CNC control should generate gears as accurately as possible. The latest machine from NUM's Asian customer produced gears with a tooth profile quality of DIN class 7. During the development process, NUM found that the diamond-plated dressing wheel did not come up to specification. To overcome this problem without incurring major tooling costs, NUM decided to support their customer by helping to modify the technology programs. The positive results of this action far exceeded expectations, and NUM's system can help a machine to consistently grind gear teeth profiles to within 3.5 microns, comfortably achieving DIN class 3 - an improvement of four class levels.

This gear grinding development is an example of one of the major principles underpinning NUM's business philosophy: a willingness to customise its CNC technology for machine makers. NUM supports this with a decentralised R&D structure which locates engineering staff around the world to allow it to work closely with machine builders. In this case, the new gear grinding system was jointly developed by NUM's HQ in Switzerland and the company's technology centre in Chanzhou, China, which is close to many major gear manufacturing machine builders and is currently undergoing major expansion.

Peter von Rti, CEO of NUM Group, says: "NUM is committed to helping its customers develop market-leading machines through close partnership. Our local presence and willingness to work directly with customers to resolve technical issues very quickly provides both parties with a key competitive advantage."

Regional support

NUM an established player in the CNC market, having brought out its first numerical controller in 1961. Expansion in Asia has become promising for NUM as Asian manufacturers have progressively improved the capabilities and quality of their machines. To support this development, NUM is currently making significant investments in its Asian infrastructure, including the recent opening of a new regional support centre in Seoul, South Korea, and the expansion of its technology centre in Chanzhou, China, which opened in 2010.

Peter von Rti points out that the European market for NUM and its partners is also promising. He says: "NUM's ability to create individual solutions for different machines provides medium-sized companies with a huge competitive advantage. The open and flexible nature of our products, and our decentralised development structure, combined with the know-how of our customers, provides unique market opportunities. We welcome the chance to become involved in new projects."

To learn more about NUM's high-performance CNC system for gear production machines please visit www.num.com.