NUM has announced a high performance CNC solution for gear production machines that fully automates threaded wheel grinding. Incorporating unique high speed gear alignment technology that is believed to be an order of magnitude faster than comparable control schemes, the new CNC system dramatically reduces grinding machine threading-in times to accelerate throughput significantly.

Based on NUM’s new-generation Flexium+ CNC platform, the threaded wheel grinding solution 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 solutions for a broad range of gear manufacturing processes, including shaping, grinding and honing, NUM explains.

A high performance CNC system with modified electronic gearbox

NUM developed the latest 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.

At the heart of the new 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 synchronized. 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 minimize synchronization time. Together with the Fast Gear Alignment, it forms part of the new NUMgear threaded wheel grinding application.

Needless to acquire acoustic signatures during dressing or grinding

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 its newly-developed Fast Gear Alignment Function eliminates the need for this entirely, the company says. As an example, aligning the grinding wheel with a 180 mm 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 helped to modify the technology programs. According to NUM, its solution 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.

NUM is one of the longest established players in the CNC market, having brought out its first numerical controller in 1961. Expansion in Asia has become promising for the company as Asian manufacturers have progressively improved the capabilities and quality of their machines.