linear actuator instead of 'nodding' cam enables gear profile changeovers in minutes instead of hours

Stoke-on-Trent, UK - Advanced gear shaping software and motion control hardware from NUM has been used to bring an old manually-controlled gear shaper machine up to modern day control standards. The five-axis Stanko machine is now controlled by a NUM Axium Power CNC system, using electronic gearbox techniques to synchronise the rotary cutter, gear blank and stroking axes. It also incorporates an innovative programmable replacement for the stroking axis, which reduces product changeover time from hours to minutes - significantly improving productivity.

The gear shaper was bought by DePe Gear Company, which specialises in the design, manufacture and refurbishment of gears and gearboxes for a diverse range of industrial and commercial applications, including the steel processing, rail, mining, quarrying and aeronautical industries. The company operates a considerable number of gear cutting, shaping and grinding machines at its Stoke-on-Trent manufacturing facility and is no stranger to NUM - 3 of its current gear cutting machines are equipped with NUM Axium CNC systems and NUMgear software. In this particular case, DePe Gear Company purchased the Russian-built Stanko gear shaper initially for manufacturing large internal gears for the wind turbine industry, and subsequently commissioned machine tool engineering company Euro CNC to carry out the necessary refurbishment work.

Euro CNC specialises in retrofitting, rebuilding and upgrading machines. This often involves equipping manual machines with partial or full CNC systems, and the company consequently maintains a close working relationship with NUM, providing it with access to the latest CNC technology, control software, digital drives and motors. In recent years, Euro CNC has built up considerable knowledge of machine tools for gear production, and nowadays handles a wide variety of gear hobbing and shaping machines.

Euro CNC quickly ascertained that although the machine was fully mechanically serviceable, it would benefit from being equipped with new motors and drives, including high performance digital units for all axes, together with a CNC system for operational flexibility and a customised HMI to replace outmoded mechanical switchgear.

Traditionally, gear shaping machines employ a complex cam-driven 'nodding' axis arrangement to move the cutting tool up and down the gear blank as it is cut, the stroke of which needs to be synchronised to the rotation of the tool and the blank. This approach suffers from numerous disadvantages: it can involve up to three axes of movement, each subject to error, and is extremely difficult and time-consuming to set up, which does not sit well with the fast and flexible changeover requirements of modern manufacturing. Euro CNC consequently decided to develop an entirely new form of stroking axis, based on a fully programmable linear actuator. The end position, length and speed of the stroke can be freely changed under software control.

In addition to the stroking axis, the gear shaper has three rotary axes - to rotate the cutting tool and the gear blank, and to retract the cutting tool on the up stroke - together with a linear positioner based on a motor and ballscrew, which drives the gear blank to the cutting tool. All of these axes are controlled by NUMDrive C servo drives and NUM brushless motors.

Euro CNC chose to use a NUM Axium Power CNC system to control all five machine axes, networked to a NUM industrial PC and a large touch-sensitive screen. The software includes NUM's powerful NUMgear package, but in this instance it is used mainly to provide the electronic gearbox functions for synchronising the cutting tool rotation, gear blank rotation and linear stroking axes. The HMI for the gear shaper machine is primarily created by a special version of NUM's PC ProCam software, which was jointly developed by Euro CNC and NUM's USA facility specifically for this type of application. The software combines a highly intuitive graphical user interface using common gear shaping terminology with a 'conversational' style of programming, enabling operators who are not familiar with CNC-based machines to become proficient very quickly.

The refurbished Stanko gear shaper was recently installed at DePe Gear Company's Stoke-on-Trent facilities, and aside from a few minor initial issues has performed flawlessly.

Nigel Parker, Technical Director of DePe Gear Company, points out that, "We are using the gear shaper for a variety of internally cut gears, including spur gears for wind turbine generator gearboxes and a variety of splined gears. Although it is too early to provide quantified data, we are definitely seeing a reduction in setup and operating times. Like our other CNC machines, the most significant benefit comes from the sheer versatility of this all-digital approach, which enables us to switch freely from manufacturing one type of gear to another under software control. Machine operators no longer need to laboriously count the number of teeth being cut, but simply push the appropriate button on the menu, which helps maximise throughput."

According to Tim Clarke, Director of Euro CNC, "We have worked with NUM for about five years now, and have found their CNC products to be extremely reliable. We also benefit from excellent technical support from their UK facility, and have recently experienced a similar level of backing from NUM USA. So far, we have installed PC ProCam on some 25 machines - mostly gear hobbers rather than gear shapers - and have been delighted with the positive feedback from customers."