CNC upgrade rewrites the economics of centreless grinding

Initially, the new NUM CNC-based machine is targeted at centreless grinding applications in the aerospace industry, and comes with application-specific software to automate the production of the specialist countersink, button-head and relief style fasteners used in aviation fuselage and engine production.

RefreshEng's CNC upgrade product is offered in four variants, with a choice of three autoloading options. The NUM-based upgrades transform the Cincinnati 2-OM's original hydraulic- and mechanical-dressing architecture - with its fixed cam-and-stylus control - to an advanced CNC software-based system with up to seven axes of servomotor-based motion, depending on customer choices.

To complete the automation upgrade to the required high standards, RefreshEng incorporates numerous advanced features to optimise productivity, precision and operator safety. These include acoustic sensors that automatically monitor and compensate for grinding wheel wear. The machine also uses the sensing system to dynamically adjust grinding wheel feedrate to provide "gap elimination'; this feature alone can reduce grinding cycle times by almost 20 per cent across a batch of raw material parts with varying dimensions. Higher resolution control of movement, and the ability to interpolate movement of motion axes, improves both grinding accuracy and extends the range of shapes that can be ground. The grinding wheel has been fitted with a Schmitt Balancing System, which dynamically eliminates vibration. Wheel speed can also be varied to suit different component materials. Another key feature is a choice of drop-, finger- or front-loading loaders to automate the broad range of common centreless grinding applications. The finger loader accepts a very large variation in part size from 10mm long × 3mm diameter up to 200 × 25mm.

This idea for the project span out of RefreshEng's intimate knowledge of the centreless grinding business, derived from its long-established tooling services in the UK and Europe. Many of its clients wanted to re-control their old machines to an advanced level, to increase throughput and eliminate manual operations, but had found it difficult to source the technical support for such work. RefreshEng recognised the opportunity, especially for the popular Cincinnati 2-OM, as it estimates there are still some 2000 of these machines in the UK alone.

Virtual partner

RefreshEng - who have staff with grinding machine design experience - had clear ideas of how to update the mechanical architecture. This involved the complete replacement of hydraulics in favour of servomotor-controlled motion, with numerous modifications to the underlying framework including new castings to mount the electro-mechanics. The key hurdle for RefreshEng's CEO Damian Clements was finding a CNC supplier that would be prepared to complement his company's know-how with high-level control system software skills. In order to make the project financially viable, RefreshEng also wanted the CNC supplier to defer the return on their development efforts until sales of the machine started to build. Previous good experience with NUM led Clements to discuss the project first with the CNC vendor's UK applications centre. NUM offered to act as a virtual partner, allowing its programming staff to work alongside RefreshEng's staff as part of the development team.

RefreshEng provided NUM's software developers with flow charts of the way it wanted the new machine to function, so that the control logic and operator interface software could be developed. The companies' engineers then worked together - often using internet communications to link remotely to the prototype - to realise and test the new control system. Even though the type of custom human-machine interface (HMI) RefreshEng wanted was seemingly fresh to this type of machine, NUM's software developers completed the work very quickly, within just 3-4 man-months. The open programmability of Flexium's man-machine interface, which is purpose-designed to support customisation, was the catalyst for this short design cycle. In addition to providing the control structure, NUM also exploited the HMI programmability of the Flexium platform to generate a distinctive look-and-feel for the re-engineered machine's control software, to simplify use and to start building a brand feel for RefreshEng's entry into the higher echelons of the centreless grinding machinery market.

The first release of RefreshEng's software targets aerospace fastener production. NUM's operating software employs dialogue boxes to simplify programming, allowing new grinding profiles to be created in less than a minute. The operator simply populates data fields on a sequence of screens, which include graphical representations of the fastener style selected, and the profile is automatically generated. Parts can then be produced completely automatically, with the machine's software also automatically performing housekeeping tasks such as dressing the wheel.

Flexium 68 CNC kernel

The hardware upgrade is based on NUM's economic Flexium 68 CNC kernel, with an FS152i touch-screen HMI, machine panel with handwheel for operator programming and control, plus MDLU3 drives and BPX servomotors fitted with precision absolute encoders. The seven axes controlled by the CNC depending on the machine model are control wheel-infeed, -traverse and -rotation, dresser-infeed and -traverse, backstop and spindle lateral adjust.

Steve Moore of NUM UK says: "This project exemplifies the way NUM likes to work. Because our business is built on helping small to medium-sized machine builders to compete, we have invested in a decentralised R&D structure which locates engineering staff all around the world, and we are very willing to customise our CNC technology to support clients - as in the case of this innovative re-engineering project."

Damian Clements, CEO of RefreshEng says: "The Flexium upgrade we've devised provides an economic CNC solution that brings the workhorse 2-OM range of machines bang up to date in terms of precision, programming flexibility and automation - boosting productivity substantially. Capital investment cost is reduced by such a large margin compared with a new machine that payback can be as short as a few months, which is critical for many of the manufacturers in this highly competitive sector. The new machine also automates all aspects of the centreless grinding process, eliminating any need for manual interventions such as loading and hand finishing, to deliver a much higher level of safety."

For further information about NUM's Flexium CNC kernel, please visit www.num.com.