CNC rewrites economics of aerospace centreless grinding app

Controlled by NUM's Flexium CNC kernel, the upgrade solution converts any of the veteran Cincinnati 2-OM family of centreless grinder machines to the same kind of automated and precision machining available on state-of-the-art grinders - but for an outlay that is some 60% lower than a new machine.

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 solution 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 highest 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% 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 x 3mm diameter up to 200 x 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.

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 opeNike