'Super Precision' CNC turning machines - are all designed to provide significant performances - (better part accuracy, more cost-efficient manufacture) when hard turning parts.
There is no 'mystery' about hard turning 'Super Precision' CNC turning machines - are all designed to provide significant performances - (better part accuracy, more cost-efficient manufacture) when hard turning parts. For years the debate has raged on about the relative merits of hard turning components in favour of more 'traditional' grinding methods. Adding its considerable weight in favour of hard turning is market-leading machine tool specialist and hard turning authority Hardinge, which has introduced a number of Super Precision (SP) CNC turning machines onto the market - all designed to provide customers with significant performance benefits - (better part accuracy, more cost-efficient manufacture, increased productivity, etc) when hard turning parts.

However, to do justice to the whole issue of turning vs.

grinding 'hard' materials - engineers at Hardinge point out that to achieve optimum hard turning results is not simply a matter of plugging-in and playing one of their newly-launched machines.

Instead they suggest that customers can only optimise their performance by understanding the complexities, and subtleties, of hard turning technology - and the interrelationship between machine tool, cutting tools, coolant and the specific application in question.

* What is Hard Turning?

- Essentially hard turning refers to machining parts from materials with Rockwell C hardness greater than 45 Rc).

Although amongst some hard turning aficionados - 60 Rc and above is now considered a more accurate description of 'hard' materials.

Specific materials that fall within this 'hard' materials definition include: case-hardened steels, Inconel, Hastelloy, Stellite and other exotics, etc Parts that are usually manufactured using hard turning operations are diverse but typically include - transmission gears, punches and dies, injector nozzles, shafts and bearings, etc * Performance benefits over grinding - cylindrical grinding of hard materials presents customers with a number of manufacturing and commercial headaches that are eliminated (or certainly reduced) if hard turning is adopted as an alternative method of production.

The benefits of hard turning over grinding are as follows.

* Reduced job set-ups.

* Faster cycle times.

* Higher removal rates.

* Reduced number of machining operations and less fixturing requirements.

* Less expensive process.

What is more these significant benefits and advantages can also be achieved alongside some outstanding performance results, e g, 5 micron size repeatability, 0.5 micron roundness and 0.1 micron Ra surface finish on Hardinge (SP) turning centres.

* Requirements for hard turning - achieving such impressive results requires advanced CNC machine tool technology and a good appreciation of the hard turning process.

Happily at Hardinge both of these can be achieved and accessed.

1 - Machine tool build - to deliver the cutting performance required (accuracy, finish, extended tool life etc) turning centres need to be of a rigid construction and design.

A polymer composite base combined with wide-spaced, heavy-duty linear guides; super-finished tracks and centrally-located, short-pitch ball screws help reduce vibration and minimise stick/slip movement.

Hardinge turning centres are also perfectly balanced exhibiting no overhang - and they are equipped with direct-seated, colletted spindles (spindle bearing closer to workpiece) and hydrostatic ways (optional) for extra accuracy.

2 - Part rigidity - there is little point attempting to hard turn a part that does not have sufficient inherent rigidity to withstand the cutting forces generated by the process.

To understand whether parts are literally up to the job - Hardinge recommends that customers consider the length (L): diameter (D) ratio of the part.

As a rule of thumb a L:D ratio of 4:1 for unsupported components and 8:1 for supported ones - produce optimum results.

If the ratio is exceeded (for longer parts supported with a tailstock), it is likely that chatter will result.

3 - Cutting tools/inserts - CBN tools are widely used for both continuous and interrupted hard turning applications as they deliver exceptional cutting performance with low wear.

However, because of CBN's high cost - alternative cutting tools or inserts can be used - i e, Cermet and Ceramic.

It is worth noting that Hardinge engineers advocate the use of CBN - but also advise customers to work in partnership with their cutting tool supplier to ensure that the optimum cutting tools are selected in conjunction with the most appropriate coolant.

To get the best results from hard turning requires an understanding of the process and access to advanced machine tool turning technology.

Customers working closely with Hardinge now have a genuine alternative to grinding and are taking advantage of all the tremendous business benefits that hard turning provides.