High precision gears can be made to order

Holroyd is harnessing the DIN 2 capabilities of its new 'smart' GTG2 gear grinder to provide a bespoke service for high precision helical/spur gears in diameters up to 350mm and 160mm gear face width. The new service meets the market need for ever increasing accuracy of small volume, high precision gears in aerospace and high performance automotive applications, industrial optics and custom designed industrial products. 'The helical service is a complement to our existing and well proven high precision wormgear business', says Paul Hannah, Holroyd Sales Director.

'Using the newly introduced GTG2 machine, we can grind even small batches of helical/spur gears to DIN 2 levels of quality with some features achieving DIN 1'.

'This sort of performance means that our service is ideal for providing items such as master gears for prototyping, timing gears for use in aerospace applications and helical gears for use in high performance automotive gearboxes and oil pumps'.

'What differentiates our service in a competitive market is that we provide a package of design advice and manufacturing which not only ensures the highest levels of precision, but also optimises gear performance'.

One of the major problems in helical gear manufacture is predicting actual stresses.

This is important because the more pressure on the gear teeth, the more risk there is of pitting (macro or micro) and eventual gear failure.

Says Hannah: 'We address this problem with unique stress prediction software, which was developed by Holroyd engineers, and enables us to optimise gear design, with profile and lead modifications to achieve the optimum contact conditions for low noise and high strength'.

'The software, however, is only one part of the package'.

'Crucially, we must be able to replicate the profile derived from software on a gear grinding machine'.

'On conventional machines this can be difficult, but the GTG2 is designed with just this capability'.

'It's onboard scanning probe and dresser compensation enables us to replicate, faithfully, any lead and profile modification from our prediction software to minimise contact stress and pitting'.

In addition to profile modification, users of Holroyd's new gear service also benefit from the additional features of the GTG2 machine, which uses form grinding rather than the generation method.

Besides higher productivity from single wheels, form grinding offers improved flexibility for flank and root profiles, and produces a better (quieter) surface texture, with reduced risk of thermal damage.

The machine also has a unique method of compensating for 'helical twist', an unwelcome condition that occurs when helical gears are 'lead crowned' to reduce transmission errors which often occur when the gears experience misalignments or deflections under load.

Lead crowning varies the amount of material removed from the flank of a tooth across the face width, by causing the tool motion to deviate from a true helix.

Besides giving the desirable 'relief' to the helix, this gives an undesirable 'lean' to the profile where the crowning is greatest.

In many applications.

this deviation is not of concern, but in high precision and low noise applications it affects gear wheel performance by concentrating loads on particular areas of the teeth during meshing.

Correction of this problem is possible with the GTG2.

It is achieved by calculating additional motions of the grinding wheel and controlling them during the grinding operation using Holroyd's unique software.

This modifies the angle of inclination of the grinding wheel during the grinding operation, either alone or in combination with other axis deviations.

The result is better tooth contact during meshing, giving improvements in load bearing and transmission accuracy, ie smoother, more durable gears.

Developed in collaboration with the respected Gear Design Unit at Newcastle University, Holroyd's machine is the first CNC gear grinder to be designed, produced and marketed in the UK, and is believed to be the only gear grinding system available which uses a continuously variable wheel angle in this way.

Patents are pending, and the machine is now available for sale.

Summing-up the benefits of the new service, Paul Hannah stressed Holroyd's unrivalled experience in designing and manufacturing grinding machines for the global market - the same machines that Holroyd uses for its own bespoke gear production.