Holroyd Machine Tools wins Chinese aerospace order

Holroyd Machine Tools has just concluded a deal with a leading Chinese aerospace company worth $1.2million US to supply a full turnkey production facility for the manufacture of jet engine drive shafts. The production cell is based around a version of Holroyd's large TG350E thread grinding machine, modified to accept a grinding arm attachment that allows the grinding of internal threads. Recently developed, the internal grinding arm and accompanying software allow extremely high accuracy internal and external threads to be ground quickly and consistently on one machine, in a variety of materials including hard, heat resistant nickel alloys.

The move towards manufacturing jet engine drive shafts from high temperature superalloys in preference to more traditional stainless steel derivatives is being driven by the requirement for modern engines to deliver ever increasing efficiency and power from a more compact unit. The new generation of engines being designed and manufactured in China will follow this trend, running hotter and requiring more exotic, harder materials for the majority of components, not just at the 'hot end' behind the combustion stage.

The Chinese aerospace company that has placed the order is also continuing to manufacture engines with stainless steel shafts and so required the new grinding cell to be able to handle a variety of materials without the need for complex tool changes. The Holroyd TG350E requires a simple grinding wheel change to adapt to the new materials, thanks to the flexibility of the machine design and depth of embedded knowledge in the software. The contract was open to general tender and awarded to Holroyd in preference to cheaper proposals, based upon the capability to meet productivity targets in all materials.

Holroyd's simple-to-use and intuitive software allows the user to input straightforward dimensional data and material type to the machine. When the component is loaded, the TG350E can then grind either internal or external threads and splines. Once the number of threads has been entered and the type of thread selected, the machine then calculates the complete thread form and grinds it to micron accuracy.   The machine automatically dresses the grinding wheel and measures the grinding accuracy results using an on-board ruby tipped probe identical to that used on a dedicated CMM measuring machine. Highly complex thread forms are calculated, executed and confirmed by the machine, speeding the production time up by a whole order of magnitude; typically from hours to minutes.

By completing the grinding and measurement process on one machine, both the accuracy and the repeatability are increased over more traditional grinding methods, which are slow and require the work piece to be removed from the machine, independently measured on a separate CMM machine, and then returned to the grinding machine to be re-ground.  The measurement and grinding accuracy of TG350E is kept consistent by a recalibration routine that is also built into the machine's operation.

Holroyd uses it's own machines for contract manufacture of parts, so buying a complete production cell including all the training necessary and any design expertise required from the company is a routine occurrence. The TG350E is not the only Holroyd machine to be used for manufacturing aerospace parts, Rolls-Royce have recently purchased several Holroyd Edgetek Super Abrasive grinding machines to speed up production and improve the finish of jet engine compressor blades. Although employing a different high speed, high removal rate (HEDG) grinding technology the machines are used for grinding a variety of hard aerospace alloys such as Inconel and Waspalloy, providing the company with a wealth of experience in this field.

Selling to China is also a relatively smooth process for Holroyd as there is an existing installed base of machines in the country and both sales and technical support are provided via parent company Renold Precision Technologies offices in Shanghai.

Paul Hannah, Vice President of Sales at Holroyd comments, 'The development of the aerospace industry in China is illustrated by the use of the higher temperature materials in their new designs; our machines have been developed to deliver repeatable, high accuracy production that is also flexible and fast moving. We hope that other major aerospace companies take a serious look at what we have offer because the rest of the world is catching up quickly.'

The TG350E machine has a bed capacity of 1900mm, a main grinding wheel with a 450mm diameter and two internal grinding spindles. The larger of the two internal grinding spindles is a 2kw, 4800 rpm unit accommodating wheel diameters from 85 to 100mm and a smaller higher speed 1.1kw spinning up to 18000 rpm with a wheel diameter from 30 to 40mm. Grinding wheels are specially developed porous single crystal aluminium oxide and have been developed specifically for the application working in tandem with an extremely high-pressure 3000bar cooling fluid jetting system.

An automatic dressing system uses diamond edged wheels and the grinding head offers four axis machining in addition to the internal grinding arm that employs a bespoke smaller wheel, spindle and coolant system designed for this machine. The internal grinding attachment will be an option on other Holroyd grinding machines including the new GTG2 gear grinding machine that has achieved record breaking DIN1 accuracy on individual helical tooth forms. Used predominantly for the automotive industry, the GTG2 is also used to manufacture gear components for US defence helicopters and vertical takeoff support aircraft.

Sales and technical support are provided from both the US and UK offices with offices and agents worldwide to support end users and dealers worldwide.