One of China’s leading manufacturers of air compressors has once again demonstrated its confidence in the ultra-precise technologies offered by UK-based Holroyd Precision.

Only last year, the Chinese screw compressor specialist invested in one of Holroyd Precision’s industry leading Zenith 400 helical profile grinders. Now, just over 12 months later, the business has returned to Holroyd for an 8EX rotor milling machine and a CS700E tool management centre. Newly developed, the CS700E machines have been designed especially for the grinding of high accuracy profile forms on finish milling cutters of up to 700mm in diameter. Scheduled for shipping in March 2019, the combined order is valued at several million pounds.

“Our EX Series rotor milling machines have earned global acclaim for their high speed, high levels of precision and unrivalled build quality,” comments Holroyd Precision’s Regional Sales Director, Steven Benn.

“The 8EX model, as chosen by this customer, represents a new generation in high capacity rotor milling. Offering precision milling of particularly deep helical profiles, it brings exciting opportunities to organisations that wish to machine highly accurate, large diameter compressor rotors. By also purchasing the CS700E, the customer will benefit from unprecedented control of the profile forms they use.”

EX Series: speed, precision and efficiency

Delivering class-leading reliability and performance, Holroyd’s ‘standard’ EX range of rotor milling machines begins with the 1EX – a machine capable of milling helical components of as little as 30mm OD – and offers stepped increases in capability, right up to the 8EX, an 850mm OD rotor miller. A ‘special order’ 10EX machine is also available for components exceeding one metre OD. In addition, various bespoke EX models are offered. These include a recently introduced machine with a specially extended drum rotation for milling compressors for Roots-type (positive displacement lobe pump) superchargers, and the EX-HS Series – machines designed to operate at much higher speeds than standard models.

High surface speeds

All Holroyd EX Series rotor milling machines are designed with the ability to maximise the high surface speeds demanded by the very latest cutting technologies. Surface speeds in excess of 200m/min, for example, are often used when cutting rotor profile forms in a single pass, to leave only the allowance of 0.3mm stock for the finishing operation. EX-HS Series machines provide an even higher speed solution for machining profiles in aluminium supercharger or fuel cell rotors, the latter being developed extensively for hydrogen-powered electric vehicles.

EX machines cut a full-depth groove by traversing the cutting tool through the material at the relevant helix angle, while at the same time rotating the component in the ‘C’ axis. Accurate synchronisation between the axes is maintained via CNC, with digital drive technology controlling all axis movements. The cutting head is able to remove so much material in one step because the majority of heat generated is transferred to the swarf chips. These are then removed from inside the machine by means of a conveyor system.

CS700E: providing precise control of cutting tool technology

Holroyd’s newly developed CS700E tool management centre has been designed to grind high-accuracy profile forms on finish milling cutters of up to 700mm in diameter. The machine provides a larger diameter alternative to Holroyd’s highly successful CS500E (500mm max. diameter) model that was introduced in 1990.

Accuracy and repeatability

“The accuracy of any helical screw form relates directly to the accuracy of the cutting tool that is used to create it,” adds Steven Benn. “With the CS700E, we are enabling manufacturers of larger helical components to achieve even greater levels of accuracy and repeatability, by benefiting from complete control of all aspects of the cutting tools they use. The CS700E produces high accuracy profile forms on a wide range of tool materials, from traditional high-speed steel, to exotic materials such as carbide and cermet finish machining systems.”

Automatic dressing capability

The CS700E tool management centre incorporates automatic dressing stations to ensure optimum integrity of the grinding wheel at all times. The stations are equipped to condition CBN and diamond grinding wheels, while the use of HSK-A160 arbors (as fitted to 8EX rotor milling machines), enables rapid wheel changeover times and further enhances accuracy.

Advanced features

At the heart of the CS700E is Holroyd’s user-friendly touch screen programming system, which provides complete control over production accuracies. Automatic scanning of the tool profile during the grinding cycle is another major benefit offered by the CS700E. Following probing, the tool profile is graphically superimposed over the theoretical profile and displayed within user-defined tolerance bands to ensure that all cutter blades are ground within tightly controlled limits.

HSK-A160 arbor

Multi-bladed cutters can be sharpened on the Holroyd CS700E. The cutter indexing process is carried out automatically. The cutter is located on an HSK-A160 arbor for precise positioning on the 8EX rotor milling machine, or on other rotor millers employing the same arbor. The maximum profile height is 120mm.

PTG. The first name in precision

Incorporating the brands of Holroyd, Holroyd Precision Rotors, Binns & Berry and Crawford Swift, PTG has established itself at the forefront of high precision machine tool design, build and supply. The PTG range includes ultra precision grinding machines for rotor, thread and gear operations; rotor milling machines; heavy duty lathes; deep hole boring machines; friction stir welding machines and special purpose machine tools for the manufacture of precision components. Industrial sectors served range from aerospace, medical and mould tool & die to marine, power generation, mining, oil & gas, steel, high end and heavy automotive.