A recently developed dual-purpose CNC rotor milling machine from PTG Holroyd aims to increase the manufacturing capabilities of a leading German maker of compressed air, gas and vacuum technologies. Currently in build at PTG Holroyd’s Rochdale-based machine tool technology center, the machine, a PTG-Holroyd 4EX-R-BL (BL = blower) model, will be used to precision-mill both helical rotors and Roots-type blower air ends. In doing so, it will equip the German manufacturer with exceptional levels of speed, flexibility and efficiency.

Transforming the manufacture of straight-fluted rotors

“We have long been aware of a gap in the market for a rotor milling machine that can fulfil the needs of manufacturers who wish to produce both traditional compressor rotors and low-pressure output displacement compressors, such as Roots-type, rotary lobe blowers,” comments PTG Holroyd Sales Director, Mark Curran. “It is for that reason we developed the 4EX-R-BL – a machine tool that applies the high speed, precision and performance of PTG Holroyd EX Series milling machines to the production of Roots-type blowers. Fully appreciating the attributes of the 4EX-R-BL, our German customer believes the machine will transform the way in which their straight-fluted, infinitive lead rotors are milled, significantly reducing manufacturing time and increasing the accuracy of the production process.”  

Incorporating Siemens’ Sinumerik ONE CNC

In line with PTG Holroyd’s objective of simplifying the production of even the most complex of helical components, the company’s new 4EX-R-BL model utilizes Siemens’ Sinumerik ONE future-proof CNC. PTG Holroyd is believed to be the first UK manufacturer to offer the Sinumerik ONE control with its machine tool technologies and, only last year chose the automation system for its new range of HG Series gear and rotor grinding machines. 

“We selected the Sinumerik ONE CNC for its ease of use, ability to accommodate each customer’s Industry 4.0 strategy, rich, real-time reporting of machine health and performance data, and uncompromising levels of industrial security,” adds Mark Curran. “We also embraced the ‘Create my virtual machine’ and ‘Run my virtual machine’ capabilities of the Sinumerik ONE software suite to build and run a virtual ‘digital twin’ of the 4EX-R-BL on the desktop. This proved invaluable throughout the development stages of the new machine.”

30-minute milling time, floor-to-floor

Although sitting within PTG Holroyd’s EX range of rotor milling machines, the 4EX-R-BL is a new concept designed from the ground up. Equipped to mill helical rotors of up to 450 mm in diameter, the 4EX-R-BL will also rough mill blower blanks of around 320 mm in diameter and 900 mm body length, into straight fluted rotors in 30 minutes floor-to-floor, ready for finish profile milling to absolute size. This represents a significant time saving when compared to the one-and-a-half to two hours typically required to cut individual Roots-type blower rotor flutes using traditional milling techniques. 

Improving the manufacturing process

“Traditionally, manufacturers producing rotors for Roots-type blowers have relied on NC flatbed milling machines or machining centers that have been retrofitted to absorb the considerable vibrations that occur during the flute milling process,” continues Mark Curran. “When you consider that with either one of these production methods each flute has to be milled in a separate operation, it is easy to see why the machining process for Roots-type rotors has historically been labor-intensive. By comparison, the technology offered by the 4EX-R-BL moves the manufacture of Roots-type rotors away from traditional flatbed milling [where the component would be manually turned after each flute was cut], to a fully automated, programmable process, able to machine both two- and three-flute blowers in one sequence.”

 No manual intervention

Removing the need for manual intervention or indexing during the milling of each flute, the Holroyd 4EX-R-BL features a bespoke steadying system that has been designed to withstand the additional forces that are generated during the milling of straight flutes. Specially developed ‘finger clamps’ ensure the workpiece is held securely while a flute is being milled, then release to enable automatic rotation and positioning ready for milling of the next flute. 

 Considerable versatility

“In what has been a genuine ‘from the ground up’ development of a completely new kind of machining centre, in the 4EX-R-BL we have designed a model that is able to produce all helixes from horizontal to vertical, for helical rotors, infinitive lead blowers, helical blowers, compressor rotors and vacuum pumps. This significant level of versatility makes the 4EX-R-BL well suited to manufacturers, such as our German customer, who make different rotor types and therefore need considerable flexibility in their machining technologies.”

holroyd.com