Pioneers in Machining Technology
Established in 1953 and known principally as one of Europe’s largest specialist manufacturers and suppliers of top quality gear racks, pinions, leadscrews and nuts, Halifax Rack & Screw (HRS - www.halifaxrs.com) has more recently started producing round gears as well at its Brighouse factory in West Yorkshire.
To take advantage of the latest technique for machining them accurately and quickly, the firm has invested in a gear skiving machine, a Multus U3000-2SW from Okuma, Japan. The bar-fed, multi-tasking lathe was supplied last year by sole UK agent NCMT (www.ncmt.co.uk
), which is about to retrofit automation equipment of its own manufacture to speed the handling of components, free up operator time and make the process even more efficient.
Simon Matthews, Sales Engineer at HRS, who has been heavily involved in the project commented, "For medium to large batch production of gears, skiving has become the technology of choice.
"For example, in the case of the first three gears we are producing for our US customer, Vermeer, the 25-minute cycle times for the two larger gears would be three to four times longer by hobbing or using other gear cutting machines.
"We opted for the Multus from Okuma, as it was the first multi-function machine manufacturer to develop a generic platform for skiving high precision gears to DIN5 quality. I estimate that the Japanese company is 18 months ahead in this technology."
A crucial element in gear skiving on a multi-tasking lathe is being able to synchronise accurately the B-axis rotary movement of the upper tool spindle carrying the skiving tool with the C-axis rotation of the main spindle. It is notable that Okuma is able to achieve an unprecedented level of productivity and accuracy partly due to the rigidity of its machines, but more importantly because the company manufactures its own highly accurate rotary encoders, linear scales and control system, for which an easy-to-use gear cutting app has been developed. All these in-house-manufactured elements communicate with each other seamlessly.
Currently, three types of fairly open tolerance DIN8 gear for a US-built horizontal drilling machine are being produced on the Multus U3000 in Brighouse. Two are complex, shaft-type components and the third is a smaller, consumable item. They are all turned and skived from AISI 4140 steel bar or billet, the bar being fed from an Iemca Kid 80 short magazine capable of handling 1.1 m long stock up to 85 mm in diameter.
Around 3,500 each of the two gear shafts are needed annually, while the consumable item requirement is 2,400 per year. They are checked for accuracy on a Mitutoyo Crysta-ApexS CNC coordinate measuring machine that has been provided with full gear inspection software. Before delivery, all three components are surface treated after machining using the Tufftride QPQ process. As of July 2019, production of the next gear to be supplied to Vermeer started on the Multus, with another six parts in the pipeline.
Investment in production equipment at the Brighouse factory has exceeded £3.0 million in the last five years. In addition to the Okuma Multus and the CMM, a hobber for producing larger round gears has been installed as well as a CNC slotting machine for producing internal gears. One operator is required to run the three production machines, which are positioned within a cell alongside the measuring machine, leading to significant economy in labour costs bearing in mind the machines run for two shifts, five days a week.
Mr Matthews concluded, "The gear skiving process on Okuma's turn-mill platform has proved a great success and has allowed us to penetrate a new sector of the market, namely the economical production of round gears.