Stable milling option for tough alloys

Stroud-based LB Bentley machines a range of difficult nickel alloys and stainless steels. When it needed to replace a pair of ageing vertical machining centres, it found Whitehouse Machine Tools offered the best solution with its 4-axis Wele machines.

A direct-drive spindle motor and linear guideways on a milling centre enable high-speed metalcutting but that configuration does not lend itself to efficient machining of highly alloyed nickels like Inconel or Duplex and Super Duplex stainless steels. A gearbox drive and box ways are more appropriate, but they are difficult to find on smaller, C-frame, vertical machining centres (VMCs).

However, LB Bentley, based at the Kingfisher Business Park in Stroud, part of the Severn Glocon Group, has identified an ideal platform for producing its subsea valves, and also its filter and dryer equipment, from tough materials.

It is the AA1165 VMC with 1,100 x 650 x 600mm working envelope built by Toyoda joint co-operation company Wele. One was installed at the start of January 2019 and a second is due for delivery shortly. The sales and service agent in the UK and Ireland for the Taiwanese machine manufacturer is Whitehouse Machine Tools, Kenilworth.

Although LB Bentley’s existing production equipment has served them well, the company wanted initially to replace two VMCs with new machines capable of meeting the tight positional tolerances and surface finish required when producing components from a range of difficult materials including 625, 718, 725, 825 and 925 nickel alloys and Duplex/Super Duplex stainless steels.

Two speed torque

One of the difficulties with the ageing VMCs was the inability to mill by circular interpolation a sealing surface without four quadrants being visible and lines apparent at each change of axis direction, with the attendant risk of parts being rejected. Quality is paramount, with ±1.5µm dimensional accuracy and 0.4mm Ra surface finish required.

The AA1165 machine, fitted with a high pressure (70 bar) coolant system, has proved itself easily capable of achieving the drawing tolerances when machining nickel and steel alloys.

Features of the Wele that secure a combination of heavy cutting performance and precision finishing include two-speed, auto change gearbox drive to the 18.5/15kW BIG Plus 8,000rpm spindle, which delivers up to 469Nm of torque, hand-scraped square-section guideways, rigid construction, up to 10m/minute cutting feed rate and 36m/minute rapids in X and Y, 20m/minute in Z.

The machine's Fanuc 0i-MF CNC is already prepared for controlling a fourth axis, which is an optional extra offered by Whitehouse on the AA1165, whose 1,300 x 650mm table has plenty of room at one end to accommodate it.

LB Bentley's operations manager Andrew Kethro comments: "We have been extremely pleased with the performance of our new machine. It is very rigid and the load monitor highlights that the machine can easily cope with the materials and depths of cut specified. So these machines should be well set to take us into the future, regardless of what the industry throws our way.

"Our machinists have commented how quiet the machine is when cutting at high torques and low speeds, 1,500rpm being a maximum here when milling our difficult alloys.

“With limited factory space here, the small footprint of the Wele is supporting our 5S initiative and the continuing improvements we are making on our shopfloor. LB Bentley looks forward to receiving a second, identical machine this Spring."

Machine shop supervisor Tracey Harnden was part of the team tasked with sourcing the new capacity.

He explains: "We shortlisted two alternatives to the Wele and asked both potential suppliers to run a trial using one of our existing programs for cutting an Inconel part. The spindle stalled on one machine, while the other company were unable to point us to a single user installation where their equipment cuts our type of alloys.

“Other CNC mills we looked at were light, high-speed models that were obviously unsuitable and the original supplier of the VMCs that are being replaced did not even call us back."

Mr Harnden says that Whitehouse carried out the cutting trial on LB Bentley's material using the program and tooling from Stroud for the designated part, which initially needs rigorous fly cutting across the top of the billet.

He witnessed the demonstration at the supplier's technical centre in Kenilworth and noted the quietness of the process due to the machine's rigidity and hence low levels of vibration. The latter attribute contributed also to the required accuracy of machining and surface finish being achieved.

Keeping low

A further point in Wele's favour was the low spindle load when cutting the part. Operators in the Stroud factory extensively monitor the load meter on all machining centres so that they can see when it rises, indicating that a tool is wearing and starting to compromise accuracy.

Mr Kethro says: "The service provided by Whitehouse has been excellent. They recognised and understood the requirements of the machine needed by LB Bentley and were able to prove its suitability during the trial. Details of other users worldwide were provided.

"They have also been supportive in making minor changes to the software in the Fanuc control to allow us to run our existing programs on the new machine. The second machine will be similarly modified.”

Tracey Harnden concludes: “When it arrives and the two mills they are replacing have gone, there will only be Fanuc CNCs on the shopfloor, making it easier for operators to move between VMCs and giving us a greater degree of flexibility to allocate jobs to the available resource.

“The 4-axis Wele centres will work around the clock five days a week and at weekends alongside seven other machining centres and a similar number of lathes.”

Whitehouse Machine Tools www.wmtcnc.com

LB Bentley www.lb-bentley.com