The design and machine tool development team at Citizen Miyano in Japan have incorporated Citizen Machinery’s patented LFV (low-frequency vibration) machining technology in the first of Miyano’s range of fixed-head bar and chucking turn-mill centres.

LFV machining, which is already being applied with considerable success on Citizen sliding-head turn-mill centres, allows the size of chip from a variety of machining operations to be controlled.

Moreover, this technology can be applied to a wide range of material types — from plastics, aluminium and copper to high-tensile stainless steels and other high-grade steels.

The ability for the operator to control the size of chip produced via LFV eliminates problems such as ‘bird nesting’, improves depth-of-cut capability and surface finish, delays the onset of built-up edge on cutting tools and dramatically aids the management of swarf.

Moreover, it can be applied to turning, profiling, facing, taper and interrupted cutting sequences, as well as drilling and thread cutting.

LFV, which will be progressively applied to all machines in the Miyano range, is just one of the ‘productivity enhancements’ that result from some 25% of the Group’s turnover being re-invested in research and development with the aim of further increasing flexibility, productivity and spindle utilisation — as highlighted by the variety of machine types in Miyano’s product line-up.

For example, the ABX range offers a 6 or 8in chucking capacity, 51 or 64mm bar capacity, three turrets, two spindles and up to 12 axes. The 10-axis 42mm bar-capacity BNA is available with a choice of one or two spindles and turrets, while the 51mm bar-capacity six-axis BND incorporates two spindles and a single turret.

The BNE is a 51mm bar machine with eight axes, two spindles and two turrets, while BNJ machines offer 41 or 51mm bar capacities plus seven axes, two spindles and two turrets.

Focus on rigidity

Miyano has installed over 40,000 machines around the world, with more than 800 in the UK. The company says it has established a reputation for machines that offer high levels of rigidity based on the use of single heavy-duty bed castings that carry hardened, ground and scraped boxway slides designed to provide the large areas of contact and surface support required to minimise vibration and allow “serious levels of metal removal” to be undertaken without impairing accuracy or repeatability.

Miyano machines also feature what the company refers to as a ‘single plane structure’ that features substantial ribbing and is designed to minimise distortion through thermal effects.

Spindles feature shrink-fit large-diameter bearings (a combination of angular contact and roller bearings) housed in thick-walled castings, while Miyano’s turret design is based on a wide ‘one-box’ structure that optimises surface contact and maximises rigidity — particularly when milling.

Furthermore, tool-holders are attached by a two-guide-pin system that enhances stability and ensures high levels of repeatability when compared with the more commonly used pin-and-key location systems.

Darren Wilkins, deputy managing director of Bushey-based Citizen Machinery UK Ltd (www.citizenmachinery.co.uk), said: “Machines using a lighter construction and bearing techniques will often re-position faster, which can reduce floor-to-floor times, but a rigid thermally efficient machine structure will enable more-effective cutting, while offering further gains in tool life, production consistency, repeatability and overall accuracy over extended periods of time.

“Accuracy and consistency are further enhanced by the use of thermal compensation software within the control system.”

Further Citizen enhancements to machining performance that are now incorporated on Miyano machines include Synchronous Operation and Super-imposed Operation.

Patented and developed for Citizen’s sliding-head machines, these enhancements improve flexibility and increase productivity of the BNA, BNE and BNJ bar machines and allow non-cutting times to be reduced by up to 50%.

Synchronous Operation enables multiple machining functions to be performed simultaneously, such as when two axes are programmed to operate at precisely the same time in conjunction with each other; Superimposed Operation enables independent machining involving the motion of the main Z1 axis overlapping any motion of the Z2 axis.

Verifiable results

Blackburn-based scuba-diving specialist Apeks Marine Equipment found within just eight weeks of installing a Miyano BNE-51MSY turn-mill centre that it had made savings of almost £4,000 on production costs.

In addition, setting times were halved, and the finishing of an important sealing feature on two safety-critical regulator-valve components is now included in the machining cycle.

Apeks, which is part of Aqua Lung International, employs 150 people and sells a vast range of regulator units (plus bladders), instruments and accessories to some 50 countries.
The capabilities of the new Miyano BNE-51MSY allow a critical valve seating to be finished to 0.2µm CLA, a tolerance of 0.05mm to be maintained on the depths of key ports, a 0.02mm tolerance to be held on a special internal radius (with a 0.04mm positional tolerance from a 45deg angle intersection point), and a concentricity within 0.08mm TIR — even though the part has to be relocated between the spindles.

Machine shop supervisor Stuart Davis said: “The BNE machine is highly flexible, with an overlapping capability that allows up to three tools to cut simultaneously for major reductions in cycle times.”

In the example of a four-port CZ121 brass regulator body produced in batches of 1,000, the cycle time has been reduced from 4.93min to 2.9min using 28 tools mounted on both the 12-station turrets (with the aid of special holders).

Setting times have also been reduced — from 4hr to just 2hr.

Meanwhile, another brass port body is now produced in 2.9min, saving 51sec per part. In addition, a hand-wheel required in quantities of over 24,000 a year is being produced in 1.9min — 20% faster than before.

In conclusion, Mr Davis said: “Without doubt, the specification of the Miyano and the quality of its build ticked all our boxes — and it was mid-range on price compared with other machine suppliers. The BNE-51MSY has contributed to our drive to achieve ‘cost-down’, while at the same time assuring us of machining a high-quality product that meets our strict safety demands.”

The technology behind LFV

Darren Wilkins, deputy managing director of Citizen Machinery UK says LFV (low-frequency vibration) fundamentally changes the way metal is cut.

“Most high-speed machines are intended to run unattended, but for this to happen reliably, swarf has to be managed effectively.

“Many years ago we tried using macros to interrupt the cut and break the swarf; and while that helped the situation regarding swarf control, it resulted in cutting tools rubbing.

The later use of high-pressure coolant helped to break up swarf, but this approach also had associated problems.

“Developed in conjunction with Mitsubishi, LFV is patented by Citizen and synchronises movement of the tool with rotation to give ‘air cutting’ time, resulting in swarf being broken into small chips that can be readily expelled.

This ‘air cutting’ time also prevents the machining temperature rising, prolonging tool life and mini-mising the various problems associated with chips.

Furthermore, the control we have with LFV means we can even program the length of chips we want to produce.

“Citizen has been producing LFV machines in Japan for over two years, with all components — including slides,bballscrews and ballscrew nuts — designed for LFV operation, and detailed analysis of these parts following extended operation reveals no signs of wear.

Last year, Citizen installed more than 580 LFV machines, all using ‘regular’ tools and ‘regular’ coolant.

In the UK, we have been installing LFV machines with 100% success — and we can guarantee to produce optimal chips on a vast array of materials, including plastics, coppers and Hastelloy.

“Moreover, the benefits for our customers — mostly sub-contractors — are significant. The use of LFV can increase up-time by at least 10% when machining stainless steel — and considerably more when machining materials such as
Hastelloy.”