Turn-milling technology at NDB Engineering

New machinery enables specialist-fastener manufacturer to reliably meet increased demand

Posted on 24 Dec 2018 and read 971 times
Turn-milling technology at NDB EngineeringNDB Engineering is a manufacturer of special fasteners and precision-turned components.

Its range of fasteners includes many that are bespoke, while most of the turned components are machined from toughened and corrosion-resistant super-alloys such as Hastelloy and super-duplex stainless steel, as well as cobalt and nickel alloys.

Managing director Andy Williams said: “With customers in the oil and gas, chemical-processing and power generation sectors, as well as the MoD, machining capability and quality are key to our success.

“We simply cannot afford any errors, hence our on-going investment in the latest machining technology, with some £500,000 spent on turn-milling machines in the last 12 months alone.”

Bought from Bushey-based Citizen Machinery UK Ltd (www.citizenmachinery.co.uk) via its tailored finance package, the machines comprised two Citizen Cincom L20-VIIILFV sliding-head turn-mill centres and a Miyano BNE-51MSY fixed-head turn-mill centre — with Citizen’s Alkart CNC Wizard programming aid.

This latest investment has provided access to higher levels of productivity and spindle utilisation — and confidence that the necessary quality will be maintained.

Mr Williams added: “These machines have also saved us having to seek help from sub-contractors to meet our growing order book and risking the loss of direct control over quality.”

NDB was set up in Birmingham in 1998, with Mr Williams a founder member. He subsequently led a management buy-out with joint director Rebecca Dainter in May 2017.

They have since focused on selling direct, rather than through distributors; the company now has sales of £3.1 million and a head count of 41.

NDB fasteners are in use around the world, including Argentina, Australia and Brazil. The company also supplies to China and India, both of which have highly competitive indigenous suppliers.

Material usage

Ms Dainter said: “During the last nine months, we have spent over £500,000 on high-specification material from leading European and American suppliers, so scrap parts are a concern — and a financial burden.

“While we have continued to install the latest sliding-head machines over the past 15 years, swarf control necessitated constant machine attention.

“This situation not only affected output and threatened productivity targets but could also degrade quality.

“As soon as Low Frequency Vibration — LFV — technology became available from Citizen, we saw that it could bring greater security and control when machining difficult materials.

“Our machines with LFV have eliminated the swarf-nesting problems that demanded constant attention from our machine setters.

“We have also improved our productivity by being able to run unmanned — and we can now run many parts unmanned through the night. Moreover, with LFV, one setter can run three machines.”

Turn milling pic 2Regarding the decision to buy the Miyano BNE-51MSY, Mr Williams said: “This machine gives us a greater bar capacity than our sliding-head machines; it also has the rigidity and power required to process difficult-to-machine materials.

“For example, a nickel alloy fastener with a milled hexagon head was previously a troublesome part to produce, requiring three operations and a 6min cycle.

“It is now machined complete in one operation that takes just 2min — giving us the ‘shortest route to invoice’ and helping our cash-flow.

“Moreover, we are achieving a level of accuracy that we could only have dreamed of before — plus a better surface finish.”

Patented technology

Regarding the LFV technology on NDB’s Citizen Cincom machines, Darren Wilkins — deputy managing director of Citizen Machinery UK — says it 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; 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 of the part 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, so it prolongs tool life and minimises 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 almost three years, with all components — including slides, ballscrews and ballscrew nuts — designed for LFV operation, and detailed analysis of these parts after extended operation reveals no signs of wear.

“Furthermore, LFV can be switched in or out of the programmed cycle as required; it also helps to reduce the onset of built-up edge on the tool tip, thus extending — as NDB soon found — its in-cut life.

“LFV also allows greater depths of cut to be taken, and improved surface quality to be achieved, thanks to the ‘wiping action’ of the tool.”

Machining confidently

Ms Dainter: “We are still running with the same tooling as before, and our already well-proven cycle times on the new Citizens with LFV are about the same. However, in our view that is not what it’s about.

Turn milling pic 3“What we are now achieving is the machining of parts with which we previously had difficulty achieving the required drawing tolerances — or even had difficulty machining in the case of certain materials.

“We are now very confident that we can successfully produce all parts out of bar up to 20mm in diameter.

“Our productivity has increased dramatically, with the machines running continuously and swarf problems eliminated.”

Cycle times on the five-axis L20-VIIILFV are typically between 52 and 120sec. The machine has 37 tool positions, a 3.7kW 10,000rev/min main spindle and a 1.5kW 8,000rev/min back spindle.

The driven tools on the gang tool-post are rated at 1kW 6,000rev/min, while the opposite and back tool-posts both have 0.75kW 7,500rev/min drives; the B-axis driven tools are powered by a 1kW 8,000rev/min motor.

The rapid-traverse rates are 32m/min (8m/min for the Y axis).

Meanwhile, the eight-axis Miyano BNE-51MSY can cut with up to three tools simultaneously.

The machine has two 12-station driven turrets (one with three axes, the other with two) that can simultaneously access either spindle or both spindles.

The main spindle has a 15kW drive, and the secondary two-axis spindle is powered by a 7.5kW motor; both spindles have a 51mm capacity and a maximum speed of 5,000rev/min.

Each driven tool position can undertake milling via a 2.2kW high-torque (25Nm) 6,000rev/min drive.

Since the management buy-out, NDB has also spent over £100,000 revamping its freehold premises in Willenhall; the firm was also able to avoid the recent oil industry slow-down as demand for specialist fittings from one customer in particular — a large company in North America’s oil and gas sector — continued unabated.

NBD supplies SAE-, ASTM- and ISO-grade fasteners that include stud bolts, hexagonal bolts, socket-head cap screws and nuts.

It also supplies high-tensile fasteners, power coupling fasteners and safety-critical high-integrity fasteners to the defence industry (including the MoD).

As for the future, the two directors are considering acquisitions, so as to establish a small group of complementary firms that will provide a greater breadth of sector coverage and security for the business.

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