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PLASTICS MACHINING SPECIALISTS INVEST IN SLIDING-HEAD LATHE WITH NOVEL CHIPBREAKING SOFTWARE

Gloucester subcontractor Stratos Precision Engineering, a majority of whose business comes from machining plastics, has strengthened and diversified its turning department with the addition of its first sliding-headstock lathe, a Citizen Cincom L32-VIIILFV. Installed in September 2019, the twin-spindle, 35mm capacity, bar-fed turn-milling centre joined an already impressive plant list of five fixed-head, single-spindle chucking lathes for turning parts up to 650mm in diameter.

Purchase of the 7-axis CNC Swiss-type lathe was part of an investment of more than £1 million since the fourth quarter of 2018, which has also seen the arrival in Gloucester of a new big bore lathe and a 3m x 2m automatic tool change CNC router as well as refurbishment of the 8,000 sq ft premises. During the same period, the number of staff has doubled to 16 and in the last financial year, turnover increased by nearly 50 per cent over the previous 12 months.

Stratos’ managing director Jonathan Caple said, “For some years we had been looking at buying a bar-fed lathe to increase our competitiveness, win new business and enter new industries by machining larger quantities of parts with tighter tolerances. We favoured the sliding-head type over fixed-head lathes, as the short axis movements lead to higher productivity.

“The twin-spindle configuration and extensive driven tooling on the machine means one-hit production often supersedes two or three operations on different machines.

“However, to reap the full benefits of the investment, we need to be able to leave the machine to run 24/7 either unattended or with reduced labour overnight to maximise production output.

“That was previously impossible for us due to the stringy swarf that is produced when machining plastic, which regularly needs to be manually cleared by an operator.”

The situation continued until 2016, when Citizen invented and patented its LFV (low frequency vibration) software. Part of the operating system in the Mitsubishi control of Cincom machines, and switchable on and off if required during the program, it vibrates the servo axis in the cutting direction so that the tool tip leaves the surface of the material being machined for regular, ultra-brief periods.

The effect is to break the long strands of swarf normally generated when turning plastics into short lengths of just a few millimetres, preventing it from birds-nesting in the machining area and melting back onto the workpiece, which normally means scrapping the part.

A recent trend in the subcontractor’s business has been a shift to machining more metals, notably aluminium for a large packaging machinery contract but also ferrous metals including stainless steel. This material also results in stringy swarf forming around the tool and workpiece and therefore benefits greatly from using Citizen’s chipbreaking software.

Mr Caple and Stratos’ co-owner, operations director Mark Vine, recognised how beneficial LFV technology would be for the business when turning plastics. Unlike metals, whose finish can be adjusted by fettling after machining, this is not practical with plastic as it needs to come off any machine tool in a finished condition.

The importance of improving turn-milling efficiency to increase competitiveness was reinforced when Stratos was required to produce 2,000 parts over a short period and the existing machinery would only achieve 400 per day. However with the new sliding-head machine and LFV technology, Stratos is now able to produce the 2,000 parts in 48 hours.

With a new sense of urgency, the directors’ research took them to MACH 2018 and to online testimonials from other users. A series of demonstrations at Citizen’s technical centre and showroom in Brierley Hill decided the directors in favour of LFV over other chipbreaking methodologies that involve macros in the program. Additionally, as Mr Caple pointed out, Cincom machines are built from the ground up to withstand the high-frequency, low-amplitude vibration caused by the intermittent, chip-generating cutting action.

The transition on the shop floor at Stratos to the new turning technology, as well as to the first Mitsubishi control on site, has been seamless. One of the sliding-head lathe operators, who normally runs five machining centres at the Gloucester facility, quickly picked up programming of the L32 using Citizen’s Alkart Wizard off-line software. He and others received two days’ instruction at Brierley Hill, followed by a week of on-site operator training. In the period from machine installation to the end of January 2020, more than 30 jobs had been produced on the new lathe, which included some around-the-clock running.

A major benefit of a twin-spindle lathe is the ability to produce components machined at both ends in a single cycle that would otherwise require two separate operations. This is assisted by the availability of a multitude of tools including driven cutters that enable the inclusion of extra operations such as deburring, eliminating further subsequent processes.

Speed of production is consequently much higher on the bar-fed Citizen compared with the fixed-head chuckers. For example, a 400-off contract that used to take a full day is now finished in a couple of hours on the slider. It also means that Stratos often manufactures in bulk, as the bar does not need to be changed as frequently as for multiple jobs. Stratos can now run, say, 1000-off, deliver 400 to the customer and stock the remainder on consignment. The customer benefits through more flexible supply and the certainty of prompt deliveries, while Stratos gains through more economical cost-per-part manufacture, which is passed on to the customer through improved rates and prices.

Another recent example of accelerated production was the machining of 5,000-off steel pins for a chain conveyor, which was completed in five days working a single shift. The job would previously have needed two operations on a pair of chuckers requiring two operators. Either the contract would not have been economical or the margin would have been unacceptably small.

Mr Vine concluded, “The accuracy and surface finish we are achieving on the slider are fantastic.

“We recently ran the machine unattended around-the-clock with LFV, with coolant running to keep the temperature stable, and produced 3,000 Ultem® Polyetherimide thermoplastic parts for a customer in the flow control sector.

“All of them were within the required -0 / +0.05 mm tolerance band, which is impressive and can be difficult to achieve in this material, without having to make any adjustments whatsoever to the machine.

“Overall, our new machinery has enabled us to be a more competitive subcontractor for plastic and metal machining and is contributing towards the impressive growth of our business.”

PUMP MANUFACTURER INSTALLS FIRST SLIDING-HEAD LATHE

Two-year payback expected by bringing subcontracted work in-house

One of the UK’s largest pump manufacturers shipping more than 200,000 units per year, Charles Austen Pumps (www.charlesausten.com), has invested in its first sliding-headstock bar auto, a Cincom L20-X from Citizen Machinery UK (www.citizenmachinery.co.uk). It was installed in the OEM’s Byfleet factory in June 2019 and has taken over the turn-milling of parts up to 25 mm diameter, the vast majority of which are brass. A few aluminium, stainless steel and plastic components are also produced.

Established nearly 75 years ago by Charles Austen, the company is credited with inventing the diaphragm pump, which in the 1950s helped John Enders develop the polio vaccine. The firm’s products later assisted the development of Concorde and the Apollo 15 mission to put a rover on the moon. A wide range of pump types is now manufactured and the firm has been so successful that growth over the last six years has been an amazing 30 per cent per annum, driven by strong home sales and a buoyant export market.

Naturally that has put a strain on all areas of the operation, not least the machine shop. While prismatic metalcutting including the milling and drilling of parts for pumps, as well as injection mould manufacture, is largely carried out in-house, the two fixed-head, 57 mm bar capacity CNC lathes on site struggled to cope with the production volumes of rotational parts. The result was that lately as much as two-thirds of the turning requirement was subcontracted out at a cost of more than £100,000 per year.

Machine shop manager at the Byfleet facility Matt Wright commented, “More than 80 per cent of our turned components are between 16 and 19 mm in diameter, so we needed a lathe of relatively small bar capacity to start bringing work back to our factory. Our bigger lathes are not so efficient when machining these smaller workpieces due to their longer tool movements and slower axis travels.

“We considered fixed-head as well as sliding-head technology, as our parts are generally short compared with their diameter. We concluded that sliding-head turn-milling would be more productive because the tools are mounted on gang posts rather than turrets, so are quicker into the cuts as they have less distance to move. Also, as we do not need to use the guide bush the bar remnants are shorter, saving money on material.

“Should we ever need it, we also have the flexibility of quickly installing the guide bush for true Swiss-type turning of shaft-type workpieces over 2.5D.”

He advised that they initially reviewed most of the sliding-head lathe providers and said that their choice of Citizen was primarily down its reputation for quality machines and for providing good applications support, training and after-sales service, which since the L20-X was installed he describes as “brilliant”.

A selection of turn-milled components for the OEM’s pumps was taken to the machine supplier’s Bushey technical centre, where their engineers recommended the best machine for producing the parts. This was deemed to be the twin spindle L20-X turning centre in optional, oversize configuration capable of machining bar up to 25 mm in diameter. An Iemca barfeed for three-metre stock was also supplied as well as a workpiece conveyor.

Standard features of the machine include up to 44 cutters including rotary stations on the gang, opposing and back tool posts, with Y-axis movement of the first two tool carriers. The LFV version of the machine with its patented, 2-axis CNC chipbreaking software in the control’s operating system was not needed, as free-cutting brass is mainly machined at Byfleet.

Batch sizes produced on the Cincom vary greatly from ones and twos for the R&D department up to 10,000-off. The first job on the machine was a brass cam that ran continuously for 96 hours, from Monday morning to Thursday evening. Machined in one 105-second cycle to tolerances down to + 10 / -5 microns, including in-cycle engraving for traceability, the part previously needed two operations taking three times longer, plus additional handling for manual chamfering and stamping. Matt advised that machine attendance was minimal during the day and non-existent overnight. When he arrived at the factory the next morning and measured the parts, all were not only within the 15 microns tolerance band but right in the middle of it.

Another brass component, this time a 19 mm diameter disc-type part just 0.6 mm thick, saw its two operations in 2.5 minutes reduced to one 50-second cycle – another three-fold saving – plus elimination of handling. A third example, a double eccentric with an offset hole and an offset spigot with a 5-micron limit, is now produced in under three minutes instead of five, including engraving which previously had to be done manually. Surface finish on all parts coming off the L20-X is noticeably better, according to Matt.

An element of the service provided by Citizen Machinery prior to delivery of the lathe was the provision of programs for machining two components. Since then, the Cincom machine operators including Matt’s son Ryan have been using the supplier’s Alkart CNC Wizard programming software. It is easy to learn and a simple process to cut, modify and paste elements from the original programs and add new blocks for other features using the wizard’s G-code and M-code library built into the software.

Matt concluded, “We are already bringing turned parts manufacture back in-house and that will accelerate in the coming months. We have hundreds of component variations lined up to put on the L20-X. By Easter 2020, we should be turn-milling them all in our factory.

“With the amount we have been spending lately on subcontracting services, I calculate that the Citizen Cincom slider will pay for itself in a little less than two years.”

Chance purchase of a second-hand lathe triggers transformation of subcontractor’s machine shop

When a customer of subcontractor Apsley Precision Engineering suddenly stopped manufacturing components in-house, one of the redundant machine tools, a Miyano fixed-head, twin-spindle, single-turret lathe, was purchased by the contract machinist’s managing director, Peter Aymes.

Its arrival in 2012 on the shop floor at the company’s 12,000 sq ft facility in High Post, near Salisbury, heralded the start of a big improvement in CNC turning capability. Following the purchase of two more second-hand Miyanos, August this year (2019) saw the arrival from Citizen Machinery UK of the first new model, a BNJ-51SY twin-spindle, twin-turret lathe with a Y-axis.

Mr Aymes said, “We were aware of this make of bar auto and knew they rarely come onto the second-hand market, so we were lucky to be able to buy the first machine, a BND-51S twin-spindle lathe with live tooling in the turret.

“Compared with our single-spindle, bar-fed lathes without driven tools, it approximately halved cycle times for machining parts up to 51 mm diameter. Generally we were able to start producing components in one hit rather than two or three operations, reducing handling and work-in-progress.

“That in turn improved accuracy and allowed us to manufacture more cost-effectively, so we became more profitable. It is difficult to overstate the improvement the machine made.”

Another notable benefit was that an operator could set the Miyano and walk away for long periods to carry out other tasks, as it is unusual to have to change offsets owing to the consistency of machining. That is not the case with the subcontractor’s other bar autos, which tend to occupy an experienced setter for much of the time, raising the labour cost content of manufacture.

Based on all these advantages, a second Miyano BND arrived one year later. Purchased at auction, it turn-mills parts from bar up to 42 mm in diameter but is otherwise similarly specified to the first machine. Despite being 12 years old at the time, it was and still is capable of holding tolerances down to ± 5 microns, which Mr Aymes describes as “amazing”.

He continued, “By that time it was abundantly clear just how good these machines are. They are heavy, compact and very robust, which leads to high accuracy, repeatability and reliability. They need very little money spent on them for repair, so cost of ownership is low.

“It is rare to operate a machine that is almost completely trouble-free. With the Miyanos, that applies to the electronics and electrics as well as the mechanics.”

The third Miyano to be installed at the High Post factory, in 2015, was a second 42 mm machine of similar age acquired from another subcontractor, this time a BNJ model with two turrets. It was bought to cope with the increasing amount of work these machines were generating and to exploit the higher productivity possible due to the presence of a second turret to serve the sub-spindle while the other turret operates at the main spindle. It resulted in higher production output, better prices for customers and shorter delivery lead-times.

With a view to increasing production output still further, as well as to access the latest technology and provide back-up for the 51 mm capacity lathe, the subcontractor’s first new Miyano, a BNJ-51SY, was delivered in July 2019 by Citizen Machinery UK. As its designation implies, the machine has additional Y-axis movement on the main turret that is proving invaluable for machining off-centreline and providing flexibility and accuracy of milled features.

Mr Aymes cited one component that is produced much more efficiently with this feature. It is a tubular, thin-wall aerospace part machined from solid 304 stainless steel bar of 38 mm diameter. It requires a blind, longitudinal hole to be drilled and bored and the outside diameter (OD) to be turned to leave two lugs. Not only does the Y-axis allow the lugs to be drilled in-cycle, instead of the component having to visit a machining centre for completion, but by being able to program both Y-and C-axis movements into the OD turning, cutter deflection is minimised and accuracy is improved. As the component is required in batch sizes ranging from 200 to 800, the benefit is considerable.

Even more advantageous with the new machine, however, is the ability to take advantage of ghost-shift running, which is theoretically possible with the other Miyanos but practically not feasible due to the absence of load monitoring to detect worn or broken tools and automatically stop the machine.

The latest lathe, with its fail-safe features and reliability, is regularly left to operate unattended overnight. So also is a multi-pallet, 5-axis machining centre added to Apsley’s prismatic machining department in April 2018. Mr Aymes predicts that these two machines will pay for themselves faster than all the others on the shop floor. He asserts that if a production centre is capable of running lights-out and is of the right quality, rapid amortisation renders the initial purchase price much less important.

When Citizen installed the latest lathe, it also supplied the subcontractor with the latest version of its Alkart CNC Wizard programming software. It assists and simplifies the creation of even complex cycles using a built-in G-code and M-code library plus reference material and diagrams. Inexperienced users in particular benefit, such as Apsley’s Jay Pritchard, who is halfway through a four-year mechanical engineering apprenticeship. He said he finds the wizard useful when operating the new Miyano if his mentor is not available and the relevant manuals are not to hand. It also helps with understanding how to use the machine.

Founded in 1984 by Peter Aymes’ father Graham, the subcontract engineering firm has always split its machining approximately half and half between turning and milling. Key sectors supplied with high tolerance, complex parts and assemblies are aerospace, defence, medical and pharmaceutical. Non-kanban batch size is typically in the range 20 to the low hundreds and the company also operates a toolroom facility for smaller batch runs, prototype production and the manufacture of tooling and fixtures.

However, one-third of the company’s business derives from supply of components and assemblies just-in-time, providing price stability through the ability of the subcontractor to produce much larger quantities for consignment stock, with customer call-off typically at a rate of 1,000 pieces per week.

TWIN-SPINDLE TWIN-TURRET LATHES ARE IDEAL FOR HYDRAULIC COMPONENT PRODUCTION

A second pair of Miyano BNE-51MSY turn-mill centres from Citizen Machinery UK has been installed at contract machinists Unicut Precision, Welwyn Garden City. Joining two identical twin-spindle, twin-turret lathes with live tooling and a Y-axis on the upper turret supplied at the end of 2017, they form the mainstay of highly efficient production of complex components for the hydraulics industry, which accounts for a large proportion of Unicut’s business.

Established in 1990 by 24-year-old Jason Nicholson and a partner, who has since left the company, in a double garage in East Barnet with £5,000 to spend on second-hand manual and cam-controlled machines, Unicut has been a turned parts subcontractor for most of its existence, progressing to CNC turning in 1993. However, in 2017 the company diversified into prismatic machining with the purchase of a multi-pallet machining cell, followed quickly by a second. A third cell is now on order for delivery later in 2019, which will be a record year for capital investment at £2.3 million.

Over the years, Mr Nicholson has bought 104 CNC lathes, 93 of which were either Citizen Cincom sliding-head models or fixed-head lathes from Miyano, which merged with Citizen in 2011. Today, Unicut operates 22 Cincom lathes with up to 13 CNC axes, 80 cutting tools and 2,000 psi coolant pressure, as well as eight Miyano machines deploying up to 72 cutters. The machines are usually replaced every five to seven years to take advantage of the high residual value of the lathes at that age.

While turning machines have been sourced mainly from this supplier, each purchase is rigorously analysed by Mr Nicholson with respect to machine cost and achievable cycle times to ensure lowest cost per part produced and the most rapid return on investment. Ease of machine integration and use and the desired quality of component are also paramount considerations. Additionally, prompt provision of service is an important deciding factor.

1999 saw the first Cincom sliding-head lathe delivered to Unicut, a 12 mm bar auto, and within a year three more were installed followed three months later by a 32 mm model. The first Miyano appeared on the shop floor in 2002. The CNC lathes replaced cam-controlled turning machines, which had all gone by 2003. CNC equipment was by then achieving similar cycle times to cam-type lathes, with the added advantages of higher quality and unattended running including overnight, leading to much higher profitability.

To distinguish Unicut from other subcontractors, Mr Nicholson decided early on to adopt a different business model by approaching OEMs, analysing their main cost drivers, investigating the possibility of re-engineering components for more efficient production, establishing desired cycle times, identifying machine tools needed to machine components within those times and then proposing to make the required capital investments, subject to the manufacturer’s commitment to a fixed-term contract. Strategic supplier status is what Unicut seeks in its business relationships with customers and 80 per cent of throughput at the Welwyn Garden City factory is produced on this basis.

For machining larger diameter parts, a 51 mm capacity Miyano costs about the same as a top-end 32 mm Cincom slider. Unless a high component length-to-diameter ratio dictates otherwise, Mr Nicholson prefers the fixed-head option based on a number of factors including rigidity, thermal stability, value for money and speed. Bar capacity is greater, offering more flexibility; spindle power is higher, leading to increased productivity; cycle times are comparable; access is easy for setting up, despite the compact machining area; and the Mitsubishi control supports superimposed machining whereby three tools can be in cut at the same time, a facility regularly used at the Welwyn Garden City facility for elevated levels of productivity.

Once a BNE-51MSY is set, Mr Nicolson said that it will produce a run of say 1,000 components to very high accuracy without having to touch the machine by the simple expedient of including macros in the program to offset tools automatically after a predetermined number of parts have been produced. Tolerances down to ± 2 microns can be held and surface finish is described as impeccable. He favours the Mitsubishi CNC system fitted to Miyano and Cincom lathes due to its flexibility and ease of operation using the drop-down menus and comprehensive graphical support. Citizen’s off-line Alkart Wizard software helps to ensure jobs are quickly into production. However, for larger production runs, time can generally be cut from a cycle by tweaking the program at the control.

Citizen’s operating system in the CNC system fitted to one of Unicut’s Cincom sliders features patented LFV (low frequency vibration) software that operates in two CNC axes simultaneously, allowing stringy swarf to be broken into shorter chips of a length to suit the material being cut and the swarf conveyor. The feature is popular with operators, as it enables uninterrupted production without having to stop the lathe due to birds nests clogging the workpiece and tools.

Citing a 320 stainless steel part that was previously impossible to run unattended even during the day, yet is now routinely left to run lights-out with LFV, Mr Nicholson said, “The feature is easy to use and does not require any special skill set. The software can be switched on and off, either manually or within a program, and parameters can be adjusted. It is especially good for processing plastics unattended as well as other difficult-to-machine metals such as Duplex and titanium. It just works.”

In conclusion, he shared his thoughts on the current buoyancy of the subcontract machining sector due to the weakness of the pound against overseas currencies. It has cut 20 per cent off the price of components that Unicut exports and has boosted turnover, despite raw material and indeed the equipment on which to machine it being more expensive to buy. The firm’s first order from China was delivered in August this year and exports overall currently account for 40 per cent of turnover, up from 10 to 30 per cent in previous years.

CITIZEN’S NEW 32 mm SLIDING-HEAD LATHES HAVE LOW FREQUENCY VIBRATION SOFTWARE

Two new sliding-headstock, twin-spindle, turn-milling centres of 32 mm bar capacity have been added to Citizen Machinery’s Cincom programme. Designated L32-X LFV and L32-XII LFV, both feature the firm’s patented, low frequency vibration software in the control’s operating system that acts in two axes to convert what would normally be long, stringy swarf into short, more manageable chips. It is particularly helpful when machining stainless steels, plastics and copper and can be applied not only to turning but also to grooving, thread cutting and drilling.

Unlike the two other L32 bar autos in the range, the 8-axis L32-X adds a Y2 axis to the Z2 axis on the back tool post. So also does the 9-axis L32-XII, which additionally has +90 / -45 degree B-axis swivel on the front gang tool post, whose rotary tools can work at either spindle to produce angled holes. Both machines are available in 35 mm and 38 mm bar diameter versions and all may be used with or without the guide bush to suit the application.

The new L32 design is modular, enabling a user to optimise their manufacturing costs by selecting functions that achieve the ideal machine configuration for their needs, while retaining the option of being able to add extra functionality later. A workpiece conveyor is standard equipment. Control is by the Industry 4.0-ready Mitsubishi 800 CNC system, which allows up to three tools to be in cut at the same time.

Up to 44 tools for front, back and cross machining are available in the -X model, while the B-axis -XII version accepts four fewer. Speed range of the 3.7 / 7.5 kW main spindle and 2.2 / 3.7 kW counter spindle is up to 8,000 rpm. Both have a C-axis for use in conjunction with driven tool stations in the three tool carriers. Fast acceleration of tool rotation up to 6,000 rpm minimises cycle times. Rapid traverse in the linear axes is 32 m/min except in Y2, which moves at 24 m/min.

VERSATILE BAR AUTO IS HIGHLY PRODUCTIVE

A new, twin-spindle, 10-axis CNC turn-mill centre, the Miyano BNA-42GTY LFV, has been introduced by Citizen for manufacturing complex components in one hit from bar stock up to 42 mm diameter. The hybrid machine is of fixed-headstock design, but the head is also able to move in and out of the working area for extra versatility, similar to that offered by a sliding-head machine operated in non-guide bush mode.

The 8-station, 3-axis turret including Y-axis movement has a half-indexing mechanism that allows tools to be mounted at up to 16 positions, while multiple toolholders can further expand the number of cutters deployed. There is also Y-axis travel on a gang toolpost, giving extra flexibility when machining at either spindle, especially as the counter spindle moves in the X-axis as well as the Z-axis.

In total, up to 45 tools can be resident in the working area. A superimposition function within the Mitsubishi M730VS control provides the possibility for shortening cycle times even more by enabling up to three tools to be in cut simultaneously at both spindles.

The 3.74-tonne BNA-42GTY enjoys the same rigid, high precision build and thermo-symmetrical design as other lathes in the Miyano range, leading to high accuracy machining. Slideways are hand scraped in all axes and have exceptional damping characteristics, enabling heavy metal removal and helping to prolong tool life. Machine specification includes a 6000 rpm / 11 kW main spindle with 0.001° C-axis, a 5000 rpm / 5.5 kW C-axis counter spindle and feed rates up to 30 m/min.

Numerous options are available to add to the flexibility of the turning centre, including high-pressure coolant, spindle air blow, chip conveyor, parts catcher, parts conveyor and drill breakage detection. Likewise, the capable control can be augmented with the addition of helical interpolation, corner radiusing, synchronous tapping and multiple canned cycles.

The BNA-42GTY is the first Miyano machine to gain the benefit of Citizen’s LFV chipbreaking software, until now exclusively provided on the manufacturer’s Cincom Swiss-type lathes. The patented, two-axis chipbreaking functionality is part of the control’s operating system and involves the axis servo drives and spindle drives.

The position of the tool tip is oscillated by 20 microns, just sufficient to break the swarf. The number of oscillations per revolution (mode 1) or the number of revolutions per oscillation (mode 2) determines the length of the swarf removed from any type of material. The user can define the exact chip length in the program, giving the ability to choose the optimum size for the swarf conveyor to handle efficiently.

The more exotic and difficult to chip the material, the more effective LFV is. It means that high pressure coolant is not needed to assist in breaking long stringy swarf, such as that generated when machining such materials as stainless steel, copper and plastic. So it is no longer necessary to stop the cycle to remove accumulated swarf that is hampering the machining process. Shorter chips also take up less room in the swarf bin, so it needs emptying less frequently.

In some applications, particularly when processing exotic materials, productivity can be increased fivefold due to not having to stop the machine repeatedly to clear swarf that has entangled itself around the tool or workpiece, or both.

With LFV there is an element of air cutting, which allows more coolant to access the point of contact between the tool and the material. Enhanced coolant penetration lowers the operating temperature of the tip, so it can last five or even 10 times longer. This is especially the case if, as frequently occurs on other makes of CNC lathe, a chipbreaking macro has been written into the program. These are notorious for causing rubbing of the tool, built-up edge, machining inaccuracy and premature failure of the tip.

An LFV oscillation results in a turned face that is no longer flat by an amount measured in microns. The machine control knows where the oscillation took place and on the second revolution the high spot on the face is turned away. If required, on the third revolution the tool will finish that process to eliminate the waviness completely at that location.

As an element of air cutting – albeit miniscule – is introduced by LFV, productivity can be slightly reduced when the function is switched on. However, it can be turned off at the control, allowing the possibility of maximum output during attended day shifts when an operator is present to clear swarf. It may be, however, that these machine stoppages lower production output by more than LFV.

Switching the function on at night allows a ghost shift to be instigated without fear of swarf build-up automatically halting production during unattended running. So a manufacturer is virtually guaranteed a full shift’s worth of good components on arrival the next morning.

LATHE WILL PAY FOR ITSELF IN 18 MONTHS

Installation by Citizen Machinery of a fixed-head Miyano BNE-51MSY twin-spindle, twin-turret turning centre at electrical wiring conduit manufacturer ABB Cable Management Product, Coleshill, heralds a fundamental change in the way the company turn-mills its cable end fittings.

Cycle time savings of up to 70 per cent with more to come, reductions in manufacturing cost, scrap and returns, and elimination of the need to outsource 10 per cent of production to subcontractors will combine to amortise the cost of the Miyano well within 18 months of its installation at the beginning of January 2019. Manufacturing unit manager Andrew Fellows describes this payback time on a major item of capital expenditure as “brilliant”.

Every week, 100,000 metres of flexible metal conduit and 65,000 metres of nylon conduit find their way predominantly into the automotive, rail and mining industries across Europe, the Middle East, China and as far afield as Australia, while some are destined for installation in the parent group’s robot systems. From these numbers it is clear there is a high demand for the mainly brass fittings, plus some stainless steel, aluminium and plastic varieties, that are needed at both ends of every length of conduit.

Fittings needed in large volumes are produced in-house on six cam-type multi-spindle autos, while the shorter runs are completed on four single-spindle, single-turret CNC lathes and now the Miyano twin-spindle, twin-turret turning centre, which replaced a similarly specified, ageing model on which one of the turrets was defective.

Comparing the performance of the latter two lathes, Mr Fellows advised, “In the first two weeks of the Miyano arriving, we transferred onto the new machine the manufacture of four fast-moving products, all of which benefitted from drilling on both end faces simultaneously at the main and counter spindles.

“Average cycle time saving was 59 per cent. The largest reduction was 70 per cent in the case of a fitting that previously required 133 seconds to produce. The turn-mill cycle now takes 40 seconds to complete on the Miyano.”

Senior operator Dan Gardner added, “We have only taken advantage so far of cutting with two tools at a time, but the superimposition function in the Mitsubishi M730VS control, coupled with Y-axis movement of the upper turret and X-axis travel of the counter spindle, allows three tools to be in cut at the same time.

“After five days’ training from Citizen, both on- and off-site, we carried out a time study on a complex fitting that will see an 80 per cent reduction in cycle time from 230 to 46 seconds.”

He went on to describe a further benefit that comes from the ability to have 6,000 rpm live tools with 20 Nm of torque at all stations in both turrets, a total of 24 positions. Whereas 85 per cent of production on the single-spindle lathes is currently from hexagonal bar, the plan is to reduce this to zero in favour of round bar over the coming years as the machines are upgraded and powerful driven cutters are able to mill the flats economically. This process is starting with the Miyano.

The main advantage will be longer service life of the lathes and of the bar magazines feeding them due to the absence of interrupted cutting of hexagonal stock and hence lower vibration levels. In the case of the Miyano, it will also allow round bar at the full 51 mm diameter capacity to be rotated in both spindles at the maximum speed of 5,000 rpm, whereas it would need to be backed off by 75 per cent to run the largest possible size of hexagonal stock. For this reason, such material currently machined on the BNE-51MSY at Coleshill is restricted to 38 mm, which can be rotated at full speed.

Mr Gardner advised that despite utilising mainly hexagonal stock at present, the rigidity provided by the Miyano machine’s bed, hand-scraped box slideways, spindles and turrets is nevertheless sufficient to allow total tolerances down to 30 microns to be held on fittings, a level of accuracy needed for explosion-proof and watertight conduits.

Data collection and display on dashboards of overall equipment effectiveness has been instigated by Mr Fellows since his arrival at the factory in July 2018. Optimisation of every aspect of around-the-clock production has resulted in 24 per cent more output in five days than was achieved before in seven days, lowering manufacturing cost by 17 per cent and raising competitiveness.

Installation of the Miyano, with its elevated level of productivity, will improve these figures further. So also will the imminent arrival of a presetter for off-line tool setting, which will cut two-thirds to three-quarters off the present 60-minute changeover time for the next batch run, which can be as low as 50-off.

According to Mr Fellows, selection of the Citizen Miyano BNE-51MSY was down to the capital cost being 30 to 40 per cent less than two alternatives considered by ABB Cable Management Product, in line with company policy. Lead-time from order to delivery was also the shortest at just 12 weeks.

SUBCONTRACTOR TREBLES IN SIZE WITH THE HELP OF SLIDING-HEAD LATHES

Patented swarf management software allows extended unattended production

Since moving premises in Bicester at the beginning of 2015, subcontractor SRD Engineering has approximately trebled its turnover and headcount, a rate of growth that accelerated during 2018 due to the arrival of three new sliding-headstock (Swiss-type) CNC turning centres from Citizen Machinery.

Joining a 20 mm bar capacity Citizen Cincom L20 Type VII lathe installed in 2009, which helped the contract machinists to weather the recession, two further models for processing similar size stock were installed in March and August last year, followed by a 32 mm capacity machine in November. It is noteworthy that the decade-old lathe is currently running 24/7 and still holding tolerance well.

Top precision machining is essential in the 18,000 sq ft Bicester factory, as 60 per cent of the company’s business comes from Formula One, with most of the remainder received from customers in the aerospace and electronics sectors. Dimensional and concentricity tolerances down to 6 microns are held on some 50 to 60 mm long, 3 mm diameter components, for example.

To help achieve this level of accuracy reliably, even during unmanned running, all of the latest sliding-head lathes are equipped with Citizen’s LFV (low frequency vibration) functionality – www.youtube.com/watch?v=2tpgc_pHRl4. The patented system allows stringy swarf generated when machining aluminium, stainless steel, nickel alloys, copper and plastics to be broken into shorter chips, the length of which can be controlled by the cutting program.

Mark Bonham, joint managing director with his brother Paul of the 30 years established, family owned precision machinists commented, “We had no hesitation in choosing the LFV option on the new Citizen lathes, as being a subcontractor we have to process a broad variety of materials.

“Often they are not short chipping and it is difficult to break the swarf using chipbreaker geometry on the cutting tool and/or high-pressure coolant.

“With LFV, which acts in two CNC axes simultaneously and is part of the control’s operating system, as distinct from a macro in the part program, it is possible to regulate chip size closely without compromising the life of the cutters – in fact, they tend to last longer and break less often.”

He explained that not only can the length of the chip be specified in any given program according to the material being cut, but LFV can be applied to different parts of the cycle, for example when turning a deep groove in stainless steel, an operation that is particularly prone to producing a tangle of swarf. It avoids a ‘bird’s nest’ forming around the sub-spindle and inhibiting synchronous component pick-up for reverse-end machining, or entanglement of a tool leading to its breakage or compromised component accuracy and surface quality.

The reason LFV is not necessarily applied continuously to a whole program is that the technology lengthens slightly those parts of the cycle due to repeated periods of air cutting lasting microseconds. It is this action that breaks the swarf into short chips and it also has the effect of improving penetration of coolant to the cutting zone, which is a prime reason for the extended tool life.

If a job is particularly price-sensitive, LFV use can be minimised or even switched off during manned operation, but the system is so flexible it can be reintroduced for lights-out running to ensure a full ghost shift’s production in the bin the next morning, without fear of stringy swarf impairing turning and drilling efficiency and possibly recycling from the conveyor back into the working area and jamming the machine. Thus a weekend’s worth of parts can be reliably produced, whereas without LFV there is a likelihood of only four hours of output before the lathe stops automatically in the absence of an operator to clear the swarf.

Mr Bonham added, “LFV chipbreaking is a huge selling point for Citizen turning centres. We visited their headquarters and showroom in Bushey to see a demonstration and it was clear that the technology is able to resolve a lot of difficulties related to swarf management and temperature control when turning and deep hole drilling. The benefits include better accuracy of machined components and longer tool life.”

The impetus last March for installing a 7-axis Cincom L20 Type XII LFV with a Y-axis on the counter spindle and a 135-degree B-axis spindle integrated into the gang tool block for both front and back machining was down to the original Swiss-type lathe being fully occupied, while enquiries kept coming in for large volume runs of typically 10,000-off per month. One of the contracts won involves producing a two-part, press-fit assembly with a threaded insert that forms a stainless steel oil restrictor used in the aerospace industry.

The machine is more or less devoted to this ongoing job, so a Cincom L20 Type VIII LFV was purchased on spec five months later and was immediately busy producing diverse parts for a number of existing and new customers. It was at this point that the Bonham brothers and their father Steve, who is still active in the business, really appreciated how much money can be made using this type of manufacturing plant.

As a rule of thumb, they noted that the cost of a Swiss-type lathe is around twice that of a fixed-head machine, but the former is able to produce twice as many parts, allowing a subcontractor to invoice around double the amount per month per machine compared with fixed-head capacity. Earnings per pound invested is therefore equivalent. The big saving is that one operator is able to attend all four of SRD Engineering’s Cincom sliding-head turning centres, whereas to achieve the same output from double the number of fixed-head lathes, which have to be individually manned for F1 work, eight operators would be needed, resulting in much higher labour costs.

With this in mind and having received a request to quote for producing 10,000 one-inch diameter Nylon fasteners per month, a 32 mm bar capacity Cincom L32 Type VIII LFV was sourced from Citizen last November and has been machining the parts ever since. Here again, low frequency vibration chipbreaking has proved invaluable for keeping production going during periods of unattended running.

CITIZEN RESPONDS TO RAPID EXPANSION OF IRISH MEDICAL DEVICE SUBCONTRACT MANUFACTURER

Twenty-four Cincom sliding-headstock CNC bar autos were installed between last summer and the beginning of this year (2019) by Citizen Machinery UK at one of the two factory units operated by Shannon-based medical component manufacturer, Smithstown Light Engineering.

The major investment followed Smithstown’s receipt of a contract from a multinational medical firm for machining multiple variants of two types of endoscopic device parts from 303 stainless steel bar. Annual quantity is currently 18 million for the production of nine million assemblies.

Managing director Gerard King had identified the business opportunity in 2017 and machined sample parts on a 20 mm bar capacity Cincom L20 installed three years previously to fulfil another contract, which is still running, for turning a 316 stainless steel spindle for a medical delivery device.

Discussions progressed and to develop the process further, he decided to buy on-spec a 12 mm bar capacity Cincom L12, which is of more appropriate size for producing the endoscope parts in short cycle times. The lathe was installed in August 2017 in a second, newly acquired and extensively refurbished unit on the same industrial estate in Shannon, where an extension currently being built will bring the subcontractor’s total factory space to 80,000 sq ft.

Further successful trials continued with the assistance of applications engineers at Citizen Machinery UK’s Bushey and Brierley Hill technical centres, where programs were optimised and early samples were turn-milled. In April 2018, the medical equipment OEM was ready to award the ongoing contract, which by then had grown to its current production level. Further increases are likely, perhaps even a doubling of quantities.

Mr King commented, “The first of the L12s started arriving here in July 2018 and the last ones were on site by January this year. All are operating 24/7. The lead-time from the customer signing the contract and our shipping the first parts in production quantities was five months. Citizen supported us well during this ramp-up phase.

“A lot of the success of the project was down to the partnership that has developed between our engineers and those at Citizen Machinery UK, which incidentally has two application and service engineers in Ireland dedicated to this market.

“Before delivering the machines, Citizen set them up at their technical centres complete with high-pressure coolant, mist extraction and full tooling packages, so they were production-ready when they arrived.”

He added that the Cincom L12s are so accurate, being easily able to hold dimensions to within 5 microns, that with the relatively open tolerances on the endoscope component drawings, a process performance in excess of Ppk 2 is being achieved, better than the Ppk 1.33 stipulated. It means that there is never a need to chase tolerance, so fewer operators are able to attend the 24 bar autos is than would otherwise be needed.

All of the latest sliding-head lathes are equipped with Citizen’s patented LFV (low frequency vibration) software, part of the control’s operating system that assists chip breaking when machining materials that tend to generate long, stringy swarf when they are being turned.

In conclusion Mr King said, “More than one-third of a billion endoscopies are performed every year around the world and we are currently manufacturing about 2.5 per cent of the associated consumables at the premium end of the market.

“There are many medical contracts that involve these sorts of numbers. Now that we have proved ourselves to be capable of realising a mass production facility in a very short timeframe, we are hopeful of winning more high-volume business.

“While medical devices for endoscopy constitute around two-fifths of our turnover, we are also very active in machining coronary delivery devices as well as cobalt chrome implants, with trials in titanium currently in progress, so future projects could involve any of these.”

View our L12

RENISHAW INSTALLS FIVE MORE CITIZEN SLIDING-HEAD LATHES

Renishaw’s installation last December (2018) of five more Cincom CNC sliding-headstock turning centres from Citizen Machinery raises the metrology equipment producer’s tally of lathes from this supplier to 58. The annual output of components from the machines exceeds 2.5 million.

Three of the latest 12 mm capacity Cincom B12 lathes fitted with Iemca Elite 112 bar magazines were installed at Renishaw’s Miskin plant in South Wales, where 20 Citizen sliding-head turn-mill centres were already in use, while the other two went to the company’s Stonehouse factory in Gloucestershire.

Senior production engineer Robert Horsley advised, “The latest investment in Citizen lathes, which raised the number we use by nearly 10 per cent, was driven by increased worldwide demand for our measurement technology.

“The B12 lathes are mainly devoted to ultra-fast turning and milling of 303 stainless steel bar to manufacture styli and other components for our probes, which are needed in large volumes. We normally produce a month’s worth for stock, which can be anything from 1,200- to 30,000-off, before we change over a machine to start a new batch. Run times are at least eight hours.

“All of our Cincom turning centres have live tooling and most are twin-spindle models to enable single-hit production. However, we also have three single-spindle F-series lathes of 12 mm and 16 mm capacity in Miskin dating back to the mid-80s. They still make high quality parts in relatively low volumes, such as those needed for some of our metal 3D printers, position encoders, laser calibration products and spectrometers.”

An extensive variety of materials is processed, ranging from mild, stainless, carbon and low alloy steels through brass and aluminium to corrosion resistant copper-nickel-zinc alloys. According to Mr Horsley, all of the lathes hold tolerances down to ± 20 microns parallelism and squareness and ± 50 microns on milled features. Surface finish down to Ra 0.4 is easily achievable, doing away with the need to cylindrically grind cosmetic features on products.

Siemens NX CAD is used by Renishaw to design components and GibbsCam to prepare programs offline for transfer to the Mitsubishi controls on the multi-tasking Cincom machines, which are of 12, 16, 20 and 32 mm capacity. Some have seven CNC axes with a Y-axis on both spindles, others offer 15,000 rpm at the main spindle, while several deploy 53 static and driven tools in the working area and up to three tools cutting simultaneously for turn-milling highly complex parts in short cycle times.

Chris Pockett, head of communications for Renishaw summarised, “We have standardised on Citizen sliding-head turning machines since the 1980s, when the company demonstrated what at the time was ground-breaking technology.

“The commonality of lathe layout ensures ease of training and complete flexibility for our production engineering staff to develop processes and program any machine.

“Similarly, operators are able to migrate between different turning centre groups and optimise productivity to meet our business needs. Having common platforms also benefits our maintenance operation.”

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