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    MANUFACTURER BUYS SLIDING-HEAD LATHES BUT MACHINES COMPONENTS WITHOUT THE GUIDE BUSH

    The decision by sliding-head lathe builders to introduce the ability to remove the guide bush heralded a natural successor to the single-spindle cam auto

    Top quality brass lampholder manufacturer S Lilley & Son Ltd, now in its sixth generation of family ownership, has nearly finished phasing out the 20 or so cam-type, single-spindle bar autos it has used in its Birmingham factory since the 1950s. In their place are to be found 11 modern CNC, twin-spindle, bar-fed lathes up to 65 mm capacity with driven tooling, six of them supplied by Citizen Machinery UK.

    Two are Miyano BNA42-MSY fixed-head turning centres of 42 mm capacity installed in 2017 and 2021, while the other four are Cincom sliding-head models (sliders), two for turning, milling and drilling 32 mm bar and two for processing 20 mm stock. Interestingly, to achieve the high speed of production for which outdated cam technology is renowned and couple it with the inherent advantages of CNC technology, namely unattended running and rapid changeover for smaller economical batch sizes, the company operates the sliding-head machines almost exclusively without the guide bush in place.

    The reason S Lilley & Son Ltd is able to do this is that most components for the light fittings it makes are shorter than 3.5 times their diameter (3.5D). Normally a ratio of 2.5D is approximately the limit when stock is not supported in a bushing (or by another means such as a tailstock or sub spindle), otherwise the protruding length of bar deflects under pressure from the tool, causing inaccuracy during machining. However, the relatively open tolerances of the lampholder parts produced in Birmingham allows the company to push the limit higher, lowering the cost of manufacturing parts up to 40 percent longer by taking advantage of higher speed production without the guide bush.

    Advantages of guide bush-less operation

    The rationale for investing in sliding-head lathes and choosing to operate them without the guide bush for most of the time, rather than buying a fixed-head lathe, is due to the sheer speed of production that is possible using the in-line ganged cutters typically found in a sliding-head machine. It allows the linear cross slide to effect very fast tool changes between cuts. Cycles times are considerably shorter and sometimes even halved compared with using a fixed-head turning centre, in which the tool carrier is generally a revolving turret that takes longer to index the next cutter into position.

    Due to the bar being clamped by a collet closer to the spindle nose on a slider when it is used without the guide bush, Z-axis stroke is restricted to around one quarter of what is possible when stock slides through a bushing. It is because the whole spindle head rather than just the bar moves in and out of the working area to present the part to platen-mounted tools that can only move in X and Y. However, the shorter Z-axis travel is unimportant in the Birmingham factory, as most components are less than 3.5D.

    As the collet grips the bar much nearer the work than in classical sliding-head turning, the more rigid clamping allows deeper cuts to be taken without chatter, resulting in further efficiency gains as well as better surface finishes, even when machining demanding materials.

    Guide bush-less operation on a slider brings with it numerous other advantages in addition to all the productivity benefits. Bar of lower dimensional quality and price can be tolerated, as there is no bush for it to seize in. The remnant after the last part has been machined from a bar is around one-third the length left after true sliding-head turning, so there is less material wastage. It can equate to a considerable monetary saving, especially when prices are as high as they are presently, the more so when expensive alloys are being processed. Notable also is that bar of cross section other than round, such as hexagonal or extruded, may be machined if the guide bush is not present.

    Indeed, if support is not necessary for the stability of a part during machining, it is better to remove the guide bush as it can actually compromise accuracy. Holding roundness then becomes easier on short components, as the ability to achieve tolerance is dictated by the high quality spindle rather than the bushing. Furthermore it is possible to run at higher rotational speeds to achieve better production rates and surface finishes.

    An extra benefit of turning outside diameters in this mode is that multiple passes are feasible, so shallow roughing cuts may be taken to alleviate the chip breaking problems of turning to size in one pass, plus there is potential to prolong tool life. It is not possible to retract components of reduced diameter back into a guide bush if they are longer than the land area of the bush, as the component would not be supported and vibration would occur.

    Transition from cams to CNC

    S Lilley & Son Ltd’s transition from cam-type to CNC lathes started in 2008, somewhat later than in many manufacturing companies for three reasons. First, as tolerances on its electrical products are not particularly tight, their production is relatively unaffected by the age of a machine tool; second, the fittings are frequently needed in large volumes commensurate with single-spindle cam auto operation; and third, the company was fortunate to employ a highly skilled cam auto setter-operator who retired as recently as 2019. That was when the penultimate cam-controlled machine was sold, the single remaining auto being devoted to a particular long-running job.

    The employee’s departure was the trigger for the Lilley family to accelerate the purchase of Cincom sliders. A pair of 20 mm capacity A20-VII models was installed, one in 2019 and another in 2020, as direct, more productive replacements for the former single-spindle cam autos. The A20s also have the advantage of a compact footprint on the shop floor, the area of which is limited in the Birmingham factory.

    The new sliders joined an L32 Cincom model installed in 2012 for producing parts up to 32 mm diameter. The machine was swapped in 2017 for a more modern L32-XII. Likewise, this slider is only occasionally used with the guide bush fitted for producing some longer components from bar or tube.

    Director Simon Lilley is of the opinion that, even though cam-type lathes can produce more components per hour than their CNC counterparts, the ability to set the latter machines so much more quickly and run them unattended through the night during the week and into a ghost shift on Saturday mornings means that in terms of production output, one Cincom is able to do the work of three of the older single-spindle cam autos.

    He described as “a massive advantage” the ability to produce long runs of components on the CNC machines without an operator in attendance, for example 100,000 Lilley hexagonal lock nuts. During the daytime the sliders are ideal for producing smaller quantities of say 500-off, whereas cam-type lathes would need to be set to run a minimum of 10,000-off to be economical and in any case most of this type of work has long since disappeared overseas. Being able to reduce economical batch size so substantially, down to about 100-off, has resulted in substantial savings in inventory and space and the cost of holding large stocks.

    Moreover, CNC turning centres seamlessly include what would traditionally be separate second operations. The need for these previously made certain jobs uneconomical on lathes with cam-actuated slideways if a suitable and often expensive attachment could not be sourced.

    Chip breaking software raises efficiency

    In January 2022 a fourth Cincom arrived, an L32-XIILFV with Citizen’s latest low frequency vibration (LFV) chip breaking technology in the Mitsubishi control. The three existing sliders plus the Miyanos and other fixed-head lathes were approaching full capacity, so the new machine provided flexibility to swap work around on the shop floor and it is also back-up for the remaining, ageing single-spindle cam auto.

    Additionally it is the mainstay for manufacturing increasing quantities of a particular type of screw lampholder known as the Edison E14, a heavy brass product available in a range of decorative finishes that is proving extraordinarily popular on world markets.

    As with the other sliders on site, the machine is rarely used with the guide bush fitted. So resolute is S Lilley & Son Ltd’s policy in this regard that longer parts up to 5D, which could be regarded as being best produced by sliding-head turning, are instead machined half way in the main spindle and transferred to the sub spindle for the remainder of the turning and milling to be completed. It saves half an hour’s work installing the guide bush and another half an hour removing it, maximising productivity.

    More than 95 percent of the Birmingham firm’s turned parts are made from free-machining brass bar, but lately there has been an increase in demand from its customer base for aluminium parts up to 32 mm diameter and for plastic components such as acrylic LED lenses and acetal grommets. About a quarter of the company’s throughput is contract machining of such special components for luminaire manufacturers already buying Lilley brass lampholders and lighting accessories.

    Craig Lilley, another director and family member concluded, “Anodising quality 2011 T3 aluminium is not as free-machining as it is made out to be and the 6026 T9 grade we turn is even worse in terms of its tendency to generate stringy swarf. Most plastics are similarly problematic when machined.

    “LFV repeatedly oscillates the tool clear of the bar surface for a fraction of a second, fragmenting the swarf into manageable chip sizes. There is no longer a need to stop the machine to clear swarf tangled around the tool and component, so production output is maintained.

    “By the simple insertion of G-codes, the function can be programmed to cut in and out during a cycle. It is turned off automatically when it is not needed for chip breaking, so the slight reduction in material removal rate during LFV machining is minimised. It really could not be more flexible.”

    Reshoring and exports boost subcontractor’s growth

    In response to an upturn in business over the past few years, Merseyside subcontract machining company Wealdpark is to treble the size of its factory. The first phase of expansion, due to begin immediately, will add an extension a little larger than the 6,000 sq ft unit it presently operates in Sutton Road, St Helens. By the end of 2023, another 5,000 sq ft unit is scheduled for completion on an adjacent plot that was purchased recently.

    Mainly a precision turned parts subcontractor, the family owned and run firm operates two vertical machining centres and 15 sliding-head lathes on the shop floor, alongside six Miyano fixed-head turning centres from Citizen Machinery UK.

    The latest to arrive, in April 2022, was a Miyano ABX-64SYY, bringing to four the number of these 65 mm diameter bar capacity machines purchased since 2014. In use also are 51 mm and 42 mm capacity models. All have twin spindles and twin 12-station, Y-axis turrets with driven tooling for efficient, one-hit production. Despite the machines being bar fed, 40 percent of the time they are employed for turning billet in 6-inch and even 8-inch chucks, enabling the production of much larger diameter parts with an operator in attendance.

    Together with father Jim and brother Steve, Phil Smith is a director and joint owner of Wealdpark. He said, “We have increased turnover by a quarter in the two years since the start of the pandemic and sales during each of the first five months of 2022 were at a record level compared with previous years.

    “Production of parts for the hydraulic, pneumatic and yellow goods industries is particularly strong at the moment. We are also active in the aerospace, automotive, electrical fastener, fire-fighting, military and temperature measurement sectors.

    “Manufacture of parts for ventilators has been an established part of our business for many years and it of course continued through 2020 and 2021. We have been able to turn this into a growth area by supplying similar components to Europe and North America.

    “Admittedly part of the rising sales figures is down to an increase in material costs but the underlying growth is undeniable, due in part I believe to the trend towards re-shoring.

    “It has given us the confidence to invest in new infrastructure and capacity to develop our business and part of that strategy will be the continuing purchase of top quality plant like Miyano lathes, which we have used since 2007.”

    There are no other makes of fixed-head turning/milling centres in the factory. It is because once Wealdpark’s directors had satisfied themselves that the Japanese-built machines are of good quality and value, reliable and accurate, the acquisition of further similar lathes provides the flexibility to be able to swap tools and programs easily across the shop floor.

    In fact it was other members of the British Turned Parts Manufacturers Association (BTMA) that recommended the Miyano brand in the early days when the subcontractor was transitioning from a cam auto shop with 53 machines to a fully CNC-equipped company. The process started in 2001 and was complete within a decade.

    Both Phil and production manager Neil Ireland are waiting for Citizen to introduce its LFV (low frequency vibration) chipbreaking software, which is already available on a pair of 42 mm bar capacity Miyano models, to larger machines in the series. It will certainly be adopted in the St Helens factory, as it will be ideal for automatically breaking up stringy swarf into manageable chips when machining certain materials.

    They include highly ductile C101 copper, much of which is turned, milled and drilled in the St Helens factory for producing electrical components, and AMS5629, a martensitic, precipitation-hardening stainless steel used widely by the aerospace industry. Both are problematic in their tendency to birds-nest when machined, as are aluminium and a number of plastics. Even EN3B mild steel, which is supposed to have good machinability, is proving difficult to turn without swarf clogging the working area, due perhaps to the current shortage of good quality material.

    Another issue that occupies Neil’s thoughts is whether to continue using twin-turret fixed-head lathes or progress to triple-turret models. For example, instead of the latest ABX-64SYY 9-axis CNC lathe with upper and lower turrets, Citizen Machinery could have supplied a 12-axis Miyano ABX-64THY with a third Y-axis turret positioned above the spindle centreline. All three tool carriers can be in cut simultaneously to achieve very high levels of productivity.

    Neil’s view for the time being is that the extra time required for setting such a lathe and then programming it to incorporate the movements of a third turret cannot be justified for Wealdpark’s relatively small batch sizes of typically between 1,000- and 3,000-off. Additionally, the upper turret of the Miyanos on the shop floor often holds a U-Drill of large diameter for reverse-end axial machining and a third turret would restrict its movement. Nevertheless, the potential offered by a three-turret solution is constantly under review.

    Notable also regarding the fixed-head lathes is their speed of production, despite their large size. Occasionally, when the sliding-head lathes are particularly busy, a production run is transferred to a fixed-head lathe with very little increase in cycle time. One component machined from 20 mm hexagonal bar, for example, takes 28 seconds to produce on a sliding-head lathe with gang tooling and only 32 seconds using a 65 mm capacity Miyano with turret tooling.

    Generally, Wealdpark operates a 37-hour week and sets up all lathes at the end of the day for a considerable amount of unattended machining of free-cutting materials overnight and into the weekend. However, the recent increase in workload has necessitated occasional three-shift attendance and 24/7 operation.

    Reliable autonomous operation of the Miyanos is ensured by comprehensive load monitoring of both spindles and of the three linear axes of both turrets, as well as of the live rotary tools. The parameters of each channel can be set separately according to the job to ensure safe operation combined with minimal disruption to production.

    Programming is carried out mainly at the Fanuc Series 30i-B control on the shop floor, although offline-created content is sometimes added including engraving and deburring routines generated using the Alkart Wizard programming software provided by Citizen Machinery.

    In preparation for the impending expansion, at the start of 2022 Wealdpark took on three extra staff, an experienced setter-operator and two apprentices who in September this year will start a four-year NVQ level 2 diploma course on day release to St Helens College. Further new appointments will follow to increase the company’s headcount over the next couple of years.

    TURNED PARTS SUBCONTRACTOR PROGRESSES WITH MODERN SLIDING-HEAD TECHNOLOGY

    An electrical maintenance engineer by trade and with a solid grounding in mechanical engineering, Tom Pearce started his career as a prototype machine builder in the rubber industry. He subsequently worked for 11 years in his father’s company commissioning production machinery. In 2016 he started his own business, CIRC Manufacturing in Westbury, Wiltshire and after initially concentrating on welding, a skill that has been retained, he decided to branch out into subcontract machining.

    His current CNC capacity includes a vertical machining centre and two fixed-head lathes, all pre-owned, and three Citizen Cincom sliding-head lathes also purchased second-hand due to financial constraints during the start-up phase. His stated aim is to gravitate towards using more of the latter machines to produce complex, small to medium diameter, high added value components, as this is where he sees a profitable future.

    The first CNC lathes on the shop floor were the two fixed-head models with live tooling, which have no bar feeder but are able to accept a one-metre length of bar up to 65 mm diameter through the spindle. Mr Pearce took advantage of this by employing a bar puller in the turret and including a macro in his programs to advance the bar automatically after each component is parted off. It allows up to five hours’ unattended running, depending on the size and complexity of the parts being produced, and brought home to the entrepreneur the benefits of automation.

    CIRC was receiving more and more enquiries for machining components of much smaller diameter, however, including from his existing customer base. To keep them happy the company was having to subcontract out this work, as it was not economical to use the relatively large lathes on the shop floor. New plant was needed and a sliding-head turning centre was the preferred option, as it is capable of producing long, slender parts as well as those of larger aspect ratio. An internet search strongly indicated that a Citizen would be the best make to buy.

    So in 2019 Mr Pearce bought a 1995-built Cincom L20-VII slider with a 3-metre bar magazine sight-unseen for £4,000 from a website and used his engineering skills to refurbish it himself. He did not feel sufficiently confident to commission it so asked Citizen Machinery UK to align the bar feeder, bolt down the machine and check the axis movements. The company was very receptive to doing so and promptly sent in an engineer to complete the work.

    The lathe proved to be easy to operate by simply reading the manual. Word soon spread throughout Wiltshire and further afield that the capacity was available and CIRC started receiving more enquiries for complex turned parts. Most were fulfilled, although some had to be turned down as the machine does not have a full C-axis on the main and sub spindles, only 15-degree indexing.

    That prompted Mr Pearce in 2020 to approach Citizen Machinery UK directly for a machine with C-axis spindles and he also wanted higher speed driven tooling. The supplier offered a K16E-VII built in 2011, a 16 mm capacity slider that ticked the right boxes and is one of the fastest lathes that Citizen has ever manufactured. The supplier duly delivered the machine and in Mr Pearce’s words “nailed the installation and commissioning in one day, then provided a full day’s training the next”, so the lathe was quickly into production.

    A copper contact pin, a development part that was being produced on the L20-VII, required holding a ± 5 µm tolerance on diameter, which was difficult to achieve. Additionally, cycle times were unduly long. The work was immediately transferred to the K16E-VII and at the same time, as luck would have it, the batch size increased dramatically to 20,000-off. The accuracy needed was easy to attain and the cycle time fell threefold from one minute to 20 seconds, which translated into much more economical production. The contract has since expanded and the subcontractor is now producing a family of pins in long runs for a customer in the electrical industry.

    Mr Pearce added, “If we don’t run the K16E-VII overnight, it needs to be warmed up in the morning to achieve the tight tolerance on the connector pins. After 40 minutes the lathe, with its 45-degree tool platen driven by two ballscrews to achieve high resolution movement, is able to hold ± 5 µm all day.

    “We currently use three digital micrometres and a toolmaker’s microscope for quality control of these parts, but intend to invest in an optical, non-contact shaft measurement machine to take over this metrology task.”

    Having seen the benefits of more modern sliding-head turning technology, he was keen to harness it for the production of components larger than 16 mm diameter. Accordingly in January 2022 he bought a two-year-old Citizen Cincom L20-VIIILFV, again on the open market, and achieved another step change in productivity.

    Although nominally a 20 mm capacity sliding-head lathe, the guide bush is removable (as an option) to allow stock up to 25.4 mm (1 inch) to be turn-milled in fixed-head mode. The first job put on the machine was the production of 20,000 stainless steel gland nuts of 22.22 mm (7/8 inch) diameter for an electrical equipment manufacturer.

    When interviewed towards the end of April 2022, Mr Pearce had produced numerous different components on the machine but the guide bush had still not been used. He says the advantage is that the roundness and straightness of the bar is not so critical when the lathe is used in this mode, added to which the remnant lengths are much shorter, both of which saves cost and results in more economical production. He estimates that the guide bush will only be used for about one-quarter of the jobs produced on the machine, underlining the flexibility of modern sliders.

    The L20-VIIILFV has even faster and more powerful spindles and live tooling than the previous two Cincoms installed in the Westbury factory. It also has integral driven tools for reverse end working and an uncluttered working area to provide more space to facilitate cutter exchange at up to 37 tool positions. After installation, the machine immediately started taking sub-20 mm diameter workload off the fixed-head lathes, freeing them to produce larger parts. Across a wide spread of components from 1 mm to 1 inch diameter, the L20-VIIILFV is executing some extremely fine work involving, for example, a 0.3 mm slitting saw and profile boring of a pre-drilled, 1.5 mm diameter hole.

    There are generally two impediments to lights-out production, according to Mr Pearce, namely component dimensions drifting out of tolerance and swarf build-up in the machining area requiring operator attendance to remove it. The latest lathe avoids both problems and therefore frequently runs unmanned overnight. The first issue is addressed by the presence of thermal compensation sensors around the machine and the second by Citizen’s LFV (low frequency vibration) technology running in the operating system of the Mitsubishi control.

    Mr Pearce explained, “Sliding-head lathes when used with the guide bush in place have an inherent drawback. It is not really feasible to rough and then finish turn a part, as the smaller diameter of the roughed section when drawn back into the guide bush would cause vibration and impair the finishing pass.

    “It is therefore necessary to turn to size in one operation, but that tends to produce long, stringy swarf when machining certain malleable materials. The LFV software prevents this from happening by lifting the tool tip away from the surface of the material periodically for a few microseconds.

    “The frequency of the oscillation can be adjusted in the part program to control the size of the much shorter chips, added to which the LFV function can be turned off by G-code when it is more expedient, i.e. slightly quicker, to cut without it.

    “Overall, productivity is increased by enabling reliable unattended operation, eliminating the need to include axis shuffles in programs to shake swarf off components, especially from grooves, and avoiding the need to stop the machine to clear swarf.”

    The job on the lathe when it was photographed, a tubular Duplex stainless steel weld collar for the oil and gas industry, is a good example of how the benefits of LFV can be utilised. The high strength material has a tendency to work harden as it is being machined, the impact of which can be reduced by taking deep cuts to remove the work-hardened layer from the previous pass.

    The problem is that taking deep cuts in such tough, ductile materials inhibits chip breaking and normally results in a bird’s nest of swarf wrapping itself around the component and tool, to the detriment of both and perhaps even rendering them useless. LFV prevents this from happening, so every part produced is perfect and tools last longer. In the case of the weld collar, LFV is switched on for facing the bar and turning a chamfer, then to maintain a high production rate it is switched off for simultaneously boring and turning the OD.

    Mr Pearce is enthused that the chip breaking software also reduces problems and raises productivity when machining other materials such as pure copper, exotic alloys, other stainless steels and most plastics, especially nylons.

    Combined with the availability of high-pressure coolant on the L20-VIIILFV, the chipping function will also prove useful in the production in one hit of CIRC’s single proprietary product, a ballpoint pen housing and cap turned from Nitronic 60 stainless steel alloy. The use of carbide tooling and neat cutting oil in its production gives each individually-numbered writing instrument a beautiful micro-planished surface.

    Mr Pearce concluded, “The three Cincoms are the bedrock of our subcontract machining service. All feature main and sub spindles, full length bar feeds and a multitude of tools for driven cross working, end face milling and off-centre drilling.

    “They enable us to offer economical done-in-one manufacture, without the need for secondary operations. This in turn allows us to run our machines unmanned, so we can offer competitive prices and hence fantastic value to our clients.

    “The only thing holding us back at the moment is difficulty in finding skilled machinists to employ.”

    REPLACEMENT SLIDING-HEAD LATHES GREATLY INCREASE TURN-MILLING CAPACITY

    Good quality machine tools operate reliably and hold tolerance for two decades or more. The problem is that technology moves ahead so fast over such an extended period that the productivity of older machines cannot match that of their newer counterparts.

    This was the situation Redruth subcontractor DP Engineering found itself in until it purchased three new Cincom lathes from Citizen Machinery UK. They are an L20-XLFV installed three years ago, an identical machine that arrived in autumn 2021 and an M32-VIIILFV bought at the end of last year. The latter two machines were direct replacements for equivalent 20 mm and 32 mm capacity sliders of similar type and make bought around the turn of the millennium, several machine generations ago.

    Philip Anthony, DP Engineering’s Sales and Marketing Director commented, “The faster rapid traverses and higher power and speed of the main and sub spindles as well as of the driven tools on the new lathes have increased our capacity considerably. One stainless steel aerospace part we previously turn-milled in one hit on an L20 that is 20-plus years old now takes half that time to produce on its modern replacement.

    “It is a similar story on the 32 mm machine, which is more user-friendly than the former generation lathe and has better access and visibility into the machining area. Moreover, the addition of a rotary B-axis on the gang tool post enables us to machine more complex parts than was previously possible on our sliders.”

    LFV programmable tool oscillation for automatic chip breaking

    A notable technological advance from Citizen since DP Engineering purchased the earlier Cincoms was the introduction five years ago of its proprietary LFV (low frequency vibration) chip breaking software running in the Mitsubishi control. It has resulted in a significant increase in productivity when machining malleable materials such as titanium and stainless steel.

    It is particularly beneficial for the subcontractor, as one-third of its turnover is derived from the aerospace sector in which the use of such materials is commonplace, as it is in the medical industry, which has also generated more work since the start of the pandemic. Normally during machining, stringy swarf often entangles itself around the tool and component, risking damage to both and necessitating lathe stoppage to clear it from the machining area.

    Mr Anthony explained, “The first L20 we bought in 2019 has LFV. We knew about the technology and sent a team of engineers to Citizen Machinery’s Brierley Hill centre to see demonstrations of the chip breaking function in action.

    “For certain parts of cycles, it is very effective at ensuring that what usually becomes a bird’s nest of swarf is broken up into shorter chips, avoiding having to stop the machine to remove it and the consequent loss of production.

    “The best part is that LFV can be programmed to stop during a cycle when it is not needed by inserting a G-code, minimising the slight reduction in metal removal rate during the periods when the tool oscillates away from the component’s surface to break the chips.

    “On some jobs, even when cutting stainless steel, we don’t have to use LFV at all. It depends on the component design, the tolerances that have to be held and the tooling used. However, it is fantastic to have it there for when we need it.”

    He added that, in practice, LFV is particularly effective at controlling swarf on the L20s during turning and drilling operations, while on the M32 it speeds roughing and also plays a role when thread cutting. Overall, having complete control over swarf generation ensures that processes are more reliable and repeatable, added to which tool life is noticeably increased.

    Guide bush-less operation saves costs

    Another attribute of the latest three Cincom lathes that increases their versatility, apart from the extended periods of spindle uptime and unmanned running made possible by the LFV chip breaking software, is the ability to turn-mill shorter components in fixed-head mode without the guide bush, which can be removed and replaced within half an hour.

    This allows lower quality, unground bar to be used, increases by several millimetres the maximum diameter of stock that can be accepted and also reduces bar wastage due to much shorter remnant lengths. Consequently this mode of operation is frequent in the Redruth factory, especially for the significant amount of kanban production fulfilled by DP Engineering for its customers.

    Mr Anthony remarked that overall, taking into account the higher speed of machining, the LFV chip breaking function and the option of guide bush-less operation, the latest three lathes give DP Engineering not only considerably higher productivity but also a lot more flexibility when allocating jobs to the 18 turning machines around the factory, including the current tally of five Cincoms.

    A couple of dozen jobs have already been transferred from multi-turret fixed-head lathes to the new sliding-head models for one-hit machining, freeing up the former for other production duties. Such versatility is ideal for a subcontracting environment, leading to faster deliveries to customers, enhanced reputation and more orders.

    Mr Anthony also pointed out that as space on the shop floor in Redruth is fairly limited, replacing machines with models that are much more productive is an ideal way to grow the business without the expense and disruption of having to move to larger premises. This is especially important in respect of his turned parts production, which accounts for three-quarters of throughput.

    About DP Engineering

    DP Engineering is a cog in the wheel of Cornwall’s £732 million manufacturing industry. It was the brainchild of a keen motorcycle rider, the late David Paull, who was frustrated at not being able to obtain engine parts for his bike and decided to machine his own. In 1952 he started a motor reconditioning business, David Paull Motor Cycles, which led him into subcontract machining and was the forerunner of the current firm.

    In 2008, DP Engineering gained AS9100 accreditation in addition to ISO 9001: 2000 and established itself as a supplier to the aerospace industry. Due to business expansion, in 2014 the company purchased a purpose-built, 17,000 sq ft premises in Redruth, where the subcontractor operates today under the watchful eye of CEO Martin Legg.

    Major sectors served include aerospace, defence, oil and gas, marine and renewables. The company is known for being a low-to-medium volume shop, producing parts typically from 10- to 50,000-off. Lean manufacturing principles allow cost effective production, from prototypes through to batch work, and over 500 kanban items can be produced for next day delivery.

    Other capital investments made by the subcontractor within the past 12 months, apart from the two Cincom lathes, include a Matsuura 5-axis, 10-pallet cell for automated machining of prismatic components, an Aberlink coordinate measuring machine to inspect them, and a ViciVision optical, non-contact measuring machine for quality control of rotational parts.

    SLIDING-HEAD LATHES ARE THE PERFECT CHOICE FOR START-UP TURNED PARTS SUBCONTRACTOR

    Glenn Poleykett began his career in manufacturing in 2006 at his uncle’s firm, making components for darts on Cincom sliding-head and Miyano fixed-head mill-turn centres. They are built by Citizen in Japan and sold in Britain and Ireland through subsidiary company Citizen Machinery UK. He quickly realised that sliding-head lathes with driven tooling were capable of producing virtually any part, provided that it was from 32 mm diameter bar or smaller, whereas fixed-head models were incapable of machining shaft-type components to tight tolerances.

    Twelve years on, when he decided to start his own subcontracting business, Stellar Precision Components on the Raynham Road Industrial Estate in Bishops Stortford, he remembered that lesson. He went to the same supplier to purchase two Cincoms, an L32-VIIILFV and an A20-VII. They have since been joined by a third sliding-head lathe, an L20-VIIILFV, which arrived on the shop floor in April 2020.

    Mr Poleykett said, “In the intervening years I worked at a number of subcontractors on various makes of slider, but I always regarded Citizens as the best machines.

    “My opinion was reinforced when a few years ago the manufacturer introduced its patented LFV (low frequency vibration) operating system software in the Mitsubishi control system.

    “It is programmable via G-codes to start and stop during any program, breaking what would normally be stringy swarf into smaller chips that cannot wrap around the tool or component and damage them.”

    He witnessed LFV in action at Citizen’s UK headquarters and technical centre in Bushey before he bought the first two lathes and described the functionality as “incredible”. When machining short-chipping metals such as mild steel, 303 stainless and brass, he does not employ the function as it is not needed and the extremely short periods of air cutting slightly lengthen cutting cycles.

    However when turning and drilling 304 or 316 stainless, aluminium, copper and plastics, he always turns on the function for at least part of the cycle. It has the effect of greatly improving production output through not having to stop the lathe to clear swarf and by being able to leave the machine to run unattended with confidence. He would have ordered an LFV version of the A20-VII, but it had not been introduced on that model at the time, which is why the machine is devoted to producing components from free-cutting metals.

    LFV oscillation of the tool by tens of microns not only breaks the swarf but also allows coolant to penetrate the cut more efficiently for the brief periods when the tip lifts clear of the component surface, reducing heat and prolonging tool life. Depth of cut may be increased substantially, even when processing tough materials, significantly shortening cycle times.

    Swapping between the two modes of LFV is a simple matter, according to Mr Poleykett. If the second, more vigorous chip-breaking action is required, for example when cutting plastics, and the other mode has been inserted in a program by Citizen’s Alkart CNC Wizard off-line part programming software, manual insertion of a single line of code at the start and finish is all that is necessary.

    It is noteworthy that, as is the case on more and more Cincoms and on some Miyano lathes, the most recent L20-VIIILFV delivered to Bishops Stortford has the chip-breaking functionality on both the main and sub spindle, whereas on earlier models it is applied to the main spindle only. The latest machine at Stellar was purchased for manufacturing ventilator parts for the NHS. Funding through Citizen UK Finance and a six-month payment holiday smoothed the acquisition process at a difficult time.

    Much of the subcontractor’s throughput is destined for the aerospace, medical, electrical connector and pneumatics industries. Batch size ranges from 10 to 40,000 pieces and the factory operates 24/7, with two manned shifts per day and three hours of lights-out operation during the early hours of the morning. The security of operator attendance for a majority of the time is needed, as many of the components that the subcontractor produces are of very high accuracy, from a general tolerance of ± 0.1 mm right down to ± 5 microns.

    Components up to the maximum bar size can be produced on both L-series lathes either when the guide bush is in place or in guide bush-less mode, the latter being a standard feature of the machines. The L32 was installed with an optional extension kit that allows bar up to 38 mm diameter to be accommodated, higher than the lathe’s nominal capacity of 32 mm. This additional capability is regularly used and has allowed new business to be won.

    Mr Poleykett takes full advantage of non-guide bush operation when producing shorter components, as it avoids having to use expensive ground stock. Plastic rod, which is always oversize, can be accommodated as well as unground bar of harder metals on which high spots can catch in the guide bush, alarming out the machine. A further benefit is material savings due to much shorter remnants.

    LATEST SLIDING-HEAD LATHE HOLDS SINGLE-FIGURE MICRON ACCURACY

    Aerospace component manufacturer reinvents itself during the pandemic

    Rugby-based subcontractor Technoset, with 70% of turnover in the aerospace sector, was not a good situation last March (2020) when COVID-19 grounded most aircraft and orders plummeted seven-fold. Towards the end of 2021, the company’s production of aircraft parts is still below one-quarter of previous volumes.

    With the business facing an existential crisis, managing director Kevan Kane and the firm’s owners set about restructuring the operation, positioning Technoset as a solutions provider rather than a supplier of components. It also started targeting challenging contracts for the supply of tight-tolerance components to more industries, notably lasers, fibre optics and telecoms.

    The success of these policies has seen the number of components going through the shop floor for the first time for both existing and new customers more than treble from 10 to 33%. A large proportion have benefited from design-for-manufacture expertise from Technoset engineers to reduce piece part costs for customers.

    The first new machine tool the company has bought since the onset of the pandemic was a highly specified, twin-spindle Cincom M32-VIIILFV bar-fed, sliding-head mill-turn centre, which was delivered by Citizen Machinery UK in spring this year (2021). Replacing two smaller M12 and M16 Cincoms that were about 20 years old, it joined a previous-generation M32-VIII bought in 2017, all numbers representing maximum bar capacity. There are also eight twin-spindle, fixed-head Miyano bar-fed lathes on-site from the same supplier for turning and milling components from stock up to 64 mm in diameter.

    A primary reason for acquiring the latest M32 was a need to machine complex telecoms components, in particular a family of 12 mainly aluminium connector parts for use in the defence industry. Many of them are complex, with a lot of milled detail, and drawing tolerances are below 10 microns.

    That level of accuracy is achieved reliably, even when running lights-out, partly because the lathe incorporates Citizen’s LFV (low frequency vibration) software in the Mitsubishi control’s operating system. Variants of the LFV function can be called up automatically in any part program to break what would normally be stringy swarf into manageable chips. It is no longer necessary to stop the lathe to untangle and clear potentially harmful swarf from the tool and/or component.

    Productivity is therefore maximised, the operator is freed to carry out other tasks on the shop floor and the machine can be left with confidence to run unattended. The programmable chip-breaking software is not only beneficial when machining the aluminium connector parts but will also prove invaluable when Technoset restarts producing aircraft components in significant volumes from Inconel, titanium, Waspaloy, Nimonic and other superalloys, all of which tend to birds-nest when turned and drilled.

    In anticipation of acceleration in the return of aerospace work, the subcontractor introduced a second shift in early September 2021. It is to ensure that contracts for aircraft components, which typically involve batch runs of 1,000 to 2,000-off, do not dominate the shop floor and dilute the production of new work that has been taken on in other industries. Consequently, aerospace work at the AS9100-accredited contract machinists is unlikely to exceed 50% of throughput in the future.

    Rapid development of turning machine technology

    Mr Kane commented “Citizen Machinery’s M32 sliding-head lathe, the manufacturer’s flagship model, has been the most important contributor to Technoset’s business since we bought the first one in 2000.

    “Something that has surprised me is the speed with which the machine technology has advanced. Our latest M32 is of the fifth generation, which has been beefed up and completely redesigned since we installed the last, fourth generation model in 2017.

    “The result has been a step change in performance. I regard the machine as the epitome of sliding head-technology in terms of productivity, flexibility and speed. It is ideal for mill-turning high value piece parts.”

    Improvements to the turning centre include 1.5 times faster live tools powered by a 2.2 kW motor and a programmable, 9,000 rpm B-axis to enable simultaneous machining in five CNC axes rather than four. Combined with the back tool post whose Y-axis now has adjustable-angle tooling, it enables faster production of more complex parts. Superimposed machining allows three tools to be in cut at the same time, further shortening cycle times and raising productivity.

    The 10-station turret incorporates a new tooling system employing a single, heavier duty drive, also rated at 2.2 kW, to an increased number of live cutters. Only the selected tool rotates, suppressing heat generation and vibration to enhance machining accuracy and surface finish. As nearly every part that is turned in the Rugby factory also requires prismatic operations such as milling and drilling to achieve one-hit manufacture, the improvements to the driven tool stations are of considerable benefit.

    Mr Kane added, “The upgraded specification of the M32, which includes an 8,000 rpm main spindle uprated to 5.5 / 7.5 kW and an identical counter spindle, much more powerful than before, means that the machine is able to match the speed of the M12 and M16 that it replaces.

    “Normally, to achieve cost-effective levels of productivity when mill-turning components from smaller diameter bar, you would not put that work on a lathe with double the bar capacity or more, as you would expect it to be slower.

    “That is not the case with the fifth generation M32, which means we can consolidate jobs onto one platform. The reduced mix of machines on the shop floor promotes knowledge transfer and helps to mitigate manufacturing’s industry-wide skills shortage problem.”

    He singled out Citizen Machinery UK’s engineering backup as worthy of special mention; it is applicable not only to Technoset but also to group member Technoturn, St Leonards, where a similar number of Cincom and Miyano lathes are in operation. Responsive service is appreciated, but especially beneficial is the application support.

    Recently, Technoset found itself pitching for work and were stuck on a cycle time of 90 seconds, which was too long to achieve the target price. Mr Kane contacted the supplier’s Bushey headquarters by email and an engineer came back within 24 hours with an application-optimised cycle time of 60 seconds. The one-third decrease resulted in the subcontractor winning the new business.

    Looking to the future

    Focusing on digitalisation and automation, Technoset’s plans are wide-ranging. The turning side of the business, which currently accounts for around two-thirds of turnover, is already automated through the use of bar magazines. The milling side will take a significant step forward in spring 2022 with the installation of a 5-axis machining centre with built-in robotic component load/unload and on-board part probing. It will be the first automated prismatic component manufacturing cell on-site.

    Helping to fund the purchase is a £100,000 Aerospace Unlocking Potential (Aerospace UP) grant recently awarded to Technoset. Delivered through the University of Nottingham and the Midlands Aerospace Alliance, the initiative aims to support the aerospace supply chain in the Midlands.

    Part of the money will also be spent on acquiring a CADCAM suite for off-line programming, a function that is currently performed mainly by manual data input at the machines. Consideration will also be given to investment in laser cutting, part marking, a painting facility and special deburring equipment to achieve the high standards demanded by the aerospace and laser industries.

    As any manufacturer knows, use of the best machine tools comes to nothing without skilled people to run them. Mr Kane ensures that highly trained setter-operators are always coming through the system by continually taking on apprentices. Thre are progressing through a four-year program with Midland Group Training Services and two are aligned with the programme delivered by the Manufacturing Technology Centre.

    GUIDE BUSH-LESS OPERATION AND CHIP BREAKING SOFTWARE TRANSFORM TURNING OF ALUMINIUM

    “We believe that investment in the very latest technology is the key to quality, reliability and competitiveness,” said Dave Zollo, joint owner of contract machinists IML (UK). He and Jerry Way started the business in 1995 and moved into the current, 14,000 sq ft premises in Weymouth in 2011. One year later the first sliding-head lathe arrived, a Citizen Cincom A32-VII with 32 mm bar capacity, followed in 2013 by a 16 mm bar model, a Cincom C16-VI.

    The early investments were triggered by an increase in contracts from the medical industry and a desire to be able to manufacture components in one hit, such as endoscope cleaning equipment parts. To cope with an ever increasing level of work, including for the high-end automotive sector which has grown over the past couple of years to become more than 50% of turnover, there are now four different models of sliding-head lathe on site from the same supplier.

    The latest two, designated L20-XLFV and L32-XLFV, were installed in 2018 and 2020. Unlike the first two Cincoms, they offer the flexibility to allow removal of the guide bush, as well as having the notable benefit of low frequency vibration (LFV) software built into the operating system of the control. Mr Zollo noted that the more modern machines are also more user-friendly, allow better access and are quicker and easier to set.

    He explained, “These advanced, twin-spindle, sliding-head lathes are helping to keep us competitive on the world stage, as is automation throughout the factory.

    “All of our lathes including four fixed-head models are bar-fed and work 24/7, with the sliders able to accommodate a wide range of batch sizes from typically 50- to 30,000-off. Dimensional tolerances of less than ± 10 microns may be easily held.

    “Even smaller quantities are economical to produce, partly because we have adopted a policy of standardising on one size of stock on each of the Cincoms, so we do not have to waste time changing over bar sets.

    “We have also invested in automation on the milling side of our business, which accounts for more than half of turnover. Our four vertical machining centres are equipped with robotic loading and remote monitoring, while two horizontal machining centres on the shop floor have a twin automatic pallet changer to minimise idle times.

    “It all helps to keep costs down and allows us to quote our customers prices that are very similar to those we were charging two decades ago.”

    Aluminium bar, which accounts for a significant proportion of throughput of turn-milled parts, is the villain of the piece as regards sliding-head turning in the Weymouth factory. The material is often of variable quality in terms of straightness and diameter variation, so can jam in the guide bush of sliders and requires frequent supervision by the operator to adjust the collet.

    The ability to remove the guide bush on the L20 and L32 in less than half an hour allows the subcontractor to turn aluminium bar into shorter components in fixed-head mode without problems. It also has the advantage of reducing the remnant length from typically 275 mm to 100 mm. Completion of one recent IML (UK) contract consumed 300 bars, so it is clear that a lot of material and money can be saved.

    When turning difficult to chip materials, Citizen’s LFV software, which is part of the control’s operating system, breaks swarf into manageable chip sizes, whereas normally it would be stringy and entangle itself around the tool and component. This capability to manage the size of swarf is in addition to any chip breaking features that may be ground into an indexable insert. Mr Zollo singles out aluminium as well as stainless steel bar to be particularly problematic in terms of bird’s nesting.

    To alleviate it, the LFV function can be switched on and off via G-codes in the part program, enabling optimal use of the feature during different parts of a cycle. It is, however, not a pecking macro in the CNC program itself. As one operator looks after the four sliding-head lathes, LFV is helpful in minimising periodic attendance at the machines to disentangle clogged swarf. It is notable that the 8-axis L32 has LFV on both the main and counter spindles, allowing the oscillations that produce the chip breaking action to assist in the production of both front- and reverse-end turned, milled and drilled features.

    LFV oscillation lifts the tool tip clear of the component surface by tens of microns for ultra-brief periods to allow coolant to penetrate the cut more efficiently. It reduces heat and prolongs cutter life, while at the same time enabling depth of cut to be increased, even when processing tough materials. It often eliminates the need for a roughing pass and significantly shortens cycle times. Mr Zollo advised that it is of major benefit during attended day and night shifts and especially so during the weekend when staff are not present.

    He concluded, “Swarf build-up is really the only thing that stops modern bar-fed CNC lathes, which are inherently very reliable. LFV on the Citizen sliders virtually eliminates the hassle of clearing away swarf and consequent loss of production, especially during minimally attended operation.

    “Even when we are running them unattended at the weekend, it is unusual for them to stop before the bar runs out. Should there be a problem, however, the on-board cameras allow us to monitor production and come into the factory if necessary to take remedial action.”

    AIRCRAFT EQUIPMENT MANUFACTURER IMPROVES MACHINING EFFICIENCY FOR LARGER COMPONENTS

    Father and son team Andy and Owen Phillips, both of whom are pilots and aviation engineering enthusiasts, started a subcontract machining business in Havant in 1994. After four years, they applied their extensive knowledge acquired over many years of building and flying aircraft to transition their firm, Andair, into a manufacturer of fuel system components for light aircraft in the sport, amateur-build and commercial aviation sectors.

    The business, which is certified by QAS International and to ISO 9001:2008, is now a leading global producer of such equipment, with 90 percent of its fuel selectors, filters, check valves, gascolators and fuel pumps going to export markets. Regular customers include Cessna, Cirrus, Czech Sport Aircraft, Diamond, Grob, Grumman-Northrop, Rotax/Bombardier, Scaled Composites, Technam and Vans.

    Miyano fixed-head, twin-spindle CNC lathes from Citizen Machinery UK have underpinned production of Andair’s turned and milled parts since January 2005, when the first turning centre with sub spindle was delivered to the Havant factory, a 5-axis BND-42S. It proved so efficient that a second, identical model was ordered six weeks later. Fast-forward 16 years and the company has bought a total of seven Miyanos, the latest being the first 80 mm bar capacity ABX lathe to be installed in the UK. It arrived on the shop floor in June 2020 equipped with an Iemca KID 80 short bar magazine.

    Andair had been waiting eagerly for the launch of the 80 mm version of this twin-spindle machine with two Y-axis turrets, having since 2015 been producing 3 inch and 2.75 inch diameter components from billet held in a Hainbuch chuck in the main spindle of a smaller ABX-64SYY, of which there are two in the Havant factory. The high requirement for components of this size meant that the lathes were being used for chuck work 60 percent of the time.

    Owen said, “Production efficiency of our larger components used to be lower because we could only manufacture a limited number of components from a billet, say five or perhaps seven. In the case of the aluminium body for an oil-air separator we are currently machining, we could only produce one per billet.

    “Now all these parts can be machined from bar using the 80 mm capacity lathe, saving a lot of time. It runs continuously throughout the day and although we are not set up for 24/7 operation at present, with this machine and our other Miyano bar autos is it is feasible in the future.”

    The other lathes in the factory all have twin turrets and Owen had ordered a similar specification for the 80 mm model. Due to the cancellation of the MACH 2020 machine tool exhibition, however, which should have been held in Birmingham last April, Citizen Machinery had in stock a triple-turret ABX-64THY (80 max dia) 12-axis model with a Fanuc control system that it had intended to launch at the show. Owen was initially hesitant when offered the machine, having never used a lathe of that configuration before, but decided to buy it anyway as it was available immediately. It turned out to be a revelation.

    He enthused, “I would not buy another twin-turret machine in future, because having three turrets is so much more productive. I would like a four-turret version if Miyano made one.

    “It is no problem to transfer work to the more complex lathe, as a new program can be checked easily using the manual retrace function in the control, avoiding any possibility of interference between tool and workpiece.”

    He explained that the two turrets positioned above the spindle centreline, each with 12 live stations, are dedicated to working at the main and counter spindles respectively. The third turret is located below and has unrestricted travel to operate at either spindle to provide flexibility for balancing front and reverse end machining. Three tools can be in cut simultaneously to achieve very high levels of machining efficiency.

    About 60 different parts have so far been produced on the new lathe, all from 3 inch diameter bar. In fact, in one instance where a customer required a large valve machined from a 4.5 inch diameter billet, Owen turned the end of it down to 80 mm so that it could be machined in the collet.

    In the case of the oil-air separator body, it is now possible to machine five from bar in 30 minutes whereas before, with an operator loading billets manually into the chuck of an ABX-64SYY, it took at least 45 minutes to achieve the same output. In other words, productivity has been boosted by more than 50 percent. A further benefit to Andair is that the two 64 mm bar lathes can now be devoted to the collet work for which they were originally intended.

    Another example of where the 80 mm bar machine has introduced benefits is when machining one of the few Andair components the pilot actually sees, a fuel selector fascia plate that requires a very high surface finish, which is achieved on the aluminium part using a diamond tipped tool. The plate is also engraved to indicate which tank has been selected. Previously, after turning it from a billet, a second operation was required on a machining centre to mill material from the reverse and to drill four holes.

    The method of manufacture has now been altered, whereby milling and drilling as well as turning are carried out from bar on the Miyano, leaving only a small operation to clean the bore on a separate machine. Cycle time has been reduced by at least two minutes and an operation has been eliminated.

    In the case of another component, in fact the first part that was made on the ABX-64THY (80 max dia), all three turrets had almost an identical amount of work to perform. Cycle time is 2 minutes 15 seconds including parting-off and the component comes off finished, whereas previously the cycle was 4 minutes, plus there was a need for a second operation, requiring extra time for both metalcutting and inter-machine handling.

    Aluminium accounts for three quarters of throughput at the Havant factory, with a wide range of other materials also machined including brass, bronze, plastics, tool steel and other steels including stainless. Batch sizes are relatively low, normally between 100- and 500-off, so there is a lot of machine preparation.

    The Miyanos are quick to set up however, as they have built-in tool setters and programs are prepared off-line using an Esprit CAM system. Typical tolerance that needs to be held is ± 0.02 mm and Owen declared that if it is exceeded on any occasion, it is always the tool that is at fault, as the machines do not move.

    He concluded, “I am a big fan of Miyanos. They are very productive, accurate machines and have beautiful spindles that produce excellent surface quality. I wouldn’t look at another make of lathe.

    “Support from Citizen has been fantastic, from sales to delivery, installation and commissioning – they are absolutely incredible.”

    AIR BEARINGS MANUFACTURER BRINGS SLIDING-HEAD TURNING IN-HOUSE

    The first sliding-head turn-milling centre to be installed at the Ferndown, Dorset factory of Air Bearings Ltd (ABL) is a Citizen Cincom L20-VIII LFV. Delivered in June 2019, it has brought in-house the production of nearly all shaft-type components, saving around £8,000 per month previously spent on subcontract Swiss-type turning. As a consequence, the machine paid for itself within 18 months.

    Speeds up to 350,000 rpm are attained by ABL’s air bearings, which are used globally in machinery for semiconductor wafer slicing, printed circuit board drilling, and micro-machining applications as diverse as polymer lens manufacture for cataract operations, edge grinding of toughened glass for mobile phone screens, watch component manufacture and milling of coining dies. The high rotational speeds demand that sub-micron tolerances be held on some turned bores and other features of component parts of the air bearing.

    This in turn means that operations prior to diamond turning and grinding of the bore and outside diameter must also be very accurate to meet pre-finishing requirements. In this department, ABL operates two vertical machining centres, seven 2-axis chuckers, two multi-axis, bar-fed, fixed-head lathes and now the Citizen L20 slider.

    Only top-end machine tools are purchased by ABL to meet the levels of precision required to ensure rotational motion of the air bearing spindle to within a couple of microns. The shaft assembly with its six key parts is especially critical.

    ABL’s senior production controller Dave Stacey advised, “Take the collet, for example, produced from 13 mm diameter tool steel bar. The concentricity of the front bore to the taper is tied up to 30 microns TIR (total indicator reading).

    “Dimensional tolerances on diameter and length need to be within 50 microns or sometimes 25 microns to allow post machining to sub-micron accuracy, while there is a 6-micron limit in the bore.

    “Originally, before our decision to use subcontract services, these collets were machined in-house in two operations – turning and boring on a fixed-head lathe and then drilling of eight radial holes on a machining centre.

    “The time-consuming process led to our pre-finishing department only producing the quantity that was needed, which could be as low as 15-off, yet external heat treatment and stress relieving before final finishing still cost £250 a time, irrespective of component quantity.

    “Now, with single-hit turn-milling of the collets on the Cincom L20, we run off typically 500, representing three months’ supply, at a fraction of the cost of subcontracting them out, added to which we can take full advantage of the fixed-cost heat treatment service.”

    It is a similar story with the other rotational components in the shaft assembly of an air bearing spindle, such as the EN57 stainless steel collet studs and guide pistons, of which there are six variants. All are produced more economically on the slider, as they involve classical Swiss-type turning from bar less than 13 mm in diameter.

    The largest part produced on the Cincom L20 is a 250 mm long push rod turned from 16 mm silver steel bar down to 7 mm diameter in one pass. It would not be feasible to turn the component in several passes, as it is longer than the guide bush; while recourse to turning between centres using the sub-spindle would unduly extend the cycle time and leave a witness mark.

    Taking a 9 mm depth of cut in this high carbon steel over much of the component’s length is an ideal time to activate Citizen’s patented LFV (low frequency vibration) chipbreaking software in the Mitsubishi control. It allows what would normally be long, stringy swarf to be broken into shorter lengths, the size of which is determined within the program, to avoid birds-nesting around the component and tool and the need to remove the swarf repeatedly from the machining area by hand. Economy of production is greatly increased, as there are no stoppages for swarf clearance, and the lathe can be left to run unattended. Additionally, absence of chatter improves the surface finish on machined components.

    Notably, LFV may be switched on and off during a cycle by G-code command, but is not a chipbreaking macro within the program itself. Instead, and distinct from other systems, it is part of the CNC operating system and as such does not compromise tool life.

    Mr Stacey concluded, “The Cincom lathe is so fast at producing rotational parts from bar for our air bearings, even with the larger batches we are running, that the machine is often waiting for work during the day.

    “We are therefore looking at putting classical fixed-head work onto the machine, parts that are shorter compared with their diameter, which will provide an opportunity to bring further subcontracted turning in-house.

    “For this purpose, the ability to run the Cincom L20 in guide bush-less mode to save material by shortening the minimum bar remnant will provide an additional saving.”

    SLIDING-HEAD LATHE WITH TWO TOOL PLATENS SLASHES PRODUCTION CYCLE TIMES

    At the subcontract machining facility of Witon Engineering, Barnstaple, turn-milling of relatively complex components from 16 mm diameter bar used to be carried out on 32 mm capacity sliding-head lathes, rather than smaller capacity models, to take advantage of the extra CNC axes and tools available on the larger machines. This type of work has now been transferred to a more nimble, 25 mm bar capacity Citizen Cincom D25-VIIILFV sliding-head turning centre, installed in January 2021. The first two jobs have shown significant cycle time reductions of 20 percent or more.

    Since the mid-90s, the contract machinist has bought 17 bar-fed lathes from this supplier, of which one was a 42 mm bar capacity Miyano fixed-head machine, the others being various Cincom sliding-head models for turning up to 32 mm stock. There are currently 11 Citizen machines on the shop floor, earlier models having been exchanged over the years. Lathes from this supplier therefore account for approaching half of the 25 of bar autos in the factory, comprising 13 sliding-head models, eight single-spindle fixed-head turning centres and four CNC multi-spindle automatics.

    The first component to be transferred to the D25 was an EN1A steel shaft for a lawnmower. The part was formerly produced on an L32-VII, of which there are three on site. As 180,000 have to be produced to fulfil the current contract, the 20 percent cycle time reduction leads to a significant production cost saving.

    The second component benefiting from being machined on the D25 is a 304 stainless steel fuel inlet fitting for an automotive customer. It used to be turn-milled on one of a pair of Cincom M32s in a cycle time of 72 seconds. This has been cut to 53 seconds, representing a 26 percent saving. With 55,000-off needed, the economy gained is significant.

    Ian Clapp, workshop manager at the Barnstaple factory explained, “We operate a couple of 20 mm capacity, dual-platen sliders of another make and knew this configuration offered quick cycle times.

    “However, we saw what our longstanding sliding-head lathe supplier Citizen was offering in the D25, a machine with larger bar capacity plus the ability to carry out work up to 32 mm diameter without the guide bush for more economical material usage when producing shorter components.

    “The model also has the benefit of a programmable B-axis, so we decided to go for this option.”

    The gang tool platens are in front of and behind the spindle centreline, with Z-axis motion provided on the rear carrier to allow balanced turning, milling or drilling, or simultaneous rough and finish turning. The B-axis on the front post, carrying up to four driven tools on either side to service either the main or counter spindle, swivels by up to 135 degrees. A further feature of the lathe is that three axis groups can be controlled simultaneously by the Mitsubishi 800 CNC system, so three tools can be in cut at the same time.

    Another potential benefit of this 12-axis CNC turn-mill centre is that it incorporates Citizen’s programmable LFV (low frequency vibration) chipbreaking technology in the control. It automatically breaks into smaller pieces the long, stringy swarf produced when machining materials such as copper, plastics and high alloy steels. Birds-nesting around the tool and component and the consequent damage that may be caused is therefore avoided. Although LFV cycles have not been included in programs run so far on the D25 at Barnstaple, it is nevertheless there to use when appropriate jobs come along.

    Witon Engineering underwent a change of management at the end of 2016 when second-generation owner and managing director Ian Sheldon retired. The firm is now run by Ian’s son-in-law Tom Courtney, who is the general manager and Ian’s daughters, directors Hayley Neate and Gemma Courtney. Operations still predominantly centre on precision turned parts production on CNC lathes, the cam multi-spindle auto shop having closed in 2018. Two 3-axis, vertical-spindle machining centres are also in use.

    Large batch runs are the norm: one electrical connector part is produced at a rate of 100,000 per month and even one of the machining centres is currently completing a contract for 500,000-off prismatic components.

    Mrs Neate commented, “We are keeping Witon Engineering basically on the same trajectory, with the accent on turning and long periods of unattended running of our bar autos during the day and to the end of a twilight shift finishing at 12.30 am every weekday.

    “The onset of the pandemic reduced business early on, especially as work for the automotive sector, traditionally a large proportion of our business, was badly affected. However, we have gained extra contracts in other sectors to compensate, such as parts for lubrication systems and household goods.

    “When the automotive work returns, our production throughput will be at a record high and we will carry on investing in top quality plant like Citizen lathes to meet the demand.”

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