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Tornos has reported that its MultiAlpha 8×20 range of multi-spindle automatic turning machines are being used by Stryker to improve the production of medical parts.

Motorex high-performance machining fluids are being used on the machinery.

In its Stryker Spine plant in Switzerland, high-tech products such as implants and poly-axial screws are produced for spinal surgery purposes.

The production of complex components is renowned for needing several separate machining steps, which often involves using different machines that require multiple fixture settings.

Throughput time lengthens and the repeatability of precision levels starts to diminish, making the manufacture of components for the medical technology sector more expensive, since these are very niche products.

Stryker Spine is using the MultiAlpha 8×20 from Tornos for repeatability, precision and speed.

The MultiAlpha has eight motor-spindles capable of operating at different speeds, and this was customised to include a combined tailstock machining facility, two programmable manipulators and in integral workpiece extraction unit.

Tornos said the MultiAlpha 8×20 provides optimum cutting values in every machining situation and has a blocking and positioning fixture on every spindle.

This provides Stryker with a high level of productivity and flexibility.

With scope for implementing a diverse range of tools and a universal programming system, Stryker said it is confident that it has the most efficient machine tool partner for its facility.

Every year, Stryker Spine processes tons of titanium alloy (soft), stainless steel (tough) and chrome-cobalt (extremely tough).

These materials could not be more different from one another.

The same is true of the machining steps involved, with all operations - from turning to milling - always performed at the optimal cutting speed.

This application profile imposes extreme demands on the machine tool and cutting oil.

In particular, the fast dissipation of heat and the cooling action of the cooling system integrated in the oil circuit are key factors in the process of maintaining dimensional integrity.

At Stryker Spine, work is carried out to the nearest micron.

Demonstrating this accuracy achieved by the Tornos MultiAlpha 8X20, only a 1C change in the temperature of the cutting oil would have an impact on the dimensional integrity of the workpiece.

This means that the front doors of the machine should only ever be opened in genuine emergency situations.

In particular, it is on the MultiAlpha 8×20 that the true benefits of the Motorex Ortho NF-X formulation can be seen.

The heat between workpiece and tool tip resulting from the high cutting pressure and the optimum cutting speed is utilised to enhance high-pressure stability.

This is of particular benefit during machining operations.

The homogeneous and stable film of lubricant between tool blade and workpiece acts as a protective cushion.

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The Citizen A32 CNC sliding-head turn mill has increased productivity at Labfacility of Bognor Regis, a large manufacturer of temperature sensors.

Tony Russell, general manager of the Connector Division, said: ‘The Citizen A32 installation in November 2008 provided us with a much needed increase in turn-mill capacity (from 16mm bar) to 32mm.
Also, due to its inherent rigidity coupled with its rapid control processing speed, 45m/min traverse rate and overlapping tool slide capability, the machine has cut existing cycle times by at least 30 per cent,’ he added.

Labfacility is recognising a growth rate of around 10 per cent and exports have grown by 20 per cent over recent years for its range of sensors and connectors that includes standard and miniature, plugs and sockets, some able to withstand temperatures up to 560C.

It also produces thermocouples, infrared sensors, thermometers, temperature measurement devices and process control and transmitting devices, and also has a calibration facility for temperature probes between -10C to 1,200C.

Originally set up to provide a precision turned parts service for its own OEM component production with a capacity up to 42mm diameter bar size, the service was expanded into subcontract supply.

This now contributes sales of 25 per cent to the business turnover.

‘The need for temperature and process control has never been greater because the monitoring of any change is so important today over a multitude of sectors and applications from food and drink, refrigerated vehicles, aerospace, automotive, petrochemical and electronics to medical and plastics industry,’ said Russell.

For the company, in-house production is critical due to the specialist involvement required and need to control production of so many different and unusual types of materials - that can also be difficult to source and tend to be very expensive.

‘This means our selection of production equipment and in-house skill levels are vital to our existence,’ said Russell.

‘Our capability has also been drawn to the attention of other companies that are seeking a reliable and experienced turned parts supplier and led to this side of the business growing quite quickly,’ he added.

In his view, this puts his Citizen machines well into the context.

A K-16 sliding head installed in 2006 allowed the company to combine operations into a single cycle - something that could never be achieved with two-axis lathes.

The K-16 also freed up design restraints for more complex components and enabled previous subcontracted parts to be brought back inside.

‘We made an immediate 25 per cent saving with that machine, and the Citizen A-32 gives us an even greater contribution to our productivity,’ said Russell.

The installation of the Citizen A32 has recorded 18-hour day production runs through the single-shift operation.

According to Russell’s records, it is also achieving a utilisation level that is exceeding 55 per cent and still growing, a great achievement for small batch work.

The K-16 is running at 75 per cent, which tends to be on longer running jobs with fewer changeovers.

Helping improve the result of greater frequency for changeover and tool change is its use of the Sandvik QC quick-change tool system on the Citizen A32, which allows the setter to change all six turning tools in less than 10 minutes.

To Labfacility this is important as thermocouple materials are so demanding to machine especially when nickel chrome, nickel aluminium and cupro-nickel alloys are involved.

These are in addition to a wide array of stainless materials such as 431 magnetic iron and the normal copper, brass and steels.

Due to the expectation of swarf problems from these materials, Russell’s machine specification for the A32 included Citizen’s 2,000psi Coolblaster II and from experiences gained, this programmable high-pressure coolant system is to be retro fitted to the K-16 as well.

‘Coolblaster gives so much added security to the turning process, helping to avoid “birds nesting” of swarf that would be so troublesome when running unmanned with these difficult materials,’ said Russell.

He also cites its advantage when drilling deep holes; the system has the pressure to evacuate swarf chips without pecking cycles and the ability to keep coolant at the cutting edge of the tools.

Coolblaster also ensures the collet on the subspindle is regularly flushed and is free from contamination ensuring a true pick-up of parts for finish machining once they are exchanged from the main spindle.

Parts produced include compression fittings, glands and plain and threaded pot seals between 0.5mm and 6mm diameter, probe tips, terminal head fittings, connector pins, bayonet caps and adaptors, caps and adaptors and locknuts, which currently total some 300,000 parts a year.

Batches tend to be between 1,000 and 5,000 parts.

However, a connector pin can be required in batches up to 10,000 in difficult materials, and these are mainly run on the K-16 at a frequency of every three weeks or so.

To simplify changeovers, Labfacility is able to group together some of the 13 different product types produced for its own use into standard material sizes of 8mm, 13mm and 16mm.

One important saving on material has proven to be very welcome by the production team through the turn-mill capability of Citizen machines and particularly the extra torque given by the A32.

This has produced savings of up to 40 per cent against the price of each metre length of some of the more difficult materials by milling hexagons on the machine rather than having all the problems associated with bought-in hexagon material.

‘Setting and machining can be faster, tooling lasts longer and a milled hexagon really looks a precision part, and this round material is easier to obtain and stock,’ said Russell.

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Citizen has developed an adaptive guide bushing (AGB) solution, which is intended to enable the use of a cheaper bright bar instead of the normal ground or specially prepared bar material.

The AGB solution is available on the company’s range of CNC sliding-head lathes.

The system will accommodate any tolerance variation on the outside diameter of the cheaper material, while allowing the normal machining speeds and feeds, consistent accuracy and high concentricity levels to be maintained on components.

Available on all new Citizen machines supplied through Citizen Machinery UK of Watford, the AGB system replaces the standard rotary guide bushing, which, because of its operating diameter, is fixed and requires the use of close-tolerance ground material when strict size and geometric tolerances have to be maintained.

The problem with more standard bright bar material is the wider tolerance limits of the rolled material, which permits the outside diameter to fluctuate in size from bar to bar, according to the company.

On all sliding-head machines, the standard rotary guide bush uses a single taper to provide the mechanical actuation, meaning that the length of the bearing surface of the bush to support the bar is normally restricted to between 15mm and 19mm.

It also creates a non-parallel closing action for the bush, meaning that if the barstock is on minimum tolerance, it is only gripped by the front of the collet.

This effect can also cause the headstock collet to lose position and have a detrimental influence on the surface finish of the part.

If, however, the material is close to its top limit, the gripping action of the collet is only applied to its back end.

Further problems can also emerge when machining titanium, for instance, or gummy materials such as certain stainless steels when the sliding-head machining process attempts to draw the bar back into the guide bush.

The Citizen AGB has a double taper that initiates a more positive parallel closing action along its material support length of 50mm, which is up to three times longer than is achieved with the single taper.

As a result, constant pressure is applied around the bar material and, as a result of its positive action, the bushing is able to accommodate material with a size variance of +/-0.1mm in diameter.

Since the Citizen AGB always maintains a constant pressure, the bar material will remain on the machine centre line, minimising run-out and enabling tighter concentricity to be maintained during the cutting process.

With the AGB system, a protective shield disc is provided to minimise contamination from fine particles of swarf and, with its locking nose cap, quick and easy removal from the front of the machine spindle is possible using a wrench and pin spanner.

The unit can also be assembled away from the operating area.

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Gibbs Gears Precision Engineers produces around 200,000 of its gears at its Stoke Mandeville subcontract and development machine shop on a Citizen M32-V CNC sliding-head mill-turn centre.

These gears are produced in single-cycle operations involving turning and gear hobbing, with certain gears also requiring the additional milling of drive hexagons.

On the back of the Citizen installation, Gibbs Gears was able to secure a contract that resulted in the retention of gear production in the UK and reversed plans by the customer to source these volume parts offshore and, as a result, close its UK gear machining facility.

‘When we originally found out the customer was possibly closing its UK operation for gear machining, we made an approach and, with the help of Citizen Machinery UK, quoted against its targeted overseas suppliers for the range of 30 fine-pitch spur gears between 5mm-diameter 0.3 module and 18mm 0.8 module,’ said Reece Garrod, managing director.

During the negotiations, technical director David Worthington approached the supplier of sliding-head machines and had sample components produced.

Due to the locality of Citizen Machinery UK at nearby Watford, he ordered the Citizen M32-V.

Worthington said: ‘Although the machine was over capacity with its 32mm bar size for our immediate needs, when the largest gear we were quoting for was being produced from 18mm material, the machine guaranteed the additional rigidity for heavier and greater consistency for hobbing teeth without vibration.

‘It also gave us the added flexibility to produce further subcontract components when needed,’ he added.

The type of contract that Gibbs Gears is now servicing tends to be more demanding and margins are being squeezed, especially in the early days of projects, but, according to Garrod, the use of technology such as the Citizen gives added flexibility for change and the development of processes that help to boost productivity and performance.

Gibbs Gears has invested approximately GBP600,000 over the last 18 months, with CNC replacing a considerable number of manual gear cutting machines.

The business is also said to be reaping success in subcontract machining involving five-axis turning and milling, for which it has now added the capability to produce very complex 32mm turned part machining on the 13-axis Citizen M32-V.

This machine is able to carry up to 72 tools and cut with three tools simultaneously, which reduces cycle times.

Worthington describes the Citizen as the perfect example of automating the gear cutting process.

Previously, the customer’s in-house machine shop produced the 30 spur gear types on a CNC lathe followed by autoloaded hobbing cycles.

He said: ‘With the Citizen, we go from bar, perform perfectly balanced turning and milling as required, then rough and finish hob the teeth.

‘The parts, produced in batch sizes of between 250 and 5,000, pass seamlessly from main to subspindle and into the collection tray in cycle times of between 60 and 90 seconds depending on size.

‘The only time we have to do any further work is if we have to broach splines or keyways, meet very special process requirements such as heat treatment, grinding or special surface finishing,’ added Worthington.

Most gears are made from EN34 steels.

However, to meet the latest medical contract, component parts are also turned and hobbed out of stainless steel.

Production control and setters work together to group parts into material types and, while bar sizes tend to be 10mm, 13mm and 18mm, to further reduce lead times and speed changeovers investigations are under way to standardise on one material size and use the rigidity and twin-tool turning capability of the Citizen to quickly size the part.

The Class 8 spur gears range from 6mm in diameter by 39mm in length with a 2mm bore and 0.3 module gear teeth to 18mm in diameter by 19mm in height with an 8mm bore size and 0.8 module.

Using carbide hobs, cutting speed trials have been performed to strike an economic balance between floor-to-floor time and effective tool life.

In developing the process, Citizen Machinery UK’s application engineers used the machine’s synchronised hobbing software to provide the flexibility to experiment with the number of passes and feeds and speeds to not only minimise cycle time, but to obtain the level of quality in surface finish on the tooth form to meet the classification required.

As a result, it was found to be significantly quicker to rough and finish the gear than hob the teeth in a single pass.

By roughing using two passes at 1,100rev/min and 0.09mm/rev feed rate, the gear is finish hobbed with the same tool at 3,000rev/min and 0.02mm/rev feed.

Within the machine software, the hob is automatically returned to the start position, which means that it provides the flexibility to action the roughing and finishing operations at the most cost-effective and practical point in the overall machining cycle.

Speeds and feeds can also be independently selected to obtain the desired cycle time or surface finish and are not locked into set mechanical ratios between hob and spindle rotation.

Through a macro, Citizen Machinery UK was also able to introduce to the program a hob shift via one of the two Y axes of the machine.

This enabled the cutter to be automatically moved a distance of one tooth pitch following the processing of five gears.

Not only does this ensure even wear and effective control over the tool, but it also helps to maintain a consistent tooth form without burrs.

Around 2,000 parts are produced per hob before it is reground or replaced.

A further advantage from the Citizen software on the M32 is hob phase, which allows features such as the milling of the drive hexagon on one type of gear shaft to be synchronised and aligned to a particular gear tooth or another key element of a component.

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Rem Sales has announced the introduction of two Tsugami Precision Swiss turns, available for delivery from March 2010.

The 20mm models, the Tsugami S205 and Tsugami S206, are suitable for the production of complex parts.

Live tools for cross and face operations are found on the main and sub spindle.

A two-path control permits true, simultaneous operation of the main and sub spindle, which reduces cycle times.

The modular, spacious tool zone allows driven tools to be moved from main to sub spindle and from face to cross positions with ease.

The S206 has the same capabilities of the S205, plus backworking y-axis movement.

A Fanuc 31-iA control is standard on both models, which also can accommodate an optional ‘chucker kit’ that allows the machine to be run as a Swiss turn or fixed-headstock lathe.

The fixed-headstock configuration can use unground bar stock, eliminating bar remnants and improving part concentricity.

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Conmed Linvatec Biomaterials is using a Krauss-Maffei Berstorff Ultra Glide laboratory extruder to produce biodegradable compounds based on lactic acid.

The Finnish-based manufacturer of medical products opted for the extruder as it meets stringent requirements of this special field of industry.

For the production of implants used in the human body, such as screws, plates or pins applied for fixing bone fractures, for instance, cleanroom conditions are a definite must.

The Krauss-Maffei Berstorff extruder was designed in strict compliance with the Good Automated Manufacturing Practice (GAMP), an internationally accepted guideline for the validation of computer-assisted systems in the pharmaceutical industry.

The control system used for this application has to operate like a black box documenting all production steps involved.

Implants based on polylactide plastics fix the bones in position just like conventional implants offering at the same time the decisive advantage that they need not be removed in a second surgery after the fracture has healed.

As they are made of absorbable polymers, they enhance the fracture healing process so that the patient is relieved from pain within less time.

Krauss-Maffei Berstorff said that this extruder has been proven for producing PLA compounds.

The Ultra Torque model in the ZE series is characterised by high drive power for screw speeds of up to 1,200rev/min and high material output rates.

At the same time, the machine ensures rapid and careful processing, which is of particular importance with these compounds.

With the Ultra Glide version, the extruder screw is extracted within a minute from the processing section, which facilitates access to the screw and substantially reduces the cleaning time in the case of a recipe change.

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Holton Crest has introduced the Holton2 range of continuous rotary extruders.

The three models in the range - the HC1100, HC2200 and HC4000 - are wholly European-sourced.

Many of their features can be integrated into Holton’s existing products and designs for material handling, material conditioning and product handling.

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The Inoex Advantage system for automated dimensional product changes during production of plastic pipes is a retrofitting technology that can be delivered as an integral part of an extrusion line.

Chinese extrusion specialist Liansu has decided to offer this combination.

On request, extrusion lines are now equipped ex works with an integral Advantage system.

On this ground, a cooperation was set up with Inoex.

The Liansu Group manufactures plastic pipes and extrusion lines.

Liansu’s machinery manufacturing division engineers, produces and supplies extrusion lines including extrusion dies for processing PVC, PP and PE.

The cooperation contract set up with Inoex covers the full integration of Advantage when requested by the customer.

This solution will be added to the product range offered by the China-based company.

Presently, Advantage still has its own operation terminal.

In the future, the plan is to integrate the control unit for automated dimensional changes into Liansu’s extruder control.

The cooperation agreement also encompasses other Inoex systems: the gravimetric product series (Saveomat) and ultrasonic measuring systems (Aurex).

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Putnam Plastics has developed technology for producing thin walled, large diameter, low durometer urethane extrusions.

Commonly used in minimally invasive medical devices, such extrusions have been fraught with design challenges.

The development of this advanced fabrication technology has provided medical-device OEMs with increased design freedom and production capabilities and clinicians with more sophisticated tools with which to improve the quality of care for their patients.

The motto in many medical-tubing applications is ‘bigger, softer, thinner’.

With the continuing evolution of less invasive surgical techniques, clinicians are pushing device engineers to fit more and more technology through a working channel of limited size.

New techniques such as Notes (Natural Orifice Transluminal Endoscopic Surgery) and SPA (Single Port Access) are driving device designs consisting of fewer and larger access points, with the goal of maximising the working space within.

These advanced techniques also require considerable articulation of the device within the body with minimal operating forces.

For the device engineer, this results in the need to use on the outer body of the device extrusions that are larger in diameter, have thinner walls and are highly flexible and durable.

From a functionality standpoint, thermoplastic urethane is a prime choice for such demanding applications.

However, when considering design-for-manufacturability, there are tremendous challenges to overcome.

Byron Flagg, product manager at Putnam Plastics, said: ‘As diameter increases and wall thickness and durometer decrease, the extrusion process becomes more unstable.

‘This instability, which results in larger tolerances and lower yield rates, has forced device engineers to compromise their designs accordingly.

‘Even after fabrication, such extrusions are extremely difficult to handle without contamination or damage, resulting in quality non-conformances, higher unit price and overall lower value for the customer.’ After extensive development, Putnam Plastics has implemented a proprietary combination of custom equipment and advanced processing conditions to address the historical challenges involved in the fabrication of this type of tubing.

Improved process stability results in a larger design envelope for device engineers; improved material-handling techniques reduce costs by increasing yields and product quality.

Take, for example, any given 80A durometer urethane extrusion with a diameter greater than 0.5in (12.7mm).

If the minimum feasible wall thickness had previously been 0.015in (0.38mm), it has now been reduced to 0.003in (0.08mm).

If the OD tolerance had previously been +/- 0.010in (0.25mm), it has now been reduced to +/- 0.002in (0.05mm).

These tangible improvements reduce tolerance stack-up and allow more efficient device design.

After fabrication, advanced handling techniques allow the finished components to move on to the next stage of manufacture, free of defects or contamination.

This new capability is widely applicable across a broad range of custom extrusion designs with the greatest impact in ODs greater than 0.500in and wall thicknesses of less than 0.015in in urethane durometers lower than 90A.

As with all of Putnam Plastics’ custom fabrication technologies, this new capability can be applied cross functionally and integrated into designs that include features such as co-extrusion, multi-lumen and wire reinforcement.

The end result is a wider envelope of possibility for device-design engineers to meet the functional needs of clinicians without compromise.

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