Small parts machinist described Citizen CNC sliding head automatic lathes with linear motor axis drives as ’seriously quick’ and very consistent in maintaining quality.
Precision small parts sub-contractor, Tenable Screw Co, recently had installed four Citizen R07 Type VI CNC sliding head automatic lathes The machines feature linear drive technology for fast machining of bar stock components They complement Tenable Screw’s existing Escomatic coil fed machine production of small components, where previously sourced coil is no longer readily available.
Managing director, Simon Schlaefli, of Tenable Screw described the new Citizens as: “Seriously quick, very consistent in maintaining the high levels of quality demanded and a first class competitor to cam machines”.
The first three R07 installations demonstrated that they achieved the same output as five previous Citizen B12-V machines. The job was a high volume, high accuracy, automotive contract, for which a further machine was ordered and installed.
Each of the original Citizen RO7s, had been running the same 150 production hours/week as the five B12’s but producing parts 42% faster, said Citizen.
Schlaefli first saw the compact linear driven Citizen machine in its original R04 version in operation at a watchmaker in Switzerland.
He realised the potential for the type of small turned parts his company is producing at his Merton, near Wimbledon, machine shop.
At the time, he felt that its 4mm capacity could possibly be too restrictive .
When Citizen introduced the larger R07 7mm capacity version in 2006, Schlaefli changed his mind and suggested to Citizen Machinery UK of Watford certain changes to make it more versatile for his production.
Citizen agreed a process application would be developed with his company for the automotive component in question.
As part of the agreement, Citizen Machinery UK loaned the first machine for three months.
An application team, with Citizen in Japan’s approval, worked with Schlaefli and his machine setters to carry out the changes that enabled a massive reduction in cycle time of 14s on an automotive part.
Indeed, such was the success and the return generated from the trials, that Tenable Screw paid for the machine, ordered two more.
Tenable even paid a premium to air freight the two machines from Japan rather than face delays for the normal sea transport.
Schlaefli said: “It’s simple economics – our savings meant the additional cost of air freight was recovered in just four weeks’ production.
Also, we were able to release the five B12s to free existing bottlenecks on shorter running jobs which all helped with the decision”.
* Close working relationship – although Schlaefli keeps a watchful eye on developments from other machine tool suppliers, the close working relationship with Citizen Machinery UK and familiarity of control and setting has become a serious preference on the shopfloor.
He made the point: “Our first Citizen B12 bought in 1997 is still performing well and runs round-the-clock.” He maintained that back-up and support and the constant development of the machine range means there is always a justification to acquire more machines from the same supplier.
About the Citizen R07 Schaefli said: “The B12-V was originally seen as being very quick on automotive parts but the new linear driven machines have delivered the economies that have kept us competitive in an important contract”.
He continued: “Meanwhile, we have not been exposed by the investment should the contract be reduced or lost.
A machine such as this will deliver savings on a whole host of other components thus making it an ideal investment”.
Tenable Screw’s customer base spans consumer and automotive electronics covering Tier 2 and 3 suppliers, wiring harnesses, dental, armature and solenoid parts, aerospace connectors, inserts for moulding and even musical instrument components.
Schlaefli commented: “We have a distinct advantage from our mechanical machine tool experiences in that we are able to engineer special applications on medium to long running jobs”.
* Mechanical knowledge – this mechanical knowledge is what spurred the process development of the Citizen R07 with Citizen Machinery UK to produce the high volume 90mm long automotive components.
The machine spindle is run at 14,000 rev/min and the cycle involves simultaneous rough and finish turning within a 0.05mm tolerance using opposed tools in the platen slides.
Schlaefli said: “The advantage of having two platen slides performing machining operations together enabled us to reduce cycle times by almost 14s, compared to the B12, which has helped ‘offset’ the 50% hike in raw material costs since the job started”.
* Machine modifications – one of the most important changes devised by Tenable Screw and Citizen Machinery UK was to fit a self-opening, fixed bush arrangement that enabled the single stroke of the machine to be increased from 50mm to 90mm without re-chucking.
As the headstock is closer to the bush, Tenable Screw is now able to get an extra component out of a 3m bar length.
Also, by reducing the length of the bar end remnant, an additional 3% of material is now saved per bar.
Further savings have resulted from the IEMCA 118 bar feed system: the bar end is ejected much quicker saving 10s on each bar loading cycle.
For another component produced on the Citizen R07, Tenable Screw specified the polygon milling function to replace the hexagon milling operation on a 3.8mm diameter hexagon socket.
The change allowed some 6s to be saved on the cycle time.
The part has a tolerance of 0.03mm and the complete cycle involves the following.
* Drilling.
* Milling of two slots 0.2mm wide by 5mm deep.
* Milling of a bucket area for solder connection.
* Facing of the front of the component.
* OD (outside diameter) turning and complete deburring to remove all sharp edges.
The 11mm long hexagon is polygon turned to avoid the additional cost of purchasing non-standard bar.
It also solved problems associated with machining hexagon rod such as straightness, restriction on speed, special collets and possible added down time.
In addition, to complete the ’single hit’ cycle, as the part is ejected, two tangs are automatically clinched ready for assembly.
The Tenable Screw developed polygon tool is held in the front tool post and comprises two carbide blades brazed into the body of the tool.
The cycle time takes just 1.5s to produce the six flats with the driven tool rotated at 7,500 rev/min synchronised with the 2,500 rev/min spindle speed programmed into the machine’s control.
For the rest of the cycle, the machine is run at 12,000 rev/min.
* Citizen R07 sliding head automatic lathe – the linear slideway 6-axis Citizen R07 has a subspindle and will hold up to 13 tools, three of which are driven.
The machine is very compact, having a ‘footprint’ of 560mm x 1265mm.
It is totally electric and electronic in action and therefore does not require hydraulics or pneumatic connection.
The main spindle is powered by a 1.1kW motor and operates at up to 16,000 rev/min.
The subspindle is driven by an 0.5kW drive at up to 8,000 rev/min.
* About Tenable Screw – Tenable Screw has three operational centres in the UK: the headquarters in Merton operates 45 CNC machines; a production site in Coventry, largely involved in second operation machining and multi-spindle production, serves the Midlands and another sited in Marlborough covers production of high volume components using cam and rotary transfer machines.
Altogether 110 people are employed and company turnover is some GBP 8 million.
Almost 25% of production is directly exported and around a further 20% is subsequently exported by Tenable Screw’s UK customers for final assembly overseas.
Quite late in investing in CNC equipment, the company installed its first in 1997.
In 10 years it has purchased 45 CNC machines, of which 30 are Citizen.
In the financial year ending August 2007, six Citizens were installed at Merton; three L20s, two incorporating the 2000 lb/in2 CoolBlaster high pressure coolant system and the R07s.
The fourth RO7 was installed in December 2007 for producing the connector parts. Request a free brochure from Citizen Machinery UK …