R07 Work Area
“Seriously quick, very consistent in maintaining the high levels of quality demanded and a first class competitor to cam machines,” is how Simon Schlaefli, managing director of precision small parts contractor Tenable Screw Co, describes the recent installations of four Citizen R07 Type VI CNC sliding head autos. The machines, that feature linear drive technology, enable fast machining of bar stock components and complement Tenable Screw’s existing Escomatic coil fed machine production of small components where previously sourced coil is no longer readily available.
Indeed, such has been the effect on the business by the R07 installations, where the initial three machines were achieving the same output as five previous Citizen B12-V machines on a high volume, high accuracy automotive contract, that a further machine was ordered and installed. Each of the original Citizen RO7s, had been running the same 150 production hours a week as the five B12’s but producing parts 42 per cent faster.
Mr Schlaefli first saw the compact linear driven Citizen machine in its original R04 version in operation at a watchmaker in Switzerland and realised the potential for the type of small turned parts his company is producing at his Merton, near Wimbledon, machine shop. However, in the cold light of day it was felt its 4 mm capacity could possibly be restrictive due to its work size capacity in the future.
But his view was changed when Citizen introduced the larger R07, a 7 mm material size version in 2006 and Mr Schlaefli put a proposal to Citizen Machinery UK of Watford on certain changes he would like on the machine to make it more versatile for his production. Following his approach it was then agreed a process application would be developed with his company for the automotive component.
As part of the agreement, Citizen Machinery UK loaned the first machine for three months and its application team, with Citizen in Japan’s approval, worked with Mr Schlaefli and his setters to carry out the changes that enabled the massive reduction in cycle time of 14 secs on an automotive part to be achieved. Indeed, such was the success and the return generated from the trials, that Tenable Screw paid for the machine, ordered two more and even paid a premium to air freight the two purchases from Japan rather than face delays for the normal sea transport. Said Mr Schlaefli: “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.”
Said Mr Schlaefli: “Investment has never been a problem for our company providing it can be justified.” Tenable Screw has three operational centres: the headquarters in Merton running 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 that covers production of high volume components using cam and rotary transfer machines.
Altogether 110 people are employed with a turnover of some £8 million. Almost 25 per cent of production is directly exported and around a further 20 per cent 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, and such has been the justification for improvement, that in the financial year ending August 2007 six Citizens were installed at Merton; three L20s, two incorporating the 2000 psi CoolBlaster high pressure coolant system and the R07s. The fourth RO7 was installed in December 2007 for producing the connector parts.
Although Mr 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. Also he points out: “Our first Citizen B12 bought in 1997 is still performing well and runs round-the-clock.” He maintains 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.
The Citizen R07 is a case in point. He says: “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. 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. “This,” said Mr Schlaefli, “requires a diverse range of skills. 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.”
This mechanical knowledge is what spurred the process development of the Citizen R07 with Citizen Machinery UK to produce the high volume 90 mm long automotive components. The machine spindle is run at 14,000 revs/min and the cycle involves simultaneous rough and finish turning to a 0.05 mm tolerance using opposed tools in the platen slides.
Said Mr Schlaefli: “The advantage of having two platen slides performing machining operations together enabled us to reduce cycle times by almost 14 seconds, compared to the B12 which has helped ‘offset’ the 50 per cent hike in raw material costs since the job started.”
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 50 mm to 90 mm without re-chucking. Due to the headstock being closer to the bush, Tenable Screw is now able to get an extra component out of a 3 m bar length and, by reducing the length of the bar end remnant, an additional 3 per cent of material is now saved per bar. And, further savings have been made in conjunction with the IEMCA 118 bar feed system whereby the bar end is ejected much quicker saving 10 secs 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 3.8 mm diameter hexagon socket which allowed some six seconds to be saved on the cycle time.
The part has a tolerance of 0.03 mm and the complete cycle involves drilling, the milling of two slots 0.2 mm wide by 5 mm deep, the milling of a bucket area for solder connection, facing of the front of the component, OD turning and complete deburring to remove all sharp edges. The 11 mm long hexagon is polygon turned saving the additional cost of purchasing non-standard bar and 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 1.5 secs to produce the six flats with the driven tool rotated at 7,500 revs/min synchronised with the 2,500 revs/min spindle speed programmed into the machine’s control. For the rest of the cycle, the machine is run at 12,000 revs/min.
The linear slideway Citizen R07 has six axes, a subspindle and will hold up to 13 tools, three of which are driven. The machine is very compact requiring very little floor space and has a footprint of 560 mm by 1,265 mm. It is totally electric and electronic in action and therefore does not require hydraulics or pneumatic connection. The main spindle is powered by a 1.1 kW motor delivering 16,000 revs/min and the subspindle by a 0.5 kW drive giving 8,000 revs/min.