Since a bar-fed CNC lathe was installed, it has operated virtually 24 hours a day with very little manual intervention other than for set-up, bar replenishment and part inspection.
Usually when a machine sits unattended in the corner of a workshop it means that something is not quite right. However, in the case of the Colchester Tornado 'Lights-out' A50 CNC lathe installed by RK International of Erith, at Vire Engineering of Totnes, nothing could be further from the truth. Since the machine was installed, it has operated virtually 24 hours a day with very little manual intervention other than for set-up, bar replenishment and part inspection.

This has firmly established a reputation within the company for consistency, reliability and accuracy and the only complaint from the shopfloor being that there is only one installed.

The south Devon based company is the machining subcontract arm of a small group of companies under the ownership of Mrs Jan Vincent.

One of its principal activities is to produce a range of high quality hose and pipe fittings for motor sport applications from Clubman up to Formula One.

They are supplied to sister company Exact Engineering for distribution as discrete fittings and made-up hose assemblies for brake, fuel, oil and coolant systems.

In addition, Vire also produces precision turned components for defence and aerospace applications.

As Mrs Vincent explains: 'Most of the parts we produce are to established designs which add up to around 2,500 different components made from stainless steel, aluminium, titanium and mild steel.

As part of the production process, many are plated, polished or specialist treated.

Most parts are produced from bar which have a hose attachment at one end and a coupling or banjo union at the other in batches that range between 50 and 2,000.' The company is a long time user of CNC machine tools, particularly for external subcontract machining.

In the past, most of its fittings have been produced using plugboard semi-automatic lathes which were very cost competitive because of the low hourly rate.

This is particularly so on larger batches due to the use of form tools to generate outside diameter profiles.

Les Hutchings, Vire's general manager, comments: 'Accuracy requirements on the couplings range from +/-0.1 mm down to +/-0.025 which was just within the capability of the plugboard machines.

We tended to use CNC for subcontract work but in the run-up to buying the Tornado from RK International we were looking to find a machine that could service both sides of the business.

In practice, the Tornado has proved very productive which we put down to the 'Lights-Out' package supplied with it.' The Colchester 'Lights-out' package comprises the Colchester developed MBF 1000 short bar magazine, Renishaw turret-mounted Tool-Eye probing for tool set-up, an infra-red linked Renishaw touch probe for parts gauging, a parts picker with conveyorised off-load and a swarf conveyor.

The turret has the standard 12 tool stations of the Tornado and control is by a Fanuc 21-Ti system.

However, the machine is different due to the integrated axis torque monitoring, work scheduling software and a sister tool replacement capability.

The MBF 1000 bar feed will hold 12, 40mm bars and up to 10, 65mm diameter bars and is fully integrated with the machine.

This means changeover takes less than 15 minutes to switch say from hexagon to round bar and programming is quick at the machine's Fanuc control due to the dialogue input.

To help control production quantities when running unmanned, each bar is measured by the bar feed system and the number of programmed pieces available from each bar calculated which ensures the machining cycle is stopped when the batch is completed.

'We saw the Tornado as filling the gap between the plugboard machines and our existing CNC lathes.' Les Hutchings explained: 'In practice the unmanned running capability makes it cost-competitive with the plugboard machines as the direct labour requirement is so much lower.

The Tornado provides far more consistent accuracy than the plugboard machines with very little need for adjustment so its proven to be very popular on the shopfloor.' This statement is borne out by Ian Andrews who regularly programs and sets the machine.

'We set the Tornado for batches of 1,000 to 15,000 parts and then do a routine dimensional check every 45 minutes or so.

During the time that the machine has been in use I rarely make any offset adjustments to keep a job in tolerance because the tool monitoring system is so effective and repeatable once the limits are established.' The axis torque monitoring limits are set to replicate empty, worn or broken tools by teach repeat, operator input or by insertion into the part program.

When the critical point is reached the software automatically initiates an immediate stop or sister tool replacement.

At anytime the operator can check look at the screen to see in real time the tool loadings.

Explains Ian Andrews: 'In practice, we use the sister tool replenishment to double up on the roughing tool and small diameter drills and find we get very consistent results in terms of both surface finish and tool wear patterns.

While most jobs are mild steel the Tornado also performs well on stainless steel parts.

It has the advantage of constant surface speed machining while the short bar magazine means we can run at optimum speed at anytime without vibration, so finish is always very good.' Tim Woodward, Vire's assistant foreman points out that due to the single point turning advantage against the plugboard methods, once the tool is initially set the insert can be quickly indexed or replaced in situ and an offset adjustment made.

Because the plugboard machines used form tools they need to be taken-off, reground and re-set.

'Even if there is a spare tool to hand, the changeover process took far longer which means on small batch work we can sometimes set the Tornado and complete the run in less time then it would take to set a part up on the plugboard.' Reflecting the decision to purchase from RK International, Mrs Vincent comments: 'The Tornado has really proven to be cost-effective because it can be left unmanned at night.

It is reliable and has been holding tolerances consistently across a complete batch of work.'