Keeping an open mind saves machining cycle time

While some companies prefer a particular supplier, this subcontractor keeps an 'open mind' policy that often saves cycle times, as in this case with a sliding head lathe.

Companies often standardise on a particular make of machine to minimise operator training and so reach full production quicker, as well as to streamline programming and be able to interchange jobs easily.

Turned parts specialists using CNC sliding-head lathes tend to be particularly loyal to one machine vendor, but subcontractor Unicut Precision in Welwyn Garden City has always kept an open mind and carefully researches the market each time it reinvests, regularly going to the MACH and EMO exhibitions to keep abreast of latest developments.

Said joint managing director, Charles Kenny, "We came into 2003 with a record order book valued at over GBP 400,000, partly as a result of a new contract for three million fasteners from one of the leading aerospace companies in the USA.

Clearly we needed new sliders to fulfill the business, so we asked the leading vendors to carry out a cycle time study on the mild steel part.

"A and S Precision, the UK subsidiary of the Japanese sliding-head lathe builder, Star, came back with a solution that was 25 per cent faster than that achieved by other sliding-head lathe suppliers, taking the cycle time to below 10 seconds.

"We had looked at Star in the past but they did not have the right machine at the right price for our components.

However, the upgraded SA-16R was absolutely ideal for the US fastener, so we bought two of the Star machines, complete with FMB Minimag bar magazines from the same supplier, to give us the required capacity and to assure continuity of manufacture." Charles' partner and co-director, Jason Nicholson, went on to explain that the lathe has a driven rotary guide bush giving good control over turning operations, four rear end-working tools rather than the three offered by other machine builders on this class of machine, and three cross-working driven tools instead of the usual two.

Simultaneous machining is possible with main and sub spindles and there are driven tools for front-end working plus a 6-station tool post offering fast tool change.

Rapid traverse is 18m/min in all axes and spindle acceleration is high due to the integrated, 3.7kW / 12,000 rpm, high torque motor/spindle unit.

All these attributes combine to result in a highly productive machine with short idle times.

However, for machining the US fastener, the large discrepancy between cycle times achieved by A and S Precision and the other suppliers was only partly due to the specification of the Star lathe.

Indeed, there are no operations requiring driven tooling on this particular component and just two end working tools are used.

The main advantage derives from the ability of the SA-16R to minimise the non-cutting elements of the process.

It should be noted that all machine suppliers could have offered solutions capable of achieving similar cycle times, but not at Unicut's budget price of GBP 140,000 for the two-machine package.

Both Charles and Jason regard the SA-16R as particularly good value for money for the specification, especially as it is a 16mm diameter capacity lathe for a price equivalent to that of 12 mm machines offered by the competition.

Moreover, the Star lathes were available on short delivery, both machines being in full production within two weeks of order placement.

Now in its 11th year of trading, Unicut has since 1999 installed 11 sliding-head turning centers, systematically replacing all its single- and multi-spindle cam automatics as well as its second-operation machines, mainly two-axis fixed-head CNC lathes and milling machines.

All sliders on site have a sub-spindle, end working stations and driven tooling, so are capable of machining almost any component in one hit.

In this way, 99 per cent of second operations have disappeared from Unicut's shop floor.

Turnover has trebled in three years yet the number of staff has risen by only 15 per cent.

Crucially, work-in-progress has reduced from up to 60 per cent of output at any one time to virtually nil; so now if a bottleneck occurs, it tends to be in the cleaning and packing department.

"Had we not gone down this route we would not be here now," declares Charles Kenny.

"You have to lower your hourly rate more and more these days to win business.

If you are involved in a lot of second operation work you cannot make money, especially in an expensive part of the country like Hertfordshire.

"Compounding the problem is that people tend to order smaller volumes for short-lead-time, just-in-time supply, so a job can easily become unprofitable and you find yourself doing it just to keep the customer happy.

"As it is, thanks to our policy of going all out for single-hit machining on modern plant, we have gone from strength to strength.

Minimum economic batch size is down to, say, 10-off for a very complex part or 200-off for a simpler job.

Such is our reputation for quality that every time we install a new sliding-head lathe, we quickly fill it with work.

Concluded Jason Nicholson, "We use a tool management system whereby an insert or drill is never run to destruction but always replaced in good time.

Coupled with our policy of backing off from maximum possible speeds and feeds by about 15 per cent, we are able to engineer quality into our components, minimise inspection and end up with all good parts at the end of a shift.

"We progressed from 16- to 24-hour operation last year.

Our manufacturing philosophy allows just two staff to look after all 11 sliding-head lathes during the night shift, with very little setting, and we achieve up to 97 per cent availability across all our machines.".

Back to top