Auto Turned Products

October 9, 2015

Discipline: Turning
Machine Type: Multi-Spindle
Manufacturer/Model: INDEX MS 40
Materials: Steel
Client Type: OEM/Subcontractor
Sector: Automotive & Petrochemical

Background

In 2012, turned parts subcontractor Auto Turned Products (ATP), a long-time user of cam-type multi-spindle autos and CNC single-spindle lathes, decided to evaluate CNC multi-spindle turn-milling. A German-built Index MS 32 six-spindle CNC auto of 32 mm bar capacity and with an opposed spindle for endworking was duly bought from UK agent, Geo Kingsbury.

Since that time, the machine has been largely dedicated to producing a specific family of automotive components economically in batch quantities from 250,000 down to 10,000-off, work which otherwise would have been done by six single-spindle lathes.

The subcontractor’s experience with the first CNC multi was so positive that it decided to standardise on this type of equipment for all turning machine purchases in the foreseeable future. It has already installed a 40 mm capacity Index MS 40, which arrived in July 2014, and a second, similar model is due for delivery in August 2015.

Eventually the company plans to have nine Index CNC multis installed in a specific area that is currently a cam auto shop within its factory in Round Spinney, near Northampton. All of the company’s 40 remaining single-spindle cam-type lathes were sold or scrapped by the end of March 2015 and the stock of 22 multi-spindle cam autos will be gradually reduced, although a few will remain long-term for carrying out simpler, long-running jobs.

Production engineer Vic Pais, who is in charge of all machine tools at the Northampton factory, described the transition to CNC multi-spindle machining as extremely rewarding. He added that ATP would have struggled to cope with the significantly raised level of throughput at the factory without the high production output from the CNC multis.

Financial manager Eddie Craddock advised that the first Index multi paid for itself within two years. He said, “Buying a CNC multi involves a considerable investment, so embarking on a business plan to own nine of them is not for the financially faint-hearted.

“Nevertheless, we have calculated that investing in these machines is justified. It is not only because the high output reduces unit production costs but is also a result of the speed of programming and set-up, which lowers economical batch size to the low thousands.

“Around 80 per cent of our work is in the automotive sector, to which the Index MS machines are devoted. They produce batches of components down to typically 10,000-off for prestigious marques including Jaguar, Land Rover, Rolls-Royce, Bentley and Aston Martin.

“However, we are now targeting petrochemical work, because the difficult materials used in that industry play to the strengths of the Index multis, and we would consider runs as low as 3,000-off because the machines are so quick to change over.”

Mr Pais confirmed, “If the same bar is used, a setter can retool an Index multi for a new job in a couple of hours, which increases to about half a day if the bar size needs to be changed over as well. The equivalent time for a cam multi could be two weeks.”

In the 50-plus years since it was founded, ATP has used a wide range of turning machines, including cam-type and CNC multi-spindle autos and twin-opposed-spindle, single-spindle lathes, both sliding-head and fixed-head types.

Generally speaking, the output from one CNC multi is equivalent to that of three to four CNC, single-spindle lathes, but in a more compact footprint and with lower operator overhead.

Comparing a CNC multi with a cam-type multi, Mr Pais said that the former can produce more complex components three times faster than the latter. Factored into the calculation is 95 per cent uptime of the CNC spindles compared with 60 per cent for a cam multi, as well as the latter’s long resetting time. It means that for a given production output, factory space take up by Index multis is three times less than that required by cam multis, with a consequent reduction in power consumption.

Furthermore, one setter and one operator can attend three of each type of machine, so for the same output there is a three-fold saving in labour with the Index CNC multi. This will lower ATP’s headcount as time progresses and a policy is already in place of not replacing staff that retire; two have already done so this year.

Mr Pais continued, “These are not the only benefits. The quality of finish on machined components is far superior on an Index multi compared with all other lathes we use.

“Unlike with CNC multis, cam-type equivalents suffer from having to use the same feeds and speeds at each spindle position, compromising cutting conditions at some stations – and they are not able to perform second operations either.

“They also have to deploy expensive form tools to achieve certain features that are trivial to single-point cut using low-cost indexable inserts on a CNC equivalent.

“For example, we transferred the production of fairly complex body mount spacers in S355 steel to the MS 40. Form tools previously wore out quickly on the cam multi and the surface finish deteriorated, so we sometimes found ourselves producing scrap, whereas the Index multi machines them without a problem.”

Vastly longer tool life on an Index multi, sometimes by a factor of 30 or more compared with all other types of lathe, is another significant advantage for ATP in terms of both reduced tooling costs and less production downtime for replacing cutters. The harder and tougher the material being machined, the greater the benefit. Tool longevity is partly a result of the Index multis’ 80-bar through-tool coolant with particle filtration to 20 microns, and also down to the rigidity and vibration resistance of the machine construction.

Mr Pais cites a particular job where an M14 tap performs 100,000 operations on an Index multi before it is routinely replaced, even though it would operate satisfactorily for longer. The same job on a cam multi requires the tap to be replaced every 3,000 to 4,000 parts.

In another case, an end mill lasts for 2,000 components when machining steel components on a sliding-head lathe, yet it cuts 21,000 parts on an Index multi. A further instance is an insert that can part-off 300 components on a slider but 4,000 on a CNC multi.

Not only is productivity increased through fewer tool changes, but bar wastage is lower as well, as cutter reliability reduces the chance of the tool breaking and producing scrap. Stock savings can be substantial, especially when tool breakages are avoided during unattended running.

Mr Pais concluded, “Index multis are the future for our company. They inject big numbers of high-accuracy components into our system in a short amount of time and are economical for shorter batches.

“The only problem we have is loading 3.2 metre bar or tube into the six-channel bar magazines quickly enough, as the machine gets through stock at an incredible rate, especially when a relatively simple part is coming out every few seconds.”

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