Product category:
CNC automatic lathes
News Release from: Star Micronics GB | Subject: Star SR-20R sliding-headstock lathes
Edited by the Manufacturingtalk Editorial
Team on 09 October 2002
CNC sliding head autos bring shafts back
home
A major restructuring of shaft production at a lawn mower factory has resulted in the company's electric motor armature shafts being manufactured in-house on CNC sliding head autos.
A major restructuring of shaft production at the Stowmarket factory of Atco Qualcast, part of Bosch Lawn and Garden Division, has resulted in the company's electric motor armature shafts being manufactured entirely in-house, whereas 50 per cent were previously subcontracted The shafts are used in a wide range of products including lawnmowers, hedge cutters and trimmers
This article was originally published on Manufacturingtalk on 14 Jul 2000 at 8.00am (UK)
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Two new bar magazines capable of increasing the productivity of an automatic turning machine by typically 10 percent have been introduced to Britain and Ireland by A and S Precision
Underpinning the initiative is the installation of a new turning cell that works round the clock, five days a week and at weekends as well according to demand.
The cell comprises four Star SR-20R sliding-headstock lathes supplied as a turnkey package by A and S Precision.
Included on each machine are a long parts collector to accept shafts as they are pushed through the sub-spindle guide tube, a swarf conveyor, initial programs for the capability trials, Berkswell Graf tooling and FMB bar magazines.
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Magazine feeds small diameter, full-length bars
Designed for feeding sliding-head and fixed-head automatic lathes with bar in the diameter range 2 to 16 mm, the new Turbo 2-16 has been added to the lower end of FMB's standard bar magazine range.
Only the statistical process control equipment was sourced separately from Mitutoyo.
According to Manufacturing Engineer, Steve Gooding, GBP 200,000 per year is being saved on bought-in armatures and there is a further GBP 65,000 labour cost reduction internally.
The latter results from being able to machine the armatures on the Stars in a single hit, whereas the previous time-consuming method involved two and sometimes three operations.
The first Star was installed in 2000 to produce a cylinder spindle for a popular model of lawn mower.
This mill-turning sliding-head machine replaced two fixed-head lathes and eliminated subsequent operations on a grinder and a drill.
The project was so successful that by the end of 2001, a further three Stars had been added in a project costing GBP 330,000, an investment that will be amortised within one and a half years.
The three latest machines have replaced a further nine lathes on the Stowmarket site, mostly CNC and all fixed-head, plus the same number of second-operation machines.
One setter / operator now looks after the entire cell.
Explained Mr Gooding, "Eighty to eighty-five per cent of the 25,000 steel shafts we produce each week are armatures.
Of those supplied by the previous subcontractor, some were found to be outside tolerance on key diameters.
We constantly achieve tolerance in-house on the Stars, as well as excellent roundness and concentricity, so quality is better not only of the armatures but also of other shafts we produce including the spindles for mower cylinders and rollers.
"Even the shafts we formerly produced ourselves on fixed-head lathes were not as accurate as they are now.
It would have been impossible to produce them in a single hit without using steady rests, which would have reduced production flexibility, and in any case accuracy would not have been guaranteed.
Star sliding-head machines lend themselves to shaft production as the gang tool post works directly at the guide bush, so there is no deflection of the part during OD turning.
"In addition, some of our larger armatures need reverse endworking and cross drilling and these operations are completed in-cycle by live tooling stations in the Star lathes.
This also contributes to accuracy by eliminating tolerance build-up through multiple set-ups." To prove the point, Atco Qualcast has installed a Mitutoyo SPC system comprising a dedicated laser micrometer fixture for armature shafts and a PC running Measurelink Plus software.
Six diameters are checked every hour and if values start to drift out of the tolerance band, the relevant offset is changed at the machine concerned.
This is in addition to first- and last-off quality checks for each production run plus patrol inspection.
He went on to say that choosing good quality bar and handling it properly is also important in precision turning.
Atco Qualcast has standardised on procuring steel bar, mainly EN8 and 226M44, directly from the mill in wooden containers to guarantee straightness.
The containers are mounted on stands by each of the four machines so the cell operator is able to pick up a supply of bar at a convenient level and move only a short distance to replenish the inclined table of each FMB Turbo 3-26 magazine.
Ten different bar sizes are needed to produce all shafts, which range from 6 to 20mm in diameter and up to 600mm long.
"The bar magazine also impacts significantly on production efficiency," says Mr Gooding.
"We looked at four suppliers for the cell before choosing A and S Precision and the bar feeds offered by the others were all slower to change over than the FMBs.
"We are not talking about seconds here; the FMB can be re-equipped including collet change to accept a new bar size in around five minutes, whereas the worst of the other magazines took 45 minutes.
It is also easy to learn how to change over an FMB and punch in the data to suit the length of the next component." All bar magazine manufacturers have standard packages to interface with a wide variety of lathes, but in the case of Star and FMB, there is a special relationship in that A and S Precision is Star's UK subsidiary as well as being the UK sole agent for the German-built magazines.
It follows that the standard offering to customers by A and S will be this combination and many hundreds have been installed throughout the UK and Eire.
From a customer's standpoint, this supplier's experience of interfacing these two pieces of equipment is complemented by having a single source of responsibility for service as well as supply.
Another part of the 'package' supplied to Atco Qualcast to speed changeover, implemented shortly after the initial installation, was the provision by Star of a smart card (32 MB memory PCMCIA card) able to store all of the 70 programs used in the cell.
Each shift operator carries it around and when a Star needs to be changed over for the next batch, the card is simply plugged into the Fanuc control and the program extracted in about 30 seconds.
The previous method of downloading programs from a laptop could take as long as five minutes.
Concluded Mr Gooding, "The cell has transformed our shaft production, giving us full control over armature quality as well as improving productivity, supply to assembly and ultimately the quality of the end product.".
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