CLAMPING MULTIPLE WORKPIECES AND 4TH AXIS INDEXING RAISE PROFITABILITY
The way in which workpieces are clamped for milling and drilling can make a big difference to a manufacturer’s bottom line. With this in mind, Armac Martin, a manufacturer of luxury fittings for kitchens and furniture, uses Chick Workholding equipment from the USA to increase profitability and at the same time improve quality.
Salisbury-based 1st Machine Tool Accessories, Chick’s UK distributor, provides the equipment and ongoing advice. The original contact was eight years ago, when Armac Martin progressed from using manual CNC turret mills in its Birmingham factory and started installing vertical machining centres (VMCs) from XYZ.
Their larger working areas were exploited to accommodate more components at a time in dual-station workholding units. Instead of having one component under the spindle of a turret mill, at least four and sometimes six components were mounted in two or three Chick Qwik-Loks on the 610 x 370 mm table of a 560 Minimill. When the first 710 VMC with 760 x 430 mm table was added, the number of components under the spindle could be increased to eight. If parts are sufficiently small, two may be mounted in each jaw, doubling the above numbers.
The major benefit is that while the amount of metalcutting per component is unaltered, the number of tool changes is reduced by a factor equal to the number of parts on the table. The associated rapids traverses are similarly reduced. Non-cutting time is therefore significantly less, lowering the overall cycle time per part.
Neil Nally, foreman at Armac Martin confirmed, “We went down this route in 2007 when an existing customer that manufactures cubicles for changing rooms significantly increased the aluminium door fittings it was ordering to 3,000-off per month.
“We calculated that by setting up four parts at a time on the first Minimill VMC, rather than one on a turret mill, and replacing slow manual tool changes with one rapid automatic tool change per cutter on the machining centre, manufacturing cost per part could be reduced by 20 per cent.
“It was immediately obvious that this was the way to go and a second Minimill and more Qwik-Loks arrived less than a year later.”
A Chick foundation plate fixed to the machine table allows quicker and more flexible placement of the Qwik-Loks across an array of pre-drilled holes in the plate and avoids having to use toe clamps and T-nuts to anchor them to the table. Moreover, the round and diamond pin sets supplied for mounting the clamps onto the foundation plate give a high degree of repeatability and consistency of machining from one batch to the next.
Each Qwik-Lok allows two parts to be squeezed simultaneously against a common, fixed jaw in the centre by turning a single handle. Opposing forces are cancelled and a reliable reference point is provided for machining. Profiling in the Chick jaws creates a pull-down action when they close for added rigidity, prolonging tool life. Sometimes, two or more Qwik-Loks are ganged on a machining centre table to allow large components to be clamped.
Phase two of the workholding makeover started in the summer of 2014, when Armac Martin called in 1st MTA again to advise on possible improvements to some workpiece clamping arrangements.
More and more handle blocks and other window and door furniture such as bolts and catches are having to be machined on the sides as well as the face. If such components are held in a standard Qwik-Lok, further set-ups and separate operations are needed to complete each part, lengthening floor-to-floor times and potentially compromising accuracy due to repeated relocation.
The solution provided by 1st MTA was a four-sided Multi-Lok mounted horizontally between a rotary indexing table and a tailstock clamped to the machine table. The complete unit is referred to as a Chick ISS (indexing subsystem) and the first was delivered in August 2014.
It is essentially four Qwik-Loks mounted on each face of a square section column and uses the same snap on / snap off interface, so jaw sets and other accessories are interchangeable between Qwik-Lok and Multi-Lok / ISS systems.
After the faces of the first components have been machined on any given side of the ISS, one or two edges of each component (and potentially more) can be accessed after indexing for further operations to be performed, reducing the need for additional set-ups to a maximum of one. 90-degree indexing is normally programmed, as workpieces are usually orthogonal, but occasionally components are set at intermediate angles for machining.
The flexibility of the indexable Multi-Lok is underlined by its ability to present components in four sets of twin jaws for face machining in a cycle time similar to if they had been in four separate Qwik-Loks. Thus it is not necessary to take the ISS off the machine table, as it can handle all jobs equally efficiently. Armac Martin had no hesitation in buying a second in February this year.
Some drawing tolerances are surprisingly tight for this type of product, down to ± 0.1 mm, the idea being to minimise subsequent hand finishing and preserve the form of the fittings. Handles can cost hundreds of pounds each when installed in venues like the Dorchester hotel, London or the Waldorf Astoria in Edinburgh. Repeatability is also important so that the luxury items look identical when placed side by side in a top-end kitchen.
Many of the mainly brass as well as aluminium, stainless steel and plastic components produced by Armac Martin are turned in a shop dating back to 1918 that now sports the most up-to-date fixed-head and sliding-head CNC turning centres.
Of 6,660 part numbers, about one-quarter requires some prismatic machining and the proportion is increasing as fittings become ever more complex. Of those, 25 per cent can be machined in one hit but the remainder requires a second operation. To produce these components, equal numbers of parts are secured in both halves of the jaw positions for Op 1 and Op 2 to be performed sequentially, allowing finished parts to emerge each time the doors open.
There are now eight XYZ machining centres on the shop floor, including a relocatable 2-OP model if extra operations are needed. All machines can be equipped with Qwik-Loks, of which there are two dozen on site, although two of the 710 VMCs deploy the two Multi-Lok / ISSs for most of the time.
Hundreds of soft aluminium jaw sets, some machined for specific jobs and others used for families of parts, may be fitted to any of the workholding units. Such jaws allow parts of irregular shape to be held more securely and heavier cuts to be taken compared with if hard jaws were to be used.
Mr Nally concluded, “We are delighted with the performance of Chick products. Right from the start, when 1st MTA sold us the first units, they transformed the productivity of our milling section.
“I don’t think there were any similar clamping products available at the time and eight years on the brand still appears to be the market leader, so we have not needed to go elsewhere.
“With the latest indexers, profitability has increased further by avoiding unnecessary set-ups, which has the added bonus of improving the accuracy of our high value fittings and reducing the labour content of hand finishing.”
The full range of Chick System 5 products are available from 1st MTA. If you have any questions or queries about the products mentioned in this article, please don’t hesitate to contact us on 0800 783 0510 or email@example.com.