The Cwmbran-based sub-contractor James Brown Industries receives two-thirds of its business from companies in the oil and gas sector. Earlier this year, one customer significantly increased the volumes of stainless-steel and nickel-alloy components it was ordering for daily Kanban delivery. Furthermore, new component variants were being added.
As a result, three of JBI’s twin-pallet three-axis vertical machining centres were struggling to keep up, even working ‘round the clock’. The problem was solved by adopting more-advanced component-fixturing methods supplied by 1st Machine Tool Accessories Ltd (1st MTA), Salisbury (
www.1mta.com).
A family of 28 parts was originally involved, which increased to 32, with each part having to be machined on four, five or six faces. Not only were multiple set-ups needed per component, the variety and quantity of parts meant that four or five change-overs were needed daily on each machine, taking 3-5hr every time. Moreover, the parts are cost-sensitive and the customer was looking for a price
reduction.
Clearly, something had to be done. An engineer from 1st MTA was called in to advise on how to fixture the components more efficiently on the Doosan VC510 VMCs with a view to reducing spindle idle time. The aim was not only to ensure that parts flow smoothly out of the factory to the customer but also to reduce production cost per part.
A suite of Chick Qwik-Lok System 5 twin-station work-holding systems provided the answer. Three are mounted side by side on each machine pallet, replacing the same number of conventional wind-up vices, each of which held one component.
Single action
The Qwik-Lok has two clamping stations that are tightened with a single handle against a fixed central jaw, doubling the number of components that can be held. By superimposing a Chick face-plate with 24 clamping stations, up to 72 smaller parts can be secured on each machine pallet.
Normally, setting up so many components at once on a VMC would require a rotary table and a tailstock supporting a trunnion that offered four clamping surfaces. This would add extra cost and might compromise rigidity and accuracy, especially when cutting tough metals.
JBI machined the face-plates in-house, converting each twin-station work-holding system into three similar but smaller twin stations. With each of the six positions capable of holding up to four parts, 24 parts are held per Qwik-Lok — 72 parts per pallet. Clamping is achieved by tightening Allen bolts on three central pillars, to push pads into components on either side and force them against the fixed jaws. This element of the solution was also introduced by 1st MTA.
On average, eight different cutters are needed per cycle; and with more components under the spindle, fewer tool changes are needed overall, so the cycle time per part is shorter. Fixturing more components also means that set-up time is a smaller proportion of the floor-to-floor time per component. In practice, 28 parts now come off a machine per hr; this compares with seven parts per hr previously.
Cost benefits
Managing director Martin Brown, who has owned the firm since 2004, said: “A machine with a fixed overhead turning out four-times as many components translates into a reduction of 75% in the value-added manufacturing cost of a part. Materials like Duplex and Hastelloy are quite expensive, so they account for around one-third of a component by value, but cutting the remaining two-thirds by 75% still halves the overall cost of the part.
“This is a massive saving. It allows us to hold or reduce our prices, while at the same time investing more in up-to-date plant to generate even greater efficiencies. It also means that we can quote more competitively for new work — we are already winning additional contracts as a result.”
An extra benefit of being able to fixture so many components is that the longer cycle time per pallet normally allows the next batch of components to be set up on the second pallet while one batch is being machined. The worst-case scenario at Cwmbran is a 15min delay between cycle end and pallet change. Comparing this with the previous 3-4hr change-overs, there is a 12- to 16-fold saving, increasing production time by several hours per day across all the machines.
Another factor that shortens set-up time is the ability of the Chick jaws to provide a reliable datum face when loading parts. With the old vice jaws, it was necessary to clock into position some tightly toleranced parts, such as stainless-steel manifold blocks on which the seal faces have to be machined to within ± 0.05mm. Skilled operators formerly had to attend the machines to position components accurately, but now less experienced staff can load the machines, leading to further savings.
A fourth Doosan twin-pallet three-axis VMC at Cwmbran has been similarly set up with three Chick Qwik-Loks per pallet to streamline the machining of castings for off-road braking systems — another key area of the business.
There are 13 Doosan VMCs in use throughout the factory. Another Chick work-holding product is to be found on many of them — namely, a One-Lok quick-acting vice. The benefit of this device is that the moveable jaw can be slid over a ratchet to within a few handle turns of the component, allowing it to be secured much faster than when a conventional wind-up vice was used.
One-Loks increase productivity when machining one-offs and small batches; they also share the Qwik-Lok’s virtue of accurate component location. One, two or three One-Loks are used per machine pallet at JBI, and 1st MTA has to date supplied 25 of these clamping units to the sub-contractor.