Fast-acting pallet handling systems cut downtime

Three fast-acting pallet handling systems now deliver palletised vacuum pump components to machining centre systems and considerably reduce cranage, waiting and handling times.

Since the early 1990s, manufacture of vacuum pump components using flexible manufacturing (FM) systems comprising horizontal machining centres with automated pallet storage systems has helped BOC Edwards, Shoreham, to survive the volatile world of the semi-conductor industry, despite at times 60 per cent of its business being in this sector.

Before that, the company used twin-pallet machining centres.

However, the time needed to fixture the next parts was often greater than the cycle time for the parts being machined, so pallets had to be craned on and off the second station to keep the spindles running.

The three latest FM storage and handling systems, supplied by Fastems, were installed in two separate factories linking a total of 14 machines (2 X 5 and 1 X 4) and were commissioned during the first half of 2000.

Each system manages both 630 X 630mm machine pallets and 900 X 900mm Kanban material bins.

Said BOC Edwards' manufacturing engineering manager, Mike Atkins, "For the larger of the two projects, there was little to choose between the reliability and performance of our two preferred machine tools, so we decided to set up a competitive environment to better evaluate the two machining centre suppliers.

Along one side of a factory unit we installed a line of five Makino A77s and on the opposite side a similar number of Mori Seiki SH630s, both integrated with similar Fastems systems''.

"We did not choose the machine manufacturers' own pallet storage systems, as we had done in the past, because we wanted the flexibility of being able to add other makes and types of machine into the lines to meet future requirements.

So we opted instead for open-architecture handling and storage systems from Fastems, which are of modular construction and were erected in a just few weeks.

"In any case, the systems offered by Makino and Mori Seiki at that time were not able to hold material bins as well as machine pallets, whereas the multi-level Fastems systems have sufficient capacity to store both.

As factory space at Shoreham is at a premium, we wanted a system that could maximise storage capacity by using the available factory height.

Fastems offered just that." The Makino's produce different versions of head plates and stators while the Mori Seiki's make varieties of end covers, gear covers and rotors for booster pumps used in semiconductor component manufacture.

There are four basic variants of pump, although this is increasing all the time as customers become more specific in their demands.

All parts are of high grade, non-porous cast iron.

Both lines are served by identical, 45 metre long Fastems systems, each having 48 machine pallet locations and 36 positions for material bins.

Equipped with a 3-axis CNC stacker crane mounted between an upper and lower guide rail travelling at up to 3m/s, the system is dynamic in its operation with machine pallets having dedicated storage places whilst the material bins have 'free' places.

The Fastems MMS control monitors all pallet / material movements within the system and records and tracks each move on an event file.

Between them, these Fastems systems account for about 20 per cent of horizontal machining capacity at Shoreham and have the capacity to produce 600 booster pumps per month, working 24 hours a day, seven days a week.

Bob McKeller, manufacturing engineer, recalled, "We needed all the capacity we could get in 2000 and ran the systems on a low variety of parts at very high volumes.

However, we are currently running at much lower volumes due to the downturn in the semiconductor market, so booster pumps accounts for four fifths of FMS throughput on a reduced shift pattern.

Due to the inherent flexibility of these lines, we are able to interweave production of small volumes of unrelated parts as well." Located by each FM system, and under its command, are a pallet load / unload station and two material stations where material bins of castings enter and leave.

The operator offloads machined components at the load / unload station and fixtures new castings taken from the bins before returning both the pallet and the bins into the system.

The Fastems control software facilitates the automatic delivery of material bins to enable replenishment of a specific fixture.

Bins go back into storage while the machine pallets are added to the machining queue, eventually being sent to a machine tool with an associated manufacturing route for machining.

The Fastems PC-based MMS (Manufacturing Management System) software, running under Windows, automatically ensures that the pallet goes through the steps defined in the route and that the correct CNC program starts when the pallet is transferred to the designated machine resource.

If a resource is not free, the pallet is put into store to await processing.

Average time that a pallet of components undergoes metalcutting operations is 60 minutes on the Mori Seiki's and 75 minutes on the Makino's, although cycle times for identical components are the same irrespective of the machine.

With five machines in each system, the average takt time (actual machining time per resource) is 12 and 15 minutes respectively, although the system has the capability to produce economically with tact times as low as three minutes.

Tolerances are tight, especially on bores and geometries, which contribute to leak paths, as these directly affect running costs of the vacuum equipment.

Bores must be within +/-10 microns, surfaces flat and parallel to 20 and 15 microns respectively, while general positional tolerance is less than 40 microns in some instances.

Once the components are machined, they leave the system immediately via the load / unload station, as BOC Edwards operates lean manufacture and just-in-time delivery to its customers, based on a lead time from order to shipment of a maximum of five days.

It is worth mentioning, however, that in some production environments where Fastems systems are in use, pallets of finish-machined components are also stored until called up by assembly stations, which may be incorporated within the system itself.

The Fastems MMS software provides integrated control over all functions of the FMS.

Within the scope of the base MMS-1000 module, in addition to control over movement of the hardware elements, are advanced diagnostics and stacker crane utilisation data, supported by on-screen graphics showing in real time the position and status of pallets, bins, crane and machine tools.

Sitting above MMS-1000 are numerous additional software modules orchestrating material management and delivery, work list generation, and capacity simulation for short-term production planning and scheduling.

Other modules provide DNC interfaces for high-level communication between the MMS control and the machine tool CNC systems.

Resource management also uses the DNC interface to transfer programs and tool information between the machine control and the MMS.

All 120 tools in each Mori Seiki magazine and the 132 tools deployed by each Makino are 'mirrored' within their respective MMS controls.

Every tool is continuously monitored as to its position and remaining life as well as the location of sister tools if they exist.

At the front of each part program is a tool list with cutting times which allows the control to carry out tool magazine planning.

This evaluates which machine(s) are free and suitably tooled to produce the components fixtured on the pallet.

The system uses simulation software to check whether any tool will exceed its preset life before the end of the production run, diverting the pallet to the best-equipped machine.

By utilising the MMS4200 module tool management is extended to so-called passive tools that are set and outside the machines' ATC magazines.

When using tool simulation, MMS also considers these tools.

The Mori Seiki's are equipped with a touch probe for tool breakage detection, while the Makino's employ a mechanical arm for the same purpose.

Spindle load monitoring takes place on all machines.

If a tool should break mid-cycle and there is no sister replacement, a message appears on the screen telling the operator which tool needs to be exchanged into which pocket number.

"Before we had tool life and breakage monitoring, we were smashing cutters and scrapping components," commented McKeller.

"Now this never happens, resulting in significant monetary savings and no lost production." BOC Edwards has recently installed an Isis tool database system and is currently rationalising the 2,000 or so toolholders in use across both FMS.

The target is to reduce the number by a third, which will greatly increase the flexibility of the shop in terms of the choice of machines to which any given pallet can be directed.

The database will link to the Catia CAD stations used by the designers, who will have to take account of the permissible tooling when introducing new features.

Atkins concluded, "These first two Fastems systems were installed immediately before a similar, four-machine Fastems/Makino system entered service at one of our other manufacturing facilities for machining different pump components.

From past knowledge we knew that one 4-machine FM system would give the same output as six stand-alone, twin-pallet machines, i.e half as many again, requiring considerably more labour.

"Fastems technology allows us to continue to be efficient even in times of lower demand, as the lines produce small batches cost-effectively with minimal manning.

We have a Seiki Systems link monitoring all three of our Fastems systems.

The figures we observe are over 99 per cent availability, and 94 per cent production efficiency if we operate the them at full tilt, outside Kanban scheduling.".

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