Maximizing Productivity from Machining Cells

Copyright © IFAC Information Control Problems in Manufacturing Technology. Madrid . Spain 1989

MAXIMIZING PRODUCTIVITY FROM MACHINING CELLS T. M. Hammond Flexible Manufacturing Technology Limited, Brighton, UK

Abstract. With ccrrpanies becaning increasingly more aware of the need to maintain profits in a ccmpetitive world market, FMT offer a solution which is available on a progressive step-by,-step basis, which enables users to maximise the productivity for their machining cell. This involves using proven FMT technology in simulating production orders and tooling requirements, linking with engineering design offices and other support facilities, to enable the machines to produce for periods either unmanned or with minimal manning, on a 24-hour basis. The experience gained in approximately (40) cell installations is available to all our potential users, together with our proposal engineering services. Keywords. CNC; Flexible manufacturing; Machine Production Control; Reliability; Simulation.

tools;

Management

systems;

The FMT cell installed consists of two Fleximatic machining centres linked by the Roevatran which services 16 pallet stations. Fig. 1.

For most manufacturing carpanies the objective must be to focus the rusiness and manufacturing strategy where they can achieve most benefits. This means they are interested in setting up manufacturing cells to produce high value added parts which are critical to the quality of end product.

FMT FMT See

The machines are FMT Fleximatic FM100 Horizontal Spindle CNC Machining Centres with a brief specification as follows:-

With these carpanies, it is essential that they invest in cells of proven technology and install ~e, on a progressive basis as the equipnent is technically absorbed in the carpany and achieves a payback.

FMT Fleximatic FM100 Traverses

X Axis 750mn Y

Many large custaners are now insisting that a qualified supplier must reduce prices by per cent per year, provide quality control charts and provide on-time supply and they will then sign 2-3 year contracts. Faced with these demands the smaller carpany is faced with two options - improve response time, quality, and Just in Time (JIT) deliVery or succumb to competition and close down.

Axis 650mn

Z Axis 500mn

Pallet Shuttle Power

Speed Range

Autanatic Tool Changer Feedrate

problem they face is that the traditional methods of justifying capital investment in machine tools and manufacturing cells are too restrictive and take too narrow a view to identify all the major benefits of advanced manufacturing technology. Machining cells make the greatest inpact outside the area of direct canponent machining costs, with the emphasis upon reduced handling and storage costs, easier assembly inl>roved quality faster response to market demand and the two biggest factors of all - reduced inventory and work-in-progress. One

Features include

Control System

Rotary with 2 pallets 15 Kw 20 to 4500 rpm 2 drums each of 40 tools with randan selection. 1rrrn/ min to 15 metres/min. Deluge coolant Swarf Conveyor Str ingent Guarding Broken Toel Detection Probe facility Siemens Sinumerik

8M Transporter

For the UK based carpany Victor Products the choice they made was to move into machining cells and for their first they selected a FMT Two-Machine Cell as part of a £2 million modernisation plan. Tool Setting 'nle carpany produces mining accessories, service plugs and sockets and underground mains connectors. 'lbese existing products, machined mainly fron brass and gun-fl'etal, were produced on lathes, milling machines and conventional borers.

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Part Progranrne Storage 128K The transporter linking the two Fleximatic FM100 ' s is the FMT Roevatran rail guided vehicle. Tool Setting is by way of Frenco P40 machine. This is linked directly back to the host CCtTpUter library of setting information.

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T. M. Hammond Supervisory Carputer

The host CCl1"Plter is a Hewlett Package HP1000 A600. The configuration installation gives a total of 2Mb main memory together with 39.5Mb of fixed disc storage. The functional system design for this supervisory CCl1"Plter was prepared by the Hoskyns Group to Victor Products' specification with the co-operation of FM!'. The purpose of the CCl1"Plter system was to upgrade the control of the cell to carry out the following functions: direct numerical control; CCl1"Plter enhanced cell scheduling; CCl1"Plter controlled materials handling; tcol management; cell management/status monitoring; prcduction management/ reporting.

The company committed itself step by step:- first one Machining Centre standing alone, - then the second Machining Centre and the Transporter , - finally and only after the system was working under the direction of the machine controller, the host CCl1"Plter and the full ONC linkage. This Two Machine Cell reduced the value of work in progress fran £225,000 with conventional machines to £ 1 25,000. Direct machining costs have been reduced by £75,000 and lead times halved fran 12 weeks to 6 weeks for critical underground mains catp:>nents. One inq:lortant aspect of the Cell is the ability to operate 4.5 hours unmanned between shifts which is a critical aspect when cost justifying machining cells. The ability to siJrulate the operation of the cell and determine for the operator which longest cycle time fixtures should be loaded for the processing between shifts can mean for the Production Engineer the difference between success or failure of the cost justification. This vital factor together with the tangible and intangible benefits described has made siJrulation a vital factor in cost justification. FM!' have invested heavily in CCl1"Plter simulation and have developed generic sinulation Irodels which allow the cells and systems to be re-configured and re-costed quickly and easily.

The ability to vary batch sizes, number of different carq:x:>nents, number of machines, cycle times, number of controlled vehicles and the number of operators and the utilisation of these at the load and unload station is vital if the overall business strategy is to be achieved. More important is the ability of the Chief Executive to obtain these alternatives quickly in order to create a dynamic planning process. As 24 hours or one week's production can be run in a matter of

minutes the ability to create a dynamic planning process is greatly enhanced. However, a machining cell is more than an number of machines linked by a carq:x:>nent handling system. It is an all-enbracing philosophy that impacts upon all aspects of a manufacturer's activities rather than machining cycle times in isolation. That's why the first step to maximise a machining cell's productivity must start long before any hardware is even considered. For many companies the installation of their embryo machining cell represents the first tangible evidence of their move towards Advanced Manufacturing Technology. TJ:lat's because they have followed an AMr rule of thumb that says, "Plan Down - Implement Up". To expand on this: Plan Down means review the company's prcduct and manufacturing strategy for the next five years, in depth and in all aspects. Not just production engineering rot also design; material resource planning; handling and storage; production planning and inventory; and last rot not least, management data reporting to give better, more accurate control and faster response to an ever-changing market place. Planning dawn starts with strategic data required by management to improve control of the canpany. It then works down through all aspects of the company activity - right down to the capacity and number of machines required on the shop floor and peripheral activities. Does this canponent stores really require heavy expenditure on autanated handling equipnent? Or will the dramatically reduced inventory pranised by a machining cell negate this requirement? This could be a major indirect saving associated with a machining cell. One of the most positive benefits of just the planning aspect of AMr is that inter-departmental barriers are broken dawn. When departments such as design, quality control, manufacture, finance and sales all work fran a cam-on data base, there is no roan for isolationism. Implement up often results in the machining cell being the most logical starting point for a company's first venture into AMr. In theory a machining cell ought to be able to handle any carq:x:>nent that fits in the physical capacity envelope of the machines. In practice this amount of "elasticity" can put too great a demand on auxiliary aspects of the cell such as fixtures, tooling and prograrrrne store capacity. Most cells start life dedicated to a family of carq:x:>nents. At FM!' for example we have worked together with custaners on cells that prcduce such diverse carq:x:>nents as valves; autanobile engine parts; mining equipnent; gearbox and transmission units; machining tools and electric motors. The words "worked together" were carefully chosen. Maximum productivity for any machining cell can only be achieved with the closest co-operation between the machine tool manufacturer and the user over an extended pericd of time. This can be two to three years. For most companies the leap fran conventional machines, or even standard NC and CNC machines to a cell is just too big to be undertaken in one bold leap. I t stretches both the technical and financial resources of the company. That's why FM!' pioneered the "Step-by-Step" approach.

Maximizing Productivity from Machining Cells Today, proven roodules of hardware and software can be progressively integrated into a cell. The pace of implementation is totally controlled by the user in both terms of number of machines and software-based manufacturing technology. IrIplementation of hardware and software can be two parallel, rut inter-related functions. In general terms ilTplementation of . hardware means more capacity in the form of addit~onal mach~ne tools coupled with ilTprovement component handling.

These additions usually start by silTply duplicating the original machine to increase capacity. Then, specialist machines can be introduced. Cells are all about flexibility. Two cases

fron FM!" s experience spring to mind; autarobile cylinder heads, and gate valves . The cylinder head design may change the inlet/ outlet ports, rut holes for the studs in the block are very unlikely to change.

On gate valves, bolt hole patterns are often qoverned by SS or ISO standards and are therefore unlikely to change. Both these cases can benefit fron the productivity of multi-spindle drilling incorporated into the machining cell. Similar arguments can be mustered for introducing the productivity of specialised machining stations such as gun-drilling, boring machines or high speed

tapping units . a cell grows, improved by bringing control of the cell. For example, washing that clean, correct assembly immediately As

productivity can be further additional functions under the followed by inspection insures components are available f or after machining.

'l\1rning to the progressive ilTplementation of software, here the benefits can be enormous - rut they are almost invariably indirect to the lMChining process. Faster design to production; better use of resources; dramatically reduced inventory are all quantifiable benefits, rut again have little to do with the component cycle time on the machine . Even the embryo cell must contain software capabilities such as tool monitoring, sister tool replacement, component identification, probing cycles etc. Together, these adj up to its unmanned operation capability. These software foundations can be built on. A DNC link with version control allows part-programmes to be stored away fron the machines then transmitted to the machine in response to production schedules. 'n1e facility to transfer programmes back to the central computer system, after editing on the shop floor, provides a secure method of updating records. manufacturers move to Canputer Aided Design (CAD) it makes sense to evaluate at the same time CAD/ClIM (Ccrrputer Aided Manufacturing) link. This allows CAD data to be processed to produce part programmes. This, canbined with the DNC facility provides a paperless environment fron design to finished part.

As

Further software developnent can embrace a host carputer which links the machining cell to other business systems. The ultimate goal is fully carputer integrated manufacturing (CIM). Here, financial, canmercial and manufacturing departments share a carrron data base. At Victor Products the HP1000 is linked directly to the canpany's MRP system and the cell driven dynamically by the overall canpany requirements.

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If productivity is to be maximised, then it's useful to have some sort of yardstick against which to measure benefits that accrue .

This is where the NEIlO report on "Advanced Manufacturing Technology" , "The Impact of new technology on engineering batch production" is a useful, independent publication to consider. It examines eight canpanies with turnovers of £3M 20M and product mixes qualified as standard, custanised or special. The results are startling, inventory down by anything fron a factor of 3 or 4. That means up to 75% reduction in dead money locked up in stock. Stock that could concei vabl y become worthless as advances in technology make it obsolete. It is worth noting that industry in the UK has an estimated £16 billion locked up in inventory. Reduce that by an overall 25% (not unrealistic when viewed against examples of 75% already being achieved) and a massive £4 billion is available for investment - without going near the Banks for additional funds. Canpare that with an annual £2 billion investment in fixed assets expenditure in manufacturing industry and it is easy to see the potential for industrial revival. It is probable that the figures for Spain are of a similar magnitude.

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T. M. Hammond

Figure 1: SCHEMATIC OF FLEXIBLE CELL