The role of part programmingworkstations within a CIMenvironment

by Keith SchofieldApplicon-MDSI UK Ltd.

One of the consequences of the availability of less expensive graphics,processing and memory facilities is that language-based partprogramming systems are likely to be displaced by workstation systemsusing interactive graphics. This article considers the growing role of thepart programming workstation as companies move towards integrationof their engineering and manufacturing operations.

CAM market trends

The specialist computer-aided manu-facturing (CAM) companies as we knewthem in the 1960s and 1970s have migr-ated to the computer-aided design andmanufacturing (CADCAM) equipmentsuppliers of today. Market demandshave been changing rapidly in recentyears, influenced by considerablestrides in computer hardware and soft-ware and ever more stringent demandsfrom design engineers. Other contribu-tory factors have been the proliferationof computer numerically controlled(CNC) production machines and effortsto integrate them into a total manufac-turing environment (computer inte-grated manufacture or CIM), and tosome extent Government financialpolicies and the world economy.

Languages for part programminghave been superseded by interactivegraphics input. The appeal of this tech-nique is a result of the efficiency and'friendliness' of these systems. Thehigh-technology glamour of suchmethods owes its acceptance in man-ufacturing industry to CAD vendors,who introduced graphics to industry.

NC/CNC technology is now matureand is no longer a rapidly expandingmarket. Except for suppliers who havefound a special niche fortheir products,CAM companies have had to adopt newand high-growth applications.

Competitive demands from the mar-

ketplace and influence from Govern-ment have motivated many large- andmedium-sized companies to invest inCADCAM. CAM vendors were forced tochange their strategy and either joinforces with the traditional CAD com-panies or introduce a CAD product oftheir own. Weakness in world andnational economy annihilated CAMcompanies which failed to change.Indeed, many CADCAM companiesthat did not keep pace with availabletechnology have either closed their

operations or suffered severe financiallosses.

More cost-effective computer hard-ware has also had a considerable effecton the market. At the low-cost end ofthe range, microcomputers havereplaced minicomputers and bureautime-sharing services. Mid-rangeperformance is available on 32 bit work-stations and supermicrocomputerswhich also offer the capability of beinglinked together through local area net-works (LANs). Large turnkey and high-performance systems have moved awayfrom 16bit computing onto 32bit super-minicomputers. The ability to eithernetwork or cluster such computersgives the performance of a mainframecomputer. Large systems can also beenhanced by the inclusion of work-stations which can communicate with asupermini or a mainframe.

Fig. 1 A typical CAM graphics display, showing the tool path for an area clearance routine on aturned component

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Fig. 2 Three stages in the manufacture of a gearbox

a The component on a CADCAM graphics terminalb Manufacturing the component on a CNC vertical machining centre using the programgenerated by the CADCAM systemc The finished gearbox

By the end of this decade language-based systems for part programmingwill be almost non-existent. More work-stations are needed because graphicsinput is more terminal intensive in usethan the old language methods, but thishas been, and is being increasingly, off-set by less expensive hardware. Newsoftware developments, especially inthe field of expert systems, will improveproductivity and job satisfaction for theprogrammer.

Current and future workstationcomponents

Workstation design is constantlymoving towards increasing levels ofcommunication with other manufactur-ing systems. The value of databases,such as design drawings, productionprocesses, assembly control and qualitymethods, has been recognised forsome time by industry. Efficient flow ofdata is the basis of the concept of CIM.If a company could reduce its costs by 3or 4% and increase its market share by afew percentage points, the benefits ofintegration would be considerable andits justification automatic.

Levels of efficiency are constantlybeing increased; flow of commonlyused geometry is employed in the over-all manufacturing process; high levelsof integration between design and CNCprogramming are becoming welldefined. Practical implementation ofsuch methods does not happen over-night, however, as it takes several yearsto create databases and replace existingdisciplines, and benefits may take along time to be realised.

Improvements can be expected withthe introduction of faster processingand better communications. Worksta-tions and supermicrocomputers nowhave powerful data processingcapability. With the decreasing cost ofcomputer hardware, the effect onNC/CNC programming will be toincrease the number of workstationsthat can be justified. In large com-panies, clusters or networks of work-stations will be able to access a commondatabase from each application area,such as design, test, NC fabrication, NCfor FMS (flexible manufacturing sys-tems), toolmaking, jig and fixturemanufacturing, as well as generalNC/CNC production.

Production control will be able todirect CNC programs using DNC (directnumerical control), taking into accountthe production processing demandsand availablility of material from stock.Tighter control over work in progressand stocks of finished parts providesthe justification for this leap forward inefficiency.

A significant advance will occur with

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the introduction of expert systems andartificial intelligence. Without doubt,the most difficult problem facing theNC programmer is the lack of certaintythat his machining method will besatisfactory.

There are many definitions of an'expert system', which have been com-prehensively covered by Prof. J. L. Alty[1]. Basically, it implies expert 'know-ledge' held within the computer to as-sist the preparation of programs. Forinstance, a CAM program may doexactly what the programmer wanted,but still may not operate satisfactorily.The depth of cut and tool selection maycut the part inefficiently or not at all;feeds and speeds may produce an unac-ceptable finish; workholding may beinadequate or overelaborate; collisionsmay occur either with the cutting toolor, more difficult to predict, with a non-cutting tool. Expert systems offer theprogrammer a method which has pre-viously been proved, together with anexplanation.

Clearly, the expert system has to betaught the rules, and, although many ofthese will be in-built by the systems sup-plier, the usercompany will still need toadd its personality to the methods.

The result will be of major impactwithin manufacturing industry, in thatthe NC programmer will truly fulfil hisrole as a production engineer. Insteadof spending his time as a part-timeclerk, draftsman and shopfloor chaser,he will be able to access data auto-matically, prove the method and toolingaway from the machine tool, and pro-duce more effective CNC programs.

Off-machine versus manual datainput programming

Over-the last few years there has been aproliferation of computer numericalcontrols with manual data input facilityfor shopfloor programming, some ofwhich have not even had the requiredinterfaces to accept externally preparedprograms. These systems have mainlyoriginated from Japan, where manufac-turing often relies on the 'just in time'(JIT) or KANBAN techniques.

The main reason for this stems fromthe policy of large Japanese companiesto design and assemble products, put-ting out component part manufactureto many small subcontractors thatdeliver exact quantities at tightly spec-ified times to a precisely definedquality. Often, the same kind of compo-nent is sourced from several competingsuppliers. Very small subcontractorscannot afford the luxury of job specialis-ation, and often the man who programsthe parts may also operate the machine,sweep the floor and deliver the finished

Fig. 3 Complex three-dimensional parts such as this aerofoil may be very quickly designed on aCAD system

components. Manual data input (MDI)lends itself to this environment.

Importers of machine tools from theFar East attempt to persuade Britishcompanies of the benefits of MDI.Some systems are very attractive, withinteractive graphics displays, limitedcomputer-aided processing capabilityand the ability to both program and con-trol the machine. However, unless JITmethods are adopted, machine utilisa-tion and quality control are impaired.Standing in a noisy machine shop ishardly the acceptable and efficient wayto program parts.

European and US companies, on theother hand, have adopted the inte-grated manufacturing concept. Theapproach by Western countries offersthe promise of success in the future andgreater social acceptance. There is alsoa need for a universal method of pro-gramming to maintain consistency anddiscipline within large manufacturingorganisations.

There are applications where MDIcan be efficiently used. Small sub-contractors without the resources tobuy CAE (computer-aided engineering)equipment obviously benefit. Com-panies with very high batch quantitiesmay also find manual programmingadvantageous. Almost all companies,however, will find the integrated CAD-CAM solution to be more beneficial.

Relationship with drafting anddesign

An ideal CAM system will be fully inte-grated with a three-dimensionalmodelling, analysis and drafting sys-tem, so offering the user many time-saving benefits. The same commandentry protocols used for design etc. may

be used to either create or manipulatethe shape of the component. Themachine datum (zero reference loca-tion) can be changed to suit the pro-grammer and machine.

Views of parts can be selected. Forexample, the part programmer usuallyrequires two rotated views of a shaft sothat machining of each end can beachieved. The designer only needs toshow one view to specify the shape. Inthe case of complex shapes with sculp-tured surfaces, a three-dimensionalgeometric modeller must be fully inte-grated within the CAD/CAM/CAE sys-tem to permit the part design andsubsequent manipulation.

Machining tolerances and allowancesfor other manufacturing operationssuch as grinding can be added or sub-tracted from the designed dimensions.The part programmer has the licence tomodify designs for manufacturing pur-poses. Tooling libraries can be accessedand displayed by the programmer, andcollision checking of non-cutting toolscan be executed.

Associated work such as tool design,as well as jig and fixture design, may becarried out more easily with a fully inte-grated system. Clearly there is a need totransfer data in both directions betweenthe design and part programming sys-tem. A component can be designed andsubsequently transferred to the partprogramming department to have thetool paths added. A fixture can then bedesigned after transferring the resultantpart shape and tool paths back into thedesign system with the secure know-ledge that the fixture will actually fit thepart. Fixture design can take intoaccount the tool motion so that theoptimum fixture design may beachieved.

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Fig. 4 A typical CADCAM system — the EQINOX 7000 from Applicon-MDSI

DNC — direct or distributed?

Before discussing the distinctionbetween, and relative merits of, directand distributed numerical control ofmachine tools, it is worthwhile sum-marising why DNC is being increasinglyadopted in manufacturing industries.

Broadly, DNC is the technology forcontrolling CNC machines directly froma computer without using external datamedia (paper tape, magnetic tape etc.)to transfer the program. The principaladvantage of electronic data transfer isin terms of reliability and productioncontrol.

Paper tape became universally usedas the means of transferring programsto machines because it was inexpensiveand capable of being inspected visually.Despite its acceptance over magnetictape or magnetic cassette, paper tapepunching is inherently unreliable andlikely to produce errors of 1 in 10000because of failure in moving parts in thepunching mechanism. Worn punchescause greater errors when the criticalclearance between the punch and diegenerates ragged edges on holes. Papertape readers are undoubtedly the leastreliable part of CNC controls, especiallyin view of the harsh shopfloor environ-ment in which they are required towork.

Complex parts for the aerospaceindustry, for example, require pro-grams of enormous length. Shapesoften comprise a series of non-circularsmooth curves which, in CNC terms,are defined as many straight lines.Mathematically, the lines representchords limited by the tolerance bandwhich bounds the curve. If paper tapewere used, the program for a typicalpart would be hundreds or even thou-sands of feet in length.

Although other solutions such asmagnetic tape and floppy disk driveshave been used, DNC is a better con-tender for this task. In fact, the originalmeaning of DNC — direct numericalcontrol — became used for the methodof dispatching programs in a pro-gression of short bursts of data to amachine control. The direct methodwas used to send enough blocks of datato a buffer store behind the tape reader,which in turn fed an active store in themachine control. When the active storebecame empty the buffer would refill itand was in turn replenished with datafrom the DNC supervisor on the hostcomputer.

One of the problems of early DNCsystems was the cost of data storage,especially in the days of magnetic corestores. The distributed method requiresstorage which is approximately relatedto the square of the number of machinetools that the DNC system can address(talk to). Currently, storage is much lessexpensive. Consequently, whole orvery long parts of CNC programs can bedistributed to machine tools. DNC thustakes on the new meaning of dis-tributed NC.

Rapid growth in the use of DNC canbe predicted. Users with large numbersof CNC machines, for example, requirea level of organisation that will benefitfrom immediate availability of the pro-gram. Manufacturing companies have a

very low level of efficiency if measuredas the time the tools are cutting metalcompared with machine availability.Typically the efficiency is lower than15%. One of the factors contributing tothis problem is that the correct programis not available for the correct machinetool at the right time.

Furthermore, there will be a growthin the number of users who make com-plex parts using CNC, and the benefitsof DNC already discussed will beincreasingly adopted by these users. Inaddition to companies in the aircraftindustry, plastics and die mould makersare using CNC machines to producetheir complex parts because of the cost-effective new technology. Further-more, there is an increasing use of alter-native materials to iron and steel, whichwill increase the die mould work formedium- and large-sized companies.

In addition, increasing use of hightechnology such as flexible manufactur-ing systems demands efficient use ofplant which has an exceptionally highinvestment value.

Adoption by more and more com-panies of computer-aided engineeringsystems wjll increase the use of DNC.Interactive colour graphics which willaddress the host computer from theshopfloor for faster prove-out of pro-duction engineering methods is onebenefit of full integration. Increasinguse of computer-aided processingrequires a link to the shopfloor viaDNC. The link also provides immediateinformation on machine availability,management information services andother data for costing and control,direct from the shopfloor.

In view of the trends, one must con-clude that it is crucial, when selecting asystem or workstation for NC/CNC pro-gramming, to consider the actions andconsequences on the existing andfuture investment. Products must becapable of being integrated into boththe engineering design and shopfloorcommunications environment. In thefirst instance, this may mean that theintegration to CAD and DNC must beidentified and implemented. If progressover the next ten years is only as fast asdevelopments in the last decade, thiskind of integration will soon seem as oldand mature as NC/CNC technology istoday.

Reference

1 ALTY, J. L.pp. 2-9

'Use of expert systems', Computer-Aided Engineering Journal, 1985, 2, (1),

K. Schofield is Sales Manager with Applicon-MDSI UK Ltd., Radcliffe House, Blenheim Court,Solihull, West Midlands B91 ZAA, England.

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