DELTACAM SHAPES UPFrom 2D to 3D, CAD packages can now make fully rounded models

from the flattest of designs. Ed Lambourne, Technical Director ofDeltacam Systems Limited looks at some of the advances that make

CAD more than just a designer's toy.

Here are some that have been prepared already - complex shapesdesigned and made using the DUCT system.

I any of the newer develop-ments in the 3D design andmanufacture of complexshapes are in no small

neasure linked with impressive develop-ments in the hardware on which thesoftware runs. Engineering workstations,now within the budget of small compan-ies, are capable of both computing andgraphics processing performance that,only a few years ago, was available only inthe research laboratories of large organi-sations.

Today, powerful 3D dedicatedgraphics processors make it possible tolook all around a 3D computer model of amoulding or mould cavity simply bymoving a mouse, while very fast smoothshading of surfaces helps the understand-ing of geometry and the diagnosis ofsurface imperfections.

Powerful CPUs can accept more com-plex and sophisticated software whileiarger memory and disc capacity canprocess more complex models.

Improved networking interconnectshardware and stores data in a moremanageable, accessible and secure wayand improves communication betweenCAD, CAM and business systems. Fin-ally a standard operating system allowssoftware to be more transportable ontonew hardware.

Deltacam's DUCT5 is basically asurface modeller which enables a designconcept to be developed to a fullysurfaced shape in three dimensions on theworkstation screen. From the designgeometry, the system's integral machin-ing module will automatically generatetool paths which can be post processedand downloaded into a CNC machinetool controller. The designed shape willbe precisely reproduced in every detail,with simultaneous control of up to fiveaxes as a model, electrode, finishedproduct, cavity mould or die.

Modelling enhancementsIn contrast to CAD systems that split a

complex moulding into single patchsurfaces that are matched at their edges,DUCT5 splits it into multiple patchsurfaces, which remain smooth eventhough the surface may be highly twistedor contain flat portions as well as highlycurved ones.

This feature automatically ensures thatthe adjacent surface patches remain wellmatched, or have a preset discontinuity ofsurface tangent, eg at a crease or featureline in the surface. Moreover, if one partof the surface is modified, then theprogram automatically ensures that thechanges remain localised and continuitymaintained with adjacent surface areas.

Multiple patch surfaces can beassembled to make a complete part andDUCT5 will generate a smooth blend orfillet between intersecting surfaces. Byintroducing arbitrary trimming curves toform boundaries on the surface at a curveof intersection or a blend edge, the timeneeded to model complex geometricfeatures of a moulding has been signifi-cantly reduced.

Visualisation aids now include high-lighting and reflection effects which addto the realism of the modelled part.Logos, labels, legends and textures canbe scanned and mapped onto the surfaceof the 3D model.

Data exchange between non-compati-ble CAD systems is now an essentialfeature of any 3D modeller and surfacemodels can be exchanged without anyapproximation and loss of accuracy pro-vided both systems support a similarmathematical form. In DUCT5, thenon-uniform rational B-spline surface(NURB) is supported because this is thestandard IGES surface entity and canrepresent most other surface types with-out approximation.

Cavity machiningThe computer-based model of the

moulding can provide all the informationnecessary for the preparation of themachining programs used to manufac-ture the cavity and the core.

The model geometry is automaticallyconverted into tooling paths with allow-ances made for shrinkage, wall thicknessand electro-discharge machining gap.The one model provides for both male orfemale forms catering for bothbenchmark models and the finishedcavity, as required. Similarly, left andright hand parts are equally easily made.

Split faces can be determined automa-tically and split lines adjusted, if neces-sary. Split line adjustment of mouldings isusually done interactively to ensure thatthe desired appearance of the moulding isnot compromised. This adjustment is notso critical with a forging and DUCT5 willautomatically adjust the model geometryto match sensible split surfaces.

Machining is usually carried out in twoparts; a rough machining operation toremove the bulk of the material followedby a finish machining operation.

The latest innovation in roughmachining prepares the tool path for

Computerised Manufacturing June 1990

(Left) if the shoe fits... super-realism brings even the most everydaydesigns to life on the screen while (above) the system is used tomachine a lay-up mould for Dowty Aerospace.

ripping cutters or slot drills to hog out thematerial. The procedure copes automa-tically with the most complex parts andcarefully avoids gouging of the requiredfinal surfaces—which could be anextremely expensive error.

Improved methods of generating toolpaths for finish machining means that thecomplete part can be finish machinedwith a single command by the program-mer. Again full protection is providedagainst tool gouging. '

Because 3D computer models can berepresented more faithfully with trim-med surfaces, mouldable single surfacescan be easily and' quickly machinedwithout risk of cutting other surfaces.

Mould designHaving designed the cavity mould and

core, the complete mould tool needs to bedesigned around it—essentially a draf-ting activity whereby standard partsincluding plates, guide pins, bushes,cooling channels, injection and ejectionparts are added.

New generation drafting systemswhich make use of modern databasetechnology can record the interdepen-dencies of entities in a drawing from theway in which they were created, enablingthe drawings to be rapidly and automa-tically updated.

Typical examples include changing thedrawing standard or dimensional unitswith a single command or, by changing afillet radius, all adjacent lines are re-trimmed and hatching recreated.

The DUCTdraft system implementsrelational geometry in a flexible way, oneexample of its versatility being a mould-ing tool assembly drawing where thenormal operational movements of all theparts can be simulated and studied on thescreen simply by moving the base plate ofthe moving half of the mould.

CNC/DNC developmentsA new development in CNC is the

enhancement of the Swiss Atek NCsystems' CNC system for millingmachines which allows surface machin-ing paths to be completed in real time onthe shop-floor using tool size, surfacefinish and feed rates selected by themachine tool operator.

This Atek system will take surfacedefinitions from DUCT5 and is a veryflexible method of controlling a machinetool, particularly if there are no potentialsurface gouging problems.

Efficient communication between themachine tools and the CADCAM systemis an essential requirement for manufac-turing a mould or die and direct numeri-cal control has now virtually ousted thetraditional punched paper tape. Del-tacam's DNC2 uses one or more PCs onthe shop-floor to communicate simul-taneously between the CADCAM systemand a number of machine tools.

The machine tools can operate inmemory load mode or, where the pro-gram may be a substantial one, incontinuous drip-feed mode, topping upthe CNC cont ro l le r ' s memorythroughout the machining process. Thisminimises operator attention andallows for unattended overnightmachining.

DNC2 provides for machine statusreporting and flexible program organi-sation, where storage is under jobnumber and sub-operation number; aswell as program restart from any pointand editing.

Editing can be done at any timewithout interrupting machining opera-tions on any of the connected machinetools. NC programs can be transmittedboth ways so that edited programs anddigitising data can be loaded back to theCADCAM systems.

DigitisingAn alternative to designing a product

from scratch on the computer screen is tostart from an existing product or artist'smodel which involves inputting data forgeneration of the necessary machininginstructions.

Some CNC systems, eg Fidia, allowdigitising of the model, storage of thedata and automatic generation of acutting tool path to produce a replica.While this type of system can mirrorimage a left hand model, it cannotproduce a male from a female model orreadily machine with a cutting tool that isshaped differently from the probe stylus.

Recent developments enable lowercost CNC systems such as Heidenhain touse a touch trigger probe, such asRenishaw, to take points from a model bymoving down to th.e surface along thespindle axis at points defined along aregular rectangular grid. This point datacan be processed by the CADCAMsystem and used more flexibly. Users ofthe DUCT system have the option ofuploading digitised point data from theirmilling machines via DNC2.

Once in DUCT5 it can be kept as densepoint data or converted into a surfacemodel. In both cases, the user can verifythe geometry graphically and also gener-ate rough and finish machining paths formale and female forms as well as chang-ing the cutting tool.

The digitising technique imposes somelimitations on finish and accuracy so thatit might be preferable to digitise a smallernumber of surface points and use theCADCAM system to fit a surface.DUCT5 can interface to the measuringmachine in real time to allow it to be usedas a three dimensional digitiser fromwithin the CAD system—a powerful datacapture technique. MFor more information circle ME 133

Computerised Manufacturing June 1990