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From CAD User Mechanical Magazine  Vol 20 No 04 - APRIL/MAY 2007

VX Mould and Die, together with VX hybrid modelling, provides a complete design to production mould and die making solution

Those of you who are already in the mould making business are well aware of all of the steps involved in making moulds. It's a pretty complicated business, and involves much more than just designing the part that the plastic is poured into. For starters the mould has to be set up in mould plates along with all of the other paraphernalia that attaches the moulds to the moulten plastic feeds.

I was brought bang up to date with the latest software during a prolonged session with Akela, distributors of VX hybrid modelling software throughout the UK, Australia and New Zealand, who demonstrated just how far, and how fast, CAD/CAM vendors are developing the technology.

VX mould making is just one element of the VX suite of CAD Tools. The software has developed a devoted following in those markets that like to incorporate good design with mechanical innovation. This is in large part due to the hybrid aspect of the software that enables designers to switch between surface and solid modelling techniques, taking advantage of the best practices of each.

Mould making is part of VX’s CAD/CAM suite. It allows designers to follow on from the design concept by preparing the model for production using one of the various moulding technologies, and using that model to create the mould itself.
Version 12 improvements

The last release of the software included some important enhancements for mould making. Part of the global top ten requests made by users worldwide - and after VX installed its own cutting machines to tune up their software - it brings improved speed and quality to toolpaths, and eliminates a lot of fresh air cutting. Other enhancements include improved electrode blanks, smart components and the way in which the software can handle point clouds.

All of this brings together one of the most comprehensive mould-making solutions available, supported by VX’s hybrid modelling technology.

Creating Moulds
from 3D Models

VX is popular within the plastics industry because of the way it can be used to create complex and aesthetic shapes, using either surface or solid modelling technology. Using the software (and its welcome capacity for unlimited undo’s and redo’s) designers can modify all aspects of the model to enable it to be moulded.

This part of the operation has been substantially speeded up by chaining commands, allowing, for instance, all fillets to be modified with a couple of key strokes, by creating a loop fillet - picking all edges and applying the command once. This introduces an aspect of feature modelling where command histories are not required to modify the model - typically STEP or IGES files coming in from other CAD software packages. It also allows parts to use reverse engineering tools in the core system. The software also allows designers to scale the model for shrinkage - typically 6%, after the moulded part leaves the mould.

Its shape creation tools are supported by numerous visual analysis tools, such as zebra striping, isophotic analysis (colour), gaussian and mean curvature, and a new tool, 'z' height analysis - vital for mould making - which provides banded colours to indicate the depth of the intended mould.

Mould and Die

Mould and Die operations are accessible from within VX. For more advanced users, specific toolbars can be created that include their own macros - but as the mould making part of the software is not utilised by all users on a constant basis, but rather at the culmination of the design process, VX has kept the sequences and operations as simple and intuitive as possible, so that users don't have to re-learn the software every time they want to use it.

The first task is to create a split line and parting faces - either automatically or user defined - so that the user can put in draft angles themselves. This ensures that the moulded part can subsequently be removed from the mould.
There are different types of basic moulds; vacuum forming, for instance, for large moulds (Baths, body parts, etc.,) may make provision for flanges on each section of the mould. Blow moulding is used for producing bottles etc., and injection moulding requires hot plastic to be injected under immense pressure. The design of the model has to reflect the different characteristics of each type. And, as we are not producing solid objects from the mould, the parting faces must show both the outer parting lines, and the inner faces, and produce a parting curve.

Core cavity removal is also an automatic process, achieved with just a couple of mouse clicks. As well as parting faces, the software can be used to create inserts, cooling channels, connectors and ejector pins. Again, simplifying and speeding up processes, VX has introduced an electrode Wizard that automatically creates mould electrodes that handle electrode offset, using a unique planar operation that is 40% faster than other methods - a powerful tool for complex moulds and dies.

Creating the mould

The next stage in the process is to produce the extruded shape that will surround the part - filleted at the front, so that it can be slotted into the mould block. One shape is then divided by the other to produce the split moulds. This is a powerful feature that depends on VX's hybrid modelling technology. The parting faces are used to create the separation. If you don't use hybrid modelling this is a very complex procedure, as the part has to first be converted to a solid. Not a problem with a part that only has a few surfaces - but some of the more complex parts being produced by this method can comprise up to 200,000 separate surfaces! The operation is completed for the top and bottom part of the mould, and also for the cavity.
That is far from the end of the process though! The mould is held between mould plates, clamps and risers. The plates are available from a number of suppliers, and VX has a library of those that are available (Hasco, etc.) and the software can determine the most suitable model or size for basic moulds.

A number of plates are used, bound together with bolts, the size and length of which also being calculated automatically from the start and end plates, once the user has defined their x and y locations.

Ejectors are used to push awkward bits of the part out of the mould. Again, these are standard items, and are merely accessed from the library and dragged into position in the mould. Similarly with retaining rings, which auto-locate on the top of the mould.
Finally there is the bolt, or ring, that needs to be accessed from the library and placed on top of the mould, to ensure that the heavy mould can be picked up and moved into place, and the water connectors for attaching water pipes to the cooling lines - drilled into the plates - which are used to cool the mould. And, as you would expect, all components used in creating the mould are used to compile a BOM.

Enhancements within Version 13 of the software, due out later this year, will provide users with greater control over visualisation of the mould and part - allowing them to switch rapidly between wire and shaded models, so that users can see inside the mould to position components. Sliced parts will also be shown in conjunction with the rest of the mould in wire frame. Besides providing unparalleled visual access to the whole mould, this is useful for positioning or orientating the uniquely shaped ejectors.

Conclusion

VX can be used for more than just designing advanced parts. It can fulfil all other aspects of the production process as well, creating the moulds used for different moulding technologies, and also creating the cutting paths and operations used to mill the dies. In effect it provides a complete solution for consumer product manufacturers. www.akelaltd.com

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