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CNC program motions can cause expensive damage, so simulating a job in the computer before it gets anywhere near the shop floor makes good sense. Charles Clarke explains.

Before using an expensive machine tool to cut a costly piece of stock material, it is reassuring to know that the motions of the CNC program are not going to cause unexpected or severe damage to either.

This reassurance can be gained by simulating the whole process graphically in the computer before the job gets anywhere near the shop floor. Generally the simulation should be able to depict the actual tool configuration limits and constraints and its full motions.

The simulation should also be controlled by the same mathematical output that the post-processor uses to generate the machine tool motions. But this is not the case in many instances where the simulations are produced from within the same software that is used to generate the CNC part programs.

It’s a bit like a trade or professional body investigating itself — the simulations are interesting, but unless the simulator is a separate application, such as Vericut from CG Tech, the information provided cannot be completely relied upon. In such cases ‘fresh air’ try-outs, or trial machining using soft materials, are the only alternatives.

An interesting development called MachineSim from Open Mind Tech-nologies — the developer of hyperMILL — takes this notion one step further, allowing the verification of a selected process without tying up valuable machine time.

Like other simulators, MachineSim allows the machining process to be run virtually, while at the same time dynamically rotating and zooming the 3D model of the machine and workpiece — including jigs and fixtures — to check for any gouging or collisions.

Simulations can be fast-forwarded, paused and rewound so that confidence of running increasingly complex parts on machines at extremely high speeds can be built up quickly, thus avoiding costly mistakes.

The key element here is hyperMILL’s patented Collision Avoidance Technology. Unlike Collision Detection, which will simply detect a collision and leaves the CAM programmer to work out a satisfactory resolution, Collision Avoidance means the collision is avoided automatically with no further action necessary — saving considerable time and effort.

According to Open Mind, after two to three months, hyperMILL customers have sufficient confidence in their toolpaths and post-processors that further investment in toolpath verification and machine tool simulation is unnecessary.

The company claims this is one of the main reasons why a growing number of UK sectors — including aerospace and Formula 1 — are moving to it.

F1 is significant here because recently a prominent racing engine manufacturer switched from its incumbent integrated high-end CAM system to hyperMILL after an exhaustive benchmarking process.

The CAD system has been retained, presumably for compatibility reasons, but the CAM has been replaced. This speaks volumes for hyperMILL and it’s no wonder it is growing over 200 per cent year-on-year in the UK.

Leading CNC simulator Vericut’s latest release, Vericut Version 6.1, contains a host of improvements — mostly as a result of user-feedback.

The program simulates all types of CNC machine tools, including those from Mazak, Makino, Matsuura, Hermle, DMG, DIXI, Mori Seiki and Chiron.

It runs standalone, but can also be integrated with leading CAM systems such as Catia V5, Unigraphics, PTC, MasterCAM and EdgeCAM. In addition to verifying CNC part programs it also optimises them to save time and produce higher quality surface finish. By doing so it also reduces scrap loss and re-work.

In Vericut 6.1, NC Program Review is now integrated into the main desktop allowing for navigation backwards from the last NC program line simulated. Error messages and NC program text are highlighted when a collision on the stock or fixture is selected.

Also, material can be replaced while stepping backwards, and then removed again while stepping forwards, allowing for the easy identification of problem areas. Both machine views and profile views are now active in Review mode, including an optional toolpath line display in the profile view. Synchronised sub-system simulation, such as for Mill/Turn and multi-channel controls, can now be displayed in Review mode.

For companies with multiple machines and several NC programmers it is now possible to ‘lock-down’ Vericut’s machine configurations using encrypted files to stop the machine configurations from being inadvertently modified.

Menu features are reorganised so ‘project-specific’ settings used during NC simulation tasks are clearly separated from ‘machine/control’ configuration settings. Using encrypted machine/control files automatically disables machine/control configuration menus. This configuration menu can also be completely removed from the main menu bar if desired.

Gibbs and Associates, which developed GibbsCAM, is introducing the GibbsCAM Machine Simulation option later this month. This capability complements the software’s Cut Part Rendering process simulation and allows for the entire machine tool motion of a CNC programme to be validated in an accurate simulation.

‘The latest class of multi-tasking machine tools represents just the beginning for machine tool complexity and configurability,’ said Gibbs president and founder Bill Gibbs. ‘We fully expect that multi-tasking machine tools will continue to evolve, and place even more extreme requirements on programming systems.’

Multi-task machine tools such as Mill/Turn represent one of the market’s fastest-growing machine tool segments. Their popularity is due to their ability to machine a wide variety of parts entirely within their working space — without human intervention.

Delcam’s PowerMILL 5-Axis has been enhanced so that it can generate a five-axis equivalent of any three-axis toolpath for multi-task machines. This might be necessary, for example, when a three-axis approach is being used for most of a job, but where some five-axis moves are needed to avoid an obstacle or to machine as closely as possible to a steep face.

The software automatically tilts the cutter away from the obstacle by the specified tolerance and then returns the cutting angle to the value set for the overall toolpath once the problem area has been cleared.

Now the system has been even further developed to allow fast, efficient programming of the most demanding machining applications.

Options for both roughing and finishing include machining to or from a point, orientation through a line or curve, programming using a reference surface and swarf machining for either surface or wireframe geometry.

Additional functionality — including trochoidal machining, parametric offset machining and Delcam’s patented Race Line machining — has been designed to help companies achieve ultra-fast machining speeds with an even greatly improved surface finish.