A growing number of manufacturers are now using software to simulate the CNC machining process prior to machining an actual workpiece. The demand for this software has been fueled by the increased use of more sophisticated machine tools such as high speed, 5-axis, multi-headed, and mill/turn machines. Manufacturers benefit from machine simulation by avoiding the expense caused by machine crashes, damaged components, and unprofitable use of their machines while proofing NC programs.

Technology enables improved software

While machine simulation technology has been available since the early 90's, the software tended to be expensive and inefficient on the computing platforms at that time. Subsequent advances in computing and software technology have enabled CAM software vendors to now offer affordable, robust, and fully integrated machine simulation with their CAM systems.

Tool path Verification vs. Machine Simulation

Tool path verification is useful to verify the accuracy, safety and efficiency of your NC programs, but it does not detect machine specific problems. This is particularly true where complex five-axis moves and/or high-speed machining are involved. Simulating the actual machine movement provides greater assurance that an expensive and possibly catastrophic collision will not occur.

Expensive material

Prices for metallic materials have increased dramatically in recent years. $11,000 is a lot of money", says Dave Wilhelm, Lead Programmer at Metalex Mfg Inc. in Cincinnati, Ohio. That is the cost of just one piece of stock for an impeller manufactured by Metalex. "We cannot take any chances, so every program is simulated before it is sent to the machine", says Mr. Wilhelm. Metalex specializes in manufacturing complex components often made from difficult machine materials. "Because of the time it takes to receive and prepare the material, the expense is much greater than simply the cost of the damaged material", continued Mr. Wilhelm further underscoring the importance of detecting problems before an actual part is destroyed.

Complex rotary axis configurations

Metalex employs several different 5-axis machine configurations. For one particular job it was necessary to mount a 90-degree head onto the spindle of a horizontal machine equipped with a B-axis rotary table mounted on an A-axis trunnion. "With such a complicated configuration, it can be difficult to predict exactly how the machine will move when performing 5-axis cutting operations", says Wilhelm. "When running our initial NC programs through the simulator, we were able to see that our tool path strategy would cause the machine to move the 90-degree spindle to the opposite side of the trunnion which would have caused leverage and travel problems. To our benefit, the software enabled us to modify the tool path strategy to correct the problem without ever putting the program on the machine", stated Wilhelm.

Optimizing setups

"How the workpiece is mounted on the machine can be critical when performing 5-axis operations. We can simulate different setups to ensure that we achieve optimum machine movement," explained Wilhelm. Such use of the simulator reduces machine downtime and cycle time.

Automated part handling

To achieve higher efficiency, machines are often equipped with moveable pallet systems, bar feeders, automatic clamping systems, etc. Such systems can cause interference problems. Astro Spar, Inc. based in City of Industry, CA has recently installed two high-speed 5-axis machines from Handtmann A-Punkt Automation GmbH of Baienfurt, Germany. The machines are equipped with an A/C style 5-axis head and an automated clamping system. The clamping system allows clamps to be moved to different locations on the workpiece during the machining cycle. Says Astro Spar NC Programmer, Don Barnes, "Machine simulation is critical when using the automated clamping system. Without it, a collision could occur with a clamp resulting in serious damage to the machine".

High speed machining

The Handtmann PBZ NT used at Astro Spar has a spindle speed of 28,000, and programmed feedrates often exceed 800 inches per minute. Says Barnes, "Our machines are used for cutting production parts, not for simulating NC programs. At 800 inches per minute it would be difficult to stop a collision before it is too late. Therefore, proofing the NC program is handled safely and cost effectively using the machine simulator."