Cut the crashes: Medical Manufacturing

All images courtesy of CNC Software

Simulation provides an accurate 3-D visual representation of the amount of stock removed from a virtual workpiece at any stage of the cutting process.

achine shops of all sizes are purchasing record numbers of 5-axis CNC machines, and for good reason. These machines enable single-setup manufacturing strategies, which are much more productive than conventional machining using several pieces of equipment. Keeping manufacturing all in one setup also eliminates stack-up errors and resulting scrap.

In addition, many advanced, complex part designs are impossible to produce on anything but a 5-axis machine. To quote those parts, shops must invest in the equipment, and prices for reasonably accurate 5-axis systems have dropped significantly.

Along with the many opportunities 5-axis machining creates, there are substantial risks. Five-axis CNC programs are geometrically more complex than 3-axis programs, which can create more opportunities to damage cutting tools, toolholders, equipment and the part itself via a crash. For example, if a shop has hundreds of hours invested in a complex piece made from a single piece of stock, a crash would be extremely costly.

On the other hand, time on a 5-axis machine is far too valuable to be wasted by having operators hover over the machine as it cycles through its operations to verify they are safe and correct. This is especially true for small runs.

With so much to gain—and lose—various forms of machine simulation have become the 5-axis CNC programmer’s constant companion. Simulation is the first line of defense against damage and lost productivity. It also gives the programmer additional tools to solve fixture-design-for-manufacturability challenges and make parts more productively. Manufacturers that have previously not used their CAM systems’ simulation capabilities often become converts as soon as they install their first 5-axis machine. They are frequently surprised at the depth of simulation resources provided.

Program Simulation

High-end CAM software has built-in simulation capabilities that allow programmers to ascertain that the program they have written will perform cutting operations exactly as they had in mind when they wrote them. The software typically includes the following features.

Backplot simulation.Almost every CAM programmer relies on backplotting—on-screen geometrical “tracing” of the contact point—to visualize tool movement through various CNC manufacturing operations. Backplotting provides fast, visual confirmation that a tool is performing the desired cutting operations in the most efficient sequence. As the backplot simulation progresses, information about the tool choices appears in a separate window. Backplot simulation serves as a sequential template for checking the appropriateness of tools and settings at each stage of the process.

The backplot simulation also generates a close approximation of machining time not including tool-change time. This can be invaluable for estimating costs, especially when they involve CNC cutting programs that will run for many hours, if not days.

If the programmer and machinist are different people, conferring over the backplot simulation helps them get on the same page. The machinist will have a clearer understanding of how he should set up and run a process and the programmer can confirm that the strategies he has chosen are appropriate for the equipment and shop conditions.

Stock-removal simulation.This type of simulation provides an accurate 3-D visual representation of the amount of stock removed from a virtual workpiece at any stage of the cutting process. This representation may be color-coded to indicate that material removal falls within the specification or may automatically highlight areas where too much or too little material has been removed. Skilled 5-axis programmers frequently run the stock-removal simulation at high speed, as if it were time-lapse photography, dynamically zooming in and out of areas of concern on the fly.

Those who program 5-axis machines find themselves using backplot, verify and full-blown machine simulation after programming every operation. This makes them better programmers because they quickly learn what will and won’t work. It also gives them powerful tools that allow for safe experimentation with different manufacturing strategies. Used this way, machine simulation is the safest, most-effective way to create effective and efficient production methods.

Beyond the Basics