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When it Comes to Simulation Software, Seeing is Believing

https://www.flickr.com/photos/31274959@N08/17939530228
Manufacturing Engineering Magazine November 2018
By ME Staff Report

Tired of riding the red button? Simulation software is the key to safer, shorter machine setups.

In a perfect CNC world, the first part is always a good one. There’s no need for extra blanks or barstock. Setup times are only as long as is needed to swap out a few tools and load a new program. There’s never a crash, never the need to reprogram an inefficient bit of code. The operator just pushes the green button and out pops a finished workpiece minutes or hours later.

What is the magical technology that makes this world possible? It’s called simulation software, and even though it’s brought very few shops to the state of manufacturing nirvana described above, it’s an important move in that direction.

By giving programmers the ability to simulate everything about the machining process—the toolholders, spindles and turrets, the constantly changing workpiece and the cutting tools moving around and through it—software developers are making their virtual worlds into highly accurate predictors of everything that will occur once that green button does get pushed. The bottom line is clear; if your shop isn’t using toolpath simulation software to prove out its NC programs, you’re not only wasting valuable production time but also putting expensive machine tools and your safety record at risk.

Taking Out Insurance

According to Ben Mund, senior market analyst for Mastercam CAD/CAM developer CNC Software Inc., there may be some very good reasons to do investment for simulation. Most CAM systems today offer some level of toolpath simulation that is perfectly acceptable for the majority of machining applications. The difference between this and dedicated simulation software is that CAM packages, as a rule, do not read the actual post-processed G-code used by the machine tool. Because of this, standalone toolpath simulation provides an added layer of security for extremely high-value jobs and complex machining applications. It’s like taking out an insurance policy.

As with everything else in manufacturing, however, CAM software is increasingly capable, and that includes the ability to simulate more of the machining process – where crude wireframe models of the cutting tool and workpiece were once the norm, Mastercam and others now offer surprisingly realistic representations of the entire machining environment, including the workholding, toolholders, and even the CNC itself.

Powering Through

Very few of our customers use specialized simulation packages, as they are confident with the reliability of their CAM simulation. The small percentage of customers that don invest in standalone packages typically do so because they have multiple CAM solutions, perhaps from different suppliers, and a single, specialized solution provides consistent results. These are generally larger customers, such as aerospace or defense firms, which also tend to be the ones using different CAM packages for their mill-turn lathes, five-axis machining centers, EDM equipment and so on.

Ironically, standalone simulation software’s biggest advantage is the ability to read machine G-code.

The downside of simulating outside of the CAM program is that the user only discovers problems after the part has been programmed. If the error is early in the machining process, then many subsequent toolpaths will need to be reprogrammed. But by simulating everything in the CAM program, these unnecessary and costly recalculations can be avoided.

Built-in simulation gives programmers the ability to quickly determine the effects of toolpath changes, but added that this is not be-all, end-all solution for a number of companies.

Do Me a Solid

Like the other software providers interviewed, Dassault Systems CAM products offer accurate, realistic simulation capabilities, with complete 3D representations of the machine tool, including clamping devices, chucks and jaws, and indexing heads.

An integrated system allows all the accessibility and reachability challenges to be checked in very early in the program definition, including toolpath errors such as rapid traversing into the material or overly aggressive cutting parameters, as well as possible collision between any of the elements just listed.

however, that integrated CAM simulation is in some ways limited: Some customers don’t want to believe simulations coming from the software creating the tool path, fearing that the software vendor cannot be both judge and jury.

When the customer is using several CAM solutions in its facility, a single external simulation program—assuming it has an accurate interface to the CAM software—is preferred for its ability to provide homogeneous validation.

Specialized simulation software is often more comprehensive than CAM-based simulation, which tends to be more toolpath oriented and does not consider the canned cycles and subroutines used on most controls.

Use the Force

Reading the code used by the machine controller is perhaps the key differentiator between standalone and integrated simulation software. A number of people are trying to dispel the value of third-party simulation by claiming it’s unnecessary, or it’s overkill. But in order to attain a digital twin of the machine tool and machining process, you have to include things like five-axis compensation, tool length and fixture offsets, macros and subroutines, and how the cutting tool really moves while in positioning mode, elements that aren’t considered when internal instructions from the CAM system are used to build the simulation.

Optimization is not about CAM-specific routines focused on effective pocket clearing and constant chip loads, although those are admittedly necessary parts of the machining equation. What’s more important, he said, is finding ways to optimize toolpaths based on what the machine tool is capable of, given the workpiece material and cutting tools being used.

This is where Force comes in, a software module within the VERICUT suite that complements toolpath simulation and CAM software alike, no matter whose logo is on the box. This represents an entirely new level of Industry 4.0 programming intelligence, and CGTech as well as other software developers are really just scratching the surface of this capability. Every cutting tool manufacturer will tell you their tools can be pushed harder and optimization is the best way to achieve that.

Reading the G

Straddling the fence between standalone and integrated simulation is Siemens PLM Software Inc. which was one of CGTech’s earliest partners and continues in that role today. But as Siemens’ Senior Director for Advanced Part Manufacturing Vynce Paradise explained, the company decided along the way to develop its own spin on simulation, one that is an integral part of its NX CAM software.

There are many good CAM systems out there and all offer some level of toolpath simulation, but it’s important to recognize that there are multiple levels available. There’s the basic simulation where you can see the stock model, the cutting tool, and maybe the toolholder, each moving relative to one another. We call that toolpath verification, and while useful, it’s just a starting point.

Spring Forward

The first is that simulation is not only for the shops with highly complex machine tools or expensive parts. Of course the primary customers are the ones with multi-channe lathes and five-axis machining centers, but as we seeing an increase in shops that want to optimize their NC programs, and this includes those with basic two- an three-axis machinery. While no one can afford to crash any piece of capital equipment, it’s the smaller shops that are most affected when this unfortunate event occurs.

Toolpath optimization from Vericut toolpath simulation and verification software from CGTech is based on projected cutting forces and helps to improve tool life and eliminate the vibration that leads to chatter, according to the company.

With toolpath simulation, programmers always know where the tool was, and where it’s going next, such as in this Mastercam module.

To the critics who suggest that the use of standalone simulation software is both time-consuming and error prone, Proisy said users should look to automation as the next step in toolpath simulation; by installing NCSIMUL on a server connected to the shop floor network, it’s possible to send toolpath files to a “black box” and have them verified automatically—unless there’s a problem, the only effort is reading the emailed report that the G-code is good to go. This is but the first step down the automation road.

According to Prosiy, his company’s software is currently able to reprocess NC programs for use in other machine tools, and do so “with the push of a button.” Going forward, he envisions a flexible but smart interface that will take care of that step automatically based on which machine the job has been assigned to.

CAMpleting the Sim Puzzle

In terms of Industry 4.0 functionality, though, it’s CAMplete’s Intelligent Protection System (IPS) that offers the clearest indicator of the direction the manufacturing community is taking. Developed in partnership with machine builder Matsuura, IPS leverages TruePath’s simulation capabilities to deliver intelligent look-ahead based on in-process machine data. The result is a virtually crash-proof machine environment, even while in manual operation mode, according to Fritsch.

Considering the increased use of complex mill-turn lathes and multitasking machines, accurate machining simulation, such as that provided by DELMIA from Dassault Systèmes, is more important than ever.

As with other simulation systems, TruePath reads the G-code and verifies that it will be safe to run in the machine,” he said. “But at the end of the day, no one can make sure the operator actually puts the proper tool into the spindle and that the part is located where it’s supposed to be.”

IPS works in conjunction with TruePath to eliminate this potential problem, he said. Instead of relying on the CAM system for various values, there’s a high-speed fiber optic connection directly to the machine controller—there’s no need to make assumptions about offsets or macro values because they are read in real-time, and the machine is stopped safely before the problematic position.

Though not yet available for other machine brands, IPS is coming, as is intelligent machine probing that will measure parts, make the appropriate offsets, and automatically re-run whatever part of the program is needed to correct an out-of-tolerance condition.

“This is no different than what a human operator would do, but we’re doing it with software,” Fritsch said. “Right now we’re in the process of building this logic so that the machine can start relying on automated feedback to make decisions, ultimately improving part quality while reducing cycle times and operating costs. Shops shouldn’t have to machine two or three parts to make one good one, or waste time taking parts out of the machine to be measured—it should be first part, good part, without all the human interaction. That’s our goal.”


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