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Simulation Software For Error-Free Metalcutting

Pat Waurzyniak
By Patrick Waurzyniak Contributing Editor, SME Media

The latest simulation packages offer CAD/CAM and NC-level code-checking to ensure fast, error-free machining processes

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The Reviewer App in VERICUT illustrates a program showing that the machine spindle will collide with the part during the process.

Manufacturers must avoid costly machine errors that cause catastrophic damage to both machine tools and expensive workpieces. Even a minor error in, say, a titanium aerospace component can be a major expense. Ensuring top quality means using high-fidelity simulations to set up the cut. It has never been more critical.

Today’s simulation tools offer a variety of ways to prevent such costly programming errors.

Most CAD/CAM systems offer a basic level of simulation, based on cutter location (CL) data. Users can also turn to third-party simulation packages that feature more accurate and sophisticated G-code simulations. These give highly realistic visualizations of all the parameters in machining, from cutters to machine tool components and accessories—even the parts being cut.

Faster, More Accurate Simulations

Manufacturers are looking for improvements in simulation speed, visual quality and accuracy, noted Gene Granata, product manager for VERICUT NC simulation, verification and optimization software, developed by CGTech, Irvine, Calif. “Users want simulations to look more realistic and run faster, while still calculating extremely complicated material removal and collision checking.”

Today’s users need better digital twin virtual machines, Granata said. “Simulation [based on] the post-processed NC code that drives the actual machine offers the highest level of verification,” he noted. “Digital twin machines must accurately simulate machine motions, mimic tool and work offset handling, process subroutines and emulate complex control functions that change motion behavior on the machine. CGTech’s machine building specialists even go as far as extracting parameter settings from the CNC and incorporating them into the digital twin for the most accurate ‘twinning.’”

Third-party simulation systems like CGTech’s VERICUT and the NCSIMUL package offered by Hexagon Manufacturing Intelligence Division, North Kingstown, R.I., typically feature higher-fidelity visualizations of the entire machining process based on the actual G-code running the process rather than on CL data. Hexagon’s latest NCSIMUL CAM simulation in the company’s Product Software portfolio adds new features to its Optipower and 4CAM programs, as well as many interface enhancements.

Helping manufacturers bring their factories in line with the Industry 4.0 philosophy of smart production, Hexagon said its NCSIMUL 2020.1 simulation update introduces an additional parameter to NCSIMUL Machine. Optipower compliments the Optitool module by adding the necessary power and torque to remove material. Hexagon Technical Director Philippe Legoupi said it is used as a limiting parameter, which optimizes the program and limits power, avoiding risks of breakage. “It takes into account the type of material, the chosen tool, and the definition of its angles,” Legoupi said. A graph shows the evolution of the power on the tool, so it can be limited to avoid possible flexions, overheating and premature deterioration.

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The Hexagon NCSIMUL full G-code simulator showing a mill-turn machining process simulation.

“Hexagon is helping improve quality and productivity for NCSIMUL users with accelerated implementation, working with cutting tool and CNC machine providers,” added Silvere Proisy, NCSIMUL U.S. general manager. He said NCSIMUL provides a platform of solutions, from design to metrology, including the full process of engineering and manufacturing. “NCSIMUL is a direct slice of the company vision,” said Proisy. “By providing G-code simulation since the beginning of the ’90s, NCSIMUL provides true digital twin machines, with all the functionalities CNC users will find on the real machines. NCSIMUL 2021 provides an improved user interface and full integration of CAD and CAM connectivity with CAD native format reader, simplifying the data transfer for the end user.”

Other simulation options include the recently updated CAD/CAM simulation modules from Aachen, Germany-based software components developer ModuleWorks. The company’s latest ModuleWorks 2019.12 CAD/CAM components update included updates to its three- and five -axis machining modules, which are plugged into partner companies’ CAD/CAM software, as well as a Cutting and Adding Material Simulator that is said to add new algorithmic enhancements that improve the visual accuracy of simulations.

Expanding Simulation’s Reach

Two trends in simulation represent further movement toward machine awareness and the push for interactive data, according to Ben Mund, senior market analyst for CNC Software Inc., Tolland, Conn., the developer of Mastercam CAD/CAM software. “True machine awareness involves digital twins of all CNC-driven machines with full simulation of any physical and process components, including tool motion, complete machine motion, and true material removal/addition simulation,” Mund stated. “The industry has seen dramatic advances in this field in the last several years, but there’s still work to be done.”

Interactive data helps improve automation by feeding information from the simulation back to the CAM software to help maximize the efficiency of a machine tool, Mund said. “This interactivity can be useful beyond, for example, just maximizing a machine’s output by helping to give preemptive warnings about a machine’s physical state.”

One of the big obstacles manufacturers have to overcome with simulation is the huge number of options in machine hardware and tooling, he added. “While this means today’s shop is far more versatile than before, it also poses one of the most interesting hurdles to modern simulation,” Mund said, noting several issues. “The number of CNC languages poses a challenge to true G-Code simulation. Modern machine tool and controller flexibility means that there are a seemingly infinite number of custom parameter combinations between them. The preferred custom outputs of CNC operators add another layer of flexibility, simulation and complexity. And, finally, working to bring all these elements together to achieve machine awareness—a closed loop between CAM and machine simulation—represents one of the biggest efforts in modern simulation.”

Mastercam includes three levels of simulation in a common interface, letting users focus on one specific element of a job or the entire process as a whole, Mund noted. “Users can simulate toolpath motion with path backplotting, material removal simulation and stock collision checking, or full machine simulation with active collision detection between the tool, stock, holders/fixtures, and the machine components.”

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A boneplate component being machined on a DMG Mori system is simulated in Mastercam CAD/CAM software.

There is a balance between comprehensive simulation for toolpath programming and full G-code simulation that is customized to machines on the shop floor, Mund said. “With more than a quarter-million installed seats, we try to provide the best possible tools, but there will always be a level of customization that is best done by a G-Code simulation package. Mastercam delivers built-in verification capable of complete machine simulation. We also have a plug-in for the VERICUT independent G-code simulator. We work to give Mastercam users flexibility and choice in the level of simulation to meet their specific needs.”

Machining Complexity Increasing

A key trend is simulating more complex machines with complex attachments, workholding, and tooling, said Marc Bissell, senior applications specialist for HCL Technologies Ltd., the Noida, India-based developer of CAMWorks software. “Flexible machining cells, robotic loaders, and automated palletized systems are becoming more common, increasing the need for simulating these devices,” Bissell said.

Another trend he sees is a preference towards true G-code simulation rather than simulation based on CL data. “True G-code simulation provides assurance that any errors in post-processing can be detected and avoided,” Bissell said. “There is also a trend towards integrating simulation into the CNC programming process instead of simulating after the program is complete.” For this, CAMWorks runs simulations as each operation is being created and programs parts in SOLIDWORKS Assembly Mode, he noted. In assembly mode, programmers see workholding and tooling during part programming and simulation, detecting any collisions or other issues earlier in the process.

“One of the biggest ongoing obstacles we face is access to accurate solid models of the machine tools,” Bissell added. Some companies like Haas Automation make solid models of their machines readily available to CAM companies online. “However, other machine tool builders want to charge for models and/or make it difficult to acquire usable solid models for simulation,” he said.

“Another obstacle is performance versus accuracy. Partly because STL files are still predominantly used for simulation, maintaining both accuracy and performance has long been, and continues to be, an issue,” he said. “However, more powerful and faster hardware is helping to compensate. Lastly, detailed models of the tooling, fixtures, and workholding devices are required to run accurate simulations, and the time and effort required to acquire and assemble these makes integrated CAD/CAM with machine simulation a necessity. As an added benefit, all of the CAD and CAM data is stored within a single file and the toolpaths developed by the CAM programmer will update automatically to design changes, so the current revision of the part is always the one being machined.”

With part designs and manufacturing processes becoming more complex and expensive, many companies struggle to keep up with technology, noted CGTech’s Granata. “Manufacturing technology is expanding at a frightening rate,” Granata said. “With the explosion of additive manufacturing [AM] and hybrid methods, most companies realize they must invest in expensive equipment and learn how to apply these new processes. Simulation plays a critical role in learning to use these unfamiliar machines. Diversity of CNC machines and manufacturing methods can lead to many CAD/CAM and related applications used to create programs for them. Having one simulation software that verifies all the NC processes helps programmers be more efficient, and enables them to see the entire manufacturing process end-to-end for making the part.”

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CAMWorks ShopFloor provides users with an application to leverage simulation, CAM data, and solid models with MBD and PMI information on the shop floor at a fraction of the price of a full CAD/CAM system, according to the developer.

The key is making it all work, he added. “Using simulation software like VERICUT, where virtual machines can be easily built, also enables manufacturers to create and ‘test drive’ machines they do not own.” Or, they can virtually modify existing machines by, for example, adding auxiliary rotary tables or angled head attachments, or even design new machines that may better handle the task of making their parts.

Validating Machines and Processes

Modern machine tools can have complex kinematics, such as multiple channels with two or more multiple tools cutting the same part simultaneously, or multiple parts mounted at multiple spindles, noted Sashko Kurciski, senior product marketing manager, NX for manufacturing solutions, Siemens Digital Industries Software Inc., Plano, Texas. For example, five-axis machine tools typically have three linear and two rotary axes, which support unlimited tool positions and orientations within the workspace of the machine tool.

“For simultaneous five-axis motions, it is extremely important to understand how the actual controller executes the NC code, i.e., which kinematics solution is picked in order to avoid collisions or gouges,” Kurciski said. “These sophisticated machine tools only amplify the need for accurate NC code simulation not only for toolpath validation, but also for machining process planning to avoid possible collisions and to optimize cutting times. Using a highly-accurate simulation is critical to be able to stay competitive.” It requires using a comprehensive digital twin of the machine, controller, and the entire process, he added.

Manufacturers need the digital model of the machine model to be accurate, Kurciski added. “Possible issues might include incomplete definition of the kinematics of the machine tool and missing information about the controller and the underlying software. Typically, the in-CAM simulation is based on the internal representation of the toolpath, which is different from the G-code [NC program] that controls the machine,” he said.

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A milling operation shown in Siemens NX CAD/CAM uses full G-code simulation.

To stay competitive, manufacturers need to deliver increasingly complex parts faster with better quality, while reducing production costs (due to shrinking profit margins), Kurciski said. This requires maximizing machine uptime, minimizing errors in production and shorter machining cycles. Digital validation of the machining process is the critical component in achieving these goals.

“Some form of machining simulation is available in many CAM systems. While in most cases the CAM systems can simulate the internal representation of the toolpath, this can differ from the G-code that runs the machine,” he said. “This causes a disconnect between the virtual and physical words of manufacturing that can result in costly errors on the shop floor.”

To address limitations of in-CAM simulation modules, Kurciski noted that some machine shops use third-party simulation software in addition to their CAM systems. “Introducing a stand-alone system in the process introduces more inefficiencies and possibilities to use incorrect data due to multiple data transfers between systems,” he said. “Additionally, this disjointed process relies on multiple systems and can make the process inflexible and slow.” He thinks it prevents manufacturers from quickly reacting to design or process changes that require automated toolpath recalculations and validation of the updated machining sequence.

Systems such as NX CAM include integrated G-code-based simulation, which enables programmers to ensure that the same NC program that runs the machine tool is used to simulate and verify in the same NC programming system, Kurciski said.

“You can achieve high-fidelity simulation only if the NC simulation module considers all the machine kinematics data and all the moves, which will finally be executed on the physical machine tool,” he said. “Without using G-code in simulation, you cannot accurately simulate the machining process. For example, using the actual G-code for simulation enables companies to get accurate machining time estimates, including cutting motions, position and transfer moves, and tool changes.”

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An impeller machining operation is simulated in Dassault Systèmes’ CAM software. Dassault features simulation functionality in both its SOLIDWORKS and DELMIA manufacturing software.

NX offers one more level of simulation using Virtual NC Controller Kernel (VNCK) from Siemens’ Sinumerik controllers, Kurciski said, enabling a new level of accuracy when using 3D simulations to validate machining operations. “The integrated Virtual NC Controller Kernel solution is driven by an accurate and complete software model that is provided by the controller manufacturer and calibrated for your machine tool,” he said. “The resulting simulation responds exactly like a real machine with the same toolpath and setup. The integrated solution facilitates the closest possible digital representation of actual machine tool motion with highly accurate swept paths, speeds and accelerations, and tool changes. The solution’s software is calibrated for specific machine tools with the hundreds of unique performance parameters taken from the real machine and controller.”

Simulation a Must for Industry 4.0

Fast, accurate simulations are a must for manufacturers seeking to capitalize on smart manufacturing initiatives. “Time is money. Companies that are investing in Industry 4.0 and smart manufacturing realize that for them to stay competitive, they need to digitally validate the entire manufacturing process before any work is done on the shop floor,” stated Mike Buchli, senior product portfolio manager, manufacturing, Solidworks, for Vélizy-Villacoublay, France-based developer Dassault Systèmes. “Simulating toolpaths and machines is critical in the success of digital validation.”

The biggest challenges for manufacturers today are the workflow of programming toolpaths and simulating the kinematics, Buchli said. “Often, these workflows require the use of multiple applications, which means a user has to manipulate two different interfaces. As CAM technologies evolve, users will see the ability to program and validate in one interface, which removes the barriers to test different scenarios as they apply the toolpaths.

“Both SOLIDWORKS CAM and DELMIA (Dassault Systèmes’ brands) provide easy-to-use simulation as you program,” he continued. “Often there are two distinct methods for toolpath simulation. One is the more traditional cutter location validation, which is quick and provides feedback on validation for simple machines, such as three-axis mills, traditional engine lathes, waterjets, plasma cutters, and lasers. SOLIDWORKS CAM provides a simple, easy-to-use interface to validate these toolpaths quickly and efficiently.”

As users move into complex machining of multi-axis programming with complex machine movements, DELMIA provides the ability to program with the machine in real-time to validate the kinematics using both cutter location data and actual G-code, according to Buchli. “By allowing the user to load the machine with kinematics into a digital environment, the user can see in real time how the toolpaths are going to be leveraged in the real world,” he said. “This instant feedback gives the programmer a full understanding of how their decisions affect the efficiency of the component to be machined.”

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