The Changing Role of Simulation (CGTech)

Going Beyond the NC Programming Department

Most NC programmers are aware of the importance of accurate workpiece verification and many are now finding CNC machine simulation to be a necessity as well. What some NC programmers don’t realize however, is that information gathered during NC program simulation can be used throughout the enterprise for a variety of other purposes outside the NC programming department.

For example, a complete electronic model of the in-process workpiece is automatically created during simulation of each NC operation. This geometry is not available anywhere else in the mechanical CAD software environment unless manually created in a CAD program. Most manufacturers are unaware that NC program simulation information can be used to automatically produce process documentation and robust in-process inspection documentation. And, in the near future, CNC machine probing programs can be created using this same in-process geometry. The benefits of simulation have moved beyond the NC programming department–process planners, machine set-up, production operations, quality assurance and even design engineering can all save a significant amount of time by using the data created by CNC machine simulation technology.

Getting Started with NC Verification Software

This “virtual machining” process is quite similar to setting up and running an actual prove-out on the machine tool. First, the user specifies the stock from which the part will be cut, either by entering dimensions into the software or importing a CAD model. Then, after selecting cutting tools, the NC program (either G-code data or native CAM output) is used to simulate the motion of the tool removing material from the stock. The programmer can watch the material removal process and see details of how each cut changes the shape of the part. This eliminates having to try to imagine how cuts from the current operation will affect subsequent operations.

During the cutting simulation, the NC program is verified to detect problems such as fast feed errors, gouges, and collisions that could potentially scrap the part, break the cutter, or crash the machine. If an error is discovered, the programmer immediately identifies the offending NC program record by mouse-clicking on the error. The problem can then be fixed during the programming phase so that by the time the NC program reaches the shop floor it is error-free.

Analysis of the “as-cut” part delves deeper into the verification process. Is the resulting cut part dimensionally accurate? Does it match the final desired part shape? NC verification software enables the user to zoom in on suspect areas for in-depth inspection. The part can be rotated and cross-sectioned at any angle to check areas that would otherwise be impossible to see, such as the intersection of drilled holes. Detailed measurement tools enable the user to verify dimensions such as wall and floor thickness, hole diameters, corner radii, scallop heights, depth, gaps, distances, angles, volumes, etc. VERICUT® also provides the ability to automatically compare the as-cut part with the original design. The AUTO-Diff module of VERICUT can embed the CAD design model inside the stock, automatically comparing the design to the in-process workpiece in order to reveal any discrepancies such as gouges or excess material not removed by the machining processes.

After running the simulation and making sure the NC program contains no errors, and that the resulting part is dimensionally accurate and matches the design, the NC program can be run on the machine without needing to waste time machining a test part.

Simulating the Entire Machining Process

In addition to simulating and verifying that the NC program produces the correct finished part, VERICUT enables manufacturers to build and simulate entire CNC machines in order to eliminate potentially disastrous machine crashes. A machine crash can be very expensive, potentially ruining the machine, and delaying the entire manufacturing schedule. But by simulating the machine and machining process beforehand, the chance for error is dramatically reduced. Proving-out new programs on the machine becomes an unnecessary step saving valuable production time.

VERICUT machine simulation software detects collisions and near-misses between all machine tool components such as axis slides, heads, turrets, rotary tables, spindles, tool changers, fixtures, work pieces, and cutting tools. The software can detect near-misses between machine components to check for close calls, and also detect over-travel errors.

The virtual machine tool model used during simulation can be created by the user or it can be supplied by CGTech. Several sample machines are supplied with the software and may be used as a starting point to create your specific machine configuration. Most importantly, CNC control files are supplied. These control files emulate the CNC control’s behavior and include various models of controls from Fanuc, Siemens, Heidenhain, Okuma, Mitsubishi and other manufacturers. Simulation of tool change, motion, cycles, sub-routines, macros, loops, etc. for all popular CNC controllers are supported.

Getting the Most from the CNC Machine

The final step in the verification and simulation process ensures that the NC programs sent to the shop are both accurate and efficient. To create the most efficient machining processes possible, optimization software can determine the best feed rates to use for each cutting operation. Achieving the best feed rates for each cut in an NC program has always been a goal for NC programmers, but has traditionally been a very difficult task plagued by a number of problems. First, trying to imagine the cutter contact and cutting conditions for each cut in a large NC program is virtually impossible. And manually inserting different feed rates for each changing condition is not practical. An incorrect feed rate estimate can break the cutting tool, damage the fixture, or scrap the part.

Typically either a single conservative feed rate is used for an entire machining sequence, or a higher (i.e. “high speed”) feed rate is used, but with a very conservative machining strategy. Both methods attempt to ensure that the cutter is not overloaded, but at the expense of very inefficient machining. Both of these strategies result in too slow cutting speeds or too light removal rates that waste time, increase costs, and prematurely wear cutters.

To address this issue, CGTech has developed the OptiPath® module for VERICUT. OptiPath is a knowledge-based machining package that essentially adds intelligence to the cutter. During the simulation, VERICUT knows the exact depth, width, and angle of each cut because the software also knows the exact shape of the in-process material at every instant of the machining sequence. And, it knows exactly how much material is removed by each cut segment, and the exact shape of the cutter contact with the material.

With this unique knowledge set, OptiPath determines the best feed rate for each cutting condition encountered, taking into account volume of material removed, chip load, and machine acceleration and deceleration requirements. If desired, the software can also divide cuts into smaller segments and vary the feed rates as needed in order to maintain a consistent chip load or volume removal rate. It then creates a new NC program, with the same trajectory as the original, but with improved feed rates. [see graphic]

Moving Beyond the NC Programming Department: NC Program Simulation for Product Engineers and Designers

Engineers often need a method of getting a model of the as-manufactured part back into the CAD system for a variety of reasons. Maybe the required CAD model does not exist but legacy NC program data to create it does. Frequently the as-cut part contains features (fillets, blends, etc.) not present in the original CAD design. But an accurate and complete model is needed for finite element modeling or environmental simulation or further engineering analysis. And sometimes simulating pseudo NC paths is the fastest and simplest way to create complex offset surface shapes.

Whatever the reason, VERICUT’s Model Export option can create either surface or solid model representations of the simulated machined part. The exported model can be either a surface or solid b-rep model with geometric shapes (cylinder, cone, plane, torus sweep, etc.) that represent machined features such as drilled holes, pocket corners and walls, filleted blends and other common manufacturing features. Very small machined features such as scallops created by ball-end mill contouring of complex shapes can be collected together into large surface patches representing the nominal feature intended by the machining operation.

Models can be exported in STL, IGES, STEP, ACIS, or CATIA V5 formats.

In-Process Geometry for Manufacturing Engineering

In addition to design engineering’s need for an as-manufactured CAD model, other manufacturing engineering and planning functions could use the information.

It is difficult to imagine, plan and design all the resources required for subsequent operations (NC programs, fixtures, custom cutting tools, inspection tools, work handling devices, transfer methods, etc.) without an accurate representation of the initial material state left by the previous operation. The accuracy, efficiency, and “correctness” of each operation depend on the NC programmer, tool designer, and process planner knowing the material’s initial geometric shape. Until now, the only way to create an in-process CAD model is with expensive, labor-intensive, error-prone, and inaccurate methods. However, exporting a CAD model of the in-process or as-machined solid model created automatically from the verification step makes it possible to avoid these time-consuming activities. Users can create the CAD model at any stage in the machining process.

Simulation for Set-Up and Production

VERICUT includes powerful tools for creating custom reports, tailored for a specific user/department/company’s needs, containing useful process information generated during the simulation. The automatically generated documents can be used for shop floor or in-process documentation, NC programming documentation, or to capture valuable process information generated during the VERICUT session.

Produced in standard HTML or PDF format, the report layout is highly customizable, including the ability to specify page design, fonts, graphics, tables, pictures, statistics, and user-defined information critical to documenting the CNC machining process.

Simulation for Process Planning, Scheduling and QA

In order for process planners to do their job effectively, it is crucial to know accurate machining times. This can be easily obtained by simulating the NC program in VERICUT. Times are calculated for every step in the machining process including the amount of time it takes to change tools, pallets, or other miscellaneous machine actions. This information can be essential to keeping the production floor operating to its full capacity.

Additionally, the Process Planners can use VERICUT to create robust inspection instructions in very little time. Typically, a manufacturing engineer, NC programmer or process planner manually creates these instructions to tell the machine operator what to measure and how to document the results. Without an in-process model of the part, manual methods are very tedious and prone to mistakes. The highly-customizable inspection instructions can be created by VERICUT automatically. This helps to establish a formal, but incredibly easy and efficient method to create the necessary documentation. This feature works by using VERICUT’s built-in measurement features. The software outputs the inspection instructions based on the dimensions of the simulated cut stock (as-cut semi-finished wall thickness= .15″, for example). The accurate in-process geometry contained in VERICUT is required to automatically generate this type of document, and is only available by simulating the NC program.

Simulating CAM output to view basic workpiece material removal is no longer enough in today’s incredibly competitive global marketplace. It is critical to be operating as efficiently as possible; modern simulation and optimization software has become a key tool to minimize the cost and time of production while maintaining or increasing product quality. It has evolved into an important process that protects and frees up CNC machines, helps to eliminates scraped parts, and creates in-process information that can be utilized throughout the manufacturing enterprise.

 

For more information about CGTech and VERICUT® software, please visit www.cgtech.com or call (949) 753-1050.

VERICUT71.jpg

A screen shot from VERICUT. The All machine tool components such as axis slides, heads, turrets, rotary tables, spindles, tool changers, fixtures, work pieces, and cutting tools are simulated to prevent a potentially disastrous collision. The G-code driving the simulation is displayed on the right.

VERICUT_reports1.jpg

VERICUT includes powerful tools for creating custom reports, tailored for a specific user/department/company’s needs, containing useful process information generated during the simulation. The automatically generated documents can be used for shop floor or in-process documentation, NC programming documentation, or to capture valuable process information generated during the VERICUT session.

 VERICUT_inspection_sequence-report1.jpg

Highly-customizable inspection instructions can be created by VERICUT automatically. This feature works by using VERICUT’s built-in measurement features. The software outputs the inspection instructions based on the dimensions of the simulated cut stock The accurate in-process geometry contained in VERICUT is required to automatically generate this type of document, and is only available by simulating the NC program.

OptiPath_optimization1.jpg

 

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