Visualization of Simulated and Measured Process Data
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Although process monitoring can facilitate to detect deviations from required part quality and safe process conditions, the analysis and postprocessing of the measured data are not embedded into the CAx workflow. Binding the measurement data together with material removal simulation creates a powerful tool for CAM programmers and process engineers. The user can analyze 3D visualization of the machining process more intuitively. A developed CAM integration simulates material removal considering the actual tool coordinates (measured during the process) and can depict the acquired and simulated cutting conditions (spindle torque, axes accelerations, etc.) with various color schemes on in-process stock simulation.
KeywordsVisualization CAM CNC Machine tool Monitoring Simulation Milling
Over the last century, companies and research institutions have put significant efforts into improving the performance of machining operations. The progress was achieved in improving tool life through optimization of cutting tool geometry, cutting material, coolants, and coatings. Nowadays, these advances can be considered traditional and, to a large extent, this area seems to be over-researched, resulting in marginal output from research. In order to push back the frontiers of industrial practice, more sophisticated tools and approaches must be used to address process monitoring and controlling the conditions of the machine and tool .
Since computer numerical controls (CNCs) are used in almost all kinds of production processes, there is a way to improve CNCs such that the entire production chain may benefit from such an improvement. Because CNCs depend on the production cycles of the hardware to which they are connected, CNC implementations need to assure a certain level of interoperability. The technological standards of current CNC user interfaces do not provide the rich user experience expected of today’s HMIs. In addition, not all available information is connected and provided to the user. Information such as the current axis values and machining program are displayed as text, and only experienced users are able to use the information directly. When new data is introduced into these systems, either by exchanging the CNC, by adding hardware to the system or by adding simulation software, it is difficult to connect this new data to the information currently in the system.
Moreover, it seems that most of the publications target visualization of simulation results only. Apparently, computing of cutting forces and other process parameters can become an important issue for the industry, because it may facilitate reduction in ramp-up time and associated costs for batch production. Process monitoring data are often used to tune process parameters for batch production. Several parts are machined before the batch production in order to define the specification of a stable process. In contrast, a fully fledged virtual machining environment will result in reliable prediction of cutting conditions without performing real trials. It is likely that postprocessing and analysis of the data acquired after actual machining will become nearly obsolete after virtual manufacturing paradigm becomes an industry standard. Simulation approaches will avoid performing expensive trials. Creating a strategy that combines measurement and simulation data sources has a high potential.
Geometric simulation/verification based on the measured machine axis positions;
Colorization of the simulated workpiece geometry based on the simulated/measured process parameters (spindle torque, cutting forces, etc.);
Comparison of the simulated and measured process parameters.
On the software side, the aim is to replace the standard data display methods (tables, graphs, etc.) with a graphical interface that shows the current shape of the workpiece and the machine to enable users to immediately see what is currently happening. This directly connects the real world of the process, the machine, and the workpiece with the data at a certain instant in time. This allows users to directly find correlations and problems and apply the needed modifications to the process.
This chapter presents visualization functionalities provided by ModuleWorks to Twin-Control. This includes explanation of the principles of the underlying 3D simulation methods along with the description of the developed visualization features providing advanced visualization of measured and simulated cutting force values that are mapped on the predicted shape of the workpiece.
14.2 3D Volumetric Simulation
14.3 3D Simulation and Interfaces Combined
To connect the real-world shapes, a virtual representation of the machine and the current shape of the workpiece need to be maintained throughout the entire process. ModuleWorks uses its industry-proven MachSim (the machine and its kinematic) and CutSim (actual shape of the workpiece during the manufacturing process) software to create the 3D representation of the workpiece geometry and machine that can then be integrated into the CNC user interface.
For the Twin-Control project, this methodology has been extended and optimized. It has developed an interface to exchange internal simulation data for processing analytic modules that allow the prediction of process behavior such as stability and cutting forces. To display this information to the user at the machine, a second interface connects this data with the workpiece shape that was calculated in parallel. The other interfaces take real-world measurement data and integrate it into the same representation of the workpiece shape. The virtual system is completed by a system that delivers warnings to users and delivers additional security to the machine. Users can directly correlate data with the current shape of the workpiece. On the machine, this system can stop the process to avoid crashes and other unwanted process errors.
14.4 Additional Visualization Features
- Visualization of the tool–workpiece engagement. Figure 14.8 shows the contact area between a tool and the workpiece. This functionality is useful to analyze how cutting forces change along a part program.
- Visualization of the cutting marks on the machined surface. Figure 14.9a shows which surface outlook can be expected after grinding. This feature is expected to be necessary for aesthetic applications.
Visualization of future shape and position of machine components. Figure 14.9b shows two tools and spindles. The transparent ones are attributed to the future positions acquired from the CNC as the output of the look-ahead functionality. The real axis positions, machine geometries, and workpiece position are taken into account. The predicted position is examined toward potential collisions and may signal to halt the machine before the actual collision occurs.
Integration of the process monitoring data into CAM simulation is a tangible progress in the evolution of the CAx chain. Previously, the analysis of the cutting process measurements could not be performed in the CAM environment. In an extended CAM, immediate access to stored process parameters allows more robust verification and modification of NC programs. Three-dimensional machined surface colored according to the measurement can be analyzed more intuitively than graph plots. Also, it can be detected whether the extreme or unfavorable cutting conditions do really affect the machined surface. In a case of an actual or foreseeable failure, results of cutting force simulation can be exploited for operation re-planning to avoid tool and workpiece damage.
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