Simulation of Machining Operations Based on the VMT Concept
This section focusses on the dynamic modelling of the machine tool including its computer numeric control, and its interaction with the machining process. To properly simulate modern machine tools in machining condition, the virtual machine tool model based on SAMCEF Mecano is used to account for close interaction between the dynamic behaviour of the mechanical structure, drives and the control. To fully capture the dynamic behaviour of the machine, force interactions between the cutting tool and the workpiece are also considered. A strong coupling between the mechatronic model of the machine tool and a machining simulation tool is implemented. A specialized cutting force element has been developed. It considers the dynamics of the tooltip combined with the tool-workpiece engagement to generate cutting forces. The use of such digital twin model is demonstrated considering some machining operations.
KeywordsMachine tool Machining process Simulation Digital twin Integrated simulation Control
Furthermore, an integrated cutting force model is used to capture force interactions between the tool and the workpiece to fully capture the dynamic behaviour of the machine tool during the machining operations. This chapter deals with the integration of this cutting force model with the developed VMT module.
11.2 Machining Module
11.3 Coupling Architecture
In SAMCEF Mecano, two specific elements have been developed to manage these dynamics libraries. The first one, called DIGI element, allows coupling the mechanical model to any Simulink model and, in particular, control systems. The implemented staggered method is a fixed time step sampling, where both codes will exchange data (positions, forces …). Both codes manage their own time step and can compute several instants between two sampling times without updating exchanged data. This weak coupling is usually stable thanks to the small sampling times imposed by the control loops, which imposes passing times to the Mecano solver.
11.4 Simulation of Machining Sequences
11.4.1 Simple Machining Process with the High-Speed Box-in-Box Machine
Move z-axis forward to have a cutting depth of 4 mm.
Move y-axis up to simulate one cutting pass (milling with an end-milling cutter) as shown in the zoom of Fig. 11.6. The nominal tool y-velocity is 1.9 m/min.
Tool spinning velocity is 12,250 rpm.
Technological parameters correspond to two cutters end-milling tool that machines an aluminium holed workpiece.
11.4.2 Machining Process with Tool Change on a Multi-spindle Machine
Spindle 1 (right) is equipped by an end-milling tool (Diameter 10 mm–three cutters–corner radius 2 mm).
Spindle 2 (centre) is equipped by an end-milling tool (Diameter 12 mm–two cutters–corner radius 6 mm).
Z-axis is moved down to have a 4 mm cutting depth.
X-axis is moved forward to simulate a first cutting pass. The nominal tool x-velocity is 3 m min−1.
Set spindle speed to 12,250 rpm.
Once first pass is done, tools get out of the workpiece, and the machine gets back to its initial configuration. Tools are exchanged between both spindles, machine is shifted in the Y-direction and the operation is repeated.
During the simulation, the CAD representation of the workpiece is updated at each evaluation of the TWE. At the end of the simulation, this STL file is made available to the user for evaluation of the final workpiece geometry, including the effects of errors in the tool motion. The final workpiece configuration is shown on the machine CAD model, the effect of the tool change (zoomed area) is clearly observed.
11.4.3 Industrial Machining Process
In this chapter, the Gepro’s five-axes machine is considered. It is used to manufacture an aluminium workpiece defined as Twin-Control target project application, which includes all type of machining operations done with this machine [7, 8].
This machining sequence of about 1 min is simulated in about 2 h on a normal laptop. Even if far away from real time, this is acceptable for this kind of accurate model (142,000 time—steps–4176 degree of freedom) used for designing new machine or preparing machining sequence, but not for on-line monitoring.
The VMT concept is used for virtual prototyping of machine tools in working conditions. The proposed technology has been applied to build mechatronic flexible multibody models of several machines. This virtual machine tool is fully coupled to a cutting force module. This approach provides comprehensive simulations capabilities for virtual machine tool prototyping in machining conditions. The resulting Twin-Control simulation package is intended for both machine tool builders for design activities and machine tool users to improve their processes. In both cases, this virtual model can be used to avoid performing many costly physical tests.
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