Berechnung von Werkzeugmaschinen in der ANSYS Umgebung. Roberto Rossetti, CADFEM (Suisse) AG

Transcription

1 Berechnung von Werkzeugmaschinen in der ANSYS Umgebung Roberto Rossetti, CADFEM (Suisse) AG

2 Machine tool simulation in the ANSYS environment - 1 -

3 Overview Stiffness analysis Harmonic analysis Weight influence Modal analysis Transient structural analysis Influence of a temperature Command control MOR4ANSYS, Model Order Reduction Transient thermal analysis - 2-

4 Stiffness analysis Loading Goal is to create a load case similar to the real loading Define action and reaction forces at the Tool Cutting Point (TCP), defining the stiffness loop of the machine-tool Idealise the liaison of the machine to the ground - 3 / 38-

5 Stiffness analysis Results Goal is to obtain the maximum amount of information Deformation plots Stress plots (giving information about areas to be modified) Stiffness matrixes (overview of stiffness and crosstalk terms) T - 4 / 38-

6 Stiffness analysis Parametric study Goal is to evaluate the stiffness at different working positions Simulate the machine-tool at different position Parameter environment of ANSYS Workbench - 5 / 38-

7 Weight Influence on accuracy Results Deformation in function of the position Relative value is determining Axis makes waves along Z axis z - 6 / 38-

8 Temperature difference & Accuracy Concept What is the influence of a temperature difference on the accuracy? Let s say the machine-tool is set up at 8am. Room temperature is 22 C During the day, the room temperature rises to 23 C. The machine-tool will change its size due to dilatation. What is the influence on accuracy? Steps 3D parts are needed to replace bushings, for example so that the spindle expansion can be taken into account. As the temperature is uniform, there is no gradient no thermal coefficients are needed. - 7 / 38-

9 Temperature difference & Accuracy Definition of the temperature difference. Important is the displacement difference between tool and workpiece Total deformation x-dir. y-dir. z-dir. 2.1 μm -3.0 μm -0.1 μm - 8 / 38-

10 Modal analysis Concept Find the first eigenfrequencies and eigenmodes of the machine tool. Generally speaking, for a given energy, the higher the eigenfrequency, the lower the amplitude. Goal is to Identify the eigenmodes that might influence the machining process Find constructive modifications that will change these modes and / or increase the corresponding frequency. Steps Similar to a static analysis Define point masses replacing non-idealised parts The liaison to the ground is very important - 9 / 38-

11 Harmonic analysis Concept The machine is excited over a frequency range by a given force. Amplitudes and phases are computed Results accuracy depend greatly on the accuracy of the input force and on the damping used Very useful to determine how much an eigenmode will influence the machining process and to get amplitudes between modes. Steps Similar to a static and modal analysis Define frequency range and sampling / 38-

12 Harmonic analysis Important is the displacement difference between tool and workpiece - 11 / 38-

13 Transient structural analysis Concept The machine is excited by an event. The reaction of the machine-tool is analysed Results accuracy depend greatly on the accuracy of the input force and on the damping used Useful to assess the machine dynamic properties and non-linear effects Steps Define an initial state and an excitation Damping is important to obtain realistic amplitudes Perform the transient analysis over a given number of time steps - 12 / 38-

14 Amplitude Transient analysis Example : An initial velocity is applied to the Y-axis. The axis is then stopped. This event excite some eigenmodes. The vibrations are then damped out. V 0 Time - 13-

15 Command control Principle It is possible to take into account the command control. A specific tool box is available in ANSYS Mechanical APDL. Influence of the command control on an harmonic analysis Response of the machine-tool to command control targets Response of the machine-tool to external excitations Electrical schematic as ANSYS elements S E TR UE PG S RE IT D FI R EL CE IN O SE R DR T VIE W SPLIT PLOT SCOP PLOT ES SENS PLOT ANIM STD ATES TR. IN/OU T IN- CONST IN- SPRUNG IN- RAMPE IN-SINE U- SENSOR V- SENSOR A- SENSOR AKTOR ADDSCO PE RUN TRAN SIEN HAR T MONI MOD C AL MISC BEAM MASS SCH WING ER ELEME NTS P-GLIED I-GLIED D-GLIED D2- GLIED PI- GLIED PD- GLIED PID- GLIED PT1- GLIED PT2- GLIED CONNEC T NEGIER EN MECH P-GLIED D-GLIED PT1- GLIED PT2- GLIED SUMME NGL. DIFFERE NZGL. COMB IN37 P- GLIED I- GLIED D- GLIED SUMM ENGL. DIFFE RENZG L NODE TRANSF ERDOF DECOUP / 38-

16 Command control Harmonic analysis The harmonic response of the machine-tool will be influenced by the command control. Resonances due to the command control are visible. Kindly provided by Gebr. Heller Maschinenfabrik GmbH - 15-

17 Command control Transient analysis The entire system is modelled into ANSYS. Target position f(t) Control Velocity sensor Position sensor Axis Spindle Motor Actuator Maschine bed - 16-

18 Command control Transient analysis Scenario 1 : positioning error. Input curve Control Error is the difference between the input and the output curves Axis Maschine bed - 17-

19 Command control Transient analysis Scenario 3 : response to a force or perturbation. Input curve Control Displacement as an output F Axis Maschine bed - 18-

20 Y 20,00 18,00 16,00 14,00 12,00 10,00 8,00 6,00 4,00 2,00 für verschiedene Kv- und Kp-Werte 0,00-12,50-7,50-2,50 2,50 7,50 12,50 X Soll Ist 1 Ist 2 Command control Time domain Frequency domain Positioning Kreisformtest Perturbation damping

21 MOR4ANSYS Model Order Reduction Principle The main idea is to reduce the size of the model by performing a so called Model Order Reduction. Mass, Stiffness and Damping matrices are extracted from ANSYS and then dimensionally reduced to smaller matrices

22 MOR4ANSYS Model Order Reduction Principle The dimensionally reduced matrices are then imported into Simplorer. Simplorer permits to idealise a complex system with block corresponding to different physics

23 MOR4ANSYS Model Order Reduction Application The whole machine-tool system can be idealised into simplorer: Command control (electrical circuits) Structural parts (Model Order Reduction) All scenarios discussed before can be played with this idealisation - 22-

24 MOR4ANSYS Model Order Reduction Advanced application - CHATTERING The Simplorer model contains : Command control Machine-tool model obtained with MOR4ANSYS Cutting process as mathematical model - 23-

25 MOR4ANSYS Model Order Reduction Advanced application - CHATTERING The stability of the machining process can be assessed. not stable stable - 24-

26 Transient Thermal Example Coupled simulation: control of unsymmetrical heating 1 Spindle (machining) 2 Motor 3 Belt drive 4 Bearing 5 Bearing 6 Housing 7 Guideway 8 Housing 9 Spindle (drive) RED = Heat source - 25-

27 Transient Thermal Example Coupled simulation: control of unsymmetrical heating - 26-

28 Transient Thermal Example Coupled simulation: control of unsymmetrical heating - 27-

29 Thanks! CADFEM (Suisse) AG Avenue de Cour Lausanne Tél.: