Berechnung von Werkzeugmaschinen
in der ANSYS Umgebung
Roberto Rossetti, CADFEM (Suisse) AG
- 1 -
Machine tool simulation in the ANSYS environment
- 2-
Overview
Stiffness analysis
Weight influence
Influence of a temperature
Modal analysis
Harmonic analysis
Transient
structural analysis
Command control
MOR4ANSYS,
Model Order
Reduction
Transient thermal
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-
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)
- 4 / 38-
Stiffness analysis
T
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-
Stiffness analysis
Results
Deformation in function of the position
Relative value is determining
Axis makes waves along Z axis
- 6 / 38-
Weight Influence on accuracy
z
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?
- 7 / 38-
Temperature difference & 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.
Definition of the temperature difference.
Important is the displacement difference between tool and workpiece
- 8 / 38-
Temperature difference & Accuracy
Total deformation
x-dir. 2.1 μm
y-dir. -3.0 μm
z-dir. -0.1 μm
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.
- 9 / 38-
Modal analysis
Steps
Similar to a static analysis
Define point masses replacing non-idealised parts
The liaison to the ground is very important
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.
- 10 / 38-
Harmonic analysis
Steps
Similar to a static and modal analysis
Define frequency range and sampling.
- 11 / 38-
Harmonic analysis
Important is the displacement difference between tool and workpiece
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
- 12 / 38-
Transient structural analysis
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
Example :
- 13-
Transient analysis
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.
V0
Time
Am
plit
ude
Principle
- 14 / 38-
Command control
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
DECOUP37
TRANSFERDOF
NODE
NEGIEREN
CONNECT
ADDSCOPE
PT2-GLIED
AKTORPT1-GLIED
A-SENSOR
PID-GLIED
DIFFERENZGL.
V-SENSOR
PD-GLIED
DIFFERENZGL
SUMMENGL.
U-SENSOR
PI-GLIED
ANIMATESTR.
SUMMENGL.
PT2-GLIED
IN-SINED2-GLIED
PLOTSTD
D-GLIED
PT1-GLIED
SCHWINGER
MODAL
IN-RAMPE
D-GLIEDPLOTSENS
I-GLIED
D-GLIEDMASSHARMONIC
IN-SPRUNG
I-GLIEDPLOTSCOPES
INSERT
GRID
P-GLIED
P-GLIEDBEAMTRANSIENT
IN-CONST
P-GLIEDSPLIT
RECO
RD
RESE
T
COMBIN37
MECHMISCRUNIN/OUT
ELEMENTS
VIEW
FILE
SETUP
Electrical
schematic as
ANSYS
elements
Harmonic analysis
- 15-
Command control
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
Transient analysis
- 16-
Command control
The entire system is modelled into ANSYS.
Actuator
Velocity sensor
Control
Position sensor
Maschine bed
Axis
MotorSpindle
Target position f(t)
Transient analysis
- 17-
Command control
Scenario 1 : positioning error .
Control
Maschine bed
Axis
Error is the difference between
the input and the output curves
Input curve
Transient analysis
- 18-
Command control
Scenario 3 : response to a force or perturbation.
Control
Maschine bed
Axis
Displacement
as an output
Input curve
F
- 19-19
Time domain
PositioningKreisformtest
für verschiedene Kv- und Kp-Werte
0,00
2,00
4,00
6,00
8,00
10,00
12,00
14,00
16,00
18,00
20,00
-12,50 -7,50 -2,50 2,50 7,50 12,50
X
Y
Soll
Ist 1
Ist 2
Perturbation
damping
Frequency domain
Command control
Principle
- 20-
MOR4ANSYS – Model Order Reduction
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.
Principle
- 21-
MOR4ANSYS – Model Order Reduction
The dimensionally reduced matrices are then imported into Simplorer.
Simplorer permits to idealise a complex system with block
corresponding to different physics.
Application
- 22-
MOR4ANSYS – Model Order Reduction
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
Advanced application - CHATTERING
- 23-
MOR4ANSYS – Model Order Reduction
The Simplorer model contains :
• Command control
• Machine-tool model obtained with MOR4ANSYS
• Cutting process as mathematical model
Advanced application - CHATTERING
- 24-
MOR4ANSYS – Model Order Reduction
The stability of the machining process can be assessed.
stable
not stable
Example
- 25-
Transient Thermal
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
Example
- 26-
Transient Thermal
Coupled simulation: control of unsymmetrical heating
Example
- 27-
Transient Thermal
Coupled simulation: control of unsymmetrical heating
Thanks!
CADFEM (Suisse) AG
Avenue de Cour 74
1007 Lausanne
Tél.: 021 601 70 80
www.cadfem.ch