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

info@cadfem.ch

www.cadfem.ch