user-friendly fea for electromagnetic...

ANSYS Conference & 32nd CADFEM Users' Meeting 2014June 4 – 6, 2014, NCC Ost, Messe Nürnberg

User-friendly FEA for Electromagnetic Forming

Dr. Charlotte Beerwald, Moritz Beerwald, Dr. Uwe Dirksen, Artur Henselek

Poynting GmbH, Dortmund, Germany


Simulation of Electromagnetic Formingwith SMU-SimTool

User-friendly FEA of EMF with SMU-SimToolElectromagneticformingprocess EMF


Company Profile

POYNTING company performs contract research, development and equipment manufacturing in the field of

Pulsed Power Technologies

Our intention is to bring new research-based technologies into application and make them available for diverse industrial branches.

Fields of activity comprise

• components and assemblies for pulsed power systems (high current, high voltage supplies) as well as complete turn-key systems,

• to design and build unique instrumentation for research and scientific use, and

• customer-specific equipment for industrial series production when processes are based on high-level electrical or electromagnetic field impulses

Pulse Modulator for ESS, Lundwith integratedHigh Voltage Power Supply225 kW, 6 kV


Characteristic for this technology is that a large amount of energy [up to Megajoule range] will be charged and stored in a capacitance or in an inductance or in an accelerated mass to be suddenly discharged within a very short impulse of a few micro- or milliseconds.

As a result of this it is possible to generate temporarily extremely high power levels [in a Gigawatt range], which demands high electrical, but most of all mechanical requirements to the used components and structures.

Typically the peak values are much higher than the mean values. This can be used to initiate threshold reactions or to benefit from special non-linear effects.

Pulsed power technologies can be used advantageously if it is possible to achieve a better result compared to conventional methods, or if the pulsed power principle even enables a desired application for the first time.

Pulsed Power Technologies

What does ‘Pulsed Power‘ mean?


HV Power Suppliespower categoriesup to several hundred kW

Pulse Generatorse.g. SMU machinescompact or modular design

Components, Individual Parts, AssembliesTool Coil Design

Feasibility Studies

Product Range - Hardware

Pulsed Power Equipment

• The hardware product range of Poynting mainly consist of high-voltage power supplies, pulse generators, and accessory equipment

• Normally, in our high-current and high-voltage applications the high forces induced by the magnetic fields are undesired

• Nevertheless, applications exists where these high forces are welcome.

• In the Electromagnetic Forming EMF process the magnetic pressure impulse is used to form and join metallic workpieces

• SMU machines are special pulse generators usedfor the EMF process

• On the left side two coils for the EMF process areshown


High Current Switch

Workpiece(tubular)

C

Li

Ri

EMF – Process Principle

p = 1/2 µ0 H 2

µ0: permeability of vacuum

Magn. Pressure

Process Time

H: magn. field strength

• On the left side you can see a simplified process setup for Electromagnetic Forming

• The pulse generator is represented by its equivalent electrical circuit with resistance Ri, inductance Li, and capacitor bank C

• The Electromagnetic Forming process starts with charging the capacitor bank

• The energy in the capacitor bank is discharged if the high current switch is closed

• The high current switch must switch very fast and the power loss must be low (max. current can be up to 1000 kA)

• If the high current switch is closed a current starts to flow through thecoil

Electromagnetic Forming is a High Velocity Forming Process using the energy densityof a pulsed magnetic field to form or accelerateworkpieces of good electrical conductivity.

Pulse generator

Coil Current

Process Time

Compression Coil


Magnetic Field Strength H(pressure zone)

EMF – Process Principle

p = 1/2 µ0 H 2


Magn. Pressure

Process Time


Coil Current

Process Time

• As the current flows through the coil a magnetic field develops around the coil

• The magnetic field induces eddy currents in the metallic workpiece which also develop a magnetic field

• The higher the electrical conductivity of the workpiece thehigher the eddy currents and the developed magnetic field

High Current Switch

Workpiece(tubular)

C

Li

Ri

Compression Coil


Coil Current

Process Time

High Current Switch

Workpiece(tubular)

C

Li

Ri

Magnetic Field Strength H(pressure zone)

I (t) H (t) p (t)

SMU – Process Principle

p = 1/2 µ0 H 2


Magn. Pressure

Process Time


• If the magnetic field strength H is known the magneticpressure p can be determined

• If the pressure p is high enough the workpiece is plasticlyformed

• The current I directly influences the pressure and accordinglythe forming of the workpiece

• Electromagnetic Forming is a high velocity process and theprocess duration of workpiece forming is in the range of 10 µs to 1 ms

Compression Coil


Compression

Expansion

Flat Forming

Electromagnetic Forming is a High Velocity Forming Process using the energy density of a pulsed magnetic field to form or accelerate workpieces of good electrical conductivity.

Process Typesresulting of the coil-workpiece arrangement

Capacitor Bank

High Current Switch

Workpiece(tubular)

Compression Coil

C

Li

Ri

SMU – Process Principle

• Electromagnetic Forming can be used to form tubes andsheets

• The used process type depends on the coil shape andthe coil-workpiece arrangement

1. Flat forming:A flat spiral coil can be used to form sheet metals

2. Compression:A metallic tube inside of a spiral coil can reducethe radius of the tube

3. Expansion:A metallic tube outside of a spiral coil can expandthe radius of the tube


Fluid Pipes for Automotive Applications

(coated aluminium tube and steel fitting)

Assembling and Oil Tight Sealing of

Hydraulic Compen-

sating Bellows

Joining of Multi-Material Components

(high strength FRP – aluminium parts)Chassis

Components

(Cross-Steering

BMW M3 CSL)

Joining by EMF – Tubes + Profiles

Joining of Car Body Components

(aluminium spaceframe components)

• Electromagnetic Forming can be used for joining, cutting, and forming of tubes and sheet metals

• Joining of tube-shape workpieces is the most important process type at the moment. It is a mechanical joining where at least one joining partner is formed. The join can be realized as force-fit and form fit. At high impact velocities a firmly bonded join is also possible

• Due to the contact-less forming process no tool marks on the workpiece coated workpieces can be used

• Only the formed workpiece must have a good electrical conductivity

Joins with material combinations of different metals and metal / non-metal can be manufactured


Fluid Pipes for Automotive Applications

(coated aluminium tube and steel fitting)

Assembling and Oil Tight Sealing of

Hydraulic Compen-

sating Bellows

Joining of Multi-Material Components

(high strength FRP – aluminium parts)Chassis

Components

(Cross-Steering

BMW M3 CSL)

Joining by EMF – Tubes + Profiles

Joining of Car Body Components

(aluminium spaceframe components)


Research Project

Grant Agreement Nr: 609039Collaborative Project - FP7-2013-NMP-ICT-FOF(RTD)

Optimization of joining processes for new automotive metal-composite hybrid parts


Relevant Propertiesfor Simulation of EMF Process

SMU-COMPACT 3020-FS (max. 30 kJ, max. 20 kV)

• Simulation of a manufacturing process requiresan understanding of the relevant processcomponents and properties

• For the EMF process an important processparameter is the current. It mainly depends on the SMU machine, the energy conduction systemand the consumer load which consist of the toolcoil and the workpiece

• These components build the discharge circuitwhich can be simplified to the equivalentelectrical circuit below. The consumer load isdescribed with Ra and La separatly becausethese values changes during the process


Relevant Propertiesfor Simulation of EMF Process

SMU-COMPACT 3020-FS (max. 30 kJ, max. 20 kV)

• The current is responsible for creation of the magnetic fields• The magnetic fields creates the magnetic pressure which deforms the

workpiece• Deformation of the workpiece changes the inductance of the

consumer load• Joule heating in the conductors increase the temperature in the

conductors• Changes in the temperature also changes electrical and mechanical

properties of the components (workpiece, coil, etc.)


Physical Domains and their Dependencies

Electrica loscilla ting

circu it

E lectro-m agnetic

fie ld

Tem peratureS tructura l

m echanics

• Modeling of the Electromagnetic Forming requires considering the “physical domains”:

• Electrical circuit• Electromagnetic field• Structural mechanics• Temperature


Physical Domains and their Dependencies


circu it

E lectro-m agnetic

fie ld


m echanics

• The “physical domains“ depend from each other and their values

change over process time• Simulation of the EMF process requires one simulation which can

solve all „physical domains“ or coupling of different simulations whichindividually solve the „physical domains“


Element Selection


circu it

E lectro-m agnetic

fie ld


m echanics

Phys. Domain

Circu124 / Circu125

2D 3D

Circu124 / Circu125

Plane233: 2D 8 node electromagnetic solid

Plane223: 2D 8 node coupled-field solid

Plane223: 2D 8 node coupled-field solid

Solid226: 3D 20 node coupled-field solid

Solid226: 3D 20 node coupled-field solid

Solid236: 3D 20 node electromagnetic solid

Electrical circuit

Electromagn. field

Structural mech.

Temperature

• Required components of the electrical circuit can bedescribed using the elements Circu124 and Circu125

• The electromagnetic fields can be presented using theelement Plane223 for 2D and Solid236 for 3D

• The structural mechanics and the changes in temperature can be described using the coupled-fieldelements Plane223 for 2D and Solid226 for 3D


Simulation System Model


Simulation System Model

The simulation model:

• Implementation starts with ANSYS v13 using ANSYS classic

• Fully automized using APDL scripts

• Two main sub-simulations (sparse solver)

• El-Mag-Simulation solves electrical circuit and electromagnetic fields

• Mech-Ther-Simulation solves structural mechanics and changes in temperature

• Both sub-simulations uses the same mesh. Mesh is automatically generated using a feature-

based description of the process components

• The types of the elements are updated between the sub-simulation and results are transfered

using the LDREAD APDL-command

• After each sub-simulation results are post-processed and can be evaluated by the user

• Number of sub-steps in the Mech-Ther sub-simulation are adjusted according to the maximum

velocity of elements


Meshing

r

z

Compression Coil Field shaper

Tube

Mandrel

Symmetry axisat r = 0

Skin depth s in conductors(coil, field shaper, workpiece) must be considered

Air must be meshed

𝛿𝑠 =1

𝜋 𝑓 𝜇 𝜅

: Frequency of current

: Magnetic permeability: Electrical conductivity

𝑓𝜇𝜅

Skin depth

Skin depth s in copperat = 10 kHz: s = 660 µm𝑓


Meshing

r

z


Tube

Mandrel


Skin depth s in conductors(coil, field shaper, workpiece) must be considered

Air must be meshed

𝛿𝑠 =1

𝜋 𝑓 𝜇 𝜅

: Frequency of current

: Magnetic permeability: Electrical conductivity

𝑓𝜇𝜅

Skin depth

Skin depth s in copperat = 10 kHz: s = 660 µm𝑓

• Determination of the electromagnetic fields requires meshing the air between

the workpiece, joining partner, coil, and field shaper1

• The EMF process uses AC currents which requires considering the skin effect

in meshing the components. The skin effect describes the effect that the

current density is not equal across the cross section at AC currents. Instead of

it decreases from the surface to the inner parts. At the skin depth the current

is decreased to 1/e of the current on the surface.

Describing the skin effect accurately requires suitable number of elements

and elements sizes in the coil, field shaper, and workpiece

1Field shaper is used to concentrate the magnetic field generated by the coil


Coupling of Electrical Circuit and Coil

r

z


Compression Coil

Field shaper

Tube

Mandrel


Coupling of Electrical Circuit and Coil

r

z


Compression Coil

Field shaper

Tube

Mandrel

• The pulse generator and the energy conduction system are summarized in theequivalent electrical circuit using the resistor R, the inductor L and thecapacitor C

• The electrical circuit is coupled to the coil elements using a constraintequation

• At the beginning of the simulation the capacitor is initialized with the loadvoltage Ucircuit


Contact Definition

• Using one mesh for El-Mag sub-simulation and Mech-Ther sub-simulations means that between the contact partners alwaysexist elements representing the air. These elements are requiredfor computation of the magnetic field

• A contact gap of at least 50 µm must be defined to avoidcollapsing of the air elements


System Model of SMU-SimTool


System Model of SMU-SimTool

• The simulation model for the EMF process is rather complicated• The product and process designer do not want to take care on these aspects!• Poynting has developed the simulation tool SMU-SimTool which hides the setup of a 2D

process simulation and the required pre- and post-processing for the EMF process• SMU-SimTool is implemented for operating systems Windows and Linux• SMU-SimTool is separated in two components: frontend and backend• SMU-SimTool frontend

• Installed on user side• Feature-based modelling of the product and process components. Process

components can be selected from libraries.• Configuration of main parameters of simulation process such as final process

time, contact gap and so on• Controlling of simulation (start, stop, restart)• Visualization of already post-processed relevant simulation results

• SMU-SimTool backend• Running at Poynting• SMU-SimTool frontend transfers product and process data to the backend if the

users starts or restarts the simulation• The backend automatically starts the simulation model on ANSYS• After each simulation step relevant results are post-processed and transferred to

the users SMU-SimTool frontend for evaluation


SMU-SimTool: Modelling in 5 Steps


SMU-SimTool: Modelling in 5 Steps

• Modelling of the product and process components is feature-based

• For each component a base type is selected and further detailed using a small

number of parameters

• Material, coil, and pulse generators can be easily selected from libraries

• The selected SMU machine is configured by switching on the requested

capacitor banks and defining the requested load energy or load voltage

• Only five steps are required for defining the model!


SMU-SimTool: Application Example

r

z


TubeØ75mm x 2.5mm

Mandrel withconical groove


Desired time curvesat certain position z = 0



r

z

Compression Coil Field shaperFF75l15

Tube, AW6060 T6Ø75mm x 2.5mm

Mandrel, S235conical groove


Desired time curvesat certain position z = 0

• The application examples shows the simulation of the EMF process type

compression. A tube is formed on an inner joining partner. Therefore a coil with

four turns and a field shaper are used.

• After each load step the following data is sent to the SMU-SimTool frontend

and displayed as curve

• Current

• At one specified location on the outer side of the tube

• Displacement in x-direction

• Velocity in x-direction

• Magnetic pressure

On next page:

• Beside time data also contour plots are created and transferred to the SMU-

SimTool frontend

All data transferred to the SMU-SimTool frontend is stored locally and can offline

be further evaluated


Summary and Outlook

Fully-coupled simulation for EMF process• APDL scripts with two main simulations using 1 mesh

User-friendly FEA of EMF process with SMU-SimTool• No FEA simulation knowledge required• Fast modelling due to feature-based modelling• Define process time and press START button• Relevant simulation results are already post-processed

• Time data• Contour plots

Future work• Multi-frame restart• Automatic air-remeshing in 3D• …

user-friendly fea for electromagnetic...

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