Current joining research at KTH Production EngineeringXPRES

Arne Melander

Contents:

Overview of research activities

Example 1: Friction stir welding of hybrid joints

Example 2: Distortion in laser welding

Overview current research at KTH, IIP

Hybrid joining

Al/thermoplastics

Al/thermoplastic composites

Al/steel

Laser welding

distortion prediction with FEM

Spot welding

Process planning with FEM

Joining of aluminium alloys tothermoplastics with the Friction StirWelding method

Wallop Ratanthavorn and Arne Melander

Production engineering

XPRES

KTH

Aim

Purpose of work:

• To join thermoplastic sheet with aluminium in overlap

joints.

Joining process

• FSW is used to generate the joints.

• FSW tool applied from the aluminium sheet side.

• Adhesive and mechanical locking are generated.

AA6111• Mostly used in automobile structures as aluminium alloy

sheet parts in hood and door

• The main alloying elements of AA6111 aluminium alloy

are 0.63 %Si, 0.75 %Cu, 0.76 %Mg with a balance of Al.

Polyphenylene sulfide (PPS)• High performance thermoplastic that exhibits good

thermal stability and chemical resistance

• High degradation temp. = 500 °C

• Melting temp. = 285 °C

Joined materials

• Lap joints between AA6111 (top sheet) and PPS (bottom sheet) were joined by FSW

Joining technique

Mixture of Al fragments and thermoplastic

Smooth surface on the bottom side

How the joint looks like?

Three trends from tensile

testing results;

• Small translation speed

leads to the formation of

void and gap at interface

• Large translation speed

leads to large metallic

chips

• Smooth interface at

large translation speed –

negative to strength

Results – Joint strength

Results – Fracture surfaces

Results – Fracture surfaces (continued)

• Friction stir welding can successfully be used to

form joints between aluminium alloys and

thermoplastics

•The joint formation process is very different from

FSW applied to aluminium alloys

Conclusions

Karl Fahlström Swerea/Högskolan Väst karl.fahlstrom@swerea.se

Oscar Andersson VCC / KTH oanderss@kth.se

Distortion control in laser welding of UHSS

Increased use of UHSS

Increased use of laser beam

welding

Manufacturing

Simulation

Fixturing & process

Lighter and stronger

Occurring distortions during welding…

…needs to be controlled and understood!

Geometries and material grades

Type cases chosen simulating A- and B-pillar

Grades used (t = 1.0 mm):

• MBW-1500P

• Docol 1700M

• DP800

• Docol 200

Weld clamping and sequence

Clamping designed for research • 10 clamps in total

• 5 clamps on each flange

• Individually controlled by pneumatics

Weld sequence• Welding along flanges

• Cooling after welding

• Unclamping in sequence

Three types of simulations

• 1) Simplified simulations using commerciallyavailable software, ESI Weld Planner

• 2) Developed simplified simulations in LaserLight using Abaqus.

• 3) Detailed simulations using ESI Sysweld.

2) Simplified simulations

Step 1: Local thermal model

• Moving cylidnrical heat source

• Temperature dependent material data

• Computation time: 30 – 45 min

• Output: peak temperatures in sheet

Step 2: Global mechanical model

• Static model, shell elements

• Load: peak temperatures near weld

• Output: geometrical distortions

Dominating distortions for single hat

Simulation resultsSimplfied model

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Sim

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Experimental measurement [mm]

MBW-1500, 1.5 m/min

MBW-1500, 3.5 m/min

MBW-1500, 7.5 m/min

DP800, 1.5 m/min

DP800, 3.5 m/min

DP800, 7.5 m/min

Mild Steel, 1.5 m/min

Mild Steel, 3.5 m/min

Mild Steel, 7.5 m/min

Detailed simulations with Sysweld

Thermal laser heat source

Thermaldata:

Density

Specific heat

Heat conductivity

Temperature field

Thermalstrains

Mechanicldata:

Elastisk dataDistortions

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Sim

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mm

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Experiment [mm]

MBW-1500 3.5 m/min

MBW-1500 7.5 m/min

MS 3.5 m/min

MS 7.5 m/min

Simulation resultsDetailed simulations

Conclusions:

Distortion in laser welding of thin sheet structures can be made with FE methods of different complexity.

Methods can be designed for quick process planning and for detailed process analysis.

Thank You!