The Ultrasonic Weld Mechanism State of the technology Edgar de Vries Karl Graff

Welding Engineering Program WE Graduate Seminar, Autumn 1999

Overview Welding Engineering Program

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Objectives Introduction Considered weld mechanisms Current model for joint formation Common practices and main issues today Recent research results Summary

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Objectives Welding Engineering Program

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Collect and summarize the available literature on Ultrasonic Metal Welding (USMW). Review key developments over 50+ years. Identify the most recent theories on the mechanism of USMW. Identify areas where further research is needed.

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Introduction Welding Engineering Program

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USMW was discovered 1949 (by accident) Extensive ‘50’s-’60’s research in the US Research started in USSR and East Germany in ’50’s In Japan work started in early ’70’s Current research continues in Germany, Japan and the US

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Basic USMW Systems Welding Engineering Program Static Force

Reed/Sonotrode Transducer

Transducer

Sonotrode Vibration

Power Supply

Anvil

Vibration

Workpieces

Workpieces

Wedge-Reed

Anvil

Static Force

Lateral-Drive

Power Supply

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Matching Circuit

Transducer

Load

USMW and Related Processes Welding Engineering Program

Cold Pressure Friction Welding (CPW) Depending on the Application Welding (FW) materials, power and frequency USMW is more comparable to F F CPW or FW FS M Plastic Deformation Zone

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Microbonding Ductile Materials Low Power High frequency

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FA

Sheet Metal Hard materials High Power Low Frequency

F

Welding Parameter Interaction Welding Engineering Program

Welding Time

Amplitude

Pressure

el. Power

Frequency

Material Properties

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Bonding Mechanisms Welding Engineering Program

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Fusion-Melting has been considered possible at the interface. Interface microstructure has been associated with melting and rapid solidification. But USMW now considered a solid state process. Recrystallization- Observed in ultrasonically welded joints but a gross reorientation of grains or the microstructure is generally not possible.

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Bonding Mechanisms (cont’d) Welding Engineering Program

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Diffusion- Has been observed, especially along gain boundaries, but generally bulk diffusion does not take place. Plastic deformation with metallic adhesionObserved in all USMW interfaces. The material mixing and subsequent metallic adhesion is considered the most important bonding mechanism. All other processes are possible, but are not necessary.

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Evolution of the Weld Welding Engineering Program

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a. Contacting Surfaces due to Normal Load

Cavities

FS

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Unbonded Surface

b. Bonded Area due to interface Slip

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FS

c. Fully Grown Bonded Area by Sublayer Plastic Deformation

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Normal load presses the surface asperities into contact Slip deforms the asperities and adjusts the surfaces Sublayer deformation causes Oxides to dissipate and intense material mixing

Typical USMW Joint Interface Welding Engineering Program

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Weld interface

Weld edge

Sequence of Joint Formation Welding Engineering Program

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1st Stage: Metals are forced into close contact, asperities deform, contaminations start to dissipate. 2nd Stage: Metallic adhesion bonds and active centers form, (topo-)chemical reactions start 3rd Stage: Interface grain structure destroyed, residual stresses and active centers relax, atoms change their functional locationsleading to microscopic recrystallization and diffusion.

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Model (cont’d) Welding Engineering Program

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The three stages take place simultaneously or within a very short time difference. The last stage is responsible for the formation of a strong joint, because exchange effects occur between the metallic substances. This stage relies on elevated temperatures. If metals are welded that have no solubility, the joint strength relies only on inter atomic interaction.

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Weldability Guidelines Welding Engineering Program Weldability class/weldab ility

Lattice structure

Metals

Hardness/ HV

1/very good

cfs

Al,Au,Ag, Cu,Ni,Pd,Pt

300..1000

2/good

cfc cbc

Th αFe,Nb,Ta,V

1000..2000 300..1000

3/feasible

cfc cbc hex

Mn Mo,Zr Mg,Ti,Zn, Sb

2000..3000 1000..2000 300..1000

4/unlikely, not possible

cfc cbc hex

Ir,Rh,(Pb) Cr,W Be,Cd,Co, Si

>3000 >2000 >1000

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Based on the model of weldability, classes can be formed based on deformability. Only classes 1 and 2 are suitable for USMW, metals in class 3 have low fracture loads. If different materials are to be welded the difference in hardness should not exceed 1000 HV.

Common Practices and Issues Welding Engineering Program

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Lateral Drive system with rigid anvil, amplitude controlled sonotrode and energy controlled weld process – widely used. If aluminum sheet metal is welded, good weld strength often is accompanied by “tip sticking.” Welding parameters change as surface conditions change. However control systems do not account for changing conditionsleading to a variable process.

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Recent Experiments-Background Welding Engineering Program

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USMW process still not fully understood. The Wedge Reed design has provided strong joint strength with low sonotrode sticking. Correlate the sequence of events (initial, welding, extrusion stage) to vibration conditions. If surface conditions are not well controlled, weld process is also unreliable.

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Experimental Setup Welding Engineering Program

Point in time when sonotrode sticking starts during welding

H Ca igh m sp er e e a d

Transducer & Mechanical Wave guide

Matching network & Power supply RF-cable Current

Vib. direction

Two channel Fotonic sensor

Oscilloscope & Data processing

Oscilloscope & Data processing

Resonant anvil

Channel 1&2

Specimen

Voltage

Anvil and Sonotrode Vibration amplitude during Welding UIA 2002, New York, NY

Power curve during welding

Results Welding Engineering Program

Power and Vibration amplitudes 3000

50

Welding (joint formation) Stage

Power/W

2000

40 35 30

1500

25 20

1000 15 10 500 5 0

0 0

0.05

Initial Stage

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0.1

0.15

0.2

0.25

0.3

0.35

time/s Power/W

tip

anvil

0.4

0.45

0.5

pk-pk amplitude

2500

45

Over Welding Stage

Summary Welding Engineering Program

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Research on USMW has been conducted for 50+ years. USMW is commonly used for electrical connections, tube and package sealing and wire bonding. Models for basic parameter interactions and weld mechanism have been developed. For aluminum sheet metal welding, large scale applications remain a challenge.

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