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Laser Welding with Fanuc i RVision

Stan Ream

EWI

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Project Funding

• This research was funded by the US Department of Energy

through the Nuclear Fabrication Consortium (operated by

EWI)

• The Nuclear Fabrication Consortium (NFC) was established

to independently develop fabrication approaches and data

that support the re-establishment of a vibrant US nuclear

industry

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Project Background

• Select three laser applications that

offer significant productivity gains over

the current processes being used in

the nuclear industry

– Single-pass, thick-section welding of 316L

stainless steel

– Single-bead per layer, narrow-groove, thick-

section welding

– Tube to tube-sheet welding

• Down-select an application and

perform a technology demonstration

for the nuclear industry

12.7-mm

Inconel

690 Tube

Filler Metal

82 Clad

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Tube-to-Tube-Sheet Heat Exchangers

• Not just nuclear

• Usually GTAW (TIG) welded with wire

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Demonstration Objectives

• To demonstrate a compilation of commercially available

equipment and technology suitable for laser welding tube-

to-tubesheet on a large scale

– Welding Optics

– Manipulator

– Vision System

– Laser

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Automotive Application Example: Gear Assembly Welding

• Identify that all critical components have been assembled and are in the

correct location.

Is the Pinion Present? Is the Pin Present? Is the Tab in Place?

Are the Teeth Present? Is the Pin Welded in Place?

Courtesy

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The Tube Sheet Welding Challenge…

• Consistently finding the

‘invisible’ weld joint

– Current GTAW methods can use

locators that physically contact

the ID of the tube

– An alternative option is to visually

find the center of the tube and

determine the location of the joint

based on the drilled hole

diameter

Mock Joint for Demonstration

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Preferred Welding Optics

• Several options were investigated

– Standard welding optics

• Dependent on a manipulator to

produce a circular pattern

– Remote (scanner) welding optics

• Potentially the highest productivity

solution, but introduces challenges

for shielding gas and vision

– Rotary Wedge Scanner

• Preferred due to its relative simplicity,

integrated shielding nozzle, and

coaxial camera

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Rotary Wedge Scanner

• Rotary Wedge Scanner

(LaserMech)

– Uses the refractive optical

effects of a wedge to produce

precision circles (or other

shapes with advanced model)

– The diameter of the circular

pattern can be adjusted by

manually indexing the wedges

– Coaxial camera mount for

vision system integration

Process Fiber Input

Motor and Wedge Assembly

Camera Mount

Focusing Optic

Shielding Nozzle

Collimating Optic

90º, partially-

reflective mirror

Rotating Wedge

Assembly Circles result as the

wedge assembly rotates

Focusing

Optic

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Preferred Manipulator

• Several options were investigated

– 3-axis, CNC controlled positioner

– A custom system that would mount

directly to the tubesheet

– 6-axis robotic

• A Fanuc robot with iRVision was

selected as the preferred solution

– Pre-integrated vision system eliminates

the need for a third party vision package

– Support from one supplier for both vision

and robot support

– Easily scalable to tackle large tubesheet

applications

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Finding the Center of the Tube-I.D.

• Welding solution assumes constant wall thickness

• Lighting is essential for robust vision analysis

Measured

Trepan Center

Robot Move

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Fanuc i RVision System

• The vision system (digital camera) compares what it ‘sees’ to a master

image (taught during set-up)

• If the current image does not match the master, a 2D offset is

calculated and the robot adjusts its position

Prior to the relative position offset

After the relative position offset

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Fanuc i RVision System at EWI

• 1.5-kW laser power

– 360-μm spot size

– 80-IPM weld speed

• 49 tube welds in 5:20

(~6.5 seconds per

tube)

– Typical GTAW process

takes nearly 2 minutes

per tube

– Robot speed, weld

speed, and vision

system program could

be adjusted to further

reduce cycle time

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Results

• Cross-sections taken from the 2nd and 48th weld

– Profile and penetration nearly identical

Inconel

600 Tube Filler Metal

52 Clad

Inconel

600 Tube Filler Metal

52 Clad

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Results

• Additional sections showing challenges to overcome

– Mis-alignment due to chamfer on ID of tube

– Keyhole porosity

• Contaminants at joint interface?

• Keyhole instability?

Inconel

690 Tbe

Inconel

600 Tube

Filler Metal

52 Clad

Inconel

600 Tube

Filler Metal

52 Clad

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Demonstration at B&W

• The equipment was set up in

a temporary enclosure at

B&W’s research center

• A 4-kW fiber laser was

supplied be IPG Photonics

• Over 150 laser welds were

produced throughout the day

for a group of nearly 100

people from the nuclear

industry

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Summary and things to remember

• Laser tube-tube-sheet welding requires vision for precision.

• Custom optics can provide local motion precision.

• Laser + robot + optics + vision can offer cost effective

solutions to precision joining challenges.

• Vision systems (hardware and software) will become much

more prevalent in robotic laser welding.

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Special Thanks

• The project was completed with the support of

several companies:

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