Laser welding – Efficiency and Strength

Laser Joining of Steel

Basic Principles

• Laser beam provides a highly concentrated heat source
• Melts metal and even produce vapor (plasma)
• As the laser beam moves along the joint, weld is created upon solidification

Opportunities

Relatively Higher Capital Equipment cost

• Costs -> prices are reducing all the time now
• Cost savings -> high productivity -> reduction of scrap and re-work

Good part fit-up required

• New processing techniques (twin spot, wobble) to bridge gaps
• Laser welding with filler material, hybrid techniques

Precision alignment required

• Automatic control with seam tracking and height sensing
• State- of-the-art closed loop process monitoring systems

Champion required

• More training programs are available
• Applications are growing very fast
• High quality parts with minimal distortion and narrow weld bead
• Easily automated with consistent weld quality
• Ability to weld in difficult to reach areas with single sided access
• High strength welds with improved stiffness and crash performance
• Reduced flange widths with reduction of component size / weight

Automotive Applications

• Body in White
• Tubes and Closures
• Powertrain
• Tailor Welded Blanks

1. Eliminates bolted assembly for weight reduction and material cost saving!
2. Less assembly steps, remove the need for machining holes and bolting assembly!
3. Minimal heat input and distortion.
4. Proven performance and durability.

Enhanced Crash Performance

• Locally modify material properties to optimize collapse and energy absorption during crash.
• Crash performance of steel parts can be modified.

Different Types of Joining Processes

• Laser Welding with Filler Wire
• Remote Laser Welding
• Laser Brazing

Limitations of Autogenous Laser Welding

1. Weld defects due to

• alloy metallurgical incompatibility
• dissimilar material

2. Weld geometry not meeting specifications

Solutions: Laser Welding with filler wire

3. Welded surface not aesthetically smooth

4. High power melts the zinc coating

Solutions: Laser Brazing

5. No fast movement between the welds

Solutions: Laser Remote Welding

Laser Welding with Filler Wire

Basic Principle

• During laser welding, external wire is fed into the melt pool
• As the laser beam and wire moves along the joint, the weld is created upon solidification
• Filler material
  • Metal cold/hot wire

Applicability

• Otherwise not laser weldable materials
• Overcome poor weld geometry or fit up
• Change weld chemistry and properties

Application

• Welding of Dissimilar Material
  • Steel 4320 – Steel 8620 using Ni-based filler wire
• Laser welding can weld conventionally un-weldable materials such as higher carbon steels and cast irons using filler wire or pre heat techniques

Remote Laser Welding

Basic Principle

• Uses a relatively long focusing optic (hence “remote”)
• Highly dynamic scanning mirrors enable extremely fast indexing in-between welds,
• Therefore laser is spending more time joining parts and much less time waiting

Applicability

• Fast and Flexible
• No limitation of weld geometry and speed
• Sheet metal welding

Weight Saving

Reduction of flange width

• Additional potential for mass reduction
• High beam to seam accuracy is required
• Seam tracking with remote welding head can be utilized

Seam Tracking

• High speed camera with on-axis illumination
• Auto-focus of camera along z-axis
• Edge detection with a resolution of ~ 0.1 mm
• Omni-directional 3D on-the-fly welding with tracking

Laser Brazing

Basic Principle

• Laser beam heats filler metal (braze) above melting point
• Filler material flows between two close-fitting parts by capillary action.
• Braze material
  • Bronze wire

Applicability

• Smooth surfaces, no finishing required
• Ability to avoid melting the zinc coating
• Joining of dissimilar metals

Latest generation of automobiles use one or more laser brazed seams to connect sheet metal in the car’s body.

• Tailgate / Liftgate (License plate) / Roof

Laser Hardening

Basic Principle

• Laser beam heats the surface just below the melting point
• Very high cooling rate is obtained by moving the beam
• High hardness is achieved

Applications

• Trim Dies and Tools
• Engine Components

Laser Softening

Basic Principle

• Laser beam heats steel sheet above transition temperature
• By moving the beam, a larger area is treated and cooling rate is controlled
• Suitable microstructures are formed by rearrangement and softening is achieved
  Applications
• Selective softening for easier formability or mechanical fastening
• High speed process compared to conventional heat treatments
• Tailored microstructures

Laser joining applications employed by automotive industry for steel

•  Laser Welding
• Laser Welding with Filler Wire
• Remote Laser Welding
• Laser Brazing
• The automotive industry has incorporated laser processing in virtually every sub system of the automobile
• Ongoing innovations will continue to make laser implementation more and more affordable
• Lasers are a key technology enabler for mass reduction in steel vehicles!