Metal Repairs: Laser Welding

LASER  “light amplification by stimulated emission of radiation.”  Electrons are atomic particles that exist at specific energy levels. These energy levels are unique and are different for every atom or molecule.  Electrons in outer rings are at higher energy levels than those in the inner rings. A flash of light can bump electrons to higher energy levels by the injection of energy. When an electron drops from an outer ring to an inner ring or level, the excess of energy is given off as light.  The wavelength or the color emitted is related to the amount of energy released.

I. The LaserStar® Workstation The LaserStar® Workstation is an Nd:YAG laser. The host material is a cylindrical crystal of yttrium- aluminum -garnet (Y 3 Al 5 O 12 ), YAG doped by weight with neodymium (Nd3+) ions. Laser emission takes place at μm (infrared).

 Part of the laser light passes through the semi-reflecting mirror and performs the welding function.  produces a very high energy density light beam, many times higher than is possible with normal light  The energy -“hot light”- created at the focal point in a relatively short time  (0.5 to 20 ms) heats the metal beyond its melting point and thus enables a weld.

Laser Power Joules: The “hot light” energy output is measured in joules. This industry term by definition is “ the capacity for doing work”. Hot light energy output is determined by the amount of voltage and pulse-length selected by the operator

Welding effects: When a pulse of “hot light” energy penetrates an alloy, the resulting affect creates gaseous, liquid, and molten zones in the bombardment area

Effect parameters while welding metals is as follows: The voltage first influences the welding depth. The pulse length predominantly influences the diameter of the welding point. The focus influences the welding depth as well as the diameter of the welding spot. When increasing the diameter, the welding depth is reduced at the same time.

Parameter Adjustments-Bombardment Zone Results

Keypad ON SYSTEM ON: This light comes on when the main switch of the product is turned “on” and the key switch is set to the “ON” position. ● CLOSE SHUTTER: This key closes the shutter. A continuous indicator light indicates that the shutter is closed. O OPEN SHUTTER: This key enables the opening of the laser shutter. Green indicator light flashes when the shutter is ready to open; continuous when the shutter has opened.  ENTER KEY: To enter or accept system variables and/or navigate menus. OK Green light indicates laser is ready, Red: no pulse can be released (recovery time) or the system is still in the startup phase after being switched “on.” ! FAULT: System fault (yellow light). To reset fault must be corrected. ↑ / ↓ To change system variables and navigate menus. MENU To enter the menu mode.

Welding chamber/area controls  Gas Flow Control These controls used to control the flow of inert gas. Right control for center tube, left control for left tube.  Beam Expander: Focus setting: This changes the diameter of the focal spot (model dependant)  Safety Shutter (Open Shutter) Used to open laser shutter from inside the welding chamber/area.  Brightness This control allows you to control the brightness of the lights in the welding chamber/area.  + / - When the joystick is pushed toward the +, this will increase the value in the display for the parameter flashing. When the joystick is pushed toward the -, this will decrease the value in the display for the parameter flashing.  < Menu The joystick is pushed toward the < Menu symbol to select the parameter to be changed going to the left in the display.  Menu > The joystick is pushed toward the Menu > symbol to select the parameter to be changed going to the right in the display.

Joining Metals  Joint Preparation: To ensure a strong laser welding joint it is important to properly evaluate your application and material thickness first before selecting one of the joint preparation methods  Bonding the joint: Strong homogenous allow flow is achieved using the appropriate parameter combinations and the 50% overlap firing method. This ensures a structurally sound joint while virtually eliminating the possibility of gaseous pockets or cold welds

 Surface filling the joint: laser welding vaporizes some of the alloy. Filler material is used to fill these voids. The filler material should be the same alloy if possible. Filler wire diameter should be no lager than 0.50mm or.020”.

Welding a Connector  Keyhole Weld- used for thick connectors is a deep core penetrating weld that will hold the part together. A proper keyhole weld will penetrate at least halfway into the gauge of the parts to be welded  Surface Weld- used for tin connectors. Thin connectors need less penetration. Therefore, a Surface weld is recommended

Quadrant Method  Quadrant Tacking Metal contracts and expands during the welding process. For this reason we must tack the connector in diametrically opposed quadrants.  Quadrant Welding To maintain equal, consistent heating and equal metal displacement of the structure, we must weld the connector in diametrically opposed quadrants as well. This prevents distortion of the metal during the weld process.

Filler Materials  Large gaps: Require fabricating a large insert (often thick wire or casted piece) of the same material  Small gaps: often require a quick application of a thin filler wire to correct or complete the laser welding application  Shallow blemishes: require a quick application of a thin filler wire to correct the laser welding application

Porosity  Deep porosity: can be repaired in two steps: first using high voltage-short pulse duration with a tight beam diameter, burnout any investment remaining and expose the complete porosity pocket; Second, use the filler material to refill the porosity pocket

Hammering and Smoothing  After the core laser welding process has been completed, it is recommended to adjust to a lower power, wide laser pulse diameter and medium to fast auto-pulsing setting. This will smooth over or hammer the surface which eliminates most rough surfaces and reduces secondary finishing techniques to the laser welded area.