Laser-Beam Machining (LBM)

   

                  Laser beam machining

            Laser Beam machining (LBM) is an unconventional machining process in which a beam of highly coherent light called a Laser is directed towards the work piece for machining. Since the rays of a laser beam are monochromatic and parallel it can be focused to a very small diameter and can produce energy as high as 100 MW of energy for a square millimeter of area. It is especially suited to making accurately placed holes. It can be used to perform precision micro-machining on all microelectronic substrates such as ceramic, silicon, diamond, and graphite. Examples of microelectronic micro-machining include cutting, scribing & drilling all substrates, trimming any hybrid resistors, patterning displays of glass or plastic and trace cutting on semiconductor wafers and chips. A pulsed ruby laser is normally used for developing a high power.

 

Process description
A coherent beam of monochromatic light is focused on the workpiece causing material removal by vaporisation. Machines are generally CAD/CAM compatible, with 3-axis and 5-axis machines being generally available.
Profile creation of sheet metal parts is the most common applications, but it is also possible to drill holes and create blind features in many different types of material.
Gas-assisted laser beam machining is common. The gas type can be oxygen, inert gas, or air, depending on material type and quality requirements.

  Typical Uses

• Profiling of sheet parts.
• Holes (0.005mm diameter to 1.3mm), profiling, scribing, engraving and trimming.
• Prototype parts.
• Non-standard shaped holes, slots and profiling.
• Features in silicon wafers (electronics industry).
• Small diameter lubrication holes.
• Suitable for thin or delicate parts as there is no mechanical contact.

 

 Design guidelines

• Lasers work best on materials such as carbon steel or stainless steels. Metals such as aluminium and copper alloys are more difficult to cut due to their ability to reflect the light as well as absorb and conduct heat. This requires lasers that are more powerful.
• LBM is not a bulk material removal process. It is most suited to contour cutting, slitting and drilling small diameter deep holes (length to diameter ratios of up to 50:1 are possible).
• There are special methods to create blind or stepped features, but they are less accurate.
• Sharp corners are possible, but radii should be provided for in the design.
• Some distortion may be caused in very thin parts.
• Maximum workpiece thickness: mild steel = 25mm, stainless steel = 13mm, aluminium 10mm.
• Localised thermal stresses and heat affected zones result.

Process variations

• LBT (Laser Beam Torch). Uses a simultaneous gas stream
• Laser Texturing and Laser Etching are performed at lower energy levels.
• Surface hardening. Laser Beam Welding (LBW).
• Laser marking or laser printing can be used to create graphics, text or barcodes on most materials.
  
• LBM can also be integrated well with sheet metal cutting processes. For example, the Trumpf Laserpress (created in 1979).

The environment

• The heat may potentially cause the generation of toxic fumes.

The economics

• Production rates are moderate to high.
• Higher material removal rate than with conventional machining.
• High power consumption.
• Short lead times.
• Tooling and equipment costs very high. Some skilled labour required.
• Very fast with high degree of automation possible.
• Burrs are very small, reducing the need for secondary finishing operations.
  
• Considerable economies can be obtained by stacking sheets for simultaneous cutting.