How are lasers used in metal work such as cutting, welding and drilling?

In one line

A focused laser beam delivers a very high power density to a tiny spot, which heats metal fast enough to melt or vaporise it, so it can cut, weld, drill, mark and harden metals precisely.

Explained simply

Using a magnifying glass to burn paper on a sunny day shows the idea: focusing light onto a small spot raises its intensity enormously. A laser's beam is already intense and directional, so a lens can focus it to a spot well under a millimetre, enough to melt steel.

How it works

1. Cutting: the focused beam melts or vaporises a line of metal while an assist gas (oxygen or nitrogen) blows the molten metal away. CO₂ lasers (10.6 μm) and fibre lasers are common.
2. Welding: the beam melts the edges of two parts, which fuse on cooling. The heat-affected zone is small, so there is little distortion. Nd:YAG (1.064 μm) and fibre lasers are widely used.
3. Drilling: short, high-energy pulses vaporise material to make very fine holes, for example cooling holes in turbine blades.
4. Marking and engraving: the beam changes the surface to print serial numbers or logos.
5. Heat treatment: scanning the beam hardens a thin surface layer without heating the whole part.

Why lasers: no tool contact or wear, very narrow cut width, high precision, easy computer control and automation, can work on hard or heat-sensitive metals, and can weld dissimilar metals.

Key formula

Intensity at the focus: \(I = \dfrac{P}{\pi r^2}\), with \(P\) the beam power (W) and \(r\) the focal spot radius (m); \(I\) is in W/m².

Quick example

A 1 kW laser focused to a spot of radius 0.1 mm gives \(I = 1000/(\pi\times10^{-8}) \approx 3.2\times10^{10}\) W/m², far more than any flame, which is why it melts steel quickly. Car body panels are commonly laser-welded on robotic lines.

Common mistakes

• Saying lasers cut by "pressure" of light; they cut by heating, melting and vaporising.
• Forgetting the assist gas in cutting.
• Listing only advantages without naming the laser types used.

How MU asks it

Usually "Explain applications of laser in metal work / industry" (3 to 5 marks). Write separate short paragraphs on cutting, welding and drilling, name the lasers used, and list four advantages over conventional machining.