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Lesson 6.2CutChapter 6 · Cutting and non-traditional machining

Laser cutting

Focused light melts or vaporizes a narrow cut

Laser cutting traces a shape in flat material with a focused beam of light that melts a narrow line through it. Many metal brackets, enclosure panels and acrylic signs start this way. It needs no tooling: the machine cuts straight from a drawing file, so a single part is as easy to make as a thousand.

Laser cutting: a real photo
Photo: EGU-Metall, CC BY-SA 3.0, via Wikimedia Commons
A focused laser beam melts a narrow line and a gas jet blows the melt awaySide section along the cut, not to scale1Laser sourcefiber or CO2fiber cableCutting headFocusing lensNozzle2Assist gasoxygen, nitrogen or airKerf (cut slot): already cutSheet, not yet cut3Cutting direction5Melt blown out as sparks4support slatsCut, seen end-onKerf, typically 0.1 to 0.5 mmSheetMachine partsLaser beam and molten metalAssist gas
Laser cutting head over a sheet, side section along the cutThe figure is a side section along the cut: the head moves right and leaves the kerf behind. Circled numbers match the steps below.

How it works

  1. Make the beam. A laser source turns electricity into an intense, invisible infrared beam. Fiber lasers (the beam is generated inside a glass fiber) dominate metal cutting; CO2 lasers (the beam comes from a gas mixture) are common for wood and plastics.

  2. Focus it. A fiber cable (or mirrors, for CO2) carries the beam to the cutting head. A lens concentrates it into a spot a fraction of a millimeter wide.

  3. Melt. At that spot the energy is so concentrated that the material melts, or partly vaporizes, through its full thickness.

  4. Blow out. An assist gas flows through the nozzle around the beam and blows the molten metal out of the bottom of the cut as sparks. Oxygen also burns steel and adds heat; nitrogen leaves a clean, bright edge.

  5. Trace the outline. A CNC system (computer numerical control) moves the head along the outline, leaving a narrow kerf (the slot the cut makes). A sensor keeps the nozzle about 1 mm above the sheet.

Most machines cut flat sheet lying on a bed of pointed support slats. Tube lasers rotate a tube under the head to cut holes, slots and angled ends.

Key facts

Materials
Mild and stainless steel, aluminum, copper and brass (fiber lasers); wood, acrylic, cardboard, fabric and leather (CO2 lasers)
Typical parts
Brackets, enclosure panels, gaskets, signs and lettering, flat parts nested on a sheet
Part size
Flat sheets typically up to 1.5 × 3 m or 2 × 4 m; steel up to about 25 mm thick on common machines
Precision
Often about ±0.1 mm
Surface finish
Smooth cut face with fine vertical lines; a thin heat-affected zone (a band whose structure the heat has changed)
Batch size it suits
From one part to large series, with no tooling and automatic sheet loading
Tooling and machine cost
No part-specific tooling; hobby CO2 cutters cost a few thousand dollars, industrial fiber machines a few hundred thousand
Speed
Tens of meters per minute in thin sheet; around 1 m/min in 20 mm steel

Strengths and limits

Strengths

  • No tooling: any 2D outline straight from a drawing file
  • Narrow kerf and fine detail, often about ±0.1 mm
  • Fast in thin sheet; parts are nested (packed tightly on the sheet) to save material
  • One machine handles many metals, or wood and plastics with a CO2 source

Limits

  • Mostly flat sheet and tube; thick plate is slow
  • Heat leaves a thin altered zone and can warp thin parts
  • Shiny copper and brass need fiber lasers and care
  • Some plastics, such as PVC, give off toxic gas and must not be laser cut

Where it's used

  • Sheet-metal job shopsBrackets, panels, machine guards, one-off parts
  • AutomotivePrototype body parts, trimming of formed parts with 5-axis lasers, exhaust parts
  • Machinery and agricultureFrames, flanges, gussets, mounting plates
  • Architecture and signsDecorative facade screens, lettering, stair parts
  • ElectronicsStainless solder-paste stencils, thin shielding parts
  • Makers and designAcrylic displays, plywood models, leather goods

How to recognize it

  • Very fine, regular vertical lines (striations) on the cut face, and a crisp, square edge.
  • Tiny tabs or nicks on the edge: micro-joints, small bridges left to hold parts in the sheet and broken off later.
  • A small pierce mark where each cut started, where the beam first burned through, often just off the final outline.
  • On wood, a browned, slightly charred edge; on acrylic, a glossy, flame-polished edge.

Compare with

Plasma cutting6.3cheaper and faster in thick steel plate, but with a wider kerf and a rougher, slightly beveled edge.Waterjet cutting6.4no heat at all and cuts stone, glass and very thick metal, but it is slower.Punching6.1faster for many identical holes in thin sheet, but every shape needs its own tool.

Watch it

Ponoko Laser Cutting · The parts of a laser cutter, explained simply

Small Things · Why focused light can melt steel

TRUMPF Inc. · A fiber laser cutting 25 mm plate, sparks and all

Ray Frith · Everyday shop-floor cutting of 3 mm sheet

See real photos

Remember

  • A lens focuses the beam to a tiny spot that melts a line through the material.
  • The assist gas blows the melt out; oxygen adds heat, nitrogen keeps the edge clean.
  • No tooling and about ±0.1 mm: the default for flat parts in thin to medium sheet.

More in Cutting and non-traditional machining

All 100 processes
6.1Punching and shearingA punch shears shapes out of sheet against a dieOpen the lesson6.3Plasma cuttingA superheated gas jet melts through conductive plateOpen the lesson6.4Waterjet cuttingVery high-pressure water, usually with abrasive, erodes a cutOpen the lesson6.5Wire EDMSparks from a thin moving wire cut through-profilesOpen the lesson6.6Sinker EDMSparks copy a shaped electrode into a blind cavityOpen the lesson6.7Electrochemical machining (ECM)Electrolysis dissolves metal in the shape of the toolOpen the lesson6.8Chemical machining and photochemical etchingA light-printed mask lets an etchant dissolve only bare metalOpen the lesson6.9Ultrasonic machiningA vibrating tool hammers abrasive grains into the surfaceOpen the lesson

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