Laser cutter

How it works

A laser beam is led by mirrors to a focusing lens above the work and brought to a spot a fraction of a millimeter across. In the first gas-assisted cutting trials at the UK Welding Institute (TWI) in 1967 the beam passed through a lens of about 300 mm focal length and a pressure window into a chamber, and left through a nozzle with a 2.5 mm circular orifice held 1.5 mm from the work. TWI’s Paul Hilton describes this arrangement as remarkably close to commercial nozzles in use today.

The gas stream does part of the work. The 1971 Sullivan and Houldcroft patent describes directing a gas that reacts exothermically with the heated metal onto the point where the beam is concentrated, so that the gas both adds heat and sweeps away the products of combustion, with oxygen named as the example. In the 1967 trials the cut was narrow: the kerf, about 0.5 mm, depended on the focused spot size and not on the size of the gas jet.

The machine moves the beam or the work along a path supplied as a drawing file. The MIT Center for Bits and Atoms tutorial for a 100 watt carbon dioxide machine with a 32 by 18 inch bed says that thin lines in the drawing are cut as vectors, that wider lines and images are engraved as rasters, and that line colors in the print driver are mapped to speed, power and pulses per inch. The same document says that machine cuts acrylic, wood, paper and foamcore and cannot cut metal.

Anatomy

Laser source: In the TWI trials of 1967 a 300 watt slow-flow carbon dioxide laser built at the Services Electronic Research Laboratory, Harlow, 10 m long with five discharge sections.
Mirrors and beam path: TWI’s first setup diverted the horizontal beam onto the focusing lens with an aluminized steel mirror. The MIT tutorial’s machine moves a mirror and lens carriage over the bed.
Focusing lens: In 1967, sodium chloride, later potassium chloride. The MIT tutorial says the lens collects residue in normal use, is removed with three thumbscrews, and is checked at the start of each session.
Nozzle and assist gas: A coaxial nozzle, with the gas held in a pressure chamber closed by a window above the nozzle in the 1967 design.
Bed or table: Holds the sheet. The MIT tutorial notes that the machine’s own ruler borders can be cut if the origin is set wrongly.
Exhaust and enclosure: OSHA’s Technical Manual notes that most Class I industrial lasers are a higher-class laser enclosed in an interlocked, labeled protective housing, and calls for ventilation to remove fumes from laser cutting.

Variants

Gas-assisted CO2 laser cutter: The form first demonstrated at TWI in May 1967 with a 300 watt laser cutting 1 mm steel sheet with oxygen assist.
Flat-bed, moving-optics machine: TWI’s Hilton credits Laser Work AG of Switzerland with probably supplying, in 1975, the first commercially available moving-optics CO2 cutting system with a configuration recognizable today.
Laser mounted on a flame-cutting gantry: In 1971 Andrew Greenslade fitted a Ferranti MF-series laser to a BOC Falcon flame-cutting machine, probably the first two-axis sheet metal laser cutting system in the UK, per Hilton.
Desktop CO2 engraver and cutter: Machines of the class described in the MIT tutorial, which cut non-metals and engrave a wider range of materials.

Specifications

Laser power · W: 300 W in the 1967 TWI trials; 100 W for the MIT tutorial’s machine. No sourced typical value.
Kerf width · mm: About 0.5 mm in the 1967 trials, set by the focused spot size, which the paper gives as 0.4 mm.
Bed size · in: 32 by 18 in for the MIT tutorial’s machine. No sourced typical value.

Made to

IEC 60825-1
ANSI Z136.1
ANSI B11.21
ISO 11553-1
ISO 9013

Safety and care

Safety

OSHA states that the human eye is almost always more vulnerable to laser injury than the skin.
OSHA’s Technical Manual classes high-power Class IV lasers as hazardous to view directly or as diffuse reflection, and as a potential fire hazard and skin hazard.
OSHA states that ventilation must keep fumes and vapors from laser cutting below the applicable exposure limits.
The MIT tutorial states that the machine must remain under constant supervision while it is running, and reports a fire that began when the beam reflected off a skewed mirror.
The MIT tutorial states never to cut PVC or other chlorinated plastics, because PVC gives off chlorine gas that corrodes the machine and endangers people nearby.
The MIT tutorial warns that acrylic, cardboard and wood are readily flammable and that acrylic gives off noxious fumes.

Care

The MIT tutorial says to remove the lens at the start of each cutting session, check it for accumulated material, and clean removable grit with a clean swab and a drop or two of cleaning fluid. It reports that cutting with a dirty lens can ignite particles and destroy the lens.

Tips

Set lines to hairline width to get a cut
The MIT tutorial says lines should be set to the minimum hairline width, 0.004 inch, to be kept as vector cuts. Wider lines are rasterized into a series of pixel-like burns, which is much slower and gives a poorer finish.1
Run an unpowered air cut first
The MIT tutorial recommends a draft cut with the red tracer beam, started with the lid raised, to confirm the path before cutting. It also says to check the origin, because the machine keeps origin settings between runs, even after power-off.1
Focus before every job
The tutorial says the cutter must be focused with the plastic focus tool and the Z adjustment before use. Poor focus gives a poor cut and more residue and gas, which it calls especially problematic with acrylic and other plastics.1
Cut inner features before the outer border
The tutorial notes that when the outer border is cut, the part often falls out of the stock and skews slightly, so the order of cuts matters. Light materials such as card and thin plastic should be taped to the bed so the head’s motion and air displacement do not move them.1
Let the gas jet do the cutting on metal
The 1971 patent says the oxygen jet with the laser beam cuts stainless steel, which cannot be cut by an oxyacetylene process, and that the exothermic reaction stays confined because heat spreads little from the zone.1
Leave the lid closed on a Class 1 machine
OSHA explains that Class I industrial lasers are mostly higher-power lasers inside an interlocked, labeled housing, so the classification depends on the enclosure staying intact.1

History

Earliest documented

May 1967

Cambridge, England (The Welding Institute, with a laser at the Services Electronic Research Laboratory, Harlow)

TWI’s Paul Hilton reports that the first gas-assisted laser cutting was done in May 1967, when Peter Houldcroft used oxygen assist gas to cut 1 mm steel sheet with a focused CO2 laser beam. Cuts were made in tool steel and stainless steel up to 2.5 mm thick at speeds up to 1 m/min, and the results were published in August 1967 as “Gas-jet laser cutting” by Sullivan and Houldcroft in the British Welding Journal. Hilton calls this the probable start of laser materials processing as it is known today; the Western Electric work on diamond dies of 1966 is earlier and is covered in disputed.1 2

The laser cutter was made possible by the laser itself and then by a change in how the beam was used. Schawlow and Townes patented in 1960 a maser design that extended to the infrared, visible and ultraviolet, and Maiman’s ruby laser patent was filed in 1961, though it was not granted until 1967. The patents that matter for cutting are later. Hilton records that a 300 watt CO2 laser, built for military applications, was already running at the Services Electronic Research Laboratory by 1965, which supplied the power that earlier lasers lacked.

The decisive step was the gas jet. Houldcroft saw that a focused beam combined with oxygen could improve the precision and speed of thermal cutting. The 1971 patent that came from the work states the reasoning: existing thermal cutting heated a wide area, which made the cut inaccurate and distorted the work, whereas a laser beam concentrates heat on a very small zone, and oxygen then adds heat there by reacting with the metal while sweeping out the products. The patent claims that the combination cuts stainless steel, which oxyacetylene cannot.

The 1967 apparatus fixed the layout that later machines kept. Hilton says the nozzle design, with its circular orifice and small stand-off distance, is remarkably close to commercial nozzles used today, and that the kerf of about 0.5 mm depended on the focused spot size and not on the gas jet. What changed afterward was the machine around the optics: Boeing authors in 1969 proposed a laser cutting machine tool in an artist’s concept, Greenslade put a laser on a flame-cutting gantry in 1971, and by 1975 a moving-optics machine was on the market.

The tool displaced flame and early plasma cutting in sheet work where precision mattered, and it added a machine that could be driven from a drawing. Messer Cutting Systems, a flame-cutting machine maker, says it was already delivering numerically controlled laser machines by 1969. The desktop machines described in university shop guides keep the same elements: a CO2 source, a lens that must be inspected and focused, an assist of air or gas, and a driver that turns line weights and colors into cut or engrave settings.

The record of who first applied a laser to industrial work is not simple. Western Electric engineers published in 1966 on laser piercing of diamond dies, a drilling application. TWI’s Hilton, writing on cutting, calls the May 1967 experiment the probable start of laser materials processing in its present form. This entry treats the two as different processes and records both.

Timeline

1960
Schawlow and Townes are granted US Patent 2,929,922, assigned to Bell Telephone Laboratories, for masers and a maser communications system that includes generation and amplification in the infrared, visible and ultraviolet. The application was filed 30 July 1958.1
1961
Theodore Maiman’s application for Ruby Laser Systems is filed on 13 April 1961; US Patent 3,353,115, assigned to Hughes Aircraft Company, is granted on 14 November 1967 from that original application.1
1965
TWI learns that a 300 watt CO2 laser built for military use is operating at the Services Electronic Research Laboratory in Harlow.1
1966
Western Electric engineers report in Wire & Wire Products on piercing holes in diamond wire-drawing dies with laser beams.1 2
May 1967
Houldcroft and Sullivan cut 1 mm steel with a focused CO2 laser and an oxygen jet at the SERL laser. The results are published in August as “Gas-jet laser cutting” in the British Welding Journal.1 2
1969
Three Boeing authors publish “A powerful CO2 cutting tool” in Laser Focus, August 1969, on assist-gas laser cutting of titanium, Hastelloy and ceramic. Messer Cutting Systems says that its predecessor CRO Engineering delivered the first American-built numerically controlled laser cutting machine in 1969, for shape cutting titanium in the aerospace industry.1 2
1971
Andrew Greenslade mounts a Ferranti MF-series laser on a BOC Falcon flame-cutting machine, probably the first UK two-axis sheet metal laser cutting system. In the same year, 3 August, Sullivan and Houldcroft’s US Patent 3,597,578 for thermal cutting with a laser beam and an exothermically reacting gas is granted.1 2
1975
Laser Work AG of Switzerland probably supplies the first commercially available moving-optics CO2 laser cutting system, with a configuration comparable to equipment available today, according to Hilton.1

Where the sources disagree

What was the first industrial application of the laser in material processing?

Gas-assisted laser cutting of steel at TWI in May 1967 was the first experiment in laser materials processing that evolved into a significant industrial process, and probably marks the start of laser materials processing as it is known today.1 2
P. A. Hilton, TWI (TWI is the institution that did the work)
Piercing holes in diamond wire-drawing dies with laser beams was in use at Western Electric by 1966, when the company’s engineers published on it and reported possible time and cost reductions in die production.1 2
Wire Association International catalog records of the 1966 Wire & Wire Products articles by Western Electric authors

Gaps in the record (7)

The Western Electric work is known only from catalog records of 1966 articles; the articles themselves and the start date of the work (reported by the person who proposed this lead as 1965) have not been located.
The priority date of the Sullivan and Houldcroft patent application was not legible in the patent scan and is not given.
Patel’s CO2 laser work, cited by TWI, has not been sourced independently.
The Boeing 1969 paper (Brod, Brasier and Parks, Laser Focus, August 1969) is known only from Hilton’s reference list.
The Messer claim about a 1969 numerically controlled laser machine is the company’s own statement and has not been checked against another source.
No sourced typical specifications for current desktop or industrial machines.
Standards are named but their texts have not been read.

Plasma cutter