“The laser cut clean through iron as though it were mud”, this is no exaggeration.

Let’s take a look at the laser!

What is a laser?

The laser is a kind of enhanced light obtained by stimulated radiation.

Its basic characteristics:

  • High intensity and high brightness
  • Wavelength frequency determination, good monochrome
  • Good coherence and long coherence length
  • Good directionality, it’s almost a bunch of parallel light

Laser cutting working principle

When the laser beam is irradiated onto the surface of the workpiece, the light energy is absorbed and converted into heat energy, so that the temperature at the irradiation spot is rapidly increased, melted, and vaporized to form a small pit. The metal around the spots melts due to thermal diffusion. The metal vapor in the small pit rapidly expands, causing a micro-explosion, and the molten material is ejected at a high speed to generate a highly directional anti-shock wave, so that a hole with a large upper side and a small lower side is formed on the surface to be processed.

 

Comparison of ordinary lighting and laser:

Comparison of ordinary lighting and laser

The Generation of Laser

The Generation of Laser

Laser Generating Gas

Laser generating gas is different from cutting gas.

Laser generating gas composition:

N2: The energy generated by the RF generator first excites N2, causing it to be in a transition state.

CO2: N2 in the transition state will excite C02 which causes CO2 to transition, and releases the laser.

He: Absorb CO2 and excess energy, cool the system and turn it into heat.

The proportional relationship between the above mentioned three gas is:

N2:CO2:He = 1:4:5

Laser Cutting Features

Compared with other thermal cutting methods, laser cutting is characterized by high cutting speed and high quality.

Specifically summarized as the following aspects.

(1) Good cutting quality

Laser cutting can achieve better cutting quality due to the small laser spot, high energy density and fast cutting speed.

① The laser cutting incision is narrow, the slits are parallel and perpendicular to the surface, and the dimensional accuracy of the cutting parts can reach ±0.05mm.

② The cutting surface is smooth and beautiful, the surface roughness is only a few tens of micrometers, and even laser cutting can be used as the last process. No machining is required, and the parts can be used directly.

③ After laser cutting, the width of the heat-affected zone is small, the performance of the material near the slit is almost unaffected, and the deformation of the workpiece is small, the cutting precision is high, the geometry of the slit is good, and the shape of the slit cross-section is relatively regular rectangular.

The comparison of laser cutting, oxyacetylene cutting and plasma cutting methods is shown in Table 1. The cutting material is low carbon steel plate with 6.2mm thickness.

(2) High cutting efficiency

Due to the transmission characteristics of the laser, the laser cutting machine is generally equipped with multiple numerical control worktables, and the entire cutting process can realize numerical control.

During operation, it is only necessary to change the numerical control program to apply the cutting of different shapes of parts, which can perform two-dimensional cutting and three-dimensional cutting.

(3) Fast cutting speed

Cutting a 2mm low carbon steel plate with a fiber laser cutting machine in the power of 1200W, the cutting speed can reach 600cm/min; and if cutting a 5mm polypropylene resin plate, the cutting speed can reach 1200cm/min.

The material does not need to be clamped and fixed during laser cutting, which saves the fixture and saves the auxiliary time of loading and unloading.

Table 1 Comparison of laser cutting, oxyacetylene cutting and plasma cutting methods

Cutting Methods Slit Width/mm Heat Affected Zone Width/mm Slit Form Cutting Speed Equipment Cost
Laser cutting 0.2-0.3 0.04-0.06 Parallel Fast High
Oxyacetylene cutting 0.9-1.2 0.6-1.2 Relatively Parallel Slow Low
Plasma cutting 3.0-4.0 0.5-1.0 Wedge & Tilt Fast Medium

(4) Non-contact cutting

There is no contact between the torch and the workpiece during laser cutting, and there is no tool wear.

To process parts of different shapes, there is no need to change the “tool”, just change the output parameters of the laser.

The laser cutting process has low noise, low vibration and no pollution.

(5) Many types of cutting materials

The materials that can be cut by a laser cutting machine including metal matrix composites, leather, wood and fiber.

However, for different materials, due to their different thermophysical properties and different absorption rates of laser light, different laser cutting adaptability is exhibited.

The laser cutting performance of various materials is shown in Table 2 when using a CO2 laser source.(6) Disadvantages

Due to the limitation of laser power and equipment dimensions, laser cutting can only be used to cut plates and tubes in medium and small thickness, and the cutting speed decreases significantly as the thickness of the workpiece increases.

Laser cutting equipment is expensive and has a big one-time investment.

Materials Ability to absorb laser light Cutting performance
Metal Au, Ag, Cu, Al Low absorption of laser light In general, it is more difficult to process, and 1-2mm Cu and Al sheets can be cut by laser.
W,Mo,Cr,Ti Large absorption of laser light If low-speed processing is used, the thin plate can be cut, and metals such as single Ti and Zr need to use air as the auxiliary gas.
Fe,Ni,Pb,Sn Easier to process
Non-metal Organic material Acrylic, polyethylene, polypropylene, polyester, PTFE Permeate to incandescence light Most materials can be cut with a small power laser. Because these materials are flammable, the cut surface is easily carbonized. Acrylic acid and polytetrafluoroethylene are not easily carbonized. Generally, nitrogen or dry air can be used as an auxiliary gas.
Leather, wood, cloth, rubber, paper, glass, epoxy, phenolic plastic Can’t permeate to incandescence light
Inorganic material Glass, fiberglass Large thermal expansion Glass, ceramics, porcelain, etc. are prone to cracking during or after processing, and quartz glass with a thickness of less than 2 mm has good cutting properties.
Ceramic, quartz glass, asbestos, mica, porcelain Small thermal expansion

Application of Laser Cutting

Most laser cutting machines are controlled by CNC programs or made into cutting robots.

As a sophisticated machining method, laser cutting can cut almost all materials, including 2D or 3D cutting of thin metal sheets.

In the field of automobile manufacturing, the cutting technology of space curves such as car roof windows has been widely used.

Volkswagen AG uses a 500W laser to cut complex body sheets and various curved parts.

In the aerospace industry, laser cutting technology is mainly used for the cutting of special aviation materials, such as titanium alloy, aluminum alloy, nickel alloy, chrome alloy, stainless steel, cerium oxide, composite materials, plastics, ceramics and quartz.

Aerospace components processed by laser cutting include engine flame tube, titanium alloy thin-wall machine, aircraft frame, titanium alloy skin, wing long stern, tail siding, helicopter main rotor, space shuttle ceramic heat insulation tile, etc.

Laser cutting forming technology also has a wide range of applications in the field of non-metallic materials. It can cut not only materials in high hardness and brittle, such as silicon nitride, ceramics, quartz, etc., but also flexible materials such as cloth, paper, plastic sheets, rubber, etc., such as laser cutting for clothing, which can saving 10 %~12% material and improving the efficacy by more than 3 times.

Laser Cutter Structure

Laser Cutter Structure

Laser Cutting Process

Laser Cutting Process

1) lens
2) the laser beam
3) airflow
4) the line
5) molten material
6) cutting surface
7) nozzle
8) cutting direction

A: Empty height
B: Puncture height
C: Cutting height
T: Sheet thickness

Laser Light Path

Laser Light Path

  • The core component adjusts the curvature of the lens surface by water pressure, thereby changing the divergence angle of the laser beam, and finally adjusting the laser focus up and down movement.
  • Compensation for focus changes due to different spot diameters at different working positions of the machine.

Laser Light Path Drawing

Laser Generator

Laser Generator

  • High-quality laser beam, laser energy can achieve stepless regulation
  • Using RF technology, low gas loss rate

Laser Cutting Head

Laser Cutting Head

Laser Cutting Head Breakdown Drawing

From Drawings to Parts

From Drawings to Parts

Factors Affect Laser Cutting

Factors Affect Laser Cutting

Laser Cutting Types

Classified by cutting gas:

Flame burning cutting Melt cutting
Cutting Gas Oxygen Nitrogen
Features Large cutting thickness Cutting section without oxide layer
Fast cutting speed Less cutting burrs
Has oxidized layer Cutting gas is expensive
Cutting section with rear tow line Slow cutting speed
Part of the material requires oxygen to participate in the puncture
Applicable material Carbon steel Stainless steel, aluminum, galvanized sheet

Focus Position

Focus Position

In practical applications, the height of the focus varies with the material and the cutting machine.

Laser Cutting with Different Focus Position

How to Improve Cutting Quality

Hardware factor

  • Is the lens clean?
  • Is the laser beam at the center of the nozzle?
  • Is the actual focal length position matches the focal length position on the scale

Parameter factor

  • Relative to the sheet surface position
  • Cutting speed
  • Cutting pressure
  • Cutting power
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