The sharp focusing of a laser beam coupled with high power density at the focus makes it an attractive tool for material cutting. Laser cutting is the most established laser material processing technology. The laser cutting process is carried out by a CNC control moving a tiny focused laser beam (spot size diameter in the range of .2 mil to 8 mil or 5 µm to 200 µm) along the surface of a workpiece. Laser cutting is a non-contact, vibration-free and flexible process. It has the ability to cut any random non-linear shape with small kerf widths. Depending on laser wavelength (photon energy), laser pulse width (laser-material interaction) and type of material (optical and thermophysical properties, band gap energy), different laser cutting processes such as vaporization cutting, fusion cutting, reactive fusion cutting and bond breaking cutting or a combination of some of them, can be applied to achieve the highest throughput or cut quality. Critical concerning issues with laser cutting are cutting speed, kerf width, burrs formation, surface contamination, heat affected zone and dimensional tolerance. ponents, including material handling and process monitoring.
Laser vaporization cutting
In laser vaporization cutting, the material removal is mainly realized by material evaporation. Under high laser power density (over 106 W/cm 2), the temperature of the material quickly reaches its vapor temperature and the vapor material is primarily ejected by its recoil pressure. This is the cutting method to achieve small heat affected zone and high cleanliness. Pulsed lasers with pulse duration varying from femto- to microseconds are used for this cutting mode. The quality of the cut is determined by the quantity of melt, which may form burrs and recast on the surface. The shorter the pulse, the higher is the pulse peak power and the shorter is the time the material reaches the boiling point. As a result, more material will be removed as vapor than ejecta (melt ejection). The material removal rate per pulse is relatively low, especially with nano and femto second lasers. Laser vaporization cutting is also used for cutting of acrylics, some thermoplastic polymers, rubbers, woods, paper, leather, some ceramics and thin metal sheets. While sealed CO2 lasers with average power up to 200 W are the most effective cutting tools for non-metallic materials, vaporization cutting of metals is realized by using repetitive microsecond pulsed Nd:YAG lasers with pulse peak powers up to 100 kW. A process gas jet is applied to further assist the material removal. It blows the vapor and condensed material out of the kerf. The generated cutting kerf is typically slightly larger than the focal spot diameter. Our laser micro and fine cutting utilizes the vaporization cutting mechanism for precise cutting of materials with thickness up to 2 mm (.080”) with minimal kerf width and high finishing quality. In some cases, instead of single pass cutting, the laser beam has to travel back and forth (multiple pass cutting) in order to completely cut through the workpiece. In single pass cutting, the cut quality on the beam entrance side is always better than that on the beam exit side. In contrast, debris and burrs build up mainly on the beam entrance side in multiple pass cutting. In many situations, the laser beam is linear polarized as a result of the laser cavity design. The cutting results are often polarization dependent and thus a circular polarized beam is desirable to obtain high-quality cut in both x-and y-cutting direction. A quarter wave plate is applicable to convert a linear to a circular polarized beam.
Laser fusion cutting
Fusion cutting is a single pass melt-and-blow cutting method, whereas the material is heat up above the molten temperature and blown out of the kerf by a high pressure (up to 20 bar) inert gas jet. Nitrogen is commonly used as the cutting gas. The gas jet is responsible for melt ejection and for shielding the heated material from the surrounding air. The resulting cut edges are free of oxidation. Fusion cutting is applicable to all metals, especially stainless and high alloyed steels, aluminium, titanium and copper alloys. High power continuous wave or modulated CO2 lasers, fiber and disk lasers of up to several kWs are commonly selected as the cutting tool. This method is suitable to cut thick materials (up to 25 mm or 1”). The main technical demand is to avoid adherent dross and excessive heat affected zone at the bottom edges of the kerf. The design of the nozzle and the alignment of the nozzle with the laser generated kerf are important areas of concern. Besides high gas pressure (above 10 bars), nozzle diameter, nozzle stand-off distance, focus position and cutting speed are critical parameters to ensure that cut edges are free of burrs and recast (slag).
Laser reactive fusion cutting
Laser reactive fusion cutting, also called laser oxygen cutting, uses oxygen as the cutting gas. The exothermic reaction of oxygen with the material (mainly steel) supports the laser cutting process by providing additional heat input. The result is higher cutting speed compared to laser fusion cutting with inert gases. It is important to balance the laser power and other process parameters to avoid variation of kerf width and burning out of sharp corners and narrow bridges. Using this method, high gas pressures are still required for cutting thin materials (below 1 mm) with laser average output power less than 500 W. However, significantly lower oxygen gas pressures are needed for cutting thick steel sheets (above 3 mm) with high power lasers (above 1 kW average power).
Laser cutting via bond breaking
Laser bond breaking cutting or also called as laser photo ablation uses ultraviolet (UV) lasers with high photon energies to break atom or molecular bonds of the material (cold ablation). Depending on the band gap energy of the material, either third or fourth harmonic solid state lasers or excimer lasers are selected. The material removal rate is mainly determined by the material and the laser wavelength and is usually an order lower than the aforementioned methods. Laser bond-breaking cutting is used in machining materials which are hard to machine with other types of lasers, or where very high precision is required. For example, excimer lasers are useful for cutting biological tissue where a clean cut is required without thermal damage to the surrounding tissue.
In practice, the cutting process is often not based on one individual cutting process but rather on two or more simultaneous reactions. For reducing costs sometimes compressed air is used instead of oxygen or nitrogen as cutting gas. Another example is the single pass cutting of thin sheet metal with high pulse peak powers and micro-second pulses resulting in both vaporization and melting of the material.
There are a number of special or modified variants of laser cutting. The specialties take place at either laser or process side to achieve a debris free cutting with a maximum material removal rate.
- Multiple beam cutting (using a DOE to split the single primary beam into a line of secondary beams)
- Water jet guided laser cutting (high pressure micro water jet guiding the laser beam to the workpiece)
- Laser cutting with a flowing thin water or etchant liquid film
- Laser cutting under etching gases containing halide, halogen, chlorine or hydrofluorcarbon
- Laser cutting via explosive boiling (e.g. for dicing silicon wafers)
- Material separation by laser induced thermal stress (glass separation with lasers)
- Laser separation using non linear absorption effect under irradiation of high intensity and ultrashort laser pulses
Area of expertise
KJ Laser Micromachining is a leading service provider for laser precision and micro cutting. Our expertise covers a wide range of laser cutting technology, including debris- and burrs-free cutting, process parameter optimization, beam shaping, beam delivery configuration and system customization. We are also equipped with rotary stages for tubular laser cutting of tubes, cylinders or spheres. We can cut finest contours and complex part geometries of miniature components within a minimum tolerance of ±.0001? for dimensions up to 40?x50?. Our fully equipped facility and experienced laser engineers are prepared to satisfy your most demanding requirements. Applying state-of-the-art high accuracy linear stages, multiple wavelength systems and comprehensive process & quality control we are capable to get your parts done perfectly and consistently.
Our variety of far-infrared, infrared, green and UV lasers allows the selection of an appropriate laser wavelength for your particular laser processing application, whether the material is metals, ceramics or plastics. We can cut almost any type of materials, from stainless steels, plastics and rubbers to super hard materials (e.g. alumina, polycrystalline diamond, tungsten carbide), transparent materials (e.g. glass, sapphire, Teflon) or heat sensitive materials (e.g. Nitinol, paper). For example, we can effectively cut stainless or mild steel or Invar material with thickness from 10 µm to 3 mm (.0005” to .120”) and acrylic Plexiglass with thickness up to 12.5 mm (1/2”). We also cut aluminium, copper and their alloys with thickness up to 2 mm.
Sub-contract micromachining and R&D
Our precision and micro cutting services provide world-class micro machining technology for the mass production of thousands of parts per month. We can also play a vital role during your product design and development period by conducting scientific and innovative R&D investigations in laser precision and micro cutting.
System development and process automation
KJ Laser Micromachining also cooperates with its customers to design and develop laser cutting systems for the high-volume and automated manufacture of parts or components, including material handling and process monitoring.