Understanding Laser Cutting

Need a refresh on laser cutting?

According to Thomas Net:

“Laser cutting is a fabrication process which employs a focused, high-powered laser beam to cut material into custom shapes and designs. This process is suitable for a wide range of materials, including metal, plastic, wood, gemstone, glass, and paper, and can produce precise, intricate, and complex parts without the need for custom-designed tooling.

“There are several different types of laser cutting available, including fusion cutting, oxidation cutting, and scribing. Each laser cutting process can produce parts with precision, accuracy, and high-quality edge finishes, and with generally less material contamination, physical damage, and waste than with other conventional cutting processes, such as mechanical cutting and waterjet cutting. However, while laser cutting demonstrates certain advantages over more conventional cutting processes, some manufacturing applications can be problematic, such as cutting reflective material or material requiring secondary machining and finishing work. The requirements and specifications demanded by a particular cutting application—e.g., materials and their properties, energy and power consumption limits, secondary finishing, etc.—help determine the type of cutting process most suitable for use.

“While each cutting process has its advantages and disadvantages, this article focuses on laser cutting, outlining the basics of the laser cutting process and the necessary components and mechanics of the laser cutting machine. Additionally, the article explores various laser cutting methods and applications, the benefits and limitations of the process, and comparisons between laser cutting and other types of cutting processes.  

The Laser Cutting Machine and Process

“Laser cutting is a non-contact, thermal-based fabrication process suitable for metal and non-metal materials. For the laser cutting process to run smoothly and at optimum capacity, several factors should be taken into consideration, such as the laser cutting machine’s configuration and settings, the material being cut and its properties, and the type of laser and assist gas employed.

Overview of Laser Machine Components and Mechanics

“In contrast to mechanical cutting, which utilizes cutting tools and power-driven equipment, and waterjet cutting, which utilizes pressurized water and abrasive material, laser cutting employs a laser cutting machine to produce cuts, engravings, and markings. While laser cutting machines vary from model to model and application to application, the typical setup includes a laser resonator assembly, mirrors, and a laser cutting head which contains a laser focusing lens, a pressurized gas assembly, and a nozzle. The basic laser cutting process includes the following stages:

• “beam generation
• “beam focusing
• “localized heating and melting
• “material ejection
• “beam movement

“Each stage is integral to the laser cutting process and, when properly executed, producing a precise cut.

Beam Generation

“The term “laser” comes from the acronym LASER or Light Amplification by Stimulated Emission of Radiation. Essentially, this acronym summarizes the basic principles of laser generation—stimulation and amplification. Along with these principles, the laser resonator employs the processes of spontaneous emission and stimulated emission to produce a high-intensity beam of light that is both spatially and spectrally coherent (i.e., a laser beam).  

• “Spontaneous emission: The laser resonator contains an active laser medium (e.g., CO₂, Nd:YAG, etc.), the electrons of which are stimulated by an external energy source, such as a flash lamp or electrical arc. As the medium receives and absorbs energy, its atoms experience a process known as spontaneous emission. During this process, energy absorbed by an atom causes the atom’s electrons to briefly jump to a higher energy level and then return to their ground state. Upon the electrons’ return to their ground state, the atom emits a photon of light.
• “Stimulated Emission: The photons that are produced by spontaneous emission travel within the medium, which is contained in a cavity of the laser resonator between two mirrors. One mirror is reflective to keep photons traveling within the medium, so they continue to propagate stimulated emissions, and the other mirror is partially transmissive to allow some photons to escape. Stimulated emission is the process in which a photon (i.e., the incident photon) stimulates an atom that is already at a higher energy level. This interaction forces the stimulated atom to drop to its ground state by emitting a second photon of the same fixed wavelength or coherent with the incident photon.

“The process of one photon propagating the emission of another photon amplifies the strength and intensity of the light beam. Thus the stimulated emission of light photons (i.e., a type of electromagnetic radiation) causes the amplification of light; in other words, light amplification by stimulated emission of radiation. Improperly aligned photons within the resonator pass through the partially transmissive mirror without being reflected into the medium, generating the initial laser beam. Once generated, the beam enters the laser cutting head and is directed by mirrors into the focusing lens.

Beam Focusing

“The focusing lens focuses the laser beam through the center of the nozzle at the end of the laser cutting head incident to the workpiece’s surface. By focusing the beam, the lens concentrates the beam’s energy into a smaller spot, which increases the beam’s intensity (I). The following equation illustrates the underlying principle behind this occurrence:

“Where P represents the power of the initial laser beam, and πr² represents the cross-sectional area of the beam. As the lens focuses the laser beam, the radius (r) of the beam decreases; this decrease in radius reduces the cross-sectional area of the beam, which in turn increases its intensity since its power is now distributed across a smaller area.

Localized Heating and Melting, and Material Ejection 

“As the beam strikes the material’s surface, the material absorbs the radiation, increasing the internal energy and generating heat. The high intensity of the laser beam allows it to heat, melt, and partially or completely vaporize a localized area of the workpiece’s surface. The weakening and removal of the affected area of the material forms the desired cuts. Siphoned into the laser cutting head and flowing coaxially to the focused beam, the assist gas—also referred to as the cutting gas—is used to protect and cool the focusing lens, and may be used to expel melted material out of the kerf—the width of the material removed and of the cut produced—and support the cutting process. Laser cutting employs several different types of material cutting and removal mechanisms, including fusion cutting, chemical degradation cutting, evaporation cutting, scribing, and oxidation cutting.

• “Fusion Cutting: Also referred to as inert gas melt shearing or inert gas cutting, fusion cutting is employed by CO₂ and Nd:YAG laser cutting machines. The laser beam produced by the cutting machine melts the workpiece, and melted material is expelled through the bottom of the kerf by a jet of the assist gas employed. The assist gas and the assist gas pressure employed are dependent on the type of material being cut, but the inert gas is always chosen based on its lack of chemical reactivity in regards to the material. This mechanism is suitable for laser cutting most metals and thermoplastics.
• “Chemical Degradation: Chemical degradation is employed by CO₂ laser cutting machines and is suitable for laser cutting thermoset polymers and organic material, such as wood. As thermoset and organic materials do not melt when heat is applied, the laser beam burns the material instead, reducing it to carbon and smoke.
• “Evaporation Cutting: Evaporation cutting is employed by CO₂ laser cutting machines and is suitable for materials such as laser cutting acrylic and polyacetal due to the closeness of their melting and boiling points. Since the laser evaporates material evaporates along the cut, the edge produced is generally glossy and polished.
• “Scribing: Scribing is employed by CO₂ and Nd:YAG laser cutting machines to produce partial or fully penetrating grooves or perforations, usually on ceramics or silicon chips. These grooves and perforations allow for mechanical breaking along the weakened structural lines.
• “Oxidation Cutting: Also referred to as flame oxygen cutting, oxidation cutting is employed by CO₂ and Nd:YAG laser cutting machines and is suitable for laser cutting of mild and carbon steel. Oxidation cutting is one example of the reactive gas melt shearing cutting mechanism, which specifically employs chemically reactive assist gases. As with inertness, the reactivity of an assist gas is relative to the material being cut. Oxidation cutting, as the name implies, employs oxygen as the assist gas, which exothermically reacts with the material. The heat generated accelerates the cutting process and produces an oxidized melted edge which can be easily removed by a gas jet to allow for a cleaner, laser-cut edge.

Beam Movement

“Once the localized heating, melting, or vaporizing has started, the machine moves the area of material removal across the workpiece to produce the full cut. The machine achieves the movement either by adjusting the reflective mirrors, controlling the laser cutting head, or manipulating the workpiece. There are three different configurations for laser cutting machines, defined by the way in which the laser beam moves or is moved over the material: moving material, flying optics, and hybrid laser cutting systems.

• “Moving Material: Moving material laser cutting machines feature a stationary laser beam and a movable cutting surface to which the material is affixed. The workpiece is mechanically moved around the stationary beam to produce the necessary cuts. This configuration allows for a uniform and consistent standoff distance and requires fewer optical components.
• “Flying Optics: Flying optics laser cutting machines feature a movable laser cutter head and a stationary workpiece. The cutting head moves the beam across the stationary workpiece in the X- and Y-axes to produce the necessary cuts. The flexibility of flying optics machines is suitable for cutting materials with variable thickness and sizes, as well as allowing for faster processing times. However, since the beam is continually moving, the changing beam length has to be taken into consideration throughout the process. The changing beam length can be controlled by collimation (alignment of the optics), using a constant beam length axis, or employing an adaptive optics or capacitive height control system capable of making the necessary adjustments in real time.
• “Hybrid: Hybrid laser cutting machines offer a combination of the attributes found on moving material and flying optics machines. These machines feature a material handling table that moves on one axis (usually the X-axis) and a laser head that moves on another (usually the Y-axis). Hybrid systems allow for more consistent beam delivery, and reduced power loss and greater capacity per watt compared to flying optics systems.

“Lasers are produced as either pulsed beams or continuous wave beams. The suitability of each depends on the properties of the material being cut and the requirements of the laser cutting applications. Pulsed beams are produced as short bursts of power output, while continuous wave beams are produced as continuous, high power output. The former is typically employed for scribing or evaporation cutting applications and is suitable for cutting delicate designs or piercing through thick materials, while the latter is suitable for high-efficiency and high-speed cutting applications.

Types of Assist Gases

“Laser cutting employs a variety of assist gases to aid the cutting process. The cutting process employed and the material being cut determine the type of assist gas—either inert or active—that is most suitable for use.

“Inert gas cutting (i.e., fusion cutting or inert gas melt shearing), as indicated by the name, employs chemically inert assist gases. The particular assist gas employed depends on the material’s reactive properties. For example, since molten thermoplastics do not react with nitrogen and oxygen, compressed air can be used as the assist gas when laser cutting such materials. On the other hand, since molten titanium does react with nitrogen and oxygen, argon—or another similarly chemically inert gas—must be used as the assist gas in laser cutting applications involving this material. When laser cutting stainless steel via the inert gas cutting process, nitrogen is typically used as the assist gas; this is because molten stainless steel chemically reacts with oxygen.

“When laser cutting material via the reactive melt shearing process, an active (i.e., chemically reactive) assist gas—typically oxygen—is employed to accelerate the cutting process. While in inert gas cutting the material is heated, melted, and vaporized solely by the power of the laser, in reactive gas cutting the reaction between the assist gas and the material creates additional heat which aids the cutting process. Because of this exothermic reaction, reactive gas cutting typically requires lower laser power levels to cut through a material compared to the power level necessary when cutting the same material via the inert gas cutting process.

“The cutting pressure of the assist gas employed is also determined by the cutting process employed and the properties and thickness of the material being cut. For example, polymers typically require gas jet pressures of 2–6 bar during the inert gas cutting process, while stainless steel requires gas jet pressures of 8–14 bar. Accordingly, thinner materials also generally require lower pressures, and thicker materials generally require greater pressures. In oxidation cutting, the opposite is true: the thicker the material, the lower the pressure required and the thinner the material, the higher the pressure required.

Types of Laser Cutting Machines

“There are several types of laser cutting machines available which are categorized into gas, liquid, and solid state lasers. The types are differentiated based on the state of the active laser medium—i.e., whether the medium is a gas, liquid, or solid material—and what the active laser medium consists of (e.g., CO₂, Nd:YAG, etc.). The main two types of lasers employed are CO₂ and solid-state lasers.

“One of the most commonly employed gas state lasers, a CO₂ laser employs a carbon dioxide mixture as the active laser medium. CO₂ lasers are typically used to cut non-metal materials since early models were not powerful enough to cut through metals. Laser technology has since evolved to enable CO₂ lasers to cut through metals, but CO₂ lasers are still better suited for cutting through non-metals and organic materials (such as rubber, leather, or wood) and simply engraving metals or other hard materials. Pure nitrogen lasers are another commonly used gas state laser. These lasers are used for applications that require the material not oxidize as it is cut.

“There are several varieties of solid-state lasers available, including crystal and fiber lasers. Crystal lasers employ a variety of crystal mediums—e.g., neodymium-doped yttrium aluminum garnet (Nd:YAG) or neodymium-doped yttrium orthovanadate (Nd:YVO₄)—which allow for high-powered metal and non-metal laser cutting. Although versatile in regards to their material cutting capabilities, crystal lasers are typically more expensive and have shorter lifespans than other types of lasers. Fiber lasers offer a cheaper and longer lasting alternative to crystal lasers. This type of laser first generates a beam through a series of laser diodes which is then transmitted through optical fibers, amplified, and focused on the workpiece to perform the necessary cuts.

Laser Cutting Machine Considerations

“As described in the previous section, the type of laser suitable for a laser cutting application is largely determined by the material being cut. However, other considerations may be taken into account when choosing and setting up a laser cutting machine for a specific application, such as the machine configuration, laser power, wavelength, temporal mode, spatial mode, and focal spot size.

“Machine Configuration: See Beam Movement, above

“Laser Power: The laser power, or wattage, can increase or decrease the total processing time for a cutting application. This occurrence is due to the increasing intensity of the beam as the laser’s power increases (Power density (Intensity) = P/πr²). The price of a laser cutting machine is typically dependent upon the power of the laser; the more powerful the laser, the more expensive the equipment. Therefore manufacturers and job shops must find a balance between processing costs and equipment costs when choosing a laser machine based on laser power. 

“Wavelength: The wavelength of the laser beam is the spatial length of one complete cycle of vibration for a photon within the beam. The particular wavelength of the laser beam partially determines the material’s radiation absorption rate, which is what allows the material to be heated, melted, and vaporized to produce the necessary cuts.

“Beam Mode: The mode refers to how the laser beam’s intensity is distributed across the cross-sectional area of the beam. The mode affects the size of the beam’s focal spot and the intensity of the beam, which in turns affects the quality of the cut. Typically, the optimal mode has a Gaussian intensity distribution (TEM₀₀).

“Focal Spot: The beam is directed through a lens or a specialized mirror and focused to a small spot of high intensity. The point at which the beam’s diameter is the smallest is called the focal spot, or focus. The optimal position of the focus for a laser cutting application is dependent on several factors, including the material’s properties and thickness, beam shape and mode, type of assist gas, and the state of the focal lens.

Material Considerations

“Laser cutting is suitable for a variety of metal and non-metal materials, including plastic, wood, gemstone, glass, and paper. As mentioned in the previous sections, the type of material being cut and its properties largely determine the optimal cutting mechanism, cutting gas and cutting gas pressure, and laser machine to use for the laser cutting application.

Table 1, below, illustrates the suitability of each laser cutting mechanism described previously for cutting a material.

Table 1 – Suitability of Laser Cutting Mechanisms for Cutting Various Materials

Table 2, below, illustrates the suitability of each commonly employed assist gas for cutting a material.

Table 2 – Suitability of Assist Gases for Cutting Various Materials

Table 3, below, illustrates the suitability of each type of laser previously described for cutting a material.

Table 3 – Suitability of Laser Machine Types for Cutting Various Materials

“Besides the reactive or non-reactive properties of the material being cut, another material consideration that manufacturers and job shops may take into account when deciding on the suitability of laser cutting for their cutting application is reflectivity. The greater the reflectivity of a material, the larger the percentage of radiation reflected rather than absorbed by it. This lower absorption rate slows the cutting process and lengthens turnaround, as well as increases the laser power requirements for cutting the material. Highly reflective materials, such as copper and aluminum, can also cause damage to the laser machine as the beam may bounce back towards the components of a laser cutter.

Benefits of Laser Cutting

“Compared to other types of cutting, laser cutting offers several advantages. These include:

• “Greater cutting precision and accuracy
• “Higher quality edges
• “Narrower kerf widths
• “Smaller HAZ and less material distortion
• “Less material contamination and waste
• “Lower maintenance and repair costs
• “Greater operator safety

“Laser cutting machines are capable of cutting a wide range of designs with a greater degree of precision and accuracy than more conventional cutting machines. Since laser cutting machines can be fully CNC controlled, they can repeatedly and consistently produce complex and intricate parts to high tolerances. Laser cutting also produces high-quality cuts and edges which generally do not require further cleaning, treating, or finishing, decreasing the need for additional finishing processes.

“The focused beam allows for narrower kerf widths, and the localized heating allows for minimal thermal input to the bulk of the material being cut. The smaller kerf minimizes the amount of material removed, and the low thermal input minimizes the heat affected zones (HAZs) which in turn decreases the extent of thermal distortion. The non-contact nature of the laser cutting process also decreases the risk of mechanical distortion, especially for flexible or thin materials, as well as decreases the risk of material contamination. Owing to the tighter tolerances, narrower kerf widths, smaller heat affected zones, and lesser degrees of material distortion, laser cut part designs can be arranged closer together on the material. This closeness of design reduces the amount of material waste, leading to lower materials costs over time.  

“While the initial investment in laser cutting equipment is typically higher than with other cutting processes, running and maintenance costs are comparatively low. Laser cutting machines are capable of performing multiple operations and applications without the need for purchasing or changing out separate, custom-designed tooling; this characteristic of laser cutting decreases both the total equipment costs and the lead time between different processes and applications. Additionally, as laser cutting is a non-contact process, the laser components experience less fatigue—and consequently last longer—than components in contact cutting processes such as mechanical cutting or rotary die cutting. Together with the relative inexpensiveness of replacement laser components, the durability of laser components further decreases the total equipment costs over time.

“Other advantages of laser cutting include decreased risk of operator injury and quieter operations. The laser cutting process employs little to no mechanical components and occurs within an enclosure, therefore there is less risk of operator injury. As there is less noise produced during the laser cutting process, the overall workplace environment is also improved.

Limitations of Laser Cutting

“While laser cutting demonstrates advantages over other forms of cutting, there are also limitations to the process, including:

• “The range of suitable materials
• “Inconsistent production rate
• “Metal hardening
• “Higher energy and power consumption
• “Higher equipment costs

“As indicated in previous sections, laser cutting is suitable for a wide range of metals and non-metals. However, the material being cut and its properties often limits the suitability of some cutting mechanisms, assist gases, and laser types. Additionally, the material thickness plays a significant factor in the determination of the optimal laser power, assist gas pressure, and focal position for a laser cutting application. Varying materials or varying thicknesses within a single material also necessitate adjustments to the cut speed and depth throughout the cutting process. These adjustments create inconsistencies in production time, as well as increase the turnaround time, especially in large production runs.

“One advantage of the laser cutting is the production of high-quality cuts which generally do not require extensive secondary cleaning, treating, or finishing. While in some respect this is advantageous, the resultant work hardening of the laser cut edges may be problematic for some applications. For example, parts requiring further processing, such as powder coating or painting, will first need surface treatment following the laser cutting process before receiving the necessary coating or paint. The addition of this step increases both the turnaround time and total processing costs.

“While laser cutting can have lower maintenance and material costs over time, for some manufacturing applications, it may be more cost-effective to use other cutting processes. For example, while both metal and non-metal materials can be laser cut, laser cutting plastic causes the emission of potentially harmful and toxic gases. These emissions necessitate air pollution control equipment, increasing the necessary equipment costs. For manufacturers and job shops starting up, although replacement and maintenance parts are relatively inexpensive, the initial investment in laser cutting equipment also tends to be much higher compared to more conventional cutting processes. Additionally, laser cutting equipment typically consumes more power and energy than other cutting processes, leading to further increases in operating costs. Altogether, the high initial equipment and operating costs may make laser cutting unsuitable for low budget operations.

Alternative Cutting Processes

“Although laser cutting can produce high tolerance, complex, and precision parts, it may not be appropriate for every manufacturing application, and other cutting processes may be more suitable and cost-effective. Illustrated below are some comparisons between laser cutting and other cutting processes.

Table 4 – Comparisons between Laser Cutting and Mechanical Cutting Processes

“Mechanical cutting is a fabrication process which employs power-driven equipment—e.g., lathes, mills, and presses—to cut, form, and shear material into custom shapes and designs. As illustrated in Table 4, above, laser cutting holds several advantages over mechanical cutting; it allows for greater precision and higher tolerances, as well as offers lower material (e.g., less waste) and maintenance costs. However, laser cutting also typically requires much higher initial investment and operational costs than mechanical cutting due to the expensive laser cutting equipment and high power and energy consumption of the equipment.

Table 5 – Comparisons between Laser Cutting and Die Cutting Processes

“Die cut part production is one manufacturing application for which laser cutting may serve as an alternative solution to mechanical cutting processes, such as flatbed die cutting or rotary die cutting. As illustrated in Table 5, above, laser cutting offers capabilities for higher precision and faster prototyping. While die cutting is capable of producing precision parts to an extent, laser cutting offers even tighter tolerances for more intricate designs and patterns. Additionally, laser cutting is more cost-effective for prototyping and design adjustments as the process does not require the creation of separate die components to test out new designs. However, die cutting—specifically rotary die cutting—does offer certain advantages over laser cutting. For example, rotary die cutting allows for multiple in line operations, as well as constant and continuous cutting pressures. Altogether these considerations allow rotary die cutting to provide faster turnaround than laser cutting, especially for large or long production runs.

Table 6 – Comparisons between Laser Cutting and Waterjet Cutting Processes

“Waterjet cutting is a fabrication process which employs pressurized water—as well as abrasives, such as garnet or aluminum oxide—to cut and form material into custom shapes and designs. As illustrated in Table 6, above, laser cutting can produce parts with greater precision and intricacy than waterjet cutting, while waterjet cutting can produce parts from thicker and multi-layer materials that may be problematic for the laser cutting process. While there is less risk of mechanical distortion with laser cutting, waterjet cutting offers a lower risk of thermal distortion. Compared to laser cutting, waterjet cutting also generates more noise and more waste—i.e., used water and abrasive mixtures—which require cleanup and disposal, increasing operation costs.

Table 7 – Comparisons between Laser Cutting and Plasma Cutting Processes

G.E. Mathis Company

“Plasma cutting, also referred to as plasma arc cutting, is a fabrication process which employs a cone of superheated ionized gas to cut and form electrically conductive material into custom shapes and designs. As illustrated by Table 7, above, compared to laser cutting which is capable of cutting metal and non-metal materials, plasma cutting has a more limited range of suitable materials as only electrically conductive materials can be cut via the plasma cutting process. Additionally, plasma cut parts are produced with significantly less precision and lower tolerances due to the wider kerf produced during the process. Despite these limitations, plasma cutting offers lower equipment and operating costs (due to generally lower power and energy consumption) and faster turnaround compared to laser cutting, as well as capabilities for cutting thicker and multi-layer materials.”

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