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How to Choose Lasers for Laser Marking Machines?

Laser marking boasts fast marking speed, precise control, high yield, durable marks, minimal surface damage to materials, low noise, and easy maintenance, gradually surpassing traditional marking technologies such as steel stamping, electrochemical marking, dot peen, engraving, electro-erosion, and inkjet printing. Today, laser marking machines, with their powerful capabilities, have become the new generation of productivity enhancement tools.

Within a laser machine lies a crucial component: the laser. It is responsible for generating and emitting the laser beam. The quality of the laser directly impacts the performance of the laser marking machine. This article delves into the working principles, processing effects, and pros and cons analysis of three common types of lasers: fiber lasers, UV lasers, and diode lasers, providing readers with a comprehensive understanding.

Lasers Introduction

The working medium of a fiber laser is fiber, and the terms “Q-switched” and “MOPA” lasers are named after their core technologies; in fact, they both utilize fiber lasers.

A UV laser, short for ultraviolet laser, is named after the wavelength it generates. It utilizes a solid-state laser.

A diode laser, also known as a semiconductor laser, has a working core structure composed of semiconductor materials. Here, we mainly discuss blue diode lasers, also known as blue lasers.

Working Principles

Laser Generation

The working medium of a fiber laser is fiber, usually excited by a diode to stimulate the rare-earth-doped fiber, thus generating the laser.

The working medium of a UV laser is solid, and it generates the laser by optically exciting the dopant laser-active ions within the solid medium.

The working core of a diode laser is the p-region (positive) and n-region (negative) comprising the p-n junction structure. When the junction receives a certain intensity of DC electrical signal from the outside, electrons are excited in the n-region, crossing the boundary between the n-region and the p-region, recombining with holes in the p-region, releasing photons; after resonator cavity enhancement, a laser beam is ultimately produced. In simple terms, a diode laser can directly achieve electro-optical conversion. The current intensity of the diode laser must exceed a certain threshold; otherwise, the diode will behave as an LED. At this time, the beam produced by the diode laser has poor coherence and weak energy, not truly laser-like.

Wavelength Range

The laser family includes lasers of different wavelengths such as ultraviolet, visible light, near-infrared, mid-infrared, and far-infrared lasers; specific to a laser, it outputs a specific wavelength of laser based on the working medium of the laser itself, wavelength modulation, and structural design.

Fiber lasers, including Q-switched and MOPA, usually output laser wavelengths around 1064nm, which happens to be in the “atmospheric window” range of 1~3μm, where the atmospheric transmittance is relatively high, and air absorption and losses of laser are relatively low.

Moreover, various common metals, such as stainless steel, aluminum, and copper, effectively absorb light in the near-infrared wavelength range, allowing fiber lasers to easily mark and engrave these non-metal materials.

However, fiber lasers operate in the human-invisible wavelength band, invisible to the naked eye; Raycus Laser combines the visible indicator red light with the invisible laser path, achieving laser visualization. Since the indicator red light is harmless to the human eye, we can click the border button before processing to directly observe the indication red light frame out of range, confirming the area the laser will process to ensure processing safety and accuracy. Please note that during laser processing, the door cover needs to be closed to ensure safety and avoid direct eye exposure to the laser.

As the name implies, ultraviolet lasers emit ultraviolet light, typically with a wavelength around 350±5nm.

Unlike fiber near-infrared lasers, ultraviolet laser wavelengths do not fall within any “atmospheric window” bands; in other words, under the same optical path, air absorbs ultraviolet laser light far more than it does infrared laser light from fibers. With its shorter wavelength, ultraviolet laser directly affects material at the molecular level during processing, resulting in minimal thermal effects. Therefore, ultraviolet laser marking machines are suitable for marking on most materials except for a few highly reflective metals, including metals, wood, plastics, and particularly for materials sensitive to heat such as glass and thermoplastics.

In contrast, diode lasers have a broader wavelength range, typically between 400-2000nm. Wavelengths commonly used for laser processing include 532nm (green), 450±5nm (blue), and 405nm (violet). These laser wavelengths are within the visible light range and can be seen by the naked eye. However, this does not mean that direct viewing of visible lasers is safe; direct exposure to any type of laser can damage the eyes and pose a danger.

Unlike fiber near-infrared lasers, visible laser wavelengths do not fall within any “atmospheric window” bands; under the same optical path, air absorbs blue laser light far more than it does infrared laser light from fibers. Diode laser wavelengths can be used to process non-metallic materials and are also suitable for processing metallic materials because metals can effectively absorb these shorter wavelengths of light. Among them, blue lasers are particularly suitable for processing yellowish reflective metals such as brass and gold.

Laser Quality

The quality of a laser beam is measured by parameters such as M². M² represents the ratio of the actual beam to an ideal Gaussian beam. The closer M² is to 1, the better the beam quality, with smaller divergence angles. In practical terms, better beam quality means smaller spot sizes, higher power density, and better processing quality.

Fiber lasers have high beam quality, with an M² value less than 1.2, meaning they can generate a beam close to an ideal Gaussian distribution. This makes them suitable for applications requiring high precision and resolution. Their high beam quality is mainly due to their unique optical source structure and operating principles. The gain medium of fiber lasers is doped with rare-earth elements, allowing the laser mode to be well confined within the fiber core, resulting in a high-quality beam. Additionally, fiber laser beam quality is less affected by external environmental changes, ensuring stability and consistency during processing.

Ultraviolet lasers also have high beam quality, with an M² value less than 1.2, making them suitable for high-precision and high-resolution applications. The short wavelength of ultraviolet lasers allows for a very small focused spot on materials, which is advantageous for precise marking applications. However, the beam quality of ultraviolet lasers may be affected by working environment factors such as temperature fluctuations and mechanical vibrations.

The M² value of diode lasers typically ranges from 1.1 to 1.7. The beam quality of diode lasers is influenced by their laser structure. The size and shape of the laser spot are closely related to the laser’s structure and operating conditions. Compared to other lasers such as gas and solid-state lasers, diode lasers have more variable and irregular beam shapes. Low-power diode lasers usually have higher beam quality, while high-power diode lasers have poorer beam quality. Therefore, commercial small to medium-sized laser cutting and engraving machines often use multiple low-power diode lasers instead of a single high-power diode laser to achieve higher total output power.

Solid-state lasers output a fine collimated beam. However, due to the special structure and small size of diodes, the output laser undergoes refraction at the laser’s output end, resulting in a larger emission angle. Additional prisms are required to convert the laser beam into a parallel beam, which is then focused through lenses.

In summary, the design, manufacturing precision, materials, and technologies used in lasers determine the beam quality.

Operating Modes

Depending on the emission mode of the laser during operation, lasers can be divided into continuous-wave lasers and pulsed lasers. Fiber lasers and ultraviolet lasers belong to pulsed lasers, while diode lasers belong to continuous-wave lasers.

In simple terms, continuous-wave lasers continuously emit light during operation, similar to a continuously flowing water pipe. In contrast, pulsed lasers emit light intermittently, emitting a certain number of laser pulses in a unit of time, with no light between two pulses, similar to raindrops falling from the sky. Continuous-wave lasers exhibit more pronounced thermal effects, while some pulsed lasers have minimal thermal effects.

Please note: The emission mode of a laser, whether continuous or pulsed, is independent of its working medium and excitation method. RF-excited CO2 lasers can achieve continuous, pulsed, and super-pulsed outputs, while MOPA fiber lasers can output in continuous and pulsed modes. To determine whether a particular laser device is continuous or pulsed, please consult the supplier.

In general laser equipment operations, laser marking machines typically use pulsed lasers, while laser cutting and engraving machines typically use continuous-wave lasers. Therefore, although diode laser cutting and engraving machines can process non-metallic materials and metallic materials, their performance on metal is not as good as that of laser marking machines.

Pulsed Lasers

Pulsed lasers can emit a large number of laser pulses within one second, with very short time intervals between each pulse. The laser does not emit light during these very short time intervals.

Pulsed lasers have two power parameters: average power and peak power. Average power measures the power output of a pulsed laser within one second, including both the time when pulses are emitted and the time intervals when no light is emitted. Peak power, on the other hand, measures the instantaneous power during one pulse duration, excluding the time intervals when no light is emitted. In practice, the peak power of a pulsed laser can be hundreds of times higher than its average power.

Peak power is different from “maximum power,” which applies to continuous-wave lasers and can be directly set in software. Peak power is specific to pulsed lasers and cannot be directly set in software. It can only be indirectly controlled by adjusting parameters such as pulse width. In Q-switched marking machines and other lasers with non-adjustable pulse widths, peak power cannot be adjusted. Q-switched marking machines cannot achieve blackening on anodized aluminum or color marking on stainless steel, while MOPA marking machines can, because Q-switched marking machines have non-adjustable pulse widths, whereas MOPA marking machines allow adjustable pulse widths.

Continuous-Wave Lasers

Continuous-wave lasers operate by emitting light continuously, continuously emitting laser pulses per unit time. In practical applications, some continuous-wave lasers can modulate the laser output into pulsed light by adjusting the PWM signal, but the pulse energy is far less than that of true pulsed lasers.

The common unit of measure for laser power is watts. However, when setting laser material parameters, you may see power units expressed as a percentage. Why is this? When describing different models of lasers, you may hear about 30W lasers or 80W lasers. These numbers represent the maximum limit of power that the laser can provide. For example, a 30W laser can provide power ranging from 0 to 30W.

When setting the power parameter, you are actually setting the laser’s output power. For example, with a 30W laser, setting the power to 20% results in an actual output power of 30W * 20% = 6W. The higher the output power, the greater the energy of the laser beam produced.

Processing Performance

Processing Time

The processing time of diode laser cutting and engraving machines is far greater than that of marking machines, which is related to the maximum processing speed of the laser machine. Generally, the processing speed of small and medium-sized diode laser cutting and engraving machines cannot exceed 1000mm/s. In comparison, regardless of the type of laser used, marking machines can achieve maximum processing speeds of over 2000mm/s. This is determined by the motion system. The laser beam movement of marking machines is controlled by a galvanometer system, which is fast but can only achieve precise processing within a small range without distortion, resulting in a small working area. On the other hand, the motion system of laser cutting and engraving machines is composed of motors, rails, and transmission belts, which are relatively slower in speed.

Applicable Materials

Q-switched laser marking machines and MOPA laser marking machines can mark metals such as brass, white copper, bronze, phosphor bronze, 304 (food-grade) stainless steel, mirror stainless steel, carbon steel, pure iron, galvanized iron sheet, zinc alloy, gold-plated zinc alloy, zinc, magnesium, nickel, aluminum, anodized aluminum, titanium, as well as non-metal materials such as PBT, PET, epoxy resin, PU leather, slate, etc. They can also be used for coating removal of coated metals, painted ABS, etc.

UV laser marking belongs to cold light marking, directly affecting the molecular structure of materials during processing without heating them. This can avoid material ignition during processing and prevent material damage from heat. Additionally, no dust or smoke is generated during UV marking. Therefore, UV laser marking machines are suitable for marking most materials except for a few highly reflective metals, including metals, wood, plastics, etc., and are particularly suitable for materials sensitive to heat such as glass and thermoplastic plastics. They are also suitable for ultra-fine marking, such as marking food and medical packaging materials and micro-hole processing of silicon wafers.

Diode blue laser can process wood, leather, paper, cardboard, opaque acrylic, stone, coated glass, coated ceramics, stainless steel, titanium, iron, and aluminum oxide. However, the processing effects of blue laser vary.

Processing Effects

In material processing, lasers of different wavelengths have different effects on plastics. UV lasers can provide high processing accuracy, suitable for fine processing at the micron or even nanometer level. In some plastics, such as white beverage bottles, the marking effect is clear and vivid, comparable to printing, without causing any pollution or damage.

When engraving plastic products with fiber lasers, there is almost no residue, and the effect is very good. In contrast, using blue laser engraving may leave residues at the edges of the pattern, appearing dirty, and the effect is not ideal. Additionally, the engraving effect of blue laser on acrylic materials is not very obvious, while fiber lasers can engrave clear and bright patterns on acrylic.

Regarding metal marking, fiber lasers usually have very clear and precise engraving effects on metal materials, leaving high-quality marks on most metal surfaces. In comparison, when engraving metals with blue laser engraving machines, the engraving depth may not be uniform, the quality of color marking is poor, and it is not stable enough, suitable only for DIY rather than commercial scenarios. Additionally, the thermal effects produced by blue laser engraving machines on metals during processing are significant, which may cause deformation of the metal.

Both Q-switched and MOPA fiber lasers with a wavelength of 1064nm have limited marking colors compared to MOPA: Raycus Laser found that for metals such as brass, 304 stainless steel, carbon steel, mirror stainless steel, galvanized iron sheet, magnesium plate, etc., it can achieve two effects: black and white marking; for titanium plates, stable color marking can be achieved, which has practical value; it can also mark stainless steel and nickel plates in color, but it is not highly recommended.

MOPA laser marking machines can achieve all marking functions of Q-switched laser marking machines; on this basis, the marking colors of MOPA laser marking machines are more splendid, capable of black marking on aluminum oxide and stable color marking on stainless steel, etc. Additionally, the marking effect of MOPA laser marking machines is finer, with smoother marking and fewer bottom patterns.

Overall Machine

Lifespan

The lifespan of fiber lasers is relatively long, usually exceeding 20,000 to 30,000 hours. Some suppliers of Q-switched fiber lasers claim that their lasers can last up to 100,000 hours. The lifespan of UV lasers can exceed 20,000 hours. The actual lifespan of lasers is influenced by operating conditions, environmental factors, and maintenance.

The lifespan of diode lasers is about 10,000 hours. However, some diode lasers may not reach their expected lifespan. This is because diode lasers generally have lower power, requiring long-term operation at high power or even 100% power to achieve satisfactory results. Prolonged operation at high power can accelerate the aging of laser components, reducing the laser’s lifespan. Reports suggest that after continuous operation at 100% power for several tens of hours, the output power of diode lasers may decrease by 30-40% and cannot be restored. This may be due to the significant influence of temperature on the properties of diodes. High-power operation can cause intense heating of the laser, leading to temperature rise, which can alter the emission spectrum and threshold current of the diode.

Additionally, long-term high-power operation can increase the risk of failures, affect stability, and damage optical components.

Cooling Method

Laser machines generate significant heat during prolonged operation, leading to issues such as unstable laser output and decreased beam quality. Therefore, laser equipment is typically equipped with cooling systems to ensure stable processing over extended periods. Laser marking machines generally use air-cooled heat dissipation.

The advantage of air-cooled heat dissipation lies in its simplicity of installation and maintenance, and convenient integration. However, its heat dissipation may not be as efficient as water cooling, primarily suitable for small and medium-sized laser equipment. The operation of cooling fans may generate some noise, which could be a concern if you require a very quiet working environment.

To reduce the noise generated by fan cooling, Raycus Laser has designed a fan speed control board specifically for air cooling, which can intelligently adjust the operation of the cooling fan at four speeds: 1 to 4. When the machine is idle, it operates at the lowest speed (1); during processing, at power levels between 0-24%, it operates at speed 1; at power levels between 25-44%, it operates at speed 2; at power levels between 45-64%, it operates at speed 3; and at power levels between 65-100%, it operates at speed 4. Through intelligent adjustment, noise interference can be greatly reduced.

Volume and Weight

The Aurora series Q-switched laser machine from Raycus weighs 71kg, while the MOPA laser machine weighs 76kg, and the UV laser weighs 92.5kg.

Diode lasers have a simple structure, high efficiency, and compact size, making them lightweight. They are commonly used in handheld machines and other small-scale applications in the non-metal laser marking field.

Application Scenarios

When choosing a laser, it’s essential to consider specific application requirements and environmental conditions to determine the most suitable type. Each type of laser has its unique application scenarios and performance characteristics. For customers who want to understand the differences between the three types of lasers and how to choose, focus on the specific processing needs, budget constraints, and equipment usage environment to select the most suitable type of laser.

Fiber Lasers

Fiber laser marking machines have advantages such as long lifespan and low maintenance costs, making them more suitable for commercial and industrial scenarios. Q-switched laser marking machines have basic marking functions, capable of marking metals such as ABS and aluminum, as well as some non-metals, easily creating crafts and marking logos. Q-switched laser marking machines can achieve stable color marking on titanium plates, which has practical value; they can also mark stainless steel and nickel plates in color, but the effect is unstable and not suitable for commercial use.

MOPA laser marking machines can achieve all marking functions of Q-switched laser marking machines. On this basis, MOPA laser marking machines have more splendid marking colors, capable of achieving black marking on aluminum oxide and stable color marking on stainless steel, making them ideal for crafting. Additionally, the marking effect of MOPA laser marking machines is finer, with smoother marking and fewer bottom patterns, suitable for precision processing.

UV Lasers

UV laser marking machines are more suitable for industrial applications: when producing products, product information such as production dates, batch numbers, and traceability codes cannot be pre-printed and need to be marked immediately after production. UV laser marking, using cold light marking technology, performs well on plastic outer packaging of food, daily necessities, and electrical appliances; good marking effects can rival inkjet printing, without causing pollution like ink, or the risk of piercing packaging, heating products, or generating toxic and harmful substances. UV laser marking machines also have wide applications in industries such as fine processing of flexible circuit boards and manufacturing of translucent buttons.

Diode Lasers

Diode lasers are suitable for various application fields, but they have some limitations in beam quality, short pulses, and temperature effects. Compared to fiber lasers, diode lasers have poorer performance in terms of application range, power, and processing speed on non-metallic materials. However, they are cost-effective, easy to transport, and have certain appeal to those who only occasionally use lasers, do not require mass production, have limited space, or need to move lasers frequently, such as street vendors.

Although diode laser engraving machines can engrave on metals, their processing effects are not as good as diode laser marking machines; they are only suitable for DIY enthusiasts. To achieve satisfactory results, additional treatments such as painting are usually required for materials.

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