Laser marking plastic

Recent studies show that laser marking technologies have become increasingly efficient and effective for different types of plastics. Short-pulse lasers yield impressive results across various marking types, depending heavily on factors such as the type of plastic, the laser wavelength, and any additives included. To enhance visibility and quality in marking, incorporating laser-sensitive additives into certain industrial plastics is advisable, while maintaining the fundamental properties of the plastics.

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A significant factor in the process of marking plastics is the laser wavelength which varies according to the application at hand. Utilizing frequency-doubled (532 nm, green) or tripled (355 nm, UV) solid-state lasers allows for a greater variety of plastics to be effectively marked, often producing superior results compared to traditional systems operating at wavelengths of 1,064 or 1,030 nm.

DENNIS KAMINSKI

In the realm of laser marking, selecting the appropriate laser depends on the material type, the desired marking quality, and the required speed. While solid-state continuous-wave and CO2 lasers find their applications predominantly in materials other than metal, this discussion will narrow its focus to solid-state pulsed lasers. Within the pulsed laser category, options like Nd:YAG, Nd:YVO4 (vanadate), and fiber lasers each present unique advantages and limitations.

Understanding how the material in question absorbs laser light at specific wavelengths is crucial. For instance, ferrous and non-ferrous materials demonstrate optimal absorption at certain wavelengths, whereas precious metals absorb more efficiently at 355 and 532 nm. Interestingly, plastics also show a considerable absorption for higher wavelength outputs (see Fig. 1).

Laser technologies

Introduced over 25 years ago, the Nd:YAG laser has established itself as a cornerstone in the industry. Initially lamp-pumped, this technology has transitioned primarily to diode pumping, yielding robust systems with excellent mean time before failure (MTBF). Some manufacturers anticipate diode longevity exceeding 35,000 hours. One notable advantage of Nd:YAG lasers is their superior beam quality, resulting in smaller spot sizes. This combination of small spot size and short pulses generates high peak power, advantageous for applications demanding deep engraving with clear, precise marks and intricate characters.

The vanadate laser operates at three distinct wavelengths: 532 nm (green), 355 nm (blue), and one additional wavelength. Like Nd:YAG lasers, these are diode-pumped and provide consistent beam quality, particularly beneficial in ablation marking and minimizing heat-affected zones (HAZ). A notable application of the vanadate laser is in automotive day/night marking, where a top coating is effectively removed to backlight buttons at night, exposing a lower surface without incurring damage.

Roughly six years ago, fiber lasers broke onto the marking scene, generating extensive discussion among industry professionals. Although fiber lasers may lack the beam quality prevalent in Nd:YAG or vanadate lasers, they compensate with longer pulse widths and larger spot sizes to apply more heat and facilitate the carbon draw to the surface effectively. It is worth noting that only a handful of manufacturers offer fiber-laser sources for integration into marking systems.

In terms of operational costs and consumability, Nd:YAG, vanadate, and fiber laser technologies are comparably priced, allowing end-users to select the most suitable laser solution without significant cost considerations. Importantly, the output power of all solid-state lasers declines over time, although calibration can help in preserving consistent marking quality and speed similar to that of the system's initial production day.

Beam properties Laser marking beam quality is typically expressed as an M2 value, a standard provided by laser manufacturers. An M2 value of 1 denotes a Gaussian beam, enabling the smallest possible spot size relative to the wavelength and optics used. The top beam quality in Nd:YAG and vanadate marking systems achieves an M2 of 1.2, whereas fiber-based systems often present an M2 value of 1.7, resulting in a larger spot size and lower power density. Overall, higher beam quality results in sharper contours, enhanced marking speeds (due to increased power density), and deeper engravings.

Pulse repetition rate Concerning peak power and pulse repetition frequency range, YAG and vanadate lasers contrast significantly with fiber lasers. For instance, pulse durations emitted by fiber configurations such as the master oscillator fiber power amplifier (MOFPA) can be tailored, directly influencing the available pulse repetition rates suitable for optimal laser marking processes (see table).

YAG

Vanadate

Ytterbium (fiber)

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10-150

5-30

10-200

<1.2

<1.2

<2

High, 100 kW range

Medium, 80 kW range

Low, 10 kW range

5-30

5-40

10-50

5-80 kHz

20-120 kHz

20 kHz-1 MHz

Applications

The terminology surrounding laser marking encompasses engraving, annealing, ablation, and color alteration of plastics. The lasers detailed previously can be selectively chosen to enhance the laser marking workflow. When engaging in ablation for day/night design components, vanadate lasers excel due to their short pulse capabilities and stable pulse repetition at elevated rates, effectively removing painted surfaces while safeguarding pad-printed plastic bases (see Fig. 2). Additionally, ablation is frequently employed in the marking of anodized aluminum, widely recognized as one of the most forgiving laser marking processes.

Reach out to us to explore your needs regarding a mini fiber laser marking machine. Our knowledgeable sales team is prepared to assist you in identifying the options best suited to your requirements.