Each of the three major types of laser crystals (Nd:YAG, CTH:YAG and Nd:YVO4 has its own unique characteristics that are best suited for certain applications.
Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG) is a solid laser material with the best comprehensive performance. It has high gain, a low threshold, high efficiency, low loss, good thermal conductivity and thermal shock resistance. It is suitable for a variety of laser working modes, such as continuous, pulse, Q-switching, mode locking, frequency doubling, etc. These crystals are widely used in industrial, medical, military and scientific research fields.
Characteristics of Nd:YAG '
Chromium Thulium Homium-doped Yttrium Aluminum Garnet (CTH:YAG) or (Cr, Tm, Ho: YAG) is one of the hot areas for solid-state laser research in recent years. These materials produce excellent crystals for 2.1 μm wavelength lasers. These lasers are commonly used in medicine and optical communications. These crystals also show promise for other applications, such as remote sensing, LiDAR, laser chemistry, laser spectroscopy, material processing.
The main advantages of CTH:YAG '
Neodymium-doped yttrium orthovanadate (Nd:YVO4) has a larger stimulated emission cross section and a higher absorption coefficient for pump light compared to Nd:YAG. Nd:YVO4. is a laser crystal with excellent performance, suitable for manufacturing laser diode pumps, especially for low and medium power lasers. These crystals are used in all solid-state lasers with output near infrared, green, blue, and ultraviolet. Nd:YVO4 lasers have been widely used in materials processing, machinery, wafer inspection, medical inspection and other fields. Nd:YVO4 diode-pumped solid-state lasers are rapidly replacing the traditional water-cooled ion lasers and lamp-pumped lasers in the field.
The main advantages of Nd:YVO '
CRYSTECH Inc. is a global supplier of laser crystals, Q-switches, NLO crystals, laser optics, -nm bonded crystals, reflectors, laser handpieces, and other products. The company has become one of the leading manufacturers of KTP crystals and laser components in the world. CRYSTECH has workshops for crystal growth, orienting, dicing, polishing, and coating.
The laser cutting process uses a tightly focused high-energy light/radiation laser beam to create rapid, high-temperature-gradient heating of a single, small-diameter spot. This triggers rapid melting/vaporization of the target material, allowing the spot to travel down through the material thickness rapidly and precisely.
The hot spot is blasted with gas, blowing away the melted/vaporized material. This process exposes the cut bottom to allow renewed melting and localized cooling, enabling the cut to proceed. For lighter and more reactive metals, the gas assist uses nitrogen to minimize oxidation. Alternatively, for steel, oxygen assistance accelerates the cut process by locally oxidizing material to assist in slag clearance and reduce the reattachment of melted/cut material.
Laser cutting machines are built in a variety of formats. The most common type keeps the workpiece stationary while laser optics (mirrors) move in both the X and Y axes. Alternatively, a 'fixed optic' format keeps the laser head stationary and the workpiece moves. A third option is a hybrid of the two previous methods. All methods execute 2D and 2.5D G-code patterns using a computer-controlled programming system to deliver fully automated, complex cutting paths. Figure 1 is an example of a laser cutting process:
Laser cutting advantages include: high precision, no material contamination, high speed, unlimited 2D complexity, a wide variety of materials, and a wide variety of applications and industries.
The narrowness of the energy beam and the precision with which the material and/or the laser optics can be moved ensures extremely high cutting quality. Laser cutting allows the execution of intricate designs that can be cut at high feed rates, even in difficult or fragile material substrates.
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Traditional rotary cutter processing of materials requires coolants to be applied. The coolant can contaminate the cut parts, which must then be de-greased. Grinding processes may also require coolant/lubricant to be applied. The ablation of the grinding wheel, a natural part of the process, leaves carbide granules that are a hazard in many products. Similarly, water cutting leaves garnet residues. Laser cutting involves only energy and gases and poses no risk of material contamination of the resulting parts.
Few production methods can come close in processing speed to laser cutting. The ability to cut a 40 mm steel sheet using a 12 kW oxygen-assisted laser provides speeds some 10x faster than a bandsaw and 50'100 times faster than wire cutting.
Laser cutting allows intricacy through the nature of the G-code movement control method of positioning and the small size of the applied energy hot spot. Features that are only weakly attached to the main body are cut without any application of force, so the process is essentially limited by material properties, rather than process capabilities.
Laser cutting is a flexible technology that can be adapted to cut widely different materials efficiently, including: acrylic and other polymers, stainless steel, mild steel, titanium, hastelloy, and tungsten. This versatility is increasing as technology develops. For example, dual frequency lasers can be applied to cut carbon fiber reinforced composites'one frequency for the fiber, one for the bonding agent.
Laser cutting finds application in many manufacturing industries because of the combination of versatility, high processing speeds, and precision. Sheet materials are key to production across most manufacturing industries. Applications of laser cutting across industries include: airframes, ships, medical implants, electronics, prototyping, and mass production.
Laser cutting disadvantages include: limitations on material thickness, harmful gases and fumes, high energy consumption, and upfront costs.
Most laser cutting machines sit in the <6 kW range. Their cut depth is limited to ~12 mm in metal thickness'and they accomplish that only slowly (~10 mm/s). It requires the largest and most powerful machines to reach the practical limits of cutting. However, similar limits apply to waterjet and wire erosion cutting. All three processes perform these deeper cuts faster than can otherwise be achieved.
While many materials'particularly metals'do not produce harmful gases in the cutting process, many polymers and some metals do. For example, PTFE and various fluoropolymers produce phosgene gas (which is incompatible with human environments) when heated to high temperatures. These materials require controlled atmosphere processing.
Laser cutting machines have a higher energy consumption rate than other cutting tools. A 3-axis CNC machine cutting out 40 mm steel plate blanks will consume around 1/10th of the power of a laser cutting machine extracting the same part. However, if the processing time is 1 minute on the laser cutter and 20 minutes on the CNC, the net power usage is 2:1 in favor of the laser cutter. Each part will have a different profile in this regard, but the differentials are rarely simple to analyze.
The alternatives to laser cutting are wire cutting, plasma cutting, waterjet cutting, and CNC machining.
Plasma cutting is similar to electrical discharge machining (EDM) in that it erodes material by applying an arc to ablate the substrate. However, the arc is conducted from an electrode on a superheated gas plasma stream that directs the arc and blasts out the molten material from the cut. Plasma cutting and laser cutting are similar in that both are capable of cutting metal parts. Additionally, plasma cutting is suited to heavy materials and relatively coarse processing, for example, preparing heavy steel components for architectural and ship projects. It is a much less clean process and generally requires significant post-cut cleanup to make presentable parts, unlike laser cutting.
Waterjet cutting is typically a small machine process for the precise processing of a wide range of materials. The garnet abrasive employed is considerably harder than the majority of processed materials, but the hardest workpieces do pose a challenge for the process. Waterjet cannot match the processing speeds of laser cutting on thicker, hard substrates. In terms of similarities, both waterjet cutting and laser cutting produce high-quality cut parts, are suitable for working with many materials, and both processes have a small kerf (cut) width.
CNC machining is considered one of the more traditional methods of extracting parts from flat material stock. It is similar to laser cutting in that both produce high-precision parts, are fast, reliable, and provide excellent repeatability. Compared to laser cutting, CNC requires more setup and more processing time. CNC also delivers lower throughput/capacity and requires greater manual intervention. However, results can be of similar quality, albeit at a generally higher cost. Rotating cutting tools apply considerable forces to the cut material and can result in more extensive local heating. The main advantages of CNC processing are the ability to accommodate complex 3D designs and to perform partial depth (rather than through) cuts.