Views: 2 Author: hu Publish Time: 2021-09-29 Origin: dapeng
Allen County Fabrica-tion, located in Lima, Ohio, is a manufacturer engaged in the processing and manufacturing industry. It uses TRUMPF's L3050 5kW CO2 laser to process various materials. In particular, the company needs to process carbon steel up to 1 inch thick, while the stainless steel that needs to be processed is up to 3/4 inch thick, and the aluminum plate is up to 1/2 inch thick.
Regarding the gas supply device, Jeff Thompson, the company's laser technician, specifically consulted with Bob Montgomery, the regional director of CONCOA. Allen County Fabrication hopes to build a gas supply facility to deliver gas to the laser. The laser gas will be stored in a high-pressure cylinder. The usual practice is to let the auxiliary gas from a hydraulic cylinder with a pressure of 500 PSI (pounds per square inch).
However, as the business develops, it is more ideal to store the gas in a large-capacity cylinder, so that there is no need to replace the gas regulator and the multi-pipe device. In addition, when cutting stainless steel or aluminum plates with a thickness of 3/8 to 1/2 inch or thicker, the use of a 2.3 mm nozzle often causes the gas to stop delivering. Therefore, Allen County Fabrication hopes that the new equipment can avoid this type of system shutdown problem. In these applications, the auxiliary gas nitrogen has high fluidity, which caused the company to experience a pressure drop on the production line, which would trigger the laser's protection circuit and cause the laser to be turned off. When the company cuts these materials, it shuts down three times a day on average, and the required repair time is about 15 minutes each time.
Laser gas or cavity gas is easy to transport. CO2, nitrogen, and helium are supplied by a high-pressure cylinder with a pressure of 2200 PSIG (pounds per square inch, gauge pressure). This gas supply method is both cost-effective and convenient because the gas consumption rate of the resonant cavity is very low. For each gas, the pressure when flowing into the laser cavity is 80 PSIG, and the flow rate ranges from 0.005 to 0.70 scfh (standard cubic feet per hour).
TRUMPF's requirements for laser gas purity are: Helium-4.6 grade/99.996% purity; CO2-4.5 grade/99.995% purity; Nitrogen-5 grade/99.999% purity.
In fact, through detailed regulations on the purity level of the gas, it was discovered that there are three main types of pollution that need to be reduced: hydrocarbons, humidity and particulate matter. The hydrocarbon content must be limited to less than one part per million, the humidity must be less than five parts per million, and the particles must be less than 10 microns. The existence of these types of pollution will cause serious loss of beam power. Moreover, they may also leave deposits or corrosion spots on the mirrors of the resonance cavity, which reduces the effectiveness of the mirrors and shortens their service life.
For laser gas, Allen County Fabrication has established a switching system for each gas, with one hydraulic cylinder as the main air supply source and the other hydraulic cylinder as the backup air supply source. Once the hydraulic cylinder as the main air supply source is empty, the hydraulic cylinder as the backup air supply source is switched over to supply air, thus avoiding the situation that the laser is automatically turned off when the main air supply source is exhausted. The terminal control panel has a three-way controller, which can fine-tune the inlet pressure at the entrance of the laser. For the regulating device, the leakage rate of helium is about 1X 10-8 scc/s (standard cubic centimeter per second, after conversion, the leakage rate of helium is about 1 cubic centimeter/3.3 years). Stainless steel pipes and pipeline compression devices are used to maintain the high purity of the gas. The conversion device also integrates a T-shaped filter that can remove any contaminants that enter the pipeline. These contaminants may come from the initial construction phase, or when the hydraulic cylinder is replaced, or any leaks that may appear in the pipeline. When the gas enters the laser, a filter with a precision of 2 microns and a large flow safety valve provide the final protection to avoid particle contamination or overpressure.
Allen County Fabrication has stricter requirements for auxiliary gas. The company uses oxygen as an auxiliary gas when cutting carbon steel. The size of the oxygen nozzle is between 1.0 mm and 2.3 mm, the maximum nozzle pressure can reach 50 PSIG, and the flow rate can reach 250 scfh. Because the pressure drop in the laser and pipeline can reach 100 PSIG, the pressure at the regulator is likely to be set high to ensure that there is sufficient pressure at the nozzle. TRUMPF recommends that the oxygen purity should be at least 99.95% or 3.5, but if the gas purity is higher, the resulting cutting speed will be higher.
Nitrogen can be used for auxiliary cutting of carbon steel, stainless steel, and aluminum materials. The cutting speed of carbon steel obtained when using nitrogen gas is lower than that obtained when using oxygen gas. However, the use of nitrogen will avoid the deposition of oxides on the cut surface. When using nitrogen, the size of the nozzle ranges from 1.0 mm to 2.3 mm, the maximum pressure at the nozzle can reach 265 PSIG, and the flow rate can reach 1800 scfh. TRUMPF recommends that the purity of nitrogen should be at least 99.996% or 4.6. Similarly, if the gas purity is higher, the resulting cutting speed will be higher and the cut will be cleaner. All equipment related to auxiliary gas must also be specially designed to maintain the high purity of the gas.
The higher flow rate of the auxiliary gas makes the hydraulic cylinder or Dewar a more cost-effective source of gas compared to the high-pressure cylinder. Because what is stored is a liquid substance under low temperature conditions, the vaporized gas is stored in the headspace. Common hydraulic cylinders have different types of safety valves, and their air supply pressure is 230, 350 or 500 PSI respectively. Generally, a hydraulic cylinder with a pressure of 500 PSI (also called a laser hydraulic cylinder) is the only suitable model because the laser assist gas requires a high pressure. The substance can be extracted from the hydraulic cylinder in a gaseous or liquid form. However, only gaseous substances can pass through the laser and laser adjustment device. If liquefied gas is used, the liquefied gas must be vaporized by an external vaporizer before it can be used.
It should be pointed out that the process of extracting gas from the hydraulic cylinder can be quite complicated. The maximum rate of gas extraction from a single Dewar cylinder is about 350 cubic feet per hour. In continuous use, the extraction rate will continue to decline because the capacity of the hydraulic cylinder begins to decrease. The application of multiple pipe devices in different hydraulic cylinders does not always play a positive role. Because the velocity obtained by the top pressure of different hydraulic cylinders will not be equal, and the air flow in the hydraulic cylinder with strong pressure may block the air flow obtained from the hydraulic cylinder with low pressure. When using a multi-tube device, each additional hydraulic cylinder only increases 20% of the original Dewar flow rate (that is, 70 cubic feet per hour). In order to increase the air flow of the hydraulic cylinder multi-tube device, a multi-tube valve must be installed. The multi-pipe valve can make the air pressure at the top of each hydraulic cylinder more even, so that the extraction process of the gas in different hydraulic cylinders is also more even. When using a multi-pipe valve, each additional hydraulic cylinder can increase approximately 80% of the original Dewar flow rate (that is, 280 cubic feet per hour).
In the case of oxygen and nitrogen as auxiliary gases, Allen County Fabrication prefers hydraulic cylinders for air supply. In the future, the company hopes that the nitrogen supply method will become a solid tank. Because the oxygen requirements are not very high, the highest is only 50 PSI and 250 scfh, which can be connected to a dome pressurization, balance rod regulator through two hydraulic cylinders using multiple pipes. The balance bar design allows the hourly flow rate to be as high as 10,000 cubic feet per hour, and the pressure drop is very small, about 30-40 PSI. Traditional reverse valve seat regulators are not suitable for this application because their airflow curve has a severe drop. As the flow rate requirements of the regulators increase, the pressure at the outlet they obtain drops more severely. In this way, when the minimum pressure in the laser cannot be maintained, the protection circuit is triggered and the laser is automatically turned off.
The dome pressurization feature of the regulator allows a small portion of the gas to be discharged from the primary regulator and sent to the secondary regulator, which then sends the gas back to the dome of the primary regulator. Use these gases, instead of springs, to press the diaphragm to open the valve seat, allowing downstream gases to pass through. This design allows the pressure at the outlet to vary between 0-100 PSI or between 0-2000 PSI, and even though the pressure at the inlet fluctuates, the flow rate and pressure at the outlet can remain unchanged.
It is not very practical to supply nitrogen by means of a hydraulic cylinder. Because the required maximum flow rate is 1800 scfh and the pressure is 256 PSIG, this will require eight hydraulic cylinders for multi-pipe air supply, and multi-pipe valves must be used to achieve this task. However, if the liquid is extracted from the two liquid tanks, and then sent to a fin-type vaporizer with a flow rate of 5000 scf. The nitrogen from the vaporizer is sent to a dome pressurized, balance rod regulator similar to the oxygen supply equipment.
In order to speed up the process of extracting gas from the liquid tank and maintain the pressure at the top of the two hydraulic cylinders, the company used a Dewar as a pusher. The nitrogen extracted from the hydraulic cylinder is sent by the regulator to the two original hydraulic cylinders at a flow rate of 450 PSIG.
Both oxygen and nitrogen gas supply devices include a T-shaped filter with a precision of 40 microns and a large flow safety valve at the entrance of the laser. Similar to the resonant cavity gas, these devices play a final protective role to prevent particle contamination and overpressure.
For Allen County Fabrication, the launch of the new device not only improved efficiency, but also saved costs. In the three months since they started using the new air supply system, the laser has never been automatically shut down, and after using hydraulic cylinders, the company's revenue has increased by 20% to 25%. In addition to the savings in gas, the company has also reduced the number of replacement liquid tanks, which takes about 30 minutes for each replacement. The cost savings are approximately US$700 to US$1,000 per month.