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By optimizing cutting parameters, adjusting subroutines, and adding auxiliary tooling, the quality and production efficiency of the laser cutting machine in thin plate processing is improved.

Laser cutting machines are mainly used in the processing of sheet metal parts and medium and thick plate products. Its advantages are a wide range of applications and high processing accuracy. Metal and non-metals of different materials and thicknesses can be processed, especially in curve processing and There is a big advantage in small-batch processing of special-shaped parts. Due to the high value of fixed assets of laser cutting machines, how to improve the production efficiency and processing quality of laser processing and reduce production costs during use is an important link that needs to be resolved on-site.

The laser cutting parts processed by the company for the professional automobile sheet supporting company are materials for car doors. The parts are first cut with a laser and then laser welded with high-strength sheets of different thicknesses, and then punched and formed to achieve It can not only reduce the weight of the components, improve the utilization rate of materials, but also meet the requirements of the local strength of the components.

Technical Requirements For Laser Cutting Parts

The monthly output of this piece is about 4000 pieces, the delivery time is short, and the product processing accuracy is required to be high, as shown in Figure-1.

• The size of the cutting piece is larger, 0.65mm×1730mm×910mm, the thickness of the sheet is thin, and it is easy to deform;

• After cutting, the straightness a is required to be within 0.05mm, and the burr b is required to be within 0.03mm;
• After cutting, the diagonal c is required to be within 1.0mm, and the flatness d is required to be within 1.0mm;
• Symmetry e after cutting is required to be within 0.5mm.

Due to the high complexity of the laser cutting machine equipment, especially the control and programming parts, the imported parts are used. The Chinese operating instructions are too simple to write, and there is no instruction for calling and modifying the corresponding subroutines. There are many in the initial operation of the laser cutting machine. Aspects need to be explored and familiarized in practice.

Through sample trial cutting, the statistics of product defects are shown in Figure 2. From the statistics of trial cutting, it can be seen that in the poor quality of laser cutting parts, the proportion of burrs is the highest, followed by symmetry, and there is also the problem of low product production efficiency.

Reason Analysis

1. Since the laser cutting machine is a newly purchased equipment, if you want to process high-quality products, you need to be familiar with the adjustment of related parameters, and you must have a deep understanding of machine tool performance and rich operating experience. The main reasons that affect cutting burrs are Improper laser focus setting; Improper adjustment of laser power; Improper adjustment of cutting speed; Improper adjustment of gas pressure.
2. As the length and width of the material is 1730mm×910mm, and the length has an error of 7mm, it is difficult to guarantee the accuracy of the symmetry e after cutting, and it affects the production efficiency of laser processing.
3. In the manual, the cutting gas used for cutting different materials is different. For carbon steel cutting, high-purity oxygen is used, and high-purity nitrogen is used for cutting non-ferrous metals and stainless steel. The material to be cut is SPT83BQ (Japanese steel grade), which is a high-strength carbon steel with a zinc alloy anti-rust layer on the surface. Pure oxygen was used as the cutting gas during trial cutting, resulting in serious nodules on the cutting section.
4. The laser cutting machine is a precision equipment, which has certain requirements for dust and vibration in the on-site environment. Since the laser cutting machine is currently installed in the stamping center plant, which is close to the blanking area and riveting welding operation area, the dust in the blanking area and the fumes during the riveting welding operation are serious, and the vibration of the shearing machine is also higher. Large, it will have a certain impact on the processing accuracy of the laser cutting machine.
5. The dimensional accuracy of processing depends on the movement accuracy of the laser cutting head itself on the one hand, and on the other hand, it is necessary to eliminate the kerf size error by selecting the corresponding compensation amount.

Through the above analysis, the main reasons that affect the quality of laser cutting are Unreasonable adjustment of cutting parameters; Improper selection of material cutting gas; Improper selection of compensation amount corresponding to laser slitting.

The main reasons that affect the cutting production efficiency are the length error of the sheet material and the choice of the best cutting path.

Technical improvement countermeasures and implementation

Countermeasure 1: Determine the best cutting parameters

1. Determine the position parameters of the laser focus point

By debugging and comparing the thin plate cutting quality of the laser focus point at different positions with a material thickness of 0.65mm, it is determined that the quality of the cut section is the best when the focus point is at the center of the plate thickness.

• Determine the matching parameters of laser power and cutting speed

Through repeated debugging many times, the cutting speed is increased from the original 3m/min to 5m/min, and the matching laser power is increased to 1200W, which can ensure that the quality after cutting meets the requirements.

• Determine the gas pressure matching parameters

At a cutting speed of 5m/min, the stability of air pressure has a greater impact on cutting burrs, and the maximum range of air pressure fluctuations should be controlled within (1.0±0.2) MPa to ensure that the quality after cutting meets the requirements.

Countermeasure 2: Make sure that the thin plate cutting material is the cutting gas of the SPT83BQ steel plate

According to the operating instructions, carbon steel cutting gas uses pure oxygen, but SPT83BQ is high-strength carbon steel with a zinc alloy anti-rust layer on the surface. Due to the low melting point of the zinc alloy on the surface of the material, oxidation and nodules are serious. After testing, it was decided to cut with 99.99% pure nitrogen according to the stainless steel cutting mode, and the burrs after cutting can meet the user’s requirements.

Countermeasure 3: Determine the optimal cutting path

The default cutting path of the machine is shown in Figure-3. By manually modifying the program, the cutting path can be optimized, as shown in Figure-4, which saves more than 1 minute of cutting time.

Countermeasure 4: Design and manufacture fast positioning tooling

In order to ensure the requirement of symmetry after thin plate cutting, and to achieve fast and efficient positioning, reduce the time for adjustment due to sheet length errors, improve production efficiency, design and manufacture fast positioning tooling, as shown in Figure-5.

Implementation Effect Check

After the countermeasures are implemented, the quality of laser-cut parts after 2000 pieces of continuous production will be counted, as shown in Table 1.

Judging from the above statistics, the pass rate of thin plate cutting burrs is 99.6%, which is a greater improvement than the trial production. However, in actual operation, it is found that the cutting gas used in production is 5.3m3/bottle of pure nitrogen. When each bottle of nitrogen is almost used up, the operator must adjust the cutting air pressure in time due to the drop in air pressure, otherwise, the cutting burrs will become larger. In addition, due to the high consumption of nitrogen when cutting with nitrogen, a bottle of nitrogen needs to be replaced every time about 15 pieces are cut. The replacement time of each bottle of nitrogen takes about 7 minutes, and it takes 49 minutes to change air every day. The production efficiency is low and the site There are a lot of gas cylinders piled up, which seriously occupies the production site.

Develop Improvement Measures

• To reduce the time taken for changing bottles and improve production efficiency, it was decided to use 120kg/tank of liquid nitrogen, and each tank of liquid nitrogen is equivalent to 20 bottles of 5.3m³/bottle of pure nitrogen.
• To solve the problem of serious icing on the surface of the tank body during the gasification of liquid nitrogen, the gasification volume cannot keep up with the gas consumption during cutting, consider adding a set of vaporizer and using two tanks of liquid nitrogen in parallel to meet Production needs.
• Modify the subroutines in the cutting program and close the nitrogen control valve during the idle stroke to save gas consumption.
• Strengthen the monitoring of the gas cylinder pressure, and stipulate that the cylinder pressure should be checked every 100 pieces cut.

Improved Implementation Effect

After the improvement measures were implemented, the cutting quality of laser-cut parts was relatively stable, the monthly output was stable at 4000-5000 pieces, and the final inspection pass rate reached 99.9%. Since a large tank of liquid nitrogen is used instead of a small bottle of nitrogen, each large tank of liquid nitrogen can cut about 300 pieces, while a small bottle of pure nitrogen can only cut 15 pieces, and each piece can save about USD0.5 of nitrogen. In addition, due to the modification of the numerical control subprogram, the nitrogen consumption when the idle stroke is closed can save USD0.02 per piece. The frequency of gas replacement has also been reduced from 7 times a day to once every 2 days, which can save USD1,500 in manufacturing costs one year.

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