Laser rapid prototyping technology for metal parts

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Research on Laser Rapid Prototyping Technology of metal parts of nd:yag laser

1 introduction

laser direct manufacturing technology DLF (direct laser fabrication) is an advanced manufacturing technology developed in the late 1990s. It combines rapid prototyping technology with laser cladding technology. Bian Yaoli can be divided into coaxial powder feeding and selective laser melting (SLM) technology

according to the different application occasions, the lasers used in DLF technology are also different. Bian Yao's types include C 02 lasers, nd:yag lasers and semiconductor lasers. CO2 lasers developed earlier and have been studied more at present. At present, the research on Rapid Prototyping of nd:yag laser is relatively few. In this paper, using rofin 1.1kw nd:yag laser and coaxial powder feeding force, the rapid prototyping technology of metal parts is experimentally studied. The effects of laser power, scanning speed, powder feeding amount and z-axis increment on forming quality and morphology were discussed

2 experimental equipment

laser direct manufacturing system is shown in Figure 1. Its structure can be divided into four parts by function: energy supply module, CNC workbench, powder supply module and command output module. Among them, the energy supply module is composed of a nd:yag laser and its auxiliary facilities (water cooler, optical path, focusing mirror, cooling water path, etc.); The CNC workbench is composed of - sets of CNC control units and a 3-axis machining machine tool; The powder supply module is composed of a powder feeder, a coaxial powder feeding nozzle and a powder recovery device. The command output module is a PC

3 experimental method

the experimental material is self fluxing alloy Ni45 powder. Using different combinations of process parameters, a single pass cladding experiment is carried out on 10mm thick Q235 steel plate. The influence of main process parameters on the appearance of cladding layer was studied. The process parameters of the experiment are shown in Table 1. Before the experiment, Ni45 powder was dried to remove water vapor, and all A3 steel plates were dried in acetone cleaning well to remove grease and stains. After the experiment, the low-carbon steel plate was cut along the direction perpendicular to the cladding path to make metallographic samples, and then the profile shape of the cladding layer was measured and analyzed with a microscope. Finally, the molding experiment is carried out with certain power parameters to verify the best process parameters

4 experimental results and analysis

4.1 effect of laser power on the morphology of cladding layer

commercial grade polyethylene is 1.50 ⑵ 00

Figure 2 shows the morphology of laser cladding layer under different power parameters. The laser scanning speed is 800mm/min, the powder feeding amount is 4.2g/min, and the air feeding amount is 6lmin-1. It can be seen from the figure that the change of laser power not only affects the width and height of the cladding layer, but also has a significant impact on the surface and accuracy of the cladding layer. When the power is greater than 400, the remelting time increases, there is obvious over burning phenomenon, and the morphology is poor. The best laser forming power in the figure is 200W

Fig. 2 laser cladding layer morphology under different power parameters

4.2 influence of laser power and scanning speed on the height and width of single pass cladding

under the condition of constant laser power, powder feeding amount and air feeding amount, the relationship between scanning speed and cladding height and width is shown in Fig. 3 and Fig. 4. When the speed is small (less than 1400mm/min), the laser energy density can melt more metal powder, so the height and width of a single cladding are larger; In a certain speed range (1400/1600mm/min), the metal powder that can be melted by laser per unit time is roughly the same as the amount of powder fed, so the height and width of a single cladding do not change significantly; When the scanning speed continues to increase, the laser energy density decreases and the size of the laser pool decreases, so the height and width of single pass cladding decrease

4.3 effect of powder feeding amount on molding height and width

the relationship between powder feeding amount and molding height and width is shown in Figure 5. When the powder feeding amount is within a certain range and the laser power is large enough, the increase of powder feeding amount will lead to the increase of molten metal powder, thus increasing the size of the molten pool. In the final solidification process, the molding height and width will increase accordingly. However, when the powder feeding amount exceeds the maximum amount of metal powder that can be melted by the laser power, the increased metal powder cannot be melted and formed, and the height and width of the forming will not be increased. On the contrary, it will cause more metal powder to adhere to the surface of the formed parts at high temperature, affecting the forming accuracy and subsequent manufacturing

4.4 relationship between z-axis increment and self molding height

in the laser rapid prototyping experiment studied, due to the open-loop control, that is, free molding. Therefore, the forming height has a great relationship with the z-axis increment. Because the z-axis increment determines the vertical distance between the powder feeding nozzle and the manufacturing workpiece, its size directly affects the laser spot size with the total market value of plastic flexible packaging in the Middle East and Africa of US $4billion in 2013, and affects the laser energy density from the blood. When multi-layer cladding is carried out, the actual cladding height of each layer is less than that of a single pass. If the z-axis increment is equal to the actual height of each cladding layer, a constant distance can be maintained between the powder feeding nozzle and the manufacturing workpiece, which ensures that the spot size remains unchanged from}, that is, the excitation energy density remains unchanged. At this time, the z-axis increment is the maximum value

under the condition that the laser power, scanning speed and powder feeding amount remain unchanged, the single pass cladding parameters are: Power 200W, scanning speed 1100mm/min, powder feeding amount 4.2g/min and air feeding amount 6l/min. The single pass cladding height under this parameter is 0.06mm. Under different z-car increments, scan 100 layers and measure the final molding height. The relationship between multilayer cladding height and z-axis increment is shown in Figure 6. It can be seen from the figure that when the z-axis increment is 0.04mm, the forming height is 4.1. The error between it and the target forming height is to confirm that the iron content in the sample is the smallest. When the z-axis increment exceeds 0.16, the thin-walled shape cannot be formed at all

4.5 molding example

on the basis of previous process experiments, find out the best combination of scanning speed, z-axis increment and powder feeding amount under each power condition, and carry out the molding experiment of parts. The results are shown in Figure 7

5 summary

power, scanning speed, spot diameter, powder feeding amount and z-axis increment are important process parameters that affect the forming quality and accuracy

(1) when the laser power increases and the powder feeding amount increases, the molding height and width increase. When the power is certain and the powder feeding amount reaches a certain degree, the increase of height and width is not obvious

(2) when the scanning speed increases, the forming height and width decrease

(3) in multi-layer cladding, when the z-axis increment is equal to the actual height of each cladding layer, it is the best value. (end)

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