Thermoforming of PET sheet can be divided into three pr […]
Thermoforming of PET sheet can be divided into three processing methods: negative pressure thermoforming, positive pressure thermoforming and positive and negative pressure thermoforming. Now take the 510x570 plastic air pressure forming machine manufactured by Zhejiang Honghua Plastic Co., Ltd. as an example to describe its forming process principle. Its characteristic is to produce positive and negative pressure difference to achieve the purpose of product molding. Its forming is divided into four sections: heating section, forming section, slicing section and demolding section. The heating section is shown in Figure 1(a). The lower mold plate is closed, the upper mold plate air inlet valve is opened, and compressed air with a certain pressure enters the mold cavity to make the PET sheet close to the heating plate for heating; The work section is shown in Figure 1(b). The air inlet valve of a F template is opened, and the air outlet valve of the upper template is opened at the same time, so that the PET sheet is fully attached to the mold cavity; the slicing section is shown in Figure 1(.), bottom A pressurized cylinder of the template moves to make the knife on the mold cut the PET sheet; the demolding section is shown in Figure 1(d), the lower template opens, the upper template intake valve opens, and a certain pressure of compressed air enters The human model cavity makes the product leave the mold cavity. The processing cycle is about 3 to 45, and the entire thermoforming process repeats itself and runs repeatedly, realizing high-speed automated production.
3 PET sheet thermoforming processing technology 3.1 Thermoforming process Thermoforming can be divided into two types according to the heating method: patch type flat plate thermoforming process (positive pressure thermoforming, Figure 2) and tunnel type upper and lower furnace thermoforming process (negative Pressure thermoforming, positive and negative pressure thermoforming, Figure 3).
4 PET sheet thermoforming mold making 4.1 Layout and the layout method of edge-lapped thermoformed products on the cylindrical PET sheet is called layout. The significance of layout is to reduce material consumption, increase labor productivity, and extend the service life of molds. It calculates the utilization rate of the material (w) to measure the rationality of the layout. The larger the value, the less the waste, the higher the utilization rate of the material, and the layout is reasonable. The calculation formula is as follows:, 2 (F0/ F) x; F = month x B; where,-material utilization rate F.-the total area of the thermoformed product,? 2F-the area of the barrel type P art 1'sheet material required for forming, mr spear B ―Width of the cylindrical PET sheet material, mmL――The total length of the cylindrical P staring sheet material, n. Overlap, that is, the remaining material left between thermoformed products and between the product and the PET sheet during layout. Although the edge is formed as waste, it has a great effect on the deep processing of PET sheet. Its function is to maintain a certain rigidity of the PET sheet, which is convenient for the high-speed automatic feeding of the molding equipment and ensures high-efficiency production; and it can compensate for the film movement. The positioning error of the feeding piece at the time. The edge value (a) is generally 6～-20°, and comprehensively considered according to the shape of the thermoformed product and the die-cutting surface, feeding time, and feeding length of the product: After the method is determined, it is possible to determine the slitting width of the tube type P, the strip material, that is, the width B of the strip material described by L, and the calculation formula is: B=D ten knives. Width in the direction of the piece n―the number of overlapping edges a―the value of overlapping edges.