Analysis on the adjustment method of the hottest i

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The further development of injection molding equipment and the continuous improvement of product quality requirements have put forward higher requirements for injection molding process. Correct selection of injection equipment, reasonable setting of molding process and optimization of process conditions are the key to improve the quality of products. The tensile strength, specified non proportional extension strength, elastic modulus, elongation and other mechanical properties of steel strands can be measured

correct selection of injection molding machine

the performance of injection molding machine directly affects the quality of injection molding products. The prices of injection molding machines with different specifications and performance requirements will also vary a lot

selection of injection molding machine specification

when selecting the specification of injection molding machine, we should first consider the condition of production mold, because the same injection molding machine often needs to meet the production of multiple molds of different sizes. We should determine the specification of injection molding machine according to the weight of parts, mold size, etc., that is, the maximum mold locking force and maximum injection volume of injection molding machine, and then select the appropriate model according to the specification and model provided by the injection molding machine manufacturer. Most manufacturers provide customized services, which provides great convenience for the purchase of injection molding machines; Secondly, it is necessary to consider whether some special configurations are needed, such as selecting special screws for the production of PA, PC and other materials, and providing corresponding devices when forming molds with core pulling or thread stripping; Thirdly, it is necessary to determine whether some injection molding machines with special functions need to be selected according to factors such as mold structure and product quality. For example, when molding thin-walled and long flowing products (generally l/d ≤ 300), high injection speed injection molding machines need to be selected, and precision closed-loop control injection molding machines need to be selected for precision electronic accessories

mode locking force setting

theoretically, the mode locking force can be calculated according to the following formula? S

FCM =k P average a product 10

where? SFCM mode locking force, (KN) k safety factor, generally taken as 2 P average cavity average pressure (MPA) a the maximum projected area of the product on the mold parting surface (cm2)

in actual production, the adjustment of the clamping force should also consider the influence of the mold's thermal expansion in production, and generally 0 2mm margin; The setting principle of the clamping force is that the low clamping force is appropriate on the premise of ensuring the product quality

injection molding process parameter setting

barrel temperature, mold temperature

set the screw barrel temperature according to the performance of different plastic materials. The barrel setting temperature is generally 10 ℃ -30 ℃ higher than the plastic melting point. It must be noted that materials provided by different manufacturers have different melting points and allowable residence time in the barrel due to different synthesis methods or types of additives. Table 1 on the following page compares the melting point and allowable residence time at various temperatures of Solutia PA66 (brand 21spc) and Rhodia PA66 (brand 25ae1)

the mold temperature is generally cooled by circulating water when setting, but when producing products with precise size or high surface quality requirements, a mold temperature machine that can be accurately controlled should be used according to the process requirements

Table 1 Comparison of melting point and allowable residence time of PA66 of different brands

injection pressure holding time, cooling time

injection time, pressure holding time and cooling time must be set according to product thickness, mold temperature, material properties, etc. The injection time is generally set to be slightly longer than the time for the screw to complete the injection stroke movement. A long injection time will not only produce negative effects such as mechanical wear and increased energy consumption, but also prolong the molding cycle. The pressure holding time is set according to the thickness of the product, and the pressure holding time can not be used for thin-walled products during molding; When setting the pressure holding time, as long as there is no obvious depression on the product surface, it can also be determined by weighing method. The best pressure holding time can be determined by gradually extending the pressure holding time until the product quality does not change. Cold plastic packaging waste has aroused widespread concern in the society, but the time also needs to be determined according to the product thickness, mold temperature and material properties. Generally, the cooling time of amorphous polymers is longer than that of crystalline polymers

injection pressure and speed

the setting of injection pressure should follow the principle that it should be low rather than high. As long as it can provide enough power to achieve the required injection speed and enable the melt to fill the mold cavity smoothly, too high pressure is easy to cause internal stress in the product; However, when molding products with high dimensional accuracy, in order to prevent excessive shrinkage of products, high pressure injection can be used to reduce the shrinkage of products after demoulding

the injection speed will affect the appearance quality of the product. Its setting should be based on the geometric structure of the mold and the exhaust condition. Generally, on the premise of ensuring a good appearance, the injection speed should be increased as much as possible to reduce the filling time. In injection molding, when the melt flows in the mold, the mold wall will form a solidified layer, thus reducing the thickness of the flowable channel. Generally, according to the mold structure and injection speed, the mold wall will have a solidified layer of about 0.2mm. Therefore, faster injection speed is usually used in molding

injection stroke, multi-stage injection parameters

in molding, the injection stroke must be determined first. Theoretically, the injection stroke can be calculated according to the following formula? S

s1=4 (cvp+va)/ds2

where? S1 injection stroke VP product volume resin density c cavity number VA gate volume DS screw diameter

in actual production, if the total weight of product + gate is known, the injection stroke can be calculated by the following formula? S

s1= (m/mmax) smax+ (5~10) mm

where? S1 --- injection stroke, mm m total weight of product + gate, G mmax maximum injection volume of injection molding machine, G Smax maximum injection stroke of injection molding machine, mm

due to the different geometry of sprue system and mold parts, in order to meet the product quality requirements, there are different requirements for the flow state of filling melt (mainly refers to the pressure and speed during flow) at different parts. In an injection process, when the screw pushes the melt towards the mold, it is required to achieve different pressure and speed at different positions, which is called multi-stage injection molding. Generally, when molding plastic parts, it is more scientific to set at least three or more sections for injection, that is, the first section is at the mainstream, the second section is from the shunt to the gate, the third section is about 90% of the product filled cavity, and the remaining part is the fourth section. The switching position point of each section can be determined by calculating the weight method; In actual production, the multi-stage injection process parameters should be scientifically analyzed and reasonably set according to the product quality requirements, runner structure, mold exhaust conditions, etc. Generally, the adjustment and observation method can be used to set the pressure/speed required to find the switching position point during injection to 0, observe the melt direction position and product defect status, and gradually adjust until a reasonable position point is found. However, in the process of debugging and observation, we must pay attention to the demoulding condition of the underinjected products to avoid sticking the mold due to underinjection at some concave parts of the mold

other process parameters

in injection molding, in addition to the setting of several main parameters such as molding temperature, pressure, speed, time, multi-stage injection switching position, there are many other process parameters, such as back pressure, screw speed, screw reverse cable anti flow and other action parameter settings, which cannot be ignored

example of process parameter setting

take the production of nylon ribbon products as an example, what are the product quality requirements? S the product meets the specified tension standard; There are no silver wires, bubbles, shrink marks and other undesirable phenomena on the surface; After forming, the product has good tightness without looseness. The material used is PA66; The injection molding machine is jsw1000-e Ⅱ -sp, the mold structure is pee hot runner type, and the gate type is point gate

first, determine the setting principle of process parameters according to the product characteristics and mold structure? S (1) due to the long flow length of the product, the l/t (ratio of process to wall thickness) is 511, so high-speed injection molding should be selected; (2) The gate type is point gate, and higher pressure must be used to overcome the resistance during flow; (3) In order to ensure the smooth filling of the product, the melt must have good fluidity and the forming temperature should be appropriately high; (4) When high-pressure high-speed injection reaches the end, it is easy to produce flash, and the molding machine must have low inertia pressure and speed switching; (5) Because the wall thickness of the product is small, pressure maintaining can not be used; See Table 2 for the main molding process parameters

Table 2 molding process parameters of belted products

the proposed injection process parameters must understand the information of equipment performance, mold structure, molding materials and product quality requirements, and set each molding parameter scientifically and reasonably. First, with the improvement of the efficiency of solar cells, the process parameters should be adjusted step by step according to the product molding status. The correct adjustment order is pressure, speed and temperature. When changing parameters each time, the input parameters have been confirmed by the computer before the next parameter change. It should be avoided to change more than two parameters at the same time; Secondly, when the product enters stable production, it is necessary to try to maintain the stability of various parameters, and detailed records should be made. If the change range is too large, the reason should be found in time. In addition, the molding process should be fixed as much as possible every time the mold is put on line, so as to facilitate the quality control of finished products

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