Polyolefin injection molding parameter optimization method

Abstract

The invention provides a polyolefin injection molding parameter optimization method, and belongs to the technical field of injection molding processes. The problem that the benefits of a production workshop are affected in the prior art is solved. The polyolefin injection molding parameter optimization method comprises the following steps: obtaining the melt glue amount of an injection molding machine table in unit millimeter; according to the theoretical weight of the injection molding product, the glue melting position and the glue melting amount, the pressure transfer and maintaining position is determined; injection molding pressure, injection molding speed, injection molding time and dwell pressure are obtained through a mold flow simulation technology; the pressure maintaining time is preset, and the injection molding machine conducts pressurized injection and pressure maintaining treatment on the mold according to the parameters; calculating cooling time; after the injection molding product is cooled for a time period, demolding and weighing; after the pressure maintaining time is adjusted according to the gradient, injection molding is conducted again to obtain an injection product, and weighing is conducted; the final pressure maintaining time is selected according to the weight difference of the injection molding products, and finally the final cooling time is confirmed; and making the finally determined parameters into a process card, and then carrying out injection molding according to the parameters on the process card. According to the invention, the product forming quality and efficiency are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of injection molding technology and relates to a polyolefin injection molding parameter optimization method. Background Art

[0002] Injection molding, also known as injection molding, is a molding method that combines injection and molding, and is suitable for mass production and complex-shaped products. Injection molding is a method in which completely molten plastic material is stirred by a screw at a certain temperature, injected into a mold cavity with high pressure, and then cooled and solidified to obtain a molded product.

[0003] Polyolefin plastics, i.e. polymers of olefins, are a type of polymer material with the largest output and the most applications. Among them, polyethylene and polypropylene are the most important, but they have large shrinkage, are easy to deform, have poor dimensional stability, and are difficult to produce high-precision products. In order to make the injection molding of polyolefin materials conform to the mold design dimensions as much as possible, in some cases the cycle time will be sacrificed to make the product meet the requirements, thereby greatly increasing the energy consumption of product molding. Sometimes, under incorrect injection molding parameters, some injection molds are repeatedly modified under unstable product dimensions, which seriously affects the efficiency of the production workshop. Summary of the invention

[0004] The purpose of the present invention is to address the above-mentioned problems existing in the prior art and to propose a method for optimizing polyolefin injection molding parameters. The technical problem to be solved is: how to improve product molding quality and efficiency.

[0005] The object of the present invention can be achieved by the following technical scheme: A method for optimizing polyolefin injection molding parameters, comprising the following steps:

[0006] A. Determine the theoretical weight of the injection molding product, select the corresponding injection molding machine according to the theoretical weight of the product; obtain the amount of melt per millimeter of the injection molding machine;

[0007] B. Set the melt position according to the theoretical weight of the injection molded product, and determine the pressure holding position according to the theoretical weight, melt position and melt amount of the injection molded product;

[0008] C. Input the parameters of the injection molding machine and the injection molding material and obtain the injection pressure, injection speed, injection time and holding pressure through mold flow simulation technology;

[0009] D. Preset holding time. The injection molding machine performs pressurized injection and holding treatment on the mold according to the obtained injection pressure, injection speed, injection time, holding pressure, holding time and holding position;

[0010] E. Calculate the cooling time based on the mold temperature, thickness of the injection molded product, average melt temperature, demolding temperature of the injection molded product, and the holding time entered by the user;

[0011] After cooling for a cooling time, the mold is removed to obtain an injection molded product and the injection molded product is weighed;

[0012] F. Based on the preset holding time in step D, increase or decrease the value according to the gradient, and repeat the other steps of step D and step E;

[0013] According to the increasing order of holding time, the weights of each injection molded product are compared in turn, and the final holding time is selected according to the weight difference of the injection molded products, and finally the final cooling time is confirmed;

[0014] The injection pressure, injection speed, injection time, holding pressure, final holding time, final cooling time and holding position determined above are formulated into an injection molding machine process card, and the melt volume and corresponding product weight are recorded on the injection molding machine process card. Then the injection molding machine performs injection molding according to the parameters on the process card.

[0015] When applying this polyolefin injection molding parameter optimization method, first select the corresponding injection molding machine according to the theoretical weight of the pre-injection molded product. Selecting a suitable machine can avoid the problem that the tonnage of the machine is too large and the gram weight is too small, which causes waste of resources and low production efficiency; or the tonnage of the machine is too small and the gram weight is too large, which puts too much burden on the machine and even causes failure. Then test and determine the amount of melt per millimeter of the injection molding machine. The amount of melt measured is relatively unchanged when the equipment is not damaged, the raw materials are not replaced, and the melt process parameters remain unchanged. After knowing the amount of melt, the transfer and holding pressure position can be determined according to the amount of melt and the product weight. The boundary position between injection and holding pressure can be determined by the transfer and holding pressure position, so as to improve the quality of the appearance of the injection molded product. Then, the injection molding machine preliminarily determines the injection pressure, injection speed and injection time of the injection molding product and the holding pressure of the injection molding product through mold flow simulation technology, presets the holding time, and the injection molding product is held for the preset holding time. Then, the injection molding product is cooled according to the calculated cooling time. After cooling, the mold is removed to obtain the injection molding product, and then the injection molding product is weighed. When the injection molding is performed again, the holding time is adjusted. The holding time is increased or decreased according to the gradient based on the original time. Injection molding is performed according to the adjusted process parameters to obtain the injection molding product and weigh it. The weight of the injection molding product generated by injection molding under different holding times is compared, and the time point with the smallest weight difference is selected as the final holding time. The final cooling time is determined according to the final holding time to ensure that the injection molding product is injected with the optimal process parameters, and the production efficiency and production quality of the product are guaranteed. The setting of the process card makes the operation more standardized, and stable process parameters can be used for injection molding, which ensures the consistency and stability of product quality.

[0016] In the above polyolefin injection molding parameter optimization method, in step A, the operation of obtaining the amount of melt per millimeter of the injection molding machine includes:

[0017] Control the injection molding machine to shoot the material at the X1mm melt position;

[0018] The material at the melt position of X1 mm is weighed, and the obtained weight is set as m1, then the melt amount per unit millimeter of the injection molding machine G=m1 / X1. The acquisition of the melt amount G provides a basis for other parameters of product injection molding, and through the acquisition of the melt amount, it is also possible to timely discover equipment damage or changes in the fluidity of raw materials, further improving the production efficiency of the product.

[0019] In the above polyolefin injection molding parameter optimization method, in step B, the theoretical weight of the injection molded product, the melt position and the melt amount are calculated according to the following formula to obtain the pressure holding position:

[0020] X3=X2-P×(m2 / G),

[0021] Among them, X3 is the position of pressure transfer; P is the expansion coefficient, which is set to 80-95%; G is the amount of melt; X2 is the melt position; m2 is the theoretical weight of the product. The position of pressure transfer can be used to determine the boundary between injection and pressure holding, so that the product can be switched at the appropriate position of pressure transfer, ensuring uniform compaction of the material, compensating for cooling shrinkage, making the product size more accurate, and effectively improving the product quality. After the pressure transfer position is clarified, the debugging time is reduced, the scrap rate is reduced, and the production efficiency is effectively improved.

[0022] In the above polyolefin injection molding parameter optimization method, in step C, it also includes setting the holding speed, and the holding speed is set to 50% to 80% of the injection speed. During the injection molding process, the closer to the end of the injection molding, the greater the change in air pressure. When holding the pressure, the injection molding machine has injected 80-95% of the product, so the holding speed is set to be reduced based on the injection speed. It can be reduced with more optimal parameters to facilitate exhaust, making the product fuller and further improving the quality of the injection molded product.

[0023] In the above-mentioned polyolefin injection molding parameter optimization method, in the step D, the holding time is preset by the following formula:

[0024] t1=0.6d 2 +0.3d,

[0025] Among them, t1 is the holding time, and d is the thickness of the injection molded product. The purpose of holding is to maintain a certain pressure when the melt cools / solidifies and shrinks, and continue to inject the melt to fill the shrinkage space, reducing or avoiding the formation of dents. The upper limit of the time is the time for the product channel to solidify. The solidification time is affected by the wall thickness of the injection molded product. Therefore, using this formula to calculate the holding time can be closer to the optimal value. In addition, using this value for gradient addition and subtraction for correction can more quickly determine the final holding time and improve efficiency.

[0026] In the above-mentioned polyolefin injection molding parameter optimization method, in the step E, the operation of calculating the cooling time includes:

[0027] The total cooling time t is initially set by formula 1;

[0028] Formula 1: ;

[0029] Among them, t includes the holding time and cooling time, is the average melt temperature, is the mold temperature, is the demoulding temperature of the injection molded product, is the thermal diffusivity of the plastic;

[0030] Calculate the cooling time t2 by formula 2;

[0031] Formula 2: t2=t-t1×0.8. Cooling time is the process when the product starts to shrink and solidify. The cooling water channel of the mold is running throughout the injection molding process. In the actual pressure holding process, the new heat brought into the product is very small, and a large part of the time has been spent on cooling. Therefore, the sum of the pressure holding time and the cooling time is taken as the total cooling time. When the pressure holding time is increased, the cooling time can be relatively reduced to maintain the cycle unchanged and the production cost unchanged. In this way, while improving product quality, the workshop production cycle is effectively reduced.

[0032] In the above-mentioned polyolefin injection molding parameter optimization method, in the step E, it also includes:

[0033] The obtained injection molding products are quality inspected, and the injection pressure, injection speed, injection time and holding pressure are corrected according to the quality inspection results. In the next injection molding, the injection pressure, injection speed, injection time and holding pressure are used for injection molding. The injection pressure, injection speed, injection time and holding pressure are corrected according to the quality inspection results. For example, if the product size is incomplete, then the injection pressure can be increased; if the product has burrs or flash, the injection pressure and injection speed can be reduced; if the product surface has defects and the structural strength is insufficient, the injection speed can be increased; if the product is burnt, the injection speed can be reduced or the transfer holding position can be appropriately increased; if the product is short of material or the filling is not timely, the injection time or injection speed can be increased; if the product changes color or the performance deteriorates, the injection time can be reduced, etc. Through this correction and adjustment, each parameter is adjusted to the optimal parameter value, providing quality and efficiency guarantee for subsequent product injection molding.

[0034] In the above polyolefin injection molding parameter optimization method, in step F, the operation of selecting the final holding time according to the weight difference of the injection molded product is:

[0035] The weight of the injection molded product generated by injection molding under adjacent holding times is subtracted to obtain the difference. When the difference is judged to be within the preset range, one of the adjacent holding times is set as the final holding time. The weight reflects the fullness of the product, so the influence of the holding time on the fullness of the product can be accurately reflected by weighing, so as to correct the final holding time of the product, improve the accuracy of the holding time parameter, and thus improve the quality of the injection molded product.

[0036] In the above polyolefin injection molding parameter optimization method, in the step F, it also includes the step of correcting the injection molding machine process card:

[0037] During the injection molding process, if any of the following parameters change: injection pressure, injection speed, injection time, holding pressure, final holding time, final cooling time, holding position and melt volume, modify the corresponding parameters on the process card and record the modification process. The modification of the process card ensures that the injection molding products are molded with the optimal parameters, thus improving the quality and production efficiency of the injection molding products.

[0038] In the above polyolefin injection molding parameter optimization method, in step F, the process card also records the temperature of the injection molding machine, mold temperature, thickness of the injection molded product, average melt temperature, and demolding temperature of the injection molded product. By recording the temperature of the injection molding machine, mold temperature, thickness of the injection molded product, average melt temperature, and demolding temperature of the injection molded product, the injection molding process can be more accurately controlled.

[0039] Compared with the prior art, the polyolefin injection molding parameter optimization method has the following advantages:

[0040] 1. The present invention standardizes and practices the injection molding process of polyolefin products, and the product quality stability is stronger.

[0041] 2. The present invention clearly distinguishes the functions of the pressing time and the cooling time, thereby significantly shortening the product cycle time while ensuring product quality.

[0042] 3. After parameter optimization, the present invention performs injection molding according to stable process parameters and through detailed process records, which reduces the repetitiveness of mold repair and effectively improves the production efficiency of the cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a control flow chart of the present invention. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical scheme and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] like Figure 1 As shown, when the polyolefin injection molding parameter optimization method is applied, the theoretical weight of the injection molded product is first determined, and the corresponding injection molding machine is selected according to the theoretical weight of the product to avoid the problem that the selected injection molding machine has too large a tonnage and too small a gram weight, resulting in waste of resources and low production efficiency, or too small a tonnage and too large a gram weight, resulting in excessive burden and even leading to malfunctions.

[0046] Then, the amount of melt glue per millimeter of the injection molding machine is obtained; the operation includes: controlling the injection molding machine to empty-shoot the material at the melt glue position of X1 mm; weighing the material at the melt glue position of X1 mm, and setting the obtained weight as m1, then the amount of melt glue per millimeter of the injection molding machine G=m1 / X1. If the equipment is not damaged, the raw materials are not replaced, and the melt glue process parameters remain unchanged, the amount of melt glue is relatively unchanged. This parameter can be used to check the damage of the equipment or the change in the fluidity of the raw materials.

[0047] Then, the melt position is set according to the theoretical weight of the injection molded product, and the pressure holding position is determined according to the theoretical weight of the injection molded product, the melt position and the melt amount. The pressure holding position is calculated according to the following formula:

[0048] X3=X2-P×(m2 / G),

[0049] Among them, X3 is the position for switching to pressure holding; P is the expansion coefficient, which is set to 80-95%; G is the amount of melt; X2 is the melt position, which can be set by human experience or by calculating m2 / G; m2 is the theoretical weight of the product.

[0050] Then, the injection molding machine parameters and injection material parameters are input into the mold flow simulation software, and the injection pressure, injection speed, injection time and holding pressure are obtained through mold flow simulation technology; and the holding pressure speed is set to 50%~80% of the injection speed.

[0051] Then use t1=0.6d 2 +0.3d formula is used to preset the holding time, where t1 is the holding time and d is the thickness of the injection molded product. After the holding time is preset, the injection molding machine performs pressurized injection and holding treatment on the mold according to the obtained injection pressure, injection speed, injection time, holding pressure, holding time and transfer holding position;

[0052] The cooling time is calculated based on the detected mold temperature, injection product thickness, average melt temperature, injection product demolding temperature, and the holding time entered by the user. The operation includes:

[0053] The total cooling time t is initially set by formula 1;

[0054] Formula 1: ;

[0055] Among them, t includes the holding time and cooling time, is the average melt temperature, is the mold temperature, is the demoulding temperature of the injection molded product, is the thermal diffusivity of the plastic;

[0056] Calculate the cooling time t2 by formula 2;

[0057] Formula 2: t2=t-t1×0.8;

[0058] After cooling for a cooling time t2, the mold is removed to obtain an injection molded product and the injection molded product is weighed;

[0059] After the above injection molding operation, based on the preset holding time, a new holding time is obtained by increasing or decreasing the value according to the gradient, and the injection molding machine performs pressurized injection and holding treatment on the mold according to the obtained injection pressure, injection speed, injection time, holding pressure, new holding time and transfer holding position; then a new cooling time is calculated according to Formula 1 and Formula 2, and the mold is demolded after cooling according to the new cooling time to obtain another injection molded product and weigh the injection molded product. After repeating the above operation, multiple injection molded products are obtained.

[0060] In the process of adjusting the holding time, the quality of the obtained injection molded products is also inspected, and the injection pressure, injection speed, injection time and holding pressure are corrected according to the quality inspection results. For example, if it is detected that the product size is incomplete, a new injection pressure is obtained by adding a certain value to the original injection pressure; if the product has burrs or flash, the injection pressure and injection speed can be reduced; if the product has defects on the surface or insufficient structural strength, the injection speed is increased; if the product is burnt, the injection speed is reduced or the holding position is appropriately increased; if the product is short of material or filling is not timely, the injection time or injection speed is increased; if the product changes color or performance deteriorates, the injection time is reduced. After the corresponding parameters are corrected according to the inspection results, the next injection is performed according to the corrected injection pressure, injection speed, injection time and holding pressure until the optimal parameters are adjusted.

[0061] Then, according to the increasing order of the holding time, the weights of the injection molded products are compared in turn, and the final holding time is selected according to the weight difference of the injection molded products. Specifically, the weights of the injection molded products generated by injection molding at adjacent holding times are subtracted to obtain the difference. When it is judged that the difference is within the preset range, such as 1-3g, one of the adjacent holding times is set as the final holding time. Finally, the final cooling time is determined according to Formula 2.

[0062] Afterwards, the finalized injection pressure, injection speed, injection time, holding pressure, final holding time, final cooling time and transfer holding position are formulated into an injection molding machine process card, and the melt volume, corresponding injection molding product weight, injection molding machine temperature, mold temperature, injection molding product thickness, average melt temperature and injection molding product demolding temperature are recorded on the injection molding machine process card. Afterwards, the injection molding machine performs injection molding according to the parameters on the process card to ensure that the injection molding product is injected with the optimal process parameters to ensure the production efficiency and production quality of the product.

[0063] During the injection molding process, if any of the parameters such as injection pressure, injection speed, injection time, holding pressure, final holding time, final cooling time, transfer holding position and melt volume changes, modify the corresponding parameters on the process card and record the modification process. You can also set the range of each parameter, such as setting the range of variation to 0 to 5, or set other values ​​according to the parameters. When the value changes of each parameter are within the range of variation, do not modify the corresponding parameters on the process card. Otherwise, modify the corresponding parameters on the process card and record the modification process. The setting of the process card makes the operation more standardized, and stable process parameters can be used for injection molding, ensuring the consistency and stability of product quality.

[0064] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A method for optimizing polyolefin injection molding parameters, characterized in that: The polyolefin injection molding parameter optimization method comprises the following steps: A. Determine the theoretical weight of the injection molding product, select the corresponding injection molding machine according to the theoretical weight of the product; obtain the amount of melt per millimeter of the injection molding machine; B. Set the melt position according to the theoretical weight of the injection molded product, and determine the pressure holding position according to the theoretical weight, melt position and melt amount of the injection molded product; C. Input the parameters of the injection molding machine and the injection molding material and obtain the injection pressure, injection speed, injection time and holding pressure through mold flow simulation technology; D. Preset holding time. The injection molding machine performs pressurized injection and holding treatment on the mold according to the obtained injection pressure, injection speed, injection time, holding pressure, holding time and holding position; E. Calculate the cooling time based on the mold temperature, thickness of the injection molded product, average melt temperature, demolding temperature of the injection molded product, and the holding time entered by the user; After cooling for a cooling time, the mold is removed to obtain an injection molded product and the injection molded product is weighed; F. Based on the preset holding time in step D, increase or decrease the value according to the gradient, and repeat the other steps of step D and step E; According to the increasing order of holding time, the weights of each injection molded product are compared in turn, and the final holding time is selected according to the weight difference of the injection molded products, and finally the final cooling time is confirmed; The injection pressure, injection speed, injection time, holding pressure, final holding time, final cooling time and holding position determined above are formulated into an injection molding machine process card, and the melt volume and corresponding product weight are recorded on the injection molding machine process card. Then the injection molding machine performs injection molding according to the parameters on the process card.

2. The polyolefin injection molding parameter optimization method according to claim 1, characterized in that: In step A, the operation of obtaining the amount of melt per millimeter of the injection molding machine includes: Control the injection molding machine to shoot the material at the X1mm melt position; The material at the melt position of X1 mm is weighed, and the obtained weight is set as m1. The amount of melt per unit millimeter of the injection molding machine is G=m1 / X1.

3. The polyolefin injection molding parameter optimization method according to claim 2, characterized in that: In step B, the theoretical weight of the injection molded product, the melt position and the melt amount are calculated according to the following formula to obtain the pressure holding position: X3=X2-P×(m2 / G), Among them, X3 is the position for switching to pressure holding; P is the expansion coefficient, which is set to 80-95%; G is the amount of melt; X2 is the melt position; m2 is the theoretical weight of the product.

4. The polyolefin injection molding parameter optimization method according to claim 1 or 2, characterized in that: In the step C, the pressure holding speed is also set, and the pressure holding speed is set to 50% to 80% of the injection speed.

5. The polyolefin injection molding parameter optimization method according to claim 1 or 2, characterized in that: In step D, the holding time is preset by the following formula: t1=0.6d 2 +0.3d, Among them, t1 is the holding time, and d is the thickness of the injection molded product.

6. The polyolefin injection molding parameter optimization method according to claim 5, characterized in that: In step E, the operation of calculating the cooling time includes: The total cooling time t is initially set by formula 1; Formula 1: ; Among them, t includes the holding time and cooling time, is the average melt temperature, is the mold temperature, is the demoulding temperature of the injection molded product, is the thermal diffusivity of the plastic; Calculate the cooling time t2 by formula 2; Formula 2: t2=t-t1×0.

8.

7. The polyolefin injection molding parameter optimization method according to claim 1 or 2, characterized in that: In the step E, it also includes: The obtained injection molded products are quality inspected, and the injection pressure, injection speed, injection time and holding pressure are corrected according to the quality inspection results. In the next injection molding, the injection molding is performed according to the corrected injection pressure, injection speed, injection time and holding pressure.

8. The polyolefin injection molding parameter optimization method according to claim 1 or 2, characterized in that: In step F, the operation of selecting the final holding time according to the weight difference of the injection molded products is: The weights of the injection molded products generated by injection molding at adjacent holding times are subtracted to obtain a difference. When it is determined that the difference is within a preset range, one of the adjacent holding times is set as the final holding time.

9. The polyolefin injection molding parameter optimization method according to claim 1 or 2, characterized in that: In the step F, the step of correcting the process card of the injection molding machine is also included: During the injection molding process, if any of the following parameters change: injection pressure, injection speed, injection time, holding pressure, final holding time, final cooling time, holding position and melt volume, modify the corresponding parameters on the process card and record the modification process.

10. The polyolefin injection molding parameter optimization method according to claim 1 or 2, characterized in that: In the step F, the process card also records the temperature of the injection molding machine, the mold temperature, the thickness of the injection molded product, the average melt temperature and the demolding temperature of the injection molded product.

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