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What is the effect of injection molding process on product performance?
- Categories:Industry News
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- Time of issue:2021-12-22 17:24
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(Summary description)Under high vibration pressure, the tensile properties and notch impact strength of the products are improved obviously with the increase of vibration frequency. In addition, the addition of ultrasonic
What is the effect of injection molding process on product performance?
(Summary description)Under high vibration pressure, the tensile properties and notch impact strength of the products are improved obviously with the increase of vibration frequency. In addition, the addition of ultrasonic
- Categories:Industry News
- Author:
- Origin:
- Time of issue:2021-12-22 17:24
- Views:
Information
The proportion of plastic materials in life is getting higher and higher, and the requirements for its quality are getting higher and higher, injection molding as an important means of production, the improvement of technology is becoming more and more urgent, and injection molding products are more influential factors, the following introduction to the impact of various process parameters on product performance:
Injection molding conditions and effects
In the process of molding, precision molding machinery, reasonable mold design and excellent material performance can only be reflected in the reasonable molding process setting on the other hand, molding machinery, mold design and material performance defects can sometimes be made up by the appropriate molding process setting
Injection molding process conditions affect the appearance and mechanical properties of plastic products, each process condition parameters are not independent of each other, some products defects are the result of mutual influence.
01 Injection molding pressure
Injection pressure refers to the pressure exerted by the top of the screw or the plunger on the plastic melt during injection. Its function is that for mixing and plasticizing the melt, the screw (or plunger) must provide resistance to the flow of solid particles and melt in the barrel and nozzle. The plastic melt fills the cavity at a certain speed, and the injection pressure plays a role of compaction after the cavity is filled with melt.
So that the plastic parts compact, and the melt due to cooling and the contraction of the feed, so that the plastic parts to maintain accurate shape, to obtain the required performance. The injection pressure is mainly determined by the type of plastic, the type of injection molding machine, the temperature of the mold, the structure of the mold and the wall thickness of the plastic parts. The size and structure of the pouring system have a great influence on the injection pressure.
02 Holding pressure
When the melt fills the cavity, the injection pressure plays a role of compacting the melt in the mold. At this time, the injection pressure is also called the pressure holding. In actual production, the pressure holding should be equal to or less than the pressure used for injection. When the pressure is equal to the pressure of injection, the shrinkage rate of plastic parts is often reduced, and the stability and mechanical properties of plastic parts can be guaranteed.
However, it is often accompanied by the increase of residual stress during demoulding, resulting in difficult demoulding of plastic parts, making plastic parts prone to deformation, surface scratches, etc., and also easy to make plastic parts flay, affecting the apparent quality. Therefore, it is necessary to take many aspects into consideration when choosing pressure-retaining pressure.
Generally speaking, the effect of holding pressure on product quality is similar to that of injection pressure. Most of the plastic pressure in the injection pressure between one, and the specific pressure determination, mainly considering the characteristics of plastic parts and parts of the structure, and overcome the melt from the barrel to the mold cavity flow resistance, the melt into the cavity and the compaction.
03 Plasticizing pressure
Plasticizing pressure refers to the pressure exerted by the melt at the top of the screw when the screw receded. Its influence on injection molding is mainly reflected in the plasticizing effect and plasticizing ability of materials by injection machine. Generally speaking, with the increase of plasticizing pressure, the screw receding speed decreases and the pressure on the melt in the barrel increases. Therefore, the shearing effect is strengthened and the plasticizing effect is improved.
But it must be meant to increase the back pressure at the same time, too high plasticizing pressure on the one hand because of the melt in the groove edge of the reflux and leakage and reduce the plasticizing amount, may cause insufficient measurement, on the other hand will make the shear heat too high shear stress is too large, may make the material degradation, bubble or burn, affect the quality of plastic parts.
04 Mold Temperature
The mold temperature refers to the temperature of the cavity surface during the molding process. The mold temperature affects the flow behavior of the melt, the cooling rate of the product and the performance of the product after molding. The setting of the mold temperature mainly depends on the viscosity of the melt. Low mold temperature injection can be used to shorten the cooling time and improve the production efficiency. High mold temperature injection molding should be used for the melt with higher viscosity.
Generally speaking, increasing the mold temperature can make the cooling rate of the workpiece uniform, to prevent dents and cracks and other forming defects. The mold temperature control of crystalline plastics directly determines the cooling rate, which further determines the crystallization rate. When the mold temperature is high, the cooling rate is low and the crystallization rate is high, which is conducive to the relaxation process of molecules and the orientation effect is small. Too high mold temperature will prolong the molding cycle and make the product brittle.
Low mold temperature, large cooling rate, melt flow and crystallization synchronous, because the melt in the crystallization temperature + interval residence time is shortened, is not conducive to the growth of crystal, resulting in a low degree of molecular crystallization of the product, affecting its performance. In addition, the mold temperature is too low, the flow resistance of plastic melt is very large, the flow rate is slow, and even in the mold solidification hinders the follow-up feed, making the product short shot, forced orientation is large, often resulting in plastic parts lack of material, depression, fusion joints and other defects.
05 Barrel temperature
In order to ensure the normal flow of plastic melt and avoid its deterioration and decomposition, it is necessary to choose a suitable barrel temperature. The higher barrel temperature should be selected for plastics with large average molecular weight and more concentrated molecular weight distribution, as well as glass reinforced plastics. The barrel temperature is generally arranged in accordance with the principle of high in the front and low in the back, but when there is too much water in the plastic, the temperature at the back can be appropriately raised.
06 Nozzle temperature
In order to avoid the phenomenon of flow delay caused by the melt at the nozzle, it is usually necessary to make the nozzle temperature slightly lower than the highest temperature of the barrel. In the production, it is generally considered that under the condition of low-speed air injection, the eject solution flow does not bubble and smooth is regarded as the appropriate temperature standard.
07 Melt temperature
Melt temperature mainly depends on the temperature of cylinder and nozzle, which affects the plasticization of materials and injection mold filling of melt. The increase of injection temperature is mainly beneficial to improve the fluidity of melt, which is related to many characteristics of the product. With the increase of melt temperature, the mechanical and mechanical properties of plastic parts such as internal stress, impact strength, deflection and tensile strength in streamline direction can be reduced, while the impact strength, flow length and surface roughness perpendicular to streamline direction can be improved, and the post-shrinkage of products can be reduced.
On the whole, increasing the melt temperature is beneficial to improving the mold filling condition and the transfer in the mold cavity, reducing the orientation and so on, which is conducive to improving the comprehensive performance of products, but too high temperature is not desirable. When the melt temperature is close to the upper limit of injection temperature range, on the one hand, easy to produce more gas, produce plastic bubble, empty hole, discoloration, burning, etc., also due to improve liquidity too much flash, affect products quality, on the other hand, high temperature can make the plastic degradation, make the decrease of strength of plastic parts, loss of elasticity, etc., affect the using performance.
08 Injection time
Injection time is one of the parameters controlling the injection rate. The shorter the injection time, the higher the injection rate, the size of the injection rate has a great impact on the performance of plastic parts. Increasing the injection rate can increase the mold filling pressure, which is beneficial to the mold filling process, and reduce the heat loss in the mold filling, the mold cavity temperature is more uniform, and the product is uniform and dense. At the same time, it can reduce the shrinkage of products, reduce the core orientation of plastic parts and increase the strength of fusion joints.
The improvement of injection rate is beneficial to the comprehensive performance of the product, but too high injection rate will increase the pressure loss, reduce the thickness of the curing layer, improve the surface orientation of the plastic parts, and even make the melt elastic turbulence, so that the plastic parts easy to form flaying, surface cracks and so on.
Experiments have proved that too high or too low injection rate will lead to the decline of impact strength. On the other hand, too low injection rate can reduce the strength of fusion joints of plastic parts, increase the overall orientation effect, increase the internal stress and so on, which affect the mechanical properties of products.
09 Holding time
The length of holding time and cooling time also has a direct impact on the quality of plastic parts. Shorten the pressure holding time, will make the cavity pressure reduced to speed up, it is possible to produce backflow, so that the plastic parts have shrinkage, depression and other defects, and affect the stability of the size of the plastic parts.
Lengthening the holding time can improve the stability of the size of plastic parts to avoid the occurrence of the above defects, and get dense products. At the same time, it will increase the pressure of the cavity and change the internal stress caused by uneven temperature. However, it will increase the difficulty of demoulding, and sometimes it is easy to produce a scratch on the surface or the phenomenon of bending the top of the plastic parts.
The plasticizing time of materials can affect the plasticizing quality and directly affect the properties of products. Too short time can not make plasticizing uniform, consistent temperature, easy to produce hard block, silver wire, etc. And too long will make melt due to the role of screw decomposition, burn, etc., but also to bring adverse effects on product quality.
010 Influence of special process
Under high vibration pressure, the tensile properties and notch impact strength of the products are improved obviously with the increase of vibration frequency. In addition, the addition of ultrasonic technology can also play a good effect.
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In 2011, Jiangmen Jieke Hardware & Plastic Co., Ltd. was established. It is located in Chaolian, Jiangmen, Guangdong. It covers an area of 15 acres. It is a large-scale processing enterprise with 11 years of large-scale production of precision
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