The impact of injection molding process

Abstract: The proportion of plastic materials in life is getting higher and higher.And the requirements for its quality are getting higher and higher. As an important production method, injection molding is more and more urgent for the improvement of technology. There are many influencing factors, but the injection molding process conditions are one of the important influencing factors. The following will introduce the influence of various process parameters on product performance.

Traditional mold design and process parameter settings mainly rely on the designer’s experience and skills. The rationality of mold design only depends on repeated mold trials and mold repairs. The setting of process parameters can only be modified by repeated mold trials. Scientific basis, วงจรการผลิตที่ยาวนาน, high cost, and quality is difficult to guarantee.

The simulation of the กระบวนการขึ้นรูป can find the problems in the design before the mold is manufactured.So that the mold design and process parameter settings are established on the basis of scientific analysis, which can shorten the production cycle and improve the quality of the product.

With the improvement of product quality requirements, forecasting the molding process has become an indispensable link in design. ดังนั้น, it is of great significance to establish a mathematical model of the melt flow and heat transfer in the mold cavity during the injection molding process.And to use numerical simulation methods to simulate the molding process.

Since the process parameters of the molding process directly determine the flow state of the melt in the mold cavity and have the most direct and far-reaching impact on the quality of the product, finding the optimal process conditions for product molding and controlling the molding process is to improve the plastic Effective way of product quality.

This is because, during the molding process, precise molding machine, reasonable mold design and excellent material properties can only be reflected under reasonable molding process settings. ในทางกลับกัน, defects in molding machinery, mold design and material properties can sometimes be passed Appropriate molding process settings to make up for. It can be seen that the injection molding process plays a vital role in the quality of products.

Injection molding process conditions and their influence

1. แรงดันฉีด
The injection pressure refers to the pressure applied by the top of the screw or plunger to the plastic melt during the injection process. Its function is to mix and plasticize the melt, สกรู (or plunger) must provide to overcome the flow resistance of solid particles and melt in the barrel and nozzle. The plastic melt is made to fill the cavity at a certain speed, and the injection pressure plays a role of compaction after the cavity is filled with the melt.

So as to make the plastic part dense, and to supplement the shrinkage of the melt due to cooling, so that the plastic part can maintain the precise shape and obtain the required performance. The injection pressure is mainly determined by the type of plastic, the type of เครื่องฉีดขึ้นรูป, the temperature of the mold, the mold structure, and the wall thickness of the plastic part. The size and structure of the gating system have a great influence on the injection pressure. ถึง

2. Holding pressure
When the melt fills the cavity, NS แรงดันฉีด plays a role in compacting the melt in the mold. ณ ขณะนี้, we call the injection pressure also the holding pressure. ในการผลิตจริง, the holding pressure should be equal to or less than the injection The pressure used at the time. When the pressure at the time of holding pressure is equal to the pressure at the time of injection, the shrinkage rate of the plastic part is often reduced, and the stability of the plastic part and the mechanical properties of the plastic part can be ensured.

อย่างไรก็ตาม, it is often accompanied by the increase of residual stress during demolding, which makes it difficult to demold plastic parts, makes plastic parts prone to deformation, surface scratches, ฯลฯ. It is also easy to cause flashing of plastic parts, which affects the apparent quality. ดังนั้น, when choosing the holding pressure, you need to consider many aspects and choose carefully.

พูด, พูดแบบทั่วไป, พูดทั่วๆไป, the effect of holding pressure on product quality is similar to that of injection pressure. The holding pressure of most plastics is between one of the injection pressure, and the determination of the specific holding pressure mainly considers the characteristics of the plastic part material and the structure of the part, and overcomes the flow resistance of the melt from the barrel to the cavity. Feed the melt into the cavity and compact it.

3. Plasticizing pressure
The plasticizing pressure refers to the pressure that the melt on the top of the screw is subjected to when the screw is retracted. Its impact on injection molding is mainly reflected in the plasticizing effect of the injection machine on the material and its plasticizing ability.

พูด, พูดแบบทั่วไป, พูดทั่วๆไป, when the plasticizing pressure is increased, the retreat speed of the screw decreases, and the pressure on the melt in the barrel increases. ดังนั้น, the shearing effect is strengthened during plasticization, and the plasticizing effect is improved.

อย่างไรก็ตาม, it should be noted that while increasing the back pressure, the excessively high plasticizing pressure reduces the amount of plasticization due to the backflow and leakage of the melt at the edge of the screw groove, which may cause insufficient metering.

ในทางกลับกัน, Excessive shearing heat may cause excessive shearing stress, which may degrade the material, produce bubbles or burns, and affect the quality of plastic parts.

4. ในกรณีการเติมแม่พิมพ์ที่น่าพอใจ
The mold temperature refers to the temperature of the cavity surface during the molding process. The mold temperature affects the filling 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. For low melt viscosity, low mold temperature injection can be used to shorten the cooling time and improve production efficiency. Higher melt viscosity should be used for high mold temperature injection molding. ถึง

พูด, พูดแบบทั่วไป, พูดทั่วๆไป, increasing the และจะแก่ภายใต้สภาวะแสงและออกซิเจน can make the cooling rate of the part uniform and prevent the formation of dents and cracks. The mold temperature control of crystalline plastics directly determines the cooling rate, which further determines the rate of crystallization.

When the mold temperature is high, the cooling rate is small, and the crystallization rate becomes large, which is beneficial to the relaxation process of the molecules, and the molecular orientation effect is small. Too high mold temperature will prolong the molding cycle and make the product brittle.

The mold temperature is low, the cooling rate is large, and the flow of the melt is synchronized with the crystallization. Because the residence time of the melt in the crystallization temperature + interval is shortened, it is not conducive to the growth of crystals, resulting in a low degree of molecular crystallization of the product, which affects its performance.

นอกจากนี้, the mold temperature is too low, the flow resistance of the plastic melt is very large, the flow rate becomes slow, and even solidification in the mold filling prevents the subsequent feeding, causing the part to be shot short, forcing the orientation to be large, and often causing the plastic part to lack of material, dents, Defects such as weld seams.

5. Barrel temperature
In order to ensure the normal flow of the plastic melt without deterioration and decomposition, the temperature of the barrel needs to be selected appropriately. The average molecular mass is large, and the molecular mass distribution is more concentrated.

Plastics and glass reinforced plastics should be selected with higher temperature materials. Cylinder temperature. The barrel temperature is generally arranged according to the principle of high front and low back, but when the plastic contains too much water, the temperature of the rear end can also be appropriately increased. ถึง

6. Nozzle temperature
In order to avoid the melt casting phenomenon at the nozzle, it is usually necessary to make the nozzle temperature slightly lower than the maximum temperature of the barrel. In the case of low-speed air injection in production, the sprayed melt stream does not contain bubbles, and is regarded as smooth. Suitable temperature standards.

7. อุณหภูมิหลอมเหลว
ดิ อุณหภูมิละลาย mainly depends on the temperature of the barrel and the nozzle, which affects the plasticization of the material and the injection molding of the melt. The increase in injection temperature is mainly beneficial to improve the fluidity of the melt, which is related to many characteristics of the product.

Increasing the melt temperature can reduce the mechanical properties such as the internal stress of the plastic part, the impact strength and deflection in the streamline direction.And the tensile strength, and make the impact strength, flow length and surface roughness perpendicular to the streamline direction.

The performance has been improved, and the post-shrinkage of the product can be reduced.From an overall point of view, increasing the melt temperature is beneficial to improve the filling condition and transfer in the mold cavity, reduce the orientation, etc.And is beneficial to the improvement of the overall performance of the product, but too high temperature is not advisable.

When the melt temperature is close to the upper limit of the injection temperature range.On the one hand, it is easy to generate more gas, which can cause bubbles, voids, เนื่องจากความหลากหลายของพันธุ์, and scorching of the plastic parts, and flash due to excessive improvement of fluidity.

Affecting the apparent quality of the product. ในทางกลับกัน, too high temperature will cause degradation of the plastic, reduce the strength of the plastic part, lose elasticity, ฯลฯ, and affect the performance. ถึง

8. Injection time
The injection time is one of the parameters that control the injection rate. The shorter the injection time, the higher the injection rate, and the size of the injection rate has a great influence on the performance of the plastic part. Increasing the injection rate can increase the filling pressure.

Which is conducive to the filling process, and reduces the heat loss in the filling, the cavity temperature is relatively uniform, and the product is uniform and dense. ในเวลาเดียวกัน, it can reduce the shrinkage of the product, reduce the core orientation of the plastic part, and increase the strength of the welded joint.

The increase in the injection rate is beneficial to the overall performance of the product, but an excessively high injection rate will increase the pressure loss, reduce the thickness of the solidified layer, improve the surface orientation of the plastic part, and even cause the melt to produce elastic turbulence, making the plastic part easy to form flash, Surface cracks, ฯลฯ.
Experiments have proved that: too high or too low an injection rate will lead to a decrease in impact strength. ในทางกลับกัน, too low injection rate reduces the strength of the welded joint of the plastic part, increases the total orientation effect, and increases the internal stress, which affects the mechanical properties of the product. ถึง

9. Holding pressure time
The length of holding time and cooling time also have a direct impact on the quality of plastic parts. Shortening the holding time will speed up the pressure reduction of the mold cavity, which may cause backflow, cause shrinkage, depression and other defects in the plastic part, and affect the dimensional stability of the plastic part.

Lengthening the holding time can improve the dimensional stability of the plastic parts to avoid the occurrence of the above-mentioned defects and obtain dense products. ในเวลาเดียวกัน, it will increase the cavity pressure and change the internal stress caused by uneven temperature. But it will increase the difficulty of demolding, and sometimes it is easy to cause scratches on the surface or bending of the plastic parts.

The length of the plasticization time of the material can affect the quality of the plasticization and directly affect the performance of the product. The time is too short to make the plasticization uniform and the temperature is consistent, and it is easy to produce lumps and silver wires. Too long will cause the melt to decompose and burn due to the action of the screw, and it will also bring adverse effects on the product quality.

10. Special process impact
In vibration injection molding, under high vibration pressure, with the increase of vibration frequency, the tensile properties and notched impact strength of the product are obviously improved. นอกจากนี้, the addition of ultrasonic technology can also achieve good results.

in conclusion
The injection molding process conditions have an impact on the appearance and mechanical properties of plastic products. Each process condition parameter affects each other and is not independent. The defects of some products are the result of mutual influence.

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