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Five parameters of the injection molding process

Five parameters of the injection molding process

1. Temperature

Injection molding process

(1)Oil temperature: 

For the hydraulic press is due to the continuous operation of the machine hydraulic oil friction generated by heat, it is controlled by cooling water, in the boot to confirm the oil temperature at about 45 degrees Celsius, if the oil temperature is too high or too low will affect the pressure transfer.

(2)Barrel temperature: 

Barrel temperature refers to the heating temperature on the surface of the barrel. The role of barrel temperature is to make the solid granular plastic raw materials into a whole flow is very good, through the operation of the machine can make the colour pink mother accessories fully fused in the semi-liquid state, to fill the mould needs. The barrel is heated in three sections, from the hopper to the nozzle from low to high, so that the plastic is gradually melted and plasticized.

The first section is the solid conveying section near the hopper, the temperature is lower, and the hopper is cooled with cooling water. The second section is the compression section. The material is in a state of compression and gradually melting. The third section is the metering section, and the material is in a full melting state. After the pre-plastic termination, a metering chamber is formed to store the plasticized material to ensure that it is melting.

(3)Nozzle temperature: 

The nozzle can accelerate melt flow, adjust melt temperature and homogenize materials. Nozzle temperature is generally lower than the highest temperature of the barrel; on the one hand, to prevent overflow, on the other hand, is the decomposition of plastic, affecting the quality of products.

Note: barrel temperature and nozzle temperature are related to other moulding process parameters. For example, when the injection pressure is low, the temperature of the cylinder and nozzle should be raised appropriately to ensure the flow of materials. Otherwise, the temperature of the cylinder and nozzle should be reduced. Generally, the process parameters can be adjusted by “air injection” and “intuitive analysis” of the product to determine the best barrel and nozzle temperature.

(4) Mold temperature: 

Mold temperature refers to the surface temperature of the mould cavity in contact with the product, gate and runner. It greatly influences the appearance of products, such as gas lines, clamping lines, size and internal performance. Increasing the mould temperature can improve the fluidity of melt, increase the shrinkage rate of products, release and reduce the internal stress of products. The mould temperature is usually controlled by adjusting the temperature of the mould temperature machine. Mould temperature machine is auxiliary equipment, and it is not a part of the injection moulding machine, has an independent temperature rise system and media circulation device.

(5) The hot runner temperature:

it is divided into insulation and heating types. The characteristics of the hot runner system are to keep the melt of the main channel and the split channel theme from solidification during each injection moulding cycle so that it does not produce the handle and cold glue. And can reduce the consumption of plastic raw materials and energy consumption in moulding, shorten the moulding cycle. Its temperature setting is based on the processing temperature of the materials used. Generally higher than the nozzle temperature, maintaining its molten state does not produce salivation.

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2. speed

Injection mold process

A. The speed setting of opening and closing die, the setting of opening and closing die is generally according to the slow-fast-slow principle, so the setting mainly considers the machine, mould, and cycle. 

B. Top out setting: it can be set according to the product’s structure. If the structure is complex, it is best to slow out some and then use fast demoulding to shorten the cycle. 

C. rate of fire: according to the size of the product, the structure to set, if the structure is complex and thin wall can be fast, if the structure is simple and the wall thickness can be slow, but also according to the performance of the material, from slow to fast set.

3. The pressure

The key is to set the starting position of low-pressure protection, that is, the starting position of low pressure should be the point that is most likely to protect the mould and does not affect the cycle, and the end position should be the contact position of the mould before and after the slow speed of mould closing.

(2) holding pressure

When the high-temperature solution is filled with a mould cavity, it enters the stage of pressure-retaining and feeding, which continues until the gate is frozen. Therefore, the setting of holding pressure will influence the moulding process of solution and product quality.

(3) Sol back pressure

Sol backpressure is an auxiliary pressure to control the solution density in the material tube. Adjusting the back pressure can effectively discharge the raw material gas in the metering section of the material tube, can make the colour of the raw material mixed evenly, but also directly affect the shrinkage of the product, dimensional accuracy, etc.

(4) Clamping pressure

Clamping force refers to the maximum clamping force exerted by the clamping mechanism of the injection moulding machine on the mould, also known as clamping force. In an injection molding machine, the melt enters the mould cavity after passing through the tube, nozzle and gate. Part of the injection pressure is lost in the nozzle and gate, and the rest is the melt pressure in the mould cavity, which is usually called the mould cavity pressure. The setting of clamping pressure must be greater than the cavity pressure when filling the mould to prevent the mould from being split and resulting in a draping front. Too much mould lock will reduce the precision and life of the mould.

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4. Time

Refers to when the screw pushes forward, and the molten material fills the cavity. According to the size and thickness of the product and directly observe the appearance to determine the length of the shooting time. The injection time setting device of the injection moulding machine can only be set once, whether it is a multi-section or one-section injection.

(2) holding time

After filling the mould, the melt body feeding should be continued to maintain the feeding flow stage until the gate is frozen to obtain dense products. The holding time of the injection molding machine is required to set a time for each section.

(3) Cooling time

It refers to the cooling stage from the gate solidification to demoulding, which can make the products just formed in the mould have a certain rigidity and strength, to prevent the top out of deformation when demoulding. The melt body can not enter the mould cavity, the weight of the products can not be changed. Cooling time and fusing (storage) are mostly synchronous, generally long fusing time.

 

5. Position

(1) position of opening and closing die 

The key is to set the starting position of low-pressure protection, that is, the starting position of low pressure should be the point that is most likely to protect the mold and does not affect the cycle, and the end position should be the contact position of the mold before and after the slow speed of mold closing. 

(2) Top out position 

This position can meet the complete demoulding of the product, first set by increasing from small to large. Pay attention to the back position must be set as “0” when installing the mould. Otherwise, it is easy to damage the mould. 

(3) Adhesive position 

According to the size of the product and screw size, calculate the amount of material and then set the corresponding position. 

(4) V-P position

V-P position should be from large to small, namely short-short method (namely Short shot method) to find the V-P position (namely V-P switching point).

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