The process principle and requirements of high gloss injection molding

Table of Contents

High gloss injection molding process has been applied to products with no melt marks, flow lines or any other sign that the material was heated.

This includes things such as flat panel TVs and computer LCD screens among many others! With improvements in living standards people are always looking for new ways of enjoying their lives which means they need high-quality materials too – something you can be sure is delivered by these professionals when it comes time for your product needs.

People’s requirements for the appearance of items are also getting higher and higher. The appearance variety of many electronic products has become an important criterion for consumers to choose goods.

The high-gloss injection molding technology we are going to introduce today can perfectly solve the above problems and produce qualified products.

It is especially important for the 3C mold industry such as flat panel TVs and computer LCDs, and the use of high-gloss injection molding technology can solve this problem well.

What is high-gloss injection molding?

The principle of high gloss injection molding is to heat the mold, close the mold, and then inject it when the temperature reaches the set condition.

During the injection process, the mold continues to maintain a high temperature, so that the rubber can maintain good fluidity in the mold during the injection.

After the injection is completed, the injection mold is cooled down in the pressure-holding and cooling stage, which can greatly shorten the cooling time of the products and thus improve the production efficiency.

Process principle of high gloss injection molding

The mold is heated up before and during the mold closing process, and after the injection mold closing is completed, the temperature reaches the set condition for injection.

During the injection process, the mold continues to maintain a high temperature, so that the liquid silicone rubber can maintain good flowability in the mold during the injection.

When the injection is completed, the mold is cooled down during the pressure-holding and cooling process, which can greatly shorten the cooling time of the products and thus improve the production efficiency.

Defects of traditional thin wall injection molding method

The traditional practice is to use a mold temperature machine to heat the mold, but the shortcomings of this method are as follows.

(1) It cannot meet the needs of rapid temperature rise and rapid temperature drop in high-gloss injection molding.

(2) The temperature rise is small, and the fusion marks on the surface of the product can only be reduced but not eliminated.

(3) The higher the hardness of the plastic, the worse the fluidity; therefore, the hardness of the product surface can only reach HB level, which can not meet the actual user needs.

(4) The mold is heated and expanded when it heats up, and then shrinks when it cools down, making the clamping force very unstable.

It is easy to cause various defects, such as insufficient injection molded products, scorching, and large internal stress.

Advantages of high-gloss injection molding technology compared with traditional injection molding cycle
(1) This technology opens the water pipe in the injection mold and passes steam when it needs to heat up; passes cold water when it needs to cool down, and blows out the residual moisture with compressed air after cooling down to ensure that it can realize rapid heating up and cooling down.

(2) To maximize the elimination of fusion splice marks clip, waterline lack of glue, and other kinds of product failure.

(3) Due to the large temperature rise to using H or even 2H hardness level of plastic component, the surface hardness of the product is greatly improved.

(4) Since only the inner surface of the mold is heated up or cooled down when the pipe is opened inside the mold, the overall expansion of the mold is smaller, thus reducing various product defects caused by the instability of the clamping force.

Requirements of equipment needed for high-gloss injection molding

To produce high-quality high-gloss products, we need injection molding machines, molds, temperature control equipment special plastic for high-gloss plastic parts products, and boilers and cooling devices to match.

1. Configuration of the plastic machine:

The rigidity of the clamping mechanism should be good; because the whole production manufacturing process should be constantly heating up and cooling down.

Therefore, the clamping mechanism of the injection molding machine must be rigid and strong to ensure the accuracy and stability of the clamping force. To ensure the flat surface quality of the plastic injection molded parts products.

2. Choose a large clamping machine:

In this process, the clamping force required to produce the product is larger because the gas-assisted injection is no longer available.

3. Choose a smaller injection volume according to the situation:

For example, when producing flat panel TVs, LCD bezels, etc., the injection volume does not need to be larger, so try to choose an injection molding machine with a small injection volume.

The actual weight of the product is between 30% and 80% of the theoretical injection volume of the machine.

If the injection volume of the machine is too large, the glue will stay in the barrel for a long time and decompose easily, and the surface of the product will have defects such as a silver wire.

4. Equipped with a special screw to produce high-gloss products used in the plastic hardness is relatively high. The melt index is relatively low, so the screw plasticization is required to be good. At the same time, the shear of the screw should not be too large, otherwise, the rubber will be easily decomposed.

Mould configuration

1.The inner surface of the mold must have a very high degree of finish to ensure the surface quality of the product. Use a constant wall thickness Use a uniform wall thickness throughout the part (if possible) and avoid thick sections .

2.The piping inside the mold must be opened reasonably to ensure that it can be warmed up and cooled down quickly.

3.The pipes inside the mold cavity should have good thermal conductivity.

4.Since the production process requires constant heating and cooling, the steel chosen for the mold should be good.

5.Pay special attention to the maintenance of the injection mold in the process of use, to ensure dry and dust-free.

Configuration of temperature control equipment

1.Temperature control should be very accurate, which is an important guarantee of product quality.

2.The response of temperature control equipment should be very fast to ensure high production efficiency.

Specialized plastics

When producing products with high surface quality, the commonly used plastics are ABS, PC+ABS, or PMMA+ABS.

Among them, ABS has the lowest hardness, PMMA+ABS has the highest hardness, up to H, or even 2 H. But the higher the hardness, the lower the melt index.

The flowability will become worse, so you can choose the appropriate plastic according to the production needs.

Fluidity of ABS is related to both injection temperature and injection pressure, with injection pressure being slightly more sensitive.

For this reason, it is possible to start from injection pressure during plastic injection molding process to lower melt viscosity and improve filling performance.

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