Home » Injection Moulding 101
The hot runner injection moulding method was introduced in the 1950s. After a long period of promotion, its application penetration rate has increased year by year. In the mid-1980s, hot runner injection moulds in the United States accounted for 15% to 17% of the total number of injection moulds, 12% to 15% in Europe and about 10% in Japan. However, in the 1990s, hot runner injection moulds accounted for more than 40% of plastic injection moulds produced in the United States, and accounted for more than 90% of injection moulds for large products.
It can be seen that the 3 coloring methods of injection moulded parts have their own advantages. The injection moulding companies needs to select the appropriate coloring method according to its own products to make the processed products have good quality, which can not only meet the requirements of customers but also reduce the cost, to maximize economic benefits.
In recent years, the manufacturing cost of injection moulds has continuously increased, so how to reduce the cost of injection moulds has become the hot topic that we discuss. Therefore, this article tries to analyze from the various aspects of mould manufacturing, in order to reduce the cost of injection mould manufacturing. Quality, price, cycle and service are 4 major factors that mould producers and users are very concerned about. In recent years, mainly due to the continuous increase in labor costs and rising raw material energy prices, resulting in injection mould manufacturing costs are also raising, and opposite of this, the profit rate of injection moulding company is constantly falling. Some injection moulding manufacturer reflect that the quality and level of some injection moulds currently produced are worse than they were five years ago. This is really puzzling: In the past five years, there has been a lot of technological progress. How does the quality level drop? They explained that because some users (or injection mould purchasers) unilaterally and simply demanded price reductions, they were indifferent to the injection mould quality level, so they had to be forced to use low-priced materials, low-grade mould standard parts, and unreasonable simplification of the injection mould structure. Use the methods of reducing the manufacturing process and processing costs to deal with. Therefore, it is not that injection moulding companies can’t produce high-quality and high-level injection moulds. Although this phenomenon exists in the injection moulding industry, this kind of abnormally low-cost manufacturing can’t be promoted, and should be guided correctly and suppressed. Therefore, promoting low-cost manufacturing under the premise of ensuring and improving the quality and level of injection mould.
The stage of injection mould pressure preservation is also a stage of continuous pressure application. The density of plastic also increases with the increasing pressure of the injection moulding machine. In the process of injection mould pressure preservation, the cavity is slowly filled with plastic, resulting in the injection mould back pressure gradually increased. In the process of pressure preservation, the screw of the injection moulding machine moves forward slowly, and the rate of plastic is relatively slow. In this case, the flow is called pressure preservation flow. In the injection mould pressure preservation stage, the plastic is cooled, resulting in accelerated solidification, increased melt viscosity, and large resistance in the cavity. At the later stage of pressure preservation, the material density continues to increase, and the plastic parts are also moulded by injection moulding. When the gate solidifies, the stage of pressure preservation is finished, and the pressure in the cavity reaches the maximum value.
Injection moulding process is divided into many types. The rotational moulding process method is that to add plastic into the mould first, and then the mould is continuously rotated along two vertical axes and heated. The plastic in injection mould is gradually and evenly distributed under the action of gravity and heat energy, melted and adhered to the entire surface of the cavity, formed into a desired shape, and cooled and moulded.

The products produced by this process include: fuel tanks, water tanks, mechanical enclosures, fenders, etc. The main alternatives are metal parts and glass steel products.

Injection moulding processing is a technology that is based on microfabrication technology such as LIGA, and of course there are many other methods. The LIGA process is to produce a model that is needed for injection moulding, which is commonly known as "mould" . And then the liquid plastic is poured into the mould, and finally separated to form the final desired product. For example, some plastic toys, and many other products.
Quenching is rapid cooling in quenching medium such as water, oil or other inorganic salt, organic water solution, etc. The steel hardened but became brittle at the same time. Quenching purpose is to improve the mechanical properties of metals or parts and improve the performance or chemistry of certain special steel. However, some problems may be encountered when the injection moulding quenching is carried out in the injection mould factory.
What are the consequences of excessive number of injection mould trials?
The unreasonable design of the injection mould makes the number of trials increased, which increases the investment in injection moulds. In addition, it will also extend the injection mould cycle.
The best injection moulding process and suitable injection moulding machine are selected during the injection mould trial, and the physical properties of the plastic are fully understood, which can effectively reduce the number of injection mould trials.
Cracking is a common defect in plastic products. The main reason for this is due to stress and deformation. There are mainly residual stress, external stress, and stress deformation caused by the external environment.
The reason for this defect is essentially the same as insufficient filling, just to a different extent. Therefore, the solution is also basically the same as the above method. Especially for resins with poor fluidity (such as polyoxymethylene, PMMA resin, polycarbonate and PP resin, etc), attention must be taken more to properly increase the gate and proper injection time.
In order to improve the material's rigidity and wear resistance, general materials need to be heated above 1030°C. At high temperatures, various alloying elements are fully dissolved in the austenite so as to obtain a high hardness of the substrate during quenching, and in order to ensure that the parts do not undergo decarburization and oxidation, a vacuum treatment is applied accordingly. At present, high-rate gas quenching and quenching furnaces used in the semiconductor industry can heat injection mould parts under high vacuum conditions through nitrogen protection, which not only ensures the decarburization and oxidation of injection mould parts, but also prevents the evaporation of alloying elements.
After the plastic injection mould factory installs the plastic injection mould into the injection moulding machine, it needs to adjust the installed mould to ensure that the injection moulding produces a high-quality product. What steps must be taken? Let me explain in detail.
After completely positioning the plastic injection mould positioning ring into the positioning ring of the injection machine, the plastic injection mould is just started to close at a very slow speed, the press mould of the injection moulding machine presses it gently, and then the upper press plate of the plastic injection mould is pressed tightly. Then the pressure plate can have 4 - 8 pieces depending on the size of the plastic injection mould. The height of the adjusting screw of the pressure plate must be the same as the height of the die foot to ensure that the pressure plate is flat and the die foot can be pressed. Check the parallelism and verticality of the plastic injection mould, the firmness of the bracket and adjust the concentricity of the barrel and the center hole of the plastic injection mould.
In the injection moulding process, mould temperature is an important factor affecting the quality of injection moulded parts. In general, setting a higher mould temperature usually results in higher higher surface quality of injection moulded part. Cold and hot cycle plastic injection moulding process is a method of controlling mould temperature using thermal cycling during the injection moulding cycle. This technique requires that the heating temperature of mould surface is above the glass transition temperature (Tg) of plastic to facilitate injection moulding, and then the mould temperature is quickly cooled to allow the parts to be cold-solidified for easy ejection.

Cold and hot cycle plastic injection moulding process can greatly improve the surface quality of injection moulded parts, in addition, reducing the secondary processing steps such as painting and grinding and so on to eliminating surface flaws, which reduce the entire processing cost. In some cases, painting or grinding can be omitted. Cold and hot cycle plastic injection moulding can also improve the surface finish of glass-reinforced structural materials, and is used where high gloss is required on the surface of injection moulded part. Other advantages include: reducing moulding stresses, reducing or eliminating turbulence, weld seams, and other defects, and increasing the melt flow length to produce thin-walled injection moulded parts.
Plastic Injection Moulding Process
Some plastic parts are quickly swollen or bubbling on the back of the metal insert or in particularly thick areas after demoulding. This is caused by the expansion of the released gas under the effect of internal pressure when the plastic is not completely cooled and hardened. There are the following solutions:
  1. Effective cooling, reduce injection mould temperature, extend injection mould opening time, reduce material drying and injection mould processing temperature.
  2. Reduce injection mould filling rate, reduce cycle time, and reduce flow resistance.
  3. Improve holding pressure and time.
  4. Improve the condition that the walls of the products are too thick or vary in thickness.
1 2 3 4

Online tour of our plastic injection mould making factory in Shenzhen China.
Featured Articles
Mould Maker, Injection Mould Making ... Mould Maker, Injection Mould Making Company Selection TipsIt is very easy to find an injection mould maker, the most simple and effective way is to participate in relevant exhibitions. ...
10 Factors Influence Injection Mould ... 10 Factors Influence Injection Mould QualitySteel is a decisive factor of mould quality, a reasonable choice of steel is the most important. Steel selection criteria are: ...
Basics of Plastic Injection Mould ... Basics of Plastic Injection Mould DesignCollect all basic technical documents from the mould design to finish processing, such as the mission statement, parts diagrams, ...
4 tips to choose an Injection Mould ... 4 tips to choose an Injection Mould Manufacturer in ChinaFollow the points to select a suitable injection mould manufacturer Do not blindly believe the low purchasing price. Behind ...