1.The dimensional accuracy requirements for injection molded parts are not very high, The general standard is that it can be assembled well.

2. Some have relatively high requirements for the appearance of injection molded parts and may use secondary processing (such as oil spraying) to improve the appearance of defects when necessary

3.General plastic molding manufacturer does not require a special injection molding machine, nor does it require specially specified materials, and generally all commonly thermoplastics can be used for injection molding production. Therefore, General plastic molding manufacturer is widely used in various industries.

1.The dimensional repeatability of injection molded products is very high, usually with an accuracy of 0.01 to 0.001mm.

2. Requires precision injection molding machine with high injection pressure, fast injection speed and precision temperature control.

3.Injection mold design and mold manufacturing requirements are very high, Manufacturers with a wealth experience of precision plastic injection molding can be competent.

4.Raw plastic materials for plastic molding manufacturing must meet the following requirements:
High mechanical strength, Dimensional stability, Good creep Resistance,Wide range of Environmental Adaptations.

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Because engineering plastics have excellent process properties, high mechanical properties, so its application fields are increasingly widespread, and some industries even appear the trend of plastic parts instead of metal parts.

However, the precision of the metal parts to be replaced is difficult to be achieved by General plastic molding manufacturer, so precision plastic injection molding has emerged and is being rapidly developed and continuously improved.

The so-called precision injection molding refers to the plastic molding products with high precision in shape and size, good surface quality and high mechanical strength.

The factors affecting the precision of injection molded products are mainly the selection of materials, the design and manufacture of precision injection molds, precision injection molding machines and precision injection molding processes.

Polycarbonate(Including glass fiber reinforced) with high impact strength, wide temperature range (-50 -120°C), low shrinkage and dimensional stability,
When reinforced with glass fiber, the mechanical properties are better.

Polyformaldehyde (including carbon fiber and glass fiber reinforced type) has extremely high fatigue resistance, good creep resistance, wear resistance.

Polyamide (including reinforced) has high impact strength, good wear resistance, and good melt flowability during plastic injection molding; the disadvantage is that it has moisture absorption.

Therefore, moisture conditioning treatment should be carried out after the products are moulded.
This point needs to be especially reminded to your plastic molding manufacturer when you choose this material for precision injection molding.

Polybutylene terephthalate (including reinforced) has excellent heat resistance (can be used continuously at 150°C), high mechanical strength, good abrasion resistance, and good melt flow.

The mold design and mold manufacturing of precision plastic molding factory greatly impact the dimensional accuracy of injection molded products.

Therefore, when designing and manufacturing the injection molds, the following aspects should be noted.

The mold accuracy determines the injection molded parts’s accuracy.
Such as mold cavity size accuracy, parting surface accuracy

Mold production often involves precision machining, depending on the brand of the machine and the processing technology, it can reach 0.002mm to 0.008mm processing accuracy.

However, too high precision will make the mold difficult and expensive to manufacture, therefore, the precision of the mold must be determined according to the precision requirements of the products, plastic molding manufacturer must confirm this with your customers to determine the right accuracy to save cost.

In the mold design process, the processability of the mold cavity should be fully considered.
For example, when designing a mold for precision injection molding products with complex shapes, it is better to design the cavity as a panelized structure. This is beneficial not only to the grinding process, but also to the venting and heat treatment.

However, it is necessary to ensure the accuracy of the insert to avoid the joint line / insert line on the product. At the same time, the installation position of temperature measurement and cooling devices should be considered.

The shape of precision injection molded products is generally complex, and the injection pressure is high during processing, which makes it difficult to release the products. In order to prevent the products from being deformed and affecting the accuracy, when designing the mold, in addition to considering the draft angle, it is also necessary to improve the surface finishes of the mold cavity and runner, and try to use the push plate to release the molding parts.

Since the precision mold must withstand high injection pressure, and high clamping force and maintain high precision for a long time, the mold steel should be chosen from high quality alloy steel with high hardness, good wear resistance, strong corrosion resistance and high mechanical strength.

In order to assemble the mold accurately, a good positioning device is needed to ensure that there is no misalignment or misalignment during the cavity and core mold closing process.
Common positioning aids, such as guide pillar, guide bush, taper/cylinder positioning mechanism, positioning latch, etc.

Before mass production, a series of scientific injection molding tests are required.
Such as mold opening and closing, water transportation, mould temperature, and material temperature tests.
After the test, the relevant parameters must be adjusted and optimized to obtain the optimal injection speed and find the best filling percentage.

In addition, the holding pressure and holding time are also optimized in this process.

Similar to general plastic injection OEM services, There are mainly 3 points different between general plastic injection OEM and precision plastic injection OEM.

The injection pressure required for general injection molding is 40 – 180MPa, while for precision injection molding OEM, it is increased to 180 – 250MPa, and sometimes even higher, up to 400MPa.

Three purposes

Increasing the injection pressure can increase the volume compression of the plastic melt, which increases its density and decreases the coefficient of linear expansion, thus reducing the shrinkage ratio of the plastic injection OEM product and improving the precision of the injection molding OEM product.

For example, when the injection pressure is increased to about 400MPa, the shrinkage of the product is very low and does not affect the accuracy of the plastic injection OEM product.

Increasing the injection pressure can increase the flow ratio of the melt during injection molding, thus improving the molding properties of the plastic injection OEM products and enabling the production of ultra-thin-wall products.

The actual injection speed of the melt, due to the runner channel resistance, cannot reach the set value of the injection molding machine, while increasing the injection pressure is conducive to overcoming the runner channel resistance and ensuring the efficacy of the injection speed during plastic injection OEM process..

Due to the complex shape and high dimensional accuracy of precision injection molded parts,high injection speed must be used.

The temperature includes barrel temperature, nozzle temperature, mold temperature, oil temperature and ambient temperature.

In the precision injection molding OEM process, if the temperature is not precisely controlled, the fluidity of the plastic melt, the molding performance and the shrinkage of the product cannot be stabilized.

Therefore the product precision cannot be guaranteed at precision plastic injection OEM process.

Precision injection molding machine is necessary to start precision plastic injection OEM with the following requirements:

Precision injection molding machines generally use larger injection power to meet the high-pressure, high-speed injection conditions, so that the range of dimensional deviation of the product is reduced and dimensional stability is improved.

The precision injection molding machine implements multi-stage feedback control for process parameters such as:
injection volume, injection pressure, holding pressure, pre-molding pressure, injection speed and screw speed.

while the temperature of the barrel and nozzle is controlled by PID (Proportional Integral Derivative), which makes the temperature control accuracy at +/- 0.5°C, thus ensuring the stability and reproducibility of these process parameters and avoiding the products accuracy being affected by changes in the process parameters.

Mold temperature affects the products accuracy, especially for crystalline plastics.

The precision injection molding machine enhances the control of product shaping during the cooling stage in the mold cavity and the control of ambient temperature when the product is demolded from the mold.

Clamping force affects the products accuracy.
If the clamping force is too small, the product will have an overflowing edge under high pressure, which will affect the accuracy; while if the clamping force is too large, the product will be deformed by the mold and affect the accuracy during plastic injection OEM

Changes in oil temperature can cause changes in hydraulic oil viscosity and flow rate, resulting in fluctuations in injection process parameters, which can affect product accuracy.

The hydraulic oil is controlled by closed loop heating and cooling to stabilize the oil temperature at 50~55°C.

Plastic molding supplier is usually with high pressure and high speed injection process.

Since the transition between high and low pressure and high and low speed is fast, the hydraulic system is required to have a fast response speed to meet the needs of the precision injection molding process.

For this reason, hydraulic components with high sensitivity and fast response time were used in the hydraulic system, and proportional cartridge technology was adopted.

When designing the oil circuit, the flow from the control element to the actuating element was shortened.

In addition, accumulators are used to improve the hydraulic system’s response speed and absorb vibration and stabilize pressure. With the application of computer control technology on precision injection molding machines, the entire hydraulic system works under low noise, stable, sensitive and precise conditions.

plastic molding manufacturer should recognize this when you use oil hydraulic system.

The injection pressure of precision injection molding machine develops in the direction of high pressure and ultra-high pressure to reduce the shrinkage rate of products and increase the density of products; the injection speed develops in the direction of high speed to meet the injection molding requirements of products with complex shapes.

Therefore, the mold closing system should have enough rigidity to avoid deformation during the plastic injection OEM process and affect the accuracy of the products. The structure parts of the mold clamping system, such as moving and fixed mold plates, tie rods and clamping mechanism, should be carefully designed and selected to improve rigidity.

6.1 Precision plastic injection OEM has higher performance requirements than general plastic injection OEM in materials, and the price of this kind of engineering materials is often very high

6.2 In the precision injection molding OEM process, the high pressure and high temperature, as well as the need for precise adjustment of pressure, temperature and clamping force, lead to higher energy costs and equipment investment.

6.3 Moreover, due to the high requirements of precision injection molding on mold accuracy, rigidity, and hardness, it directly leads to much higher steel, processing, and trial costs than general injection molds.

6.4 Precision injection molding equipment needs to provide higher pressure and mold rigidity, and the clamping force at each time point needs to be precisely adjusted compared with general injection molding equipment, so the cost is higher again.

Because of the precision injection molding products with thin walls, lower rigidity than metal, and subject to the temperature and humidity of the measurement environment, so the measurement can not simply use the traditional metal parts measurement methods and instruments.

Such as measuring plastic products with the vernier caliper foot, plastic is easy to deformation, measurement is not accurate enough, it is best to use the optical method (microscope) measurement.

Then the three-dimensional dimensional measurement of plastic products, can be carried out on the CMM, and the use of electronic probes, to prevent plastic products from being deformed by the force and affect the measurement accuracy.

In addition, the measurement should also ensure that the environment temperature and humidity is constant and supply.