What problems should we pay attention to in injection molding of electronic equipment shell?

In the process of electronic equipment shell injection molding, we need to pay attention to the following aspects:

First, the mold

mold design

It should be designed accurately according to the shape, size and functional requirements of the electronic equipment shell. For example, if the shell has many key holes, interface slots and other structures, the parting surface design of the mold should consider how to facilitate the molding of these details and ensure the smooth demoulding. For some shells with special appearance requirements, such as smooth mirror effect or textured matte effect, the surface treatment of the mold also needs corresponding design.

Consider the cooling system of the mold. Reasonable cooling channel layout can make plastics cool evenly and avoid shell deformation caused by uneven cooling. Generally speaking, the cooling channel should be as close as possible to the surface of the cavity, and the uniform flow of cooling medium (such as water) should be ensured to improve the cooling efficiency.

Mold material selection

Because the shell of electronic equipment requires high dimensional accuracy and surface quality, the mold material should have good wear resistance, corrosion resistance and sufficient strength. Commonly used mold steel, such as P20 steel, has good machinability and polishing performance, and is suitable for general injection mold of electronic equipment shell. For high-precision and high-yield molds, H13 steel may be selected, which can still maintain high hardness and toughness at high temperature and meet the needs of long-term injection production.

Mold maintenance and maintenance

Regularly clean the mold cavity and cooling channel. In the process of injection molding, plastic residues may accumulate on the surface of the cavity, affecting the appearance and dimensional accuracy of the product; Blockage of cooling channels will lead to poor cooling effect. For example, after the cooling channel is blocked, the local temperature of the mold is too high, which will cause the shell to shrink and other defects in this part.

Check the moving parts of the mold, such as slider and thimble. If these parts are worn or stuck, it will affect the demoulding of the shell and may even damage the mold and products.

Second, the material aspect

Material selection

The mechanical properties of the material should be considered. The shell of electronic equipment needs to have certain strength and toughness to withstand external forces such as collision and extrusion in daily use. For example, ABS (acrylonitrile butadiene styrene) material has good comprehensive properties, high strength, good toughness and moderate surface hardness, and is often used in some electronic equipment housings that require high appearance and mechanical properties, such as computer cases and mobile phone housings.

The thermal properties of materials are also critical. Different injection molding processes require materials with suitable melting temperature and thermal stability. For example, polycarbonate (PC) has a high melting temperature, which requires a high barrel temperature during injection molding. However, it has good thermal stability and dimensional stability, and is suitable for some electronic equipment housings that require high precision and have large temperature changes in the working environment.

The electrical properties of materials can't be ignored. For some electronic equipment housings that need electromagnetic shielding function, materials with good conductivity should be selected or conductive fillers should be added to the materials. For example, adding metal fibers to plastic can improve the electromagnetic shielding performance of the shell.

Material drying treatment

Many plastic materials are absorbent, such as nylon (PA). If the material gets wet before injection molding, it will produce defects such as bubbles during injection molding. Therefore, it is necessary to dry these materials. Generally, special drying equipment, such as hot air drying box, is used to set the appropriate drying temperature and time according to the characteristics of materials. For example, nylon materials usually need to be dried at 80-100℃ for 4-8 hours to ensure that the moisture content in the materials is reduced to a suitable level.

Third, the injection molding process

Injection molding parameter setting

The control of injection temperature is very important. It includes barrel temperature, nozzle temperature and mold temperature. The temperature of the barrel should be set according to the melting point and fluidity of the material to ensure the uniform melting and smooth injection of plastic. For example, for PP (polypropylene) materials, the barrel temperature is generally set at 180-220℃. The nozzle temperature is usually slightly lower than the highest temperature of the barrel to prevent the plastic from solidifying in advance at the nozzle. Mold temperature will affect the cooling speed and appearance quality of the shell. For example, for some shells with high surface gloss, the mold temperature may need to be higher, generally around 80-100℃.

Adjustment of injection pressure and speed. The injection pressure should be large enough to ensure that the plastic can fill the mold cavity, but excessive pressure may lead to defects such as flash. Injection speed affects the filling method of plastic. Too fast injection speed may cause injection phenomenon and cause defects on the surface of the shell. Too slow speed will lead to too long filling time and affect production efficiency. Generally, it is necessary to make repeated experiments according to the shape, size and material characteristics of the product to determine the appropriate injection pressure and speed.

Injection molding process monitoring

It is necessary to monitor the key parameters in the injection molding process in real time, such as pressure, temperature and speed. Through the sensors and monitoring system installed on the injection molding machine, the abnormal changes of parameters can be found in time. For example, if the injection pressure suddenly rises, it may be that there is a foreign body in the mold cavity or the gate is blocked, so it is necessary to stop the machine in time to avoid producing unqualified products.

Observe the filling condition of plastic. The flow of plastic in the mold cavity can be viewed through the transparent mold observation window or using visual monitoring equipment. If uneven filling is found, such as short shot (plastic does not completely fill the cavity), the injection parameters should be adjusted in time or the gate design of the mold should be checked.

Fourth, quality control

Appearance quality inspection

Check the surface of the shell for defects, such as shrinkage, flash, bubbles, weld marks, etc. Shrinkage is caused by uneven cooling shrinkage of plastics, which is manifested as local depression on the surface of the shell; Flash is the redundant part formed by plastic overflowing at the parting surface of the mold; Bubbles are caused by water in the material or air involved in the injection molding process; Weld marks are marks formed when different plastic streams meet, which will affect the appearance and strength of the shell.

Check whether the color and luster of the shell meet the requirements. For the shell with color requirements, make sure that the color is uniform and there is no chromatic aberration. In terms of gloss, if it is required to have a high-gloss surface, there should be no foggy or matte areas.

Dimensional accuracy control

Use high-precision measuring tools, such as calipers and micrometers, to measure the key dimensions of the shell. These key dimensions include the length, width and thickness of the shell, and the dimensions of various mounting holes and interfaces. For example, for the mobile phone case, the dimension accuracy of the key hole is very high. If the dimension deviation is too large, the key will be installed weakly or cannot be installed.

Establish dimensional tolerance standards, and determine the allowable deviation range of each dimension according to product design requirements. In the production process, it is necessary to carry out sampling inspection on the dimensions to ensure the dimensional stability of the products. If the dimensional deviation is found to be beyond the tolerance range, the mold or injection process parameters should be adjusted in time.

performance test

Conduct mechanical performance tests, such as tensile strength and impact strength tests, to ensure that the shell can meet the use requirements. For example, the shell of a tablet computer should be able to withstand a certain degree of drop impact without breaking.

Conduct electrical performance tests, such as insulation resistance test and electromagnetic compatibility test. For some equipment housings with electronic components inside, good insulation performance can prevent leakage, and electromagnetic compatibility testing can ensure that the housings will not cause electromagnetic interference to the circuits inside the equipment, nor will they be affected by external electromagnetic interference.