Plastic Injection Molding
The plastic injection molding method has the characteristics of high precision and high efficiency, which can produce products with complex shapes and precise dimensions, and has a wide range of advantages and development prospects.
Thin wall injection molding is the process of adding granular or powdered plastic to the hopper of a plastic injection molding machine, where the plastic is plasticized and maintained in a flowing state, and then cooled and shaped under a certain pressure. The injection molding method can effectively produce plastic products with thin-walled structures, reduce material waste, and achieve lightweight production.
Thin wall injection molding products are usually miniaturized and thin-walled. Widely used in the manufacturing of automotive components such as bumpers, instrument panels, and door panels. In addition, the thin wall injection molding process is facing new development problems due to its advanced technology. Need to choose better and updated materials and processes.
Key Points of Thin Wall Injection Molding Design
Thin wall injection molding is different from conventional injection molding, and manufacturers need to pay more attention to design points. For example:
- Plastic Materials
During the design of thin wall injection molding, it is necessary to ensure the flow distance of plastic materials while also ensuring the other properties of the parts. High-fluidity plastics should be used. If the fluidity of the molten plastic is not enough, it can be improved by adding more gates, but this may lead to weld marks in the product. The melt index of polypropylene (PP) plastic can reach up to 60 (g/10min). The main reason why manufacturers use PS/ABS copolymers in the manufacturing of many finished products is to require the toughness of PS and the flowability of ABS, as well as high adaptability in thin wall injection molding. At present, the plastic raw materials commonly used in thin wall injection molding mainly include polypropylene (PP), polystyrene (PS), polycarbonate (PC), acrylonitrile butadiene styrene (ABS), PC/ABS blends, and PA6. These plastic raw materials usually have good fluidity and low viscosity after melting, with larger flow distance, higher impact strength, less deformation (or higher hot deformation temperature), higher stability, and can maintain relatively stable dimensions after thin wall injection molding.
Thin wall injection molding manufacturers usually take polypropylene (PP) as an example. Polypropylene has good chemical stability to most chemical solvents such as acids, alkalis, organic salts, and fats, and this chemical stability increases with the increase of molecular density. For most tableware items or packaging, high-temperature food or beverages may be stored, so thin wall injection molding materials have higher requirements for their properties at high temperatures. The melting point of polypropylene can reach 175 ℃, and the decomposition temperature is also high. It can be boiled and disinfected in boiling water.
Plastic packaging products formed by thin wall injection molding have certain defects that are difficult to shape compared to conventional injection molding. After molding, defects such as warping deformation, material shortage (short shot), porosity, and fusion marks may occur; On the other hand, manufacturers and customers generally have high requirements for thin wall injection molded products. For example, thin wall injection molding needs to ensure the exquisite appearance of the product, although the wall thickness needs to be thin, it must maintain a certain strength and hardness, and not easily deform. The current thin wall injection molding process is developing towards automation.
- Additives
Thin wall injection molding may require the addition of certain additives to enhance stiffness, toughness, transparency, etc. in the processing of cups, meal boxes, packaging, etc.
- Special Injection Molding Machine for Thin Wall Injection Molding
Compared to traditional injection molding, thin wall injection molding requires specialized processing equipment and is more complex in design and processing. Mainly including injection molding system, mold locking system, hydraulic transmission system, electrical control system, etc., these systems should be able to ensure that plastic raw materials can be uniformly injected into the mold under pressure conditions. The locking system can achieve the locking of the injection mold’s moving and fixed molds, and manufacturers need to ensure appropriate locking force during design to prevent material overflow; The hydraulic transmission and electrical control system can control the injection molding machine to have sufficient power to achieve normal operation, and the various systems controlling the injection molding machine can cooperate to achieve operation.
The injection pressure for thin wall injection molding is higher, above 200MPa; The injection speed is faster, basically above 200mm/s; The locking force is greater, and the requirements for the clamping mechanism are higher.
Thin wall injection molding molds include gating systems, cooling systems, temperature regulation systems, and demolding and ejection systems. When designing molds for thin wall injection molded plastic packaging boxes, suppliers need to provide design services based on the purpose and appearance of the packaging boxes. Thin wall injection molding molds require high strength, good impact resistance, high hardness, fast cooling speed, and good exhaust performance.
- Design of Thin wall Injection Molded Parts
The design principles and methods of thin-walled injection molded products are more complex and are greatly affected by molding limitations and material selection. Thin wall injection molded products are required to have a thinner wall thickness, higher impact strength, good appearance quality, and consistent dimensional stability, as well as good fluidity of raw materials. During the design process, the focus should be on the rigidity, impact resistance, and manufacturability of the product.
-Wall Thickness Design
Considering the relatively thin wall thickness of thin-walled injection molded plastic parts, larger plastic parts are prone to defects such as insufficient flow distance during processing, resulting in the inability to fill the mold cavity. Based on ensuring the stiffness and strength of thin-walled injection molded parts, manufacturers usually recommend selecting the wall thickness of the plastic parts between 1-5 millimeters and requiring consistency and uniformity in their appearance.
-Strengthening Tendon
The advantages of adding reinforcement ribs in thin wall injection molding mainly include: it can enhance the strength and rigidity of the product without increasing the wall thickness; Save plastic usage, reduce weight, and lower costs; Maintain uniform wall thickness and overcome uneven stress caused by the difference in wall thickness of the product, resulting in deformation of the product; Increase the flow distance of plastic melt and provide channels for smooth filling of the melt in certain areas of the plastic product body where the wall thickness is too thin. For the reinforcing ribs of thin-walled injection molded parts, the supplier recommends a thickness of 0.5-0.7 times the wall thickness, a height less than or equal to 3 times the wall thickness, and a demolding angle of approximately 2-5 degrees.
Key Points of the Thin Wall Injection Molding Process
The process of thin wall injection molding is complex and requires attention to:
-The Filling Process of Thin Wall Injection Molding
When producing thin-walled injection molded parts, the plastic melt will be directly filled into the mold cavity through diversion channels and gates, and the molten material on the mold wall will form a solidification layer, reducing the flow channel of the melt. Due to the small wall thickness of plastic parts, the flow channel is smaller than that of conventional injection molding, which may lead to the problem of insufficient injection and short shots. So the thin wall injection molding process generally requires high speed and high pressure to complete the filling.
-Thin Wall Injection Molding Process
In the application of producing thin wall injection molded parts, monitoring, and debugging of injection molding process parameters is crucial, and a specialized thin wall injection molding machine is generally required. Thin-walled injection molded parts generally use a relatively small amount of resin, so the size of the barrel is also relatively small, reducing the retention time of the molten material in the barrel and preventing its degradation. The wall thickness of the thin wall injection molding process varies, and the corresponding parameters will also vary. For plastic parts with a wall thickness of less than 1mm, the recommended injection pressure range is generally between 138~241MPa, and the filling time is about 0.1~0.5s.
Key Points for Solving Thin Wall Injection Molding Problems
The process of thin wall injection molding is unique, so the likelihood of defects occurring will correspondingly increase.
- Thin-walled plastic parts may have surface defects, mainly due to the rough surface of injection molds that are not polished promptly. For PC raw materials, sometimes due to high mold temperature, residual glue and oil stains can contaminate the surface of injection molded parts.
- Shrinkage problems often occur in areas with large or uneven wall thickness in thin wall injection molding molded parts, mainly due to inconsistent cooling or curing shrinkage of hot melt plastics.
- Bonding lines or fusion marks usually occur at the confluence of two material flows, and this problem can occur if the speed or temperature of the confluence is not consistent.
- Thin wall injection molding parts that are slender, large in area, or structurally asymmetric are prone to warping deformation due to uneven cooling stress or uneven ejection forces during molding.
- Small parts and corners of thin wall injection molding parts are usually not filled, which may be due to inadequate mold processing and improper exhaust system settings.
- The occurrence of burrs in thin-walled injection molded parts often occurs at the parting of the front and rear molds, mainly due to problems with the locking mechanism, resulting in insufficient locking force or poor mold closing; It is also possible that it is caused by insufficient material temperature or mold temperature.
- Airlines often occur at the inlet, often due to low mold temperature, high injection speed, pressure, or improper setting of the inlet.
Thin wall injection molding technology is constantly developing and will provide more automated professional services.
Related News
Applied’s expertise in modifying materials at atomic levels and on an ihdustrial scaleenables our customers to transform possibilities into reality.
