Injection molding is a method of shaping industrial products. Products are typically produced using rubber injection molding and plastic injection molding. Injection molding can also be divided into injection molding compression molding and die casting.
Plastics and Injection Molding Principles
-Molding properties of plastics
-Injection Molding Principles and Process Flow
The principle of plastic injection molding is to heat thermoplastic or thermosetting plastic raw materials to a molten state, inject them into a closed mold cavity under high pressure, and then cool and solidify to obtain a plastic product with the same shape as the mold cavity. This process achieves efficient production through a cycle of "raw material melting - injection filling - pressure holding and cooling - mold opening and part removal".
An injection molding machine (or injection molding machine for short) is the main molding equipment used to make various shapes of plastic products from thermoplastic or thermosetting materials using plastic molds. Injection molding is achieved through an injection molding machine and a mold.
Injection Molding Process Technology
-Injection Molding Process Parameters
-Setting injection molding process parameters
-Post-processing of molded parts
Injection Molding Technology Preparation
Plastic Color Matching:
Some plastic products require precise color matching; therefore, accurate color matching is essential during injection molding. Two common color matching processes are as follows:
The first process uses masterbatch, which involves uniformly mixing thermoplastic granules in a specific ratio for production. The amount of masterbatch added is typically 0.1%–5%.
The second process involves uniformly mixing thermoplastic granules with a dispersant (also called a diluent or coloring agent) and color powder to form colored granules. White oil is commonly used as a dispersant; 20–30 mL of white oil and 0.1%–5% colorant are used for 25 kg of plastic. Other dispersants that can be used include turpentine, alcohol, and some esters. Coloring thermosetting plastics is relatively easy; generally, pigments are simply mixed in.
Common Defects and Solutions in Injection Molding Production
Common Defects and Solutions in Injection Molded Products
Material shortage (under-fill) and solutions：
-Shrinkage marks and solutions
Short shot, also known as underfill, short shot, or insufficient filling, refers to the failure of molten plastic to completely fill the molding space of the mold after entering the cavity, as shown in the figure below.
Causes and Solutions for Material Shortage Defects：
① Improper Equipment Selection. Therefore, when selecting injection molding equipment, the maximum injection volume of the injection molding machine must be greater than the mass of the plastic part. During verification, the required total injection volume (including the plastic part and runner solidified material) should not exceed 85% of the plasticizing capacity of the injection molding machine.
② Insufficient Material Supply. This means there may be a "bridging" phenomenon at the bottom of the feed port of the injection molding machine hopper. The solution is to appropriately increase the injection stroke of the screw to increase the material supply.
③ Poor Raw Material Flow Properties. Efforts should be made to improve the stagnation defects in the mold gating system, such as rationally setting the runner position, enlarging the size of the gate and runner, and using larger nozzles. At the same time, appropriate additives can be added to the raw material formulation to improve the flow properties of the plastic.
④Excessive lubricant. Reduce lubricant usage or adjust the clearance between the barrel and screw.
⑤Cold slug impurities blocking the runner. Disassemble and clean the nozzle or enlarge the cross-section of the cold slug cavity and runner.
⑥Inadequate gating system design. When designing the gating system, pay attention to gate balance; the weight of the plastic part in each cavity should be proportional to the gate size to ensure that each cavity is filled simultaneously.
⑦Poor mold venting, as shown in Figure 3-5. Check for cold slug pockets.
⑧ The mold temperature is too low. To address this, the mold must be preheated to the required process temperature before starting the machine.
⑨The melt temperature is too low. Within the appropriate molding range, the melt temperature is approximately directly proportional to the mold filling process....
Common Defects and Solutions in Injection Molding Process
Unsmooth material feeding and solutions：
-Excessive noise during plasticizing and its solutions
-Sprue material (runner sprue) sticking to the mold and solutions
Unsmooth material feeding refers to the phenomenon where, during the injection molding process, the plastic raw material in the hopper sometimes fails to feed, resulting in insufficient plastic entering the injection molding machine barrel and affecting product quality. The following lists the causes and solutions for material feeding problems：
The recycled sprue/runner material has large particle size (uneven size).
① Re-crush the larger sprue/runner particles (adjust the gap of the granulator blades)
Raw materials in the hopper are caking (poor drying temperature control).
② Check/repair the drying system and replace with new material
Raw materials in the hopper show "bridging" phenomenon.
③ Inspect/clear the raw material inside the hopper
The proportion of recycled sprue/runner material is too high.
④ Reduce the ratio of recycled sprue/runner material used
The temperature of the feeding section or feeding port of the drying hopper is too high.
⑤ Lower the temperature of the feeding section or check whether there is material burning at the feeding port
Drying temperature is too high or drying time is too long (material baking).
⑥ Lower the drying temperature or shorten the drying time
Vibration from the injection molding machine.
⑦ Control the vibration of the injection machine
The feeding port or platform opening is too small.
⑧ Enlarge the feeding inlet hole or replace the feeding platform
Precision and special requirements injection molding technology
-High-gloss, seamless injection molding process
-Multi-stage injection molding process
-Injection molding process for transparent plastics
-Two-color injection molding technology
-Thin-wall injection molding technology
Precision injection molding process
Current status of precision injection molding technology：
-Technical requirements for precision injection molding
Precision injection molding differs from conventional injection molding primarily in that it leverages the rapid development of polymer materials to replace high-precision metal parts in the instrumentation and electronics industries. Currently, there are two defining indicators for precision injection molded products: dimensional repeatability and quality repeatability.
Compared to conventional injection molding, precision injection molding offers unparalleled advantages in repeatability, parameter control, and dimensional control. Precision injection molding technology can precisely control various process parameters during the injection molding process, achieving the requirements for dimensional accuracy, environmental stability, residual stress, and surface finish in high-precision injection molded parts. Precision injection molding, as an emerging technology for manufacturing plastic lenses, has unparalleled advantages. However, it also places higher demands on injection materials, experimental equipment, and injection molds. Firstly, materials suitable for precision injection molding must be plastics with strong anti-interference capabilities, good mechanical properties, and stable structures. Secondly, the injection mold must be rationally designed based on the structure of the injection-molded part, process parameters, and production efficiency. Finally, a precision injection molding machine capable of accurately controlling injection speed, holding pressure, cooling time, and other injection process parameters must be selected.
Similar to the ordinary injection molding process, the precision injection molding process can also be divided into three stages: the filling stage, the holding pressure stage, and the cooling stage, as shown in Figure 4-1.
Energy-saving technology and green manufacturing in injection molding
-Low-pressure injection molding technology
-Hot runner injection molding technology
-Gas-assisted injection molding technology
-Green manufacturing in injection molding
Energy-saving technology for injection molding
Energy consumption analysis of injection molding machines：
In the production cost of injection molded products, besides the material waste caused by defective products, electricity consumption accounts for a large proportion. In particular, for the currently widely used fixed-displacement pump injection molding machines, energy consumption during the production process accounts for more than 80% of the total electricity consumption.
Early injection molding machines were fully hydraulic, operating under varying loads during the injection process. Statistics show that energy losses due to high-pressure throttling reached 30%–70%, resulting in very high energy consumption. Simultaneously, the heating method used in the injection molding process was generally electric heating coils, transferring heat to the barrel through contact conduction. Only heat close to the inner surface of the barrel was transferred to the barrel, with most of the heat on the outer surface dissipating into the air, resulting in significant heat conduction losses and causing an increase in ambient temperature. Furthermore, resistance wire heating has a drawback: low power density, making it unsuitable for applications requiring higher temperatures. Energy-saving retrofitting of injection molding machines addresses the principles of energy loss by employing advanced technologies to save unnecessary energy.
In summary, energy-saving retrofitting of injection molding machines mainly involves three approaches: first, technically upgrading the hydraulic drive system; second, technically upgrading the heating method of the plasticizing barrel; and third, recovering and utilizing excess heat from the heating components of the injection molding machine.
Injection Molding Process Optimization and Computer Simulation Technology
-Computer simulation technology for injection molding
Injection Molding Process Parameter Optimization Technology
Injection Molding Process Parameter Optimization Principle：
-Injection Molding Process Parameter Optimization Based on Artificial Neural Network Principles
-Application of Artificial Intelligence in Injection Molding Process Parameter Optimization
-Example of an Expert System for Injection Molded Product Defects and Process Optimization
Traditional injection molding process parameter setting methods primarily rely on trial and error, depending on the operator's limited experience and relatively simple calculation formulas. However, in actual production, the flow properties of molten plastic vary greatly, mold structures are highly variable, and process parameters influence each other. Limited experience and simple formulas are insufficient to comprehensively consider and address these factors, necessitating repeated trial molding, leading to long production cycles, high costs, and difficulty in guaranteeing product quality. These problems are even more pronounced for large, complex, and precision products. With the rapid development of the plastics industry and increasingly fierce market competition, the demands for production quality and efficiency of plastic products are rising. Researching new methods for setting and optimizing injection molding machine process parameters, shortening the process setup cycle, improving product quality, and reducing production costs-ensuring that injection molding machine process parameter settings are based on scientific analysis to break free from the constraints of experience-has become crucial for the development of my country's injection molding production industry, possessing significant engineering importance and broad application prospects.
Automation and intelligentization of injection molding production
-Automation and intelligentization of injection molding production
Challenges of traditional injection molding production
-Opportunities in Injection Molding Production
Challenges faced by injection molding manufacturers：
-Challenges faced by injection molding workshops
Injection molding is a typical traditional manufacturing industry. In recent years, traditional injection molding manufacturers have faced enormous challenges due to factors such as rising raw material prices, increasing labor costs, overcapacity, fierce competition, and growing personalized customer demands.
As shown below：
1. Product lifecycles are getting shorter, and customer demands are becoming smaller and more diverse (flatter architecture, more flexible manufacturing, and smarter processes).
2. Customer requirements are becoming increasingly stringent, and the barriers to entry in the competitive market are rising.
3. How to effectively control quality and maintain quality traceability records at every stage (including the supplier side)?
4. How to transform SCM management through informatization, transparency, and datafication.
5. How to effectively manage SPC statistical process management and CRM customer orders to achieve efficient, high-quality, and timely order processing; and ensure accurate capacity assessment for downstream enterprises.
6. Challenges include personnel management, the accuracy and timeliness of equipment utilization, equipment operating status, and factory operation data, and the rationality of process routes.
At the enterprise level, facing fierce market competition and rapid technological advancements, traditional injection molding production will more or less exhibit the following phenomena.
(1) Unstable production status
(2) Short production cycle, high pressure on product delivery time
(3) Poor communication and ineffective collaboration between departments within the company
(4) Lack of basic data for injection molding production
(5) Serious "three-mute" problem (i.e., lack of coordination, and lack of expertise)
(6) Insufficient management level