The mold used for plastic injection molding is called an injection mold. An injection mold is a plastic product that can be shaped at one time with complex shapes, high dimensions, or with inserts. plastic injection molding manufacturer point that,"Seven points mold, three points process." For the injection molding, the mold has a great influence on the quality of the molded product.
Injection molding is considered to be the most versatile, as it can be used to create a variety of parts, ranging in both size and shape.
Injection molding basic principles are fairly simple, but the actual process can be quite complex when it comes to maintaining part consistency. The process involves the injection of melted plastic into a mold, which is made of steel. The mold itself has cavities that will form the parts; once injected, the molten plastic fills the cavities and the rest of the mold. Once cooled, the parts are ejected by pins.
Plastic injection molding is a highly reliable solution for producing large numbers of precise, consistent components. It’s also more efficient and cost-effective than other molding styles, in that it produces much less waste. As a result, injection molding is most often used for the manufacture of high-quality parts in high volumes.
Type of product made by plastic injection molding service :
Imagine a building material which is lightweight, durable, and doesn’t corrode; it comes in many sizes and colors and is designed for easy precise assembly. The Lego brand of building block recognized by all is made of firmer plastic granules which are heated until liquefied and then injected into metal molds in which the plastic cools and solidifies into a studded brick or other shape. But what’s important is that each brick and component is accurately molded so they’ll all fit together. It’s a precision product available in many colors, shapes, and sizes.
2. Machinery and automotive components:
Bumpers, dashboards, radio controls, cup holders, and many other elements found in cars and transportation vehicles, both interior and exterior, are made by the injection molding process.
3. The disadvantages of injection molding:
Plastic injection mold maker in China introduce that the major disadvantages of injection molding are the initial costs of the mold design, which tends to be high due to design, testing, and tooling requirements and the longer required lead times. Some custom complex parts may encounter problems during the injection molding process such as warpage or surface defects. Therefore, plastic injection parts must be designed with careful consideration to any change in geometry as they cool and the material selection to assure stability. But except this issue,its deeds outweigh its faults.
Several factors influencing injection molding:
The first thing we need to know is that the injection pressure is provided by the hydraulic system of the injection system.
The pressure of the hydraulic cylinder is transmitted to the plastic melt through the screw of the injection molding machine. Under the pressure of the plastic melt, the plastic melt enters the vertical flow channel of the mold through the nozzle of the injection molding machine (also the mainstream channel for some molds), the mainstream channel, and the split Channel, and enter the mold cavity through the gate, this process is the injection molding process, or called the filling process.
The pressure exists to overcome the resistance in the melt flow process, or conversely, the resistance in the flow process needs to be offset by the pressure of the injection molding machine to ensure that the filling process proceeds smoothly.
In the injection molding process, the pressure at the nozzle of the injection molding machine is the highest to overcome the flow resistance of the melt throughout. After that, the pressure gradually decreases along the flow length toward the front end of the melt. If the exhaust inside the mold cavity is good, the final pressure at the front end of the melt is atmospheric pressure.
Injection temperature is an important factor affecting injection pressure. The injection molding machine barrel has 5 to 6 heating sections, and each raw material has its proper processing temperature (for detailed processing temperature, please refer to the data provided by the material supplier).
The injection temperature must be controlled within a certain range. If the temperature is too low, the melt plasticization will be poor, affecting the quality of the molded parts and increasing the difficulty of the process; if the temperature is too high, the raw materials will be easily decomposed. In the actual injection molding process, the injection temperature is often higher than the barrel temperature, and the higher value is related to the injection rate and the performance of the material, up to 30 ℃.
This is due to the fact that the melt is sheared as it passes through the injection port and generates very high heat. There are two ways to compensate for this difference when doing mold flow analysis. One is to try to measure the temperature of the molten metal injection molding, and the other is to include the nozzle during modeling.
The injection time mentioned here refers to the time required for the plastic melt to fill the cavity, excluding auxiliary time such as mold opening and closing.
Although the injection time is very short and has little effect on the molding cycle, the adjustment of the injection time has a great effect on the pressure control of the gate, runner and cavity. Reasonable injection time helps the melt to fill ideally, and it is very important to improve the surface quality of the product and reduce the dimensional tolerance.
The injection time is much lower than the cooling time, which is about 1/10 to 1/15 of the cooling time. This rule can be used as the basis for predicting the total molding time of plastic parts.
In the mold flow analysis, the injection time in the analysis result is equal to the injection time set in the process conditions only when the melt is completely driven by the rotation of the screw to fill the cavity. If the pressure holding switch of the screw occurs before the cavity is filled, the analysis result will be greater than the setting of the process conditions.
4. Maintaining pressure and time.
Near the end of the injection molding process, the screw stops rotating and only advances, at which time injection molding enters the pressure holding stage. During the pressure-holding process, the nozzle of the injection molding machine continuously replenishes the cavity to fill the volume vacated by the shrinkage of the parts. If the pressure is not maintained after the cavity is filled, the part will shrink by about 25%, especially the contraction of the ribs due to excessive shrinkage. The holding pressure is generally about 85% of the maximum filling pressure, which of course should be determined according to the actual situation.
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