The success or failure of plastic processing largely depends on the effect of mold design and mold manufacturing quality, and plastic mold design is based on the correct design of plastic products.
Structural elements to be considered in plastic mold design include:
① Parting surface, that is, the contact surface between the female die and the male die when the die is closed. The selection of its position and form is affected by factors such as product shape and appearance, wall thickness, forming method, post-processing technology, mold type and structure, demoulding method and molding machine structure.
② Structural parts, i.e. sliding block, inclined top, straight top block, etc. of complex die. The design of structural parts is very critical, which is related to the service life, processing cycle, cost and product quality of the die. Therefore, the design of complex die core structure requires higher comprehensive ability of the designer, and pursues a simpler, more durable and more economical design scheme as far as possible.
③ Die accuracy, i.e. card avoidance, fine positioning, guide post, positioning pin, etc. The positioning system is related to the appearance quality of products, mold quality and service life. Different positioning methods are selected according to different mold structures. The positioning accuracy control mainly depends on processing, and the internal mold positioning is mainly considered by the designer to design a more reasonable and easy to adjust positioning method.
② The gating system, that is, the feeding channel from the nozzle of the injection molding machine to the mold cavity, includes the main flow channel, shunt channel, gate and cold material cavity. In particular, the selection of gate position should be conducive to filling the mold cavity with molten plastic under good flow state, and the solid runner and gate cold material attached to the product are easy to be ejected from the mold and removed during mold opening (except hot runner mold).
③ Plastic shrinkage and various factors affecting the dimensional accuracy of products, such as mold manufacturing and assembly errors, mold wear and so on. In addition, the matching of the process and structural parameters of the molding machine should also be considered when designing the compression mold and injection mold. Computer aided design technology has been widely used in plastic mold design.
What are the design of exhaust system of plastic mould?
Injection mold is an indispensable part of injection molding. We introduced the design principles of cavity quantity, gate position, hot runner, assembly drawing and material selection of injection mold. Today we will continue to introduce the design of exhaust system of plastic injection mold.
In addition to the original air in the cavity, the gas in the cavity also contains low molecular volatile gases produced by the heating or curing of injection molding materials. It is necessary to consider the sequential discharge of these gases. Generally speaking, for the mold with complex structure, it is difficult to estimate the accurate position of air lock in advance. Therefore, it is usually necessary to determine its position through die test, and then open the exhaust slot. The exhaust slot is usually opened where cavity Z is filled.
The exhaust mode is to open the exhaust slot for exhaust by using the matching clearance of die parts.
The molding of injection molded parts needs exhaust, and the demoulding of injection molded parts needs exhaust. For deep cavity shell injection molding parts, after injection molding, the gas in the cavity is blown away. In the demoulding process, a vacuum is formed between the appearance of plastic parts and the appearance of core, which is difficult to demould. If forced demoulding, the injection molded parts are easy to deform or damage. Therefore, it is necessary to introduce air, that is, between the injection molded part and the core, so that the plastic injection molded part can be demoulded smoothly. At the same time, several shallow grooves are processed on the parting surface to facilitate exhaust.
1. The template of cavity and core needs to use conical positioning block or precision positioning block. The guide is installed on four sides or around the mold.
2. The contact surface between the a plate of the mold base and the reset rod needs to use a flat pad or a round pad to avoid damaging the a plate.
3. The perforated part of the guide rail shall be inclined more than 2 degrees to avoid burrs and burrs. The perforated part shall not be of thin blade structure.
4. In order to prevent dents in injection molded products, the width of stiffener shall be less than 50% of the wall thickness of appearance surface (ideal value < 40%).
5. The wall thickness of the product shall be the average value, and at least sudden change shall be considered to avoid dents.
6. If the injection molded part is electroplated, the movable mold also needs polishing. Polishing requirements are second only to mirror polishing requirements to reduce the generation of cold materials in the forming process.
7. Ribs and grooves in poorly ventilated cavities and cores must be embedded to avoid dissatisfaction and scorch marks.
8. Inserts, inserts, etc. shall be positioned and fixed firmly, and the disc shall be provided with anti rotation measures. It is not allowed to pad copper and iron under the insert. If the welding pad is high, the welded part shall form a large surface contact and be ground flat.
Post time: Mar-10-2022
