Author: MULAN -Plastic Molding Manufacturer
Shanghai injection mold processing consists of a moving mold and a fixed mold. The movable mold is installed on the movable template of the injection molding machine, and the fixed mold is installed on the fixed template of the injection molding machine. During injection molding, the movable mold and the fixed mold are closed to form a gating system and cavity. When the mold is opened, the movable mold is separated from the fixed mold to take out the plastic product.
Injection molds mostly use standard mold bases to reduce heavy mold design and manufacturing workload. The following editor from Shanghai Plastic Mold Factory Xingye will introduce the steps of Shanghai injection mold processing: Gating system The gating system refers to the part of the flow path before the plastic enters the cavity from the nozzle, including the main flow path, cold material cavity, runner and pouring mouth. The gating system, also known as the runner system, is a set of feed channels that guide the plastic melt from the nozzle of the injection machine to the cavity. It usually consists of a main channel, a runner, a gate and a cold cavity.
It is directly related to the molding quality and production efficiency of plastic products. The sprue is the channel that connects the nozzle of the injection molding machine to the runner or cavity in the mold. The top of the main channel is concave and connected with the nozzle.
The mainstream inlet diameter should be slightly larger than the nozzle diameter (0.8 mm) to avoid overflow and prevent clogging due to inaccurate connections. The inlet diameter is determined according to the size of the product, generally 4-8mm. The diameter of the main channel should be expanded inwards by 3-5°, for demoulding.
The cold material cavity is a cavity at the end of the sprue, which is used to catch the cold material generated between two injections at the end of the nozzle, so as to prevent the runner or gate from being blocked. Once the cold material is mixed into the cavity, the product is prone to internal stress. The diameter of the cold feed hole is about 8-10 mm, and the depth is 6 mm.
In order to facilitate demoulding, the bottom is often borne by the demoulding rod. The top of the demoulding rod should be designed as a zigzag hook or groove, so that the debris in the main channel can be pulled out smoothly during demoulding. In the multi-slot mold, the runner is the channel connecting the sprue and each cavity.
In order to make the melt fill various cavities at a constant speed, the arrangement of the runners on the plastic mold should be symmetrical and equidistant. The shape and size of the cross-section of the runner have an impact on the flow of the plastic melt, the difficulty of product demoulding and mold manufacturing. If the flow is equal, the flow path resistance of the circular section is the least.
However, because the specific surface of the cylindrical runner is small, it is not conducive to the cooling of the debris in the runner, and the runner must be set on the two halves of the mold, which is laborious and difficult to align. Therefore, trapezoidal or semicircular cross-section runners are often used, which are set on half of the mold with ejector pins. The surface of the runner must be polished to reduce flow resistance and provide faster filling speed.
The size of the runner depends on the type of plastic, the size and thickness of the product. For most thermoplastics, the cross-sectional width of the runner does not exceed 8m, the super-large one can reach 10-12m, and the ultra-small one can reach 2-3m. Under the premise of meeting the needs, the cross-sectional area should be reduced as much as possible to increase the fertilizer in the shunt channel and prolong the cooling time.
Gate It is a channel connecting the main channel (or runner) and the cavity. The cross-sectional area of the channel can be equal to the main channel (or runner), but it is usually reduced. Therefore, it is the part with the smallest cross-sectional area in the entire runner system.
The shape and size of the gate have a great influence on the product quality. The function of the gate is: A. Control the material flow rate: B. During the injection process, due to the early solidification of this part of the melt, it can prevent backflow: C. The passing melt is strongly sheared, and the temperature rises, thereby reducing the surface Apparent viscosity, improve fluidity: It is convenient to separate the product from the runner system. The shape, size and position of the gate depends on the nature of the plastic, the size and structure of the product.
Generally, the cross-sectional shape of the gate is rectangular or circular, the cross-sectional area is small, and the length is short, not only based on the above functions, but also because small gates are easier to enlarge, while large gates are more difficult to shrink. The gate position should generally be selected at the place where the product is the thickest and does not affect the appearance. The design of the gate size should consider the properties of the plastic melt.
The cavity is the space of the plastic product in the mold. The components that make up the cavity are collectively called the molded part. Each molding part often has a special name.
The molding part that forms the shape of the product is called the die (also called the female die), and the molding part that forms the internal shape of the product (such as holes, grooves, etc.) is called the core or punch (also called the male die). When designing molded parts, the overall structure of the cavity must first be determined according to the properties of the plastic, the geometric shape of the product, the dimensional tolerance and the use requirements. Secondly, according to the determined structure, select the location of the parting surface, gate and vent hole and the demoulding method.
Finally, design parts according to the size of the control product, and determine the combination of parts. When the plastic melt enters the cavity, the pressure is very high, so the material and strength and rigidity of the molded parts should be reasonably selected. In order to ensure that the surface of the plastic product is beautiful and easy to release the mold, the surface roughness in contact with the plastic is Ra> 0.32um, should be corrosion resistant.
Formed parts are generally heat-treated to increase hardness and made of corrosion-resistant steel. Temperature adjustment system In order to meet the mold temperature requirements of the injection process, a temperature adjustment system is needed to adjust the mold temperature. Thermoplastic injection mold is mainly designed cooling system to cool the mold.
The common method of mold cooling is to set a cooling water channel in the mold, and use the circulating cooling water to take away the heat of the mold; in addition to the hot water or steam in the cooling water channel, the heating of the mold can also install electric heating elements inside and around the mold. For more information about injection molding in Shanghai, please visit the official website of Xingye: http://www.dgxingyesj.com/.