The structure of the mold, although due to the plastic varieties and properties, the shape and structure of the plastic products and the type of injection machine and so on, but the basic structure is the same. The mold is mainly composed of pouring system, temperature control system, molding parts and structural parts. Among them, the pouring system and molding parts are in direct contact with the plastic part, and with the plastic and products and changes, is the most complex mold, the biggest changes, the requirements of processing finish and accuracy of the highest part.
The injection mold consists of two parts: the moving mold and the fixed mold, the moving mold is installed on the moving 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 moving mold and the fixed mold are closed to form the pouring system and the cavity, and when the mold is opened, the moving mold and the fixed mold are separated in order to take out the plastic products. In order to reduce the heavy workload of mold design and manufacturing, most of the injection mold adopts the standard mold frame.
One, the casting system
The casting system refers to the part of the runner before the plastic enters the cavity from the injection nozzle, including the main flow channel, the cold material hole, the manifold and the gate, etc. The casting system is the part of the runner before the plastic enters the cavity from the injection nozzle.
The pouring system, also known as the runner system, is a set of feed channels that lead the plastic melt from the injection nozzle to the cavity, usually consisting of the main flow channel, manifold, gate and cold material hole. It is directly related to the molding quality of plastic products and production efficiency.
1, the main stream
It is the mold connecting the injection molding machine nozzle to the manifold or cavity of a section of the channel. The top of the main stream channel is concave in order to connect with the nozzle. Main stream inlet diameter should be slightly larger than the diameter of the nozzle (0.8mm) to avoid overflow, and to prevent the two due to inaccurate articulation and blockage. Inlet diameter according to the size of the product, generally 4-8mm. the diameter of the main stream channel should be expanded inward at an angle of 3 ° to 5 °, in order to runners flabbergasted demolding.
2, cold material cavity
It is located in the end of the main channel of a cavity, used to capture the end of the injection nozzle between the two injections of the cold material produced, so as to prevent the manifold or gate blockage. If the cold material is mixed into the cavity, it is easy to produce internal stress in the product. The diameter of the cold material cavity is about 8-10mm and the depth is 6mm, in order to facilitate the release of the mold, its bottom is often borne by the mold release lever. The top of the demolding rod should be designed into a zigzag hook shape or set up sink grooves, so that when the demolding can be pulled out of the mainstream channel smoothly superfluous.
3, manifold
It is a multi-slot mold connecting the main channel and each cavity channel. In order to make the melt to fill the cavity with equal speed, the manifold should be arranged in the mold symmetrical and equidistant distribution. The shape and size of the manifold cross-section of the plastic melt flow, product release and the ease of mold manufacturing have an impact. If according to the flow of equal amount of material, then the circular cross-section of the runner resistance is minimized. But because of the cylindrical runner surface is small, on the cooling of the manifold flotsam is unfavorable, and this manifold must be opened in the two halves of the mold, both labor-intensive and not easy to align. Therefore, often used is a trapezoidal or semi-circular cross-section of the manifold, and opened in half of the mold with the mold release lever. The runner surfaces must be polished to reduce flow resistance and provide faster mold filling. The size of the runner is determined by the type of plastic, the size and thickness of the part. For most thermoplastics, the manifold cross-section width are not more than 8mm, very large up to 10-12mm, very small 2-3mm. in order to meet the needs of the premise should try to reduce the cross-sectional area, in order to increase the manifold flabbergasted and prolong the cooling time.
4, gate
It is connected to the main flow channel (or manifold) and the cavity of the channel. The cross-sectional area of the channel can be equal to the main flow channel (or manifold), but usually are reduced. Therefore, it is the smallest part of the cross-sectional area in the whole runner system. The shape and size of the gate has a great impact on the quality of the product.
The role of the gate is:
A, to control the speed of the material flow:
B, in the injection can be stored in this part of the melt early condensation to prevent backflow:
C, so that the melt through the stronger shear and increase the temperature, thus reducing the apparent viscosity to improve the fluidity:
D, to facilitate the product and the flow of the system separation. The design of gate shape, size and position depends on the nature of the plastic, the size and structure of the product. The general cross-section shape of the gate is rectangular or round, the cross-sectional area should be small and short length, not only based on the above role, but also because the small gate is easier to get bigger, while the big gate shrinkage is very difficult. The location of the gate should generally be chosen at the thickest part of the product without affecting its appearance. The design of the gate size should take into account the nature of the plastic melt. Cavity it is molding plastic products in the space. The components used to form the cavity are collectively referred to as molding parts. Each molding parts often have special names.
The molding parts that form the shape of the product are called concave mold (also known as negative mold), and those that form the internal shape of the product (such as holes, slots, etc.) are called cores or convex molds (also known as positive mold). When designing molding parts, the first thing to do is to determine the overall structure of the cavity according to the performance of the plastic, the geometry of the product, the size tolerance and the use of the requirements. Secondly, according to the determined structure to choose the parting surface, the location of the gate and vent and the way to release the mold. Finally, according to the size of the control product to carry out the design of the parts and determine the combination between the parts. Plastic melt into the cavity has a high pressure, so the molding parts should be reasonable selection of materials and strength and rigidity of the check. In order to ensure that the surface of the plastic product is clean and beautiful and easy to take off the mold, where the surface in contact with plastic, its roughness Ra>0.32um, and to be corrosion-resistant. Molded parts are generally heat-treated to improve the hardness, and the selection of corrosion-resistant steel manufacturing.
Two, temperature control system
In order to meet the requirements of the injection process on the mold temperature, the need for temperature control system to regulate the temperature of the mold. For thermoplastic injection mold, mainly designed cooling system to make the mold cooling. Mold cooling is commonly used in the mold cooling water channel, the use of circulating cooling water to take away the heat of the mold; mold heating in addition to the use of cooling water channel hot water or steam, but also in the mold and around the installation of electric heating elements.
Three, molding parts
Molding parts refers to the shape of the product constitutes a variety of parts, including the moving mold, mold and cavity, core, molding rod and exhaust port. Molding parts are composed of core and concave mold. The core forms the inner surface of the product, and the concave mold forms the shape of the outer surface of the product. After closing the mold, the core and cavity form the cavity of the mold. According to the process and manufacturing requirements, sometimes the core and the concave mold by a number of pieces combined, sometimes made into a whole, only in the easy to damage, difficult to process the parts using inserts.
1, exhaust port
It is opened in the mold of a groove-shaped outlets, used to discharge the original and the melt into the gas. When the melt is injected into the cavity, the original air stored in the cavity and the gas brought in by the melt must be discharged at the end of the material flow through the exhaust port to the outside of the mold, otherwise it will make the products with air holes, poor joints, filling of the mold is not enough, and even the accumulation of air due to compression to produce high temperature and will be burned products. In general, the air vent can be located in the cavity at the end of the melt flow, can also be located on the parting surface of the mold. The latter is in the concave mold side of the opening depth of 0.03-0.2mm, 1.5-6mm wide shallow groove. In the injection, the vent hole will not have a lot of melt oozing out, because the melt will be cooled and solidified in the place to block the channel. Do not open the air vent to the operator to prevent the melt from accidentally spraying out and injuring people. In addition, you can also use the ejector rod and ejector hole clearance, the top block and stripper plate and core clearance to exhaust.
Four, structural parts
It refers to the composition of the mold structure of the various parts, including: guiding, demolding, core extraction, as well as a variety of parts of the parting. Such as before and after the clamping plate, before and after the buckle template, pressure plate, pressure column, guide column, release template, mold release rod and return rod and so on.
1, guiding parts
In order to ensure that the moving mold and fixed mold in the mold can be accurately centered, in the mold must be set up guiding parts. In the injection mold is usually used in four groups of guide pillar and guide sleeve to form the guide parts, sometimes also need to be set in the moving mold and fixed mold respectively coincide with the inner and outer cone to assist in positioning.
2, the launch mechanism
In the molding process, the need to launch the mechanism of the plastic products and their congealed material in the runner out or pull out. Push out the fixed plate and push plate to clamp the push rod. In the push rod is also generally fixed in the reset lever, the reset lever in the moving and fixed mold mold to make the push plate reset.
3, the side of the core mechanism
Some plastic products with side concave or side holes, before being launched must first be lateral parting, pull out the side of the core can be successfully demolded, this time the need to set up the side of the core mechanism in the mold.
The injection device is a device that injects the resin material into the mold after it is melted by heat. The resin is squeezed into the barrel from the head and the melt is conveyed to the front of the barrel by the rotation of the screw. In that process, the resin material inside the barrel is heated under the action of the heater, and the resin becomes molten under the action of the shear stress of the screw, which will be equivalent to the molded product and the main flow channel, and the molten resin of the manifold is retained at the front end of the barrel (called metering), and the screw's keeps moving forward to shoot the material into the mold cavity. When the molten resin flows in the mold, it is necessary to control the moving speed of the screw (injection speed) and control the pressure (holding pressure) with the resin after it fills the mold cavity. When the screw position and injection pressure reaches a certain value we can switch from speed control to pressure control.