While the structure of a mold can vary greatly due to differences in the type and properties of the plastic, the shape and structure of the plastic product, and the type of injection molding machine, its basic structure remains consistent. A mold mainly consists of a gating system, a temperature control system, molding parts, and structural parts. Among these, the gating system and molding parts are the parts that directly contact the plastic and vary depending on the plastic and the product; they are the most complex, most variable, and require the highest level of surface finish and precision in the mold.
An injection mold is a tool for producing plastic products; it is also a tool that gives plastic products their complete structure and precise dimensions. Injection molding is a processing method used for the mass production of certain complex-shaped parts. Specifically, it refers to injecting molten plastic under high pressure into the mold cavity using an injection molding machine, where it is then cooled and solidified to obtain the molded product.
Mold Components: While the structure of a mold can vary greatly due to differences in the type and properties of the plastic, the shape and structure of the plastic product, and the type of injection molding machine, its basic structure remains consistent. A mold mainly consists of a gating system, a temperature control system, molding parts, and structural parts. The gating system and molding parts are the parts that directly contact the plastic and vary depending on the plastic and the finished product. They are the most complex, variable, and require the highest level of surface finish and precision in the molding process.
An injection mold consists of two parts: a moving mold and a fixed mold. The moving mold is mounted on the moving platen of the injection molding machine, and the fixed mold is mounted on the fixed platen. During injection molding, the moving and fixed molds close to form the gating system and cavity. When the mold opens, the moving and fixed molds separate to remove the plastic part. To reduce the heavy workload of mold design and manufacturing, most injection molds use standard mold bases.
A single parting surface injection mold separates the moving and fixed molds when opening, allowing the plastic part to be removed. This is called a single parting surface mold, also known as a two-plate mold. It is the simplest and most basic type of injection mold. It can be designed as a single-cavity injection mold or a multi-cavity injection mold as needed, and is the most widely used type of injection mold.
Double parting surface injection molds have two parting surfaces. Compared to single parting surface injection molds, double parting surface injection molds add a partially movable intermediate plate (also called a movable sprue plate, which houses the sprue, runner, and other parts and components required by the fixed mold) to the fixed mold section. Therefore, they are also called three-plate (moving plate, intermediate plate, fixed plate) injection molds. They are commonly used in single-cavity or multi-cavity injection molds with point gate feeding. During mold opening, the intermediate plate separates from the fixed platen at a fixed distance on the guide pillars of the fixed mold to allow the solidified sprue from the gating system to be removed between the two platens. Double parting surface injection molds have a complex structure, higher manufacturing costs, and difficult component machining, and are generally not used for molding large or extra-large plastic products.
Injection molds with side parting and core-pulling mechanisms require the use of laterally movable cores or sliders when the plastic part has side holes or side recesses. After injection molding, the moving mold first moves downwards a certain distance. Then, the inclined section of the bent pin fixed to the fixed mold plate forces the slider to move outwards. Simultaneously, the ejector rod of the demolding mechanism pushes the ejector plate, causing the plastic part to detach from the core.
Injection molds with movable molding components require movable molding components due to the special structure of the plastic part. These components include movable punches, movable dies, movable inserts, movable threaded cores, or rings. During demolding, these components can be removed from the mold along with the plastic part and then separated from it.
Automatic unscrewing injection molds for threaded plastic parts require automatic demolding. Rotatable threaded cores or rings can be installed on the mold. The opening action, the rotation mechanism of the injection molding machine, or a dedicated transmission device can be used to rotate the threaded core or ring, thereby ejecting the plastic part.
Runnerless injection molds refer to injection molds that use a method of insulatingly heating the runner to keep the plastic in a molten state between the injection molding machine nozzle and the cavity, so that no solidified material from the gating system is injected when the mold is opened and the plastic part is removed. The former is called an insulated runner injection mold, and the latter is called a hot runner injection mold.
