Main Classifications of Plastic Molds
Based on different molding methods, plastic processing molds can be classified into different types corresponding to different process requirements. These mainly include injection molding molds, extrusion molding molds, vacuum forming molds, and high-density polystyrene molding molds.
1. Plastic Injection Molds
These are the most commonly used molding molds in the production of thermoplastic parts. The processing equipment for plastic injection molds is a plastic injection molding machine. The plastic is first heated and melted in the heating barrel at the bottom of the injection machine. Then, driven by the screw or plunger of the injection machine, it enters the mold cavity through the injection nozzle and the mold's gating system. The plastic cools and hardens, and the product is obtained by demolding. Its structure typically consists of molding components, a gating system, guiding components, an ejection mechanism, a temperature control system, a venting system, and supporting components. The manufacturing material is usually plastic mold steel, with commonly used materials including carbon structural steel, carbon tool steel, alloy tool steel, and high-speed steel. Injection molding is typically only suitable for the production of thermoplastic products. Plastic products manufactured using injection molding are extremely diverse, ranging from everyday consumer goods to complex machinery, electrical appliances, and transportation parts. It is the most widely used processing method in plastic product manufacturing.
2. Plastic Compression Molds
These include two types of molds: compression molding and injection molding. They are primarily used to mold thermosetting plastics, and the corresponding equipment is a compression molding machine. In compression molding, based on the properties of the plastic, the mold is heated to the molding temperature (generally 103°C–108°C). Then, metered compression molding powder is placed into the mold cavity and feeding chamber. The mold is closed, and the plastic softens and flows under high heat and pressure, solidifying and setting after a certain time to form the desired product shape. Injection molding differs from compression molding in that it has a separate feeding chamber. Before molding, the mold is closed, and the plastic is preheated and becomes viscous in the feeding chamber. Under pressure, it is then extruded into the mold cavity and hardened. Compression molds are also used to mold certain special thermoplastics, such as difficult-to-melt thermoplastics (e.g., polyvinyl fluoride) blanks (cold pressing), high-optical-performance resin lenses, and slightly foamed nitrocellulose automotive steering wheels. Compression molds mainly consist of a cavity, feeding cavity, guiding mechanism, ejection components, and heating system. Injection molds are widely used in the encapsulation of electrical components. The materials used in manufacturing compression molds are basically the same as those used in injection molds.
3. Plastic Extrusion Molds
These are molds used to produce continuous-shaped plastic products, also called extrusion die heads. They are widely used in the processing of pipes, rods, monofilaments, sheets, films, wire and cable sheathing, and profiles. The corresponding production equipment is a plastic extruder. The principle is that solid plastic melts and plasticizes under heating and pressure from the rotating screw of the extruder, and then passes through a die of a specific shape to produce continuous plastic products with the same cross-section as the die. The main materials used in their manufacture include carbon structural steel and alloy tools. Some extrusion molds also have wear-resistant materials such as diamond embedded in parts requiring wear resistance. Extrusion molding processes are typically only applicable to the production of thermoplastic products, and their structure differs significantly from injection molds and compression molds.
4. Plastic Blow Molding Molds
These molds are used to form hollow plastic containers (such as beverage bottles, daily chemical products, and various packaging containers). Blow molding methods, based on their process principles, mainly include extrusion blow molding, injection blow molding, injection stretch blow molding (commonly known as "injection stretch blow"), multi-layer blow molding, and sheet blow molding. The equipment used for blow molding hollow products is usually called a plastic blow molding machine. Blow molding is only suitable for the production of thermoplastic products. Blow molding molds have a relatively simple structure, and the materials used are mostly carbon fiber.
5. Plastic Vacuum Forming Mold
This type of mold uses plastic sheets or plates as raw materials to form simple plastic products. The principle involves using vacuum forming or compressed air molding to deform the plastic sheet or plate, which is fixed to a concave or convex mold, and then adhere it to the mold cavity to obtain the desired product. It is mainly used in the production of packaging products for daily necessities, food, and toys. Because the forming pressure is relatively low, vacuum forming molds are often made of cast aluminum or non-metallic materials, resulting in a relatively simple structure.
6. High-Expansion Polystyrene Molding Mold
This type of mold uses expandable polystyrene (a bead-like material composed of polystyrene and a foaming agent) to form various shapes of foam plastic packaging materials. The principle is that expandable polystyrene can be steam-formed within the mold. There are two types: simple manual molds and hydraulic press direct-flow foam plastic molds. These are mainly used to produce packaging products for industrial applications. Materials used to manufacture this type of mold include cast aluminum, stainless steel, and bronze.
