Functions of an Injection Mould PDF

Injection molds are the most expensive...

Injection molds are the most expensive molds used in plastics processing with very long lead times required for their design and fabrication. A mold is defined as a cavity in which a substance is shaped or the frame on or Explain the advantages and around which an object is constructed. disadvantages of a three-plate mold. Introduction The main functions of a mold are to impart List three advantages and three limitations the desired shape to the plasticized of using hot runner molds. Exercises polymer and to cool the molded part. Describe the primary function of a stack Injection molds are made up of the cavities mold. and cores, as well as the base in which the cavities and cores are mounted. The mold base is the main part of a mold, assembled from a diversity of steel plates and parts. There are various types of thermoplastic molds, including compression molds, transfer molds, injection molds, extrusion Selecting an appropriate mold base is an molds, blowing molds, and vacuum molds. important step in mold production, as the size of the selected mold bases directly influences the quality of the mold. Injection molds are the focus of this chapter. Mold Bases The selection of the mold base depends on Classification of Injection Molds Injection molding is a process of forming factors such as part structure, mold components in a closed mold from a parting requirements, cost, and the type of thermoplastic material that is conveyed gate. under pressure from an auxiliary chamber (the injection unit) through runners and gates into the closed cavity or cavities. Different mold base types, such as side Selection Principles gate, point gate, and simplified point gate, are suitable for different applications and requirements. An injection mold basically consists of two parts: a stationary half (cavity plate) and a moving half (core plate). There are several types of injection molds, including two-plate molds, three-plate Both mold halves are provided with molds, stack molds, side-acting molds, and cooling channels. unscrewing molds. The parting line is the separating line A two-plate mold has only one parting line. between the two mold halves. If a runner is used, it is connected to the The injected material is transferred Functions of an molded product and requires manual through a central feed channel called a removal and separation after the part is sprue. ejected. Two-Plate Mold Injection Mould In multi-cavity molds, the sprue feeds the This type of injection mold is the least polymer melt to a runner system. expensive to make and is commonly used for parts with relatively simple geometries. The core plate holds the main core, which Mold Construction establishes the inside configuration of the A three-plate mold has two parting lines, part. one for the runner system and one for the molded product. The core plate has a backup/support plate, which is supported by pillars against the When the injection mold opens, the runner U-shaped structure known as the ejector is automatically separated from the Core Plate housing. product to allow separate handling. The U-shaped structure, which is bolted to This eliminates the need for manual Three-Plate Mold the core plate, provides the space for the separation and removal of the sprue and ejection stroke. runner system, which may be fed directly to a recycling system. Mold design is influenced by factors such as mold life, cost restraints, component This type of mold is more expensive than detail, component material, post-molding the two-plate mold. operations, mold-making techniques, quantity, and molding machine. Mold Design Considerations In a hot runner mold, the runner system is heated up, and only the molded part is ejected. The stationary half of the mold includes components like the locating ring, sprue Hot runner molds have a higher mold Hot Runner Mold bush, top plate, cavity/A plate, and guide manufacturing cost and maintenance cost bushes. but a lower part manufacturing cost and cycle time compared to cold runner molds. Types of Injection Molds The moving half of the mold includes Mold Components components like the core insert, core/B A stack mold can have two, three, or four plate, guide pins, baffles, return pins, levels. ejector block/spacer, ejector retainer plate, ejector plate, and bottom plate. The advantage of the stack mold is that it can generally produce a larger number of products versus a two or three-plate mold utilizing the same machine clamp tonnage. Stack Mold The disadvantage is that it requires a molding press with much greater daylight opening to accommodate the mold height. This type of injection mold is much more expensive and takes longer time to build. Side-acting molds are used for molding components with external depressions or holes parallel to the parting plane. Undercuts prevent molded parts from being removed from the cavity in the axial direction. Side-Acting Mold (Slider) Side cores mounted on slides, activated by angle pins or air/hydraulic cylinders, are used to provide the side action needed to release the part. Unscrewing molding is a unique injection molding process with mold technology that includes movement and rotation to produce threaded components. Some plastic parts such as caps and closures with detailed threads cannot be Unscrewing Mold removed using standard methods and need to be carefully unscrewed from the mold to avoid damaging the threads.