Plastic Mold Design

Author: Chief Editor: Bu Jianxin
Publisher:
Publish Date: 2004-03-05
Features:
Fragment: In the modern plastic forming and processing industry, correct processing technology, efficient equipment, and advanced molds are the three major important factors affecting plastic part production. The plastic mold plays a crucial role in realizing the plastic forming and processing technology and ensuring the quality of plastic parts. Only by equipping high-efficiency automated equipment with molds suitable for automated production can its efficiency be fully utilized. The development and updating of products are based on the updating of molds. With the continuous development of the plastic industry, the requirements for the variety, quantity, and quality of plastic products will become increasingly high, and the requirements for plastic molds will also rise accordingly, thus promoting the continuous development of the plastic mold industry. The requirements for plastic molds are:
(1) To produce qualified plastic parts that meet the requirements in terms of shape, size, appearance, physical properties, and mechanical properties.
(2) Automatic and efficient, with convenient operation.
(3) Reasonable structure, easy manufacturing, and low mold-making cost.
(4) Minimize the workload of plastic part finishing and secondary processing.
(5) The structure and material selection of the mold should meet the requirements for service life.
II. Classification of Plastic Molds
There are many methods for classifying plastic molds, and different plastic forming methods use plastic molds with different principles and structures. According to the forming method, plastic molds can be classified into the following categories:
1. Injection Molding Molds
Injection molding molds can also be called injection molds or injection molds. Injection molding involves adding plastic raw materials from the hopper of the injection machine to the heated barrel. Under the drive of the injection machine screw or plunger, the molten plastic passes through the injection machine nozzle and the mold's gating system into the closed mold cavity, filling it. After pressure holding and cooling, it hardens and takes shape. Then, the mold is opened to remove the plastic part. The molds used in injection molding are called injection molding molds. Injection molding can not only form complex and high-precision plastic parts but also has high production efficiency and automation. It is mainly used for the forming of thermoplastic plastics and is one of the main methods for thermoplastic plastic forming. It can also be used for the forming of thermosetting plastics. Injection molds account for a significant proportion in plastic molds.
2. Compression Molding Molds
Compression molding molds can also be called compression molds or compression molds. Compression molding is mainly used for the forming of thermosetting plastics and can also be used for the forming of thermoplastic plastics. When forming thermosetting plastics, the measured plastic is directly added to the heated mold's feed chamber and (or) cavity. Then, the mold is closed, and the plastic melts and flows under the combined effects of heat and pressure, filling the cavity. Under further heating, the plastic molecules undergo crosslinking reactions and gradually harden and take shape. Then, the mold is opened, and the plastic part is removed. The molds used in compression molding are called compression molding molds.
3. Transfer Molding Molds
Transfer molding molds can also be called transfer molds. Transfer molding is mostly used for the forming of thermosetting plastics. The plastic raw materials are added to the preheated feed chamber, and then pressure is applied through a plunger. Under the action of high temperature and pressure, the plastic melts and passes through the mold's gating system into the closed cavity. In the mold cavity, it continues to harden and take shape under heat and pressure. Then, the mold is opened, and the plastic part is removed. The molds used in transfer molding are called transfer molding molds.
4. Extrusion Molding Molds
Extrusion molding molds are also known as dies. Extrusion molding can form almost all thermoplastic plastics and some thermosetting plastics. When forming thermoplastic plastics, the plastic raw materials are added from the hopper of the extruder to the heated barrel. The rotation of the screw melts the plastic, and under a certain pressure, it is extruded through a die with a specific cross-sectional shape. Then, it is cooled and takes shape at a lower temperature to obtain continuous materials with the desired cross-sectional shape. The molds used in extrusion molding are called extrusion molding molds.
5. Blister Molding Molds
Blister molding involves obtaining plasticized tubular billets through extrusion or injection, placing them in the mold cavity while still hot, and introducing compressed air into the billet to expand it and press it against the mold wall. After cooling and taking shape, hollow plastic parts are obtained. The molds used in blister molding are called blister molding molds.
6. Vacuum and Compressed Air Forming Molds
Vacuum and compressed air forming is also known as thermoforming. During forming, plastic sheets or films are heated and softened, and their periphery and the mold periphery are brought into close contact. By using methods such as vacuum extraction or introducing compressed air, the plastic sheets or films are pressed against the convex or concave molds. After cooling and taking shape, plastic parts are obtained. The molds used in vacuum and compressed air forming are called vacuum and compressed air forming molds.
In addition to the above types of plastic molds, there are also casting molds, foam plastic forming molds, etc.
III. Nature, Tasks, and Requirements of This Course
"Plastic Mold Design" is an important professional course for plastic forming and processing majors and mold majors. In recent years, some mechanical engineering majors have also added mold design courses to meet the demand for mold technology talents in national economic development. Through the study of this course, students should achieve the following requirements:
(1) Understand the design requirements for plastic parts in injection molding, compression molding, and transfer molding, be able to analyze the advantages and disadvantages of plastic part design based on different plastics and forming methods, propose improvement solutions for unreasonable parts, and perform general plastic part design.
(2) Master the principles, characteristics, and design calculation methods of common structures in injection molds, be able to independently design injection molds with general structures.
(3) Be familiar with the typical structures, common types, and characteristics of thermosetting plastic compression molding molds, transfer molding molds, and injection molding molds.
(4) Be familiar with the common structural types and characteristics of thermoplastic plastic extrusion molding molds, and be able to design simple die head structures.
(5) Understand the process of trial molding, be able to analyze the causes of various defects in plastic parts and propose reasonable solutions.
(6) Understand the requirements of mold parts for mold materials, be able to reasonably select mold materials and heat treatment methods.