Injection mold is a metal model tool for producing plastic products by injection molding process, it is also a tool for giving plastic products complete structure and precise dimensions. Injection process is to inject molten material into mold cavity through high pressure, obtain plastic products after cooling and solidification. According to its molding characteristics, it can be divided into thermosetting plastic molds and thermoplastic plastic molds. Although structure of injection mold is varied due to variety and performance of plastic, shape and structure of plastic product, type of injection molding machine, basic structure is same. A complete injection mold is divided according to structural parts and component functions, mainly consisting of mold base system, gating system, ejection system, demoulding system, cooling system, hydraulic system, electrical system, exhaust system, lifting system and other systems. Each system complements each other, only when each system achieves the best combination can normal use of mold and precision of molded product be guaranteed.
Mold base system refers to mold base and its auxiliary parts that play the role of fixing, supporting, installing, guiding, etc. in mold; gating system refers to part of runner before plastic melt enters cavity from nozzle (including main runner, cold slug, runner and gate.) and its related parts, standard parts, etc.; ejection system refers to device that pushes product out after injection molding to make it out of mold and all parts or components related to product ejection; demoulding system refers to mechanism that ensures smooth demoulding of undercut of product when mold is opened and closed or pushed out; cooling system refers to system that controls temperature of mold in mold to ensure smooth filling of plastic melt, solidification and shaping of product, such as water collection block components, water nozzles, water pipes, etc.; hydraulic system refers to all systems in mold that are related to oil circuit that controls action of mold, such as oil circuit components of hydraulic core puller; electrical system refers to system of all electrical devices or components that control action of mold, such as travel safety switch system, etc.; exhaust system refers to channel or components, devices, etc. that allow exhaust gas in mold to be discharged smoothly during injection molding; lifting system refers to components or parts that can lift mold, such as lifting module components, etc.; other systems refer to wear-resistant blocks, support plates, handrails and other devices or parts that are not included in aforementioned systems.

Due to complex structure of mold, small number of standard parts in the total number of parts, high requirements of mold manufacturing and product production process, in order to reduce limitation of design work on designer's personal ability and experience, premise of realizing rapid design of mold is to digitize mold design data, stored in computer in the form of a database. Mold design database includes three parts: standard parts library, parts parameter library and document attachment library. Three databases adopt relational database model and are associated with foreign keys as basis for rapid design and experience reference.

Based on structure and process characteristics of above-mentioned common molds, mold system is divided into mold base, gating, ejection, demoulding, cooling, hydraulic, electrical, exhaust, lifting and other subsystems according to functional purpose, then subsystems are divided according to structure and part types into several modules, based on which a multi-standard system parts library is established. Content of sub-modules of standard parts library is shown in Figure 1.

 

Molds can be divided into plastic molds, extrusion molds, die-casting molds, rubber molds, punching molds, etc. according to different molding processes. Various types of molds have independent structure and process characteristics. According to principle of modular development of injection molds, corresponding modules can be developed according to various types of mold structures, process characteristics, corresponding production design standard requirements, design and manufacturing experience data.

Properties of parts are shown in Table 1. In Table 1, data required by parts in mold life cycle are defined. Data in Table 1 will be combined with specific parameter values of parts in the form of wildcard replacement, and then be used by software written into 3D model.
Component Properties

Size parameters of parts are shown in Table 2, which are used to assign values to expressions in 3D model. Each standard part corresponds to a separate size parameter table, and field of table is name of expression.
Content in Table 2 is optional range of expression value. Software presents an optional drop-down list or a restricted input box. Designer adjusts parameters according to required size parameter table. Due to complex assembly levels of parts of mold, in order to achieve maximum reuse of standard parts, an associated parameter table is also designed to define size parameter relationship between sub-parts of different levels and assembly relationships within same part. Each component has an associated parameter table, primary key is ID of associated compone remaining fields are affected expressions.

 

Document attachment library uses form of a file system to store component-related explanatory documents, example pictures, etc., and defines a document path table in component parameter library, which is used to associate component with corresponding file. Primary key is component ID, and the second field is document path.

Build 3D/2D design function software based on mold design database, and establish an information system output interface. The entire rapid design software architecture is like building blocks. Different customer databases and design function software can be selected by permutation and combination, and customized rapid mold design software can be built for different needs.
Modular rapid design software is based on component database, used in 3D modeling environment and 2D drawing environment of 3D design software, as shown in Figure 2. Designer determines standard system to be adopted. As shown in Figure 3, upper left side is subsystem directory, that is, directory tree of all modules and components under system. Click directory tree to switch between different components; upper right side is parameter selection area. Constructed according to component parameter library, including 3 columns of parameter name, parameter selection range, and parameter description; Constructed according to component parameter library, including 3 columns of parameter name, parameter selection range, and parameter description; below is component description diagram, loaded by document attachment library, providing design-related picture descriptions, and presenting a preview wireframe in 3D modeling environment according to designer's selection results.
Part features and expression data of 3D model in standard parts library and related constraint data in part parameter library provide a reliable data source for 2D drawing. 2D module in rapid design software can identify and mark more than 85% of drawing features. Since customer requirements and design information have been obtained in 3D design stage, only a few user operations are required to output drawings during 2D drawing. An example of output effect is shown in Figure 4. In same principle, data source of bill of materials, which is crucial in mold manufacturing and enterprise management, is also imported into 3D model of mold during 3D design stage, and users can directly export bill of materials as needed, as shown in Figure 5.