General regulations for design and drawing of injection molds
Injection mold design drawings are crucial technical documents for mold design and manufacturing. They embody mold design concepts and serve as the foundation for mold processing, assembly, inspection, and maintenance. To ensure the standardization, readability, and consistency of mold drawings, injection mold design drawings must adhere to a series of general regulations, including drawing format, view representation, dimensioning, technical requirements, and standard component annotation. These regulations not only improve design efficiency and reduce design errors, but also facilitate effective communication between designers, manufacturers, and inspectors, ensuring mold quality.
Drawing formats and sizes must comply with national standards to ensure uniformity and standardization. According to GB/T 14689-2008, “Formats and Formats of Technical Drawings,” injection mold design drawings are available in five formats: A0 (841mm × 1189mm), A1 (594mm × 841mm), A2 (420mm × 594mm), A3 (297mm × 420mm), and A4 (210mm × 297mm). The appropriate format should be selected based on the size and complexity of the mold. Drawings must have a title bar and detail bar. The title bar, located in the lower right corner of the drawing, contains information such as the mold name, drawing number, scale, design unit, designer, and reviewer. The detail bar, located above the title bar, contains information such as the mold component serial number, name, quantity, material, and specifications, in a bottom-up order, to facilitate component inventory and procurement. The formats of the drawing’s borders, title bars, and detail columns must be unified. Use thick solid lines for the borders and thin solid lines for the title bars and detail columns to ensure that the drawings are neat and orderly.
Drawings must clearly and completely demonstrate the mold structure and component shapes, adhering to national standard projection rules. Assembly drawings for injection molds should utilize basic views such as the front, top, and side views. Auxiliary views such as sectional views, cross-sections, and enlarged details can be added as needed to illustrate the mold’s internal structure, the assembly relationships between components, and key details. For example, key components such as the mold cavity, core, gating system, and ejector mechanism must be clearly shown in sectional views, with their structural dimensions and relative positions accurately defined. For complex mold parts (such as ejector rods and sliders), part drawings are required. The views selected for these part drawings should fully demonstrate the part’s internal and external shapes and dimensions, avoiding unnecessary view overlap. The view scale should be appropriately selected based on the size of the part. Common scales include 1:1, 1:2, 1:5, and 2:1. The scale should be indicated in the title bar or below the view to ensure a clear relationship between the dimensions on the drawing and the actual dimensions.
Dimensioning must be accurate, complete, and clear, meeting the precision requirements of mold manufacturing. Dimensioning for injection molds should comply with GB/T 4458.4-2003, “Methods for Dimensioning Mechanical Drawings,” ensuring that critical dimensions of each part (such as cavity dimensions, core dimensions, and mating dimensions) are clearly marked to avoid omissions. Dimensions should be marked in millimeters (mm) without unit symbols. Mold assembly dimensions (such as the fit between guide pins and guide bushings, and the fit between ejector pins and ejector holes) must be labeled with the tolerance grade and fit type. For example, labeling a guide pin diameter as φ20H7 and a guide bushing hole diameter as φ20g6 indicates a basic hole clearance fit. The working dimensions of the cavity and core must be calculated and determined based on the part’s dimensions and shrinkage, and tolerances must be indicated to ensure dimensional accuracy. Dimensioning should avoid duplicate markings and closed dimension chains. Important dimensions should be marked directly to facilitate processing and inspection. Parameters such as the tilt angle of the ejector and the travel of the slide must be clearly marked on the drawing to ensure the assembly accuracy of moving parts.
Technical requirements are an integral part of injection mold design drawings. They describe the mold’s manufacturing accuracy, surface quality, heat treatment requirements, and assembly requirements to ensure the mold meets performance requirements. Technical requirements are typically indicated in the upper right corner of the drawing or above the title bar, using concise and clear text. Manufacturing accuracy requirements include the mold’s parting surface flatness, the coaxiality of the guide pin and guide bushing, and the dimensional accuracy of the cavity. Examples include “Parting surface flatness error no greater than 0.02mm/1000mm” and “Guide pin and guide bushing clearance 0.01-0.03mm.” Surface quality requirements include the surface roughness and polishing requirements of the cavity and core. Examples include “Cavity surface roughness Ra ≤ 0.04μm, mirror polish required” and “Ejector pin surface roughness Ra ≤ 0.8μm.” Heat treatment requirements specify the heat treatment method and hardness requirements for the part. Examples include “Cavity and core require quenching and tempering, hardness 45-50HRC” and “Ejector pin requires nitriding, surface hardness ≥ 600HV.” Assembly requirements include the mold opening and closing flexibility, the reset accuracy of the ejector mechanism, and leakage testing, for example, “the mold should open and close smoothly without any sticking”, “the ejector mechanism reset accuracy error should not exceed 0.05mm”, and “a pressure test should be performed during mold testing, maintaining a pressure of 10MPa for 5 minutes without leakage”.
The marking of standard and universal parts must comply with national standards and industry specifications to reduce design workload and improve mold versatility. Common standard parts used in injection molds include guide pins, guide bushings, ejector pins, springs, bolts, and locating pins. These parts should be labeled with their standard code, specifications, and quantity on the drawing, eliminating the need for detailed part drawings. For example, a guide pin could be labeled “Guide pin GB/T 4169.4 – 2006 φ20×150,” and an ejector pin could be labeled “Ejector pin GB/T 4169.1 – 2006 φ8×100.” The selection of standard parts should prioritize national and industry standards to ensure procurement convenience and interchangeability. For universal parts (such as mold bases and sprue bushings), the model and specifications should be labeled, such as “Mold base LKM CI2525 – A50 – B50,” and the manufacturer should be indicated in the details column. The installation location and mating dimensions of standard and universal parts should be clearly marked on the assembly drawing to ensure assembly accuracy. In addition, uniform part numbers must be used in the drawings. The numbers should be arranged in a clockwise or counterclockwise direction and correspond one-to-one with the numbers in the details column to facilitate identification and retrieval of parts.
With the widespread application of computer-aided design (CAD) technology, the design and drawing of injection molds must also comply with relevant electronic drawing specifications. The file format of electronic drawings should adopt a universal format (such as DWG and DXF) to facilitate compatibility and data exchange between different software. The layer settings of electronic drawings must be reasonable, and different types of lines (such as contour lines, dimension lines, center lines, hidden lines, etc.) should be assigned to different layers to facilitate editing and management of drawings. The printing settings of electronic drawings must ensure consistency with paper drawings, and the thickness and color of lines should meet the requirements of national standards. In addition, electronic drawings must be versioned, with version numbers and modification records clearly marked to ensure traceability and validity of the drawings. By following these general regulations, injection mold design drawings can accurately and clearly convey design intent and provide a reliable technical basis for mold manufacturing and use.
