Mold design step 1. Accept the mission statement. The mission statement for molding plastic parts is usually proposed by the part designer, and its content is as follows: ⑴The approved formal part drawings, and indicate the use of plastic brand, transparency, etc. ⑵Instructions or technical requirements for plastic parts. ⑶Production output. ⑷Plastic parts samples. Usually, the mold design task sheet is proposed by the plastic parts craftsman based on the task letter for molding plastic parts. The mold designer designs the mold based on the molding plastic parts task letter and the mold design task letter. 2. Collect, analyze, and digest original data. Collect and organize data on part design, molding technology, molding equipment, mechanical processing, and special processing for use in mold design. ⑴ Digest the drawings of plastic parts, understand the use of the parts, and analyze the technical requirements such as craftsmanship and dimensional accuracy of the plastic parts. For example, what are the requirements for plastic parts in terms of appearance, color transparency, and performance, whether the geometric structure, slope, inserts, etc. of the plastic parts are reasonable, the allowable degree of molding defects such as weld marks and shrinkage holes, and whether there is coating Assembly, electroplating, bonding, drilling and other post-processing. Select the dimension with the highest dimensional accuracy of the plastic part for analysis to see if the estimated molding tolerance is lower than the tolerance of the plastic part, and whether plastic parts that meet the requirements can be molded. In addition, you also need to understand the plasticization and molding process parameters of plastics. ⑵ Digest the process data and analyze whether the molding method, equipment model, material specification, mold structure type and other requirements proposed in the process task book are appropriate and can be implemented. Molding materials should meet the strength requirements of plastic parts and have good fluidity, uniformity, isotropy, and thermal stability. According to the use of plastic parts, the molding materials should meet the requirements for dyeing, metal plating conditions, decorative properties, necessary elasticity and plasticity, transparency or opposite reflective properties, adhesiveness or weldability. 3. Determine the molding method: direct pressure method, casting pressure method or injection method. 4. Select molding equipment. Molds are made according to the type of molding equipment, so you must be familiar with the performance, specifications, and characteristics of various molding equipment. For example, for an injection machine, you should know the following in terms of specifications: injection capacity, clamping pressure, injection pressure, mold installation dimensions, ejection device and size, nozzle hole diameter and nozzle spherical radius, gate sleeve positioning ring size, The maximum and minimum thickness of the mold, template stroke, etc., please refer to the relevant parameters for details. It is necessary to initially estimate the mold dimensions and determine whether the mold can be installed and used on the selected injection machine. 5. Specific structural plan: ⑴ Determine the mold type, such as compression mold (open, semi-closed, closed), casting mold, injection mold, etc. ⑵ Determine the main structure of the mold type. Choosing the ideal mold structure depends on determining the necessary molding equipment and the ideal number of cavities. Under absolutely reliable conditions, the mold itself can work to meet the process technology and production economic requirements of the plastic part. . The technological requirements for plastic parts are to ensure the geometric shape, surface finish and dimensional accuracy of the plastic parts. The production economic requirements are to make the cost of plastic parts low, the production efficiency high, the mold can work continuously, the service life is long, and the labor is saved. There are many factors that affect the mold structure and individual mold systems, which are very complex: ①Cavity layout. The number of cavities and their arrangement are determined based on the geometric structure characteristics of the plastic part, dimensional accuracy requirements, batch size, difficulty of mold manufacturing, mold cost, etc. For injection molds, the precision of plastic parts is level 3 and level 3a, the weight is 5 grams, a hardened pouring system is used, and the number of cavities is 4-6; the plastic parts are of general precision (level 4-5), and the molding The material is partially crystalline material, and the number of cavities can be 16-20; the weight of the plastic part is 12-16 grams, the number of cavities is 8-12; and the plastic part weighing 50-100 grams, the number of cavities is 4-8 pieces. For amorphous plastic parts, the recommended number of cavities is 24-48, 16-32 and 6-10. When the weight of plastic parts continues to increase, multi-cavity molds are rarely used. For plastic parts with level 7-9 precision, the maximum number of cavities increases to 50% compared to the plastic parts with level 4-5 precision. ②Determine the parting surface. The position of the parting surface should be conducive to mold processing, exhaust, demoulding and molding operations, as well as the surface quality of plastic parts, etc. ③Determine the pouring system (shape, location, size of main runner, sub-runner and gate) and exhaust system (exhaust method, exhaust slot location, size). ④Select the ejection method (ejector rod, ejection tube, push plate, combined ejection), and determine the undercut treatment method and core pulling method.
⑤Determine the cooling and heating methods, the shape and position of the heating and cooling grooves, and the installation location of the heating element. ⑥ According to the mold material, strength calculation or empirical data, determine the thickness and outer dimensions of the mold parts, the outer structure and the positions of all connections, positioning and guide parts. ⑦ Determine the structural form of main molded parts and structural parts. ⑧Consider the strength of each part of the mold and calculate the working dimensions of the molded parts. If the above problems are solved, the structural form of the mold will naturally be solved. At this time, you should start drawing a sketch of the mold structure to prepare for formal drawing. ⑨Drawing mold drawings is required to be drawn in accordance with national drawing standards, but it is also required to be combined with factory standards and factory customary drawing methods not specified by the state. Before drawing the mold assembly drawing, the process drawing should be drawn and must comply with the requirements of the part drawing and process data. The dimensions guaranteed by the next process should be marked with the words "process dimensions" on the drawing. If no other mechanical processing is performed after molding except for burr repair, then the process drawing will be exactly the same as the part drawing. It is best to mark the part number, name, material, material shrinkage, drawing scale, etc. below the process diagram. Usually the process is drawn on the mold assembly drawing. A. Draw the general assembly structure drawing. Try to use a 1:1 ratio when drawing the general assembly drawing. Start drawing from the cavity first, and draw the main view and other views at the same time. The mold assembly drawing should include the following contents: ① The structure of the mold forming part ② The structural form of the pouring system and exhaust system. ③Parting surface and parting pick-up method. ④The appearance structure and the position of all connecting parts, positioning and guide parts. ⑤ Mark the cavity height dimension (not required, as needed) and the overall size of the mold. ⑥Auxiliary tools (piece removal and mold removal tools, correction tools, etc.). ⑦Number all parts in order and fill in the detailed list. ⑧Mark technical requirements and instructions for use. B. Technical requirements of the mold assembly drawing: ① Performance requirements for certain systems of the mold. For example, there are assembly requirements for ejection systems and slider core-pulling structures. ②Requirements for mold assembly process. For example, after the mold is assembled, the fitting gap of the parting surface should be no greater than 0.05mm. The parallelism requirements on the upper and lower sides of the mold should be noted, and the size determined by assembly and the requirements for this size should be pointed out. ③Mold use, assembly and disassembly methods. ④Anti-oxidation treatment, mold number, engraving, marking, oil seal, storage and other requirements. ⑤Requirements related to mold trial and inspection. C. Draw all parts drawings. The order of drawing parts drawings from the assembly drawing of the mold should be: inside first then outside, complex first then simple, forming parts first, then structural parts. ①Graphic requirements: Must be drawn in proportion, and enlargement or reduction is allowed. Views are well chosen, projected correctly, and laid out appropriately. In order to make the processing patent number easy to understand and facilitate assembly, the graphics should be consistent with the assembly drawing as much as possible and the graphics should be clear. ② Dimensions must be unified, centralized, orderly, and complete. The order of marking dimensions is: first mark the dimensions of the main parts and the draft angle, then mark the matching dimensions, and then mark all dimensions. On non-main parts drawings, mark the matching dimensions first and then all dimensions. ③Surface roughness. Mark the most commonly used roughness in the upper right corner of the drawing, such as "Other 3.2." Other roughness symbols are marked on each surface of the part. ④Other contents, such as part name, mold drawing number, material grade, heat treatment and hardness requirements, surface treatment, graphic proportions, free-size processing accuracy, technical description, etc. must be filled in correctly. D. The content of proofreading, drawing review, tracing, and self-proofreading is: ①The relationship between the mold and its parts and the plastic part drawings, whether the material, hardness, dimensional accuracy, structure, etc. of the mold and mold parts meet the requirements of the plastic part drawings . ② In terms of plastic parts, whether the flow, shrinkage holes, weld marks, cracks, draft angle, etc. of the plastic material flow affect the performance, dimensional accuracy, surface quality and other requirements of the plastic parts. Is there any deficiencies in the pattern design, is the processing simple, and is the shrinkage rate of the molding material selected correctly? ③In terms of molding equipment, are the injection volume, injection pressure, and clamping force sufficient? Are there any problems with the installation of the mold, the core of the plastic parts, and the demoulding? Are there correct contacts between the nozzle of the injection machine and the mouthpiece? ④ Mold structure a. Whether the parting surface position and finishing accuracy meet the requirements, whether overflow will occur, and whether the plastic parts can be ensured to stay on the side of the mold with the ejection device after the mold is opened. b. Whether the demoulding method is correct, whether the size, position, and quantity of the extension rod and push tube are appropriate, whether the push plate will be stuck by the core, and whether it will cause scratches on the molded parts. c. Mold temperature adjustment.
The power and quantity of the heater; whether the location, size and quantity of the flow line of the cooling medium are appropriate. d. How to deal with undercuts in plastic parts, and whether the mechanism for removing undercuts is appropriate, such as whether the slider and push rod in the inclined guide column core-pulling mechanism interfere with each other. e. Whether the location and size of the pouring and exhaust systems are appropriate. f. Design drawings g. Whether the placement of each mold part on the assembly drawing is appropriate, whether the expression is clear, and whether there are any omissions h. The part number, name, production quantity, whether the part is made in-house or outsourced on the part drawing, is a standard part Are they still non-standard parts? The processing accuracy of parts, the correction processing and allowance of high-precision dimensions of molded plastic parts, and whether the materials, heat treatment, surface treatment, and surface finishing of mold parts are clearly marked and described. ⑤ Working dimensions and matching dimensions of main parts, molded parts. Size figures should be correct and do not require manufacturer conversions. ⑥ Check the view position of all parts drawings and assembly drawings, whether the projection is correct, whether the drawing method complies with the national drawing standards, and whether there are any missing dimensions. ⑦ Check the machining performance: (Whether the geometric structure, drawing method, size label, etc. of all parts are conducive to processing) ⑧ Professional proofreading of the main working dimensions of the recalculation auxiliary tool is in principle carried out according to the designer's self-checking project; but it must be focused In terms of structural principles, process performance and operational safety. When tracing, you must first digest the graphics, draw them according to the national standard requirements, and fill in all dimensions and technical requirements. After tracing, self-correct and sign. Submit the traced base drawing to the designer for proofreading and signature. The common practice is for the relevant technical personnel of the tool manufacturing unit to review, countersign, and check the manufacturing process before sending it to the public. ⑨Write the manufacturing process card. The technical personnel of the tool manufacturing unit prepare the manufacturing process card and prepare it for processing and manufacturing. In the manufacturing process of mold parts, inspection should be strengthened and the focus of inspection should be on dimensional accuracy. After the mold assembly is completed, the inspector will inspect it according to the mold inspection form. The main thing is to check whether the performance of the mold parts is good. Only in this way can the manufacturing quality of the mold be known. ⑶ Although mold trial and mold repair are carried out under the expected process conditions when selecting molding materials and molding equipment, people's understanding is often imperfect, so a trial mold test must be carried out after the mold processing is completed. , depending on the quality of the molded parts. After the discovery is made, the mold will be repaired to eliminate the error. There are many types of defects in plastic parts, and the reasons are also very complicated. There are reasons for molds and process conditions, and the two are often intertwined. Before repairing the mold, a detailed analysis and study should be conducted based on the actual adverse phenomena of the plastic parts, and the causes of the defects in the plastic parts should be found out and remedies should be proposed. Because the molding conditions are easy to change, the general approach is to change the molding conditions first. When changing the molding conditions cannot solve the problem, repair the mold is considered. You should be more cautious when repairing molds, and do not act rashly if you are not very sure. The reason is that once the mold conditions are changed, major modifications and restoration to the original state cannot be made. 6. Organize and archive data. If the mold is not used temporarily after testing, the demoulding residue, dust, oil, etc. should be completely wiped off, coated with butter or other anti-rust oil or anti-rust agent, and kept in a storage location. From designing the mold to successfully processing the mold and passing the inspection, the technical data generated during this period, such as mission sheets, part drawings, technical specifications, mold assembly drawings, mold parts drawings, base drawings, mold design instructions, and inspection records Forms, trial mold repair records, etc. shall be systematically organized, bound, numbered and filed according to regulations. This may seem troublesome, but it will be very useful for repairing molds and designing new molds in the future