The plastic injection mold manufacturing process generally includes: customer customization, mold design, mold manufacturing, mold inspection and trial molding, mold modification and repair, and mold maintenance. These will be explained in detail below.
I. Customer Customization
The production of plastic molds begins with the customer's engineers providing product drawings to the mold manufacturer. The manufacturer then collects, analyzes, and processes the product data based on the requirements for molding the plastic. This is customer customization.
1. Part Manufacturing Requirements
Understand the part's purpose, processability, dimensional accuracy, and other technical requirements. For example, what are the requirements for the plastic part's shape, color, transparency, and performance? Are the geometric structure, draft angles, inserts, etc., of the plastic part reasonable? What is the allowable level of molding defects such as weld lines and shrinkage cavities? Are there any post-processing steps such as painting, electroplating, screen printing, or drilling?
Estimate whether the molding tolerance is lower than the tolerance of the plastic part, and whether a plastic part meeting the requirements can be molded. In addition, it is necessary to understand the plasticizing and molding process parameters of the plastic.
2. Process Data
3. Selection of Molding Equipment
4. Specific Mold Structure Scheme Two-plate mold, three-plate mold. Is the mold structure reliable? Does it meet the technological requirements of plastic parts (such as geometry, surface finish, and dimensional accuracy) and economic production requirements (low part cost, high production efficiency, continuous mold operation, long service life, labor saving, etc.)?
II. Mold Design
1. Part Layout Part layout refers to arranging one or more required plastic parts according to customer requirements, based on a reasonable injection molding process and mold structure.
Part layout complements mold structure and plastic processability, and directly affects subsequent injection molding processes. The layout must consider the corresponding mold structure and be adjusted while meeting the mold structure requirements.
From an injection molding process perspective, the following points need to be considered for layout:
a. Runner length;
b. Runner waste;
c. Gate location;
d. Injection balance;
e. Cavity pressure balance.
From a mold structure perspective, the following points need to be considered:
a. Meeting sealing requirements.
b. Meeting mold structure space requirements: Space requirements for the base, slides, and ejectors; sufficient strength of mold structural components; interference between multiple moving parts; and ensuring the ejector sleeve position avoids ejector pin hole positions.
c. Fully considering screws, cooling water, and ejection devices: The placement of screws and ejectors should consider their impact on cooling water holes.
d. Whether the mold's length-to-width ratio is harmonious: The mold should be as compact as possible with appropriate length-to-width ratios, while also considering the installation requirements of the injection molding machine.
2. Drawing the quotation drawing and ordering materials.
a. The quotation drawing is the initial mold design scheme and also provides a reference for ordering mold materials. Based on the original mold layout, the quotation drawing provides a relatively detailed indication of the mold blank, its structure, and the size of the mold filler material.
b. Ordering materials involves drawing a simplified mold blank diagram based on the quotation drawing and filling out the material order form.
When ordering materials, it is important to select appropriate mold materials according to various mold requirements.
3. Mold Structure Design
The mold structure is determined by the type of injection molding machine and the characteristics of the plastic parts. The following aspects should be considered during the design process:
(1) Technical specifications of the injection molding machine;
(2) Processing properties of the plastic;
(3) Gating system, including runners, gates, etc.;
(4) Molding components;
(5) Commonly used structural components;
(6) Sliding mechanism;
(7) Ejection mechanism;
(8) Mold temperature control;
(9) Venting;
(10) Mold material.
Mold design requires comprehensive consideration of various factors, selection of a reasonable structural form, and fulfillment of the mold forming purpose.
a. Part Layout: In the 3D design stage, the layout is further refined based on the initial 2D layout.
b. Parting Layout: Select the correct parting surface, consider the sealing distance, construct a reference plane, balance lateral pressure, flatten the nozzle contact surface, handle the insertion and penetration of small holes, avoid sharp steel, and comprehensively consider the product appearance, etc.
c. Mold Strength Check and Improvement: To ensure the mold functions properly, it is necessary to check not only the overall strength of the mold but also the strength of its local structures. Specific improvements are made to the structure to enhance local strength:
d. Design of mold parts
Mold parts can be divided into forming parts and structural parts according to their function. Forming parts refer to structural components that directly participate in forming the cavity space, such as cavities, cores, inserts, slides, etc.; structural parts refer to parts used for installation, positioning, guiding, ejection, and completing various actions during forming, such as positioning rings, nozzles, screws, pull rods, ejector pins, sealing rings, spacer plates, pull hooks, etc.
The disassembly of inserts mainly considers the following aspects:
(1) No sharp steel or thin steel should be produced
(2) Easy to process
(3) Easy to adjust dimensions and maintain
(4) Ensure the strength of the forming parts
(5) Easy to assemble
(6) It should not affect the appearance
(7) Comprehensive consideration of cooling (local cooling is difficult after making inserts, so the cooling situation should be considered)
In the design of structural parts, the general principle for the arrangement of ejector pins and the layout of water channels is to first arrange the ejector pins, then arrange the water channels, and then adjust the ejector pins. However, in actual production, mold modifications often need to be considered. Water supply isn't started immediately after mold production; it can only begin after a portion of the mold has been modified, depending on the modified conditions.
Ejector Sleeve Arrangement: Ejector sleeves are generally used in molding pillars. Additionally, for deeper ribs, ejector pins are prone to whitening during ejection; ejector sleeves with ribs can assist in ejection. Generally, the ejector sleeve wall thickness is >= 1mm, and the ejector sleeve and ejector pin should be ordered together as a set.
In structural design, the pillar height should not be too high, otherwise the ejector pin is prone to bending and difficult to eject.
For the design and selection of other structural parts, such as locating rings, nozzles, screws, pull rods, sealing rings, spacer plates, pull hooks, springs, etc., those interested can find relevant materials to learn more.
e. Mold Drawing Creation
Mold drawings are crucial documents for translating design intentions into mold production. They generally need to be drawn according to national standards, and also need to consider the drawing habits of each factory.
The mold drawings include the overall assembly structure drawing and its technical requirements, as well as part drawings for all components, including various inserts.
III. Mold Manufacturing
1. Programming and Disassembling the Mold
After the mold design is completed, CNC programming must be created based on the machining requirements of each component, and whether EDM machining is required.
2. Machining
Mold machining includes CNC machining, EDM machining, wire cutting, deep hole drilling, etc. After the mold blank and materials are ordered, they are often only in a rough machining state or are just steel. At this point, a series of machining processes must be performed according to the mold design intent to produce various components.
CNC machining, or computer numerical control, requires various machining programs, tool selection, machining parameters, etc. Those interested can find relevant materials to study.
EDM machining is an electrical discharge machining process that uses electrical discharge to corrode materials to achieve the required dimensions; therefore, it can only machine conductive materials. The electrodes used are generally copper and graphite.
Wire cutting is used for machining sharp corners.
Deep hole drilling is generally used for machining water channels in large molds and for machining ejector pin and sleeve holes.
3. Fitter Assembly
Fitters play a crucial role in mold making, and their work must be carried out throughout the entire mold manufacturing process. Fitters are proficient in fitting mold assembly, turning, milling, grinding, and drilling.
4. Mold Shaving and Polishing
Mold shaving and polishing are the processes performed on mold parts using sandpaper, oilstones, diamond paste, and other tools and materials after CNC machining, EDM, and fitter machining, but before mold assembly.
IV. Mold Inspection and Trial Molding
1. Mold Inspection
The mold assembly process is essentially a mold inspection process. During fitting mold assembly, it is possible to check if the red lead is in place, if the ejector pins and sleeves move smoothly, and if there are any errors or interferences in the mold design.
2. Trial Molding
After mold manufacturing is completed, a trial molding is performed on the injection molding machine to test the mold's condition and the quality of the plastic parts structure. Trial molding allows us to understand the mold's performance during injection molding and the quality of the plastic parts structure.
For requirements regarding trial molding and improvements to plastic parts defects, please refer to other materials. V. Mold Modification and Repair
After trial molding, corresponding modifications will be made based on the trial results. Additionally, after the engineer confirms the plastic part, its structure will also be modified accordingly.
Since the mold is already manufactured, all modifications are quite complicated, sometimes even more difficult than remaking it. The best modification method must be found based on the specific situation.
For structural design, modifications must be made with a thorough understanding of the mold conditions, including whether it affects the cooling system or ejector pins, and what the easiest modification method is. Modifications can be made based on relevant information, and consultation with the mold team is recommended if necessary.
Cooling System Machining:
For cooling system machining (drilled cooling system), the front mold cooling system generally needs to be machined when the first mold modification document is issued, and the rear mold cooling system needs to be machined after the second mold modification document is issued. However, for situations where the opening or closing of the cooling system has a significant impact on the injection molding process, such as injection molding of PC materials (requiring hot oil injection), it should be opened before the first trial molding.
VI. Mold Maintenance
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