Mold Manufacturing Process Guide
In modern manufacturing, molds are known as the "mother of industry" and are widely used in key sectors such as automotive, home appliances, medical devices, and electronics. High-quality molds not only determine the molding quality of the final products but also directly impact production efficiency and cost control. To create a set of high-performance, long-lasting molds, a systematic and rigorous manufacturing process is essential. From the initial design concept, to precise machining and material selection, and finally to strict inspection and repeated trial runs, every step plays a critical role.
一. Mold Design Stage: Application of CAD/CAE
The first step in mold manufacturing begins with the design phase, which is a crucial part of the entire process. Excellent mold design not only enhances the efficiency of subsequent machining but also significantly extends the mold’s service life and reduces production costs. The design phase generally includes three parts: requirements analysis, CAD modeling, and CAE engineering analysis.
1. Requirements Analysis
Before starting the mold design, it is essential to conduct an in-depth analysis of the product itself, including:
Product Shape and Dimensions: Determine the product’s geometric shape, dimensional accuracy requirements, and surface quality standards.
Material Properties: Understand the flowability, shrinkage rate, and thermal deformation characteristics of the product material (such as ABS, PC, PP plastics).
Production Volume: Different considerations for mold type, lifespan, and cost depending on whether it is for small-batch or large-scale production.
Functional Requirements: Requirements such as heat resistance, impact resistance, and transparency.
Example:
For an automotive lamp cover, which demands extremely high transparency standards, the mold cavity surface must be exceptionally smooth to avoid any minor defects. Additionally, the gate design must be reasonable to prevent air marks or weld lines inside the product that could affect optical performance.
2. CAD (Computer-Aided Design)
After clarifying the requirements, designers use CAD software to create 3D models. Commonly used software includes AutoCAD, UG (Siemens NX), SolidWorks, and others. The main design contents include:
Cavity and Core Structure: Ensure accurate product dimensions and a reasonable structure for smooth molding.
Gate System Design: Properly arrange gates and runners to ensure even filling of molten plastic into the cavity.
Cooling System Design: Design efficient cooling channels to shorten molding cycles and reduce product deformation.
Ejection Mechanism Design: Design features such as ejector pins, lifters, and side sliders to ensure smooth demolding without damaging the surface.
Precise and detailed CAD modeling is the foundation for efficient machining and high-quality molding.
3. CAE (Computer-Aided Engineering Analysis)
After clarifying the requirements, designers use CAD software to create 3D models. Commonly used software includes AutoCAD, UG (Siemens NX), SolidWorks, and others. The main design contents include:
- Flow Analysis: Predict the flow path and pressure distribution of molten material in the cavity, and assess issues such as short shots or air pockets.
- Cooling Analysis: Simulate the effectiveness of the cooling system, optimize cooling channel layouts, improve cooling uniformity, and reduce internal stresses.
- Deformation and Shrinkage Analysis: Predict dimensional changes after molding and pre-correct mold dimensions to improve the final product’s accuracy.
Through CAE analysis, potential issues can be identified before mold manufacturing, avoiding later rework due to design flaws, thus saving a great deal of time and cost.
Summary
Every detail in the mold design phase directly affects subsequent machining and molding quality. Accurate requirements analysis, professional CAD modeling, and scientific CAE validation greatly enhance the success rate and cost-effectiveness of mold manufacturing. A high-quality mold lays its foundation for success starting from the design stage.
二.Mold Manufacturing Stage: CNC Machining and EDM Processing
After completing the mold design and passing CAE validation, the process moves into the actual manufacturing phase. This stage demands extremely high standards for equipment precision, operational skills, and process management, directly determining the final quality and service life of the mold. The main steps include material preparation, CNC machining, Electrical Discharge Machining (EDM), as well as manual finishing and assembly.
1. Material Preparation and Rough Machining
The first step in mold manufacturing is selecting the appropriate mold steel according to design requirements. Common materials include P20, H13, S136, etc., each offering different properties such as wear resistance, toughness, and corrosion resistance. The choice depends on the molding material, product specifications, and production volume.
- Blank Preparation:
The selected steel is cut into blocks close to the final dimensions, facilitating subsequent precision machining. - Rough Machining:
Using milling machines or lathes, the blanks undergo initial machining to remove excess material and form a basic outline, leaving sufficient allowance for fine machining.
2. CNC (Computer Numerical Control) Machining
The first step in mold manufacturing is selecting the appropriate mold steel according to design requirements. Common materials include P20, H13, S136, etc., each offering different properties such as wear resistance, toughness, and corrosion resistance. The choice depends on the molding material, product specifications, and production volume.
- Blank Preparation:
The selected steel is cut into blocks close to the final dimensions, facilitating subsequent precision machining. - Rough Machining:
Using milling machines or lathes, the blanks undergo initial machining to remove excess material and form a basic outline, leaving sufficient allowance for fine machining.
3. Electrical Discharge Machining (EDM)
For deep cavities, sharp corners, and tiny structures that CNC machines find difficult, EDM technology is employed.
Hole Drilling EDM:
Used for creating deep, fine holes such as cooling channel inlets and vent holes.Fine Cavity Machining:
Shapes are precisely formed through spark erosion, achieving high surface finishes suitable for demanding molding surfaces.Advantages:
EDM is unaffected by material hardness, can machine any conductive material, and is particularly advantageous for complex shapes.
4. Manual Finishing and Assembly
After mechanical machining, manual fine-tuning is necessary to ensure the final mold quality.
- Hand Polishing:
Tools such as oilstones, sandpaper, and polishing machines are used to meticulously treat key surfaces, enhancing surface smoothness and eliminating minor defects. - Parts Assembly:
Mold components (such as cores, cavity plates, ejector systems, sliders, etc.) are precisely assembled according to the design drawings, checking for fitting accuracy and smooth operation. - Preliminary Function Testing:
Basic opening, closing, and ejection actions are tested to confirm that mechanisms operate without obstruction or abnormal noise.
三.Mold Material Selection and Trial Molding Inspection
The choice of mold materials, along with subsequent trial molding and inspections, directly determines the mold’s service life, the quality of molded products, and production efficiency. Proper material selection and rigorous testing are critical to ensuring the final performance of the mold.
1. Criteria for Mold Material Selection
Selecting the appropriate mold steel based on different molding materials, product performance requirements, and production conditions is a key step in mold manufacturing. Major factors to consider include:
Wear Resistance:
Molds used in high-frequency production must resist wear. For example, when molding glass fiber-reinforced plastics, high wear-resistant steel such as H13 is preferred.Toughness:
Molds must withstand impact loads during opening, closing, and ejection. Good toughness is necessary to prevent cracking.Corrosion Resistance:
For molding corrosive plastics (e.g., PVC) or products requiring a high surface finish (e.g., medical devices), highly corrosion-resistant materials like S136 stainless steel are required.Heat Treatment Properties:
Materials should exhibit excellent thermal stability during heat treatment, with minimal deformation and uniform hardness distribution.
Example:
Molds for producing transparent PC material lampshades often use S136 mirror-finish stainless steel, which not only provides corrosion resistance but also achieves high polishability, ensuring superior optical performance.
2. Inspection Process
Once the mold manufacturing is completed, it must undergo a stringent inspection process to ensure all specifications meet the design requirements.
- Dimensional Inspection:
Coordinate Measuring Machines (CMMs) are used to accurately measure critical dimensions, ensuring all tolerances are within the specified range, especially for cavities, cores, and fitting surfaces. - Appearance Inspection:
Check the cavity surfaces for scratches, burns, dents, or other defects to ensure the molded product will have a flawless surface. - Functional Testing:
Test all moving mechanisms (such as sliders, ejector pins, lifters) to verify smooth operation, and check the cooling channels for unobstructed flow.
3. Trial Molding (T0/T1 Trials)
Trial molding is a critical validation step in the mold manufacturing process. Through actual injection molding, the overall mold performance and molding results are evaluated.
Installation and Setup:
Install the mold on the injection molding machine and set appropriate processing parameters such as temperature, pressure, and speed.First Trial (T0):
Inspect material filling, product ejection, and initially identify issues like improper gate locations, uneven filling, shrinkage, or deformation.Adjustment and Optimization:
Based on trial results, make local modifications such as adding venting channels, optimizing cooling layouts, or adjusting cavity dimensions.Second Trial (T1) and Confirmation:
After modifications, a second trial is conducted to confirm that the product’s dimensions, appearance, and performance meet all requirements, ensuring the mold’s stability and readiness for mass production.
4. Final Inspection and Delivery
After successful trial molding, a final inspection is performed and all related documentation is compiled.
- Final Inspection Contents:
Includes an overall mold appearance check, part number verification, functional tests, and issuing of dimensional inspection and trial molding reports. - Delivery Standards:
The mold must be stable, dimensionally accurate, and fully functional, accompanied by a complete user and maintenance manual to assist clients in operation and future maintenance.