Injection molding is a widely used manufacturing process for producing plastic parts and products with high efficiency and precision. The success of the injection molding process heavily relies on the design of the injection mold. In this comprehensive blog post, we will delve into the fundamental knowledge of injection mold design, including key considerations, design guidelines, and best practices to ensure successful and cost-effective production.
1. Understanding Injection Mold Design: An Overview
Injection mold design is the process of creating a custom mold that will be used to shape and form the molten plastic material into the desired product. The mold design is a critical step in the injection molding process, as it directly impacts the quality, efficiency, and cost-effectiveness of the production. The design of the mold must take into account various factors, such as the material properties, part geometry, production volume, and cooling efficiency.
2. Key Considerations in Injection Mold Design
a) Material Selection
Choosing the right material for the injection mold is crucial for ensuring its durability, thermal stability, and resistance to wear and tear. Common materials used for injection molds include steel, aluminum, and beryllium copper. The selection of the material should be based on the specific requirements of the production process and the desired lifespan of the mold.
b) Part Design and Geometry
The design and geometry of the plastic part being produced are critical factors that influence the mold design. The mold must be designed to accommodate the specific shape, size, and features of the part. Proper consideration must be given to factors such as draft angles, wall thickness, undercuts, and gating to ensure smooth and efficient filling of the mold.
c) Cooling System Design
Effective cooling is essential for the success of the injection molding process. The design of the cooling system in the mold must be carefully planned to ensure even and efficient cooling of the molten plastic. Proper cooling helps in reducing cycle time, preventing warping, and improving the overall quality of the final product.
3. Design Guidelines for Injection Mold
a) Wall Thickness
Maintaining uniform wall thickness throughout the part is crucial for achieving consistent and high-quality results. Uneven wall thickness can lead to sink marks, warping, and defects in the final product. Design guidelines recommend keeping the wall thickness as uniform as possible to ensure proper flow and cooling of the plastic material.
b) Draft Angles
Draft angles are tapered surfaces added to the part design to allow for easy ejection from the mold. Design guidelines recommend draft angles of at least 1 to 2 degrees to facilitate smooth ejection and avoid damage to the part.
c) Gate Design
The gate is the entry point through which the molten plastic material is injected into the mold. The gate design must be carefully chosen to ensure proper flow and distribution of the plastic material within the mold cavity. Common gate types include edge gates, sub-gates, and hot runners.
4. Best Practices in Injection Mold Design
a) Simulation and Analysis
Using advanced simulation and analysis tools can help optimize the mold design and identify potential issues before the actual production process. Mold flow analysis can help predict the flow of the plastic material and identify potential areas of concern, such as air traps, weld lines, and part shrinkage.
b) Prototyping and Testing
Creating a prototype of the mold and conducting testing can help validate the design and identify any necessary modifications or improvements. Prototyping allows for adjustments to be made to the mold design without incurring significant costs.
Injection mold design is a critical aspect of the injection molding process, directly impacting the quality, efficiency, and cost-effectiveness of the production. Understanding the key considerations, design guidelines, and best practices in injection mold design is essential for achieving successful and reliable results. With the right knowledge, expertise, and attention to detail, injection mold design can pave the way for innovative and high-quality plastic products that meet the demands of various industries and applications.
Injection mold design needs to pay attention to what points
Product wall thickness
- All kinds of plastics have a certain wall thickness range, generally 0.5~4mm, when the wall thickness is more than 4mm, it will cause too long cooling time, shrinkage printing and other problems, should be considered to change the product structure.
- Uneven wall thickness will cause surface shrinkage.
- Uneven wall thickness can cause pores and weld marks.
- The reasonable application of stiffeners can increase product rigidity and reduce deformation.
- The thickness of reinforcement must be ≤ (0.5~0.7) T product wall thickness, otherwise it will cause surface shrinkage.
- The single-side slope of the reinforcement should be greater than 1.5° to avoid jacking injury.
- Too small rounded corners may cause stress concentration and result in cracking.
- Too small rounded corners may cause stress concentration in the mold cavity and lead to cavity cracking.
- Setting a reasonable round corner can also improve the mold processing technology, such as the cavity can be directly milling with R knife, and avoid low efficiency of electrical machining.
- Different round corners may cause the movement of the parting line, should be combined with the actual situation to choose different round corners or corners of injection mold design what are the basic points of injection mold design what are the basic points.
Die opening direction and parting line
At the beginning of the design of each injection product, the direction of opening and parting line should be determined to ensure that the core pulling slider mechanism is reduced as much as possible and the influence of parting line on the appearance is eliminated.
- After the direction of die opening is determined, the stiffeners, buckles, bulges and other structures of the product are designed to be consistent with the direction of die opening as far as possible, so as to avoid core pulling, reduce stitching lines and prolong the life of the die.
- After the direction of die opening is determined, THE appropriate parting line can be selected to avoid the inverted direction of die opening, so as to improve the appearance and performance.
- Appropriate demoulding incline can avoid product pulling (drawing). The demoulding slope of smooth surface should be ≥0.5 degree, fine skin grain (sand surface) surface is greater than 1 degree, rough skin grain surface is greater than 1.5 degree.
- Proper demoulding incline can avoid product top damage, such as top white, top deformation, top broken injection mold design of the basic requirements
- When designing deep cavity structure products, the outer surface slope should be greater than the inner surface slope as much as possible to ensure that the mold core is not misaligned during injection molding, obtain uniform product wall thickness, and ensure the material strength of the product opening area
- The shape of the hole should be as simple as possible, generally round
- The axial direction of the hole is consistent with the direction of the die opening, which can avoid pulling the core.
- When the aspect ratio of the hole is greater than 2, the demoulding inclination should be set. In this case, the diameter of the hole should be calculated according to the path size (maximum solid size).
- The aspect ratio of the blind hole is generally not more than 4. The anti-hole needle is flushed and bent
- The distance between the hole and the edge of the product is generally greater than the aperture size.
Accuracy of injection parts
Due to the inhomogeneity and uncertainty of shrinkage during injection molding, the accuracy of injection parts is significantly lower than that of metal parts, so the dimensional tolerance of mechanical parts cannot be simply applied, and appropriate tolerance requirements should be selected according to the standard. China also released GB/T14486-93 in 1993
“Dimensional Tolerance of Engineering Plastic Molded Plastic Parts”, the designer can determine the dimensional tolerance of the parts according to the requirements of the plastic raw materials and parts used in the standard.
At the same time, according to the comprehensive strength of the factory, the design accuracy of the peer products to determine the appropriate design tolerance accuracy.
Deformation of injection molded parts
Deformation of injection molded parts is a common problem that affects the quality, appearance, and functionality of the products. Deformation occurs when different sections of the part shrink unevenly during the cooling process, resulting in warping, twisting, or bending of the shape. Deformation can be influenced by several factors, such as material properties, part geometry, mold design, and process parameters. To minimize deformation, it is important to optimize these factors and achieve a balanced and uniform cooling condition. Some of the methods that can be used to optimize the process parameters are design of experiments, artificial neural networks, genetic algorithm, response surface methodology, and Kriging model. These methods can help to find the optimal combination of parameters such as mold temperature, melt temperature, injection rate, injection pressure, holding pressure, holding and cooling duration, etc. By optimizing the process parameters, the deformation of injection molded parts can be reduced and the quality of the products can be improved.