AAA MOULD's Medical Device Injection Molding

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In modern injection molding production, product defect rates, material waste, and production halts caused by mold defects are common pain points in the industry. According to industry statistics, the first-time mold trial pass rate of molds without mold flow analysis optimization is only 40%-50%, while common defects directly lead to a production efficiency decrease of over 30%. Based on computational fluid dynamics (CFD) and thermodynamics principles, mold flow analysis can accurately simulate the entire process of plastic melt in the mold cavity, providing a scientific basis for mold design and process adjustment. The spline test mold is a key carrier for verifying analysis results, and the combination of the two forms the core system for defect control.

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I. Common Defects of Injection Molds and Their Impact on Production
1. Types of Common Defects



Typical defects in injection mold production include flash, short shot, air bubbles, warpage deformation, weld lines, and sink marks. Among these, the occurrence rate of flash in thin-walled products is as high as 60%; weld lines are common in products with complex cavities; and warpage deformation is prominent in engineering plastic products such as ABS and PC.


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2. Impact on Production Efficiency and Product Quality



The rework rate caused by flash is approximately 15%-20%, with an average rework time of 3-5 minutes per piece; material waste caused by short shots accounts for 8%-12%; and the scrap rate of products with warpage deformation can be as high as 25%. In addition, the mold shutdown and debugging time due to defect handling accounts for 20%-25% of the total production time, severely restricting production capacity.


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II. Basic Principles and Key Data of Mold Flow Analysis
1. Basic Principle of Mold Flow Analysis




By establishing a 3D mold model and a plastic material database, it simulates the entire process of melt from injection to cooling and solidification. With the help of numerical calculations, it reproduces the distribution of temperature field, pressure field, and velocity field, and predicts the location and cause of defects.


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2. Interpretation of Key Data Indicators



Core data indicators include flow time, pressure distribution, temperature distribution, shear rate, and solidification time. The difference in flow time should be controlled within ±0.3s; the maximum injection pressure in the cavity should be less than 85% of the mold's allowable pressure (the allowable pressure of general engineering plastic molds is 150-200MPa); the uniformity error of temperature distribution should be ≤5℃; the shear rate should be controlled between 1000-5000s⁻¹; and the solidification time usually accounts for 70%-80% of the total cooling time.


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III. Core Methods of Mold Flow Analysis for Optimizing Injection Mold Defects
1. Optimization of Gate Design

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(1) Determination of Gate Position: Based on the simulation of the melt flow path, the gate is set at the farthest point of melt flow in the cavity or the position with the maximum wall thickness, avoiding the key stress-bearing areas of the product. For single-cavity products, the number of gates is usually 1-2.
(2) Optimization of Gate Size: Calculated based on material fluidity and product weight, the gate diameter for small PP products is 0.8-1.2mm, and for large products, it is 1.5-2.5mm.

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2. Optimization of Runner System



(1) Runner Layout Design: Priority is given to a balanced layout to ensure consistent melt flow distance and pressure loss in each cavity. The difference in runner length should be controlled within 5%. The diameter of the main runner is 1-2mm larger than that of the sub-runners, and the diameter of the sub-runners is 4-8mm.
(2) Optimization of Runner Size: Ensure that the pressure loss of the melt in the runner is ≤30MPa, and reduce the filling time difference of multi-cavity molds to within 0.2s.


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3. Optimization of Cooling System



(1) Cooling Water Channel Design: Follow the principle of "close to the cavity and uniform distribution". The distance between the water channel and the cavity surface is 15-25mm, and the spacing between water channels is 25-35mm. Conformal water channels are used for molds with complex curved surfaces, which can improve cooling uniformity by more than 40%.
(2) Selection of Cooling Medium: Industrial cooling water (temperature 20-25℃) with a flow rate of 1.5-2.5m/s is used for ordinary products; ice water cooling (temperature 5-10℃) is used for engineering plastic or thick-walled products, and the temperature fluctuation of the mold surface is ≤3℃.


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4. Optimization of Injection Process Parameters

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(1) Injection Pressure and Speed: The injection pressure is set to 1.1-1.2 times the maximum pressure of the cavity. A segmented speed is adopted: 30-50mm/s in the initial filling stage, 60-100mm/s in the middle stage, and 20-40mm/s in the final stage.
(2) Holding Pressure and Time: The holding pressure is 60%-80% of the injection pressure. The holding time is determined by the product wall thickness—for every 1mm increase in wall thickness, the holding time is extended by 1-1.5s.
(3) Molding Temperature: The barrel temperature is 20-40℃ higher than the plastic melting point (200-240℃ for ABS materials, 260-300℃ for PC materials); for mold temperature, it is 40-80℃ for crystalline plastics and 60-120℃ for amorphous plastics.


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IV. Application of Spline Test Molds in Mold Flow Analysis
1. Overview of Spline Test Molds



A standard mold specially used to verify mold flow analysis results, adopting the size of ISO 527-2 standard tensile splines (170mm×15mm×4mm). It can be designed with single or multi-cavity, equipped with standard gates, runners, and cooling systems. By producing standard splines, it detects the consistency between material molding performance and analysis data.


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2. Key Design Points of Spline Test Molds



The mold core material is preferably S136 or H13 mold steel, with a hardness of HRC50-55 after heat treatment; the surface roughness of the cavity is Ra≤0.8μm; the ejection system uses a combination of ejector pins and ejector plates, with ejector pin diameter of 2-3mm and spacing of 30-40mm; and mounting holes for temperature sensors are reserved to monitor the cavity temperature in real time.


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3. Role of Spline Testing in Mold Flow Analysis



It serves as a "calibrator" for analysis results, correcting model parameters by comparing simulated and measured data. For example, if the mold flow analysis predicts a spline warpage of 0.5mm and the actual measurement is 0.52mm, the error can be reduced to within ±3% after adjustment. At the same time, it can verify process parameters in advance—such as testing the weld line strength of splines under different injection speeds to determine the optimal process range.


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V. Practical Case Analysis

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A company used ABS material to produce automotive door trim strips. The first mold trial showed severe weld lines and warpage deformation, with a defect rate of 12%. Mold flow analysis revealed that the single-gate design of the original mold resulted in an excessively long melt filling path, and uneven distribution of cooling water channels caused an 8℃ temperature difference in the cavity.


Optimization Plan: Add 1 auxiliary gate and adopt a balanced runner; adjust the spacing of cooling water channels to 30mm and add 2 conformal water channels. Spline testing showed that the tensile strength of the spline weld line increased from 18MPa to 25MPa, and the warpage decreased from 0.8mm to 0.3mm.


After applying the optimization plan, the weld line strength of the product met the standard, warpage deformation was controllable, the defect rate dropped to 2.5%, production efficiency increased by 28%, and material waste per batch decreased by 10%.

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VI. Development Trends of Mold Flow Analysis Technology
1. Integration with AI and Big Data



Moving towards intelligence, AI algorithms automatically identify design defects and parameter optimization spaces, and combine with big data to realize model self-learning and self-calibration. Some systems can complete the full-process analysis of complex molds within 10 minutes, improving efficiency by more than 50%.



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2. Multi-Physical Field Coupling Simulation



Strengthen the coupling analysis of flow field, temperature field, and stress field, simulate the interaction between melt flow and mold structure deformation, and combine with software collaborative simulation to realize full-chain digital verification from design to performance prediction.


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VII. Conclusion



Mold flow analysis is the core technology for optimizing injection mold defects, and spline test molds improve the reliability of optimization solutions. By optimizing design and processes, combined with spline test verification, the incidence of defects can be significantly reduced, and the first-time mold trial pass rate can be improved. With the development of technology integration, mold flow analysis will play a greater role in the field of precision injection molding, promoting the industry's transformation towards high efficiency, accuracy, and intelligence. Establishing a closed-loop system of "mold flow analysis - spline testing - mold optimization" is the key for enterprises to enhance their competitiveness.

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I. Potential Hazards of Excessive Wall Thickness in Injection Molded Parts. Potential Hazards of Excessive Wall Thickness in Injection Molded Parts



Excessive wall thickness is a common issue in the design or production of injection molded parts. It not only impairs product quality but also increases production costs and reduces production efficiency. The specific hazards are mainly reflected in the following aspects:


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1. Frequent Molding Defects: Excessive wall thickness leads to uneven cooling rates of the melt, making it difficult for internal heat to dissipate. This easily causes defects such as sink marks, depressions, bubbles, and warpage. For example, when the thick-walled area shrinks during cooling, the surface material cannot be replenished in time, resulting in obvious sink marks; the incompletely cooled melt inside continues to shrink, which may generate internal bubbles and affect the structural integrity of the product.

2. Low Production Efficiency: Increased wall thickness prolongs the melt filling time and cooling cycle, significantly reducing the efficiency of injection molding. Under the same production conditions, the cooling time of thick-walled parts may be 2-3 times that of parts with reasonable wall thickness, leading to a substantial drop in output per unit time and increased production energy consumption.

3. Material Waste and Rising Costs: Excessive wall thickness means an increase in raw material usage, directly raising material costs. Meanwhile, the extended cooling time leads to higher energy consumption and accelerated mold wear, further driving up the overall production costs.

4. Poor Mechanical Properties: Excessive wall thickness may cause uneven crystallization inside the plastic and the occurrence of stress concentration, reducing the mechanical properties of the product such as impact strength and toughness, and affecting the service life and safety of the product.


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II. Core Solutions to Excessive Wall Thickness in Injection Molded Parts. Potential Hazards of Excessive Wall Thickness in Injection Molded Parts



To address the issue of excessive wall thickness, a comprehensive approach is required from multiple aspects such as design source optimization, process adjustment, and material adaptation, aiming to achieve the goal of "reducing thickness without compromising quality".



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(I) Optimize Product Structure Design: Control Wall Thickness at the Source

Product design is the fundamental link to solve excessive wall thickness. On the premise of meeting usage requirements, unnecessary wall thickness should be reduced through scientific design while ensuring structural strength.

1. Adopt Uniform Wall Thickness Design: The ideal wall thickness of injection molded parts should be consistent, avoiding localized thick-walled areas. During design, a reasonable wall thickness range should be determined based on the product's application and stress conditions (typically, the reasonable wall thickness for thermoplastics is 1-4mm, which needs to be adjusted according to specific material properties). For parts of the product subject to high stress, methods such as adding reinforcing ribs and fillet transitions can be used instead of increasing wall thickness, which not only ensures strength but also avoids localized excessive thickness.

2. Incorporate Hollow Structures and Lightening Holes: For large-volume injection molded parts with no internal functional requirements, hollow design or lightening holes can be adopted to reduce the wall thickness of the core area. For example, for products such as home appliance casings and automotive interior parts, grid-like hollow structures can be arranged in non-stressed areas, which not only reduces material usage but also facilitates melt flow and cooling.

3. Optimize Transition Zone Design: The transition between areas of different wall thicknesses in the product should be smooth, avoiding right-angle or acute-angle abrupt changes. This prevents melt stagnation and accumulation during flow, while reducing defects caused by uneven cooling. The inclination angle of the transition zone is recommended to be controlled between 30°-60° to ensure smooth melt flow.

(II) Adjust Injection Molding Process Parameters: Adapt to Molding Requirements After Thickness Reduction

After optimizing the product structure, it is necessary to adjust the injection molding process parameters to ensure the smooth molding of the injection molded parts with reduced thickness and avoid problems such as insufficient filling and flash.

1. Improve Melt Fluidity: Appropriately increase the barrel temperature and mold temperature to reduce melt viscosity and enhance its flow capacity, ensuring that the melt can quickly fill the cavity with reduced thickness. The barrel temperature should be adjusted according to the plastic material (e.g., the temperature for PP material is usually 180-220℃, and for ABS material is 200-250℃), and the mold temperature is generally controlled at 40-80℃. This avoids material degradation caused by excessively high temperatures or poor fluidity due to excessively low temperatures.

2. Optimize Injection Pressure and Speed: Increase the injection pressure and injection speed to shorten the melt filling time and prevent insufficient filling caused by the reduced cavity wall thickness. The injection pressure is recommended to be increased by 10%-20% compared with the original parameters (adjustments should be made in combination with the mold bearing capacity). The injection speed can adopt segmented control: rapid filling in the early stage and slow pressure holding in the later stage, so as to reduce melt impact and flash generation.

3. Adjust Pressure Holding and Cooling Parameters: The cooling speed of injection molded parts with reduced thickness accelerates, so the pressure holding time and cooling time need to be adjusted accordingly. The pressure holding time can be shortened by 10%-15% to avoid product deformation caused by excessive pressure holding; the cooling time should be optimized according to the actual molding situation to ensure that the product temperature is lower than the heat distortion temperature when demolded, thereby reducing warpage.

(III) Select Suitable Materials and Improve Molds

1. Choose High-Flow Materials: For injection molded parts with thinner walls, it is recommended to select plastics with good fluidity, such as PP, PE, and ABS, or modified plastics (e.g., plasticizer-added modified PVC) to reduce molding difficulty. Avoid using materials with poor fluidity (such as PC and POM) for thin-walled products unless molding requirements can be met through process optimization or mold improvement.

2. Optimize Mold Structure: Improve the mold’s gating system by increasing gate size and shortening runner length to reduce melt flow resistance. For example, adopt pin-point gates or fan gates to enhance melt filling efficiency; install cold slugs in the runner to prevent cold material from entering the cavity and affecting molding quality. Meanwhile, the mold cavity surface should be polished to reduce melt flow friction and improve filling effectiveness.

3. Add Venting Systems: After wall thickness reduction, gas inside the cavity is more difficult to discharge, which may easily cause defects such as bubbles and burn marks on the product. Vent grooves should be arranged at the end of the mold cavity, dead corners of melt flow, and other positions. The recommended width of the vent groove is 0.01-0.03mm, and the depth is 0.5-1mm, ensuring timely gas discharge during the molding process.

(IV) Strengthen Quality Inspection and Iterative Optimization

1. Establish Wall Thickness Inspection Standards: Regularly inspect the wall thickness of injection molded parts during production using tools such as calipers and ultrasonic thickness gauges to ensure the actual wall thickness meets design requirements and avoid localized excessive thickness caused by production deviations.

2. Conduct Mold Testing and Process Iteration: After adjusting the product structure and process parameters, conduct mold testing to verify the product’s filling condition, surface quality, and mechanical properties. If problems such as insufficient filling or sink marks occur, further optimize the structural design or process parameters until the qualified standard is achieved.

3. Long-Term Monitoring and Feedback: Continuously monitor product quality during mass production, collect data on molding defects, and regularly analyze the causes to optimize the scheme. For example, if localized sink marks occur persistently, there may still be room for optimizing the wall thickness in that area, requiring re-adjustment of the structural design.

III. Precautions and Summary

To solve the problem of excessive wall thickness in injection molded parts, the principle of "design priority, process adaptation, and material matching" must be followed. The core is to minimize unnecessary wall thickness to the greatest extent on the premise of meeting product functions and mechanical properties. Meanwhile, the following points should be noted:

1. When optimizing the structure, do not excessively reduce the wall thickness. It is necessary to verify whether the product meets the usage requirements through strength tests to avoid quality problems such as product fracture and deformation caused by overly thin walls;

2. The adjustment of process parameters should be carried out step by step. Avoid drastic modifications at one time to prevent new molding defects such as flash and mold sticking;

3. Mold improvement should be combined with product structure and material characteristics. Avoid blindly adding gates or vent grooves, which may affect mold service life and product appearance.

In conclusion, solving the problem of excessive wall thickness in injection molded parts is a systematic project. It requires collaborative optimization from multiple aspects including design, process, materials, and molds. This not only addresses existing defects but also balances production efficiency and cost control, ultimately achieving a win-win situation for product quality and economic benefits.

In the injection molding process, the runner system is the "bridge" connecting the injection machine nozzle and the mold cavity. It is responsible for transporting molten plastic to each cavity stably and uniformly, directly affecting the molding quality, production efficiency and cost control of plastic parts. As the core components of the runner system, runners and sub-runners have clear division of labor and work together, which are the key links to ensure stable and efficient injection molding production. Below is a detailed analysis of their definitions, structures, functions and core differences.



I. Runners: The "Main Channel" of the Runner System
In injection molding, the runner is the first channel that molten plastic flows through after entering the mold from the injection machine nozzle. It is also the "starting end" and "main delivery pipe" of the entire runner system. It is directly connected to the injection machine nozzle and undertakes the core task of transporting high-temperature and high-pressure molten plastic from the machine to the sub-runners or directly into the cavity (for single-cavity molds). It is the part with the largest diameter and the largest flow capacity in the runner system.

1. Structural Characteristics of Runners
The structural design of the runner needs to adapt to the size of the injection machine nozzle and the flow characteristics of the plastic. It usually adopts a conical structure with a taper of 2°-5°. This design can not only reduce the flow resistance of molten plastic, but also facilitate the smooth removal of runner scrap during mold release. One end of the runner is the feed port, which is closely attached to the injection machine nozzle. The diameter of the feed port is slightly larger than that of the nozzle to avoid material leakage, material accumulation and other problems; the other end is connected to the sub-runners or the cavity to realize the smooth transition of plastic.

In addition, the runner is usually set at the center of the mold (corresponding to the center of the injection machine nozzle) to ensure uniform force when the plastic enters the mold, reduce pressure loss and temperature loss during the flow process, and is especially suitable for the runner layout of multi-cavity molds.

2. Core Functions of Runners
Transportation function: Quickly and stably transport the molten plastic injected by the injection machine to the sub-runners or cavities, ensuring sufficient plastic flow to meet the molding needs.

Transition function: Alleviate the pressure difference and temperature difference between the injection machine nozzle and the mold cavity, so that the molten plastic can smoothly transition from a high-pressure and high-speed state to a state suitable for cavity filling, reducing defects such as shrinkage marks, bubbles and material shortage in plastic parts.

Guiding function: Provide a clear flow direction for molten plastic, avoid disorderly flow of plastic in the mold, ensure the filling process is carried out in an orderly manner, and improve the dimensional accuracy of plastic parts.

II. Sub-Runners: The "Branch Pipes" of the Runner System
Sub-runners are branch channels connecting the runner and the mold cavity, mainly used in multi-cavity injection molds. After the runner transports the molten plastic to the designated position, the sub-runners will evenly distribute the plastic to each cavity, ensuring that the filling speed, pressure and temperature of each cavity remain consistent, thereby ensuring the dimensional consistency and quality stability of multi-cavity plastic parts.

1. Structural Characteristics of Sub-Runners
The structural design of sub-runners needs to be flexibly adjusted according to the number of cavities, layout and plastic part size. Common cross-sectional shapes include circular, trapezoidal, rectangular, etc., among which the circular cross-section is the most widely used—it has the smallest flow resistance and uniform heat dissipation, which can minimize the energy loss of plastic during the flow process; trapezoidal and rectangular cross-sections are convenient for mold processing and the removal of runner scrap.

The diameter of sub-runners is usually smaller than that of the main runner, and the length needs to be reasonably designed according to the cavity layout, trying to shorten the flow path and reduce bends, so as to avoid excessive pressure loss and too fast temperature drop during the plastic flow process. At the same time, the layout of sub-runners must follow the principle of "equal distance and equal diameter" to ensure consistent flow resistance of each branch and realize uniform distribution of plastic.

2. Core Functions of Sub-Runners
Distribution function: Evenly distribute the molten plastic transported by the runner to each cavity, ensuring that the filling volume and filling speed of each cavity are consistent, and avoiding material shortage in some cavities and material overflow in others.

Pressure reduction and stabilization function: Further reduce the pressure and flow rate of molten plastic, so that the plastic enters the cavity in a more stable state, reducing defects such as flow marks and gate marks on the surface of plastic parts, and improving the appearance quality of plastic parts.

Auxiliary heat dissipation function: The surface area of sub-runners is relatively large, which can assist in dissipating part of the heat of molten plastic, allowing the plastic to cool gradually during the filling process, and avoiding plastic part deformation, uneven shrinkage and other problems caused by excessive temperature.

III. Core Differences Between Runners and Sub-Runners
Although both runners and sub-runners belong to the runner system, they have obvious differences in function, structure and design requirements. The specific comparison is as follows:




Comparison Dimension
Runners
Sub-Runners


Core Function
Connect the injection machine to sub-runners/cavities and mainly transport plastic
Connect the runner to cavities and distribute plastic to each cavity


Structural Shape
Mostly conical with a taper of 2°-5°
Circular, trapezoidal, rectangular, etc., with uniform cross-section


Size Characteristics
Large diameter, the thickest part in the runner system
Diameter smaller than the runner, adjusted according to cavity layout


Application Scenario
Required for both single-cavity and multi-cavity molds
Mainly used for multi-cavity molds; can be omitted for single-cavity molds


Design Focus
Adapt to nozzle size, reduce material leakage and pressure loss
Equal distance and equal diameter to ensure uniform plastic distribution




IV. Key Design Points of Runners and Sub-Runners
The rationality of the design of runners and sub-runners directly affects the efficiency of injection molding production and the quality of plastic parts. The core design points are as follows:




Match plastic characteristics: Adjust the diameter, length and taper of the runner according to the fluidity, melting point and other parameters of the plastic—for plastics with poor fluidity (such as PC, ABS), the runner diameter needs to be increased to reduce flow resistance; for plastics with good fluidity (such as PE, PP), the runner diameter can be appropriately reduced to reduce raw material loss.
Optimize layout design: The runner must be aligned with the center of the injection machine nozzle, and the sub-runners must follow the principle of "equal distance, equal diameter and shortest path" to reduce bends and excessively long flow paths, avoiding pressure loss and temperature drop.
Facilitate mold release and cleaning: The runner design must consider the convenience of taking out the runner scrap. The conical runner and smooth inner wall of the runner can reduce the adhesion of runner scrap and lower the cleaning cost.
Control cost loss: On the premise of ensuring molding quality, try to reduce the runner size to reduce the loss of molten plastic (runner scrap needs to be recycled and reused), thereby reducing production costs.

V. Summary
Runners and sub-runners are two indispensable core parts of the injection molding runner system. They work together to form a complete transportation path for molten plastic from the injection machine to the cavity. As the "main channel", the runner undertakes the core transportation task; as the "branch pipes", the sub-runners are responsible for uniformly distributing plastic. The rationality of their design directly determines the quality, production efficiency and cost of plastic parts.

In actual injection molding production, it is necessary to optimize the structure and layout of runners and sub-runners in combination with the plastic part structure, the number of cavities, plastic characteristics and injection machine parameters, so as to achieve efficient, stable and high-quality injection molding production and escort product quality.

The surface finish, mirror effect, and overall appearance integrity of injection molded plastic parts are a direct reflection of a brand's
product quality and market competitiveness. Surface scratches are a highly prevalent, easily overlooked, yet extremely impactful appearance defect in injection molding production. These include various types such as hairline scratches, hard scratches, demolding tears, mold marks, and friction scratches.
Surface scratches directly disrupt subsequent surface decoration processes such as pad printing, screen printing, spray painting, electroplating, and laser engraving: ink easily accumulates in the scratch grooves, resulting in broken lines, color differences, unevenness, poor adhesion, and peeling; scratches remain noticeable even after spray painting, requiring rework and polishing, which is time-consuming and material-intensive, and in severe cases, the entire batch can be scrapped, causing significant cost losses and delivery delays.
Main Causes of Scratches on Injection Molded SurfacesScratches originate from the entire chain, including mold, process, demolding mechanism, product structure, manual operation, and storage environment:
1. Mold Body Causes: Insufficient polishing of the cavity and core leaves tool marks and sand marks; insufficient hardness of the mold steel leads to burrs and wear over long-term production; excessive clearance in ejector pins, sleeves, inserts, and slides results in rough surfaces and misalignment; sharp corner burrs on the parting surface and carbon buildup and corrosion in the mold cavity can all transfer or scratch the product surface.
2. Injection Molding Process Causes: Injection speed too fast causes high-speed melt to scour the mold wall, forming flow marks and scratches; insufficient cooling time results in premature demolding before the product has set; excessive cooling causes the product to cling to the mold core, increasing demolding resistance and causing scratches; imbalance between mold and material temperatures leads to deformation, friction, and scratches.
3. Product Structure and Demolding Causes: Insufficient draft angle, thin ribs, excessive undercuts, and lack of proper rounded corners significantly increase demolding resistance, resulting in hard friction during ejection and producing strip-like scratches. 4. Human and Environmental Factors: Dust, adhesive residue, and metal shavings falling into the mold cavity cause scratches; employees using sharp tools to pry products; semi-finished products lacking protective films and rubbing against each other when stacked; lack of anti-collision barriers during handling and storage, resulting in secondary scratches.
Comprehensive Prevention and Solutions for Injection Molding Surface Scratches


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1. Mold Source Control: Use high-hardness, wear-resistant mold steel; perform mirror-finish nano-polishing of the cavity and core to remove tool marks and sanding marks; perform regular mold maintenance, rust and carbon removal, and hard chrome plating to improve wear resistance; optimize the fit precision of ejector pins and slides, chamfering and removing sharp corners to ensure smooth movement without scratches.

2. Injection Molding Process Parameter Optimization: Segmented speed injection to avoid high-speed erosion of the mold wall; match reasonable mold temperature, material temperature, and cooling time to ensure uniform product shaping; uniform and slow ejection to reduce demolding friction and scratches.

3. Pre-design Product Structure Optimization:** Increase draft angles and rounded corners during the design phase; avoid deep ribs, right-angle undercuts, and other easily damaged structures; use sliding core-pulling for complex structures to reduce forced demolding.

4. Standardized Workshop Operations:** Maintain a dust-free workshop and regularly clean mold cavity debris; prohibit the use of sharp tools for demolding, and uniformly use soft plastic tools; wrap semi-finished products individually with paper dividers for layered turnover, and add soft padding to turnover boxes to prevent friction and impact.

5. Graded Scratch Repair Solution:** Minor hairline scratches: fine polishing with fine sandpaper, oilstone, and diamond paste; moderate scratches: texturing, sanding, and spray painting for coverage; deep structural scratches: mold repair and machine adjustment are necessary to prevent batch recurrence from the root cause.

III. High-Quality Plastic Parts Guarantee for Pad Printing and Screen Printing:** Plastic shells, buttons, and panels requiring pad printing and screen printing must have a zero-scratch, highly flat base surface to ensure clear printing patterns, ink adhesion, and uniform color.

AAA MOULD integrates mold design, precision injection molding, defect rectification, pad printing, and screen printing surface decoration. It strictly controls surface quality throughout the entire chain from mold polishing, structural design, injection molding process, and production operation, avoiding molding defects such as scratches and weld lines in advance, and providing a perfect base for subsequent surface printing processes, helping customers produce high-quality, durable, and cost-effective plastic products.

In injection molding production, the mold gating system serves as the core fluid channel connecting the injection molding machine and the mold cavity, acting as the "delivery artery" for plastic molding. Its design quality directly determines the melt filling effect, product molding precision, surface quality and production yield, making it an indispensable core part of injection mold structural design. This article comprehensively analyzes the structural composition, working principle, mainstream types and core design principles of injection mold gating systems, helping customers fully understand the core process logic of injection molding.



I. Core Definition and Functions of Gating Systems
An injection mold gating system refers to a series of specially designed channel structures from the nozzle of the injection molding machine to the mold cavity, dedicated to transporting, diverting, stabilizing pressure and cooling plastic melts. In short, its core function is to deliver the high-temperature molten plastic melt from the injection molding machine to each mold cavity in a stable, uniform and balanced manner, completing the entire process of filling, pressure holding and shrinkage compensation to form intact plastic products.

A high-quality gating system achieves three core values: first, stable material delivery to avoid molding defects such as melt turbulence, splashing and air bubbles; second, balanced filling to ensure consistent molding quality of products in multi-cavity molds; third, material saving to reduce residual gating waste and lower production loss and subsequent processing costs.

II. Basic Structural Composition of Gating Systems
A complete injection gating system consists of four core components: main sprue, runner, gate and cold slug well. Each component performs its own function and cooperates with others to form a complete melt delivery system.



1. Main Sprue
The main sprue is the inlet channel of the gating system, directly connected to the nozzle of the injection molding machine and serving as the first passage for melt entering the mold. It is generally designed as a tapered structure wider at the top and narrower at the bottom, which facilitates the demolding and removal of solidified sprue slugs, reduces melt flow resistance, and prevents melt retention, temperature drop and channel blockage. Undertaking the tasks of receiving all melt and preliminary flow guidance, the structural precision of the main sprue directly affects the initial flow state of the melt.

2. Runner
As an extended branch of the main sprue, the runner is mainly used to divert and distribute the melt from the main sprue to each independent cavity, widely applied in multi-cavity molds and molds for large and complex plastic parts. According to mold structural requirements, runners can be designed with circular, trapezoidal or semicircular cross-sections, among which the circular cross-section features the minimum flow resistance and the highest melt delivery efficiency. The core design logic of runners is to ensure uniform melt distribution, consistent melt pressure, flow rate and temperature in each cavity, and eliminate product defects such as dimensional deviation, short shot and sink mark.

3. Gate
The gate is a tiny connecting port between the runner and the mold cavity, as well as the final passage for melt entering the product molding area, making it the most critical precision structure of the gating system. With a miniature size, the gate can accelerate, stabilize pressure and throttle the melt, enabling the melt to fill the cavity at a high speed and in a stable state. It also effectively prevents melt backflow and ensures molding stability during the pressure holding stage. After cooling and solidification, the tiny gate slug can be easily separated from the product, greatly reducing subsequent trimming and polishing processes.

4. Cold Slug Well
Cold slug wells are reserved small storage grooves arranged at the end of the main sprue and the corners of runners. At the initial stage of injection molding, a small amount of low-temperature solidified cold slugs exist at the nozzle port. If these cold slugs directly enter the cavity, they will cause surface spots, weld lines and other defects on products. Cold slug wells intercept cold slugs and impurities in advance, filter unqualified melt, ensure pure and uniform-temperature melt entering the cavity, and effectively improve product appearance and quality.

III. Complete Working Principle of Injection Gating Systems
The working process of an injection mold gating system is a continuous and closed-loop melt delivery and molding auxiliary process, which runs synchronously with the entire injection molding procedure. It is specifically divided into four stages:



1. Melt Introduction Stage
The injection molding machine melts plastic particles into fluid melt at high temperature, and pushes the melt into the main sprue of the mold through high pressure via the machine nozzle. The tapered main sprue quickly receives the melt, reduces flow resistance, guides the melt to flow stably into the mold, and avoids melt leakage and retention.

2. Flow Division and Pressure Stabilization Stage
After entering the runners, the melt is evenly distributed to each branch channel through the preset flow path. During this process, the runner structure stabilizes the melt flow rate and pressure, eliminates melt turbulence and uneven pressure, and ensures consistent melt flow and pressure in all channels of multi-cavity molds.

3. Cavity Filling Stage
The melt after flow division and pressure stabilization is further accelerated and pressurized through the tiny gates, then injected into the mold cavity at a high and stable speed to fully fill the entire molding space. The throttling effect of the gate avoids splashing and air bubbles caused by excessive melt inflow speed, as well as short shots and sink marks caused by insufficient flow speed, ensuring full and uniform cavity filling.

4. Pressure Holding, Cooling and Slug Separation Stage
After cavity filling is completed, the gating system maintains continuous pressure to compensate for shrinkage caused by plastic cooling volume reduction, ensuring product dimensional accuracy. After the product and the melt in the gating system are completely cooled and solidified, the mold opens to eject the product, and the solidified gating slugs are ejected together with the product. Finally, the gate waste is separated from the finished product manually or by automated equipment, completing one full molding cycle.

IV. Common Types and Application Scenarios of Gating Systems
According to differences in product structure, appearance requirements and production efficiency, gating systems are divided into two main categories to meet diverse production needs:



1. Conventional Gating System (Cold Runner System)
As the most widely used traditional gating system, the melt in the main sprue and runner cools and solidifies together with the product, and the runner waste needs to be trimmed after molding. Featuring simple structure, low mold cost and wide adaptability, it is suitable for most conventional plastic products and medium and small-batch production scenarios, serving as the mainstream choice for general injection molds.

2. Hot Runner Gating System
The hot runner system is equipped with heating devices to keep the melt in the runner at a constant temperature at all times, maintaining the plastic in a molten state without forming solid slugs. Only finished products are taken out after molding with no runner waste generated. Its advantages include high material utilization, no need for subsequent trimming, high molding efficiency and excellent product consistency. It is mostly applied to high-precision, high-appearance standard and mass-produced plastic products, such as electronic accessories and precision medical device parts.

V. Core Design Principles of Gating Systems
The design quality of the gating system determines mold quality and product yield. Professional mold design must follow the following core principles:

1. Smooth Flow Principle: Adopt a concise runner layout with rounded corners to minimize melt flow resistance and avoid melt retention, degradation and burning.

2. Balanced Filling Principle: For multi-cavity molds, ensure symmetrical and uniform dimensions of all runners and gates to realize synchronous filling and eliminate product dimensional and weight deviation.

3. Quality Priority Principle: Reasonably set the position and size of gates to avoid product appearance surfaces and stress surfaces, preventing molding defects such as weld lines, sink marks, air bubbles and warpage.

4. High Efficiency and Energy Saving Principle: On the premise of meeting molding quality, simplify runner length and volume to reduce material waste, shorten the molding cycle and improve production efficiency.

5. Easy Demolding Principle: The structure of runners and gates is designed to adapt to demolding requirements, ensuring smooth removal of solidified slugs without jamming or product surface damage.

VI. Conclusion
Essentially, the injection mold gating system is a complete process system that realizesstable melt delivery, balanced filling, pressure-stabilized molding and efficient demolding through scientific channel structure design. As the core "delivery system" of injection molds, its structural design directly affects product precision, surface quality, production efficiency and production cost.

A well-designed gating system must adapt to the flow characteristics of different plastic materials and fit product structures and production requirements, balancing molding quality, production efficiency and economic benefits. It is the core key to the research and development and design of high-precision injection molds.