For previous reading, please refer to Mold Design Guide (VI - Ejection and Demolding Mechanism).
9.1 Gating System Design Principles
9.1.1 Composition of Gating System
Gating system of a mold refers to flow channel within mold from injection molding machine nozzle to cavity entrance. It can be divided into two main types: conventional runner gating systems and runnerless gating systems. A conventional runner gating system consists of a main runner, branch runners, a cold slug well, and a gate. (See Figure 9-1).

 

Figure 9-1 Composition of Gating System
1-Main runner; 2-Primary runner; 3-Gutter/Cold slug well 4-Cold slug well; 5-Secondary runner; 6-Gate
9.1.2 Following principles should be followed when designing gating system:
1. Considering cavity layout, following three points should be noted:
Use a balanced layout as much as possible so that molten plastic can fill each cavity evenly; Cavity layout and gate location should be designed to ensure uniform stress on mold during injection molding; Cavities should be arranged as compactly as possible to reduce the overall mold dimensions.
2. Minimize heat and pressure losses.
Select an appropriate runner cross-section; Determine reasonable runner dimensions; Within a certain range, using a larger runner system helps reduce flow resistance. However, when pressure drop in runner system is small, smaller dimensions should be prioritized. This reduces material usage and shortens cooling time. Minimize bends and maintain low surface roughness.
3. Gating system should capture cooler material to prevent it from entering cavity and affecting part quality;
4. Gating system should smoothly guide molten plastic to fill all corners of the cavity, allowing for smooth gas escape;
5. Prevent product defects;
Avoid defects such as incomplete filling, shrinkage marks, flash, undesirable weld line placement, residual stress, warpage, and uneven shrinkage.
6. Aim for the best product appearance quality in gate design; Gate design should avoid defects such as burn marks, serpentine patterns, and shrinkage cavities on the product appearance.
7. Gate should be located in a relatively concealed position and be easy to remove, ensuring that gate location does not affect appearance or interfere with surrounding parts.
8. Consider whether it can be automatically operated during injection molding.
9. Consider subsequent processes of the product, such as needs of processing, assembly, and management, requiring multiple products to be connected into one unit through runner.
9.2 Runner Design
9.2.1 Main Runner Design
(1) Definition: Main runner is section of runner that runs from injection molding machine nozzle to branch runner. Molten plastic first passes through it when entering mold. Generally, position of main runner inlet should coincide with center of mold as much as possible.
(2) Design Principles: Main runner of thermoplastic plastics is generally composed of a sprue bushing, which can be divided into two categories: two-plate mold sprue bushings and three-plate mold sprue bushings. Referring to Figure 9-2, regardless of type of sprue bushing, to ensure smooth removal of solidified material from main runner, following should be satisfied: D = d + (0.5~1) mm; R1 = R2 + (1~2) mm

 

Figure 9-2 Nozzle and sprue bushing matching relationship
9.2.2 Design of Cold Slug Well
(1) Definition and Function: A cold slug well is designed to remove cold material generated at the front of material flow due to contact between nozzle and low-temperature mold, which then enters cavity. It is generally located at the end of main runner. When branch runner is long, a cold slug well should also be installed at the end of branch runner.
(2) Design Principles: Generally, diameter of cylindrical body of cold slug well in main runner is 6~12 mm, and its depth is 6~0 mm. For large products, size of cold slug well can be appropriately increased. For cold slug well in branch runner, its length is (1~1.5) times runner diameter.
(3) Classification:
a. Cold slug well with ejector pin at the bottom

 

Figure 9-3 Cold sluice well with top rod at the bottom
Because the first type is easy to process, it is often used. Z-shaped pull rods should not be used simultaneously, otherwise they will be difficult to detach from gating system. If multiple Z-shaped pull rods are required, ensure that notches face same direction. However, for products that cannot move laterally during demolding, second and third types of pull rods should be used. Select different depths of undercut d according to different elongation rates of plastic. If following condition is met: (D-d)/D
Table 9-1 Elongation of Resin (%)

 

b. Cold slug well pushed out by push plate
This type of pull rod is specifically used in molds where plastic parts are demolded by push plates or top blocks. Undercut amount of pull rod can be referred to Table 9-1. Tapered head pull rod (shown in Figure 9-4 c) relies on clamping force of plastic to hold main runner, which is not as reliable as ball head pull rod and mushroom-shaped pull rod (shown in Figure 9-4 b, c). To increase friction of conical surface, a smaller taper can be used, surface roughness can be increased, or a double pull rod (shown in Figure 9-d) can be used instead. The latter two methods, due to better flow-diverting effect of pointed cone, are often used for single-cavity molded parts with a center hole, such as gear molds.

 

Figure 9-4 Pull rod for push plate mold
1-Front mold; 2-Push plate; 3-Pull rod; 4-Core fixing plate; 6-Rear mold; 6-Top block
c. Cold slug well without pull rod
For injection molds with a vertical parting line, cold slug well is placed on the center line of left and right mold halves. When mold opens, parting line separates, and part is pulled out together with cold slug at leading edge. A pull rod is not necessary for cold slug well. See Figure 9-5.

 

Figure 9-5 Cold slug well without pull rod
d. Runner cold slug well
Generally, two forms are used, as shown in Figure 9-6: Figure a shows cold slug well placed in depth direction of rear mold; Figure b shows runner extending on parting line to form cold slug well. Refer to Figure 9-6 for relevant dimensions.

 

Figure 9-6 Cold Material Well for Diversion Channels
1-Main Channel 2-Cold Material Well for Diversion Channels
9.2.3 Design of Runners
When molten plastic flows along runners, it is required to fill cavity as quickly as possible, with temperature drop during flow being as small as possible and flow resistance as low as possible. At the same time, molten plastic should be evenly distributed to each cavity. Therefore, in design of runners, following should be considered:
(1) Selection of runner cross-sectional shape
A larger cross-sectional area is beneficial to reducing flow resistance of runner; a smaller cross-sectional perimeter is beneficial to reducing heat loss of molten plastic. We call ratio of perimeter to cross-sectional area specific surface area (i.e., ratio of runner surface area to its volume), and use it to measure flow efficiency of runner. That is, the smaller specific surface area, the higher flow efficiency.

 

From Table 9-2, we can see order of flow efficiency and heat loss of runners with same cross-sectional area. Advantages of a circular cross-section are: the smallest specific surface area, less heat loss, and low resistance. Disadvantage is: it needs to be opened on both front and rear molds, they need to fit together, so manufacturing is more difficult. Flow efficiency of a U-shaped cross-section is lower than that of a circular or hexagonal cross-section, but it is easier to process and easier to demold than circular or square cross-section runners. Therefore, U-shaped runners have excellent overall performance. Above two cross-sectional shapes should be preferred, followed by trapezoidal cross-sections. Slope of two sides of U-shaped and trapezoidal cross-sections is generally 5°-10°.
(2) Runner Cross-Section Dimensions
Cross-sectional dimensions of runner should be determined based on factors such as size, wall thickness, shape of plastic part, processing properties of plastic used, injection rate, and length of runner. For commonly used wall thicknesses of (2.0~3.0) mm, diameter of circular runner generally varies between 3.5~7.0 mm. For plastics with good flow properties, such as PE, PA, and PP, diameter can be as small as Φ2.5 mm when runner is very short. For plastics with poor flow properties, such as HPVC, PC, and PMMA, diameter can be Φ10~Φ13 mm when runner is long. Experiments have shown that for most plastics, runner diameter is greatest when it is below 5-6 mm, having the greatest impact on flow. However, when diameter is above 8.0 mm, further increasing diameter has little effect on improving flow. Generally speaking, to reduce runner resistance and achieve normal pressure holding, following requirements must be met: a. When runner is not branching, cross-sectional area should not have a large abrupt change; b. Minimum cross-sectional area in runner should be greater than minimum cross-sectional area at gate. For three-plate molds, these two points should be given particular attention. In Figure 9-7a, H ³ D1 > D2 ³ D3; d1 is greater than minimum gate cross-section, generally taken as (1.5~2.0) mm, h = d1, taper a and b are generally taken as 2°~3°, and d should be as large as possible.

 

Figure 9-7 Three-plate mold flow channel structure and dimensions
To reduce resistance of pull rod to runner, runner should be enlarged at pull position, as shown in Figure 9-7c; or pull position should be made on runner push plate, as shown in Figure 9-7d. In Figure 9-7b, H ≥ D1, taper a and b are generally 2°~3°. Dimensions at junction of tapered runners differ by 0.5~1.0mm. Requirements for pull position are same as in Figure 9-7a.
9.3 Gate Design
Gate is a crucial part of gating system. Location, type, and size of gate have a significant impact on quality of molded parts. In most cases, gate is part with the smallest cross-sectional size in the entire gating system (except for direct gate of main runner type). For a circular flow section, pressure drop at both ends of circular tube is DP, and following relationship exists: From equations (9-1) and (9-2), it can be seen that when filling rate is constant, pressure drop DP at mold inlet during flow is related to following factors:
(1) The longer channel length, i.e., the longer runner and cavity length, the greater pressure loss;
(2) Pressure drop is related to cross-sectional dimensions of runner and cavity. The smaller cross-sectional dimensions of runner, the greater pressure loss. Depth of a rectangular runner has a much greater impact on pressure drop than its width. Ratio of cross-sectional area of gate to that of runner is generally about 0.03~0.09, and gate step length is about 1.0~1.5mm. Common cross-sectional shapes are rectangular, circular, or semi-circular.
9.3.1 Types of Gates

 

Figure 9-8 Direct gate
Advantages: (1) Low pressure loss; (2) Simple manufacturing.
Disadvantages: (1) High stress near gate; (2) Requires manual removal of gate (runner); (3) Leaves obvious gate scars on the surface.
Applications: Can be used for large and deep barrel-shaped plastic parts. For shallow and flat plastic parts, warping is likely due to shrinkage and stress. For plastic parts where gate marks are not acceptable on the surface, gate can be placed on inner surface of plastic part, as shown in Figure 9-8c. In this design, plastic part remains in the front mold after mold opening, and is ejected using a secondary ejection mechanism (not shown in diagram).

 

Figure 9-9 Side gate
Advantages: Simple shape, easy to process; Removing gate is relatively easy.
Disadvantages: Plastic part and gate cannot separate automatically; Gate marks are easily left on plastic part.
Parameters:
1.) Gate width W is (1.5~5.0) mm, generally W=2H. Larger or transparent plastic parts can be enlarged accordingly;
2.) Depth H is (0.5~1.5) mm. Specifically, for common materials like ABS and HIPS, H is typically taken as (0.4~0.6)d, where d is basic wall thickness of part. For materials with poor flow properties like PC and PMMA, H is taken as (0.6~0.8)d.
For materials like POM and PA, these materials have good flow properties but also fast solidification rates and large shrinkage rates. To ensure sufficient pressure holding and prevent defects such as shrinkage marks and wrinkles, a gate depth of H = (0.6~0.8)d is recommended.
For materials like PE and PP, a smaller gate facilitates melt shear thinning and reduces viscosity, so a gate depth of H = (0.4~0.5)d is recommended.
Applications: Suitable for parts of various shapes, but not for thin and long barrel-shaped parts.

 

Figure 9-10 Overlapping gate
Advantages of overlapping gates: It is an evolution of side gates, possessing all advantages of side gates; It is a typical impact gate, effectively preventing jetting flow of molten plastic.
Disadvantages: Cannot achieve self-separation of gate and plastic part; Easily leaves obvious gate scars.
Parameters: Refer to parameters of side gate for selection.
Application: Suitable for flat plastic parts with surface quality requirements.

 

Figure 9-11 Pin-point gate
Advantages: High degree of freedom in gate location selection; Gate can separate from plastic part automatically; Small gate mark; Low stress near gate location.
Disadvantages: Higher injection pressure; Generally requires a three-plate mold structure, which is more complex.
Parameters: Gate diameter d is generally (0.8~1.5) mm; Gate length L is (0.8~1.2) mm; To facilitate flush breakage of gate, a taper 'a' of approximately 15°~20° should be added to gate; junction of gate and runner should be connected by an arc R1 to prevent damage to plastic part when pinpoint gate breaks. R2 is (1.5~2.0) mm, R3 is (2.5~3.0) mm, and depth h is (0.6~0.8) mm.
Applications: Commonly used for larger surface and bottom shells; proper gate distribution helps achieve a more ideal weld line distribution; it can also be used for long, cylindrical plastic parts to improve their appearance.

 

Figure 9-12 Fan-shaped gate
Advantages: When molten plastic flows through gate, it is more evenly distributed laterally, reducing stress on plastic part; It reduces possibility of air entering cavity, avoiding defects such as silver streaks and bubbles.
Disadvantages: Gate cannot separate from molded part on its own; Edge of molded part has a long gate mark, requiring tools to smooth it out.
Parameters: Common dimensions: Depth H is (0.25~1.60) mm; Width W is 8.00 mm to 1/4 of width of cavity on gate side; Cross-sectional area of gate should not be larger than cross-sectional area of runner.
Applications: Commonly used for molding wide, thin sheet-like molded parts, flowable PMMA, etc.

 

Figure 9-13 Submerged gate
Advantages: More flexible gate location selection; Gate can separate from molded part on its own. Small gate marks; Suitable for both two-plate and three-plate molds.
Disadvantages: Glue powder easily gets trapped at gate; Burn marks easily appear at sprue; Requires manual trimming of glue sheet; Significant pressure loss from gate to cavity.
Parameters: Gate diameter d: 0.8~1.5mm; Angle a between injection direction and vertical direction: 30°~50°; Taper B of gate beak: 15°~25°; Distance A from front mold cavity: (1.0~2.0)mm.
Application: Suitable for plastic parts where gate marks cannot be visible on exterior. For multi-cavity plastic parts, resistance from gate to cavity should be as similar as possible in each cavity to avoid stagnation and achieve better flow balance.

 

Figure 9-14 Curved gate
Advantages: Gate and plastic part can be automatically separated; No additional treatment is required at gate location; No gate marks will appear on the surface of plastic part.
Disadvantages: Potential for baking marks on the surface; More complex processing; Poorly designed gates are prone to breakage and clogging.
Parameters: Diameter d of inlet end of gate is (∅0.8~∅1.2) mm, and length is (1.0~1.2) mm; Value of A is about 2.5D; ∅2.5min* refers to gradual transition from large end 0.8D to small end ∅2.5.
Application: Commonly used in ABS and HIPS. Not suitable for crystalline materials such as POM and PBT, nor for rigid materials such as PC and PMMA, to prevent arc-shaped runner from being broken and clogging gate.

 

Figure 9-15 Ear-type gate
Advantages: Helps to improve air bubbles near gate.
Disadvantages: Requires manual cutting of gate; Leaves obvious gate marks on the edge of plastic part.
Parameters: Ear length A = (10~15) mm, width B = A/2, thickness is 7/8 of cavity cross-sectional wall thickness at inlet; gate width W is 1.6; depth H is (1/2~2/3) of ear thickness, gate length 1.0.
Application: Commonly used for flat plates made of high-transparency plastics such as PC and PMMA.

 

Figure 9-16 Circular gate
Advantages: Low resistance of runner system; Reduces number of weld lines; Helps with venting; Simple to manufacture.
Disadvantages: Requires manual removal of gate; Leaves obvious gate marks.
Parameters: To facilitate gate removal, gate depth h is generally (0.4~0.6) mm; H is (2.0 2.5) mm.
Application: Suitable for plastic parts with holes in the middle.

 

Figure 9-17 Lifter Arc-Shaped Gate
Advantages: No need to worry about curved runner breaking during demolding; Offers a wide range of options for gate location; Facilitates venting.
Disadvantages: Baking marks are easily formed on the surface of plastic part; Manufacturing is relatively complex; A long span of curved runner may affect arrangement of cooling water.
Parameters: Refer to relevant parameters for side gates.
Applications: Mainly suitable for shell-shaped plastic parts with poor venting or long flow paths; To reduce resistance of curved runner, a U-shaped cross-section is recommended (see figure); Design of lifter can refer to "Section 7.7 Lifter and Rocker Mechanism"; Gate position should be selected at the corner of plastic part or in an inconspicuous location.
9.3.2 Gate Arrangement
1. Avoid weld lines on major appearance surfaces or affecting strength of part
Based on customer requirements, weld lines should be controlled in concealed locations with low stress. Simultaneously, avoid weld lines connecting holes in a straight line, as this reduces part's strength. As shown in Figure 9-18(a), weld lines formed by two holes on part connect in a straight line, which reduces part's strength. Gate position should be arranged as shown in Figure 9-18(b). To increase weld strength, a cold slug well can be opened on the outside of weld line to allow cold slug to overflow. For large frame-type parts, auxiliary runners can be added, as shown in Figure 9-19; or number of gates can be increased, as shown in Figure 9-20.

 

2. Prevent deformation of long rod-shaped plastic parts under injection pressure;
See Figure 9-21. In scheme (a), core will bend under impact of unilateral injection pressure, resulting in deformation of plastic part. Scheme (b), with balanced injection from both sides of core, effectively eliminates this defect.

 

Figure 9-21 Gate arrangement scheme for long rod-shaped plastic parts
3. Avoid affecting the assembly between parts or leaving marks on exposed surfaces;
As shown in Figure 9-22(a), to avoid affecting assembly, a notch is made on flange of button, and gate is located on notch to prevent interference with related plastic parts during assembly. As shown in Figure 9-22(b), gate is hidden in rib of plastic part, making gate location very concealed and eliminating need for additional plastic sheets, facilitating automatic production during injection molding.

 

Figure 9-19 Gate location arrangement does not affect assembly
4. Prevent snake-like patterns and burn-in marks; impact gates or bottom-mounted gates should be used.
When molten plastic enters mold cavity from runner through small-section gate, its velocity increases sharply. If there is no resistance in cavity to reduce melt velocity, jetting will occur, as shown in Figure 9-23(a). In mild cases, this produces burn marks near gate; in severe cases, it produces serpentine patterns. As shown in Figure 9-23(b), if a thick mold base is used, molten plastic will be sprayed onto front mold surface and obstructed, thus changing direction, reducing velocity, and filling cavity evenly. In Figure 9-24(a), because melt does not encounter resistance when entering cavity, air bubbles are generated at front end of plastic part; after improvement according to 9-24(b), above defects can be eliminated.

 

Figure 9-20 Gate arrangement to avoid jetting

 

5. To facilitate flow and pressure holding, gate should be located at thicker part of molded component;
6. This facilitates venting.
As shown in Figure 9-25, a cap-shaped molded component is thinner at the top than at the sides. Using a side gate, as shown in Figure (a), will create trapped air at point A at the top, leading to weld lines or scorching. An improved solution, as shown in Figure (b), involves adding appropriate amounts of molded material to top surface. However, trapped air may still occur at point A on the side. If gate is located on the top surface as shown in Figure (c), trapped air phenomenon can be eliminated.

 

Figure 9-25 Effect of gate location on venting
(1) A - weld line; purple - flow direction
As shown in Figure 9-26, if injection method in Figure (a) is used, trapped air is expected at point A. Solution (b) is recommended, as it helps to expel gas from mold cavity.

 

Figure 9-26 Influence of gate location on venting (2)
A - Expected entrapment location
7. Consider impact on quality of oriented plastic parts;
For long, flat plastic parts, gate should be located at one end of part to ensure consistent shrinkage in flow direction, as shown in Figure 9-26(a). If flow of part is relatively large, gate can be moved slightly towards center, as shown in Figure 9-26(b). However, it is not advisable to place gate in the middle of part. As can be seen from Figure 9-26(c), when gate is in the middle, resin flow is radial, causing uneven radial and tangential shrinkage, resulting in deformation.

 

Figure 9-27 Different gate locations for flat plastic parts
8. For multi-cavity molds, a balanced runner arrangement is preferred for gate;
As shown in Figure 9-28, it is recommended to use balanced runner arrangement (b) for gate, which is beneficial for balanced filling of each cavity.

 

Figure 9-28 Arranging gates according to a balanced runner system
9. Considering injection molding efficiency and facilitating separation of runner system and plastic part
After determining mold structure, ease of separation between runner system and plastic part should be considered. Using pin-point gates, submarine gates, or curved runners can achieve automatic separation of runner system and plastic part. When selecting location of a submarine gate, priority should be given to its placement within structure of plastic part itself. This reduces injection pressure and avoids need to remove plastic sheet during production. Side gates, overlapping gates, annular gates, and angled gates are relatively easy to separate. Direct gates, fan-shaped gates, and ear-type gates are more difficult to separate.
10. Considering ease of processing
For multi-cavity curved runner structures, to reduce number of inserts, curved runners should be placed on the insert surfaces of large inserts in the rear mold, as shown in Figure 9-29. Rear mold consists of 7 inserts, with half of curved runner for each cavity appearing in each insert. This simplifies processing.

 

Figure 9-29 Insert for curved flow channel
9.4 Flow Balance Analysis
Flow balance is an important principle for ensuring quality of plastic parts when designing a runner system. From perspective of a single cavity, it requires that all flow paths should be filled simultaneously with same pressure; from perspective of multiple cavities, each cavity should be filled at same instant with same pressure.
9.4.1 Unbalanced flow will produce following drawbacks:
(1) Over-compaction occurs in the first-filled area. Over-compaction may cause following four defects:
Waste of plastic material; Different shrinkage rates in different areas will lead to inconsistent plastic part dimensions and warping; Sticking to mold, whitening; Excessive stress will shorten life of plastic part.
(2) Increase injection pressure. This may result in: Flash appearing when filling cavity first; Increased clamping force of machine is required.
(3) Unbalanced flow often leads to irregular molecular orientation, causing inconsistent shrinkage rates and warping of plastic parts.
9.4.2 Methods for implementing flow balancing
In addition to adjusting dimensions of runner system, we should also consider four factors:
(1) Correct gate location and reasonable number of gates;

 

Figure 9-30 Filling time analysis results of original runner layout scheme (1)
Mold consists of eight cavities of different sizes. First, consider: a. placing the largest cavity A in position closest to main runner; b. and using two-point injection for this cavity.
Flow analysis revealed that cavity B has a shorter flow path and was filled earliest, exhibiting a significantly different flow order compared to the other seven cavities.
Further comparison of filling pressure distribution was conducted.

 

Figure 9-31 Filling pressure analysis results of original flow channel layout scheme (1)
Compared to maximum filling pressure of 71.7 MPa, cavity B will experience substantial additional pressure, leading to overcompaction.
To achieve a more ideal flow balance, a suitable gate location should be selected for cavity B, and dimensions of runner system should be further adjusted, followed by a new flow analysis.
First, examine analysis results of filling time:

 

Figure 9-32 Analysis results of filling time after optimizing runner layout (1)
Above analysis shows that flow channel balance has been significantly improved. Next, let's compare distribution of filling pressure:

 

Figure 9-33 Filling pressure analysis results after optimizing flow channel system (1)
As can be seen from analysis results, balanced runner system effectively reduces filling pressure of the entire mold.
(2) Change wall thickness of different parts of cavity;
Due to structural and appearance reasons, gate location may be fixed, as shown in Figure 9-33. Gate is located in the center of rectangular plate. If a uniform wall thickness of 2.0mm is used, see Figure 9-34(a), obviously, since flow path of light-colored area is the shortest, it will be filled before dark-colored area, forming an unbalanced flow.
Flow balance can be achieved through following methods:
a. Flow diversion, i.e., increasing wall thickness to accelerate flow. In this example, wall thickness of dark area is increased from 2.0 mm to 2.5 mm;
b. Flow restriction, i.e., decreasing wall thickness to slow down flow. In this example, wall thickness of light area is reduced from 2.0 mm to 1.5 mm. By adjusting wall thickness of plastic part, a balanced flow order is achieved, as shown in Figure 9-33(c).

 

Figure 9-34 Adjusting flow balance of plastic part through flow guidance and flow restriction
Flow diversion and flow restriction each have their advantages and disadvantages.
Flow diversion requires an increased amount of plastic and a longer cooling time, which may cause warping of plastic part due to uneven cooling. However, this method can use a lower injection pressure to reduce stress level near gate and achieve better flow balance, ultimately reducing warping deformation of plastic part. Flow restriction can save material and does not prolong cooling time, but it increases filling pressure. Which method to use depends on magnitude of stress and pressure; sometimes, using both methods simultaneously yields better results.
It is mainly used for large box lids and faceplates to prevent deformation of plastic parts or to solve local air trapping in plastic parts.
(3) For multi-cavity molds, reasonable cavity arrangement;
As shown in Figure 9-35, flow channel system cannot achieve flow balance based on original cavity arrangement. This is because larger and smaller cavities share a considerable length of flow channel, limiting adjustment of dimensions.

 

Figure 9-35 Filling time analysis results of prototype cavity arrangement
After adjusting cavity arrangement, flow channel arrangement is also adjusted to achieve better flow balance.

 

Figure 9-36 Filling time analysis results after adjusting cavity layout
From above analysis results, it can be seen that material consumption of flow channel system does not increase after adjusting cavity arrangement.
(4) Use balanced flow channels as much as possible.
As shown in Figure 9-37, unbalanced flow channel arrangement will lead to a large difference in flow order.

 

Figure 9-37 Filling time analysis results for non-equilibrium flow channel arrangement

 

Figure 9-38 Filling time analysis results after adopting balanced flow channel system
Above methods for achieving flow balance generally prioritize adjusting size of flow channel system to achieve balanced flow, but it is often difficult to achieve this through one method. One method or a combination of two or three methods can be selected according to actual situation.