1: For molds with multiple cavities, a geometrically balanced layout, or a runner layout, must be used to ensure simultaneous filling of all cavities, as shown in Figure 1-1. For special cases where an unbalanced layout or multiple-point water entry is required, sprue width or runner size should be adjusted based on mold flow analysis results to ensure simultaneous filling of all cavities. (See Figures 1-2 and 1-3.)

 

2: Runners should be as short and straight as possible to minimize heat and pressure loss, and corners must have rounded corners to ensure smooth flow. However, for transparent parts such as PC and PMMA, an "S"-shaped runner is required to prevent cold material from entering mold cavity and causing flow marks, as shown in Figure 1-4.

 

Figure 1-4 "S" shaped runner for transparent products
3: Generally, 320# or higher sandpaper should be used on runner surface to minimize gloss. However, for mirror-faced parts, 600# sandpaper should be used for runners to minimize gloss.
4: All runners must have cold wells at the ends to prevent cold material from entering mold. Cavity affects appearance quality of plastic part. Note that sprue entry point should not be directly opposite main runner, as shown in Figure 1-5.

 

Figure 1-5 A cold well must be designed at the end of runner
5: Gating system should correctly guide molten material to fill every corner of cavity and allow for smooth discharge of air within cavity.
6: Gating system should prevent defects such as underfill, shrinkage, deformation, flashing, and dimensional deviation in part, as shown in Figure 1-6.

 

Figure 1-6 Comparison of filling results before and after adjustment of nozzle position and size
7: Sprue should be easily removable (automatic sprues should be used if possible), ensuring that removal does not affect part's appearance.
8: Runner must be removable using a robot to improve production efficiency.
9: Runner must be designed in a round or U-shaped design for easy processing.
10: Runner weight should be considered during design. Sprue weight should not exceed quoted price, and ratio of sprue weight to total weight should generally be kept below 25%. Exceptions should not exceed 50%. If runner weight exceeds the quoted price, this must be stated. Contact design manager for written information.
11: For molds with multiple cavities and one cavity, number of sprues should be designed based on ratio of flow distance L to glue thickness T (flow length ratio). Mold flow analysis results should be referenced to prevent weld mark location and size from affecting product strength and appearance. Flow length ratios for commonly used plastics are shown in the table below.

12: For molds with multiple cavities and different parts, sprue and runner sizes should be determined based on mold flow analysis results to ensure that all cavities can be filled simultaneously. (See Figure 1-7.)

 

Figure 1-7 Flow balance in a multi-cavity mold with different parts
12: For molds with multiple cavities and different parts, a switch sprue insert should be installed to switch to a specific cavity to meet production needs, as shown in Figure 1-8(a). To ensure balanced filling during molding process by adjusting runner size, a runner control valve should be installed on the side of part that is easily filled. (See Figure 1-8(b).

13 Layout of a single-mold, multi-cavity mold strives for symmetry, compactness, and avoidance of uneven loading to minimize mold base specifications, reduce nozzle weight, and reduce molding machine tonnage, as shown in Figure 1-9.

 

Figure 1-9 Reasonable selection of one-mold multi-cavity mold layout
Improper layout (a) in Figure 1-9 can easily result in flashing, and improper dimensional alignment can occur when glue is fed from different locations on part. However, sometimes, due to limited nozzle location, special cases may occur. As shown in figure below, option c) is more reasonable than option d) in terms of nozzle weight. In such cases, it is necessary to comprehensively consider various factors and evaluate pros and cons of each option to determine the most reasonable layout.
Note: When mold requires eccentricity due to structural reasons, eccentricity should preferably be toward top and bottom sides, and eccentricity S should be less than 10% of L (L is mold length). As shown in Figure 1-10, when mold is eccentric, ejector pin hole must follow eccentricity, and at least two ejector pin holes should be used to ensure balanced ejection.

 

Figure 1-10 Design of eccentric mold

 

1: Sprue Nozzle SR Value:

2: Sprue Nozzle Diameter φD Value: When excluding fiberglass materials;

3: Measures for Shortening Sprue: ① Sprue nozzle in a two-plate mold should be sunken as far as possible into A-plate, and front and A-plates must be positioned. Positioning methods include nozzle positioning (as shown in Figure 1-11) and pin positioning (as shown in Figure 1-12).

② Use a large sprue nozzle in a three-plate mold;
③ Parts made of plastic materials such as ABS and PP can be heat-treated, but parts with special appearance requirements (such as transparent, etched, or mirrored) should not use a hot nozzle.

Inclined sprue is shown in Figure 1-13.

 

Figure 1-13 Inclined runner
Note: ① Avoid inclined sprues and eccentric designs whenever possible. However, for large single-cavity parts that require a large sprue mold base, inclination angle A should be less than 20°, as shown in figure above. An inclined nozzle must be square and machined to measure number of line cuts. ③ Angled nozzles cannot be used with glass fiber-containing materials such as PPS and PET+GF. Main channel slope B must be increased to 3 inches.

1: Common Runner Types:

 

2: D Value Series: 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8 (10 and 12 are for reference only).
3: D Value Selection Method: Table 1

Table 1 above shows runner dimension D when material does not contain glass fiber. When containing glass fiber, above runner dimensions must be increased by 1 mm.
4: Design standards for runner and gate dimensions are shown in table below. Specific dimensions must be determined after flow analysis.
5: Notes:
a) Use circular runners whenever possible.
b) For push-plate molds, small-gate molds, molds that produce multiple products from a single mold and require production switching, molds that require runner size adjustment, and molds where runner flows along side of a runner, runner should be designed as a "U" shape.
c) When designing a U-shaped runner, cross-sectional size of runner can be changed by adjusting H value.

6: For multi-cavity molds or single-cavity molds with multiple sprues, when designing runners, primary runner must be thicker than secondary runner (as shown in Figure 1-14). Values are based on following table. To ensure balanced filling, runners at intersection of each gate branch must be designed as overlapping runners, as shown in Figure 1-15.

 

7: Design standards for auxiliary runners: As shown in Figure 1-16, because part requires electroplating, a circular runner should be added during design to facilitate subsequent processing.

 

Figure 1-16: Electroplated hook design
Note: Only half of runner needs to be machined on the front or back mold.

Gate form, location, size, and number of points should fully meet requirements of component use, mold processing, and component production.
1: Direct Gate

 

Gate parameters: D ≤ 2t, R = 1, t = component adhesive thickness, A = 2° → 4°.
Explanation: a) Low pressure loss, easy filling. b) High pressure at gate, prone to deformation. c) Difficulty removing gate.
2: Standard Gate

 

Nozzle parameters: h = n; L = 1.5-2.5; t = plastic thickness;W = n√A/30; A = cavity surface area (mm²); n = plastic coefficient according to following table:

Notes: a) Easy mold processing; b) Easy nozzle modification; c) Effectively prevents flow marks; d) Difficult post-processing of the nozzle
3: Overlap Gate

 

Gate parameters: n = n; t = plastic thickness; W = n√A/30; A = cavity surface area (mm²); n = plastic coefficient according to following table:

Note:

a) Easy mold processing; b) Easy gate modification; c) Effectively prevents flow marks; d) Difficult post-processing of gate.

4: Point Gate

 

Nozzle Parameters: d = nC⁴√A; A = Cavity surface area (mm²); n = Plastic coefficient according to following table:

C Wall Thickness Coefficient according to following table: t = Wall thickness at glue point (mm)

Standard Specifications: (PUNCH reference)

5: Submerged Gate (as shown in Figure 1-17)
I) Submarine Gate Design Considerations:
A. Because submarine gates require a large deformation space during ejection, sufficient ejection stroke must be considered during design.
B. Sprue should not be located too close to edge of part to prevent it from being pulled out and notched.
C. Sprue mouth must have an R of 0.5 around the entire circumference to prevent breakage. Brittle PS and PMMA materials are not suitable for submarine gates.
Sprue Parameters: d =nC⁴√A; A = cavity surface area (mm²); r = plastic coefficient according to following table:

C. Wall Thickness Coefficient according to following table: t = wall thickness at glue point (mm)

a° = 60, 55, 50, 45; B° = 10, 15, 20; L1 > 8mm and > 3D; H should be as small as possible.
II) To ensure balanced runner ejection, L is generally greater than L2. However, a tapered shape can be added to ejector pin's head to ensure sprue remains fixed to pin after ejection. In this case, sprue must be removed using a robot.
Figure 1-17 Types of Submerged Gates

 

III) Selection of round-head diving port and cone-head diving port:

 

IV) Solution for poor vent ejection: As shown in Figure 1-18, prioritize (a).
Figure 1-18 Solution for poor vent ejection

 

V) Considerations for Submersible Gate Structural Design, as shown in Figure 1-19.
Figure 1-19 Considerations for Submersible Gate Structural Design
(a) To prevent gate from rebounding and damaging product after ejection, a notch is added to runner as shown. This allows gate to deform and separate from part after ejection. (This applies to both submersible gates and banana gates.)
(b) If necessary, a 3-5mm delay structure can be installed under ejector pin in runner. This structure also allows product to separate from gate after ejection. (This applies to both submersible gates and banana gates.)
(c) If submersible gate is not through, an EDM machining datum must be established, as shown in Figure 1-20. L3 dimension must be marked on 2D drawing.

6: Banana Gate

 

Note: I) Processing method: Designed as two-part assembly, secured with screws or a bracket.
II) Other design considerations are same as for submerged gates.
7: Secondary Gate

 

1: A cold slug well should be designed at the end of runner to prevent cold slug from entering mold cavity, and venting must be provided; as shown in Figure 1-21.

 

Figure 1-21 End of runner should be made of cold material and
2: Cold Slug Well in Main Runner of a Small-Gate Mold: Typically, Figure (a) is used. However, when S < 12mm and a slug hook is not possible, main runner pull method (Figure (b)) can be used. Gate Parameters:

When there are more than four branch runners and runner diameter d ≥ 5, method shown in Figure 1-22 (c) can be used to avoid material waste or main runner breakage due to poor cooling. T =3/5H.

 

Figure 1-22 Cold well in main channel of a small nozzle mold
3: Main channel cold slug well and slug puller for large sprue molds: Parameters are shown in Figure 1-23:

 

Figure 1-23 Cold well in main channel of a large sprue mold

Design Notes: Generally, type (a) is used. Type (b) can be used when material is soft rubber, mold uses an angled nozzle, or sub-gate is on the front mold side. When using multiple type (b) slug pullers, pullers must be positioned and aligned in a "Z" pattern. Direction of buckle is same to facilitate demolding.
4: Cold slug hole in the middle of main runner guide and material pulling method: as shown in Figures 1-24A and 1-24B.

 

Figure 1-24 Cold material well of main channel slide position mold
5: Cold slug hole in main runner of push plate mold and material pulling method, as shown in Figure 1-25.

 

Figure 1-25 Cold material hole and material pulling method of main channel of push plate mold
6: Cold slug hole at the end of branch runner, as shown in Figure 1-26.

 

 

1: All small-gate molds must be designed with locating posts to prevent runner displacement after mold opening, making it impossible to remove mold using a robot.
2: Locating posts must be located on the top side, as shown in Figure 1-27.

 

Figure 1-27 Design of runner positioning column
3: When high-precision parts are required (such as gears), locating posts cannot be placed directly on B branch runner and must be placed separately to avoid affecting dimensional accuracy of part, as shown in Figure 1-28.

 

Figure 1-28 Design of positioning column for gear mold