For previous reading, please refer to Mold Design Guide (Part 3: Mold Structure Design).

Mold parts can be divided into molding parts and structural parts according to their function. Molding parts refer to structural components that directly participate in forming cavity space, such as cavities, cores, inserts, and slides. Structural parts refer to parts used for installation, positioning, guiding, ejection, and completing various actions during molding, such as locating rings, nozzles, screws, pull rods, ejector pins, sealing rings, spacer plates, and pull hooks. Common structural parts are listed in next section. When designing molding parts, molding shrinkage rate of rubber compound, draft angle, manufacturability for manufacturing and maintenance should be fully considered.
5.4.1 Molding Shrinkage Rate of Rubber Compound
Molding shrinkage of rubber compound is affected by many factors, such as type of rubber compound, geometry and size of part, mold temperature, injection pressure, filling time, and holding time. Among these, type of rubber compound, geometry and wall thickness of part have the most significant impact. Different plastic materials have different shrinkage ranges (see Chapter 2, Common Plastics). Specific shrinkage rate depends on recommended value; any changes must be confirmed by relevant person in charge.
It is worth noting that when increasing shrinkage value for same plastic part, reference points selected for 3D and 2D designs should be same; otherwise, inconsistencies between 3D and 2D designs will occur.
5.4.2 Draft Angle
A reasonable draft angle is necessary for easy demolding and achieving high-quality surface finishes. Generally, a reasonable draft angle is given during plastic part design. However, due to oversights, an unreasonable draft angle may be selected or formed, which will inevitably affect surface quality of plastic part. Therefore, draft angle of plastic part should be checked during mold design, any unreasonable aspects should be discussed and resolved with relevant person in charge. Following are general requirements for draft angles:
(1) For commonly used plastic materials such as ABS, HIPS, PC, and PVC, draft angle for outer surface of plastic part should be selected according to following:
For small plastic parts with a smooth outer surface, draft angle ≥ 1˚; for large plastic parts, draft angle ≥ 3˚. For textured outer surfaces Ra < 6.3, the draft angle ≥ 3˚; for Ra ≥ 6.3, draft angle ≥ 4˚. For EDM-textured outer surfaces Ra < 3.2, draft angle ≥ 3˚; for Ra ≥ 3.2, draft angle ≥ 4˚.
(2) Regardless of whether ribs or pillars on inner surface of plastic part are designed with draft angles, draft angle should be increased or modified according to following requirements when designing mold.
Thickness at root of rib should be less than 0.5t (where "t" is wall thickness of plastic part); thickness at the top of rib should be greater than or equal to 0.8mm. Specific draft angle is determined based on determined thickness difference and height of rib. If draft angles are required on both sides of rib's length, a larger draft angle should be selected without affecting internal structure of plastic part. Requirements for pillar positions should be modified according to content of Section 3 of Chapter 3.
(3) When adding or modifying draft angle of rubbing or through-hole positions, requirements for stepped parting surfaces in Section 2 of Chapter 5 should be used. If plastic part structure is affected, a solution should be reached through consultation with relevant person in charge.
5.4.3 Processability of Molded Parts
During mold design, efforts should be made to ensure that molded parts have good assembly, processing, and maintenance performance. To improve manufacturability of formed parts, following points should be considered:
(1) Avoid producing sharp or thin steel (see Figures 5.4.1a, 5.4.1b, and 5.4.1c).
When distance D between inserts is small, to avoid thin steel, inserts should be selectively manufactured. For example, in Figure 5.4.3, when D is small, one of inserts should be selected.

 

(2) Ease of Machining
Ease of machining is a basic requirement for molded part design. When designing mold, machinability of each part should be fully considered, and machining requirements should be met through reasonable insert combinations. For example, to facilitate machining of stop area of plastic part, the insert structure shown in Figures 5.4.2a and 5.4.2b is generally used. Other combination methods or no inserts are unreasonable design structures.
(3) Ease of Dimensioning Adjustment and Maintenance
For molded parts where dimensions may change, a combination structure should be considered, as shown in Figure 5.4.3; for easily worn collision and rubbing areas, an insert structure should be used for strength and ease of maintenance.
(4) Ensure strength of formed parts (see Chapter 5, Section 3).
(5) Facilitate assembly.
For formed parts with interlocking structures, ease of assembly is a basic requirement of mold design, and errors during installation should be avoided. For regularly shaped inserts or multiple inserts with same external dimensions in mold, design should consider avoiding misaligned installation of inserts and directional installation of same insert. A common method is asymmetrical fastening or positioning of inserts, as shown in Figure 5.4.4b.
In Figure 5.4.4a, fastening positions are symmetrical, which easily leads to misaligned installation of insert 1 and insert 2, and also makes directional installation of same insert easy. In Figure 5.4.4b, fastening positions of each insert are asymmetrically arranged, fastening positions of insert 1 and insert 2 are also different, thus avoiding misaligned installation and same insert being installed in a different orientation. Alternatively, to avoid misaligned installation, an asymmetrical arrangement of locating pins can also be used.

 

(6) Must not affect appearance
When designing molded parts, not only should process requirements be considered, but also appearance requirements of plastic parts must be guaranteed. Whether plastic parts allow for presence of creases is a prerequisite for determining whether inserts can be made. If creases are allowed, an insert structure should be considered; otherwise, other structural forms must be used. In Figure 5.4.5, creases are allowed on the surface of plastic parts, so an insert structure can be used to facilitate processing; in Figure 5.4.6, creases are not allowed on the front surface of plastic parts. To facilitate processing or for other purposes, crease position is moved to side wall, thus adopting an insert structure. In Figure 5.4.7, when creases are not allowed at arc, insert structure is changed, and crease position is moved to inner wall.

 

 

(7) Take mold cooling into account. If use of an interlocking structure for molded parts causes local cooling difficulties, other cooling methods or an integral structure should be considered.

5.5.1 Locating Ring
(1) Basic Form, as shown in “4” in Figure 5.5.1.
(2) Assembly Form, as shown in Figure 5.5.1
Screw: M6x20.0mm Quantity: 2
(3) Common Specifications ∅35x∅100x15 (Refer to Chapter 15)
(4) Special Cases

 

When mold requires use of a heat insulation plate, a thickened locating ring is used, as shown in Figure 5.5.1b. Generally, a locating ring with a specification of ∅70x∅100x25 is selected.
For specifications of locating ring in a two-color mold, refer to Chapter 12.

 

5.5.2 4 Sprue Nozzles
Sprue nozzles are generally divided into two main categories: large sprue nozzles and small sprue nozzles. Large sprue nozzles are used in two-plate molds, while small sprue nozzles are used in three-plate molds. Their specific applications are described below.
A. Large Sprue Nozzles
(1) Common basic forms, as shown in Figure 5.5.2. For specifications, please refer to Chapter 15.

 

(2) Selection method for large sprue nozzles. Large sprue nozzles are usually selected based on amount of plastic required for molded part and required nozzle length. A larger nozzle is selected when a larger amount of plastic is required; conversely, a smaller type is selected when less plastic is required. Different included angles "A" are selected according to nozzle length so that diameter of nozzle end matches diameter of main runner. Generally, selection is based on mold base size: for mold bases below 3535mm, a type with D=∅12 is selected; for mold bases above 3535mm, a type with D=∅16.0 is selected.
(3) Assembly Method
Basic assembly method is shown in Figure 5.5.1.

 

Screw Specification: M4X20mm Quantity: 1
If length "L" of nozzle is to be shortened, assembly method shown in Figure 5.4.3 is recommended, and front mold must be tightened. This method is recommended when distance D between panel and main runner is ≥60mm.
B. Fine-Gate Nozzle
(1) Basic form is shown in part "2" in Figure 5.5.4. When using a heat insulation plate, H=20.0mm; without a heat insulation plate, H=10.0mm
(2) Assembly form as shown in Figure 5.5.4
Assembly requirements: Conical surface must fit tightly within height “H1” range, generally H1≥8.0mm; Ensure dimension “20.0mm” shown in figure; Screw selection specification: M8x20.0mm. Quantity: 4.

 

1-Screw 2-Fine sprue nozzle 3-Sprue plate 4-Panel 5-Insulation plate
(3) Common Specifications
See Chapter 15 for common specifications. Specifications listed in Chapter 15 are for sizes without a heat insulation plate. If a heat insulation plate is required, please add dimension “H” in Figure 5.5.4 as described above.
(4) Simplified Form (Figure 5.5.5)
Features: Simple to manufacture; simply machine head of large sprue nozzle into a conical surface.
Disadvantages: Main runner is too long, wasting material; parting distance between sprue plate and mold plate A is relatively large.
Applicable to:
A. Small mold bases, generally used for sizes below 3030.
B. When using ordinary fine sprue nozzles, pull rod is difficult to fix. This avoids increasing mold size to accommodate pull rod arrangement.

 

1-Panel 2-Pulley Rod 3-Sprue Plate 4-Sprue Nozzle 5-Mold Base A Plate
5.5.3 Fastening screws
Commonly used fastening screws in molds are mainly divided into internal hexagonal head screws (internal hexagonal screws), internal hexagonal flat-end set screws (headless screws) and hexagonal head bolts. See Chapter 15 for commonly used specifications.
In molds, fastening screws should be selected according to different needs, and at the same time, ensure that fastening force is uniform and sufficient. Following explains usage of various fastening screws.
A. Socket Head Mill Screws (Hex Socket Screws)
Preferred Hex Socket Screw Sizes: M4, M6, M10, M12
Socket head mill screws are mainly used for front and rear mold materials, cores, small inserts, and other structural components. Except for screws used for locating rings and nozzles mentioned above, screws used for inserts, skirts, and fixing plates should be selected based on suitability, while adhering to preferred sizes. For screws used to fasten front and rear mold materials, following requirements should be followed:
Size: M10 for mold material width ≤ 300mm; M12 for mold material width > 300mm. Quantity: 4 screws for mold material length ≤ 300mm; 6 screws for mold material length > 300mm and ≤ 500mm; 8 screws for mold material length > 500mm and ≤ 800mm. Center distance: Select according to following two methods (see Figure 5.5.6).
When M10 is selected, W1 = 10.5mm-14.5mm, L1 = 15n OR 20n, where n represents a multiple;
When M12 is selected, W1 = 12.5mm-13.5mm, L1 = 25n OR 30n, where n represents a multiple.

 

B. Headless Socket Socket Set Screws (Headless Screws)
Headless screws are mainly used for fastening inserts, pull rods, and ejector pins. As shown in Figure 5.5.7, in standard parts, ∅d and ∅D are related. ∅d is actual dimension used, so it is usually used as basis for selection, and selection should be made within following range.
a. When ∅d ≤ 3.0mm or 9/64", select M8.
b. When ∅d ≤ 3.5mm or 5/32", select M10.
c. When ∅d ≤ 7.0mm or 3/16", select M12.
d. When ∅d ≤ 8.0mm or 5/16", select M16.
e. When ∅d > 8.0mm or 5/16", use a clamping plate for fixing (see Chapter 8, Section 8.2 for details).

 

C. Hex Head Bolts
Hexagonal head bolts are only used as a substitute for junk nails, types used are relatively limited, generally using M10X20 and M12X20. Quantity used depends on following requirements:
When length of mold base ejector plate is ≤350, select 4; when length of mold base ejector plate is ≥400, select 6; when length of mold base ejector plate is ≥600, select 8.
5.5.4 Ejector Pins
A. Ejector Pin Arrangement Principles
(1) Ejector pin arrangement should balance ejection force as much as possible. For complex structural parts requiring greater demolding force, number of ejector pins should be increased accordingly.
(2) Ejector pins should be placed in effective locations, such as ribs, pillars, steps, metal inserts, and other complex structural parts with thick localized adhesive. Ejector pins on both sides of rib and pillar positions should be arranged as symmetrically as possible. Distance between ejector pins and edges of rib and pillar positions is generally D=1.5mm, as shown in Figure 5.5.8. Additionally, center line connecting ejector pins on both sides of pillar position should pass through center of pillar position.

 

(3) Avoid setting ejector pins across steps or on slopes. Top surface of ejector pin should be as flat as possible, and ejector pin should be placed in structural parts of plastic part where stress is relatively good. As shown in Figure 5.5.9.

 

(4) When there are deep ribs in plastic parts (depth > 20mm) or when it is difficult to place round pins, flat pins should be used. When flat pins are required, inserts should be used as much as possible to facilitate processing, as shown in Figure 5.5.10.

 

(5) Avoid sharp steel and thin steel, especially ensuring top surface of ejector pins does not touch front mold surface, see Figure 5.5.11.
(6) Ejector pin arrangement should consider distance between ejector pins and water channel edges to avoid affecting processing of water channel and causing leakage. See Section 10.2 of Chapter 10 for specific requirements.
(7) Consider venting function of ejector pins. For venting during ejection, ejector pins should be placed in areas prone to vacuum formation. For example, in areas with large cavities, although clamping force of plastic part is small, vacuum formation is easily created, leading to increased demolding force.
(8) For plastic parts with appearance requirements, ejector pins should not be placed on the appearance surface; other ejection methods should be used.
(9) For transparent plastic parts, ejector pins should not be placed in areas where light needs to pass through.
B. Ejector Pin Selection Principles
(1) Select ejector pins with larger diameters. That is, given sufficient ejection space, ejector pins with larger diameters and preferred sizes should be selected.
(2) Minimize number of ejector pin sizes. When selecting ejector pins, adjust their size to minimize number of sizes, and prioritize preferred size series. See Section 15.1 of Chapter 15 for size specifications.
(3) Selected ejector pins should meet ejection strength requirements. During ejection, ejector pins must withstand significant pressure. To prevent small ejector pins from bending and deforming, ejector pins with supports should be selected when ejector pin diameter is less than 2.5mm.
5.5.5 Sleeve
A. Conditions for Selecting a Sleeve
(1) Column height ≥ 20mm; however, sleeves cannot be used when column height requirements are strict.

 

(2) Structure at column position is complex, making it difficult to install ejector pins;
(3) For transparent parts, ejector pin marks are not allowed in any other positions besides column position;
B. Requirements for ejector sleeves
(1) Under normal circumstances, ejector sleeve wall thickness must be ≥1.0mm
(2) Length of ejector sleeve ordered should be equal to actual required length plus 5.0mm~10.0mm, and rounded to preferred size ending in "5" or "0"
(3) Ejector pin should be ordered together with ejector sleeve, and attention should be paid to length of ejector pin.
Note: For selection of headless screws, see Section 5.5.3 of Chapter 5.
5.5.6 Sealing Rings
For common specifications of sealing rings, see Section 15.5 of Chapter 15.
For assembly method of sealing rings, see Section 10.2.2 of Chapter 10.
5.5.7 Pull Rods
Pull rods are classified into hook-shaped pull rods (Figure 5.5.12) and round-headed pull rods (Figure 5.5.13) according to their structure. Hook-shaped pull rods are mainly used to ensure that runner and plastic parts (such as battery pocket) remain on back mold side. Round-headed pull rods are mainly used in three-plate molds and push-plate molds to keep runner on push plate side.

 

Following points should be noted when using pull rods:
(1) If multiple hook-shaped pull rods are used in a mold, hook direction of pull rods should be consistent.
(2) For hook-shaped pull rods at runner, a certain space must be reserved as a cold slug well, as shown in Figure 5.5.12. General reserved size is shown in figure.
(3) When using round-headed pull rods, pay attention to dimensions “D” and “L” shown in Figure 5.5.14. If dimension "D" is small, head of pull rod will obstruct flow of material; if dimension "L" is small, flow channel is prone to tearing when it detaches from pull rod.
Methods to increase dimension "D": Use a smaller diameter pull rod, typically with a diameter of ∅ = 3.0 mm; reduce "H", generally requiring H ≤ 3.0 mm; increase size of "R".

 

Method to increase size "L": Increase flow channel size around pull rod, as shown in Figure 5.5.16 by adding a truncated cone of "∅d".
5.5.8 Garbage Pins
In molds, hexagonal head bolts are commonly used as garbage pins. See Section 5.5.3 of Chapter 5 for details.
5.5.9 Springs
In molds, springs are mainly used as auxiliary power for moving components such as ejector plates and slides, and are not allowed to be used alone. Mold springs are now standardized, and table below shows basic technical specifications for mold springs.

 

Commonly used springs in molds are light-load springs. If mold is large and number of ejector pins is large, heavy-load springs must be considered. When selecting light-load springs, following aspects should be considered:
(1) Preload ratio: Generally, it is required to be 10~15% of spring's free length. Springs with larger diameters should use a smaller preload ratio, and springs with smaller diameters should use a larger preload ratio. When selecting return springs for mold ejector plates, preload ratio is generally not used; instead, preload amount is used directly. This ensures that, with consistent spring diameters, preload applied to ejector plate is unaffected by spring's free length. Preload amount is generally 10.0~18.0 mm.
(2) Compression Ratio: Generally, a compression ratio below 40% is required. The lower compression ratio, the longer service life.
(3) Spring distribution should be as symmetrical as possible.
(4) Spring diameter specifications are determined based on available space in mold and required preload. Larger diameter specifications should be selected whenever possible. Common specifications are detailed in Chapter 15, Section 15.3.
When mold base size is greater than 5050 mm, a spring with a diameter of Ø51.0 mm must be selected.
Spring's free length should be determined based on compression ratio and required compression amount.
Calculation method for free length (L) of mold return spring: (as shown in Figure 5.5.15)
H1—Ejection height of plastic part; B—Length of spring after pre-compression, B=L - Pre-compression amount. Pre-compression amount is usually 10~15mm. L = (K+Pre-compression amount)/Compression ratio

 

5.5.10 Fixed-distance pull plate
(1) Assembly form. As shown in Figure 5.5.16.
(2) Technical requirements: D1 is generally 10~12mm; D2 should be slightly larger than the total projected length of runner in mold opening direction, but not less than 110mm; D3 should be greater than 1.0mm; D4 is generally around 25mm, and other dimensions are shown in figure.
(3) Material: High-quality steel is selected.

 

5.6.1. View Format
Third view format is adopted, and markings are shown in Figure 5.6.1.

 

5.6.2. Drawing Number
Drawing numbers shall be implemented in accordance with TLWI07042.
5.6.3. Datum Marking
(1) Types of Datum Marking
Purpose of datum marking is to unify datum and placement direction of workpiece during design and processing. Currently, following two marking methods are used:
A. Single-sided Datum
A single-sided datum refers to workpiece being placed with two adjacent right-angled sides as datum and in a certain direction during design and processing. Markings and placement direction are shown in Figure 5.6.2.

 

B. Center Datum. Center datum refers to reference line of workpiece during design and processing, placed in a certain direction. Marking and placement direction are shown in Figure 5.6.3.

 

(2) Marking position and dimensions are shown in Figures 5.6.2 and 5.6.3.
Note: When R is large, dimensions in parentheses are used.
(3) Marking requirements:
A. This marking should be present on mold drawings (including assembly drawings, front mold drawings, rear mold drawings, hole and skirt drawings, ejector pin and water channel drawings) front and rear molds. Dimensions are not required.
B. This mark should be made immediately after fitter fits mold material into mold frame.
C. If this mark is damaged during processing, please make a replacement immediately.
D. During design, programming, and processing, workpiece should be placed in the form shown in Figure 5.6.2.
5.6.4 Drawing Output Requirements
1. Mark reference type used in mold design.
2. Clearly indicate distance between plastic part reference line and mold reference line, and add a thick square around it as a warning.
3. Clearly show assembly structure of typical cross-sections, shape of parting surface, and external dimensions.
4. Indicate maximum external dimensions of front and rear mold materials, including vents and skirts. If vents have stoppers, a sectional drawing with detailed dimensions is required.
5. Indicate shape, dimensions, and assembly method of inserts, etc.
6. Indicate location and size of fastening screws.
7. Indicate detailed dimensions of sliding mechanism assembly; stroke should be indicated with a thick rectangle.
8. Indicate detailed dimensions of runners and gates, and provide a sectional view.
9. Accurately represent ejector pin arrangement. If an ejector pin drawing is available, ejector pin arrangement and size dimensions do not need to be indicated in assembly drawing. Indicate detailed dimensions of each column that requires fitter fabrication.
10. Draw mold water channel layout, indicating inlet and outlet of each water channel group, using IN1, IN2… OUT1, OUT2… etc. If no water channel drawing is available, indicate size and location dimensions of water channel holes.
11. Indicate arrangement, size, and assembly dimensions of return springs.
12. Mark dimensions and size of support head arrangement.
13. In molds with multiple parts, P/N number of each plastic part must be indicated.
14. If there are no front and rear mold drawings, important dimensions and tolerances should be marked on assembly drawing, with serial numbers next to dimensions and recorded in drawing frame for fitter inspection. If there are front and rear mold drawings, important dimensions and tolerances should be marked on the front and rear mold drawings. Important dimensions include dimensions with tolerance requirements in finished product drawing and dimensions that need to be controlled in mold.
15. Regardless of drawing version, a brief description of version should be provided in "Brief Description" column in upper right corner of drawing frame.
16. When upgrading a mold drawing, an upgrade mark should be shown next to changed content, such as.

 

If only positional dimension is changed, an upgrade mark should be shown next to new dimension; if shape of finished product is changed, changed part should be circled with a thick double-dotted line, and an upgrade mark should be shown next to thick double-dotted line.
Chapter 6 Bill of Materials (BO) and Document Management

6.1.1 Basic Format of Bill of Materials (BOM)
Basic format of Bill of Materials (BOM) is shown in following example:

 

Note: Numbering method for "Mold Design Change Record" (REF: TL240X000X) and "Mold Controlled Engineering Document Receipt and Dispatch Record" (REF: TL250X0000XX) is same as numbering method for Bill of Materials (BOM) document.
6.1.2 Requirements for Bill of Materials (BOM)
(1) mold base should be described as a single component, without further subdivision.
(2) Use relatively uniform part names.
(3) Units for BOM are piece (1), millimeter (mm), kilogram (kg), and inch (").
(4) Completed BOM must be reviewed by design team leader.
(5) BOM is issued together with mold assembly drawing.
(6) Changes to BOM must be signed by person in charge.
6.1.3 BOM Process

 

Document management shall be carried out in accordance with MQP4.01 "Mold Engineering Document Control Procedure".