① Definition of mold base length, width, and height, as shown in Figure 8-1:

 

② Pin-Gate mold base Selection:
1. For molds with a large number of upper and lower mold positions, high precision requirements, a mold life of more than 50,000 cycles, and mold base specifications of 3030 or above, a standard pin-gate mold base must be used.
2. For molds with all glue points located on one side, or low precision requirements, a mold life of less than 50,000 cycles, an A-plate thickness of less than 200, and mold base specifications of 4040 or below, a simplified pin-gate mold base must be used.
3. For mold base specifications of 4040 or above, a standard pin-gate mold base must be used.
③ Mold base width should be less than distance between two guide posts of injection molding machine specified in quotation.
④ When designing non-standard mold bases, mold base length must not exceed twice mold base width.
⑤ For fine-gate mold bases, when A plate is thickened beyond standard, large tie rod diameter must be increased and corresponding panel thickness must be increased; panel thickness = tie rod diameter D + 20mm, as shown in Figure 8-2.

 

⑥ For mold bases larger than 5050, there should be a 1mm gap between A and B plates. For mold bases smaller than 5050, no gap is allowed, as shown in Figure 8-3.

 

Figure 8-3 Clearance between plates A and B
⑦ For mold bases larger than 4040, distance between ejector plate screws must be within 250mm to prevent deformation. If distance is greater than 250mm, additional screws should be added (same in length and width).

① Nylon plugs: Used to lock parting surface of small sprue mold base (PUNCH standard PPL type). Design considerations are shown in Figure 8-4 when mold temperature is below 120℃:

 

Figure 8-4 Design considerations for nylon plugs
1. Nylon plug hole on Plate A should be inverted R3, and hole wall should be polished to prevent scratching nylon plug. A venting groove should also be provided.
2. Nylon plug should be embedded 4mm into plate. A 1mm gap should be left at corresponding location on Plate B to store rubber powder.
3. Nylon plug installation position:
a. Nylon plug should be placed outside mold whenever possible.
b. Nylon plugs on the top side should not be placed within maximum projection area of inner mold to prevent rubber powder from falling and adhering to surface of part, affecting appearance. (See Figure 8-5).
c. Generally, nylon plug is fixed to Plate B. If nylon plug's position is limited and prevents part from falling out, it can be fixed to Plate A.

 

Figure 8-5 Installation position of nylon plug
4. Determine number of nylon plugs. See table below.

② External Snap-On Machine: When temperature of pinhole heating mold exceeds 120℃, an external snap-on machine must be used to control mold opening sequence, as shown in Figure 8-6. These machines generally conform to Datong standard. When ordering, please note that one set of these machines consists of two pairs.

 

Figure 8-5 Using external snap-on
③ Externally Positioned Parting Mechanism: For molds with strict opening sequences, such as front mold slides, rear mold core pulls, and secondary ejection, an externally positioned parting mechanism is required, as shown in Figure 8-7.

 

Figure 8-7 External fixed distance parting mechanism
④ Limit Screws and Dewatering Gate Screws (collectively referred to as Small Tie Rods): These screws coordinate opening and closing of faceplate, sprue plate, and A-plate, completely cutting off and removing point gate. When designing, consider whether their positioning will affect robot's ability to remove runner and whether square iron is free of air.
1. Length relationship between large and small tie rods for a standard pin-gate mold is shown in Figure 8-8:

 

Note: Tie rods, limit screws, and dewatering screws must be standard lengths.
Figure 8-8 Length relationship between large and small tie rods in a standard pinnacle mold
2. Length relationship between tie rods and small tie rods for a simplified pin-gate mold is shown in Figure 8-9:

 

Note: Tie rods, limit screws, and dewatering screws must be standard lengths.
Figure 8-9: Length relationship between large and small tie rods for a simplified pinhole mold.
3. Small Tie Rod Diameter Selection Criteria:

Due to gap between guide pins and guide sleeves, higher-precision positioning is required to ensure accurate mold closing, prevent damage to mold due to misalignment in support and insert positions. Therefore, all mold designs must consider correct mold base positioning or internal mold positioning method. Electric heating molds operate at high temperatures (typically above 120℃). Due to varying heating rates and varying thermal expansion of B plate during heating, guide pins and sleeves can experience significant misalignment, which can easily lead to damage. Furthermore, grease loss can easily cause damage to guide pins and sleeves. Therefore, purchase of positioning components should be considered based on mold usage.
① Locating Block Classification: Four types of locating blocks, A, B, and D, are directly outsourced to a mold base fabricator.

 

② Selection Method: Slope of selected locating block must be less than minimum insertion angle of part.
③ When selecting mold locating blocks, consider temperature differences within mold to avoid affecting locating effect. Four sets must be designed in a symmetrical arrangement. When using interlock and straight side locks, consider locating them in the center of mold.
④ Mold Base Locating Blocks: Mainly used for large molds with high cavities or molds requiring lateral protection on all four sides. Minimize their use to avoid material waste. (See Figure 8-10.)

 

Figure 8-10 Mold plate original positioning
⑤ Inner Mold Base Locating Blocks: Mainly used for molds with inclined or curved PL surfaces or severely asymmetrical parts. Minimize mold material waste during design. (See Figure 8-11.)

 

Figure 8-11 Positioning of original inner mold

① Length of guide pins between A and B should generally be 15-25mm longer than height of mold core protruding from PL surface. (See Figure 8-12.)

 

Figure 8-12 Guide column length under normal circumstances
② When a lateral core pull mechanism is used, guide pin length must meet following requirements: B = A + 15mm or more, as shown in Figure 8-13.

 

Figure 8-13 Guide pin length with lateral core pulling
③ In this case, if guide pin is installed upright or extended to the top of flat plate, this requirement cannot be met. Guide pin must be installed in reverse, as shown in Figure 8-14:

 

Figure 8-14 Reverse installation of guide pins

Used in point-gating molds, it temporarily secures runner of point-gating portion to runner plate and separates gate from molded product:

 

① Sprue hook diameter D and runner bottom diameter d are selected as shown in following table:

② Sprue hook size must take into account size of injection point.

① To prevent clamping force or injection pressure from causing mold plate to bend and deform, resulting in substandard molded parts, a support head must be added between base plate and plate B:
② Support head diameter should be as large as possible. In actual mold assembly, support head height H1 should be 0.05 higher than square iron height H. ~0.1mm, rounded to the nearest integer during design, as shown in Figure 8-16:

 

Figure 8-16 Height of support head
③ Support head should be positioned where injection pressure on lower mold plate is concentrated, and as close to the center of ejector plate as possible, as shown in Figure 8-17;

 

Figure 8-17 Support head setting area

As name suggests, trash pins are related to garbage. This garbage isn't household waste, but rather garbage that accumulates while mold is operating on injection molding machine. Because ejector plate and ejector base plate assembly undergo repeated movement, it's difficult to ensure that no debris (such as iron filings or sprue) falls into ejector plate during injection molding. Without trash pins, ejector plate will be held against debris during reset, preventing it from returning to its designed, correct position, and thus affecting product quality. (See Figure a)

 

Figure a) Flat head screw fixation

(1) Trash pins are generally distributed every 150mm. They must be placed away from ejector pins, knockout holes, and support column locations, as shown in table.

To prevent accidents caused by mold separation during handling and transportation, clamping clips must be installed on the sides of mold base.
① For two-plate molds, clamping clip installation location is shown in Figure 8-19. For molds under 220 tons, only one clamping clip is installed on operating side, as shown at A or C. For molds over 220 tons, two clamping clips are installed on both operating and counter-operating sides (diagonally), as shown at C+B or AD.

 

Figure 8-19 Schematic diagram of installation position of clamping buckle

② For other movable parts of molds with multiple parting surfaces, same applies.
③ When designing clamping clips, ensure they do not interfere with water supply, mold clamps, or mold hanging holes.
④ For three-plate molds, clamping clips must be installed between A and B plates, as well as between A plate and sprue plate. When installing clamping clip between A plate and sprue plate, consider preload of dewatering spring.

① For mold bases with small sprues, front and bottom plates are typically thicker due to height discrepancy between them. Therefore, front plate's mold thickness A must be consistent with bottom plate's mold thickness B during design. Thicknesses should be based on following design standards:

 

As shown in Figure 8-23, when mold base includes protruding features such as water delivery connectors, hydraulic cylinders, and slide positioning springs, following mold foot design is necessary to protect them from damage:
① Mold foot diameter D ≈ mold guide pin diameter D1 (determined by mold's weight). Length L must be greater than protruding height L1 of protected object (L/D = 5).
② For small molds with short mold feet, install as shown in Figure A. For large molds with long mold feet, consider securing with stud screws and submerging mold foot a portion L2, as shown in Figure B.
③ Install on the front and bottom plates. Four must be present and arranged symmetrically about center of gravity:

 

Figure 8-23 Design of mold foot

Function of a limiter pin is to limit travel of ejector system.
① Prevent ejector plate from overextruding, causing ejection problems, especially when mold has a slanted ejector structure.
② Most are located directly above ejector pin hole and installed on the top surface of ejector plate to prevent deformation of ejector plate.

Mold cavities have uneven adhesive distribution, so balancers are needed to withstand clamping force. To reduce amount of work on sealing surface, sufficient space is left for sealing surface to avoid gaps and facilitate machining. Therefore, balancers are needed to withstand pressure and protect narrow sealing surface. Mold steel has a certain compressive limit; exceeding this limit will cause deformation. Therefore, the greater clamping force, the greater pressure, the greater pressure area. If parting surface area is insufficient, balancers are needed to compensate.
① Protect parting surface of mold core.
② Ensure that mold evenly withstands clamping force.