Mold Base Specification Selection
Comprehensive guidelines for selecting optimal mold bases for high-quality molds for plastic injection manufacturing
Selecting the correct mold base is crucial for producing high-quality molds for plastic injection. The mold base forms the foundation of any injection mold, determining its durability, precision, and compatibility with injection molding machines. Proper specification ensures efficient production, reduces downtime, and extends the mold's service life. This guide provides detailed specifications and best practices for mold base selection in the context of molds for plastic injection.
From dimensions to auxiliary components, every aspect of mold base design plays a role in the overall performance of molds for plastic injection. By following these industry-standard specifications, manufacturers can ensure their molds meet production requirements while maintaining cost-effectiveness and reliability.
Mold Base Dimension Selection
Mold Base Width
The width of the mold base should be less than the distance between the two guide pillars of the injection molding machine. Specifically, the length (L) or width (B) of the mold should be 10mm less than the tie bar spacing of the equipment on each side. This ensures proper fit and operation within the machine's constraints, which is essential for molds for plastic injection.
In most cases, after selecting the injection molding machine, the mold base should be as large as possible while maintaining proper fit. This provides greater stability and reduces deflection during the injection process, which is particularly important for high-precision molds for plastic injection.
For molds requiring robotic part removal, ensure easy access and ejection. Additionally, the sprue plate should maintain a minimum effective space of 150mm (in the mold opening direction) × 200mm for the robotic sprue picker to enter. This consideration is becoming increasingly important as automation in molds for plastic injection production continues to grow.
Mold base width specifications diagram
Mold Base Thickness Requirements
Mold base thickness verification
The thickness of the mold base must satisfy multiple critical requirements to ensure proper functioning within injection molding equipment and to maintain mold integrity during production of molds for plastic injection.
- Within the minimum and maximum mold thickness limits of the injection molding machine, the thickness H must be between H_min + 5mm and H_max - 5mm, where H_min and H_max are the equipment's minimum and maximum allowable mold thicknesses. This ensures proper clamping force distribution in molds for plastic injection.
- It must satisfy the requirements of the mold structure, providing sufficient space for all internal components while maintaining proper alignment.
- It must meet the requirements for mold strength and rigidity, preventing deformation under injection pressure which could compromise part quality in molds for plastic injection.
Proper thickness is particularly critical for large molds for plastic injection, where deflection under pressure can significantly affect part dimensions and surface finish. Engineers must calculate expected pressures and ensure the mold base thickness provides adequate resistance.
Mold Base Plate Lifting Eye Specifications
Proper lifting eye specifications are essential for safe handling and installation of molds for plastic injection. These requirements ensure that mold plates can be safely moved and positioned without risk of damage or injury.
① All mold base plates must be drilled with lifting eye holes (at least 2, top and bottom), machined according to standard mold base screw specifications as shown in Table 1 below. This is a fundamental safety requirement for all molds for plastic injection regardless of size or application.
| Mold Base Plate Weight (G)/kg | Lifting Eye Screw Specification |
|---|---|
| <50 | M12 |
| 60<G≤100 | M16 |
| 100<G≤150 | M20 |
| 150<G≤250 | M24 |
| 250<G≤300 | M30 |
| 310<G≤400 | M36 |
Properly positioned lifting eyes on a mold base plate
- ② For each mold base plate weighing more than 25kg, upper and lower lifting eye holes are required. For plates over 100kg, lifting eye holes must be provided on all four sides. This ensures versatility in lifting configurations for heavy molds for plastic injection.
- ③ To prevent interference in special cases where screw holes might conflict with positioning blocks, slide water channels, etc., screw holes must be offset from the center of the plate. In such cases, holes must be machined in pairs to ensure balanced lifting of molds for plastic injection.
- ④ The general lifting eye screw specification series is: M12, M16, M20, M24, M30, M36, M42, M48, M64. Selection must follow this series. When using lifting eye screws of M20 or smaller, or M42 or larger, two corresponding lifting eye screws must be provided with the mold. Lifting eye positions must ensure stable lifting, with the angle between the mold fixing plate and the injection machine mounting plate being less than 5°. This is critical for preventing damage during handling of molds for plastic injection.
Mold Base Markings and Engravings
Clear and standardized markings on molds for plastic injection are essential for proper identification, assembly, and maintenance. These markings ensure that all components are correctly positioned and that maintenance personnel can easily identify critical features.
- ① After the mold base arrives at the factory, all mold base plates must be marked with steel stamps. The position and size of the markings, regardless of mold size, must use size 8 steel stamps to engrave 8mm high characters at the diagonal position of the template reference corner. Each character should be spaced 1mm apart. It is required to lightly draw a line before engraving to ensure the markings are level and clear. This standardization is crucial for consistency across all molds for plastic injection produced in a facility.
- ② Water inlet and outlet holes must be marked with "IN," "OUT," "IN1," "OUT1," etc. Proper identification of water lines is vital for correct connection to cooling systems, which directly affects cycle times and part quality in molds for plastic injection.
- ③ For components that are easily installed incorrectly, such as ejector pins, identical marks (1, 2, 3, ...) must be engraved on corresponding positions of the mold base. This prevents assembly errors that could damage molds for plastic injection or produce defective parts.
The quality of these markings is important, as they must remain legible throughout the mold's service life. Engraving depth should be sufficient to withstand repeated cleaning and handling without becoming obscured, ensuring long-term usability of molds for plastic injection.
Examples of proper mold base markings and engravings
Mold Base Auxiliary Devices
Support Pillars (Spacers)
Support pillars in a mold base assembly
Support pillars are critical components in molds for plastic injection, designed to prevent deformation of mold plates caused by clamping force or injection pressure during the molding process. Without adequate support, plate deflection can result in poor part quality, flash, or even permanent mold damage.
Requirements for support pillars in molds for plastic injection:
- ① The diameter of support pillars should be as large as possible. The height of the support pillars should be: mold spacer height + 0.05mm (for pillars 30×30mm or smaller) or + 0.1mm (for pillars larger than 30×30mm). This slight oversize ensures proper contact and support when the mold is clamped.
- ② Support pillar positions should be placed where the lower template is subjected to concentrated injection pressure, and as close to the center of the spacer plate as possible. Strategic placement maximizes their effectiveness in preventing deflection in molds for plastic injection.
The number and size of support pillars should be calculated based on the projected area of the mold cavity and the expected injection pressure, ensuring adequate support for the specific requirements of each mold for plastic injection.
Locating Blocks
Locating blocks ensure precise alignment between the upper and lower molds and help withstand the lateral forces generated by the molten material during injection. Proper alignment is essential for maintaining part dimensional accuracy in molds for plastic injection.
There are three types of locating blocks commonly used in molds for plastic injection:
- Square locating blocks
- Round locating cones
- Mold body locating blocks
Large molds for plastic injection, which are subject to greater lateral forces, typically use mold body locating features. These are integral to the mold plates themselves, providing the strongest possible alignment system capable of withstanding the higher forces encountered in large-part production.
Different types of mold locating blocks
Mold Clamps
Safety mold clamps securing mold halves
Mold clamps are essential safety features for molds for plastic injection, designed to prevent separation of mold surfaces during transportation and handling, which could cause accidents or damage to mold components.
Specifications for mold clamps in molds for plastic injection:
- Mold clamps should be selected based on actual needs, ensuring ease of use and compliance with safety standards.
- For multi-parting surface molds, clamps should be uniformly made with a 100mm screw hole spacing, individually fixed, with two clamps diagonally placed per parting surface.
- During production, clamps can be rotated 90° or 180° and secured to the mold to keep them out of the way while allowing quick reattachment when needed.
- The position of mold clamps must not interfere with or obstruct the operation of other components in molds for plastic injection.
- Mold clamps should have warning inscriptions to prevent breakage due to failure to remove them before mold operation.
- Mold clamps should be fixed using M16 screws to ensure adequate strength.
Locating Ring
The locating ring is the part that positions the mold on the injection molding machine. It ensures precise alignment between the machine's nozzle and the mold's sprue bushing. Standard or custom-made locating rings can be used for molds for plastic injection, depending on specific machine requirements.
Nozzle & Sprue Bushing
For molds for plastic injection, the space for the nozzle to enter the mold should be less than 120mm in depth and greater than 80mm in diameter. When design requirements conflict with these dimensions, custom nozzles must be manufactured. The sprue bushing should form a sealed, tapered cavity to prevent leakage.
Mold Pry Pits
All mold plates except face plates, base plates, and ejector plates must have pry pits at their corners. For A and B plates, pry pits should be 25mm×25mm×5mm. For other plates, the standard size is 20mm×20mm×3mm. These features facilitate separation of mold plates during maintenance of molds for plastic injection.
Mold Nameplate Specifications
Example of a properly formatted mold nameplate
Mold nameplates provide essential information for the identification, operation, and maintenance of molds for plastic injection. They serve as a permanent record of critical mold parameters and specifications.
① For equipment with clamping force of 350 tons and above, nameplates should measure 100×70mm.
② Nameplate material: Made of aluminum sheet with a thickness of 0.5-1mm.
Nameplate 1 Format:
- Mold Name
- Mold Type
- Mold Number
- Overall Dimensions
- Manufacturer
- Manufacturing Date
- Clamping Number
- Weight/kg
Nameplate 2 Format:
- Mold Name
- Suitable Machine
- Matching Nozzle
- Ejection Stroke
- Operation Points
- Water Connections
Notes for Nameplate Completion:
- For Nameplate 1: "Mold Name" may include only the "Part Name"; "Mold Type" refers to special processing methods such as gas-assisted, heat transfer, two-color molds, etc.; "Mold Number" follows the contract-specified numbering; "Overall Dimensions" refer to the maximum mold dimensions; for weights over 1000kg, use "t" as the unit; the "↑" symbol indicates lifting direction and should be in red; "Clamping Number" refers to the number of clamps on top, bottom, front, and rear.
- For Nameplate 2: "Mold Name" may include only the "Part Name"; "Suitable Machine" follows contract requirements; "Matching Nozzle" is selected from the specified sequence; "Ejection Stroke" indicates the range (minimum-maximum); "Operation Points" include important instructions or warnings for mold use; "Water Connections" identify each water circuit path according to general requirements.
Clear, durable nameplates are essential for proper identification and maintenance of molds for plastic injection throughout their service life. They ensure that operators and maintenance personnel have quick access to critical information.
Mold Clamping Slots
Proper mold clamping is essential for safe and efficient operation of molds for plastic injection. The method of clamping depends on the mold's dimensions relative to the available space in the injection molding machine.
- ① When the mold's overall dimensions leave sufficient space within the equipment's working area, use direct screw hole compression or U-shaped slot mounting. If using countersunk screws for direct fixing on the mold cavity, sufficient space for screw installation and removal must be considered. This is the preferred method for securing molds for plastic injection when space permits.
- ② When the mold's overall dimensions do not leave sufficient space within the equipment's working area, use I-shaped mold clamp mounting seats or straight mold opening clamping slots for compression. This method provides a secure alternative when space is limited for standard clamping methods in molds for plastic injection.
- ③ Clamping slots should be as long as possible, allowing sufficient space for two clamping clamps on each side. This ensures even pressure distribution and secure mounting, preventing mold movement during the injection process which could damage both the machine and molds for plastic injection.
The design of clamping slots must account for the clamping force requirements of the specific mold, ensuring that the mold remains securely fastened during all phases of the injection cycle. Proper clamping prevents misalignment that could cause flash, part defects, or damage to molds for plastic injection.
Mold clamping slot designs and installation
Proper specification and selection of mold bases are fundamental to producing high-quality, durable molds for plastic injection. By following these detailed guidelines, manufacturers can ensure their molds perform reliably, produce consistent parts, and maintain longevity even under demanding production conditions. Attention to every detail, from dimensions to auxiliary components, contributes to the overall success of molds for plastic injection in manufacturing operations.
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