Mold closure (clamping) process of an injection molding machine is a crucial step in injection molding. Rationality of its parameter settings directly affects production efficiency, mold life, and product quality. Mold closure process is typically divided into multiple stages, each with different speed, pressure, and position setting requirements to achieve fast, smooth, safe mold closure. Following are setting basis and specific requirements for each stage:

 

Typical mold closing process of a molding machine can be divided into following stages (taking a three-stage model as an example):
- Slow start stage (mold begins to close)
- Fast mold closing stage (mold rapidly approaches)
- Low pressure and low speed stage (mold protection stage)
- High pressure mold locking stage (final locking)

 

(1) Slow start stage
- Position range: Mold closing start position → Set point A (e.g., just before mold guide pillars make contact)
- Speed setting: Low speed (usually 10%-20% of maximum speed)
- Pressure setting: Lower pressure (only provides starting thrust)
- Setting basis:
- Smooth start: Avoid mechanical shock and extend equipment life.
- Eliminate inertial effects: Allow mold platen to accelerate smoothly from rest.
- Applicable scope: Large molds or precision molds require lower start speeds.
(2) Rapid Mold Closing Stage
- Position Range: Setpoint A → Setpoint B (before approaching mold contact point)
- Speed Setting: High speed (60%-90% of maximum speed)
- Pressure Setting: Medium to high pressure (ensuring rapid advancement)
- Setting Basis:
- Improve Efficiency: Shorten idle stroke time and increase cycle speed.
- Smooth Transition: Smoothly accelerate from slow to high speed to avoid jitter.
- Notes: When there are structures such as sliders or inclined guide pillars inside mold, speed should be appropriately reduced to avoid impact.
(3) Low-Pressure, Low-Speed Stage (Mold Protection Stage)
- Position Range: Set point B → Before the mold is fully closed (generally leaving a 0.5-2mm gap)
- Speed Setting: Low speed (5%-15% of maximum speed)
- Pressure Setting: Low pressure (usually 5%-10% of maximum clamping force)
- Setting Basis:
- Mold Protection: If there are foreign objects inside mold or product has not fallen out, low-pressure mold closing will trigger a pressure alarm and stop process, preventing mold compression.
- Buffering Effect: Prevents high-speed impact on mold, extending mold life.
- Position Accuracy: At the end of this stage, mold should be nearly closed but not fully in contact.
(4) High-Pressure Clamping Stage
- Position Range: From mold contact to complete clamping (clamping endpoint)
- Speed Setting: Medium to low speed (ensuring smooth pressure increase)
- Pressure Setting: High pressure (reaching set clamping force)
- Setting Basis:
- Ensure Clamping Force: Provide sufficient clamping force to prevent mold bulging and flash.
- Smooth Pressure Increase: Avoid pressure shocks, protect mold and machine hinges.
- Time Control: High-pressure duration should not be too long to reduce energy consumption and hydraulic system heating.

(1). Position Switching Point:
- Determined based on mold size and structure; requires fine-tuning in actual production.
- Position of low-pressure protection section must ensure that mold has slowed down before contact.
(2). Speed and Pressure Matching:
- Sufficient pressure is required during high-speed stage to avoid speed instability.
- Pressure during low-pressure stage must be below damage threshold that mold can withstand.
(3). Mold Adaptability:
- For complex molds (such as multi-slider or insert structures), mold closing speed needs to be further reduced to avoid impact.
- Deep cavity molds require an extended low-pressure section to ensure adequate venting.

- Mold closing characteristics of direct-pressure and toggle-type injection molding machines differ. Toggle-type machines have a force-boosting effect in high-pressure section; attention must be paid to timing of position switching.

(1) Initial Settings: Refer to recommended equipment parameters based on mold weight and dimensions.
(2) Dry Run Test: Without injection, observe whether mold closing action is smooth and adjust positions of each section.
(3) Low-Pressure Protection Test: Place a plastic sheet (e.g., 0.5mm thick) on mold parting surface. Mold closing should trigger a low-pressure alarm and stop process.
(4) Production Verification: After trial molding, check for defects such as flash and white spots on product, and fine-tune high-pressure position and pressure.

- Large impact during mold closing: Reduce speed of high-pressure section or switch to low-pressure section earlier.
- Frequent false alarms from low-pressure protection: Appropriately increase low-pressure level or adjust position of low-pressure section.
- Insufficient mold clamping leading to flash: Increase high-pressure level or check mold parallelism.
- Excessively long mold closing time: Increase speed of high-pressure section while ensuring smooth operation.