Injection molding, an indispensable method for processing plastic parts in modern manufacturing, relies on precise matching of injection molding machine and mold to inject molten plastic into cavity, where it cools and solidifies to obtain desired product. Stability, efficiency, and quality of this process directly depend on a deep understanding of injection molding machine's core structure and parameters, a rigorous and scientific fitting process between mold and machine, a set of process setting specifications based on material properties and product requirements.

 

An injection molding machine mainly consists of five systems that work together to complete plasticizing, injection, molding, and ejection of plastic.
Mold Closing System
Function: Enables opening, closing, and locking of mold, providing sufficient clamping force to prevent mold from expanding and producing flash during injection.
Core Components:
Plate: Fixed platen (for stationary mold), movable platen (for moving mold).
Tie Rods (Guardians): Connect platens, bear clamping force, and their internal spacing limits maximum size of mold.
Mold Adjustment Mechanism: Adjusts position of moving mold platen to accommodate molds of different thicknesses.
Ejection Mechanism: Ejects product from mold after mold opening (mechanical or hydraulic).
Safety Devices: Includes triple safety interlocking of mechanical, hydraulic, and electrical safety features to ensure operational safety.
Injection System:
Function: Heats and plasticizes plastic, meteres it, injects it into mold cavity at high pressure and high speed.
Barrel and Heating Coil: Heats and contains plastic.
Screw: Core plasticizing component, responsible for conveying, compressing, shearing, plasticizing, metering, and injection. Key parameters include diameter, length-to-diameter ratio (L/D), and compression ratio.
Nozzle: Connects barrel to mold sprue bushing; its ball diameter must match mold.
Injection Cylinder/Servo Motor: Provides injection power to screw.
Drive and Control System:
Hydraulic System: Provides power for mold closing, injection, and ejection. Pay attention to hydraulic oil operating temperature (ideally 45℃).
Electrical Control System: Core of a modern injection molding machine, used to set and monitor all process parameters (temperature, pressure, speed, position, etc.). It can be divided into open-loop and more precise closed-loop control.
Safety System: Includes emergency stop buttons, safety door locks, mechanical safety levers, etc.
Heating/Cooling System
Heating System: Electric heating coils for each section of barrel.
Cooling System: Mold cooling water circuit (water pressure typically 0.2-0.6MPa) and hydraulic oil cooler.

 

Mold adaptation is a systematic and safe operation process that must be strictly followed. Core lies in initial matching confirmation and subsequent fine-tuning.
Stage One: Pre-installation Assessment and Matching Confirmation
Before hoisting, it must be confirmed that mold and target injection molding machine are compatible in terms of physical dimensions and process capabilities.
Physical Dimension Matching:
Mold Thickness: Must be between machine's minimum and maximum mold thickness.
Mold Length and Width: Must be smaller than machine's tie rod inner spacing and be able to pass through.
Mold opening stroke: Must meet following requirement: Mold opening stroke ≥ 2 × product height + runner length + (5~10mm) ejection space.
Ejection stroke: Machine's ejection stroke must meet product's demolding requirements.
Positioning ring and nozzle: Mold positioning ring must match machine's fixed platen positioning hole; nozzle ball diameter must match mold's sprue ball pit.

 

Process capability matching: Required clamping force: Estimated based on product's projected area and material cavity pressure.
Formula: Clamping force (T) ≈ Product projected area (cm²) × Cavity pressure (kg/cm²) / 1000 × Safety factor (1.1~1.3). Maximum clamping force of selected injection molding machine must be greater than this value with a safety margin.
Required injection volume: Calculate "product weight + total weight of gating system". For non-PS materials, it needs to be converted to PS equivalent (formula: Wps = Wx × (1.05 / ρx)). Theoretical injection volume (in PS) should ideally be between 30% and 85% of required weight.

 

Phase Two: Pre-Installation Preparation
Machine Preparation: Check machine's level (horizontal and longitudinal levelness should ideally be within 0.5mm/m), safety devices, hydraulic oil level, and connect cooling water.
Mold Preparation: Measure and record key mold dimensions, and prepare lifting tools, pressure plates, bolts, etc.
Rough Mold Thickness Adjustment: In manual mode, adjust mold platen spacing to be slightly larger than mold thickness.
Phase Three: Mold Installation and Mechanical Adjustment (Core Steps, Strictly Follow Injection Molding Machine Instruction Manual)
Note: Before any manual operation, oil pump motor must be turned off to ensure safety.
Lifting and Initial Fixing: Manually open mold to sufficient space, and retract injection unit.
Turn off oil pump motor.
Lift mold in, aligning locating ring on fixed mold side with machine's locating hole and pressing it firmly against fixed mold platen.
Use pressure plates and bolts to initially fix fixed mold side of mold to fixed mold platen.
Mold Closure and Moving Mold Side Fixing:
Start oil pump and briefly close mold to allow moving mold platen to lightly contact moving mold side of mold.
First tighten fixed mold platen side pressure plate bolts, then firmly lock moving mold platen side pressure plate bolts.
Nozzle Centering (Critical): Start oil pump and close mold.
Advance injection unit until nozzle contacts mold sprue bushing.
Adjust Nozzle Center: Loosen injection unit guide rod bracket fasteners and adjust up/down and left/right adjusting screws to ensure a uniform gap between nozzle and sprue bushing (deviation should be ≤0.30mm). Tighten after adjustment.
Fine-tuning Mold Thickness and Parameter Settings:
Use machine's automatic mold adjustment function or manual mold adjustment to ensure mold closing endpoint reaches required clamping force.
Set opening/closing positions, pressures, and speeds for each stage on control panel, especially high-pressure clamping pressure.
Set parameters such as ejector pin stroke and number of strokes.
Connect mold cooling water pipes and other piping.
Stage Four: Process Debugging and Trial Run
This stage begins the injection molding process settings.

After mold installation and adjustment, process parameter setting and debugging stage begins, with goal of producing qualified products and achieving stable automated production.
Step 1: Basic Preparation and Temperature Setting
Material Preparation: Preheat and dry plastic according to material's process requirements (e.g., PC requires drying at 100-120℃ for several hours).
Ball Heating: Set temperature of each section of barrel (nozzle, front, middle, and rear) on controller. After reaching set temperature, maintain temperature for 15-30 minutes before operating screw to protect it and ensure uniform plasticization.
Mold Preheating: Preheat mold using cooling water (or a mold temperature controller) to reach required mold temperature for material.

 

Step 2: Manual Testing and Preliminary Parameter Setting
Manual Action Testing: In manual mode, set a set of lower pressures and speeds for each action (mold opening and closing, ejection, injection, material storage, etc.). Operate each action key sequentially to check if action is smooth and normal.
Preliminary Injection Parameter Settings:
Pre-plasticizing (Storage) Parameters: Roughly set storage stroke based on product weight. Initially set screw speed to slightly slower and back pressure to lower (e.g., 5-10 MPa).
Injection Parameters: To protect mold, set initial injection pressure to machine's maximum value, and start with a slightly slower injection speed. Set holding pressure and time to 0.
Clamping Force: Set a higher value initially to prevent overflow.
Injection into Empty Space and Cleaning: Perform empty injection, observe plasticization and injection process of melt, and clean old material from barrel.
Step 3: Mold Trial and Parameter Optimization:
Short Injection Method for Determining V/P Switching Point: Close safety door and perform manual or semi-automatic injection.
Gradually increase injection volume (5%-10% each time), performing a "short injection" (i.e., not filling mold cavity completely), and observe melt front position.
When product is 95%-98% filled, record screw position at this point. This position is V/P switching point from injection (speed control) to holding pressure (pressure control). This is crucial for ensuring stable molding.
Optimize Injection Speed and Pressure: Observe melt flow pattern based on short injection cycles. If trapped air or scorching occurs, reduce speed in that section or adjust venting. If flow lines or obvious weld lines appear, try increasing speed or adjusting temperature.
After filling to 95%-98%, initiate holding pressure. Gradually adjust holding pressure and time from low to high to eliminate shrinkage marks and air bubbles, and ensure gate sealing.
Optimize Holding Pressure and Cooling:
Holding Pressure: Typically 30%-80% of injection pressure. Principle is to eliminate shrinkage marks without generating flash.
Holding Time: Primarily depends on gate solidification time. It can be determined by weighing: Gradually increase holding time; optimal holding time is when product weight no longer increases.
Cooling Time: Principle is to ensure product cools sufficiently and ejects without deformation. Start with a longer time and gradually shorten it to optimize cycle time.
Optimize other parameters:
Screw speed and back pressure: Optimize while ensuring plasticizing quality (uniform melt, no bubbles) and without extending cycle time.
Mold temperature: Set according to material characteristics; strict control is required for high-gloss or precision parts.
Mold opening and closing speed: Follow "slow-fast-slow" principle to protect mold and improve efficiency.
Step 4: Process Stabilization and Automated Production
Defect Resolution: Adjust parameters to resolve issues such as "insufficient filling," "flash," "shrinkage marks," "bubbles," and "weld marks" observed during trial molding.
Confirm Process Stability: In manual/semi-automatic mode, continuously produce several molds to check if product dimensions and appearance are stable and qualified.
Switch to Automated Production: After confirming all parameters are stable, switch to semi-automatic mode and run several cycles. Finally, after confirming that safety gate, robot arm signals, and other interlocks are normal, enter fully automated production mode.
Process Recording and Calibration: Record all stable process parameters. Process calibration can be performed (e.g., weighing 40 consecutive molded products) to calculate standard deviation and coefficient of variation (CV) of weight fluctuations, thereby quantifying stability and capability of process.

Through above systematic process, good cooperation between mold and injection molding machine can be ensured, a stable and efficient injection molding production process can be established.