Clamping Unit Of Injection Molding Machine

Why is the clamping unit critical in injection molding? An injection molding machine relies heavily on its clamping unit to ensure quality and precision. In this post, you'll learn what an injection molding machine is, the importance of the clamping unit, and key details about its functions, types, and troubleshooting tips.

Overview of Injection Molding Machines

Injection molding machines are essential in manufacturing various plastic products. They consist of three main components: the clamping unit, the injection unit, and the machine bed.

Main Components of Injection Molding Machines

Clamping Unit

The clamping unit locks the mold during the injection process. It ensures the mold stays closed under high pressure. This unit also adjusts the mold size and ejects the finished product. It has safety features to protect operators from harm. Without it, the machine can't function properly.

Injection Unit

The injection unit is where the magic happens. It melts plastic pellets and injects the molten plastic into the mold. This unit needs precise temperature and pressure control. It consists of a hopper, barrel, screw, and nozzle. The injection unit's accuracy determines the quality of the molded parts.

Machine Bed

The machine bed supports all the other components. It ensures the stability and alignment of the clamping and injection units. The bed must be strong and durable to handle the machine's operations. It acts as the foundation for the entire injection molding process.

Detailed Breakdown

• Clamping Unit Functions

• Locks the mold tight.

• Adjusts to the mold size.

• Ejects the final product.

• Injection Unit Components

• Hopper: Feeds plastic pellets.

• Barrel: Melts the plastic.

• Screw: Moves molten plastic forward.

• Nozzle: Injects plastic into the mold.

• Machine Bed Importance

• Provides stability.

• Ensures proper alignment.

• Supports the entire machine.

Functions of Clamping Units

Clamping units perform several critical functions in injection molding machines. Let's explore these roles in detail.

Locking the Mold

The primary function of a clamping unit is to lock the mold securely. It prevents the mold from being blown open due to the high pressure during injection. The clamping force must be sufficient to counteract the injection force.

Adjusting the Platen

Clamping units adjust the position of the moving platen (second platen). This ensures the correct mold thickness parameter is achieved. It accommodates molds of varying sizes.

Ejecting Plastic Products

Ejectors in the clamping unit remove the molded products from the mold cavity. They push the products out, preparing the mold for the next cycle. Various ejection mechanisms are used, such as pins, sleeves, and plates.

Additional Functions

Clamping units also perform auxiliary actions like core pulling. Core pullers remove cores from the molded product. These functions are synchronized with the machine's controller for seamless operation.

Safety Features

Clamping units incorporate safety protections to prevent accidents:

• Mechanical: Guards, barriers, and interlocks

• Hydraulic: Pressure relief valves and safety circuits

• Electrical: Emergency stop buttons and sensors

Types Of Clamping Units

Injection molding machines employ various types of clamping units. Each has its unique characteristics and applications. Let's take a closer look at the three main types.

Five-point double toggle clamping unit

The five-point double toggle is a popular choice for high-speed injection molding. It uses a toggle mechanism to amplify the clamping force efficiently.

Advantages:

• Mature technology

• Less stringent processing requirements

• Widely used in Chinese injection molding machines

Disadvantages:

• Limited adjustability

• Higher maintenance due to more moving parts

Common use cases:

• High-speed, high-volume production

• Molding of precision parts

Hydraulic clamping unit

Hydraulic clamping units rely on hydraulic cylinders to generate the clamping force. The moving platen is directly connected to the hydraulic ram.

How it works:

1. Oil is pumped into the cylinder under pressure

2. The ram pushes the moving platen, closing the mold

3. Oil is released, allowing the ram to retract and open the mold

Advantages:

• Precise control over clamping speed and force

• Ability to maintain clamping force at any position

• Low maintenance

Disadvantages:

• Higher initial cost compared to toggle units

• Potential for oil leaks

Applications:

• Large-scale injection molding

• Molding of complex parts requiring precise control

Electrical clamping unit

Electrical clamping units use servo motors and ball screws to generate the clamping force. They represent the latest advancement in injection molding technology.

Technology behind electrical clamping units:

• Servo motors provide rotary motion

• Ball screws convert rotary motion to linear motion

• Precise control through servo drives and encoders

Advantages:

• High energy efficiency

• Precise and repeatable clamping force

• Clean and quiet operation

Disadvantages:

• Higher initial cost

• Requires specialized maintenance and repair

Manufacturers and availability:

• Primarily offered by Japanese and South Korean manufacturers

• Increasingly adopted in high-end injection molding applications

Calculation of Clamping Force

Determining the required clamping force is crucial for successful injection molding. It ensures the mold remains closed during the injection process. Let's dive into the formula and factors involved.

Formula for Clamping Force

The supporting mold force formula calculates the necessary clamping force:

Supporting mold force = Projected area (cm⊃2;) × Number of cavities × Mold pressure (kg/cm⊃2;)

This formula takes into account the key variables that influence the clamping force. It provides a straightforward way to estimate the required force.

Factors Affecting Clamping Force

Several factors come into play when determining the clamping force:

1. Projected Area

• It refers to the area of the molded part projected onto the parting plane.

• Larger projected areas require higher clamping forces.

2. Number of Cavities

• The formula considers the total number of cavities in the mold.

• More cavities mean a higher clamping force is needed.

3. Mold Pressure

• Mold pressure is the pressure exerted by the injected plastic inside the mold cavity.

• Higher mold pressures demand stronger clamping forces to keep the mold closed.

Through understanding these factors, you can accurately calculate the clamping force for your specific molding application. It ensures the mold remains securely closed, preventing flashing and other defects.

Remember, the clamping force must always exceed the force generated by the injection pressure. This prevents the mold from opening during the injection phase, guaranteeing consistent and high-quality parts.

Choosing the Right Clamping Unit

Selecting the appropriate clamping unit is essential for efficient and reliable injection molding. Several key factors should be considered to ensure the clamping unit meets your production requirements.

Containment

The clamping unit must be able to accommodate the mold dimensions:

• Mold width and height should fit within the machine's tie bar spacing.

• Ideally, the mold size should fall within the platen size range.

• Mold thickness should be compatible with the machine's mold thickness adjustment range.

Proper containment ensures the mold fits securely and aligns correctly within the clamping unit.

Takability

The clamping unit should provide sufficient mold opening stroke and ejection capability:

• Mold opening stroke: At least twice the product height in the mold opening direction, including the sprue length.

• Ejection stroke: Adequate to fully eject the molded products from the mold cavity.

Adequate takability ensures smooth and efficient product removal from the mold.

Lockability

The clamping unit must deliver enough clamping force to keep the mold closed during injection:

• Clamping force must exceed the force generated by the injection pressure.

• It prevents the mold from opening and ensures consistent part quality.

• The required clamping force is calculated based on the projected area, number of cavities, and mold pressure.

Sufficient lockability guarantees the mold remains securely closed throughout the injection process.

Common Faults and Solutions

Injection molding machines may encounter various issues with their clamping units. Identifying and resolving these faults is crucial for maintaining production efficiency. Let's explore some common problems and their solutions.

Mold Adjustment Issues

• Mechanical alignment: Check level and parallelism. Adjust as needed.

• Nut gap: Measure with a feeler gauge. Adjust gap to ≤ 0.05mm.

• Burned nut: Check for rotation and iron powder. Replace if necessary.

• I/O board failure: Check output signal. Repair or replace the board.

• Stuck valve core: Remove and clean the valve.

• Motor failure: Check, repair, or replace the oil motor.

Clamping Failures

• Travel switch: Check and repair the safety door switch.

• Power supply: Check 24V5A supply. Replace fuse or power supply box.

• Stuck spool: Clean the spool.

• Solenoid valve: Check I/O board output and valve power.

• Safety switch: Check hydraulic switch and mechanical lock lever.

Noise During Mold Operation

• Lubrication: Check for disconnected pipes. Increase lubrication.

• Clamping force: Reduce if too high.

• Amplifier board: Adjust current parameters.

• Parallelism: Check and adjust first and second plate parallelism.

Delayed Mold Opening

• Starting speed: Adjust screw damping hole.

• Damping screw: Replace with a thin central hole screw.

Crawling of Mold Operation

• Guide rail wear: Check and replace copper sleeve and column. Lubricate.

• Speed/pressure adjustment: Set flow rate to 20 and pressure to 99.

• Air in pipes: Exhaust the system.

Mold Not Opening

• Speed/pressure: Increase mold opening/locking speed and pressure.

• Clamping electronic scale: Re-adjust zero position after twisting.

• Reverse hinges: Check for issues.

Adjusting Mold During Production

• Solenoid valve leakage: Check valve type and power. Replace if needed.

• Manual adjustments: Check for unintended mold adjustment actions.

Slow Automatic Mold Opening

• Oil plate leakage: Check clamping valve. Replace oil plate.

• Mold opening valve leakage: Press injection table or action. Replace valve if the second plate moves.

Only Mold Opening Action

• Wiring: Check 24VDC to valve and connections.

• Valve core: Check for incorrect installation or blockage. Clean or reinstall.

Poor Mold Clamping

• A and B hole adjustment: Observe crawling at flow 20 and pressure 99. Readjust or change the valve.

• Air in oil circuit: Listen for air sound. Exhaust the system.

• Amplifier board ramp: Check current proportionality. Adjust the board.

High-Pressure Issues

• Limit switch: Check mold adjustment and motor condition.

• Hydraulic limit: Check electronic ruler stroke and mold adjustment.

No Thimble Action

• Limit switch: Check 24V proximity switch. Replace if needed.

• Valve stuck: Press valve core with a hexagon key. Clean the pressure valve.

• Limit rod: Remove and replace the broken rod.

• Switch short circuit: Check 0 voltage to ground. Replace the switch.

• Electronic ruler position: Check settings.

Thimble Control Problems

• Ejector board: Check circuit (normal voltage DV24V). Repair the board.

• Wiring: Check switch and I/O board connections. Rewire if needed.

• Mold position: Check for out-of-position issues.

• Oil cylinder piston rod: Check for damaged sealing ring.

Loud Mold Opening

• Proportional linearity: Check ramp up/down parameters. Adjust settings.

• Lubrication: Check Colin column, sliding foot, and hinges. Increase lubrication frequency.

• Clamping force: Reduce force based on product requirements. Check time position.

• Parallelism deviation: Check head board and second board parallelism. Adjust errors.

• Slow mold opening position: Lengthen slow opening position. Reduce speed.

Semi-Automatic Clamping Issues

• Clamping spool: Check for incomplete reset.

• Action delays: Increase delay time for the next action.

Importance of Clamping Units

Clamping units play a vital role in the injection molding process. They impact product quality, energy consumption, and operator safety. Let's explore the significance of clamping units in detail.

Ensuring High-Quality Production

A well-designed clamping unit is essential for producing high-quality parts consistently:

• Stability: It keeps the mold securely closed during injection, preventing flashing and other defects.

• Precision: Accurate alignment and parallelism of the platens ensure uniform clamping force distribution.

Investing in a reliable clamping unit lays the foundation for superior production results.

Energy Efficiency and Cost Savings

Optimized clamping unit design can lead to significant energy savings and reduced operating costs:

• Efficient force amplification: Toggle mechanisms or servo-driven systems minimize energy consumption.

• Reduced cycle times: Fast and precise clamping actions contribute to shorter overall cycle times.

An energy-efficient clamping unit not only benefits the environment but also improves profitability.

Safety Considerations

Clamping units must prioritize the safety of both workers and equipment:

• Operator protection: Mechanical guards, interlocks, and sensors prevent accidental contact with moving parts.

• Equipment safeguards: Pressure relief valves, safety circuits, and emergency stops protect against overloading and malfunctions.

Proper safety measures built into the clamping unit ensure a secure working environment and minimize the risk of accidents.

Advanced Clamping Technologies

As injection molding evolves, so do the clamping technologies. Advanced clamping systems offer improved performance, efficiency, and control. Let's dive into some of these cutting-edge solutions.

Toggle Type Clamping

Toggle clamping units harness mechanical advantages to amplify clamping force:

• Linkage system: Converts hydraulic force into a powerful clamping action.

• High-speed molding: Ideal for fast-cycling applications.

• Positive mold locking: Ensures secure mold closure throughout the injection process.

Toggle clamping is a proven technology widely used in the industry.

Hydraulic Clamping

Hydraulic clamping units offer precise control over clamping speed and force:

• Adjustable speed: Allows optimization of the clamping profile for different molds.

• Variable force: Enables fine-tuning of the clamping force based on molding requirements.

• Smooth operation: Provides consistent and stable clamping performance.

Hydraulic clamping is versatile and suitable for a wide range of injection molding applications.

Magnetic Clamping Units

Magnetic clamping technology brings a new level of efficiency and monitoring capabilities:

• Energy savings: Consumes power only during magnetization and demagnetization phases.

• Real-time monitoring: Offers real-time reading of clamping force for process control.

• Maintenance-free: Eliminates the need for regular maintenance, reducing downtime.

Feature	Magnetic Clamping	Toggle Clamping	Hydraulic Clamping
Energy consumption	Low	Medium	High
Clamping force monitoring	Real-time	Limited	Indirect
Maintenance requirements	Minimal	Regular	Moderate

Magnetic clamping is an emerging technology that offers unique advantages for modern injection molding operations.

Summary

In this post, we've explored the critical role of clamping units in injection molding machines. From locking the mold to ejecting the finished product, clamping units ensure the quality and consistency of molded parts.

We've discussed the various types of clamping units, including toggle, hydraulic, and magnetic systems. Each offers unique advantages in terms of force amplification, control, and efficiency.

The importance of selecting the right clamping unit cannot be overstated. It directly impacts product quality, energy consumption, and operator safety.