What is a two-color injection molding machine? How does it improve production efficiency?

1. Working principle of two-color injection molding machine

• Double barrel design Equipped with two independent injection units (barrel A and barrel B), plastics of different colors or materials (such as ABS+TPE, hard rubber+soft rubber) can be injected separately.

• Rotary mold or turntable technology

Rotary mold type: The movable mold part of the mold can rotate 180°, and the injection of two materials can be completed in one mold closing.

Turntable type: The semi-finished product is transferred to the second station for secondary injection molding through the rotating workbench.

• Integrated molding The two materials are layered or nested in the mold, without the need for subsequent assembly, reducing secondary processing.

2. Key ways to improve production efficiency

Reduce production processes

The traditional method requires the production of two parts separately and then assembles them, while the two-color injection molding machine is molded in one step, saving assembly, bonding or welding steps.

Shorten cycle time

By optimizing mold design and synchronous injection action, the cycle time is shortened by 30%-50% compared with the production of two colors/materials separately.

High degree of automation

Integrated manipulator or turntable system, automatically completes the removal, mold change and secondary injection molding, reducing manual intervention.

Reduce defective rate

Avoid the alignment deviation or weak bonding problems in traditional assembly, and the product consistency is higher.

Save energy and cost

A single device replaces multiple traditional injection molding machines, reducing space and energy consumption.

Advantages compared with traditional injection molding

3.Common problems and solutions of two-color injection molding machines

Material bonding problem

• Delamination/weak bonding

Reason:

Material incompatibility (such as PP and ABS are incompatible)

Mold temperature is too low or the temperature difference is too large

The second shot is performed only after the first shot material is completely solidified

Solution:

Choose a material combination with good compatibility (such as PP+TPE, ABS+PC)

Increase mold temperature (usually the second shot mold temperature is 10~20℃ higher than the first shot)

Shorten the interval between two injections (control within 5~10 seconds)

• Obvious bonding line

Reason:

Injection speed is too slow, the temperature of the melt front drops

Poor exhaust leads to trapped air

Solution:

Increase the injection speed of the second shot (about 80%~90% of the first shot)

Add exhaust grooves or vacuum exhaust systems at the joint

Appearance defects

• Color mixing (material color mixing)

Reason:

The previous material remains in the nozzle or barrel

Incomplete machine cleaning

Solution:

Use high melting point transition material (such as PC) to clean the barrel

Use double nozzle independent closing design to avoid cross contamination

• Flash/burr

Reason:

Insufficient clamping force (two-color machine needs 15%~20% higher than single-color machine)

Mold wear or uneven parting surface

Solution:

Increase clamping force or reduce injection pressure

Repair mold parting surface and check guide pin guidance accuracy

Dimensional accuracy problem

• Product deformation

Reason:

The shrinkage rate of the two materials is too different (such as ABS shrinkage rate 0.5%, PP shrinkage rate 1.5%)

Uneven cooling

Solution:

Select materials with similar shrinkage rates

Optimize cooling water circuit design and extend holding time

• Dimensional instability

Reason:

Injection molding process parameter fluctuation (temperature, pressure)

Uneven mold thermal expansion

Solution:

Use closed-loop control system to stabilize process parameters

Add constant temperature oil circuit to the mold to control temperature

Equipment and mold problems

• Inaccurate positioning of turntable/rotating mold

Reason:

Servo motor encoder failure

Mold bearing wear

Solution:

Recalibrate the turntable zero position

Replace high-precision bearings

• Insufficient injection volume

Reason:

Barrel or nozzle blockage

Screw wear causes plasticizing capacity to decrease

Solution:

Clean the nozzle and filter

Check the gap between the screw and the barrel (replace if wear exceeds 0.2mm)

Production efficiency issues

• Too long cycle time

Reason:

Unreasonable cooling time setting

Mold movement is not synchronized

Solution:

Use conformal cooling water circuit to shorten cooling time

Optimize hydraulic/electric system action sequence

• Failure of automatic removal

Reason:

Deviation in the gripping position of the robot

Product sticking to the mold

Solution:

Adjust the robot program or increase visual positioning

Add release agent to the mold surface or improve the ejection system

4. Troubleshooting of two-color injection molding machine<

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