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

Comparison items	Traditional single-color injection molding + assembly	Two-color injection molding machine
Production process	Multiple processes, multiple equipment	Integrated molding
Cycle time	Long (needs two molding + assembly)	Shortened by more than 30%
Labor cost	High (needs assembly personnel)	Low (fully automated)
Product accuracy	Assembly errors are prone to occur	Seamless combination, high accuracy

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

Ø General rules for troubleshooting process

Observe the phenomenon: record the specific manifestation of the fault (such as abnormal sound, alarm code, product defect type).

Lock range: determine whether it is a mechanical, hydraulic, electrical, mold or process problem based on the phenomenon.

Verify step by step: troubleshoot from simple to complex (such as checking parameter settings first, then checking mechanical parts).

Safety first: check mechanical parts after power off/pressure relief.

 

Ø Classification and troubleshooting of common faults

Injection system failure

Phenomenon: insufficient injection, unstable injection, nozzle leakage Troubleshooting steps:

Check barrel temperature: confirm that the temperature of each section meets the material requirements.

Check nozzle blockage: disassemble the nozzle to clean carbide, and check whether the heating ring is damaged.

Check screw wear: measure the gap between the screw and the barrel>0.2mm and need to be replaced.

Check the back pressure valve: unstable back pressure will lead to uneven plasticization.

Case: Insufficient second shot → Check whether the check valve of injection unit B is stuck.

 

Locking system failure

Phenomenon: Insufficient clamping force, abnormal sound when opening and closing the mold, and the mold cannot be closed. Troubleshooting steps:

Check the clamping force setting: The clamping force of the two-color machine needs to be 15%-20% higher than that of the single-color machine.

Check the lubrication of the Green column: Lack of oil will cause the template to jam (use grease).

Check the elbow mechanism: The connecting rod with severe wear needs to be replaced (clearance > 0.1mm is abnormal).

Check the mold balance: Use a 0.02mm feeler gauge to check the fit of the four corners.

Case: Alarm "Mold not closed" when closing the mold → Check whether the proximity switch is offset.

 

Rotation/turntable system failure

Phenomenon: Inaccurate positioning, rotation jam, servo alarm Troubleshooting steps:

Check the encoder: Use an oscilloscope to detect whether the encoder signal loses pulses.

Check the reducer: Whether the gear oil is deteriorated (replace every 2000 hours).

Check the bearing: The bearing clearance of the rotating mold > 0.05mm needs to be replaced.

Check the timing belt: the tension is moderate (5-8mm is the best when pressed).

Case: the stop position deviation of the turntable is ±1° → recalibrate the origin.

 

Hydraulic system failure

Phenomenon: pressure fluctuation, oil temperature is too high (＞55℃), slow action Troubleshooting steps:

Check the oil level and filter element: the oil level is lower than the lower limit or the filter element is blocked (pressure difference＞3bar needs to be replaced).

Check the oil pump: measure the pump outlet pressure (normal 16-18MPa), and check the oil distribution plate when abnormal.

Check the solenoid valve: use a multimeter to measure the coil resistance (normal 20-30Ω).

Check the cooler: clean the dust on the heat sink and test the fan speed (＞1500rpm).

Case: slow mold opening speed → check whether the mold opening valve core is stuck.

 

Electrical control system failure

Phenomenon: no response to the touch screen, temperature control fluctuation, servo drive alarm Troubleshooting steps:

Check the emergency stop circuit: confirm that all emergency stop buttons are in the released state.

Check the thermocouple: use a multimeter to measure the resistance (PT100 should be 100Ω±0.5Ω at 0℃).

Check the grounding: resistance to ground > 4Ω needs to be rectified.

Check the PLC output: test the solenoid valve action by forced output.

Case: The temperature of the heating zone jumps → replace the solid-state relay (SSR).

 

Product defect related troubleshooting table:

 

Defect type	Priority inspection items	Tools/methods
Obvious joint line	Mold exhaust, injection speed, material temperature	Mold flow analysis software, infrared thermometer
Top white/strain	Ejector polish, demolding angle (≥1°)	Surface roughness meter, 3D scanning
Dimensional deviation	Mold temperature, holding pressure curve, screw wear	Three-dimensional coordinate measuring machine, pressure sensor
Color contamination	Nozzle sealing, machine cleaning procedure	Endoscope, colorimeter

5. Preventive maintenance recommendations for two-color injection molding machines

Daily: Check the hydraulic oil level and clean the nozzle residue.

Weekly: Lubricate the guide rails and check the belt tension.

Monthly: Calibrate the temperature sensor and test the safety door interlock.

Quarterly: Replace the hydraulic oil filter and test the motor insulation resistance.