Electrical troubleshooting of injection molding machine

When the electrical control system of the injection molding machine fails, the maintenance personnel need to have a good knowledge of electrical control and be able to understand the meaning of various symbols on the electrical control circuit schematic diagram and the functions of components. In terms of electrical maintenance, the usual practices include isolation of front and rear components, comparison and substitution of good and bad component boards, visual observation and knocking, step-by-step troubleshooting, simulation experiment, node measurement (voltage, resistance, on-off), etc. Common methods are summarized as follows.

1、 Simple diagnostic method.

The simple diagnosis method is to detect the electrical control system with human sensory organs to find the fault. For example:

After the fault occurs, immediately ask the injection molding machine operator or the person reporting the fault about the abnormal conditions when the fault occurs and whether the components and boards have been replaced before the fault occurs; Directly observe whether various signal indications are correct; Check whether there are other abnormal sounds in the electrical control system; Observe whether the electrical components are discolored, deformed or cracked; Smell the components of the circuit by smell. Many components will produce burnt smell due to overheating damage; Whether the hand sensing element is abnormally hot and high temperature; Use a multimeter to measure the electrical parameters of components, especially for locations, input and output points, to judge whether they are low, high or abnormal fluctuations, and eliminate the virtual connection, which will lead to unstable operation and easy to heat and ignite; If the grounding pin has an oxide layer, the oxide layer will produce resistance effect. The oxide layer should be polished off to make it contact closely.

2、 Procedure check method.

The injection molding machine forms a cycle through the processes of closing the mold, moving the shooting table, injection, pressure maintaining, glue melting, cable reversing, mold opening, demoulding and so on. Each working link of the cycle corresponds to an independent control circuit. The program check method is to determine the control link with fault by verifying each independent control circuit and observing whether the corresponding components move normally. This method is applicable to electrical control systems with contacts, such as travel switch and relay circuit. It is also suitable for contactless control systems, such as transistors and switching diode circuits in PC control systems.

3、 Voltage measurement method.

When the control circuit is energized, the voltage on the circuit should have a determined value. If the injection molding machine does not respond to the injection action during the injection action, check whether there is voltage on the solenoid coil of the injection reversing valve. Generally, each reversing valve on the injection molding machine is controlled by DC24V. During detection, use the DC gear of the multimeter, connect the red and black probes to the two terminals of the solenoid coil, start the glue injection action, and observe whether the multimeter can detect DC24V voltage. If it is not detected, it indicates that some circuits in front of the coil have failed.

4、 Static resistance measurement.

In the electrical control system, each electronic component has a resistance value, and some forward and reverse resistance values are different. Therefore, in the case of power failure, use a multimeter to measure whether the resistance value of the circuit is normal to judge the faulty component, and also judge whether the electronic circuit is on or off.

5、 Short circuit method.

The control link circuit is composed of switch or relay and contactor contact. When a fault of an electrical component is suspected, the contact can be short circuited by twisting the wire. If the fault is eliminated, the electrical component has been damaged. Note that after replacing electrical components, do not use wire short circuit switches or switch contacts. This method is mainly used to detect the breakpoint of Shenqi logic relationship circuit, and also to detect the fault of electronic circuit.

6、 Open circuit method.

In case of contact short circuit, the open circuit method can be used to eliminate the fault. Disconnect the contact suspected of fault. If the fault disappears, it indicates that the judgment is correct, the contact shall be disconnected, and the wire connecting the contact shall be removed or the connecting wire shall be insulated.

7、 Substitution method.

If a fault is suspected at a certain point or a circuit board, the component or circuit board can be removed and replaced with a component or circuit board in good condition. If the fault is eliminated, it can be considered that the component or circuit board is damaged.