Mold Won't Open? Here's How to Diagnose and Fix Hydraulic and Mechanical Issues

When an injection molding machine fails to open the mold, production stops and troubleshooting becomes urgent. This problem is typically caused by hydraulic or mechanical issues. Below is a breakdown of the most common causes and their solutions.

Common Causes

① Worn cylinder piston seal – If the oil seal on the opening/clamping cylinder piston is damaged, internal leakage occurs. This results in a significant pressure drop during the opening stroke, leading to insufficient force to separate the mold.

② Faulty or stuck opening solenoid valve – The solenoid valve that controls the opening hydraulic circuit may have a stuck spool or internal damage, preventing the valve from shifting properly and cutting off flow to the opening cylinder.

③ Incorrect opening parameters – The position, pressure, and flow settings for the opening stroke may be improperly configured, resulting in insufficient force or speed to overcome mold resistance.

④ Mechanical wear or deformation – Wear on the toggle links, platens, or connecting rods increases sliding resistance. A bent crosshead guide rod can also cause excessive drag on the moving platen, making it difficult to open.

Solutions

① Replace the cylinder piston seal – Inspect the opening/clamping cylinder for internal leakage. If the piston seal is worn or damaged, replace it to restore proper hydraulic pressure.

② Replace the solenoid valve – If the opening solenoid valve is stuck or damaged, replace it with a new one of the same specification.

③ Adjust opening parameters – Review and adjust the opening position, pressure, and flow settings to ensure they are within recommended ranges for the mold and machine.

④ Inspect and service the mechanical clamping unit – Check whether the toggle links, platens, or other moving parts are stuck. Remove any foreign material and apply proper lubrication. If connecting rods are excessively worn beyond the allowable limit, replace them. If the crosshead guide rod is bent, replace it as well.