Fault Analysis and Solutions for Press Machines with Single Stroke but Unable to Switch to Continuous Stroke
Publish Time: 2026-03-12 Origin: Site
The fault where "single stroke operates normally but continuous stroke fails" in a press machine typically stems from three core issues: an unclosed safety protection circuit, an interrupted continuous control signal, or lagged response from the clutch/brake system. As a frontline technician, it is recommended that you prioritize checking the synchronization of the two-hand operation buttons and the photoelectric protection device, as these are the most common yet easily overlooked "soft faults." Subsequently, proceed to inspect electrical components and mechanical clearances in greater depth.
1. Safety Protection Devices Not Reset or Signal Abnormalities (Most Frequent Cause)
Continuous stroke operation imposes far stricter requirements on safety interlocks than single stroke mode. If any safety barrier is not confirmed as "absolutely safe," the control system will forcibly lock out continuous mode.
Asynchronous Two-Hand Operation Buttons: Continuous stamping requires both left and right buttons to be pressed simultaneously within an extremely short time difference (typically <0.5 seconds). If the micro-switch of one button has poor contact, sticking, or loose wiring, the system interprets this as single-hand operation and prohibits continuous running.
Troubleshooting: Remove the button box, check for oxidation on micro-switch contacts, and use a multimeter to measure whether both signal paths output synchronously.
Photoelectric Protection (Light Curtain) Interference: Dust obstruction, misalignment, or interference from nearby variable frequency drives (VFDs) can cause intermittent signal loss in the light curtain. While single-stroke mode may tolerate brief signal loss, continuous mode will trigger an immediate stop.
Solution: Clean the light curtain lenses, recalibrate the transmitter and receiver ends, and ensure the shielding wire is properly grounded.
Guard Cover Travel Switch Not Engaged: Some press machines are equipped with detection switches on transmission guards. If the cover is not fully closed or the switch is displaced, continuous stroke is disabled.
2. Electrical Control Circuit and Component Failures
If the safety circuit is normal, the issue may lie in the electrical path controlling the continuous action.
Continuous Run Relay/Contactor Fault: The coil of the intermediate relay controlling the continuous stroke may be burnt out, or its contacts may be stuck or oxidized, preventing the signal from self-locking or transmitting.
Solution: Observe the PLC output indicator lights or relay actions; replace with a relay of the same model if necessary.
Loss of Top/Bottom Dead Center Signals: Continuous stroke relies on proximity switches or encoders on the camshaft to feedback the slider position. If the switch detecting the top dead center is loose, has excessive gap (standard gap approx. 2mm), or is damaged, the control system cannot determine the cycle start point and halts continuous action.
Solution: Adjust the distance between the proximity switch and the sensor iron (induction target) to ensure the indicator light activates at the correct position; replace immediately if damaged.
Poor Contact in Mode Selection Switch: Internal contact wear in the rotary switch may prevent the "Continuous" gear signal from being input to the PLC.
3. Clutch and Brake System Abnormalities
If the response speed of the mechanical execution mechanism cannot keep up with the rhythm of the continuous stroke, protective shutdowns will be triggered.
Insufficient Clutch/Brake Air Pressure: Continuous stamping requires rapid air filling and exhausting. If the air source pressure is below the set value (typically <0.45MPa), or the solenoid valve acts sluggishly, causing delayed clutch engagement, the system will judge it as a "double-drop" risk and stop.
Solution: Check the air path for leaks, adjust the pressure reducing valve to the specified pressure, and clean or replace the dual-series solenoid valve.
Brake Lining Wear or Improper Adjustment: Worn brake pads extend braking time, preventing the slider from stopping steadily at the predetermined position, which affects the phase judgment for the next continuous start.
Solution: Adjust the brake clearance according to the equipment manual; replace friction linings if wear is severe.
4. Operational Logic and Parameter Settings
Failure to Execute "Reset" Operation: Some CNC press machines require an "origin reset" or manual cranking to the top dead center after an alarm or emergency stop before continuous mode can be re-enabled.
PLC Parameter Lockout: Check the control panel parameters to confirm whether it has been mistakenly set to "Single Stroke Limit" mode, or if the continuous stroke cycle counter has reached its upper limit.