Diagnosing Random Machine Stops in Roll Forming Machines (Electrical Troubleshooting Guide)

Diagnosing Random Machine Stops

Systematic Electrical Troubleshooting in Roll Forming & Coil Processing Lines

Random machine stops are one of the most frustrating and costly issues in roll forming operations.

The machine:

• Runs normally for hours

• Suddenly stops

• Shows no clear fault

• Restarts and runs again

• Fails unpredictably

These intermittent stops often result in:

• Scrap material

• Shear mistiming

• Production delays

• Operator frustration

• Tooling damage

• Missed delivery schedules

In over 60% of cases, random stops are electrical in origin — even if they appear mechanical.

This guide provides a structured, engineering-based method to diagnose random machine stops in roll forming systems.

1) First Rule: Do Not Guess

Random stops must be approached methodically.

Never:

• Replace components blindly

• Assume operator error

• Ignore intermittent warnings

Instead, follow structured isolation.

2) Identify the Stop Type

Determine:

Did the machine stop due to:

• Safety circuit interruption?

• VFD trip?

• PLC fault?

• Power dip?

• Hydraulic pressure fault?

• Encoder loss?

Check:

• HMI alarm log
• PLC diagnostic buffer
• Drive fault history

Documentation is critical.

3) Check Emergency Stop Circuit Integrity

Random stops are often caused by:

• Loose E-Stop terminals

• Vibration in safety relays

• Intermittent guard switches

• Broken safety channel

Test:

• Safety relay input LEDs
• Dual-channel consistency
• Wire continuity under vibration

Safety circuits must be stable.

4) Loose Terminal Connections

High-vibration roll forming lines can loosen:

• PLC input terminals

• VFD input terminals

• Motor leads

• Control transformer wiring

Symptoms:

• Momentary voltage drop

• PLC reset

• Drive fault

• HMI blackout

Re-torque all terminals.

5) Power Quality & Voltage Drop

Measure supply voltage under load.

Check for:

• Voltage dips

• Phase imbalance

• Harmonic distortion

• Loose main disconnect

Voltage dips can cause:

• PLC reboot

• VFD undervoltage trip

• Servo fault

Install power quality logger if needed.

6) PLC Fault Buffer Analysis

Access PLC diagnostics.

Look for:

• I/O error

• Communication fault

• Input timeout

• Watchdog reset

• Memory error

Intermittent PLC resets often linked to unstable 24V supply.

7) 24VDC Control Power Stability

Measure:

• 24V supply under load
• Ripple voltage
• Voltage drop during shear cycle

If 24V drops below tolerance:

• Sensors may misfire
• PLC may reset
• Safety relay may drop

Replace unstable power supplies.

8) VFD Fault History

Access drive diagnostic history.

Look for:

• Overcurrent

• Undervoltage

• Overvoltage

• Ground fault

• Phase loss

• STO fault

If drive shows repeated undervoltage:

Investigate incoming supply stability.

9) Encoder Signal Noise

Flying shear systems depend on clean encoder pulses.

Symptoms of encoder noise:

• Length drift

• Shear misfire

• Random stop due to position error

Check:

• Shield grounding
• Cable routing
• Connector integrity
• Pulse stability

Use oscilloscope if necessary.

10) Sensor Noise & False Triggers

Proximity or photoelectric sensors can falsely trigger due to:

• EMI interference

• Poor shielding

• Damaged cable

• Metal debris

Monitor PLC input status while machine vibrates.

If input flickers:

Noise or loose wiring likely.

11) Hydraulic Pressure Drop

Random stops may be caused by:

• Pressure switch fluctuation

• Transducer scaling error

• Intermittent solenoid

Monitor pressure readings during production.

Pressure dips can trigger safety shutdown.

12) Overload Relay Intermittent Trip

Check motor overload settings.

Common issues:

• Overload set too low

• Thermal overload sensitive to ambient temperature

• Loose overload wiring

Overload trip may not always log clearly in PLC.

13) Thermal Issues Inside Cabinet

Overheating causes:

• PLC reset

• Drive thermal fault

• Power supply shutdown

Check:

• Cabinet temperature
• Cooling fan operation
• Air filter blockage

Random stops may occur only during hot periods.

14) Communication Faults

If system uses:

• Modbus

• Profinet

• EtherNet/IP

Check for:

• Network interruptions

• Loose Ethernet cables

• Ground loops

Communication loss may cause drive disable.

15) Grounding & Noise Problems

Poor grounding creates:

• Analog signal instability

• Random PLC input activation

• Encoder pulse noise

Verify:

• Single-point shield grounding
• Earth continuity
• Low ground resistance

Noise-related faults are often intermittent.

16) Control Logic Issues

Random stops may not be hardware related.

Review PLC program for:

• Timer misconfiguration

• Unexpected condition logic

• Fault latch without clear reset

• Incorrect interlocks

Software bugs can mimic hardware faults.

17) Environmental Causes

Check for:

• High humidity

• Condensation in panel

• Oil contamination

• Vibration loosening connectors

Environmental stress can create intermittent failures.

18) Data Logging Strategy

If issue persists:

Install temporary monitoring:

• Voltage logger

• Current logger

• PLC event logging

• Encoder pulse monitoring

Correlate stop event with data.

Intermittent faults require recorded evidence.

19) Most Common Root Causes

1. Loose terminals

2. Unstable 24V supply

3. Encoder noise

4. Phase imbalance

5. Intermittent safety input

6. Poor shielding

7. Hydraulic pressure fluctuation

8. Overheated control cabinet

Start with simplest possibilities.

20) Structured Troubleshooting Approach

• Step 1: Review alarm log
• Step 2: Check safety circuits
• Step 3: Verify supply voltage
• Step 4: Inspect 24V stability
• Step 5: Review VFD history
• Step 6: Monitor encoder signals
• Step 7: Inspect grounding
• Step 8: Check thermal conditions

Never troubleshoot randomly.

21) Buyer Strategy (30%)

If purchasing or operating a roll forming machine, ensure:

1. Alarm history logging enabled

2. PLC diagnostic access provided

3. VFD fault history accessible

4. Encoder shield properly installed

5. 24V power supply sized correctly

6. Installation torque verification documented

7. Commissioning report includes voltage measurements

8. Grounding scheme documented

Red flags:

• “No access to fault logs.”
• “No drive history available.”
• “No commissioning voltage data.”

Machines without documented commissioning are more prone to random stops.

6 Frequently Asked Questions

1) What is most common cause of random stops?

Loose terminals or unstable control voltage.

2) Can power dips cause machine reset?

Yes, especially PLC undervoltage events.

3) How do I check encoder noise?

Monitor input pulses or use oscilloscope.

4) Why does machine stop without alarm?

Safety relay may drop before PLC logs event.

5) Can overheating cause intermittent stops?

Yes, especially in enclosed panels.

6) Should I replace PLC immediately?

No, diagnose supply and wiring first.

Final Engineering Summary

Diagnosing random machine stops in roll forming systems requires systematic investigation of:

• Safety circuits

• Supply voltage stability

• 24V control power

• VFD fault history

• Encoder integrity

• Sensor wiring

• Hydraulic pressure

• Cabinet temperature

• Grounding and shielding

Intermittent faults are rarely mysterious — they are usually:

• Electrical instability

• Loose connections

• Power quality issues

• Noise interference

Disciplined data collection and structured troubleshooting prevent unnecessary part replacement and reduce costly downtime.

In high-speed roll forming operations, electrical stability is the foundation of uninterrupted production.