Fanuc Roboshot SV0436: Servo Motor Overload — Injection Axis Diagnostics

Fanuc Roboshot Alarm SV0436 is a soft thermal overload (software thermal — the servo amplifier calculates motor winding temperature from current history, not from a physical thermal switch). It triggers when the calculated temperature of the...

Fanuc Roboshot Alarm SV0436 is a soft thermal overload (software thermal — the servo amplifier calculates motor winding temperature from current history, not from a physical thermal switch). It triggers when the calculated temperature of the injection axis servo motor windings exceeds the Class F insulation rating (155°C at the windings — the software trips at a calculated ~140°C to provide a 15°C safety margin). SV0436 means the injection axis has been operating at high torque for an extended period — it is an RMS (root-mean-square) current overload, not an instantaneous overcurrent trip (which would produce a different alarm — SV0434, instantaneous overcurrent).

Diagnosis

On the Fanuc Panel i HMI, navigate to the Servo Monitoring screen for the injection axis. Record: (1) Peak torque during injection (% of rated); (2) RMS torque over the full cycle (% of rated — motor RMS rating is typically 70-80% of peak rating for continuous duty); (3) Motor calculated temperature (°C). The overload condition clears automatically when the calculated temperature drops below the reset threshold (typically 120°C), which takes 5-15 minutes of idle time depending on ambient temperature and the motor's thermal time constant.

Root Causes: (1) Excessive backpressure for extended screw-recovery time: High backpressure during screw recovery increases the screw motor torque — but on all-electric machines, the screw rotation and injection axes are sometimes the same servo motor (switched by a mechanical clutch or driven through a gearbox with a mode-select coupling). If the motor is continuously loaded during both injection (high torque, short duration) and recovery (moderate torque, long duration), the RMS current rises above the continuous rating. Reduce backpressure or increase screw-recovery RPM (reducing the duration of moderate-torque loading) to bring RMS current within limits. (2) Processing high-viscosity material: High-temperature engineering polymers (PEEK, PPS, LCP) and highly filled compounds (40-60% glass or mineral filled) require significantly higher injection pressures and longer screw-recovery times than general-purpose resins. The injection axis servo motor specified for the machine may be sized for general-purpose processing — consult the machine builder or Fanuc for the motor's RMS torque capability and whether a higher-torque motor option is available. (3) Mechanical drag in the injection unit: Worn linear bearings on the injection sled, binding of the screw shank in the thrust bearing, or inadequate lubrication of the injection unit slides increase the mechanical load the servo motor must overcome before any polymer-related load. Measure injection-axis motor current during a DRY CYCLE (no polymer in the barrel, injection unit retracted from the mold — motor is moving only its own inertia and mechanical friction) and compare to the baseline recorded at machine commissioning. An increase of >20% from baseline indicates mechanical drag requiring maintenance.

Alarm Details

Troubleshooting Protocol

Equivalents & Cross-References

Related Diagnostics & Materials

References & Industry Standards

• ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
• UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
• MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
• ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org