Sumitomo all-electric injection molding machines have always enjoyed a strong reputation in industry, mainly due to their high precision and stable operation. Their most outstanding core features are their self-developed servo motors and intelligent servo control systems. Unlike traditional hydraulic injection molding machines, which are more commonly seen, problems with all-electric machines are primarily concentrated in servo drive system, ball screw transmission structure, and signal feedback from various precision sensors. They generally fall within these areas, and experienced repairers are quite familiar with them.

 

It's important to understand that all actions in Sumitomo all-electric machines, from injection and mold closing to ejection and material storage, are driven entirely by servo motors. Therefore, servo alarms are consistently among the most troublesome and difficult types of faults to diagnose during machine repair.
1.1 Servo Overload
Commonly observed symptoms are: machine's computer screen displays a "motor overload" message, or it displays a fixed servo alarm code, such as common 001 or 002 codes, which are almost always related to overload. A simple breakdown of technical causes: 
First, mechanical resistance is abnormal. Often, this is due to poor maintenance of ball screw, inadequate lubrication, dryness, or foreign objects causing blockage. Sumitomo machines are particularly sensitive to ball screw loads; even slight abnormal resistance can easily trigger an overload. Second, process parameters are set too extreme. For example, if injection speed is too fast, holding pressure is pushed directly to machine's upper limit, holding time is too long. Over time, motor cannot dissipate heat, which accumulates and naturally triggers an overload alarm. Another easily overlooked point is that brake is not fully released. If electromagnetic brakes on mold closing shaft or ejector shaft malfunction and jam, motor will essentially be running with brakes on, inevitably leading to overload.
When troubleshooting, we just need to follow these steps: First, disassemble and inspect components. Disconnect motor from subsequent mechanical transmission and let motor run idle on its own. If motor runs normally after disassembly, problem is definitely in lead screw or guide rails—mechanical transmission parts. Then carefully check lubrication. Check if automatic lubrication pump pressure is sufficient. Take a close look at lead screw surface for obvious wear or black powder shedding. These signs usually indicate a lubrication problem. Finally, use a multimeter to test electrical components. Check for uneven three-phase power output from servo drive to identify any circuit-related causes.
1.2 Encoder Communication Failure
Sumitomo original equipment comes with high-resolution absolute encoders. To put it simply, most of these faults are caused by electromagnetic interference, or by physical damage or poor contact at wiring connectors.
Actual troubleshooting is simple: First, check shielding of encoder connection cable. Make sure grounding at driver end is secure. If shielding is not done properly, external interference can easily enter and disrupt signal. Next, plug area is prone to grease buildup over time. Excessive grease can cause signal pulse loss. Cleaning inside of plug with a specialized precision electronic cleaner can resolve most minor communication problems.

Anyone who has used Sumitomo machines knows that their unique pressure control technology relies heavily on real-time signal feedback from pressure sensor. Even a slight inaccuracy in sensor can disrupt the entire process.
2.1 Pressure Sensor Deviation
Visually observable problems include: chaotic injection pressure waveforms, misaligned pressure holding switching points, and inconsistent product weight with significant fluctuations.
Root causes are twofold: First, weighing sensor has aged. Injection pressure of the entire motor relies on this sensor at rear of lead screw for detection. Over time, it endures high-pressure impacts, inevitably leading to zero-point drift and inaccurate data. Secondly, signal interference is a possibility. Sensor outputs a weak, millivolt-level signal, which is easily interfered with and deviates from its intended path when a high-power servo power cable is nearby.
On-site troubleshooting: First, perform a static zero-point check. Retract test stage to its final position, completely depressurized, check if pressure displayed on computer screen returns to zero. If it doesn't, zero point is drifting. Next, manually and slowly increase pressure, observing pressure rise curve. Observe smoothness of curve; fluctuating pressure indicates a problem with sensor's linearity. Finally, check physical installation. Inspect sensor's mounting bolts for looseness, ensure even stress distribution. Misalignment or looseness will affect detection accuracy.
2.2 Daily Assessment of Check Ring Wear
Sumitomo system has a built-in internal pressure monitoring function, which is quite useful. If check ring seal is not tight, screw will slowly retract during pressure holding phase due to molten material flowing back.
Here's a practical tip for troubleshooting: Directly open monitoring curves built into Sumitomo machine and compare them side-by-side to check position of screw at the end of pressure holding stage in continuous production of twenty molds. If position fluctuation exceeds 0.05 mm, it's almost certainly a sign that check ring is worn out, or there's unmelted cold material blocking barrel.

3.1 Abnormal Noise and High Temperature from Ball Screw
The most obvious symptom is a muffled metallic friction sound coming from screw when machine starts running. Touching screw seat housing, temperature exceeds 60 degrees Celsius, which is obviously abnormally hot.
Remember these key points for troubleshooting: Sumitomo machines are very strict about type of grease used. Original manufacturer usually specifies a special grease or a special lithium-based grease. Never mix in other types of grease. Improper mixing can easily lead to gumming and buildup, clogging the entire oil passage. Another issue is parallelism and levelness of template guide rails. If guide rails sag or deform, lead screw will experience additional radial force, increasing load and directly shortening its lifespan.
3.2 Wear and Aging of Elbow Mechanism
Most of these issues stem from improper mold adjustment or excessively high clamping force over time. Over time, copper bushing outside elbow pin wears thin and breaks. Identifying this is simple: monitor extension value at the moment mold clamping ends. If clamping pressure has reached set standard, but elbow is not fully extended and closed, resulting in excessive clearance, final product will inevitably have burrs and flash.

 

Sumitomo's all-motor system uses a high-speed bus communication line. Stability of the entire electrical control circuit directly determines machine's response speed and its ability to operate normally.
4.1 Unstable and Fluctuating Control Power Supply Voltage
A common occurrence is machine restarting unexpectedly during production or displaying a communication error message. In short, current fluctuation is extremely large during instantaneous start-up and shutdown of entire motor. External factory power grid voltage is inherently unstable, coupled with aging and deterioration of 24V switching power supply inside machine, motherboard's core processing program is prone to malfunction, leading to errors and system crashes.
It is highly recommended to equip each Sumitomo motor with a dedicated voltage regulator; don't skimp on this small expense. Additionally, regularly check if cooling fan inside electrical box is spinning. Dust clogging fan will hinder heat dissipation, causing motherboard module temperature to rise, resulting in frequency throttling, or even a complete black screen and system crash.
4.2 Troubleshooting Input/Output Modules and Solenoid Valves
Troubleshooting process is simple, just follow these three steps:
Open machine's built-in input/output diagnostic interface to check status; Switch to manual mode and trigger signals one by one, checking if corresponding indicator lights up. If they are lit, signal is normal; if not, wiring or module is faulty; Especially for molds with pneumatic core-pulling structures, pay special attention to checking DC 24V solenoid valve coil, as it is easily broken down by reverse induced electromotive force, directly burning out output points.

5.1 Intelligent Servo Control Alarm
The entire servo control logic is core brain of Sumitomo's servo motor operation management. If a parameter error occurs, it's highly likely that motherboard's backup battery is dead, and encoder's original absolute position has been lost.
Solution is fixed: replace backup battery with a new one, then repeat origin reset calibration procedure.
5.2 Low-Voltage Mold Protection Alarm Due to Excessive Sensitivity
Motor's torque detection is extremely precise, sensing even slight changes in resistance. Frequent mold protection alarms, besides checking for foreign objects inside mold, should be investigated in two areas: First, inadequate lubrication of mold guide pillars and bushings, leading to increased friction and jamming; Second, adjusting torque monitoring limit according to production time. As mold temperature rises, frictional resistance changes; fine-tuning monitoring window range can reduce false alarms.

To minimize malfunctions and downtime, routine maintenance must be performed according to fixed standards, not haphazardly. Below are some quantified maintenance items:

Repairing all-electric machines like Sumitomo's requires a shift away from old methods used for hydraulic presses. Simply staring at pressure gauge readings is no longer effective. Core approach to repairing all-electric machines must be to monitor motor current and operating waveform. Make good use of machine's built-in monitoring curves. Sumitomo's original system can completely record all data on torque, position, speed, and pressure for each mold. Compare standard curves during normal production with those during malfunctions; in over 90% of cases, root cause of fault can be pinpointed at a glance. Pay close attention to these invisible micro-frictional resistances. While hydraulic presses can overcome greater resistance, all-electric machine protection programs are highly sensitive; even the slightest resistance will trigger a shutdown and alarm. Therefore, routine lubrication and precision fine-tuning of mechanical parts are the key to ensuring longevity and minimal problems of all-electric injection molding machine. Furthermore, maintaining cleanliness of electrical components inside control box is crucial. Avoid piling up miscellaneous items and waste materials; keep circuit boards clean to prevent metal dust from causing short circuits and damaging boards.

 

By diligently following this troubleshooting and routine maintenance process, Sumitomo all-electric injection molding machines can easily last for fifteen years or more without any issues. Thoroughly understanding and mastering the entire servo control logic is a truly valuable skill, whether you're a senior process engineer or a seasoned equipment repair technician.