1. Common Faults and Causes in Machine Tool Electrical Control Circuits
Serious faults in machine tool electrical control circuits can force the machine tool to stop operating, causing significant economic losses to the enterprise. Faults in machine tool electrical control circuits are generally caused by faults in the electrical components themselves, power supply failures, or other faults that hinder the operation of the control circuit. Motors are a frequent source of faults in machine tool electrical control circuits. Common symptoms of motor failure include difficulty starting, difficulty operating normally after starting, abnormal noise during operation, rapid temperature rise, and excessively high temperature. Severe damage to relays or contacts can prevent the motor from starting normally. Furthermore, closed contact points in the machine tool electrical control circuit can prevent the motor from operating continuously. Severe welding problems at the main contacts of the contactor can cause the motor to stop operating. Abnormal noise during motor operation is often caused by phase loss or poor contact at connection points. Rapid motor temperature rise and high temperature are mainly caused by motor overload, poor ventilation, and inadequate heat dissipation. Electrical control circuit faults have a certain overall and hierarchical nature, typically including the following three aspects:
1.1 Short circuit fault
Short circuit faults are one of the more common forms of faults in electrical control circuits. A short circuit fault occurs when points at different locations are directly connected by a conductor, causing the entire electrical control circuit to malfunction and become unusable. Short circuit faults in electrical control circuits are likely to occur due to a variety of factors, such as: operators not strictly following relevant technical specifications when operating machine tools, leading to operational errors and causing short circuit faults; deficiencies in the maintenance of electrical control circuits, such as the lack of regular and reasonable maintenance and upkeep; and substandard quality and performance of the electrical control lines. 1.2 Open Circuit Faults
Open circuit faults are also a significant manifestation of electrical control circuit failures. If an open circuit fault occurs in an electrical control circuit, it can severely impede current flow, causing a power outage in the entire electrical control circuit and forcing all electrical equipment on the machine tool to stop operating. Most of these open circuit faults are caused by neglect of machine tool maintenance, leading to corrosion of wires operating in harsh environments. If these wires are not replaced or maintained for extended periods, they may break during long-term use, resulting in an open circuit fault. In addition, due to the actual operation of the machine tool...
The machine tool will generate a certain degree of vibration during operation, which may cause the wire connection points in the machine tool circuit to become loose or fall off, thus causing an open circuit fault.
1.3 Grounding fault
Most grounding faults in machine tool electrical control circuits are usually caused by contact problems between the ground and the electrical control circuits. Grounding faults in electrical control circuits can be classified as single-phase, two-phase, and three-phase grounding faults, with single-phase grounding faults being the most common. Prolonged operation of the machine tool and lack of regular maintenance are the main causes of single-phase grounding faults. Damage to the grounding wire insulation layer significantly reduces its insulation performance, leading to contact between the grounding wire and other grounded components, resulting in a grounding fault. If a two-phase grounding fault occurs, the operating voltage may drop sharply during normal operation, potentially causing equipment malfunction.
2. Troubleshooting and Prevention Measures for Common Faults in Machine Tool Electrical Control Circuits
2.1 Preparatory work before troubleshooting
To ensure the smooth and stable progress of troubleshooting, thorough preparation is essential when troubleshooting machine tool electrical control circuits. During the control circuit troubleshooting phase, maintenance personnel must comprehensively collect and organize all relevant machine tool information, be familiar with the machine tool's actual operating conditions, and prepare all necessary tools, especially circuit testing tools such as ammeters, ohmmeters, and voltmeters.
2.2 Fault Investigation and Analysis
During the preparation phase for control circuit fault detection, maintenance personnel also need to conduct thorough investigations, deeply observe and study the faults occurring in the machine tool, and carefully examine its appearance to gain a comprehensive understanding of the machine tool's actual operating status. When investigating faults, methods such as "asking, looking, listening, touching, and smelling" can be used. "Asking" refers to maintenance personnel consulting with operators about the operating status of the machine tool's electrical control circuits before the fault occurred, whether there were any abnormal operating states or phenomena, whether excessive cutting forces were used, whether the machine tool was started and stopped too frequently, and whether there were any modifications to the electrical control circuits. "Looking" refers to a thorough and comprehensive observation of the fuse in the fuse device. First, observe whether the fuse has melted, whether there is any welding on the contacts, whether the connection resistance has changed significantly, and whether the wire color has changed significantly. Second, observe whether any parts in the electrical device have fallen off or become loose, whether the coil has burned out, and check whether the relay device and circuit breaker device have tripped. Finally, check whether there is any phase loss in the power supply. Listening is a fault detection method that should only be used when the electrical control circuit is functioning properly and will not cause further damage to the equipment or exacerbate the problem. It primarily involves listening for abnormal noises from various components during operation to roughly determine the type of fault. Touching is mainly done after the machine tool has been running for a period of time, checking for significant temperature increases by touch. Smelling is also helpful, as vibrations during machine operation can cause intense friction, producing unusual odors. Damaged insulation in the control circuit may also produce a burnt smell, which can help in the initial identification of the fault.
2.3 Inspection and Measurement
Electrical control circuit fault inspection and measurement mainly includes two methods: voltage measurement and electronic measurement. First, voltage measurement involves using a multimeter to detect the voltage at specific locations in the electrical control circuit under the condition that the circuit is connected, based on the actual fault in the machine tool. This allows for the assessment of the health status of a particular section or segment of the circuit and is commonly used in the troubleshooting process. When using voltage measurement, it is crucial to protect the multimeter; the range should be scientifically and reasonably selected according to the measured voltage range, and the measured voltage value must never exceed the range. Step-by-step voltage measurement is often used in the process of diagnosing faulty components; by measuring different components step-by-step, the faulty component can be easily identified. Second, resistance measurement typically uses relevant measuring instruments to detect the continuity and disconnection of components in the electrical control circuit, diagnosing and locating the fault. When using this method, the power supply must be disconnected.
3. Conclusion
Common problems in machine tool electrical control circuits mainly include short circuit faults, open circuit faults, and grounding faults. When detecting faults in electrical control circuits, thorough preparation, investigation, and analysis are essential. Scientific and reasonable inspection and measurement methods should be employed, and regular comprehensive inspections and maintenance of the machine tool's electrical control circuits can significantly reduce the probability of fault occurrence. In actual teaching and internships, students must be strictly required to operate according to specifications so that they can quickly analyze and determine the causes of faults in later work, thereby enabling timely repairs.
