As a tool that relies on mechanical structure to achieve high-precision positioning and clamping, the maintenance of non-powered precision fixture is directly related to the accuracy and reliability in long-term use.
Cleaning the surface and positioning components of non-powered precision fixture is the basis of maintenance. Metal debris, cutting fluid residue, oil stains and other pollutants generated during the processing may be embedded in the guide groove, positioning hole or contact surface of the fixture, causing slight displacement of the workpiece during clamping and destroying the original precision. For example, in the scene of optical component grinding and polishing, if micron-level glass debris remains on the positioning surface of the fixture, the component clamping angle may deviate by 0.1°, which will eventually affect the optical performance. For daily cleaning, use a soft brush or compressed air to remove visible impurities. For stubborn stains (such as dried cutting fluid), wipe with anhydrous ethanol or special detergent and fine fiber cloth to avoid scratching the surface with hard tools such as metal scrapers. After cleaning, check whether there are scratches or wear marks on the positioning surface in time, and polish it if necessary to ensure that the contact surface roughness is maintained below Ra0.8.
The moving parts of non-powered fixtures (such as hinges, guides, threaded pairs, etc.) rely on reasonable lubrication to reduce wear. If the lubrication is insufficient, the sliding guide may creep due to increased friction resistance, resulting in reduced positioning accuracy during clamping; dry grinding of the hinge part will accelerate the expansion of the gap between the pin and the bushing, causing position deviation when the fixture is opened and closed. The appropriate lubricant should be selected according to the type of component: for precision guides, low-viscosity precision machine oil (such as ISO VG 32) should be used, and micro-lubrication should be used to avoid oil diffusion; threaded pairs can be coated with molybdenum disulfide grease, which has both lubrication and anti-loosening effects; moving parts made of plastic or ceramic materials need to use silicone-based grease with good compatibility to prevent chemical corrosion. The lubrication cycle needs to be formulated in combination with the frequency of use. For example, the guide rails should be drip-lubricated before starting the machine every day, and the hinge parts should be fully cleaned and re-greased every two weeks to ensure that the moving pair is always in a low-resistance state.
The accuracy of non-powered precision fixtures will drift due to long-term use, temperature changes or accidental collisions. Regular calibration is the key to maintaining high accuracy. Calibration requires the use of high-precision measuring tools (such as three-dimensional coordinate measuring machines and laser interferometers) to detect key parameters such as the flatness of the positioning surface, the spacing between positioning holes, and the verticality of the fixture. For example, in semiconductor packaging fixtures, the width tolerance of the positioning groove must be controlled within ±5μm. If the detection is found to be out of tolerance, it is necessary to repair or replace the worn parts through grinding, electroplating. For adjustable fixtures (such as positioning blocks with fine-tuning screws), compensation can be made through the fine-tuning mechanism during the calibration process. After adjustment, repeatability tests are required to ensure that the error of clamping 5 times in the same position does not exceed ±2μm. The calibration cycle is recommended to be once a quarter. For fixtures used under high load (such as working more than 12 hours a day), it can be shortened to once a month.
Different types of unpowered fixtures have different vulnerable parts and need to be inspected in a targeted manner. For spring fixtures that rely on elastic deformation to clamp, it is necessary to focus on checking the elastic attenuation of the spring. If it is found that the free length of the spring is shortened by more than 5% or rust appears on the surface, it should be replaced immediately to avoid loosening of the workpiece due to insufficient clamping force. For chuck-type fixtures, the wear of the jaws is the main problem. The degree of wear can be determined by measuring the roundness error of the inner hole of the jaws (the allowable value is ≤3μm). If the wear is serious, the jaws need to be repaired or replaced with new jaws. For fixtures that use conical positioning, the contact area of the conical surface needs to be checked (should be ≥85%). If there is eccentric wear in the contact area, it needs to be repaired by matching or grinding to ensure that the coaxiality error during positioning is less than 5μm. In addition, the fasteners of the fixture (such as bolts and nuts) need to be checked regularly for tightness, and tightened with a torque wrench according to the specified torque (such as M3 bolt torque 1.5N·m) to prevent loosening due to vibration.
The precision stability of the fixture is closely related to the use environment. Temperature fluctuations can cause the fixture material to expand and contract. For example, when the temperature of a steel fixture changes by 10°C, a dimensional change of 1.1μm may occur in the 100mm length direction, affecting precision positioning. Therefore, the storage and use environment of the fixture should maintain a constant temperature (20±2℃) and be away from heat sources (such as machine tool spindles, heating equipment). Humidity control is also important. High humidity environments can easily cause metal fixtures to rust. Desiccant or moisture-proof cabinets can be placed in the storage area to control the relative humidity at 45%-60%. For fixtures made of optical glass or ceramic materials, it is also necessary to avoid material aging caused by direct exposure to strong light, and they should be covered with a light shield during storage. In addition, the fixture should avoid contact with corrosive gases (such as volatiles of acidic cutting fluids), and the working area should be well ventilated to reduce the risk of chemical corrosion.
Correct operating habits are the basis for extending the life of the fixture. When clamping the workpiece, avoid rough operation (such as hitting the fixture hard) to prevent dents or deformation on the positioning surface; for high-precision fixtures (such as micron-level positioning fixtures), cotton gloves should be worn to avoid grease on the hands from contaminating the positioning surface. When disassembling the workpiece, the clamping mechanism should be loosened first and then removed smoothly. It is forbidden to forcefully pull the fixture to cause excessive deformation of the elastic parts. When switching production of multiple varieties, special tools should be used to replace the fixture, and the fixture should be handled with care to avoid collision with the key positioning parts of the fixture. For adjustable fixtures with scales or rulers, the current parameters need to be recorded during operation so that they can be restored to their original position later to reduce repeated calibration time. At the same time, a fixture usage ledger should be established to record the time of each use, the type of workpiece processed, and abnormal conditions, so as to facilitate the traceability of maintenance needs.
The fixture may be suddenly damaged during use due to workpiece falling, equipment failure, etc., and emergency treatment is required in time. If a collision causes local defects on the positioning surface, it should be stopped immediately and the degree of damage should be assessed: for small dents (depth <5μm), diamond grinding paste can be used for manual grinding and repair; if the damage is serious (such as cracks or large-area wear), it needs to be returned to the original factory for professional repair or replacement. For replaceable parts such as spring breakage and screw slippage, common spare parts need to be stored for quick replacement. The repaired fixture must be re-calibrated for accuracy and can only be put into use after confirmation of qualification. In addition, regular fixture operation training is conducted to enable operators to master basic damage identification and emergency treatment methods, which can reduce the spread of precision degradation caused by untimely treatment.
The maintenance of non-powered precision fixture is a systematic work, which requires the construction of a full-process control system from multiple dimensions such as cleaning, lubrication, calibration, inspection, environment, operation and emergency. By establishing a standardized maintenance manual, using a digital management system (such as scanning codes to record maintenance information), and combining preventive maintenance technology (such as vibration monitoring to predict component wear), the long-term maintenance of fixture accuracy can be achieved. At the same time, with the development of new materials (such as ceramic-based composites),
