Essential knowledge of mechanical assembly* – to help you understand the methods of mechanical assembly

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http://p1.pstatp.com/large/dfic-imagehandler/c865d0ae-4670-43fa-a0b2-c90dc7ee423b http://p3.pstatp.com/large/dfic-imagehandler/3cf78a17-2a35-40a5-9b9e-918eeec6c42a (1) Project documentation: This includes the overall assembly diagram, component assembly diagrams, part drawings, material BOM lists, etc. Until the project is completed, it is essential to ensure that the drawings are complete and well-organized, as well as that all process-related information is properly recorded. (2) Work areas: The placement of parts and assembly of components must be carried out in designated work areas. The areas for placing and assembling the entire machine must be clearly planned. Throughout the entire project, all work areas must be kept neat, standardized, and orderly. (3) Assembly materials: Before starting the work, the assembly materials specified in the assembly process must be available on time. If some non-essential materials are not available, the order of operations can be adjusted, and a material delivery request form should then be filled out and submitted to the procurement department. (4) Before assembly, one should understand the structure of the equipment, the assembly techniques, and the process requirements. Basic specifications: (1) Mechanical assembly must be carried out strictly in accordance with the assembly drawings and process requirements provided by the Design Department. It is strictly prohibited to make any unauthorized modifications to the work content or to alter parts in any abnormal manner. (2) The parts used in assembly must be those that have passed the inspection by the quality control department; if any defective parts that were not detected are found during the assembly process, they must be reported promptly. (3) The assembly environment must be clean, free from dust or other contaminants; parts should be stored in a dry, dust-free area with protective padding. (4) During assembly, the parts must not be bumped or cut, their surfaces must not be damaged, and they must not bend, twist, or deform significantly; the mating surfaces of the parts must also remain undamaged. (5) For parts in relative motion, lubricant (grease) should be applied to the contact surfaces during assembly. (6) The fit dimensions of the mating parts must be accurate. (7) During assembly, parts and tools should have dedicated storage areas; in principle, they must not be placed on the machine or directly on the floor. If necessary, protective mats or carpets should be laid in those storage areas. (8) In principle, it is not allowed to step on the machinery during assembly; if stepping on it is necessary, protective pads or carpets must be placed on the machinery. Stepping on important components and areas with low non-metallic strength is strictly prohibited. Connection method (1) Bolt connection: http://p9.pstatp.com/large/pgc-image/ebd85077d4fb43b297346c0f9e25392a. A. When tightening bolts, adjustable wrenches must not be used; no more than one identical washer should be used under each nut. After tightening set screws, their heads should be buried within the component and not protrude outward. B. Under normal circumstances, threaded connections should be equipped with lock washers; when tightening multiple bolts symmetrically, it is necessary to do so in a sequential manner. For strip-type connectors, tightening should be carried out symmetrically from the center in both directions. C. After the bolt and nut are tightened, the bolt should protrude 1–2 pitches beyond the nut ； In situations where screws are used to fasten moving devices or when it is not necessary to remove components during maintenance, thread sealant should be applied to the screws before assembly. D. For fasteners with specified tightening torque requirements, a torque wrench should be used to tighten them to the prescribed torque. For bolts for which no tightening torque is specified, the tightening torque may be referred to the provisions in the \"Appendix\". (2) Sales link: http://p1.pstatp.com/large/pgc-image/0824ed7a7b5a4eacbf98838e55dca13c. A. The end face of the positioning pin should generally be slightly above the surface of the part; when a tapered pin with a threaded shank is inserted into the corresponding part, its larger end should sink into the hole. B. After the cotter pin is inserted into the relevant parts, its tail should be spread at an angle of 60°–90°. (3) Link to http://p9.pstatp.com/large/pgc-image/699d3d69cbbe409481328c72aad68a9b. A. The sides of the keyway for flat keys and fixed keys should make even contact, with no gaps between their mating surfaces. B. After the key (or spline) with a clearance fit is assembled, there should be no uneven tightness when the parts in relative motion move axially. C. After assembly, the contact area of the hook key and wedge key shall be no less than 70% of the working area, and the non-contacting areas shall not be concentrated in one place ； The length of the exposed portion should be 10%-15% of the length of the slope. (4) Riveting http://p9.pstatp.com/large/pgc-image/94c32c5020884523a9c3a2b6d84e7073 A. The materials and specifications for riveting must meet the design requirements; the processing of rivet holes should comply with relevant standards. B. During riveting, the surface of the parts being riveted must not be damaged, nor shall it be deformed. C. Unless otherwise specified, there should be no loosening after riveting. The head of the rivet must be in close contact with the parts being riveted, and it should be smooth and round. (5) Expansion sleeve connection: http://p9.pstatp.com/large/pgc-image/fcb3caf08c8448bebf3c02f88ddd9236. Expansion sleeve assembly: Apply lubricant to the expansion sleeve, insert it into the hub hole, fit it over the shaft, adjust its position, and then tighten the bolts. The tightening sequence is divided by the split; tighten them alternately in a symmetrical left-right pattern to ensure that the specified torque value is achieved. (6) Tightening connection: http://p1.pstatp.com/large/pgc-image/38125daed736459cb3f9f3bc3c995814. The tip and the hole of the cone-shaped tightening screw should both be at 90° angles; the screw should be tightened by aligning it with the hole. Assembly of rolling bearings http://p1.pstatp.com/large/pgc-image/c9698298f5214bdc8348bada6a54729e (1) Before assembling the bearing, there must be no dirt or contaminants at the bearing location. (2) When assembling the bearing, apply a layer of lubricating oil on the surfaces of the mating parts. The end of the bearing without a model number should face inward, i.e., toward the shaft shoulder. (3) Special pressing tools should be used when assembling bearings; it is strictly prohibited to use direct hammering. When fitting the bearings, the magnitude, direction, and position of the applied force must be appropriate – the protective cage or rolling elements should not be subjected to stress, and the force should be applied evenly and symmetrically to ensure that the end faces are perpendicular to the shaft. (4) The end face of the bearing inner ring should generally be in close contact with the shaft shoulder (shaft collar). After the bearing outer ring is assembled, the contact between the positioning-end bearing cover and the washer or outer ring should be uniform. (5) After the rolling bearings are installed, the rotation of the moving parts should be smooth and effortless; if any sticking occurs, the cause of the problem should be identified and appropriate action taken. (6) During bearing assembly, if it is found that the fit between the hole and the shaft is too loose, the tolerances should be checked ； When it is too tight, forced and rough assembly should not be carried out; instead, the cause of the problem should be identified and analyzed, and appropriate actions taken. (7) The axial clearance of single-row tapered roller bearings, thrust angular contact bearings, and bidirectional thrust ball bearings shall meet the requirements specified in the drawings and manufacturing procedures during assembly. (8) For bearings that use grease and the surfaces that come into contact with them, an appropriate amount of grease should be injected after assembly. For bearings operating at temperatures not exceeding 65°C, ZG-5 grease can be used in accordance with GB491-65 “Calcium-based Grease” ； For bearings operating at temperatures above 65°C, ZN-2 or ZN-3 greases can be used in accordance with GB492-77 \"Calcium-based Greases\". (9) For ordinary bearings, the temperature rise during normal operation should not exceed 35°C, and the maximum operating temperature should not exceed 70°C. Assembly of linear bearings (1) Before assembly, grease should be applied inside the bearing. (2) When pressing the bearing into the support seat, a dedicated installation tool should be used to apply pressure to the outer ring’s end face; it is not allowed to strike the bearing directly to avoid deformation. (3) The fit between the bearing and the support base must meet the tolerance requirements; an overly tight fit, which results in interference between the guide rail shaft and the bearing, can damage the bearing ； If it is too loose, the bearing will not be able to be fixed in the support seat. (4) When inserting the guide rail shaft into the bearing, it should be inserted gently while aligning it with the center; if inserted at an angle, the balls may fall out and the cage may deform. (5) When the bearing is installed in the support seat, it must not rotate; forcing it to rotate will damage the bearing. (6) It is not allowed to use set screws to directly secure it to the outer ring of the bearing, as this will cause deformation. Assembly of linear guides: http://p1.pstatp.com/large/pgc-image/b627b959df8d410ba6d1d289a3fd0f47 (1) The area where the guide is installed must be free of contaminants, and the flatness of the installation surface must meet the required standards. (2) When there is a reference edge on the side of the guide rail, it must be installed flush against this reference edge. In the absence of a reference edge, it is necessary to ensure that the sliding direction of the guide rail conforms to the design requirements. After tightening the guide rail fixing screws, check whether there is any deviation in the sliding direction of the slider; if so, adjustments must be made. (3) If the slider is driven by a conveyor belt, once the belt and the slider are properly tensioned, there should be no diagonal pulling force on the belt; otherwise, the pulleys must be adjusted so that the direction in which the belt drives the slider is parallel to the guide rails. Assembly of sprocket chains: http://p3.pstatp.com/large/pgc-image/14f728d7e2e44274b8bb3f406e0176e2 (1) The fit between the sprocket and the shaft must meet the design requirements. (2) The geometric center planes of the teeth of the driving sprocket and the driven sprocket should coincide, with any deviation not exceeding the design specifications. If not specified in the design, it should generally be less than or equal to 2‰ of the center distance between the two wheels. (3) When the chain engages with the sprocket, the working side must be tightened to ensure smooth engagement. (4) The sag of the non-working side of the chain shall meet the design requirements. If not specified in the design, it shall be adjusted by 1%–2% of the center distance between the two sprockets. Gear assembly: http://p9.pstatp.com/large/pgc-image/57f15e2631e64b809b77ac408e538397 (1) After the meshing gears are assembled, if the width of the gear rims is 20 mm or less, the axial displacement shall not exceed 1 mm ； When the gear flange width is greater than 20 mm, the axial misalignment shall not exceed 5% of the flange width. (2) The installation accuracy requirements for spur gears, bevel gears, and worm drives shall be determined according to the accuracy and size of the driving components, in accordance with JB179-83 \"Accuracy of Spur Gears with Involute Teeth\", JB180-60 \"Tolerances for Bevel Gear Drives\", and JB162-60 \"Tolerances for Worm Drives\" respectively. (3) The gear meshing surfaces must be properly lubricated in accordance with the technical requirements, and the gearbox must have lubricant filled to the specified level line as per these requirements. (4) The noise level of the gearbox when operating at full load shall not exceed 80 dB. Assembly of synchronous pulleys: http://p1.pstatp.com/large/pgc-image/e7b576a8cd0548b29a3659974cd7bbfe (1) The shafts of the driving and driven synchronous pulleys must be parallel to each other; there should be no skewing or wobbling, and the inclination error must not exceed 2‰. (2) When the widths of two pulleys are the same, their end faces should lie in the same plane; the axial misalignment between the two pulleys must not exceed 5% of the rim width. (3) When assembling the synchronous belt, do not force it into the pulleys; instead, assemble it by reducing the distance between the centers of the two pulleys, as otherwise the tensile layer of the synchronous belt may be damaged. (4) The synchronous belt tensioner should be installed with the loose side under tension, and two tightening bolts should be fixed. Assembly of flat belts: http://p1.pstatp.com/large/pgc-image/613819517d894c0fb722b54a26ca5cf9 (1) Before installation, all conveying surfaces must be adjusted to be level. (2) The lines connecting the centers of the pulleys should be adjusted to lie on the same vertical plane, with their axes being parallel to each other. (3) The conveying direction of the flat belt should be set in accordance with the arrow indicated on the belt; otherwise, its service life will be affected. Assembly of motors and reducers: http://p1.pstatp.com/large/pgc-image/5d7643740727487fbcfcf8e3f0402254 (1) Check whether the motor model is correct and whether the reducer model is correct. (2) Before assembly, clean the connection part between the motor shaft and the reducer thoroughly. (3) Before tightening the motor flange screws, rotate the motor to correct the concentricity between the motor shaft and the reducer coupling, then connect the motor flange to the reducer and tighten the fixing bolts diagonally. (4) During the assembly of the servo motor, it is necessary to ensure that the encoder located at the back of the motor is not subjected to any external forces; hitting the shaft of the servo motor is strictly prohibited. (5) Installation of the servo reducer: A. Move the sealing screws on the outside of the reducer flange to facilitate adjusting the clamping screws. B. Unscrew the clamping screws, connect the motor flange to the reducer, and tighten the positioning bolts diagonally. C. Tighten the clamping ring with the appropriate torque, then tighten the sealing screw. D. Loosen the motor flange bolts, jog the servo motor shaft or manually rotate the motor shaft a few times to correct the concentricity between the motor shaft and the reducer coupling. E. Finally, connect the motor flange to the reducer and tighten the positioning bolts diagonally. Adjustment and connection of the frames (1): The heights of frames in different sections should be adjusted to the same level, using the same reference point. (2) The wall panels of all racks should be adjusted to the same vertical plane. (3) After each section of the frame has been adjusted into place and meets the requirements, the fixing connecting plates between them should be installed. Assembly of pneumatic components: http://p3.pstatp.com/large/pgc-image/5da4a2613cb0430e9059ef458cf1d185 (1) The configuration of each set of pneumatic drive units must be connected in strict accordance with the circuit diagrams provided by the design department; it is essential to verify that valve bodies, pipe fittings, cylinders, etc. are connected correctly. (2) The main intake pressure relief valve should have its inlet and outlet connected in the direction indicated by the arrows; the water tank and oil tank of the air filter and oil mister must be installed vertically downward. (3) The pipes should be thoroughly blown out of any cutting debris and dust before piping. (4) The pipe fittings are screwed together; if the pipe threads do not have thread sealant, Teflon tape should be wrapped around them. When wrapping it, look from the front side and wind it in a clockwise direction. The Teflon tape must not be allowed to enter inside the valve, and one thread should be left uncovered when wrapping the tape. (5) The arrangement of the air pipes should be neat and aesthetically pleasing; try to avoid crossing them. 90° elbows should be used at turns, and when fixing the air pipes, ensure that the joints are not subjected to additional stress, as this can cause leaks. (6) When connecting the solenoid valve, pay attention to the function of the numbers on each air port of the valve: P: main air inlet ； A: Exhaust 1 ； B: Exhale 2 ； R (EA): Exhaust corresponding to A ； S(EB): Exhaust corresponding to B. (7) During cylinder assembly, the axis of the piston rod should be aligned with the direction of load movement. (8) When using linear bearings for guidance, after the front end of the cylinder piston rod is connected to the load, there must be no any binding forces throughout the entire stroke; otherwise, the cylinder will be damaged. (9) When using a throttle valve, attention should be paid to its type. Generally, it is distinguished by the large arrow marked on the valve body; if the large arrow points toward the threaded end, it is intended for use with a cylinder ； The large arrow pointing toward the pipe end indicates use for a solenoid valve. Assembly inspection work: (1) After each component is assembled, it must be inspected according to the following items. Should any assembly issues be detected, they should be analyzed and addressed promptly. A. Completeness of the assembly work: verify the assembly drawings and check for any missing parts. B. The accuracy of the installation positions of each component should be checked by referring to the assembly drawings or the requirements specified in the above standards. C. The reliability of each connection part, whether the fastening screws meet the required torque for assembly, and whether special fasteners fulfill the requirements to prevent loosening. D. The flexibility of movement of the moving parts: when manual rotation or movement occurs, such as with conveyor rollers, pulleys, guide rails, etc., check for any sticking or jamming, as well as any signs of eccentricity or bending. (2) After final assembly, the main task is to check the connections between various assembled components, with the \"four properties\" specified in (1) serving as the criteria for evaluation. (3) After final assembly, remove iron shavings, debris, dust, etc. from all parts of the machine to ensure that there are no obstacles in the transmission components. (4) During testing, carefully monitor the startup process; once the machine starts, immediately check whether the main operating parameters and moving parts are functioning properly. (5) The main operating parameters include the speed of movement, the stability of movement, the rotation of each drive shaft, temperature, vibration, and noise.