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What should a mechanical design engineer know?

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Update time : 2021-09-06 21:54:25
Standard requirements:
1. The part removes oxidation skin.
2. The part processes surface, it should be no scratches, scrapes, and other defects that damage the part's surface.
3. Remove burrs and edge fin.

Heat treatment requirements:
1. Tempered, HRC50~55.
2. The parts are high frequency quenched and tempered at 350-370℃, HRC40~45.
3. Carburized to a depth of 0.3mm.
4. High-temperature aging treatment
Tolerance requirements:
1. Not annotated shape tolerance should be machined in compliance with the requirements of GB1184-80.
2. Not annotated length of the permitted size deviation is ± 0.5 mm.
3. The casting tolerance zone is symmetrical to the basic size configuration of the roughcasting.

Part's edges:
1. Not annotated radius of the round corner is R5.
2. Not annotated chamfers are all 2×45°.
3. Round off sharp edges/sharp corners/sharp angles.

Assembly requirements:
1. Each seal must be soaked with oil before assembly.
2. Assembly of rolling bearings allows to use of oil heating for hot assembly, the temperature of the oil shall not exceed 100 ℃.
3. Gear assembly, tooth contact spots, and side gaps should comply with the specifications of GB10095 and GB11365.
4. Assembly of the hydraulic system allows the use of sealing filler or sealant but should be prevented from entering the system.
5. The parts and components (including outsourced parts, outsourcing parts) wait to be assembled, must have the inspection department's certificate of compliance before assembly.
6. Parts must be cleaned before assembly, there should be no burrs, edge fin, oxide, rust, chips, oil, coloring agents and dust, etc.
7. Parts should be assembled before the main fit size, especially the interference with the size and accuracy of the relevant review.
8. Assembly process parts are not allowed to bump, touch, scratch, and rust.
9. Screws, bolts, and nuts tightening, it is strictly prohibited to strike or use unsuitable spinning tools. Screw slot, nut, and screw, bolt head must not be damaged after tightening.
10. Fasteners with tightening torque requirements must be tightened with a torque tool and fastened according to the specified tightening torque.
11. When the same part is fastened with more than one screw (bolt), each screw (bolt) should be crossed, symmetrical, gradually, and evenly tightened.
12. Tapered pin assembly should be checked with the hole should be painted, the contact rate should not be less than 60% of the mating length, and should be uniformly distributed.
13. Flat key and shaft keyway on both sides of the surface should be evenly contacted, and its mating surface shall not have a gap.
14. Spline assembly while contacting the number of teeth surfaces not less than 2/3, the contact rate in the length and height direction of the key teeth shall not be less than 50%.
15. Sliding with the flat key (or spline) assembly, the phase fittings move freely, there shall be no uneven tightness.
16. The excess adhesive should be removed after bonding.
17. The outer ring of the bearing and the open bearing seat and the semi-circular hole of the bearing cover are not allowed to have the phenomenon of jamming.
18. The outer ring of the bearing should be in good contact with the semi-circular hole of the open bearing housing and the bearing cover and should be in uniform contact with the bearing housing at 120° symmetrical to the center line and with the bearing cover at 90° symmetrical to the centerline when checked by coloring. In the above-mentioned range, when checked with a stopper, a stopper of 0.03mm shall not be inserted into 1/3 of the outer ring width.
19. The outer ring of the bearing should have uniform contact with the end face of the bearing cover at the positioning end after assembly.
20. The rolling bearing should be flexible and smooth after assembled and rotated by hand.
21. The combined surface of the upper and lower shaft tile should be closely fitted, and not into with a 0.05mm plug gauge check.
22. When fixing the shaft tile with locating pin, should ensure the tile mouth surface and end surface and the relevant bearing hole open and closed surface and end bread hold flush state drilling and reaming, with the pin. The pin should not be loosened after it is inserted.
23. Spherical bearing body and bearing seat should be uniform contact, using the coloring method to check, its contact should not be less than 70%.
24. Alloy bearing lining surface into yellow is not allowed to use, in the specified contact angle is not allowed to have the phenomenon of leaving the nucleus, in the contact angle outside the area of the nucleus shall not be greater than 10% of the total area of the non-contact area.
25. The reference end face of gear (worm wheel) and shaft shoulder (or positioning sleeve end face) should fit together and be inspected with a 0.05mm stopper. And should ensure the perpendicularity requirement of gear benchmark end face and axis.
26. The combination surface of the gearbox and cover should be in good contact.
27. Strictly check and remove the sharp corners, burrs and foreign matter left when the parts are processed before assembly. Ensure that the seal is not scratched when it is installed.

Casting requirements:
1. Cold partition, cracks, shrinkage and penetrating defects, and serious defective class defects (such as under-casting, mechanical damage, etc.) are not allowed on the surface of the casting.
2. Castings should be cleaned up, no burrs, edge fin, the non-machined surface of the sprue should be cleaned up and the casting surface flush.
3. Castings on the non-machined surface of the castings and signs should be clear and legible, the location and font should be in line with the requirements of the drawings.
4. The roughness of the non-machined surface of the casting, sand casting R, are not more than 50μm.
5. Castings should be cleared of sprues, edge spurs, etc. The residue of the sprue on the non-machined surface should be leveled and polished to meet the surface quality requirements.
6. Castings on the sand, core sand, and core bone should be cleaned up.
7. Castings have a sloping part, the size tolerance zone should be along the sloping side of the proportional configuration.
8. Castings on the type of sand, core sand, core bone, succulent, sticky sand, etc. should be shovel grinding smooth, clean up.
9. The wrong type, tab casting deviation, etc. should be corrected to achieve a smooth transition to ensure the appearance of quality.
10. The wrinkles on the non-machined surface of the casting should be less than 2mm in-depth, and the spacing should be more than 100mm.
11. The non-machined surface of the castings of machine products should be shot blasted or roller treated to reach the requirement of cleanliness Sa2 1/2 grade.
12. Castings must be treated with water toughness.
13. The surface of the casting should be flat, and the sprue, burr, and sticky sand should be removed.
14. Castings are not allowed to have casting defects such as cold compartments, cracks, holes, etc. that are detrimental to use.

Painting requirements:
1. All surfaces of steel parts to be painted must have rust, oxide, grease, dust, dirt, salt, and grime removed before painting.
2. Before removing rust, remove grease and dirt from the surface of steel parts with the organic solvent, alkali, emulsifier, steam, etc.
3. The time interval between the surface to be coated by shot blasting or manual rust removal and primer coating shall not be more than 6h.
4. Riveted parts in contact with each other's surface before the connection must be coated with a thickness of 30 ~ 40μm anti-rust paint. The edge of the lap joint should be closed with paint, putty, or bonding agent. The primer damaged due to processing or welding should be repainted.

Piping requirements:
1. All tubes should have their ends removed from edge fin, burrs, and chamfered before assembly. Use compressed air or other methods to clear the debris and floating rust attached to the inner wall of the pipe.
2. Before assembly, all steel pipes (including preformed pipes) should be degreased, pickled, neutralized, washed, and rust-proofed.
3. When assembling, the parts fixed with threaded connections such as pipe clamps, supports, flanges, and joints should be tightened to prevent loosening.
4. The welded parts of prefabricated pipes should be tested for pressure resistance.
5. When replacing or transferring the piping, the piping must be sealed with adhesive tape or plastic pipe to prevent any debris from entering and tied with a label.

Requirements for repair welding parts:
1. Before welding, the defects must be completely removed, the bevel surface should be repaired smooth and rounded, and there should be no sharp corners.
2. According to the defect situation of cast steel parts, the defects in the welding area can be removed by shovel digging, grinding, carbon arc gas planing, gas cutting, or mechanical processing.
3. The welding area and the bevel around 20mm of sticky sand, oil, water, rust, and other dirt must be thoroughly cleaned.
4. In the whole process of welding, the temperature of the preheating zone of the cast steel parts must not be lower than 350°C. 5.
5. Welding in the horizontal position as far as possible under the conditions allowed.
6. Welding rod should not do too much lateral swing when welding.
7. Cast steel surface heap welding, the overlap between the welding channel shall not be less than 1/3 of the width of the welding channel. weld flesh full, weld surface without burns, cracks, and obvious nodules. The appearance of the weld is beautiful, with no bite, slag, porosity, cracks, spatter, and other defects; weld wave uniformity.

Forging requirements:
1. The spout and riser of the ingot should have enough removal amount to ensure that the forging is free from shrinkage and serious deflection.
2. The forgings should be forged and formed on the forging press with sufficient capacity to ensure that the forgings are fully forged inside.
3. Forgings are not allowed to have cracks, folds, and other cosmetic defects visible to the naked eye that affect the use. Local defects can be removed, but the clean-up depth shall not exceed 75% of the machining allowance, and the defects on the non-machined surface of the forging shall be cleaned up and rounded transition.
4. Forgings are not allowed to have white spots, internal cracks, and residual shrinkage.

Requirements for cutting parts:
1. Parts should be inspected and accepted according to the process, and only transferred to the next process after passing the inspection in the previous process.
2. The machined parts are not allowed to have burrs.
3. The parts after finishing shall not be placed directly on the ground and shall take the necessary support and protection measures. The processing surface does not allow rust and affects the performance, life, or appearance of the bump, scratch, and other defects.
4. Rolling finishing surface, after rolling shall not have the phenomenon of peeling.
5. Final process after heat treatment of the parts, the surface should not have oxide skin. After the finishing process of the mating surface, the tooth surface should not be annealed.
6. The machined thread surface should not have defects such as black skin, bumping, messy buckle, and burr.

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