Technical Criteria for Accurate Mechanical Drawings

General technical requirements

Remove the oxide scale from the parts. The processed surfaces should be free of scratches, abrasions, or any defects that might damage their finish. Additionally, burrs and flash must be removed.

CNC Machining process1

 

Heat treatment requirements

- After quenching and tempering, the hardness is HRC 50 to 55.
- Parts are subjected to high-frequency quenching and tempering at 350 to 370℃, resulting in HRC 40 to 45.
- Carburizing depth is 0.3 mm.
- High-temperature aging treatment is applied.

 

Tolerance requirements

Uninjected shape tolerances must adhere to the requirements of GB1184-80. The allowable deviation for uninjected length dimensions is ±0.5mm. The casting tolerance zone is symmetrical to the basic size configuration of the blank casting.

 

Part edges and corners

- Uninjected fillet radius is R5.
- All uninjected chamfers are 2×45°.
- Sharp angles, pointed corners, and edges are blunted.

 

Assembly requirements

- Each seal must be soaked in oil before assembly.
- When assembling rolling bearings, hot-loading with engine oil heating is permitted, provided the oil temperature does not exceed 100℃.
- After assembling the gear, the contact spots and side clearance of the tooth surface must conform to the specifications outlined in GB10095 and GB11365.
- During the assembly of the hydraulic system, sealing fillers or sealants are permitted, but care must be taken to prevent them from entering the system.
- All parts and components (including purchased and outsourced parts) entering the assembly must have a certificate of conformity issued by the inspection department prior to assembly.

- Parts must be cleaned thoroughly before assembly, ensuring that there are no burrs, flashes, oxide scale, rust, chips, oil stains, colorants, or dust.
- Before assembly, the main matching dimensions of parts, particularly the interference fit dimensions and their related precision, should be reviewed.
- Throughout the assembly process, parts must not be knocked, hit, scratched, or allowed to rust.
- When tightening screws, bolts, and nuts, it is strictly forbidden to strike or use inappropriate screwdrivers and wrenches. After tightening, the screw slots, nuts, and heads of screws and bolts must remain undamaged.
- A torque wrench must be used for fasteners with specified tightening torque requirements, and tightening must be performed according to these specifications.

 

- When multiple screws or bolts are used to tighten the same precision machined parts, each one must be tightened in a crosswise, symmetrical, step-by-step, and even manner.

- When assembling a conical pin, the hole should be checked for color coating. The contact rate should be no less than 60% of the mating length and should be evenly distributed.
- The flat key must make uniform contact with both sides of the keyway on the shaft, ensuring that there are no gaps between the mating surfaces.
- In a spline assembly, the number of tooth surfaces in simultaneous contact must not be less than 2/3, and the contact rate must be at least 50% in both the length and height direction of the key teeth.
- After assembling a flat key (or spline) with sliding fit, the matching parts should be able to move freely, and there should be no uneven tightness.

 

- After bonding, any excess adhesive that flows out must be removed.

- The outer ring of the bearing must not be stuck to the semicircular holes of the open bearing seat or the bearing cover.
- The outer ring of the bearing should maintain good contact with the semicircular holes of both the open bearing seat and the bearing cover. When checked with color, it should be evenly in contact with the bearing seat over a range of 120° symmetrical to the center line, and with the bearing cover over a range of 90° symmetrical to the center line. Additionally, when using a feeler gauge in the specified ranges, a 0.03mm feeler gauge should not be able to be inserted into more than one-third of the outer ring’s width.
- After assembling the outer ring of the bearing, it should make even contact with the end face of the locating end bearing cover.
- Once the rolling bearing is installed, it should rotate flexibly and steadily by hand.

CNC Machining process3

- The joint surface of the upper and lower bearing shells must fit tightly together; a 0.05mm feeler gauge should not be able to be inserted during checks.
- When securing the bearing shell with a locating pin, ensure the pin is drilled and inserted while keeping the shell mouth surface and end face flush with the corresponding bearing hole’s opening and closing surfaces. The pin should not be loose after installation.
- The bearing body and bearing seat of the spherical bearing must have uniform contact. Check using the coloring method; the contact area should be at least 70%.
- Alloy bearings must not be used if the surface of the liner appears yellow. There should be no core separation within the specified contact angle, and any core separation outside this angle should not exceed 10% of the total area of the non-contact area.
- The reference end face of the gear (worm gear) should fit flush against the shaft shoulder (or the end face of the positioning sleeve). A 0.05mm feeler gauge should be used to ensure that it cannot be inserted. Ensure that the reference end face’s verticality to the axis meets requirements.

 

- The joint surface between the gearbox and its cover must be in good contact.
- Before assembly, thoroughly check for and remove any sharp angles, burrs, and foreign matter left over from part processing. Care must be taken to ensure that seals are not scratched during installation.

 

Requirements for castings

- The casting surface must be free of defects such as cold shuts, cracks, shrinkage cavities, penetrating defects, and serious issues like undercasting and mechanical damage.
- The casting should be thoroughly cleaned and free from burrs and flash. The pouring and riser gates on the non-machined surface must also be cleaned and aligned flush with the casting surface.
- The characters and logos on the non-machined surface of the casting should be clearly identifiable, and their position and font must adhere to the specifications outlined in the drawing.
- The roughness of the non-machined surface of the casting, as determined by sand casting, should not exceed 50 μm.
- All pouring and riser remnants, along with any burrs, must be removed from the casting. Any residue on the non-machined surface should be scraped and polished to meet the required surface quality standards.

 

- The molding sand, core sand, and core materials on the casting must be cleaned thoroughly.
- The dimensional tolerance zone of the inclined part of the casting should be symmetrically arranged along the inclined surface.
- Any residue from molding sand, core sand, core materials, and other contaminants such as fleshy or sticky sand on the casting should be scraped, polished, and cleaned.
- Deviations in the right and wrong types, as well as any boss casting inaccuracies, should be corrected to ensure a smooth transition and maintain high appearance quality.
- The wrinkles on the non-machined surface of the casting should be less than 2 mm in depth, with a spacing of more than 100 mm between them.

 

- The non-machined surfaces of the machine product castings must undergo shot peening or roller treatment to achieve the cleanliness standard of Sa2 1/2.
- The castings must be water-toughened.
- The surfaces of the castings should be flat, and any gates, burrs, or residual sand must be removed.
- The castings must be free from defects such as cold shuts, cracks, and holes, as these can compromise their usability.

 

Coating requirements

- All surfaces of steel milled parts that require painting must be free of rust, scale, grease, dust, dirt, and salt before the painting process begins.
- Prior to rust removal, use organic solvents, alkaline solutions, emulsifiers, or steam to eliminate grease and dirt from the surface of the steel parts.
- The interval between the completion of shot blasting or manual rust removal and the application of the primer coating should not exceed six hours.
- The surfaces of riveted parts that come into contact with each other must be coated with anti-rust paint to a thickness of 30-40 μm before they are connected. Additionally, overlapping edges should be sealed with paint, putty, or adhesive. If the primer is damaged during processing or welding, it should be reapplied.

 

Piping requirements

- Ensure that all pipes are free from flash, burrs, and chamfers before assembly. Use compressed air or other methods to remove debris and floating rust from the inner walls of the pipes.
- All steel pipes, including prefabricated pipes, must be degreased, pickled, neutralized, washed, and treated for rust prevention before assembly.
- During assembly, tighten all parts connected by threaded connections, such as pipe clamps, supports, flanges, and joints, to prevent any loosening.
- All welded joints in prefabricated pipes must undergo pressure resistance testing.
- When replacing or transferring pipes, seal the pipe separation ports with tape or plastic pipe plugs to prevent debris from entering. Additionally, ensure that labels are attached for identification.

CNC Machining process2

Requirements for repair welds

- Before welding, ensure that all defects are completely removed, and the groove surface is smooth and rounded without sharp corners.
- Depending on the type of defects in the steel castings, you can remove imperfections in the welding area using methods such as shoveling, grinding, carbon arc gouging, gas cutting, or mechanical processing.
- Thoroughly clean any dirt within 20mm around the welding area, including sticky sand, oil, water, rust, etc., as well as the groove itself.
- Throughout the entire welding process, maintain the temperature of the preheating zone of the steel casting at no less than 350°C.

- If possible, weld in a horizontal position to improve results.
- While repairing, avoid excessive horizontal movement of the electrode.
- When welding on the surface of the steel casting, ensure that the overlap between the welds is at least 1/3 of the weld width. The weld should be full, with no burns, cracks, or significant nodules on the surface. It should also have an attractive appearance and be free of defects such as undercuts, slag, pores, cracks, or spatter, with a uniform weld wave pattern.

 

Requirements for forgings

- The nozzle and riser of the ingot must be removed adequately to ensure that the forging is free from shrinkage holes or significant deflections.
- Forgings should be processed on a forging press with sufficient capacity to guarantee complete forging throughout the material.
- Forgings must not exhibit visible cracks, folds, or any other defects that could affect their usability. While local defects may be removed, the cleaning depth should not exceed 75% of the machining allowance. Additionally, any defects on the non-machined surface of the forging must be cleaned and smoothly transitioned.
- Forgings should not contain white spots, internal cracks, or residual shrinkage holes.

 

Requirements for machined parts

- Parts must be inspected and approved according to the established process before being transferred to the next stage. Transfer can only occur once the previous inspection has passed.
- Processed parts must be free of burrs.
- Finished parts should never be placed directly on the ground. Appropriate support and protection measures must be utilized. Additionally, the machined surfaces must be free from rust and defects such as bumps and scratches that could impact performance, durability, or appearance.
- The surface after the rolling finishing process must not exhibit any peeling.
- Parts that have undergone final heat treatment must have surfaces free from oxide scale. Mating surfaces and tooth surfaces must not undergo annealing after finishing.
- The processed thread surface must be clear of defects such as black skin, bumps, random buckles, and burrs.

 

 

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Post time: Dec-24-2024
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