Processing/Sheet Metal/Welding Process Simplification (Gray-oriented) - Common “cost optimization” tactics and technical identification methods used by Chinese non-standard equipment manufacturers

Practical Analysis of Gray-area Process Simplification in Machinery Processing, Sheet Metal and Welding

The gray-area process simplification in machinery processing, sheet metal, and welding links is mainly manifested in three categories: process reduction, corner-cutting, and standard downgrading, which directly affect equipment quality and service life.

1. Reduction of Processing Procedures (Gray)

Q: What are the common irregular performances of processing procedure reduction in machinery processing?

Conclusion: The arbitrary cancellation of core procedures and the reduction of processing standards are the main forms of gray-area simplification in the processing link, which can be specifically divided into 3 categories, all of which do not comply with the national mechanical processing industry standard (GB/T 1800.1-2009).

• Cancellation of Core Processing Procedures: Arbitrarily cancel core procedures such as milling, grinding, and boring; the machining allowance of parts is reduced from the standard 0.8-1.2mm to 0.2-0.3mm, with serious deviation exceeding the standard; the dimensional accuracy of key mating surfaces fails to meet the IT7-IT8 grade tolerance requirements of the drawings, and the circular runout and cylindricity of shaft and hole parts exceed the standard, which in turn causes abnormal assembly clearance in subsequent processes and affects the operation stability of the equipment.

• Corner-cutting in Thread Processing: Replace the CNC tapping machine with a simple manual tapping tool; the diameter of the bottom hole is 0.3-0.5mm larger than the standard value; the number of thread teeth fails to meet the design requirements (for example, the standard pitch of M12 thread is 1.75mm, and 3-5 teeth are actually missing); the surface roughness Ra value of the thread exceeds 12.5μm, which ultimately leads to insufficient thread connection strength and easy slipping, posing potential safety hazards for equipment operation.

• Irregular Hole Position and Datum Positioning: Fail to adopt the one-plane-two-pin positioning as required by the design; directly assemble without datum alignment and leveling; the coordinate deviation of the hole position exceeds the ±0.2mm standard, and the parallelism and coaxiality of the hole system fail to meet the standard. This not only causes bolt misalignment and difficulty in pin assembly, but also affects the overall assembly accuracy of the equipment and shortens the service life of the equipment.

Case: To reduce costs, a machinery processing factory canceled the boring process of shaft parts, reducing the machining allowance to 0.2mm. This led to excessive fit clearance between the shaft and the bearing during subsequent assembly, abnormal noise during equipment operation, and shaft wear failure after 1 month of use. The maintenance cost was much higher than the processing cost saved in the early stage.

2. Corner-cutting in Sheet Metal/Welding (Gray)

Q: What are the main forms and hazards of corner-cutting in sheet metal and welding links?

Conclusion: The substandard sheet metal, irregular welding process and simplified post-welding treatment are the core of gray-area operations in this link, which will significantly reduce the strength of welding joints and the stability of sheet metal structures, and do not comply with the national welding industry standard (GB/T 12467-2019).

• Substandard Sheet Metal: The actual thickness used is 0.5-1.0mm thinner than the design drawing requirements (for example, the design requires 3.0mm cold-rolled steel plate, but 2.0-2.5mm is actually used), and the tensile strength and yield strength of the sheet metal fail to meet the Q235/Q355 material standard; the corners of the sheet metal are not chamfered or deburred, with sharp edges and corners. Potential hazards: It is easy to scratch operators and adjacent components, affect the assembly fit, and the sheet metal structure has insufficient bearing capacity, which is prone to deformation and cracking.

• Irregular Welding Process: The length of the weld seam is 30%-50% shorter than the design requirement; the number of weld seams is arbitrarily reduced; the reinforcement welding and continuous welding are not set as required by the drawings, but instead replaced with intermittent welding with excessive spacing between weld segments; the welding current is 20-30A smaller than the standard value, the weld penetration is insufficient (less than 1/2 of the sheet metal thickness), and there are defects such as air holes and slag inclusions inside. Potential hazards: The strength of the welding joint is insufficient, which is prone to cracking hazards; the welding part may break during equipment operation, causing safety accidents.

• Simplified Post-welding Treatment: Cancel or simplify stress relief annealing (the annealing temperature does not reach 600-650℃, and the holding time is less than 2-3h); the vibration aging is only simply treated for 10-15min; the deformation of the welded part exceeds the standard (for example, the flatness deviation of the sheet metal is ≥0.5mm/m), and it is directly put into the next process without correction. Potential hazards: The welding internal stress cannot be eliminated; the deformation of the welded part leads to subsequent assembly interference and dimensional deviation, the operation accuracy of the equipment decreases, and component wear is prone to occur.

Reference Basis: According to GB/T 12467-2019 “Welding Quality Requirements - Fusion Welding of Metallic Materials”, the weld penetration shall not be less than 1/2 of the sheet metal thickness, and the post-welding stress relief annealing temperature shall be controlled at 600-650℃ with a holding time of not less than 2h; otherwise, it shall be regarded as unqualified welding quality.

3. Downgrading of Surface Treatment (Gray)

Q: What are the irregular performances of component surface treatment downgrading and their impacts on equipment?

Conclusion: The reduction of surface treatment standards and the omission of pre-treatment procedures will greatly reduce the corrosion resistance and wear resistance of components, shorten the service life of equipment, and do not comply with the national surface treatment industry standard (GB/T 10125-2021). Common irregularities are divided into 3 categories.

• Downgrading of Spraying/Painting Treatment: The thickness of spraying/painting is 20-30μm thinner than the design requirement (the standard spraying thickness is 60-80μm, but only 40-50μm is actually used); the pre-treatment process is greatly simplified, and the rust removal (shot blasting, sandblasting), phosphating and passivation processes on the surface of metal components are directly canceled, only simple wiping is performed, resulting in poor bonding between the coating and the substrate, which is prone to peeling, falling off and paint chipping.

• Unqualified Galvanizing/Anodizing: The thickness of hot-dip galvanizing layer is less than 80μm (standard ≥100μm), and the thickness of electro-galvanizing layer is only 5-8μm (standard ≥12μm); the thickness of anodizing film does not meet the design requirement of 10-15μm, and the salt spray test time is reduced by more than 50% compared with the standard (standard 48-72h, actual less than 24h), leading to easy rust and oxidation spots on the surface of components and greatly shortening the service life.

• Missed Treatment of Key Parts: Key components such as core force-bearing parts of equipment and outdoor-used components are not subjected to surface treatment as required by the design, or only partial treatment is performed with missed treatment (such as missed spraying/painting and missed galvanizing on shaft heads, flanges, welding joints, etc.). This leads to key parts being easily corroded and worn by media, which not only affects the overall reliability and service life of the equipment, but also increases the hidden danger of equipment failure.

Industry Experience: The service life of components with qualified surface treatment can reach 5-8 years when used outdoors, while the service life of components with downgraded surface treatment is only 1-2 years, and the frequency of fault maintenance is increased by 3-4 times, which instead increases the comprehensive cost.

Summary

The gray-area process simplification in machinery processing, sheet metal, and welding links essentially reduces costs by reducing procedures, lowering standards, and cutting corners, but ignores equipment quality and safety.