Comprehensive Analysis of Mechanical Technical Requirements for Various Engineering Drawings: A Standard Guide for Beginners

I. First, Understand: What Exactly Are Mechanical Technical Requirements?

• Unify Standards: Enable personnel in design, machining, quality inspection and other links to reach a consensus and avoid understanding deviations;
• Guarantee Performance: Ensure the product meets the needs of the usage scenario by specifying accuracy, strength and other requirements;
• Control Costs: Reasonable technical requirements can avoid over-processing and balance quality and manufacturing costs.

II. Follow the Map: Core Technical Requirements for Various Engineering Drawings

1. Part Drawings: “Processing Instructions” for Individual Parts

• Material and Heat Treatment Requirements: Specify the material used for the part, such as “45# Steel” or “304 Stainless Steel”; if heat treatment is required, indicate the method and hardness requirements, for example, “Quenched and Tempered, Hardness 220-250HB” or “Quenched, Hardness ≥HRC55”. Note that the material grade must comply with national standards, such as GB/T 699-2015 (High-quality Carbon Structural Steels).
• Dimensional Tolerance and Geometric Tolerance: Dimensional tolerance specifies the allowable deviation of key dimensions, such as “φ50±0.01mm”; geometric tolerance targets shape and position accuracy, such as flatness, perpendicularity, coaxiality, etc., for example, “End Face Circular Runout ≤0.02mm” or “Coaxiality of Two Holes φ0.03mm”. When dimensioning, combine with machining processes—for instance, the coaxiality requirement for shaft parts processed by lathes is usually higher than that for parts processed by milling machines.
• Surface Quality Requirements: Including surface roughness (Ra value) and surface treatment methods. Common expressions such as “Unmarked Surface Roughness Ra3.2μm” or “Outer Cylinder Surface Chrome Plated, Thickness 0.01-0.02mm, Salt Spray Test ≥48h”. For surfaces requiring sealing or fitting, the roughness requirement is higher, such as Ra≤0.8μm for bearing fitting surfaces.
• Machining Process Requirements: Specify special machining requirements, such as “All Sharp Edges Deburred C1.5”, “Inner Hole Honed” or “Threads Deburred to Ensure Smooth Engagement”. For easily deformable parts, add “Stress Relieving Treatment After Machining to Eliminate Internal Stress”.
• Inspection Requirements: Explain the inspection methods for key dimensions or performance, such as “Key Dimensions Inspected by CMM, Sampling Ratio 10%” or “Hardness Test Using Rockwell Hardness Tester, 5 Samples Sampled per Batch”.
• Other Special Requirements: Such as “Parts Free of Cracks, Porosity, Sand Holes and Other Defects” or “Non-machined Surfaces Coated with Anti-rust Paint”.

2. Assembly Drawings: “Assembly Guide” for Component Assemblies

• Assembly Accuracy Requirements: Specify the fit type (clearance fit, transition fit, interference fit) and accuracy grade between parts, such as “Shaft and Bearing Inner Ring: Interference Fit H7/k6” or “Slider and Guide Rail: Clearance Fit H8/f7”; simultaneously indicate the overall assembly accuracy, such as “Radial Circular Runout of Spindle After Assembly ≤0.015mm” or “Overall Coaxiality of Complete Machine ≤0.05mm”.
• Assembly Process Requirements: Specify the assembly sequence, method and precautions, such as “All Parts Cleaned Free of Oil Stains and Iron Chips Before Assembly”, “Bolt Tightening Sequence: Symmetrical from Middle to Both Sides, Tightening Torque 45-50N·m” or “Rolling Bearing Assembly Using Hot Mounting Method, Heating Temperature Not Exceeding 120℃”.
• Sealing and Lubrication Requirements: For parts requiring sealing, indicate the sealing method and requirements, such as “No Leakage After Oil Seal Assembly, Sealing Performance Complies with GB/T 14211-2019”; for lubrication, specify the lubricant type, filling amount and cycle, for example, “Use 32# Anti-wear Hydraulic Oil, Filling Amount to Middle of Oil Gauge, Replace Every 500 Operating Hours”.
• Overall Machine Performance Requirements: Specify the performance indicators of the assembled components, such as “Noise ≤75dB During No-load Operation of Motor and Reducer After Assembly” or “Hydraulic System Working Pressure 0.8-1.2MPa, No Pressure Loss”.
• Acceptance and Test Requirements: Explain the inspection items and standards after assembly, such as “No-load Test Run for 2 Hours After Assembly, Stable Operation Without Abnormal Vibration” or “Pressure Test Conducted at 1.5 Times Working Pressure, No Leakage for 30 Minutes of Pressure Holding”.

3. Welding Drawings: “Quality Guarantee” for Welded Structures

• Welding Material Requirements: Specify the model of welding electrodes, wires and fluxes, which must match the base material, such as “Base Material Q235A, Use E4303 Welding Electrode” or “Stainless Steel Base Material 304, Use ER308L Welding Wire”.
• Welding Process Requirements: Specify the welding method (manual arc welding, gas shielded welding, submerged arc welding, etc.), welding sequence, preheating and post-heating requirements, for example, “Use CO₂ Gas Shielded Welding, Welding Current 180-220A, Voltage 24-28V”, “Preheat Base Material to 100-150℃ Before Welding, Insulate for 2 Hours After Welding for Slow Cooling” or “Welding Sequence: From Bottom to Top, Symmetrical Welding to Reduce Deformation”.
• Weld Quality Requirements: Specify the weld grade (Grade Ⅰ, Ⅱ, Ⅲ) and defect requirements, such as “All Welds Are Grade Ⅱ, Ultrasonic Flaw Detection Required, Detection Ratio 100%, No Cracks, Incomplete Penetration, Porosity or Other Defects Allowed” or “Weld Reinforcement 2-4mm, Fillet Weld Size 8mm”.
• Post-welding Treatment Requirements: Explain the cleaning, straightening and anti-rust treatment after welding, such as “Remove Slag and Spatter After Welding, Grind Weld Surface Smooth”, “Correct Welding Deformation, Flatness ≤2mm/m” or “Paint Welds for Anti-rust After Welding, Paint Model XXX”.

4. Sheet Metal Drawings: “Forming Specifications” for Sheet Metal Parts

• Material and Thickness Requirements: Specify the sheet metal material and thickness tolerance, such as “SPCC Cold-rolled Steel Plate, Thickness 1.5mm±0.1mm” or “Aluminum Alloy Plate 6061-T6, Thickness 2.0mm”.
• Bending and Forming Requirements: Specify the bending radius, angle tolerance and forming process, such as “All Bending Inner Radii R2.0mm”, “Bending Angle Tolerance ±1°” or “Arc Forming Using Die Stamping, No Wrinkles or Cracks on Surface”. Note that the bending radius must be greater than 1.5 times the material thickness to avoid material cracking during bending.
• Notching and Punching Requirements: Specify the burr requirements for notches and dimensional tolerance for punching, such as “All Notches Deburred, No Sharp Edges” or “Punching φ8mm, Tolerance ±0.05mm, Hole Wall Perpendicularity ≤0.02mm”.
• Surface Treatment Requirements: Common surface treatment methods for sheet metal parts include spraying, electroplating, anodizing, etc., such as “Electrostatic Spraying on Surface, Color RAL7035, Coating Thickness 60-80μm, Adhesion ≥Grade 2 (Cross-cut Test)” or “Anodizing of Aluminum Alloy Parts, Oxide Film Thickness 10-15μm, Corrosion Resistance Complies with GB/T 10125-2021”.
• Assembly Fit Requirements: Explain the fit clearance or interference with other parts, such as “Fit Clearance Between Sheet Metal Cover and Base 0.5-1.0mm, No Loosening After Assembly”.

III. Pitfall Avoidance Guide: 4 Core Principles for Writing Mechanical Technical Requirements

1. Based on Standards, Accurate and Standardized

2. Combined with Processes, Practical and Feasible

3. Highlight Key Points, Concise and Clear

4. Coordinated and Consistent, No Contradictions

IV. Summary: The Core of Technical Requirements Is “Accurately Conveying Design Intent”