Structural Design Process Standards: A Detailed Guide to Machining

Chemical Coloring for CNC Machining Bronze Parts

In the field of industrial manufacturing, structural design process standards are crucial guidelines that ensure product quality and manufacturing efficiency. This article provides a detailed explanation of various process standards in machining, with specific examples to help readers understand and apply these standards effectively.

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Material Selection

Material selection is vital in the machining process. Different materials have varying physical and mechanical properties, directly affecting machining difficulty and product quality.

Metal Materials

Round Bar Series

When designing shaft and disk parts, it is advisable to select dimensions from commonly used diameter series. For example, common diameter series include 5mm, 6mm, 8mm, etc. Proper diameter selection can improve material utilization and reduce machining costs. The table below shows the common round bar diameter series:

Common Diameter Series
5; 6; 8; 10; 12; 14; 16; 18; 20; 22; 25; 28; 30; 32; 35; 40–100 (in increments of 5); 100–300 (in increments of 10)

Plate Series

For parts with low plane requirements, especially thin plates below 10mm, which are prone to deformation during machining, it is recommended to select thicknesses from the table below to reduce machining costs:

Common Plate Thickness Series
3; 4; 5; 6; 8; 10; 12; 14; 16; 18; 20; 22; 25; 28; 30; 32; 35; 40–100 (in increments of 5); 100–200 (in increments of 10)

Hexagonal Bar Series

Hexagonal bars are typically used for assembly clamping. Preferred dimensions are as follows:

Preferred Hexagonal Bar Series
5.5; 7; 8; 10; 12; 13; 14; 17; 19; 22; 24; 27; 30; 32; 36; 41; 46

Non-Metallic Materials

Non-metallic materials also have wide applications in machining. The selection of rods, plates, and pipes should prioritize the common specifications provided by suppliers.

Basic Principles of Component Structural Design

Processability of Structural Design

The structural design of parts should be simplified as much as possible while meeting technical requirements. This includes minimizing the number and area of machining surfaces and prioritizing the use of standard, universal, and purchased components to improve design processability and cost-effectiveness.

Common Design Values

  • Bending Radius for Pipes: Generally, the bending radius (R) should be greater than the pipe diameter to avoid wrinkling.
  • Corner Design for Machined Parts: Use chamfers or clear angles instead of rounded corners to improve machining efficiency.

Principles of Product Fit Tolerance Design

Tolerance design is crucial for ensuring the quality of part assemblies. Generally, tolerance grades should be lowered as much as possible to improve processability.

Common Tolerance Data

The table below shows some common tolerance data:

Basic Size (mm)IT5 (mm)IT6 (mm)IT7 (mm)IT8 (mm)IT9 (mm)IT10 (mm)IT11 (mm)

Selection of Unspecified Tolerances

For unspecified linear dimensions, it is recommended to select the m-grade tolerance according to GB/T1804, and for unspecified shape and position tolerances, select the k-grade tolerance according to GB/T1184.

Principles of Surface Roughness Design

Surface roughness should meet product functional requirements while considering process economy. The relationship between surface roughness and machining precision is closely linked. The table below shows the economic precision of common machining processes:

External Cylindrical Surface Machining Methods

Machining MethodEconomic Precision (IT)Economic Roughness (Ra/μm)Application Scope
Rough TurningIT11–1312.5–50Suitable for all metals except quenched steel
Rough Turning–Semi-Finish TurningIT8–103.2–6.3
Rough Turning–Semi-Finish Turning–Finish TurningIT7–80.8–1.6
Rough Turning–Semi-Finish Turning–Finish Turning–BurnishingIT7–80.025–0.2
Rough Turning–Semi-Finish Turning–GrindingIT7–80.4–0.8Mainly for quenched steel, not suitable for non-ferrous metals
Rough Turning–Semi-Finish Turning–Rough Grinding–Finish GrindingIT6–70.1–0.4
Rough Turning–Semi-Finish Turning–Finish Turning–Fine Turning (Diamond Turning)IT6–70.025–0.4Mainly for high-precision non-ferrous metal machining
Rough Turning–Semi-Finish Turning–Rough Grinding–Finish Grinding–HoningIT5+0.006–0.1Extremely high precision external cylindrical machining

Selection of Thread-Related Dimensions

Preferred Thread Series

To improve product interchangeability and reduce the number of thread gauges, please use the preferred thread series.

Common Thread Hole Depth Process Requirements

Different materials require different thread hole process depths. The recommended thread hole depths are as follows:

Nominal Diameter (d)Steel and Bronze (mm)Cast Iron (mm)Aluminum (mm)

Welding Processes

Characteristics of Welded Structures

Welded structures have the following advantages:

  1. High Strength of Welded Joints: The strength of the weld seam can reach or even exceed the strength of the parent material.
  2. Flexible Size and Shape: The size and shape of welded structures can meet a wide range of requirements.
  3. Manufacturing Sealed Parts: Welding is easy for manufacturing parts that require tightness.
  4. No Model Manufacturing: Welding does not require model manufacturing, making preparation work simple and production cycles short.
  5. High Finished Product Rate: The finished product rate of welded parts is high, and it is easy to repair defective products.

However, welding also has some disadvantages, such as being prone to deformation and internal stress, and uneven joint performance.

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