Custom High-Quality Metal Parts Manufacturer

(I) Geometry and Material

Machining quality generally encompasses two aspects: geometric quality and material property quality.

Geometric quality refers to geometric deviations at the interface between the outermost machined surface and the surrounding environment. It is categorized into macro-geometric errors and micro-geometric errors.

● Macro-geometric errors (e.g., roundness error, flatness error, etc.). For macro-geometric errors, the ratio of wavelength (measurement length or sampling length) to wave height (error value) is generally greater than 1000.

● Micro-geometric errors (micro-geometric irregularities, also known as surface roughness). The ratio of wavelength to wave height is generally less than 50.

● Periodic geometric errors falling between macro-geometric errors and micro-surface roughness are commonly referred to as “waviness”; the ratio of wavelength (λ) to wave height (Hλ) ranges from 50 to 1000. Waviness is primarily caused by vibrations within the machining system.

Machining accuracy refers to the degree to which a part’s geometric parameters (dimensions, shape, and relative positions of surfaces) conform to ideal geometric parameters after machining.

Machining error refers to the deviation of the actual geometric parameters from the ideal geometric parameters after the part is machined.

Clearly, the smaller the machining error, the higher the machining accuracy.

(II) Dimensional, Shape, and Positional Accuracy

The relationship between dimensional accuracy, shape accuracy, and positional accuracy

Dimensional, shape, and positional accuracies in part machining are interrelated. Generally, shape errors should be constrained within positional tolerances, while positional errors should be constrained within dimensional tolerances.

Unless otherwise specified, the shape and positional errors of a part should not exceed half of the part’s dimensional tolerance.

If there are specific requirements regarding shape or positional errors, they must be indicated separately from the dimensional tolerance. For example, regarding a fixture base plate, the dimensional distance between the top and bottom surfaces may be subject to general (free) tolerances; however, the parallelism error between the top and bottom surfaces requires strict control and must be explicitly specified.

Product quality is a key concern for customers, but without attention to process quality, it is difficult to effectively control product quality. Product quality refers to requirements specified in drawings, such as dimensional accuracy. Process quality refers to factors such as clamping pressure.

A qualified machining quality control specialist must understand the manufacturing process and CNC principles—which is why process inspectors are required to record videos of the machining process. Only by thoroughly understanding every stage of machining can quality be effectively managed. Furthermore, during the process, any tool change, fixture adjustment, or operator change—these small details—are all signs of instability in process quality and must be identified promptly.