CNC machining process requirements refer to a series of standardized requirements for the entire machining process and part design in order to achieve the expected accuracy, surface quality, and production efficiency when cutting parts on CNC machine tools. These requirements permeate the entire process from part drawing design, process planning, tool selection, clamping methods to actual cutting.

To facilitate your understanding and application, I have divided the core process requirements into two main parts: design-side requirements and process-side requirements.

I. Design-side Requirements (Design for Manufacturability)

This is the part that structural design engineers need to pay special attention to. Good design can avoid many problems in subsequent machining and effectively control costs.

Structural and Shape Constraints

Minimum Hole Diameter: Generally, the hole diameter should not be less than the tool diameter, typically not less than φ2.5mm. For smaller holes (such as φ0.5mm), special micro drills are required, which significantly increases costs.

Maximum Depth (Deep Hole Machining): For general machining operations, it is recommended that the hole depth not exceed 4-5 times the hole diameter. If this ratio is exceeded, it becomes deep hole machining, requiring special tools and processes (such as pecking drills), making chip removal difficult and increasing costs.

Internal Right Angles and Corner Cleaning: CNC machining uses rotary end mills, which cannot machine perfect internal right angles. The tool will leave a radius (R-angle) equal to the tool radius at the internal angle. Therefore, the minimum R-angle of the internal angle needs to be specified in the design (generally recommended to be ≥ R0.5mm or R1mm). Otherwise, a smaller tool is needed for corner cleaning, or electrical discharge machining (EDM) is required.

Thin-Walled Parts: When machining thin-walled parts, the material is prone to vibration and deformation under cutting forces. It is recommended that the minimum wall thickness be no less than 0.8mm (metal), and the wall thickness should be as uniform as possible. Extremely thin walls (such as below 0.3mm) require special clamping and process strategies.

Plane Dimensions: Tool accessibility must be considered. Excessively deep cavities or excessively small openings may prevent the tool from entering or cause collisions and interference between the tool holder and the workpiece.

Tolerance and Accuracy Requirements

Tolerance Grade: Typical accuracy achievable through CNC machining is around IT7-IT9. General machining can guarantee an accuracy of ±0.1mm; finish machining can achieve ±0.01-0.05mm; while ultra-high accuracy (e.g., ±0.005mm) requires a temperature-controlled workshop and special processes.

Surface Roughness: Ordinary milling can achieve Ra3.2-6.3μm; finish milling can achieve Ra1.6μm; if a higher mirror finish is required (e.g., Ra below 0.4), additional grinding or polishing processes are usually needed.

II. Process Requirements (Manufacturing Process Specifications)

This is a key consideration for process engineers and CNC operators.

Datum and Clamping

Locating Datum: The workpiece must have a reliable locating datum surface. In the first machining operation, a datum surface is usually machined first, or the blank surface is used as a rough datum.

Clamping Method: Selected according to the shape of the part.

Flat-jaw vise: Suitable for regular rectangular workpieces.

Clamping Plate/Bolt: Suitable for large or irregularly shaped workpieces.

Vacuum Chuck: Suitable for thin plates or workpieces with pre-machined bottom surfaces, preventing pinching damage.

Specialized Fixtures: For complex or high-volume parts, specialized fixtures need to be designed and manufactured.

Interference Avoidance: The clamping position must avoid the tool's machining path to ensure that the tool holder and chuck do not collide with the fixture or workpiece during machining.

Tools and Cutting Parameters

Tool Selection: For roughing, larger diameter tools are usually selected to improve material removal rate; for finishing, smaller tools are selected to ensure detail and surface quality. For machining deep cavities, tools with extended cutting edges or extended tool holders are required.

Cutting Parameters: Spindle speed, feed rate, depth of cut (depth of cut), and width of cut need to be determined comprehensively based on the workpiece material (e.g., aluminum, steel, titanium alloy), tool material (e.g., high-speed steel, cemented carbide), and machine tool rigidity.

Cooling and Lubrication: Select a suitable cutting fluid based on the material and process to achieve cooling, lubrication, and chip removal. For example, emulsions are commonly used for machining aluminum parts; extreme pressure cutting oil may be required for machining stainless steel.

Process Route Arrangement

Process Division: Follow the principle of "roughing before finishing, main machining before secondary machining, surface machining before hole machining, and datum machining first."

Roughing: Quickly remove most of the excess material, leaving a 0.3-0.5mm finishing allowance.

Semi-finishing: Smooth the surface, preparing for finishing.

Finishing: Achieve the final dimensional accuracy and surface roughness as shown in the drawing.

Heat Treatment: For parts requiring hardness or stress relief, heat treatment (such as aging, quenching, etc.) should be arranged after roughing and before finishing.

Deburring: After CNC machining, sharp burrs will appear on the edges of the workpiece. Manual or mechanical deburring must be arranged to ensure safety and assembly requirements.

III. Special Case Handling

Thread Machining: Larger diameter threads (usually M6 and above) can be directly milled on the CNC machine with a thread milling cutter or tapped. For smaller diameter threads (M6 and below), only the pilot hole is usually machined, followed by manual tapping to prevent the tap from breaking inside the hole.

Secondary clamping: If the reverse or side of the part needs to be machined, it needs to be flipped and clamped. In this case, process holes need to be designed or the already machined surface needs to be used as a positioning reference to ensure positional accuracy after flipping.

Deformation control: For easily deformable thin-walled parts or large plate parts, it may be necessary to loosen the clamping plates after rough machining to release internal stress, and then reclamp for finish machining.