CNC Machining Process Design Essentials
The core principles and methodologies behind effective precision cnc machining process design
Introduction to CNC Machining Process Design
CNC machining process design is a core element of precision cnc machining. Whether for manual programming or automatic programming, process analysis of the part to be machined must be conducted before programming. Based on the material, content, and requirements of the workpiece, a suitable processing plan must be developed, determining the processing sequence, tools, fixtures, tool paths, and cutting parameters for each工序.
In essence, CNC programming is a way of describing the specific results of process analysis using a standardized writing format. Process analysis directly impacts machining quality, efficiency, safety, and cost in precision cnc machining operations.
CNC machining process design involves various aspects, generally including the development of machining process routes and detailed operation design. A well-designed process is fundamental to achieving high-quality precision cnc machining results consistently.
2.3.1 CNC Machining Process Route Design
The design of a CNC machining process route is a crucial aspect of process design in precision cnc machining, primarily involving organizing production resources for machining content, such as selecting CNC machine tools, determining processing methods, formulating processing plans, and arranging operations.
1. Selection of CNC Machine Tools
The appropriate machine tool must be selected based on the characteristics of the part to be machined in precision cnc machining operations. The right equipment choice directly affects production efficiency, accuracy, and overall manufacturing costs.
Rotational Parts Machining
Rotational parts are typically machined on CNC lathes. These machines excel at creating cylindrical shapes, threads, and contours on round workpieces, making them indispensable in precision cnc machining for rotational components.
Hole System Parts Machining
Parts with multiple holes requiring high positional accuracy are best suited for CNC drilling machines or machining centers with point-to-point linear control, which ensure the precise hole placement essential in precision cnc machining.
Plane and Contour Machining
Simple planar contour parts, usually consisting of straight lines and arcs, can be machined on 2-axis CNC milling machines. Complex curved surfaces require 3-axis or multi-axis CNC machines or machining centers to achieve the necessary precision in precision cnc machining.
Mold Cavity Machining
Mold cavities with complex, irregular surfaces requiring high precision and surface quality, often made from high-hardness, high-toughness materials, typically use milling combined with CNC EDM (Electrical Discharge Machining) in precision cnc machining workflows.
Different types of CNC machines used in precision cnc machining operations
2. Formulation of Processing Schemes
Surfaces requiring high precision in precision cnc machining are often processed through a sequence of roughing, semi-finishing, and finishing operations. This gradual approach ensures dimensional accuracy and surface quality while minimizing material removal stresses.
For example, an IT7 precision hole of small diameter with a final reaming operation typically requires prior drilling, boring, and rough reaming. Selecting only the final processing method based on quality requirements is insufficient; a complete processing scheme from raw material to finished part must be developed for effective precision cnc machining.
When formulating a processing scheme, the initial step involves selecting appropriate processing methods based on the precision and surface roughness requirements of key surfaces. The primary principle in method selection is ensuring that the required precision and surface finish can be achieved consistently in precision cnc machining.
Since multiple processing methods can often achieve the same level of precision and surface roughness, practical selection must consider the part's shape, size, and heat treatment requirements. For instance, IT7 precision holes can be achieved through boring, reaming, or grinding in precision cnc machining, but for box-type parts, boring or reaming is generally preferred over grinding.
Common Processing Methods and Their Applications in Precision CNC Machining
| Processing Method | Typical Accuracy | Surface Roughness (Ra) | Common Applications |
|---|---|---|---|
| Drilling | IT10-IT13 | 12.5-50μm | Initial hole creation |
| Reaming | IT7-IT9 | 1.6-6.3μm | Finishing small to medium holes |
| Boring | IT6-IT8 | 0.8-3.2μm | Finishing large holes, especially in castings |
| Milling | IT7-IT10 | 0.8-6.3μm | Flat surfaces, contours, slots |
| Grinding | IT5-IT7 | 0.025-0.8μm | High-precision surfaces, hardened materials |
Additionally, productivity and economic considerations, as well as the actual production equipment available, must be factored into the decision-making process for precision cnc machining. Reference materials such as process handbooks provide detailed information on the accuracy and surface roughness achievable with various processing methods.
CNC machining process design involves numerous technical considerations, including processing content, cutting parameters, process equipment, positioning and clamping methods, tool selection, and tool paths. For those interested in delving deeper into precision cnc machining, specialized literature on these topics is available.
Key Considerations in CNC Machining Process Design
In addition to general part analysis, several specific aspects must be carefully considered in precision cnc machining process design to ensure optimal results, repeatability, and efficiency.
1. Determining Tool-Workpiece Relative Position
In precision cnc machining, establishing the correct relative position between the tool and workpiece at the start of machining is critical. This positioning is achieved through the identification of a tool setting point.
Tool setting process in precision cnc machining to establish correct tool-workpiece positioning
Tool Setting Point
The tool setting point refers to the reference point used for tool setting to determine the relative position between the tool and workpiece in precision cnc machining. This point can be set on the part being machined or on the fixture at a position with a defined dimensional relationship to the part's positioning datum. Often, the tool setting point coincides with the part's machining origin.
Principles for Selecting Tool Setting Points
- The selected tool setting point should simplify programming in precision cnc machining
- It should be easily identifiable and facilitate establishing the part's machining origin
- It should allow for convenient and reliable verification during processing
- The selection should contribute to improving machining accuracy in precision cnc machining
For example, when programming the machining of a part as shown in Figure 2-7, the intersection of the centerline of the fixture's locating pin and a safety plane (35mm above the workpiece surface) can be chosen as the tool setting point for precision cnc machining. In this case, the tool setting point also serves as the machining origin.
Tool Setting Operation
When using a tool setting point to establish the machining origin, a tool setting operation is required. Tool setting in precision cnc machining refers to the process of aligning the tool's reference point with the tool setting point.
Each tool has different radius and length dimensions. After installing a tool on the machine, its basic position must be set in the control system. The tool reference point is the tool's positioning基准点. For example:
Cylindrical milling cutter:
通常是刀具中心线与刀具底面的交点
Typically the intersection of the tool centerline and the tool's bottom surface
Ball-end mill:
通常是球头的球心点或球头顶点
Typically the center or tip of the ball
Turning tool (boring tool):
通常是刀尖或刀尖圆弧中心
Typically the tool tip or the center of the tip radius
Drill:
通常是钻头顶点
Typically the drill tip
Tool setting methods vary among different types of CNC machines, and we will discuss these methods in conjunction with specific machine types in the context of precision cnc machining.
Tool Change Point
The tool change point is designated for machines using multiple tools, such as machining centers and CNC lathes in precision cnc machining. These machines require a specific location where tool changes can occur safely without interference between the tool, workpiece, fixture, or machine components. The tool change point is typically a fixed position in the machine's coordinate system that provides sufficient clearance for all tool changes during the precision cnc machining process.
Critical Parameters in Precision CNC Machining
Proper selection of cutting parameters significantly impacts the quality, efficiency, and tool life in precision cnc machining operations. The chart below illustrates typical ranges for key parameters based on material hardness.
Recommended cutting speed ranges for different materials in precision cnc machining (m/min)
Conclusion
Effective CNC machining process design is fundamental to achieving high-quality results in precision cnc machining. By carefully selecting appropriate machine tools, developing optimal processing schemes, establishing accurate tool-workpiece positioning, and determining proper cutting parameters, manufacturers can ensure efficient production of high-precision components.
The principles outlined in this guide form the foundation of successful precision cnc machining operations, enabling consistent quality, improved productivity, and cost-effectiveness in manufacturing processes.