Quick Tips on Machining Quality (7–9)

Due to the complexity of CNC machining—involving variables such as different machine tools, materials, cutting tools, cutting methods, and parameter settings—reaching a high level of proficiency (whether in actual machining or programming) requires a significant amount of time. The following is a compilation of practical experience regarding CNC machining processes, operational steps, tool parameter selection, and process monitoring, summarized by engineers over long periods of production.

7. Q: How should machining tools be selected appropriately? What are the key factors of cutting parameters? What types of tool materials are available? How are spindle speed, cutting speed, and cutting width determined?

1. For face milling, non-resharpenable carbide face mills or end mills should be selected. For general milling, a two-pass approach is recommended: the first pass should ideally be a roughing operation using a face mill, moving continuously across the workpiece surface. The recommended cutting width per pass is 60%–75% of the tool diameter.

2. End mills and indexable carbide face mills are primarily used for machining bosses, grooves, and box-opening faces.

3. Ball-end mills and round-insert mills (also known as bull-nose mills) are commonly used for machining curved surfaces and profiles with variable draft angles. Ball-end mills are mostly used for semi-finishing and finishing, while round-insert mills are typically used for roughing.

8. Q: What is the purpose of a machining program sheet? What information should it contain?

A: (1) The machining program sheet is a component of the CNC process design and serves as a set of instructions that the operator must follow. It provides a detailed explanation of the machining program, ensuring the operator understands the program content, workholding and positioning methods, the tools selected for each operation, and any specific precautions.

(2) The machining program sheet should include: drawing and programming filenames, workpiece name, workholding sketch, program name, tools used for each program, maximum cutting depth, machining type (e.g., roughing or finishing), and estimated machining time.

9. Q: What preparations are required before CNC programming? Answer: Once the machining process has been determined, the following must be understood before programming: 1. The workpiece clamping method; 2. The size of the workpiece blank—to determine the machining scope or whether multiple setups are required; 3. The workpiece material—to select the appropriate cutting tools; and 4. The available tool inventory—to avoid having to modify the program later due to a lack of specific tools, or to allow for advance preparation if a particular tool is essential.