5 Principles of the CNC Machining Process

1. Minimum Number of Tool Changes Principle

It’s important to reduce the number of tool changes and minimize empty range time during the CNC machining process. The tool should divide the process and work steps to finish the work, focusing on the processing parts. To reduce tool change time, it’s best to use the same tool for processing as many parts as possible, avoiding multiple tool calls and installations. In a single clamping, process all parts with the same tool before using the second for other parts.

2. Maximum Concentration of CNC Machining Process Principle

In CNC machine tools, particularly machining centers, it’s best to maximize the concentration of the process. In other words, when clamping parts, try to complete most or all processes that can be processed by the CNC machine tool. This approach can reduce the number of machine tools and workpiece clamping times, minimize unnecessary positioning errors, and improve productivity. For coaxial requirements of the hole system processing, install the tools once and complete the same axis hole system of all processing through a sequence of consecutive tool changes before processing other coordinate positions of the hole to eliminate repeated positioning errors and improve the coaxially of the hole system.

3. Rough First and Refined Principle

It is important to separate the processes into roughing and finishing stages when performing numerical control processing. Semi-finishing and finishing should be performed after all roughing is completed. A machined surface should be finished in the order of roughing semi-finishing. We must ensure the processing quality and the tool’s durability during the roughing stage. It’s important to ensure that the margins of each part are as even as possible before finishing. During the finishing process, the accuracy of the parts’ machining and surface quality are the primary concerns. Therefore, the final contour of the parts should be continuously refined during the last cut. The fine machining allowance should be between 0.2-0.6mm to ensure high-quality processing. It’s recommended to allow some time between roughing and finishing so that the deformation of the part following roughing can be fully restored before finishing.

4. Near First, Far Away, Face Before Hole Principle

When processing a part, it’s best to start with the area closest to the tool setting point and work your way outwards. It reduces the tool movement distance and idle travel time. While turning, starting with the area closest to the tool setting point is also advisable to maintain the rigidity of the blank or half-finished product and improve cutting conditions.

When machining parts with milling planes and boring holes, it’s best to mill the face first and then bore the hole. It helps to recover any deformation of the part and ensure the machining accuracy of the hole. If boring is done first and the plane is milled after the hole, burrs and rough edges may be generated at the hole, which can affect the assembly of the hole.

5. Principle of CNC Machining Inside and Outside Cross

For the parts’ inner and outer surfaces to be processed, the processing order should usually be arranged for the first processing of the inner surface, followed by the outer surface. First, rough the inner and outer surfaces, then finish both surfaces. Usually, in a single clamping, it’s best not to process just one part of the part’s surface and then process the other surface of the part.