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Eight necessary knowledge for CNC machining

1. What is climb milling? What is up milling? What are the characteristics of down milling and up milling of CNC machine tools?

Climb milling: The direction of the horizontal component force Fx of the cutting force F is the same as that of the feed direction f. This milling method

Up milling: the direction of the horizontal component force Fx of the cutting force F is opposite to that of the feed direction f, this milling method

Climb milling features:

(1) It is prone to movement, and it is necessary to add a down-milling mechanism. (Due to the gap between the screw nut and the nut)

(2) The surface quality of machining is higher than that of up milling. (suitable for finishing)

Up milling features:

(1) High working stability, no up-cut milling mechanism required

(2) The surface quality of processing is lower than that of down milling (the tool wears quickly)

2. What are the methods of entering and withdrawing the tool during CNC milling?

There are mainly the following ways to withdraw the knife:

(1) Directly enter and exit the tool along the Z-axis direction of the coordinate axis

(2) Feed or retract along the given vector direction

(3) Feed or retreat in a straight line along the tangent direction of the surface

(4) Enter or withdraw the tool along the normal vector direction of the surface

(5) Feed or retreat along the direction of the arc segment

(6) The way of feeding along the helix or oblique line


For surface processing that requires high machining accuracy, the method of feeding and retracting the tool along the tangent direction of the surface or along the direction of the arc should be selected, so that no traces of the tool will be left at the tool entry or retraction of the workpiece. Affect the surface processing quality of the workpiece.

3. What factors should be considered when confirming the feeding path of the milling cutter?

The infeed road includes two parts: the in-plane infeed and the depth infeed. For the in-plane feed, cut in from the tangent direction for the external profile, and cut in from the arc for the concave profile. On the CNC milling machine with two-axis linkage, there are two ways to feed the cam in the milling plane groove: one way is to mill back and forth in the xy or (yz) plane and gradually feed the tool to a predetermined depth; the other way is First drill a process hole, and then enter the predetermined depth from the process hole.

4. What are the criteria for confirming the starting point, return point, entry point, and exit point of the program during CNC milling?

1) Starting point and returning point (confirmation criteria

In the same program, the starting point and returning point should be the same. If the processing of a part requires several programs to complete, then the starting point and returning point of these programs should also be exactly the same, so as not to cause processing operations. Trouble. It is also preferable to set the X and Y values of the starting point and the return point to be zero, so that the operation is convenient.

(2) Criteria for selection of entry points

In the process of feeding or cutting the curved surface, the tool should not be damaged. In general, for roughing, pick the highest corner point within the surface as the entry point of the surface. Since the cutting allowance at this point is small, it is not easy to damage the tool when entering the tool. For finishing, select a corner point with relatively gentle curvature in the surface as the entry point of the surface. Because at this point, the bending moment suffered by the tool is small, it is not easy to break the tool.

(3) Criteria for selecting the cut-out point

The main consideration is that the curved surface can be processed continuously and completely, and the non-cutting processing time between the curved surface and the curved surface processing should be as short as possible, and the tool change is convenient, so as to improve the effective working time of the machine tool. For the surface to be processed is an open surface, two corner points of the surface can be used as the cut-out point, according to the above criteria one: if the surface to be processed is a closed surface, only one corner point of the surface is the cut-out point, the active The system generally takes the initiative to confirm when programming.

5. Selection of fixtures for CNC lathes?

Three-jaw chucks and four-jaw single-action chucks should be selected according to the type of workpiece to be processed. The fixtures for shaft workpieces include three-jaw chucks, four-jaw single-action chucks, active clamping toggle chucks, and gear shifters. , top, three-jaw toggle chuck, etc. The chuck for disk workpieces has adjustable jaws and adjustable speed chucks. (Hydraulic chucks are mostly used now, and soft jaws are used to process materials)

6. What is the working procedure? What are the elements that make up the process and steps?

(1) The part of the process that one or a group of workers completes one or several workpieces at one work site is called a process.

The basis for distinguishing processes is whether the work site changes and whether the work is continuous.

(2) Under the condition that the processing appearance and processing tools remain unchanged, the part of the process content that is completed continuously is called a work step.

7. What is process information? What does process information include?

Process information refers to various information obtained after process processing.

This information includes: process preparation tool selection; processing plan (including tool path, cutting amount, etc.) and compensation plan and other information.

The accumulation of processing practical experience is an effective way to obtain process information.

The basis for distinguishing work steps is whether the processing appearance and things have changed.

8. What are the main contents of CNC machining technology?

(1) Select and confirm the content of CNC machining;

(2) Process analysis of CNC machining of part drawings;

(3) Mathematical processing of part graphics and confirmation of programming size setting values;

(4) Drafting of CNC machining process plan;

(5) Confirmation of working steps and feed routes;

type of machine tool;

(7) Selection and design of cutting tools, fixtures and measuring tools;

(8) Confirmation of cutting parameters;

(9) Compilation, verification and modification of processing procedures;

(10) First piece trial processing and handling of on-site problems;

(11) Finalization and archiving of numerical control processing technical documents

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