Eight essential knowledge for CNC machining

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

Down milling: The direction of the horizontal component force Fx of the cutting force F is the same as 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 the feed direction f, this kind of milling method

Down milling features:

(1) It is easy to move, and a down milling mechanism is required. (Due to the gap between the screw nut)

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(2) The surface quality of processing is higher than that of up-milling. (Suitable for finishing)

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Features of up milling:

(1) High working stability, no need for up-milling mechanism

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

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2. What are the methods for cutting in and out during CNC milling?

The main ways to retract the knife are as follows:

(1) Feed and retract directly along the Z axis of the coordinate axis

(2) Feed or retract along the given vector direction

(3) Advancing or retracting in a straight line along the tangent direction of the curved surface

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(4) Feed or retract along the normal direction of the curved surface

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(5) Tool advance or retract along the arc segment direction

(6) Approach to feed along a spiral or diagonal line

For profile machining that requires high machining accuracy, you should choose the approach of cutting in and out along the tangent direction of the curved surface or in the direction of the arc, so that it will not leave a trace of the tool at the entry or exit of the workpiece. Affect the surface processing quality of the workpiece.

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

The feed path includes two parts: in-plane feed and depth feed. For in-plane feed, cut in from the tangent direction for external generalization, and cut in from arc for concave generalization. On a two-axis CNC milling machine, there are two methods of depth feed for milling plane groove cams: one method is to mill back and forth in the xy or (yz) plane and gradually feed the tool to a predetermined depth; the other is First punch a craft hole, and then insert a predetermined depth from the craft hole.

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4. What are the confirmation criteria for the program starting point, return point, cut-in point and cut-out point 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 procedures to complete, then the starting point and returning point of these several procedures should also be exactly the same, so as not to cause processing operations. Troublesome. The coordinate values of the starting point and the returning point should also be set to zero for both X and Y to facilitate the operation.

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(2) Criteria for the selection of entry points

In the process of cutting in or cutting the surface, the tool should not be damaged. Generally speaking, for rough machining, the highest corner point in the surface is selected as the entry point of the surface. Because the cutting allowance at this point is small, the tool is not easy to damage the tool when feeding. For finishing, a corner point with a relatively flat curvature in the surface is selected as the entry point of the surface. Since the bending moment of the tool is small at this point, it is not easy to break the tool.

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(3) Criteria for selecting cut-out points

The main consideration is that the curved surface can be processed continuously and the non-cutting processing time between the curved surface and the curved surface processing is as short as possible, and the tool change is convenient, so as to improve the useful working time of the machine tool. For an open surface to be processed, two corner points of the surface can be used as the cut-out point. According to one of the above criteria: if the processed surface is a closed surface, only one corner of the surface is the cut-out point. The system generally actively confirms during programming.

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5. How to choose CNC lathe fixtures?

Three-jaw chuck and four-jaw single-action chuck should be selected according to the type of workpiece to be processed. The clamps for shaft workpieces have three-jaw chuck, four-jaw single-action chuck, active clamping dial chuck, and gear , Center, three-jaw dial chuck, etc. The clamping of disc type workpieces has adjustable jaws and adjustable speed chuck. (Hydraulic chucks are now mostly used for processing materials with soft jaws)

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6. What are processes and steps? What are the elements that make up processes and steps?

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

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

(2) Under the condition that the processing appearance and processing things remain unchanged, the part of the process content that is completed one after another is called a process step.

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7. What is process information? What does the 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.

The accumulation of processing practical experience is a useful way to obtain process information.

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

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

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

(2) Process analysis of NC machining of parts drawings;

(3) Mathematical processing of part graphics and confirmation of programmed size setting value;

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(4) Drafting of NC machining process plan;

(5) Confirmation of working steps and feed path;

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(6) Select the type of CNC machine tool;

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

(8) Confirmation of cutting parameters;

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

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

(11) Formulation and filing of technical documents for CNC machining