Eight essential knowledge for CNC machining

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

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

Down milling features:

(1) It is easy to move, and it is necessary to add a milling mechanism. (due to the gap between the screw screws)

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

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Features of reverse milling:

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

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

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2. What are the methods of feeding and retreating during CNC milling?

The methods of withdrawal are mainly as follows:

(1) Directly advance and retract the tool along the Z axis of the coordinate axis

(2) Feed or retract the tool along the given vector direction

(3) Straight in or out 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) Feed or retract the tool along the direction of the arc

(6) Feeding method along the spiral or oblique line

For profile machining that requires high machining accuracy, you should choose the method of feeding and retracting along the tangent direction of the curved surface or along the arc direction, so that there will not be a mark of tool stop at the position of the workpiece. Affect the appearance of the workpiece.

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

The feed road includes in-plane feed and depth feed. For in-plane feed, the external summary is cut from the tangent direction, and the concave summary is cut from the arc. On a two-axis CNC milling machine, there are two methods of depth feed for milling a planar grooved cam: one method is to mill back and forth in the xy or (yz) plane and gradually feed to a predetermined depth; the other method is First make a process hole, then enter a predetermined depth from the process hole.

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4. What are the criteria for confirming 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 the return point should be the same. If the processing of a part requires several programs to complete, then the starting point and the return point of these programs are also preferably the same, so as not to cause processing operations. Troublesome. The coordinate values of the starting point and the returning point are also preferably set to zero for both X and Y values, which can facilitate the operation.

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(2) Criteria for selecting entry points

In the process of feeding or cutting the surface, the tool should not be damaged. Generally speaking, for roughing, the highest corner point in the curved surface is selected as the entry point of the curved surface. Due to the small cutting allowance at this point, it is not easy to damage the tool during feed. For finishing, select a corner point with a gentle curvature in the curved surface as the entry point of the curved surface. Because at this point, the bending moment suffered by the tool is small, it is not easy to break the tool.

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(3) Criteria for selection of 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 to improve the useful 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 cut-out points, according to one of the above criteria: If the processed surface is a closed surface, only one corner point of the surface is the cut-out point, active The system generally takes the initiative to confirm during programming.

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5. Selection of CNC lathe fixtures?

The three-jaw chuck and four-jaw single-action chuck fixtures should be selected according to the type of workpiece to be processed. The clamps of the shaft workpiece have three-jaw chucks, four-jaw single-action chucks, active clamping toggle chucks, and gear teeth. , Top, three-jaw toggle chuck, etc. The clamping of the disc-like workpiece has adjustable jaws and adjustable speed chucks. (Currently, hydraulic chucks are mostly used to install soft jaws for processing materials)

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

(1) One part or a group of workers, the part of the process that is completed in a working place for one or several workpieces at the same time is called a process.

The basis for distinguishing processes is whether the work place changes and whether the work is consecutive.

(2) Under the condition that the processing appearance and the processing things are unchanged, the part of the process content that is completed in succession is called a work step.

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

Process information refers to all kinds of information obtained through process processing.

This information includes: selection of process preparation tools; processing plans (including tool paths, cutting usage, etc.) and compensation plans.

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

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

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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 parts drawings;

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

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(4) Preparation of CNC machining technology plan;

(5) Confirmation of working steps and feeding roads;

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(6) Select the type of CNC machine tool;

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

(8) Confirmation of cutting parameters;

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

(10) The first trial processing and on-site problem handling;

(11) Finalization and filing of technical documents for CNC machining process