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1. What is down milling? What is up milling? What are the characteristics of the down-cut and up-cut milling of CNC machine tools?
Climb milling: the horizontal component force Fx of the cutting force F is the same as the f in the feed direction. This milling method
Up-cut milling: the horizontal component force Fx of the cutting force F is opposite to the feed direction f, this milling method
Climb milling features:
(1) It is easy to produce turbulence, and it is necessary to add a down-cutting mechanism. (Because of the gap between the screw and the mother-in-law)
(2) The surface quality of the processing is higher than that of the reverse milling. (Applicable to finishing)
Up-cut milling features:
(1) High work stability, no need for up-cut milling mechanism
(2) The surface quality of the processing is lower than that of the down milling (the tool wears quickly)
2. What are the methods of feeding and retracting during CNC milling?
The main ways to retreat are as follows:
(1) Directly enter and retract along the Z-axis direction of the coordinate axis
(2) Infeed or retract in a given vector direction
(3) Feeding or retracting in a straight line along the tangential direction of the surface
(4) Feeding or retracting along the normal direction of the surface
(5) Infeed or retract in the direction of the arc segment
(6) Feeding along a spiral or diagonal line
For profile machining with high machining accuracy, the tool should be selected along the tangential direction of the surface or in the direction of the arc. This will not leave a knife mark on the workpiece feeding or retracting. Affect the surface finish quality of the workpiece.
3. What factors should be considered when determining the feed route of the milling cutter?
The feed route includes two steps: in-plane feed and deep feed. For in-plane feed, the outer contour is cut from the tangential direction, and the concave contour is cut from the circular arc. On a two-axis CNC milling machine, there are two methods for milling a plane groove cam: depth feeding: one method is to mill back and forth in the xy or (yz) plane and gradually feed to a given depth; the other method is First make a process hole and then feed the specified depth from the process hole.
4. What is the principle for determining the starting point, return point, and cutting point and cutting point of the program during CNC milling?
(1) Starting point, return point (determination principle)
In the same program, the starting point and the return point are preferably the same. If the processing of a part requires several programs to complete, then the starting point and the returning point of the several programs are preferably identical, so as not to cause processing operations. trouble. It is also preferable to set the coordinate values of the starting point and the return point to be zero in both the X and Y values, which makes the operation convenient.
(2) Principle of entry point selection
The tool is not damaged during the process of cutting or cutting the surface. In general, for roughing, the highest corner within the surface is selected as the point of entry for the surface. Because the cutting allowance at this point is small, it is not easy to damage the tool when feeding. For finishing, select a corner point with a gentle curvature in the surface as the point of entry for the surface. Because at this point, the tool is subjected to a small bending moment and it is not easy to break the tool.
(3) Principle of cutting out point selection
Mainly consider the continuous and complete machining of the surface and the non-cutting processing time between the surface and the surface machining 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 machined as an open surface, the two corner points of the surface can be used as the cut-out point. According to the above principle, if the surface to be machined is a closed surface, only one corner of the surface is the cut-out point, automatically The system is usually automatically determined during programming. (There is a hint at the knife in the mastercam. It is very convenient to solve these problems)
5, CNC lathe fixture selection?
The three-jaw chuck and the four-jaw single-action chuck fixture are selected according to the type of workpiece to be machined. The clamp of the shaft type workpiece has a three-jaw chuck, a four-jaw single-action chuck, an automatic clamping dial, and a tooth. , top, three-jaw dialing chucks, etc. The clamps of the disc type workpiece have adjustable jaws and speed adjustable chucks. (Currently use hydraulic chucks, soft claw processing materials)
6. What are the processes and work steps? What are the elements that make up the process and the steps?
(1) One or a group of workers, the part of the process that is continuously performed on one or several workpieces at a work site, is called a process.
The division process is based on whether the work site changes and whether the work is continuous.
(2) In the case where the processing surface and the processing tool are unchanged, the part of the process that is continuously completed is called a step.
7. What is process information? What is included in the process information?
Process information refers to various information obtained after processing through the process.
This information includes: process preparation tool selection; processing solutions (including the route, cutting amount, etc.) and compensation programs.
The accumulation of processing practice experience is an effective way to obtain process information.
The basis for dividing the work steps is whether the machined surface and tools are changing.
8. What are the main contents of the CNC machining process?
(1) Select and determine the content of CNC machining;
(2) Process analysis of the numerical control machining of the part drawing;
(3) Mathematical processing of the part graphic and determination of the programmed size setting value;
(4) Formulation of CNC machining process plan;
(5) Determination of work steps and feed routes;
(6) Select the type of CNC machine tool;
(7) Selection and design of tools, fixtures, and gauges;
(8) Determination of cutting parameters;
(9) Preparation, verification and modification of the processing program;
(10) Processing of the first piece of trial processing and on-site issues;
(11) Stereotype and archive of CNC machining process technical documents.
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