Process and Programming in the Training of CNC Lathes

CNC lathe

When numerical control technology beginner groups practice on CNC machine tools, especially those of higher vocational college students, although related professional technical courses have been studied, due to the lack of practical experience in production, considering the problem is not comprehensive enough, it is difficult to learn what they have learned. The application of knowledge to each other is good, often resulting in parts that cannot be processed to achieve the intended purpose. Now through the training examples on the combination of process and programming issues analysis and discussion.

1. Training conditions

(1) Shenzhen equipment: "GTC2E" CNC lathe.

(2) Program system: "SANYING" CNC lathe simulation system.

(3) Practical example: boring knife handle.

(4) Example blank: φ26mm round wood.

(5) Parts drawings: The boring tool handle parts are shown in the drawing.

2. Process planning process

(1) First of all, we must read the pattern carefully and divide the part drawing to see that the handle contour is composed of a truncated cone, a cylinder, and three arc-connected surfaces. Determine the origin of the workpiece coordinates and calculate the coordinates of each vertex as well as the coordinates of the connection point of the curve. See the note on the part drawing.

(2) The choice of tool is mainly to consider whether the tool structure and size can interfere with the part where the workpiece has been machined. In cutting, once the cutting point deviates from the tool tip, overcutting may occur. Shaped tools may be considered for smaller profile curves.

The handle is a non-single curved profile connected by three arcs. The turning angle of the turning tool and the selection of the auxiliary declination angle should be considered when turning with an external turning tool. The size of the main declination angle determines the shape of the workpiece and the selection of the auxiliary declination angle. Consider whether it interferes with the contour of the machined surface. The calculated declination angle should be greater than 13.4o. Therefore, two types of cutters, the right-hand right-handed knife with the main declination angle of 90o and the declination angle of 15o, and the cutting knife, were selected.

(3) According to the selected tool division process, the outer right right-handed tool is the main machining tool. All the parts that can be machined should be machined as far as possible, and then the taper and cut of the tool change should be changed, and the width of the knife should be considered. This can reduce the number of tool changes, compressed Lee stroke time.

(4) It is also necessary to consider the process of roughing and finishing. If the entire contour cycle program is used, the programming is simple, but too many idles in the first few cycles are not conducive to the high efficiency of CNC machining. Therefore, the R8mm ball head on the right end should be roughed with the car cone method, and then the R30mm concave arc should be used with the roughing cycle program. After the rough machining cuts most of the remaining amount, the surface of the car is finished again to ensure the machining accuracy and surface roughness requirements.

(5) Choosing the cutting amount rationally is generally under the premise of guaranteeing the processing quality and the tool life, give full play to the performance of the machine tool and the cutting performance of the tool, so that the cutting efficiency is the highest and the processing cost is the lowest. During roughing, low cutting speeds, large backsides, and feedrates are used. When finishing, high cutting speeds and smaller feedrates are used.

CNC lathe

3. Considerations in programming and training

(1) Programming according to process considerations, programming is to give every pass in the step. First determine the coordinate origin of the workpiece (center point of the right end of the handle), and calculate the coordinates of each folding point and the coordinates of the connection point of the curve. See the note on the part drawing. Correctly give the starting point for each step, that is, the initial position of the tool when machining a certain part. See the programming of N00040, N00110, N00210, N00300 in the example program. The correctness of the starting point directly affects the programming and the formation of the contour of the surface to be machined.

(2) According to coarse, fine machining and selected tool division process programming, rough machining program N00040 ~ N00200, remove most of the machining allowance; finishing machining program N00210 ~ N00280, improve the surface quality, by T01 knife (external right-handed knife , Deputy angle 15o) Complete; Cone and cutting procedures N00300 ~ N00340, by T02 knife (cutting knife, knife width 4mm) to complete. Consider the actual tool nose of the cutting knife. Consider the influence of the knife width when programming. See the N00300, N00320 and other programs in the example program.

(3) The G00 program cannot be directly used to make the tool directly reach the workpiece surface. The tool and the workpiece surface are also not allowed to use the G00 program to move under zero contact, but the G01 program should be used. See example program N00140, N00220, N00270, N00310 and other procedures. This can effectively avoid the possible collision between the tool and the workpiece, which can cause the tool to scratch the workpiece surface or wear the tool.

(4) Accurate tool setting, numerical control programming is based on the tool tip point as a reference along the contour of the part of the trajectory. Before the training process, the correct tool setting is adopted to make the coordinates of the tool nose coincide with the coordinates of the workpiece origin. Only in this way can the correct part contour be obtained after the tool has been programmed to operate.

(5) Enter the programming simulation. The simulation is to see the contour trace simulating the tool tip sculpted by programming. In the process of cutting, whether the cutting edge interferes with the workpiece is difficult to react in the simulation. The simulation trajectory is correct, and the contour of the final machined workpiece may not be complete. That is to say, the simulation can verify whether the programming is correct and cannot reflect all the over-cutting interference phenomena in the machining process.

4. Example programming

The programming of the boring tool handle on the "GTC2E" CNC lathe is as follows.

N00010 M03 S600

N00020 G00 X60 Z20

N00030 T1(external right-handed knife, declination angle 15o)

N00040 G00 X16 Z2

N00050 G24 X36 W-10 F50

N00060 U-5

N00070 U-5

N00120 G00 X37 Z2

N00130 G22 L2

N00140 C00 U-31

N00150 G0l W-2 F60

N00160 G03 U15.2 W-5.5 R8

N00170 G03 U4.4 W-46.9 R85

N00180 G02 U2.4 W-17.6 R30

N00185 G01 U4

N00190 G00 W72

N00200 G80

N00210 G00 X0 S1000

N00220 G01 Z0 F40

N00230 G03 X15.2 Z-5.5 R8

N00240 G03 X19.6 Z-52.4 R85

N00250 G02 X22 Z-70 R30

N00260 G01 Z-95

N00270 G0l X26

N00280 G00 X60 Z20 S500

N00290 T2 (cutting blade, knife width 4mm)

N00300 G00 X24 Z-84

N00310 GOl X17 F30

N00320 G01 X16 Z-94

N00330 G01 X0

N00340 G00 X60 Z20

N00350 M05

N00360 M02

5 Conclusion

In summary, the numerical training process can be summarized as the following steps: part drawing analysis → drafting process plan → programming and inputting → countersinking → simulation → machining parts. In the first training, do not blindly pursue complex contour artifacts. Imagine that all procedures are used. It is often difficult to achieve success. Instead, you should select a few representative surfaces to practice, and you can continue to practice on this basis. Through example training, it is possible to formulate the process plan, select the tool, program and process the training work piece according to the part drawing, so as to achieve the purpose of inferring the contrary, and to obtain a multiplier effect.