This article discusses three knowledge points and hopes to inspire everyone.
1. Under what circumstances should G41G42 be used?
2. How to choose G41G42
3. Selection of tool tip orientation
1. Why do you need to use G41G42 when programming a car?
When processing workpieces with shapes such as cones or arcs on a CNC lathe, there will be dimensional errors between the correct program written and the actual machined parts.
This error is caused by the tool tip arc.
To clarify this issue, we need to start with CNC lathe tool setting. Please see the diagram below:
picture
We know that most turning tool tips will have an arc R, as shown in the picture above:
For tool setting in the Z-axis direction, point A of the tool tip contacts the end face of the part.
In the X-axis direction, point B of the tool tip contacts the outer circle of the part.
When actually cutting the end face or outer circle, the Z-direction or X-direction size of the part is determined by point A or B. At this time, the tool tip fillet has no effect on the processing size.
However, when used to process workpieces with chamfers, tapers or arcs, the actual cutting points of the tool are the tangent points on the tool tip arc AB, not point A or point B during tool setting. As shown below:
picture
Then when processing parts with shapes such as cones or arcs, you need to use G41/G42 tool nose radius compensation.
Okay, let's explain the principle clearly, and then move on to the second knowledge point.
2. How to choose G41 G42 when programming?
For machine tools, it is divided into:
Front tool rest
Rear tool rest
Parts are divided into:
car shape
car inner hole
Then these two classification methods can be combined into the following four situations. Please refer to the following two pictures carefully:
1. Rear tool rest: The tool cuts on the right side of the workpiece
2. Front tool rest: The tool cuts on the left side of the workpiece
3. Rear tool rest: The tool cuts on the left side of the workpiece
4. Front tool rest: The tool cuts on the right side of the workpiece
picture
Remember the picture above carefully
Simple?
This trick is really simple, but very effective!
Okay, let's go straight to an example of a finishing program:
picture
%
O0001
T0101
S500 M03
G0X60.Z2.
G01 G42 Z0 F0.1. (Tool arc radius compensation)
X120.Z-150.
X200.Z-180.
Z-260
G0G40X205.Z2. (cancel radius compensation)
M30
%
3. Selection of tool tip orientation
During programming, (G41/G42) tool radius compensation is added to the program.
At this point you may be asking? ---How does the machine tool identify tool radius compensation R?
This requires us not only to add G41 or G42 to the program, but also to enter the tool tip arc R and tool tip orientation of the corresponding tool in the tool compensation panel.
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The "knife tip orientation" appears here
I intercepted the tool tip orientation diagram from the manual of the turning machine tool, as follows:
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How to apply it specifically, as shown in the diagram below:
Outer circle straight car
picture
Internal hole positive turning
picture
The above is our longest-used tool location number, that is to say:
Positive outer circle: 3
Front inner hole: 2
We use G41 or G42 in the program, and enter the tool tip arc R and tool tip orientation of the corresponding tool in the tool compensation panel.
As shown in the O0001 program above, if the tool nose arc R=0.8, I need to enter the tool nose arc R corresponding to the T0101 tool and the tool nose orientation in the tool compensation panel.
picture
By running the O0001 program in this way, the machine tool will use the G42 function to eliminate overcutting or cutting residue.
Okay, this concludes the explanation of G41/G42 in turning.
Let's share a case of rough and fine turning of a CNC macro program to inform G41/G42 of matters needing attention in programming.
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The procedure is as follows:
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Note 1: Arc R compensation needs to be in the G00 or G01 state, and cannot be compensated under the G02 or G03 command.
Note 2: Logout also needs to be in the G00 or G01 state, and cannot be logged out under the G02 or G03 command.
