Problem: The flick knife overcuts
During processing, the knife often flicks out at the corner, causing overcutting. If reasonable tools and processing methods are used, the probability of the knife flicking can be reduced.
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Elastic tool position and processing overcut
As shown in the figure below, Figure A shows the state of the tool when machining a relatively flat position. When the machine reaches position B and makes an emergency stop to prepare for reverse machining, the tool will deform due to inertia, resulting in a straighter position at position B. The knife cuts everywhere.
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Knife icon
The relational expression of tool deformation:
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From the above formula, we can know that there are three main factors that affect tool deformation:
L - tool length
D - tool diameter
P - force on the tool
L - tool length
It can be seen from the formula that the relationship between the deformation of the tool and the length of the tool is the third power. For a tool with the same diameter, when the length of the tool is doubled, the deformation will increase by three times.
During processing, shorten the tool length as much as possible to reduce the risk of tool flicking.
D - tool diameter
It can be seen from the formula that the deformation amount of the tool is related to the fourth power of the tool diameter. For a tool of the same length, when the tool diameter is doubled, the deformation amount will increase by 4 times.
When processing, if possible, choose large-diameter tools or use stronger tools for processing to reduce the risk of tool flicking. (As shown in the right picture below: A uses a hot cord and tapered neck cutter, and B uses a tool with a strengthened handle)
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P - force on the tool
It can be seen from the formula that the deformation of the tool is directly proportional to the force it experiences during processing. Reducing the force experienced by the tool can reduce the probability of the tool springing. The following methods can be used to reduce the force experienced by the tool during processing.
Reduce force analysis:
Cutting is a process of shear deformation. Each material has its own strength (σ). To separate the material, the external strength must be greater than the material itself.
σ=F/S
σ : Strength of material
F: force
S: contact area
It can be seen from the above formula that the force (F) exerted on the tool is directly proportional to its contact area (S) with the workpiece. To reduce the force on the tool, it is necessary to reduce the contact area between the tool and the workpiece.
Reducing force example 1:
Use the tool path corner function or increase the R position to reduce the load on the tool at the corner position, thereby reducing the chance of the tool flicking.
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Reduce force example 2:
When processing deeper positions, a smaller feed amount and a thin R-angle tool can be used to reduce the force on the tool during processing and reduce the risk of tool flicking.
The picture below is a comparison of the contact points with the mold material when using D50R6 tools and D50R0.8 tools to process the same depth. It can be seen that using thin R-angle tools to process deep workpieces can reduce cutting force more than large R-angle tools.
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Summarize:
Comprehensive use of the three relevant factors that affect tool deformation (tool length, tool diameter, cutting force) can reduce the probability of tool deflection, increase processing time, and obtain better processing accuracy and surface roughness.
