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CNC machining is always over-cutting, how to control it?

    1.The common problem of over-cutting of the spring knife in processing

    In the process of machining, there is often the phenomenon of overcutting at the corners. If a reasonable tool and processing method are used, the chance of the knife can be reduced.(ALUMINUM METAL CASE PANEL AMPLIFIER)

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    2. Problem analysis and countermeasures

    As shown in the figure below, picture A is the state of the tool when the tool is in a relatively flat position. When the machining stops at the B position and is ready to reverse machining, the tool will deform due to inertia, resulting in a straighter position at the B position. Overcut with bullet knife.

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    Relational expression of tool deformation:

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    From the above formula, we can know that there are three main factors that affect the deformation of the tool: L – the length of the installed tool D – the diameter of the tool P – the force on the tool
    L – knife length
    It can be seen from the formula that the relationship between the deformation amount of the tool and the length of the installed tool is the third power. For a tool with the same diameter, when the long knife is doubled, the deformation amount will increase by 3 times.
    When machining, shorten the length of the tool as much as possible to reduce the risk of snapping.
    D – Tool diameter
    It can be seen from the formula that the relationship between the deformation of the tool and the diameter of the tool is the fourth power. For the same length of the tool, when the diameter of the tool is doubled, the deformation will increase by 4 times.
    When machining, if possible, choose a large-diameter tool or use a reinforced tool for processing to reduce the risk of the knife.(ALUMINUM ENCLOSURE CUSTOM)

    (As shown in the right figure below: A uses a hot cable and a taper neck knife, and B uses a tool with a stronger shank for processing)

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    P – Force on the tool
    It can be seen from the formula that the amount of deformation of the tool is proportional to the force on the tool during processing. Reducing the force on the tool can reduce the chance of the tool bouncing. The following methods can be used to reduce the force on the tool during processing.
    Reduced 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 strength of the material itself. σ = F / Sσ : strength of material F : applied force S : contact area

    It can be seen from the above formula that the force (F) on the tool is 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.
    Reduced force example 1:
    Use the tool path corner function or the method of increasing the R position to reduce the load of the tool at the corner position, thereby reducing the probability of bouncing the knife.

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    Reduced force example 2:
    When machining a deeper position, a tool with a smaller feed rate and a thin R angle can be used to reduce the force on the tool during processing and reduce the risk of the knife.
    The figure below shows the comparison of the contact position with the mold material when using the D50R6 tool and the D50R0.8 tool to process the same depth. It can be seen that using a thin R-angle tool to process a deep workpiece can reduce the cutting force more than a large R-angle tool.

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    Summarize:

    The comprehensive use of three related factors that affect the tool deformation (tool length, tool diameter, cutting force) can reduce the probability of tool bounce, increase the processing time, and obtain better machining accuracy and surface roughness.

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