The Detection of Tool Breakage in Milling Operations

Abstract

The paper describes a rather simple and efficient algorithm for processing the milling force signal to detect cutter breakage. Using sampling synchronized with cutter teeth the basic variation per tooth is removed by calculating average forces per tooth. The first difference of these forces detects both breakage and some sudden changes in cutting conditions (cornering, milling over a slot). The second difference distinguishes between the two. The algorithm is illustrated by computational simulations as well as by measurements in milling tests.

Discrete-time Model Reference Control of Milling Forces under Fractional Order Holds. Part I: Known Plant

“…Also, when a parameter of the system changes abruptly (in this case the axial depth of cut) the model-reference control leads to large output overshoots, due to the intrinsic structure of the output. Thus, if the reference force is selected near the tool breakage limit, the large overshoot would lead to tool breakage [2,3]. In that case, some 'a priori' information about the work-piece geometry is required to design a successful control, as in [9], where a CAD model of the work-piece is used to modify the control command when the axial depth of cut changes in order to minimize the overshoots due to abrupt changes in the transfer function…”

“…The advantage of using a FROH instead of a traditional ZOH is that FROHs incorporate an additional degree of freedom, the gain of the FROH, which can be used to modify the overall closed-loop response of the system, improving, for instance, the stability of the discrete zeros or reducing the overshoot or bad transient responses which could lead, for example, to break the cutter shank, tool breakage or tool wear, [2,3]. Hence, the model reference control is the designed from the so obtained FROH based discrete model.…”

Discrete-time model reference control schemes of milling forces using fractional order holds

“…This fact modifies the overall closed-loop response of the system, improving, for instance, the stability of the discrete zeros or reducing the overshoot, avoiding tool breakage and tool wear and achieving the required surface on the workingpiece in the milling process and better inter-sample behavior [7]. Hence, the model reference control is the designed from the so obtained scheme based discrete model.…”

Adaptive Control of Milling Forces under Fractional Order Holds

“…This can lead to avoid overloading of the insert, because the maximum removed chip-thickness would not increase the principal tensile stress in the cutting wedge beyond the ultimate tensile strength of the tool material, this can also lead to prevent fracture of the shank, and fulfill the machine tool requirements, such as power and torque availability [6]. Moreover, if the reference force is selected near the tool breakage limit, the large overshot lead to tool breakage [1,2,6]. Then, if the overshoot of the system response is reduced, the reference force can be increased, improving the time production requirements.…”

“…The advantage of using a FROH instead of a traditional ZOH is that FROHs incorporate an additional degree of freedom, the gain of the FROH, which can be used to modify the overall closed-loop response of the system, improving, for instance, the stability of the discrete zeros or reducing the overshoot or bad transient responses which could lead, for example, to break the cutter shank, tool breakage or tool wear, [1,2]. Hence, the model reference control is the designed from the so obtained FROH based discrete model.…”