Self-vibratory Drilling Research Articles

Experimental study on drilling basalt with self-vibratory drilling head

Based on the goal of improving the rock breaking ability when drilling asteroid rock samples under limited energy conditions, this paper proposes a method of drilling rock using self-vibratory drilling head and develops a small self-vibratory drilling head for drilling rock. In order to analyze the dynamic characteristics of drilling rock with self-vibratory drilling head, a rock model hypothesis that the rock consists of a series of micro-segment uniform continuous media is put forward. Base on the hypothesis, the model of drilling rock is constructed, the stability lobes diagram of self-vibratory drilling head drilling basalt is plotted, and the energy mechanism of drilling rock system with self-vibratory drilling head is discussed. The comparison tests of drilling basalt by three kinds of self-vibratory drilling head with different spring stiffness and the conventional method are carried out. The rotational speed is a variable in the comparative tests. The test results show that under the specific rotational speed and spring stiffness, self-excited vibration is produced in self-vibratory drilling head drilling basalt. When self-excited vibration drilling is conducted, although the amplitude fluctuation range of the drilling thrust force is wider than that of conventional drilling, the average drilling thrust force is smaller than the conventional drilling. The amplitude of drilling thrust force increases with an increase in spring stiffness. The method of drilling rock by self-vibratory drilling head is proved to be a potential method for viable drilling of asteroid rock samples.

Моделирование динамики вибрационного сверления с контролем дробления стружки по размаху колебаний

Chip control is one of the most important problems in deep hole machining. A special self-vibratory drilling head may be used to implement chip control. However, chip control via a self-vibratory head is only possible for specific manufacturing parameters, which limits the use of this method. This paper presents an algorithm for adaptive control of vibration drilling dynamics intended to facilitate chip control and driven by peak-to-peak vibration displacement. We provide a mathematical model of drilling using a self-vibratory head, taking into account the facts that the cutting force is a non-linear function of the chip thickness and that there is additional non-linearity introduced when the drill is exiting the material. In order to validate the efficiency of the algorithm proposed, we performed numerical simulations for a wide range of variable processing parameters. The simulation results obtained confirm that the strategy proposed is efficient for chip control.

Vibratory drilling with digital adaptive control

High standards and efficiency of deep hole drilling used for hard-to-machine metals and alloys could not be achieved if chips are not segmented in the cutting zone. Chip control could be achieved through transmission of harmonic vibrations to the drill in direction of its rotating axis. One way to maintain these vibrations is to replace a drill chuck with a special self-vibratory drilling head, which includes an elastic element that allows axial movement of the tool. The right stiffness value of an elastic element and appropriate machining conditions could lead to oscillation self-excitation of a drill due to the regenerative mechanism. It is advisable to support this mechanism with a control action defined within the feedback loop, which provides process quality necessary for chip control in the broad range of process parameters. This work analyzes adaptive control algorithm for vibratory drilling process dynamics where control action over an oscillating system is proportional to drill axial vibrational velocity, and a feedback gain is determined in the adaptation loop. Dynamics modeling of a closed-loop nonlinear system “elastic system-machining process-control system” is carried out for cases with or without control proving effectiveness of control algorithm. The model was used to analyze how control system analog-to-digital conversion parameters influence vibratory process quality. Requirements, which ensure control system achieves a control aim, were approximately stated for capacity and response limit for analog-to-digital conversion.

Dynamic model of high speed machining spindle associated to a self-vibratory drilling head influence of drill torsional-axial coupling

The drilling of deep holes with small diameters remains an unsatisfactory technology, since its productivity is rather limited. The main limit to an increase in productivity is directly related to the poor chip evacuation, which induces frequent tool breakage and poor surface quality. Retreat cycles and lubrication are common industrial solutions, but they induce productivity and environmental drawbacks. An alternative response to the chip evacuation problem is the use of a vibratory drilling head, which enables the chips to be fragmented thanks to the axial self-excited vibration. Contrary to conventional machining processes, axial drilling instability is sought, thanks to an adjustment of head design parameters and appropriate conditions of use. In this paper, self-vibratory cutting conditions are established through a specific stability lobes diagram. A dynamic high-speed spindle/drilling head/tool system model is elaborated on the basis of rotor dynamics predictions. The model-based tool tip Frequency...

Machining prediction of spindle–self-vibratory drilling head

The drilling of deep holes with small diameters remains an unsatisfactory technology, since its productivity is rather limited. The main limit to an increase in productivity is directly related to the poor chip evacuation, which induces frequent tool breakage and poor surface quality. Retreat cycles and lubrication are common industrial solutions, but they induce productivity and environmental drawbacks. An alternative response to the chip evacuation problem is the use of a vibratory drilling head, which enables the chips to be fragmented thanks to the axial self-excited vibration. Contrary to conventional machining processes, axial drilling instability is sought, thanks to an adjustment of head design parameters and appropriate conditions of use. A dynamic high-speed spindle/drilling head/tool system model is elaborated on the basis of rotor dynamics predictions. In this paper, self-vibratory cutting conditions are established through a specific stability lobes diagram. Investigations are focused on the drill's torsional–axial coupling role on instability predictions. A generic accurate drilling force model is developed by taking into account the drill geometry, cutting parameters and effect of torsion on the thrust force. The model-based tool tip FRF is coupled to the proposed drilling force model into an analytical stability approach. The stability lobes are compared to experimentally determined stability boundaries for validation purposes.

Contribution to the environmental performance of the dry-vibratory drilling technology

The self-vibratory drilling (SVD) is an innovative technology that allows increasing the productivity, without coolant. The aim of this paper is to prove that the environmental impacts of SVD are significantly less than those of traditional drilling (TD) and to quantify them. The study is based on a life cycle analysis of both processes. The major contributor to the environmental impacts in TD is the coolant. The new major contributors in SVD are the twist drills. A model that links the lifespan of the twist drills and the environmental impacts of SVD has been developed to support decisions for R&D.

Model-based cutting prediction for a self-vibratory drilling head - spindle system

The drilling of deep holes remains an unsatisfactory machining operation due its limited productivity. This manufacturing process requires the chips to be evacuated through the use of retreat cycles and high-pressure lubrication, which is problematic both for productivity and the respect of the environment. An alternative response to the chip evacuation problem is the use of a vibratory drilling head which enables the chip to be split thanks to the drill's axial vibration. The high-speed drilling operation requires specific cutting conditions to be determined in order to maintain self-excited axial vibration throughout the drilling process. The prediction of adequate cutting conditions is determined on the basis of the frequency characteristics of the spindle/self-vibratory drilling head and the dynamics of the cutting process. It can be expressed in terms of a specific stability diagram indicating the zone of stable self-excited axial vibration. The aim of this study is to develop a high-speed spindle/drilling head/tool system finite element model to evaluate the system's dynamic characteristics and the adequate cutting conditions allowing stable self-excited axial vibration. The model is elaborated on the basis of rotor dynamics prediction, and takes into account the interfaces between system components, using the receptance coupling method. Using the model, adequate cutting conditions are determined by integrating the model-based tool tip transfer function into the chatter vibration stability approach proposed by Budak and Altintas. The simulated results are validated by performing vibration and drilling tests. The proposed model can be used to accurately evaluate the dynamic performance of the spindle/self-vibratory drilling head and can also be used to design an optimised spindle/drilling head for a given drilling process.

Model-based operating recommendations for high-speed spindles equipped with a self-vibratory drilling head

The drilling of deep holes requires the chips to be evacuated using retreat cycles and lubrication, which is problematic for both productivity and the environment. An alternative response to the chip evacuation problem is the use of a vibratory drilling head, which enables the chip to be split thanks to the axial self-excited drill, and hence it can easily be evacuated from the hole. The vibratory drilling head is composed of a specific tool holder with adjustable axial stiffness. In this paper, a dynamic high-speed spindle/drilling head/tool system model is elaborated on the basis of rotor dynamics predictions. The dynamic properties of interfaces between system components are identified by the receptance coupling method and integrated into the model. The model is validated by comparing the numerical FRF with experimental results. Then adequate self-vibratory cutting conditions are established by integrating the model-based tool tip FRF into the chatter approach of Budak–Altintas. Spindle rolling bearing lifespan is also investigated in order to guarantee a rational use of the spindle-tool set with respect to industrial lifespan.

Research on Breaking Chip and Drilling Force for High Temperature Alloy Based on Self-Vibratory Drilling Head

Problems to evacuate chips will arise from manufacturing deep holes, especially for small diameters. Such problems induce frequent tool breakage and poor surface quality. The vibratory drilling enables the chip to be split into small elements thanks to the axial vibrations of the drill, self-maintained by the cutting energy. This research aims to improve breaking chip concerning high temperature alloy by vibraiont drilling as well as to establish a drilling technology. The development of breaking chip technology was presented. By the aid of the self-made vibrating drilling table, the axial vibration drilling was experimented on high temperature alloy with different parameter of vibration drilling. The breaking chip effect of vibration cutting was studied, and the axial drilling force and torque of vibration drilling were analyzed. The relation of each parameter and its effect on machining process was theoretically discussed. The experiment results show that vibration drilling is in favor of breaking chip, making the volume of chip small, and removing chips fluently, and the change of drilling force is relatively steady with some drilling parameters.

Identification of thrust force models for vibratory drilling

Among the scientific problems in drilling, determining thrust forces for any drill geometry and any workmaterial remains an issue. This question is especially critical in the context of the self-vibratory drilling (SVD) technology, since thrust force governs the trajectory of cutting lips. In order to predict the dynamical behaviour of the self-vibratory drilling head (SVDH), a numerical simulator has been developed in the laboratory. In order to predict the relevant behaviour of the SVD operations, a good accuracy of the thrust force model is highly necessary. The aim of the paper is to propose an experimental methodology to identify a thrust force model for one pair “drill–workmaterial” depending on the uncut chip thickness. This methodology proposes to divide cutting edges into several parts in order to define the local contribution of this part to the macroscopic thrust force. Local models are identified during the penetration of the drill. From a limited number of experiments with various feeds, it becomes possible to identify all the coefficients of an accurate thrust force model.

Influence of the ploughing effect on the dynamic behaviour of the self-vibratory drilling head

The vibratory drilling process enables the chip to be split into small elements thanks to axial vibrations of the drill self-maintained by the cutting energy. The vibrations should remain stable when machining, and damping be removed or very limited—particularly the ploughing force induced by the chisel edge and the flank face. To predict the behaviour of the self-vibratory drilling head, a new ploughing model has been developed. In this model, the interaction of the tool flank face with the machined material can be perceived as a virtual cutting edge that produces an additional thrust force and an additional removal of material. This model improves the cutting force models and is integrated into a numerical vibratory drilling simulator. The model shows a good correlation with experimental results.

A numerical simulator to predict the dynamical behavior of the self-vibratory drilling head

The manufacturing of deep holes has to face problems to evacuate chips, especially for small diameters. Such problems induce frequent tool breakage and poor surface quality. The vibratory drilling enables the chip to be split into small elements thanks to the axial vibrations of the drill, self-maintained by the cutting energy. Thus, chips are easily evacuated from the hole. A specific tool holder with an adapted axial stiffness has been developed in order to investigate this drilling process. The cutting conditions are predetermined in order to lead to axial vibrations with a stable frequency and amplitude. During a period, the amplitude of the vibrations is higher than the feed per revolution, which enables the cutting edges to jump out of the work material. The vibrations are self-maintained and remain stable if some disturbances are absent or very limited such as the friction of the drill against the work material along its margins, the ploughing force induced by the chisel edge, the ploughing force induced by clearance face, etc. The objectives of this paper are (i) to model the dynamical behavior of the self-vibrating drilling head, the cutting and ploughing forces, and the material removal, (ii) to foresee with a numerical simulator the cutting conditions which generate good vibrations, (iii) to validate the numerical simulator with a experimental round of test. This work has also shown that the productivity of the drilling is improved by the use of the vibratory drilling. Deep hole (ratio deep/drill diameter > 20 ) can be drilled with this new technology without any coolant and any retreat cycle with the same quality as a conventional drilling operation.