Gun Drill Research Articles

Deep-hole gun drilling mechanics model of Ti6Al4V alloy based on Johnson and Cook flow stress model

Drilling mechanics model has always been the key and difficult point in the research field of gun drilling. In this paper, through theoretical analysis and processing experiments, the gun drilling mechanics model of Ti6Al4V titanium alloy is studied. On the one hand, based on the Oxley cutting model and the Johnson-Cook flow stress model, this paper takes Ti6Al4V titanium alloy as the research object and use the “microelement” method to establish the mechanical model of gun drilling, which includes cutting parameters, tool geometric parameters and material mechanical properties. On the other hand, the drilling model considers the influence of process damping and verified by experiments. The results show the calculated value of the model is consistent with the experimental value and the error is within the acceptable range. The model provides a theoretical basis for the prediction of drilling force, tool analysis and straightness error analysis.

On the influence of thermal processes on the dynamics of a drill during deep hole machining

Deep drilling process has been studied and dynamic features of interaction the cutting part of the gun drill with the detail have been identified. Thermal processes of cutting and heat sinking in the interacting chains were analyzed: “heat source – workpiece”; “heat source - chips”; heat source – tool”; “heat source – cooling liquid”. It has been noted that the vibrations lead to the loss of dimensional accuracy of the part fabrication as well as hole surface quality. Mathematical dependence of the longitudinal and torsional oscillations of the cutting drill bit is determined and the influence of heat flow pulsations on the friction coefficients and cutting force is revealed.

Thermal phenomena and dynamic features of deep holes fabrication for connections of heat exchange tubes

Abstract Deep drilling process has been studied and properties of dynamic interaction revealed between the cutting part of the gun drill with the machined surface of the hole. It was found, that the oscillations cause lesser precision and poorer quality of the hole surface. Thermal processes of cutting and heat sinking in the interacting chains were analyzed. These theoretical estimates show influence of the heat flux pulsations onto friction coefficients and cutting force. Mathematical dependence of the longitudinal and torsional oscillations of the cutting drill bit versus the above factors was defined.

Gun-Drill Insertion in Drilling Deep Holes by Means of Multifunctional Machine Tools

The drilling of deep holes by means of gun drills is investigated so as to establish the parameters of the guide hole and its production. The rate of change in the load on the tool is proportional to the active length of the primary cutting edge. Assessment of the smoothness of tool insertion on the basis of the rate of change in the load on the tool is proposed.

A gun drill mechanics model analysis based on 15-5PH solid solution stainless steel

Referencing special energy model, a new gun drill mechanics model was established and the influence of the cutting parameters on axial force and torque was based on 15-5PH solid solution stainless steel through theoretical analysis and cutting tests. On the basis of the existing model, the model coefficients were modified under various cutting conditions and the integral area of the cutting edge was enlarged. The eccentricity at the bottom of the drill groove was taken into account in the integral area of the cutting edge. In the meanwhile, the torque calculation was simplified reasonably according to the theoretical analysis. The feasibility of the model was verified by experiments and the influence of cutting parameters on the axial force and torque was analyzed. The experiment data had shown that the relative error between the calculated values and the experimental values were within the acceptable range. The axial force and torque increased with the increase in cutting speed and feed rate.

Numerical Analysis and Optimization of Hole Roundness in Gun Drilling Deep Hole Machining

According to the actual situation of gun drill processing and the fact that the guide pad has effect on improving processing quality, optimized structure with three guide pads is designed. Finite element analysis method and characteristic matrix of mechanical model is used to deduce the formula of the rifling mark when the calculation accuracy is guaranteed. The results of two kinds of gun drill worked in the same situation are compared and analysed by simulation. From the result, gun drill with three guide pads is good at inhibiting the errors and improving the machining quality.

Improving Coolant Effectiveness through Drill Design Optimization in Gundrilling

Effective coolant application is essential to prevent thermo-mechanical failures of gun drills. This paper presents a novel study that enhances coolant effectiveness in evacuating chips from the cutting zone using a computational fluid dynamic (CFD) method. Drag coefficients and transport behaviour over a wide range of Reynold numbers were first established through a series of vertical drop tests. With these, a CFD model was then developed and calibrated with a set of horizontal drilling tests. Using this CFD model, critical drill geometries that lead to poor chip evacuation including the nose grind contour, coolant hole configuration and shoulder dub-off angle in commercial gun drills are identified. From this study, a new design that consists a 20° inner edge, 15° outer edge, 0° shoulder dub-off and kidney-shaped coolant channel is proposed and experimentally proven to be more superior than all other commercial designs.

Fabrication feasibility studies for first wall of Indian LLCB TBM

The conceptual design of the Indian Lead Lithium Ceramic Breeder (LLCB) Test Blanket Module (TBM) First Wall (FW) presents a single U-shaped component made of IN-RAFM steel having 65 square channels of 20 mm × 20 mm running along the toroidal and radial direction. There are 13 circuits; each circuit consisting of 5 channels with inlet on the 1st channel of one side and the outlet on the 5th channel of other side. The conventional machining route with innovations in the existing technique was explored to develop the method to make channel mock-ups for FW application. This developed technique includes initial pre-machining and milling of higher thickness plates, making square channels by gun drilling followed by wire-cut EDM and final milling on the external surface and then hot bending into U-shape. Modified 9Cr-1Mo steel was the structural material used for this mock-up which has two flow circuits (each circuit of 5 channels). The other dimensions of this mock-up were chosen in such a way that functional requirements of full-sized FW would be fulfilled. During manufacturing, this mock-up was subjected to a series of inspection and non-destructive tests such as helium leak test and hydro-test at 150 bar pressure as a part of in-stage and final inspections. This paper describes the main activities carried out for the fabrication and factory acceptance tests of this U-shaped 10-channels TBM FW mock-up.

Simulation Analysis of RuT450 Drilling Force Based on LS-DYNA Gun Drilling

Cutting force is one of the most important parameters in the machining process, it significantly influenced machining precision of the workpiece, power consumed in the machining process, wear of the cutting tools and so on. There are many factors that affect the cutting force, such as the performance of the workpiece material, cutting speed, usage of the cutting fluid, etc. Single factor variable method was used in this paper, RuT450 was used as workpiece, welded cemented carbide gun drill was used as cutting force and LS-DYNA was used as simulation platform to established the cutting simulation model to analyzed the impact of the cutting speed and feed rate to the drilling force. Simulation results show that, at the low speed drilling stage, drilling force increases with the increase of the feed rate and decreases with the increase of the rotation feed, from the stress cloud it could be seen that the equivalent stress near the drill tip reached the maximum in the drilling process.

Effect of apex offset inconsistency on hole straightness deviation in deep hole gun drilling of Inconel 718

Abstract Hole straightness deviation is the critical performance indicator in deep hole gun drilling process, particularly in manufacturing of corrosion resistant alloys like Inconel 718 with high yield strength. Poor understanding on the root causes of straightness deviation and difficulty to reduce it has dramatically increased the complexity and the manufacturing cost of this manufacturing process. Due to the fast tool wear in machining of Inconel, gun drills have to be changed frequently after a very short drilling distance. However, it has been found that the gun drill tool geometry cannot be precisely controlled, as there is a lack of appropriate gun drill regrinding and measurement system. In this study, a customized gun drill regrinding system integrated with an in-situ gun drill measurement system is designed and developed to obtain high-quality gun drills with precisely controlled tool geometry. The effect of apex offset variation on the hole straightness deviation is studied through 12 unsupported gun drilling experiments at thin-wall positions of an Inconel 718 workpiece with 160 ksi yield strength. 4 types of apex offset variation conditions (consistent, reciprocating, decreasing and increasing) with 3 times of repetition tests are conducted, and the measurement results have shown that consistent apex offset leads to the smallest hole straightness deviation among all the conditions. Through a series of FEM analysis and further measurement of internal cylindricity of machined holes, it has been concluded that unbalanced cutting force components applied on the previous gun drilled hole due to the inconsistent apex offset will cause the new formed hole to be deviated toward thin wall, due to the relatively larger material deformation at the thin-wall side than at the thick-wall side.

Automated calculation of shaft flexure for a gun drill

For a gun drill, automatic calculation of the shaft’s parameters and flexure is proposed to prevent its contact with the surface of the hole being machined and so increase the tool life. A refined model of the forces and torque on the drill is employed.

On the question of the relationship between longitudinal and torsional vibrations in the manufacture of holes in the details

The article describes the features of the interaction between the cutting part of the tool and the part when processing deep holes. The description of the motion of the executive body is based on the second-order Lagrange equation. The differential equations of motion for five generalized coordinates derived. At the first stage of the study, only longitudinal and torsional oscillations were considered. With the use of Laplace images, a transfer function is obtained, taking into account the relationship between longitudinal and torsional oscillations. Graphically the relationship between the marked oscillations is shown. For an example, the frequency characteristic of a gun drill is brought.

A computational fluid dynamics (CFD) model for effective coolant application in deep hole gundrilling

Effective coolant application in deep hole gundrilling is crucial to prevent rapid degradation and failure of drills through high performance cooling, lubrication and chip evacuation. This paper presents a novel methodology to increase effectiveness of coolant application through strategic optimization of gun drill designs that leads to appreciable tool life improvement, based on computational fluid dynamics (CFD) analysis. Through the analyses of coolant flow characteristics and rheological properties, conventional designs of critical drill geometries like nose grind contour, coolant hole configuration and shoulder dub-off angle, which are detrimental to coolant application and hence tool life are determined. A new, optimized gun drill design for the drilling of deep holes on Ni-based alloys is proposed. All findings are experimentally substantiated.

The effects of dub-off angle on chip evacuation in single-lip deep hole gun drilling

Without proper chip evacuation, gun drills will fail under intense thermal and mechanical loading during deep hole drilling of high temperature superalloys like Inconel 718. In gundrilling, the efficiency in evacuating chips is governed by the geometry of gun drills that defines the hydraulic boundary conditions for coolant and chip flow. In this paper, we propose a novel computational fluid dynamics (CFD) model that is capable to simulate and quantify the chip transportation behavior under high pressure coolant for drill geometry optimization. This is demonstrated through a case study on improving the shoulder dub-off design of commercial gun drills, which have a high tendency in trapping chips at the hole bottom. A more effective design criterion for the shoulder dub-off is thus proposed.

Strength and Stiffness Calculation of Small Diameter Gun Drills

The results of strength and stiffness calculations of gun drills with steel and cemented carbide stems are presented. Four cross-sections of gun drills are examined and recommendation for selection of proper shape in terms of strength and stiffness is given. Finite element modeling of gun drills shown that the highest stress concentration is at the bottom of the V-shaped flute in the middle of the length of the stem. Gun drill testing under production conditions confirmed the results of finite element modeling.

Optimal Cross Section of a Hard-Alloy Core for a Gun Drill

The proposed approach to calculating the cross section of the hard-alloy core for a small–diameter gun drill ensures optimization of the core’s strength and rigidity.

Grinding Tungsten Carbide Used for Manufacturing Gun Drills

This paper presents a study of grinding cemented carbide DK460UF (91 % WC and 9 % Co), a material used to produce cutting tools with solid cutting edges. The aim is to establish the manufacturing conditions that lead to high surface quality. A model of the main factors that influence the grinding process is presented first. Following that, grinding wheel wear and surface roughness are analysed. Grinding wheel wear is studied in experimental conditions under which small diameter gun drills were sharpened with two diamond grinding wheels of different grain sizes. Finally, the wear curve can be made. The “G ratio” is used to characterise the performance of the grinding process. Next, the experimental research examines how independent parameters, depth of cut, feed, grit, and speed influence roughness. The influence of the grinding wheel wear on roughness is also studied. The aspect of ground surfaces is examined by using a scanning electron microscope (SEM). The experimental study allowed the determination of the required grinding wheel grit (46 μm) and the optimum processing parameters (depth of cut ap = 0.01 mm, feed = 0.005 mm/rev, cutting speed v = 55 m/s) to obtain the imposed surface roughness for cutting tool surfaces (Rz = 0.3 μm). The maximum allowed radial wear (Δr) of the grinding wheel is 30 μm.

Experimental investigations on single-lip deep hole drilling of superalloy Inconel 718 with small diameters

Recent trends in downsizing, as well as miniaturization of components, increase the importance of deep hole drilling with small diameters in various industrial applications. For the manufacturing of deep holes, many processes are used. In addition to mechanical cutting, processes based on thermal material removal mechanisms like electrical discharge machining (EDM), laser drilling and electron-beam drilling are established. Whereas non-mechanical processes can be used for the machining of extremely hard and high-strength materials, substantial disadvantages are the restrictions in the realizable hole diameter and depth dimensions, the long production times, the requirement for special-purpose machinery, as well as the limited bore hole quality. In the aerospace industry, where nickel-based superalloys are widespread, high requirements lie on the surface integrity due to high stress loads during operation. Hence, the major drawback of these non-mechanical processes is the alteration of the subsurface zone, which could affect the part safety. In contrast, the mechanical machining of nickel-based superalloys is extremely difficult due to material properties such as high strength, high tendency to work hardening and low thermal conductivity which results in increased mechanical tool loads and heavy abrasive and adhesive tool wear. An additional challenge is constituted by the chip removal and the unfavorable ratio of cutting edge rounding and undeformed chip thickness caused by the limitation in the feed rates, if deep hole drilling with small diameters and high-length-to-diameter ratios of difficult-to-cut materials like nickel-based superalloys is required. Up to now, the use of standard tool geometries in small diameter single-lip deep hole drilling of Inconel 718 has not been productive and leads to limited process stability and drilling lengths as well as insufficient bore hole quality. Concerning this matter, this paper presents a process adaption using a tailored cutting edge design to accomplish the predominant challenges. Substantial analysis on gun drilling in Inconel 718 regarding mechanical tool loads, chip formation, the tool wear, as well as bore hole quality will be presented.

Error Analysis for Finite Element Simulation of Orthogonal Cutting and its Validation Via Quick Stop Experiments

This work focuses on the chip formation during gun drilling of a 50CrMo4 (DIN 1.7228, AISI 4150) steel grade with a fixed set of cutting parameters and a fresh coated tool. Chip roots were investigated by means of quick stop experiments providing a measured chip width d at the chip root. Furthermore, the tool-chip contact length, L, was measured with high accuracy. Rastegaev compression tests were performed at different temperatures and strain rates for material characterization. The measured data was fit with the Johnson–Cook material model. A 2D finite element (FE) model of the orthogonal cutting process was set up starting with modelling data from literature. A parameter study was performed to determine the sensitivity of the prediction of d and L to the input parameters, i.e., the discretization, the modelling of friction and the material model. The presented error analysis of both the experimental and the numerical investigations shall serve as error estimation for similar FE simulations of the cutting process aiming at the prediction of the tool loading and/or the chip formation and breaking. Authors who have to rely on literature data may use the results presented in this work to estimate the resulting error.

Surface precision and roughness of deep holes produced by small-diameter gun drills

Experimental data are presented regarding the influence of the cutting conditions and the working profile of the tool on the surface precision and roughness of deep holes produced by small-diameter (2.05 mm) gun drills with hard-alloy and steel shafts.