Gun Drill Research Articles

Research on the influencing factors of chip forming in 304 stainless steel deep hole gun drilling

Research on the influencing factors of chip forming in 304 stainless steel deep hole gun drilling

Influence of Coolant Properties and Chip Former Geometry on Tool Life in Deep Drilling

The aim of the article is to find a correlation between a change in the properties of the cooling agent and a change in the geometry of the chipformer, as both are reflected in the service life of the tool after deep drilling. The reason for carrying out the research is the requirement of practice to obtain the economic efficiency of the production of such a demanding process as deep drilling. When applying the latest designs of gun drills, it is very important to correctly set the technological parameters to maintain the stability of the cutting process. One of the most important parameters is the correct removal of heat from the cutting site, and this will be ensured by the stability of pressure, temperature, and percentage of emulsion in the cooling medium, as well as the adjustment of the geometry of the chip former. On this basis, a large number of tests were carried out, consisting of testing the number of drilling cycles carried out by new, unfluted gun drills at constant feed rates and spindle rotation frequencies. After testing, it is possible to modify and supplement the existing methodology of deep drilling technology in terms of managing the cooling emulsion and chip-forming geometry. The tests were aimed at increasing the service life and the number of possible re-grindings of the gun drills depending on changes in the percentage of the emulsion concentration, the pressure and temperature of the cooling agent, and the associated chipformer geometry.

Research on Simulation Model of Ultra Deep Hole Machining of Nickel Base 718 Alloy

Deep hole machining technology is widely used in aerospace, military and other fields, but for difficult to cut materials such as nickel base 718 alloy, there are bottlenecks such as poor machining accuracy and low efficiency in deep hole machining with large depth to diameter ratio. In order to improve the processing quality and efficiency of deep hole machining of nickel base 718 alloy, this paper establishes a finite element model for ultra deep hole machining of nickel base 718 alloy workpiece by gun drilling and a calculation model for straightness deviation of deep hole based on gun drilling theory and finite element method, studies the influence of tools and drilling parameters on straightness deviation of deep hole, and quotes some test data of others to verify the rationality of gun drilling model, Compared with the model in this paper at different speeds and feed rates, the adaptability of the model at different apertures was discussed. The results show that the finite element model for deep hole machining of nickel base 718 alloy established in this paper has good adaptability.

Analysis of machining quality of 304 stainless steel deep hole by changing angle of gun drill

Analysis of machining quality of 304 stainless steel deep hole by changing angle of gun drill

The theoretical model of straightness error in gun drilling of small diameter and deep hole

The theoretical model of straightness error in gun drilling of small diameter and deep hole

Research on Deep-Hole Drilling of High-Strength Steel Using Slender Gun Drill

Research on Deep-Hole Drilling of High-Strength Steel Using Slender Gun Drill

Design and Engineering Support of the Process of Deep Drilling of Heat-resistant Steel

Purpose of research. To attain the specified parameters of deep drilling accuracy by creating design and engineering support for the deep drilling process corresponding to the current level of technical and technological development.Methods. Analysis of machine tools and tool systems for drilling deep holes based on the monitoring of the conditions of machinery, equipment, cutting tools and tooling market of leading domestic and global manufacturers. Synthesis of a process system that ensures the creation of a product that meets the world level of quality with maximum process performance.Results. The design and engineering support of the process of deep drilling of high-alloy heat–resistant steel using modern equipment with a high-performance tool - a gun drill, was created. The equipment for the deep drilling process – an anti-vibration rest, an oil receiver, a clamping chuck, a guide bush are proposed. The conditions for the control of flow chips formed during deep drilling with a gun drill and its removal from the processing zone with a cooling mixture are determined.Conclusion. On the basis of the tooling for deep drilling of heat-resistant steel, the possibilities of using both existing at enterprises equipment and modern but expensive equipment, taking into account the series production, are shown. Both of these ways make it possible to ensure the specified accuracy and roughness of processing.To implement the deep drilling process, it is required to design a special tool - a gun drill, taking into account the properties of the material being processed. When implementing the deep drilling process applying specialized equipment, the machining pattern is provided by the tooling of the machine. When implementing the process applying universal equipment, the selected machining pattern is connected with the design and manufacture of the tooling – a clamping chuck, an oil receiver, a guide bush. These tasks are implemented in two ways: by the specialists of the enterprise or involving third-party specialized organizations to design attachments and cutting tools. The choice of the way to implement the deep drilling process depends on the availability of equipment, the size of the batch of parts and technical and economic assessment.

Investigation of the Process of Deep Drilling of Stainless Steel

Purpose of research. Experimental assessment of the effect of deep drilling modes for high-alloy steel on the components of cutting forces. Making holes in a solid material with a hole depth equal to or greater than ten hole diameters refers to deep drilling operations. For drilling, special tools are used – drills for deep drilling - ejector, cannon, gun drills. Universal or special equipment is applied, the tooling includes travelling or fixed rests, guide bushes. To achieve this goal, it is necessary to choose equipment: type of tool for deep drilling, type of setting; create a model of the forces acting on the cutting part of the tool during deep drilling; evaluate the degree of influence of processing modes on cutting forces.Methods. The research is based on the cutting theory provisions, mechanical engineering technology, experiment planning and regression analysis.Results. Based on the provisions of mechanical engineering technology, the setting up for deep drilling with a rotating workpiece and a non-rotating drill, which is imparted only by the axial feed, was developed. A cutting tool for performing a deep drilling operation is defined – a gun drill. A pattern was created for such a processing scheme and experimental cutting forces were calculated. According to the results of the calculations, it is determined that the greatest influence on the components of the cutting force in a given range of cutting modes is exerted by the axial feed rate of the tool.Conclusion. The cutting forces that occur during deep drilling reach significant values. The polynomial equations obtained as a result of the study allow us to assess the degree of influence of processing modes on cutting forces, calculate cutting forces for further calculation for the sag of the stem of a gun drill.

Experimental study of vibration signal for a prognostic system to prevent tool breakage in micro gun drilling

Unexpected drill breakage can be foreseen and prevented. We observed a factory and identified the warning signs of tool breakage for micro gun drills, as well as a laboratory experiment for micro drills. The vibrations of stable drilling and the vibrations that warn of tool breakage were analyzed based on the time and frequency domain features. We developed a prognostic model. We conducted physical drilling experiments on a Swiss turning machine and a laboratory research platform. Stainless steel was drilled with two types of 0.9-mm-diameter tools: 125-mm-long micro gun drills on Swiss turning machine and 25-mm-long micro drills. In both types of testing, two accelerometers were installed on the tool holder to collect two-directional vibration signals; a linear discriminant function processed the Z-axis and Y-axis signals for the telltale warning signs of impending tool breakage, and obtained a 100% classification rate. To confirm the effect of drilling disturbances on the prognostic system, the entries and exits of tools to and from workpieces were studied. The results demonstrate that both types of signal features can be used without causing any misclassification.

Low-cycle fatigue behaviors of 316L austenitic stainless steels with different surface finishing in simulated pressurized water reactor primary water and an oxygenated, borated, lithiated high temperature water

Low-cycle fatigue (LCF) behaviors of 316L with different surface finishing in simulated pressurized water reactor (PWR) primary water and an oxygenated, borated, lithiated high temperature water were investigated. In the former water, the LCF life of the material completed by gun drill was promoted by using honing, while in the latter water, the change in surface finishing had no significant effect on the LCF life. Similar to 316LN, when 50 ppb DO was added into the water, the LCF life of 316L increased considerably compared with that in the simulated PWR primary water.

RECENT RESEARCH PROGRESS IN DEEP HOLE DRILLING PROCESS: A REVIEW

The requirement of deep hole drilling has tremendously increased in recent years and it extensively found applications in automobile fuel injectors, biomedical implants, aerospace landing gears, etc. These deep holes are fabricated by conventional and unconventional methods with a high aspect ratio ([Formula: see text]/[Formula: see text]) and tight tolerance. This paper is an attempt to review the research work carried out by researchers in recent years about deep hole drilling on various materials using conventional methods like Gun Drilling (GD), Boring and Trepanning Association (BTA) drilling, and Single Lip Drilling (SLD) and unconventional methods such as Laser Beam Machining (LBM), Electro-Chemical Machining (ECM), Electro Discharge Machining (EDM), and Abrasive Water Jet Machining (AWJM). The review includes the impact analysis of process parameters namely water jet pressure, stand-off distance, and abrasive mass flow rate on the responses of AWJM. The current gaps and the upcoming research directions in the deep hole drilling process are detailed.

Modeling of chatter vibrations in gun drilling process

The dynamics of the gun drilling process is analyzed in this paper. The tool shank is modeled as long straight beam vibrating in transverse direction under action of cutting forces. Axial force component is expressed as proportional to cutting thickness, which is determined as nonlinear function of beam transverse deflection with time delay. Nonlinear equations of motion of the drilling shank are derived. The stability diagram of the system dynamics was determined. The bifurcation analysis of nonlinear differential delay equations by means of multiple scale method was performed. The obtained results were verified by numerical integration of nonlinear equations. The influence of cutting conditions on system stability and chatter amplitude was observed.

Dynamic characteristic analysis of micro-hole gun drill based on ANSYS

This paper takes different material properties of gun drill as the research object. ANSYS software is used in the dynamic characteristic analysis of gun drills of different materials. According to modal analysis theory and experiment, the natural frequency and vibration mode of the drill are obtained. The analysis results show that the cemented carbide gun drill after the cubic boron nitride treatment can better withstand bending vibration and torsion during the working process. It is found that the natural frequency of the treated cemented carbide gun drill is very different from that of other materials. The performance micro-hole gun drill provides a certain theoretical basis, and at the same time provides a reference for reducing the vibration and deformation of the gun drill.

Effect of recirculation zone on debris evacuation during EDM deep hole drilling

Deep hole drilling is a technique used for producing holes in materials at high depth to diameter (L/D > 10) ratios. Applications demanding deep holes can be extensively found in aerospace, automotive, marine and oil & gas industries. Conventional drilling techniques such as twist drilling and gun drilling are commonly used for drilling deep holes in the aforementioned applications. However, these methods can cause problems of rapid tool degradation, chip clogging, premature tool failure and undesirable sub-surface alterations to the hole surface. Moreover, these problems get aggravated when the material is difficult-to-cut (Ni/Fe/Co based superalloys) in nature. Therefore, non-conventional machining process finds scope in order to overcome the problems associated with conventional drilling. Electrical discharge drilling (EDD) can be used for fabricating dimensionally accurate holes irrespective of hardness of the material. Nevertheless, the inefficiency in flushing of debris particles at higher depths and its subsequent accumulation is a critical challenge during EDM deep hole drilling. The reason behind flushing inefficiency based on fluid physics has not been completely explored by researchers yet. In this paper, the flow behaviour of micro debris particles in the flushing channel during EDD has been analysed using CFD simulation by employing discrete phase modelling (DPM). The developed model set up is also validated with a benchmark fluid mechanics problem. The steady state CFD analysis results show the formation of multiple recirculation zones in the flushing channel. This can be attributed to the adverse pressure gradient experienced when the dielectric fluid passes from the machining gap to annular gap. Moreover, the presence of recirculation zones reduces the flow momentum and thereby debris particle velocity. This leads to accumulation of micro debris particles in the recirculation zones over time. The results also show that the trajectory of the particles is dependent on the size of the particles generated during material removal. The outcomes of numerical analysis in the present paper can serve as a foundation for the future studies in improving the performance of EDM deep hole drilling.

Study of Double-Edged Gun Drills with Different Edge Types in Drilling Compacted Graphite Iron

Deep-hole machining is an important part in the field of mechanical processing of diesel engine. Gun drill has been widely used in deep-hole machining because of its high dimensional accuracy, high efficiency and good straightness. Through experiments on drilling compacted graphite iron with two different edge types of double-edged gun drills, the spindle power, axial force and tool wear were analyzed and found out one edge type which is more suitable for processing compacted graphite iron. This paper presents a simulation of deep hole drilling to validate the analysis. The research results have important guiding significance for deep hole processing of compacted graphite iron.

High throughput deep-hole drilling of Inconel 718 using PCBN gun drill

Overcoming the myriad challenges in the high-speed machining of Inconel 718, especially for deep-hole drilling (DHD), has been a long-standing area of research for several manufacturers and researchers. Owning to the difficult-to-machine characteristics of Inconel 718, the traditional carbide-tipped gun drills often get worn at an accelerated pace and require repetitive re-sharpening or replacement. This lowers productivity and increases costs. Furthermore, it is also a challenging task to meet the stringent hole-straightness requirement of 1/1000 mm for DHD of such difficult-to-machine materials, especially using those carbide gun drills. Hence, this study presents a development of polycrystalline cubic boron nitride (PCBN)-tipped gun drill to address the rapid tool degradation and poor hole-straightness issues. The developed PCBN-tipped gun drill has a layer of PCBN on its cutting tip and bearing pads. Several gun drilling tests on Inconel 718 have been performed at high drilling speed conditions to assess the performance of developed gun drill. In contrast to traditional carbide-tipped gun drills, the developed PCBN-tipped gun drill has the capability of not only performing in the higher cutting speeds but also reducing drilling forces, drilling torques, and tool wear. Furthermore, the surface quality of drilled holes is also much better than those drilled by traditional carbide gun drills. With these results, it further validates the credibility of the developed PCBN gun drill in enhancing the deep-hole drilling process with high throughput productivity and superior quality of drilled holes, especially for difficult-to-machine materials.

Retraction Note to: Effects of multi-support misalignments on hole straightness predict model in deep hole drilling

Straightness is one of the key technical indicators for deep hole gun drilling. This work studies the effect of drill shaft support misalignment on hole straightness in relation to various control factors. Misalignments occur in machine spindles, intermediate supports and pilot bushings. A predictive hole straightness deviation model for multi-support deep hole drilling process is introduced using the Euler column theory. The model considers the effect of the misalignment of whip guides in addition to the effects of the varying distance among the supports. The model also takes into account the effects of the thrust force and the drill lengths. Through simulation, this work analyzes the effect of each control factor on the results and optimizes the setting for each control factor. Further experiments on Ti6Al4V alloy then verify these estimates. Through research, fixed support at chip box has a greater influence on straightness deviation as compared to the misalignment at other supports; the distance between supports nearer to the chip box has more control on straightness deviation as compared to the other support distances.

Control of Chip Formation and Improved Chip Ejection in Drilling With Modulation-Assisted Machining

Abstract Drilling with modulation-assisted machining (MAM) superimposes a low-frequency oscillation onto the drill feed motion. The otherwise continuous cutting in the drilling process is converted into a series of discrete cutting events. The result is a discrete chip formation process and concurrent improvement in chip ejection. The discrete chip formation and ejection in drilling with MAM were investigated via systematic experiments in OFHC Cu and Ti6Al4V using a two-flute twist drill and a single-flute gun drill. Drilling thrust force and chip morphologies for various modulation conditions are examined. The continuous cutting and discrete cutting regimes of modulation-assisted drilling are compared with conditions determined by a kinematic model. The results show that chip formation in the continuous cutting regime with MAM can influence chip breakage by random fracture at thin sections of the chip, but in this regime the resulting chip size is variable and not controlled. In contrast, when MAM conditions operate in the regime of discrete cutting, the deformed chip size can be directly controlled. The ability to control the chip size improves chip ejection and drilling process stability. A set of modulation conditions for enhanced performance of chip ejection are proposed. The study shows that modulation-assisted machining offers distinct advantages as a method for deep-hole drilling applications.

Small Diameter-Deep Hole Drilling for Hard-to-Machine Metals ― Drilling of ϕ1.0×400 mm for Ti6Al4V ―

Small diameter-deep hole drilling is indispensable when several main parts of which airplane, automobile, machine tool and metal mould are manufactured. Especially, medical appliances, medical implants and surgical operation tools for brain and bone invariably need small diameter-deep hole drilling for hard-to-machine metals such as stainless steel and Ti6Al4V. The authors newly designed and manufactured a small diameter-deep hole drilling machine by applying technological developments which consist of a direct drive servo spindle motor controlled more precisely, removable steady rests to prevent for a slender fluted hollow shaft of gun drill to be deflected and a highly pressure circulation system of cutting fluid to prevent being clogged with chips. By using the small diameter-deep hole drilling machine and a special gun drill (specially made to order in BOTEK) a drilling of ϕ1.0×400 mm (L/D=400) for Ti6Al4V was carried out. As a result, it was ascertained that the drilled hole has high accuracy in the items of hole diameter, concentricity, roundness and inner surface roughness.

Effect of Groove-type Chip Breakers in Deep Hole Drilling of 42CrMo

Gun drills have widely been in use in deep-hole drilling of manufacturing in automobiles and models. They could improve straightness and surface roughness of holes. However, with the improvement of material property and the increasing need for drilling holes that have big aspect ratio, problems like breaking and removing chips when drilling deep holes continue to appear, which would break the cutting tool when these problems are severe. All these problems would greatly lower the durability and the ability of machining of gun drills. Additionally, as for drilling holes on crankshaft that’s made of 42CrMo, for example, due to its high fatigue strength and great toughness, it’s not easy to break chips and cutting tools worn down in a fast rate. Aimed at prolonging the lifetime of gun drills when drilling materials that are relatively difficult to drill and improving the manufacturing productivity, this paper presents a kind of gun drill with groove-type chip breaker and describes the geometrical parameters of groove-type chip breaker.