Single-lip Drilling Research Articles

Thermomechanical Impact of the Single-Lip Deep Hole Drilling on the Surface Integrity on the Example of Steel Components

The fatigue behavior of components made of quenched and tempered steel alloys is of elementary importance, especially in the automotive industry. To a great extent, the components’ fatigue strength is influenced by the surface integrity properties. For machined components, the generated surface is often exposed to the highest thermomechanical loads, potentially resulting in transformations of the subsurface microstructure and hardness as well as the residual stress state. While the measurement of the mechanical load using dynamometers is well established, in-process temperature measurements are challenging, especially for drilling processes due to the process kinematics and the difficult to access cutting zone. To access the impact of the thermomechanical load during the single-lip drilling process on the produced surface integrity, an in-process measurement was developed and applied for different cutting parameters. By using a two-color pyrometer for temperature measurements at the tool’s cutting edge in combination with a dynamometer for measuring the occurring force and torque, the influence of different cutting parameter variations on the thermomechanical impact on the bore surface are evaluated. By correlating force and temperature values with the resultant surface integrity, a range of process parameters can be determined in which the highest dynamic strength of the samples is expected. Thermally induced defects, such as the formation of white etching layers (WEL), can be avoided by the exact identification of critical parameter combinations whereas a mechanically induced microstructure refinement and the induction of residual compressive stresses in the subsurface zone is targeted. Further, eddy-current analysis as a non-destructive method for surface integrity evaluation is used for the characterization of the surface integrity properties.

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.

THERMAL INFLUENCE ON THE SURFACE INTEGRITY DURING SINGLE-LIP DEEP HOLE DRILLING OF STEEL COMPONENTS

The thermomechanical load on the workpiece surface during the machining process strongly influences its surface integrity and the resulting fatigue strength of the components. In single-lip drilling, the measurement of the mechanical load using dynamometers is well established, but the thermal interactions between the tool and the workpiece material in the surface area are difficult to determine with conventional test setups. In this paper, the development and implementation of an in-process measurement of the thermal load on the bore subsurface is presented. The experimental setup includes a two-color ratio pyrometer in combination with thermocouples, which enable temperature measurement on the tool’s cutting edge as well as in the bore subsurface. In combination, a force measurement dynamometer for measuring the occurring force and torque is used. Thus, the influence of different cutting parameter variations on the thermomechanical impact on the bore surface can be evaluated.

Deep Hole Drilling of Large-Diameter Titanium Alloy With a Novel Rotary Low-Frequency Vibration Device

Titanium alloy (Ti) has been widely used in aerospace industry due to excellent mechanical properties and the demands of Ti parts with a high length-to-diameter ratio and a large diameter are increasing. However, deep hole drilling of large-diameter Ti holes is usually both time-consuming and cost-consuming due to a series of problems such as unfavorable chip removal, helical structure on the hole surface, poor hole precision and severe tool wear. This paper reports on the cutting mechanism and experimental results of low-frequency vibration-assisted single-lip drilling (LFVASLD) of large-diameter Ti holes (O17mm) for the first time. In this paper, a novel rotary low-frequency vibration device was developed and the vibration generation mechanism was analyzed. Thereafter, the material removal mechanism of LFVASLD was established. Then, the comparative experiments between LFVASLD and conventional single-lip drilling (CSLD) of Ti were conducted. The experimental results show that, compared with CSLD, LFVASLD can significantly prolong the drilling depth by 9 times due to reduced tool wear and alleviate helical structure on the hole surface due to the separated cutting mode. Furthermore, the influence of drilling parameters in LFVASLD on hole quality were also investigated. It is concluded that, the LFVASLD method is suitable for deep hole drilling of large-diameter titanium alloy and the developed rotary low-frequency vibration device can be used as a machine tool accessory to significantly improve the processing capacity in the industrial practice.

Influence of the deep hole drilling process and sulphur content on the fatigue strength of AISI 4140 steel components

When using quenched and tempered steels in the automotive industry or other industrial applications the fatigue behavior is of elementary importance. The surface and subsurface integrity of machined parts is known as one key factor related to the fatigue strength of components and is strongly influenced by the machining process. Especially for the deep hole single lip drilling, a large part of the cutting force is transferred to the bore wall and the surface and subsurface zone are influenced by the interaction between the tool and the workpiece material.In this study, the approach of inserting residual stresses into the bore wall and influencing the microstructure of the bores subsurface in a way, that the components can withstand a higher mechanical and dynamic load, is investigated in detail. In a close cooperation between the authors the parameters of the single-lip drilling process and the workpiece material are correlated with the produced surface quality and subsurface microstructure as well as the resulting fatigue strength of the components. For the comparative characterization of the fatigue behavior, established test procedures of destructive material testing in combination with new non-destructive test methods, such as the Barkhausen noise analysis, are applied and developed further. The results of the fatigue tests in correlation with the results of the Barkhausen noise analysis are used to design a model for predicting the fatigue strength of drilled components.