Drill Feed Research Articles

A Self-Optimizing Control System for Hard Rock Percussive Drilling

The derivation and application of a self-optimizing control system for percussive drilling of hard rock is presented. The control system superimposes an oscillating force signal onto the drill feed force and demodulates the signal from the drill rotational torque. The resultant demodulated signal is then used to control the drill, allowing real-time maximization of penetration rate, minimum hole deviation, and measurement of rock characteristics regardless of drilling conditions. The control system allows the drill to adapt to changing rock conditions. Testing has proven the control to be reliable and to increase drilling efficiency.

Influence of Drill Geometry in Drilling Carbon Fiber Reinforced Plastics

Twist drill is widely used in hole-making process in industries, due their low production cost and ease of regrinding after wear. However, drilling of fiber reinforced plastics with twist drill often results in defects and damages, such as delamination, debonding, spalling and fiber pullout. The chisel edge of twist drill is the mainly influence for the thrust force and the hole quality in drilling carbon fiber reinforced plastic (CFRP) laminates. Pre-drilled pilot hole or reduce chisel edge can eliminate the threat for twist drill in drilling induced-delamination. Drilling-induced thrust force was selected as quality character factors to optimize the drilling parameters (drill type, feed rate and spindle speed) to get the smaller the better machining characteristics by Taguchi method. The results show that the feed rate and drill type are the most significant factor affecting the induced-thrust in drilling CFRP laminates.

An experimental and statistical study on the effect of drill geometries on force and hole quality in drilling of glass fibre reinforced plastic

Aircraft manufacturing involves drilling of large number of holes, in which the joint can be critically affected by the quality of the hole. Effect of drill geometry on drilling of glass/epoxy laminates using twist, Zhirov and Multifaceted Drills (MFD), has been studied. The thrust force and hole quality were compared for each drill geometry. Zhirov drill cuts the hole with less force and best surface finish. MFD produces less delamination when compared with the other geometries. ANOVA was used to study the effect of drill geometries, spindle speed, and feed rate on thrust force, surface finish and delamination factor.

COMPARATIVE ANALYSIS OF VARIOUS METHODS OF SURFACE ROUGHNESS IN DRILLING

Drilling is one of the most common and fundamental machining processes. Since approximately 40% of all the cutting operations are drilling in industry. It is most frequently performed, material removing process and is used as a preliminary step for many operations, such as reaming, tapping and boring. Because of their importance in nearly all production operations twist drills have been the subject of numerous investigations. Surface finish quality of a machined work piece is an issue of main concern to the manufacturing industry. The aim of the present work is to identify suitable parameters for the prediction of surface roughness. Back propagation neural networks were used for detection of surface roughness. Drill diameter, cutting speed, feed, and machining time were given as inputs to the neural network structure and surface roughness was estimated. Drilling experiments with 10 mm drill size were performed at three cutting speeds and feeds. The number of neurons were selected from 1,2,3,…, 20. The learning rate was selected as 0.01 and no smoothing factor was used. The best structure of neural networks were selected based on the criteria as the minimum of summation of square with the actual value of surface roughness. For statistical analysis, it was assumed that surface roughness depends on cutting speed, feed and machining time. For the mathematical analysis inverse coefficient matrix method was used for calculating the estimated values of surface roughness. Comparative analysis has been done between the actual values and the estimated values obtained by statistical analysis, mathematical analysis and neural network structure.

Enhancement of Drilling Safety and Quality Using Online Sensors and Artificial Neural Networks

Cutting force sensors and neural networks have been used for the occupational safety of the drilling process. The drill conditions have been online classified into 3 categories: safe, caution, and danger. This approach can change the drill just before its failure. The inputs to neural networks include drill size, feed rate, spindle speed, and features that were extracted from drilling force measurements. The outputs indicate the safety states. This detection system can reach a success rate of over 95%. Furthermore, the one misclassification during online tests was a one-step ahead pre-alarm that is acceptable from the safety and quality viewpoint. The developed online detection system is very robust and can be used in very complex manufacturing environments.

Low-frequency modulation-assisted drilling using linear drives

A new machine tool based on linear drive technology has been developed for low-frequency modulation-assisted drilling. The linear drive utilizes a novel design for generating continuous drill feed motion with a superimposed low-frequency modulation of up to 400 Hz without the use of secondary actuators. The frequency characteristics of the drive are such that a wide variety of drilling conditions can be systematically explored. Results pertaining to torque, thrust and controlled chip breakage when drilling ductile aluminium alloys are presented to demonstrate the attractive features of modulation-assisted drilling using linear drives. It has been shown that the application of a superimposed modulation of the appropriate frequency and amplitude produces consistent chip breakage, thereby facilitating the drilling process. Furthermore, under these conditions, the mean torque and mean thrust are decreased in comparison with conventional drilling. The frequency and amplitude conditions for which such beneficial effects are observed can be predicted using a simple model for chip formation and forces in modulation-assisted drilling.

プリント基板の小径ドリル加工 （第４報） ドリル送りの瞬時停止機構を用いたドリル折損防止加工の試み

Drill breakage is one of the major problems in micro drilling and in-situ breakage prediction can improve production reliability remarkably. The authors have already reported an in-process detection of small cutting torque by the new torque sensor with a thin-walled elastic cylinder. In this paper, a feed control drilling according to an overload signal from this torque sensor is described. In order to prevent the drill breakage caused by the overrun of a drill feed stage, it is necessary to stop the drill feed quickly enough according to the overload signal. A quick stop mechanism, which consists of z stage for the drill feed motion by regular NC control and z' stage for a quick retreat motion, was developed. The advancing z stage can not be stopped quickly due to electric delays of feed control and the mechanical inertia. The quick retreat motion of z' stage according to overload signal can cancel this time delay of z stage. The automatic canceling motion can prevent drill breakage during the drilling operation. Through a few drilling experiments of multi-layered printed circuit boards, the availability of the developed quick stop mechanism in automatic feed control was verified.

ばりの抑制を目的とする振動穴あけに関する研究

Burr in drilling operations has been a serious problem especially in the area of factory automation and high technology. In order to prevent burr in drilling operations ultrasonic or low frequency vibration has been applied in the direction of drill feed. In this study in order to enhance the effect of oscillation in drilling operations newly developed “radial peripheral lip drill” has been applied as well as the standard type of drill. With the radial peripheral lip drill the radial lip at the corner of drill edge is able to obliquely cut and sharply slice the stock at the hole exit, which would become burr, by the aid of oscillatory motions in the direction of drill feed. Low frequency vibration is as highly effective in preventing burr as ultrasonic vibration except that the former is effective only with the radial peripheral lip drill.

Surface quality of holes drilled into aluminium 390

Abstract The pupose of this project was to develop a model for predicting surface finish of drilled holes for different feed rates, cutting speeds, fluid concentrations, and drill diameters. A regression equation was developed for a linear model using data collected from a 25experimental design. Aluminium 390 was used as the workpiece material. Feed rate, fluid concentration, and the interaction between feed rate and drill diameter were significant at the 5% level. Cutting speed and drill diameter were not significant within the ranges tested.

Burrless Drilling by Means of Ultrasonic Vibration

Summary In order to achieve edge integrity in view of burr, flaking, shipping, material deterioration, etc, in drilling operations, ultrasonic vibration has been applied in the direction of drill feed. The multiplying effects of ultrasonic vibration and newly developed radial peripheral Lip drill has been experimentally demonstrated to be extremely effective for preventing burr and material deterioration at the exit of drilled hole of aluminum and glass fibre referred plastics.

Blowholing in PTH Solder Fillets

The drilling and preparation of a hole in FR‐4 laminate prior to the deposition of electroless copper is considered in relation to the quality of soldering achieved on the finished printed circuit board. Data pertaining to the drill speed, drill feed, and stack position are presented and the effect of drilling temperature is demonstrated. The variability of laminate is discussed in relation to outgassing during soldering. Finally the importance of the post‐drilling treatment of the hole‐wall is shown. The relative effects of baking after drilling, ultrasonic cleaning and chemical treatments such as alkaline potassium permanganate are illustrated.

Dynamic Modeling of Transverse Drill Bit Vibrations

A dynamic model is presented for the transverse vibration of drill bits, and validated experimentally. The model includes” the effects of drill rotation speed and feed rate as well as drill bit length, diameter and material properties The drill transverse natural frequencies are shown to depend on the rotation speed, and transverse instability occurs at a critical speed where the natural frequencies vanish. Simulation results snow the influence or parameters such as drill length, drill diameter, rotation speed, and feedrate on the critical speed. Experimental results confirming the predicted trends, are presented. Potential uses of the model, are discussed, and extensions to the model are suggested to account for the complex drill geometry, torsional vibrations, damping mechanisms, and distributed mass and stiffness properties.

A STUDY OF THE BASIC MECHANICS OF THE CHISEL EDGE OF A TWIST DRILL

SUMMARY A model of chip formation and an indentation model are constructed for the chisel edge region of a twist drill. From these models, predictions are made as to the shape of the wear zone about the chisel edge and equations derived for calculating the torque and thrust developed by the chisel edge given the geometry of the drill point, the cutting conditions and a shear stress factor for the work material. Using the chisel edge thrust equation, it is shown that as the drill feed tends to zero, the drill thrust approaches a finite value the magnitude of which is in reasonable agreement with that observed experimentally.