M. O. M. Osman

An investigation into the influence of helix angle on the torque-thrust coupling effect in twist drills

This paper presents an experimental investigation into the torque-thrust coupling effect in twist drills. A set of cross-coupling stiffness coefficients (Kft and Ktf) are defined. The influence of helix angle on torsional and the cross-coupling stiffnesses is studied. The coupling interaction (as measured by Kft and Ktf) is strongly influenced by the helix angle and has a distinct maxima around 28°. Also, the magnitudes of the coefficients increase parabolically with drill diameter. The pure torsional stiffness also has a maxima around the same helix angle. Under axial restraint, the torsional stiffness increases by 10 to 25% owing to the coupling effect. The larger the torque-thrust interaction, the larger is this increase in torsional stiffness. The findings of this investigation is proposed as a probable basis for the traditional popularity of a 28 to 30° helix angle for drills.

On the design and development of a new BTA tool to increase productivity and workpiece accuracy in deep hole machining

This paper presents the design and method of development of a new three-pad BTA tool. The advantages of this cutting tool over a conventional two-pad BTA tool are brought out using a probabilistic approach in both the static and dynamic case. Experiments were conducted with the new three-pad tool, and it confirmed the theoretical prediction that the three-pad tool is more stable than the conventional BTA tool. Also, the cause of grooves observed on the workpiece produced by the two-pad tool has been explained. Further, it is observed that the third pad stiffens the tool thereby improving the chip breaking effect which improves the quality of the holes produced at high feeds. Thus this new development increases the productivity and improves workpiece accuracy in deep hole machining.

On the design of deep-hole drills with non-traditional ejectors

Abstract This work deals with the development of design criteria for deep-hole drills with non-traditional ejectors of circular and plain type. An analytical method for design on non-traditional ejectors with circular jet was developed. The experimental investigation of the developed method was found suitable for the design of single lip non-traditional ejector gundrills of bigger diameter. For smaller diameter drills the results were not satisfactory. For smaller diameter size gundrills the equations analytically developed were modified to suit the experimental results. Further investigation of these modified equations found them to be appropriate. In the case of plain type ejectors, the design methods were developed based on experimental results since this type of ejector does not lend itself easily to theoretical analysis.

An experimental investigation for the stochastic modelling of the resultant force system in BTA deep hole machining

Abstract This paper presents the measurement and a statistical analysis of the resultant force system, consisting of an axial force and torque, in BTA deep hole machining. The measurements were performed using a specially designed two-component piezoelectric dynamometer and adopting the rotating cutting tool-stationary workpiece procedure. The dynamometer was calibrated for static and dynamic outputs and techniques were employed for increasing the measuring accuracy and reducing the cross-interference by obtaining the elements of the system transfer function. Experiments were carried out to measure the mean values and the dynamic fluctuations of the axial force and torque. The recorded data was processed and analysed to establish all major statistical properties of the axial force and torque. Results show that the dynamic fluctuations of the axial force and torque in BTA deep hole machining can be represented by a stationary wideband process with a gaussian density distribution function. Such a mathematic...

F0riction losses in coolant flow through kidney shaped gundrill shank

SUMMARY The factor of factional losses for both laminar and turbulent coolant flow through the passages in a gundrill has been investigated. A kidney shaped passage in the tip has been used because it is superior to both single circular and double circular passages. An extensive experimental investigation revealed a considerable deviation from the Blasius relation for circular passages. The concept of hydraulic diameter used to predict friction in circular passages fails to predict the friction in the kidney shaped passage. The results of this investigation suggest that by introducing a concept of a characteristic dimension of the passage cross-section, the friction can be predicted in a relatively simple manner similar to the Blasius approach. Computer fitting of the experimental data resulted in an empirical relation which can be used to calculate the factor of frictional tosses in a kidney shaped gundrill passage for coolant.

An analytical tim6 domain evaluation of the cutting forces in BTA deep hole machining using the thin shear plane model

This paper presents an analytical approach to describe the cutting forces in 1ST A deep hole machining processes in the time domain. The method takes into account the effect of different machining conditions. Since the cutting velocities employed in BTA deep hole machining process are relatively high, and since small chips are produced due to the presence of tool chip breakers, the analysis is developed on the basis of the thin shear plane model. The cutting velocity is a linear function of radius and the rake angle. Cutting is different in the two regions of the cutting tool, so the total cutting force acting on the cutting tool is determined by integrating the force on a small incremental thickness of the cutting tool. This approach, to predict the value of the cutting forces without resorting to any empirical techniques, clearly illustrates the effect of various system parameters on the machining process. The resultant force system on a new BTA cutting tool consists of an axial force and torque. But wi...

On the performance of cutting fluids for BTA deep-hole machining

Abstract This work deals with an investigation of the influence of various additives to a base slock cutting oil in order to develop a better oil for deep-hole machining. The investigation has been conducted at the R & D facilities of a major manufacturer for deep-hole boring tools and equipment on the basis of systematic field trials. It has been aiming at developing an oil which gives a maximum cutting efficiency at a minimum wear rate of the tool and the guiding pads. The field trials included deep hole machines of various sizes and makes, which were connected to a central oil-circulating system. The three major types of BTA || tools (solid boring, trepanning and counterboring heads) of various sizes were used. Cut ting edges and guiding pads were exclusively made of carbides of various grades. Materials attempted in the trials ranged from mild carbon steel to high alloy, high-temperature strength, stainless and nitriding steels. A total of four experimental oil charges have been tested and each was br...

Optimal design of BTA deep-hole cutting tools with staggered cutters

A concept using an optimization technique to design multi-edge BTA tools with cutters ‘taggered’ on the cutting head is developed. The cutting edges are located on the head so that they cut in a circular pattern over a portion of the hole radius, partly overlapping with each other. In many applications these tools should be superior to the conventional single-edge tools or multi-edge tools with cutters located at 180 degress to each other. When heavy cuts and large hole sizes are attempted with single-edge tools a large resultant force transmitted to the bore wall through the guiding pads causes undue rubbing and wear of the pads. This is followed by heat generation and increased power consumption and deterioration of the cutting edges. The tools with a staggered or zigzag arrangement of the cutters are designed for a predetermined cutting force resultant necessary for the tool guidance, which is controlled by appropriate radial and angular location of the cutters on the cutting head. The cutters of these...

A STOCHASTIC CHARACTERIZATION OF THE MACHINE TOOL WORKPIECE SYSTEM IN BTA DEEP HOLE MACHINING Part II: Response Analysis and Evaluation of the Tool Tip Motion

ABSTRACT In this paper, the solutions to the stochastic differential equations, which mathematically represent the machine tool work-piece system in BTA deep hole machining are presented. The solutions to the parametric stochastic differential equations have been obtained using the well known averaging technique. The non-parametric inhomogeneous equations have been solved using the Fokker-Planck equation. Based on these solutions, the true motion of the tool tip has been described using the maximum, average and minimum deviation curves. These curves predict that helical grooves will be formed on the workpiece and such helical grooves were observed on the workpieces. Also, the maximum, average and minimum values of deviation of the tool tip which is a measure of the roundness error are established. Based on these results an upper bound for the roundness error as a function of depth of hole is derived. The measurement of roundness of the specimens reveals that the experimental values be in the zone predicte...

An investigation of the static stability in self-piloting drilling

A comprehensive analysis of the static stability in self-piloting drilling is made in order to define the optimal location 7lpar;based upon the criteria of the equal pad normal reactions and equal stability coefficients) of the drills supporting pads (relative to the drills cutters). The optimal location is achieved under unsyrnmetrical location of the supporting pad relative to direction of the resultant cutting force in a plain perpendicular to the drill axis. Significant attention is paid to the drill entrance stability and three methods to reduce the bell mouth (the increase of the bore diameter and worse surface finish at the entrance) are introduced. By the detailed consideration of the drill static force system in the plain which contains the drill axis and vectors of the radial and tangential forces, a new design concept is proposed. The essence of this concept is to design the self-piloting drills with minimum offsets of the pad faces relative to the bottom of the hole being drilled. The experi...