Elso Kuljanić

Milling Titanium Compressor Blades with PCD Cutter

Abstract This paper investigates the possibility of finishing milling of titanium alloy TiAl6V4 compressor gas turbine blades with polycrystalline cubic diamond PCD cutter that can be used successfully for milling “slim” - low stiffness - blades. The tool life of PCD cutter was very long T=381 minutes while surface roughness of the machined surface was low and the geometrical accuracy was satisfactory. A suitable inclination of the cutter axis to the surface has been determined. A basic consideration of milling titanium based alloy with PCD cutter and an analysis and discussion of the chip formation are presented. Better results are obtained when cooling refrigerant was applied. Finishing milling of titanium alloy TiAI6V4 “slim” blades with PCD cutter is promising.

Macro Plastic Deformation of Cutting Edge — A Method for Maximum Utilization of Cutting Tool

Summary This paper investigates the macro plastic deformation of the cutting edge and the material near the cutting edge in rough turning. It was found that the macro plastic deformation takes place approximately three seconds after the start of cutting, when the single point cutting tool is not able to cut properly, the surface roughness of the machined surface increases and vibrations appear. A method for maximum utilization of single point cutting tool and tool selection for rough turning, grooving etc. by using the information about the macro plastic deformation of the cutting edge are proposed. Both the way of measuring the macro plastic deformation and how the macro plastic deformation can be detected by means of feed cutting force is presented. Acoustic emission sensors or sensors systems could be used for detecting the macro plastic deformation of the cutting edge.

Random Strategy Method for Determining Tool Life Equations

The reliability of cutting data or optimized cutting conditions depends on tool life equation reliability. A method to reduce the number of tool life experiments instead of applying short tool life test with less reliability, or one - variable - at - a - time approach, is proposed. Different fractional factorial design of experiments are Compared. It is shown that the Random Strategy method reduces significantly the number of tool life tests, i.e. from about 15 to 5 tests, in determining tool life equations with three independent variables, and it is suitable for laboratory, industrial work conditions, and for adaptive control applications.

Application of a Rotating Dynamometer for Cutting Force Measurement in Milling

The measurement of the cutting force is important from the theoretical and practical point of view. An investigation of cutting forces and torque in milling with a rotating dynamometer is described. Rotating dynamometer is more practical for milling, drilling and taping than the plate dynamometer, since it is mounted on the spindle of the machine tool independently of the size of the workpiece. The experimental results have been compared to estimated instantaneous forces computed by using Kronenberg’s approach. The measurement system has been tested. Also, the dynamic and static characteristics of the rotating dynamometer are presented.

OPTIMIZATION OF MACHINING PROCESS USING EVOLUTIONARY ALGORITHMS

Advanced manufacturing requires a powerful tool for reliable modeling and solving the complex machining optimization problems. This paper proposes a non-conventional approach using evolutionary algorithms inspired by Darwinian findings about the evolution of the biological species and the survival of the fittest organisms (i.e. natural selection). It is illustrated with an experiment of longitudinal hard turning. Genetic programming (GP) is used to develop the models of both the surface roughness and the tool life considering the cutting speed, the feed and the depth of cut as predetermined cutting parameters. Finally, genetic algorithm (GA) is applied for their optimization.

Machinability testing in the 21st century—integrated machinability testing concept

The trend in manufacturing is towards the intelligent machining system. The output of such a system depends significantly on machinability data of conventional and next-generation materials. This paper discusses trends in machinability testing: conventional machinability tests, short machinability tests, machinability index-rating and computerized machinability data system. A discussion of new technological conditions in manufacturing follows as well as a discussion of technological methodologies in the near future. Furthermore, the need for better understanding of machining is discussed. Finally, a proposal of an integrated manufacturing testing concept is proposed.

An Investigation of Cutoff Bars and Pipes by Horizontal Band Sawing

Summary This paper presents some unknown relationships enabling an increase of cutting rate and tool life in horizontal bandsawing - one of the most economical cutoff operation with a very high production rate - obtained in yearslong research in this field. Both cutoff bar and pipe were investigated by sawing a single piece or cutting in a bundle. It was found that the shape of the bundle has a significant effect on cutting rate and tool life, i.e. the height of the bundle should never exceed the width of the bundle. The ratio of the height and the width of the bundle should be from 0.5 to 1, and the bundle should be as large as possible. A high percentage of one tooth cutting is done by tooth side when heavy feeds are applied - at the beginning and at the end of sawing a round bar. An indirect control check to avoid the breakage of the band saw was introduced. The results obtained in this work are based on more than 22 000 different measurements. The production rate can be increased and machining cost can be decreased by applying the obtained results and given recommendations.

Some Approaches in the Machining Research

The paper discusses some approaches in machining research. Development of empirical technology, as well as of science-based (predictive) technology, and development of computer-based technology are presented. The application of mathematics of statistics and design of experiments, simulation of machining processes such as analytical simulation, geometrical simulation, finite element simulation, and supervision systems in machining are discussed. Also, the importance of machining research for computer integrated manufacturing enterprise in global market conditions is discussed.

STABILIZATION OF A MILLING MACHINE AGAINST CHATTER

This work analyzes a phenomenon of self excited vibrations (mode coupling chatter) that was observed in a machine for wood cutting during the milling of a chair back. The configuration of the system for which chatter occurs is first illustrated. It is then recognized that the most crucial factor affecting the stability of the system is the angle γ between the cutting force acting on the tool and one of the degrees of freedom of the structure. As a matter of fact, when γ becomes smaller than a certain negative value, chatter occurs. An effective way to stabilize the milling machine is presented, consisting in changing the orientation of the tool with respect to the feed direction of the workpiece, so that the value of γ is positive during the whole milling operation, and the instability zone is never entered. Tests carried out on the available milling machine proved the effectiveness of the stabilization. Finally, a theoretical framework is presented, which explains with more details how the stability of the system is affected by the value of γ. Moreover, a simple stability condition which can be useful for practical stabilization purposes is also defined.

Titanium alloy turbine blades milling with PCD cutter

Is milling of titanium alloys turbine blades possible with PCD (polycrystalline diamond) cutter and what surface roughness can be expected? In order to answer the question a basic consideration of diamond tools machining titanium alloys, chip formation and experimental results in milling of titanium alloy TiA16V4 turbine blades are presented. The milling results of a “slim” turbine blade prove that milling with PCD cutter is possible. The tool wear could not be registered after more than 100 minutes of milling. The minimum surface roughness of the machined blade was R a = 0.89 μm. Better results are obtained when wet milling has been performed. Therefore, finishing milling of titanium alloy TiAl6V4 turbine blades with PCD cutter is promising.