Janez Kopac

Tool wear monitoring during the turning process

The aim of the present research was to build a simple model for tool wear monitoring during the machining process. In addition, by this model a prediction of tool wear for a variety of different cutting speeds and feed rates should be possible. Therefore, the sound pressure at 0.5 m from the cutting zone during the turning was measured by a condenser microphone and analysed in frequency domain from 0 to 22 kHz. The measurement arrangement as well as the possibilities for on-line sensing of the tool wear are presented. The workpiece material was carbon steel Ck15 (DIN) and the cutting insert was made of cermet without coating. The depth of cut was the constant, whereas the cutting speed, feed rate and flank wear of the tool were variables. The results showed that an increase in tool wear correlates with an increase in the amplitude of the recorded sound between 6 and 20 kHz. Similarly, an increase in feed rate resulted in an increase of sound intensity between 2 and 19 kHz. In contrast with these findings, the cutting speed influenced the recorded signals considerably less. It can be concluded that under the given circumstances the monitoring of tool wear by the sound emitted is a possible and relatively simple method.

Wear mechanisms of cutting tools in high-speed cutting processes

Contemporary cutting tools used for High Speed Cutting (HSC), made on the basis of micro-grained cemented carbides with multi-layer protective coating, allow for effective machining of hardened and tempered steels of hardness over 50 HRc. The characteristic wear of such tools is affected by the fact that the cutting speed is no longer the main influential factor on wear; the wear can also be the consequence of the high-speed tool movements in the feed direction. The paper presents some original research into the wear types, as well as the phenomena in the cutting zone and their relationships to the causes and main wear mechanisms (adhesion, abrasion and diffusion) for the tools used in HSC.

Acoustic emission signals for tool wear identification

Abstract In practical machining applications, there are two different approaches to evaluate the efficiencies of tool quality or its wear resistance; tool life obtained on the basis of experimental tests or the determination of process identification parameters, considering the tool as a part of monitoring equipment. In this paper, the latter is presented. With the application of the new sensing principle of acoustic emission (AE) signals, different tool wears, as one of the main important factors connected with workpiece surface quality, are detected. Using different tool materials and their protective coatings, the tribological conditions at the tool–workpiece interface are identified to indicate changes in wear at the tool flank, especially when we exceed the upper limits of the tool wear recommended for finish machining.

Tribology of coated tools in conventional and HSC machining

Abstract The aim of research of the tribological conditions in the tool–workpiece interface in cutting processes is to find the main causes for unpredicted tool life. As is shown in the paper there are many causes for their influences on the tool wear. Not only mechanical and chemical but also thermo-chemical aspects of wear is important. The high cutting temperature, which is a result of high-speed cutting (HSC), enhances diffusion and oxidation process. Diffusion processes between the chip and the top rake surface of the cutting edge result in crater wear, and oxidation reactions with the environment induce scaling of the cutting edge. The phenomenon of central wear can be used to define the tool life in the case of HSC milling of alloyed tool steels ( hardness >45 HRC ) .

Influence of cutting material and coating on tool quality and tool life

Abstract A review of some recently used cutting materials and coatings is presented. Theoretical models and real presentations of tool wear are shown, with the emphasis on diffusion wear. Tool life is shown for several combinations of cutting material/workpiece material depending on certain technological parameters. The main influences on tool life in relation to cutting speed (vc) and feed rate (f) and grinding of high speed steel (HSS)–TiN tools are shown. A tribological model united all parameters and influences. A real model helps us to continue with optimising cutting parameters to achieve better workpiece quality and shorter production time for lower costs. Therefore, high speed cutting (HSC) technology is used and some of its advantages are presented.

Analysis of casting die failures

Cracks in the surface of a fixed die half resulting in imprints on AlSi9Cu3 alloy castings were analysed. The cracks were revealed and identified by the use of penetrants. Some of them were clearly seen by the use of a magnifying glass or even by the naked eye. Non-destructive metallographic examination by SEM of polymeric replicas was applied.

Interaction of the technological history of a workpiece material and the machining parameters on the desired quality of the surface roughness of a product

Abstract The paper analyzes the fine turning process on workpieces with different technological history. The analysis concentrates mainly on surface roughness, which is very frequently a measured quality characteristic of finished or semi-finished products. The influences of the workpiece material and its technological history, and the machining parameters on surface roughness of machined surfaces are analyzed. The statistical design and analysis of experiments was used for assessing the above-mentioned interaction in the fine turning process.

Wood: an important material in manufacturing technology

Abstract The basic properties of wood tissue are briefly presented to enable a better understanding of wood as a material. The machining of wood by cutting is a demanding technological process because of wood’s specific structure, anisotropy, and non-homogeneity. Next, some specifics in the straight cutting in three typical directions of wood tissue are presented. In addition, the paper aims to correlate the structural and mechanical properties of wood with the outcome of the cutting process, especially in the production of thin boards intended for the resonant parts of some musical instruments. The comparison of two recent experiments showed that the machining process measurably influences the acoustic properties of a wooden board; however, this influence depends on the board shape.

Hardening phenomena of Mn-austenite steels in the cutting process

Abstract Material 12Mn is a manganese austenitic (Hadfield) wear resistant steel. Its resistence can be further increased by strain hardening by cold work or by careful consideration of cutting forces. In machining of 12Mn steel, microhardness in the cutting zone extremly increases and influences on tool life. The right selection of cutting tools and parameters is a difficult task, becouse corresponding machining conditions are very constrained. The influence of heat treatment on the machinability of 12Mn is also very important.

Model of complex optimization of cutting conditions

Modern flexible production with its JUST-IN-TIME philosophy requires efficient organization, high quality tools, selected machining materials with defined mechanical and technological properties and continual determination and optimization of cutting conditions. Therefore, for successful production it is necessary to carry out a number of studies with the purpose to optimize the cutting conditions which should include understanding of tribological problems, the cutting material properties, cooling agent and its application. The rationality and economy of manufacturing which are a result of material and energy saving and shorter machining times, depend to a large extent on the right choice of selected cutting conditions and required product quality. This paper deals with the development of a model for complex optimization of cutting conditions showing that the right way from optimal cutting conditions to product quality is via process quality.