December 2013

A COMPARATIVE ANALYSIS OF LOWER SPEED CHATTER BEHAVIOUR

MM (Modern Machinery) Science Journal, December 2013

Pavel Bach1, Milos Polacek1, Petr Chvojka1, Jiri Drobilek1, Ondrej Svoboda2

1  CTU in Prague, Research Center of Manufacturing Technology, Prague, Czech Republic

2 Misan s.r.o., Lysa nad Labem, Czech Republic

e-mail: info@rcmt.cvut.cz
 
Abstract

It is known that reduced cutting speeds increase the limit of stability. However, this only applies to milling operations. In turning operations the stability limit initially drops with decreased cutting speed and subsequently rises with a further decrease in cutting speed. A minimum of attention is devoted to this phenomenon in the literature although many authors have noted the decline in the limits of stability during machining tests. In practice, it is important to know the conditions and extent of this decline. This paper summarizes previously published data and provides new data, measured by the authors of the paper. A comparison of the conditions used in the turning tests shows that the decline in the limits of stability and its subsequent increase in the area of lower cutting speed only occur when using a tool with a small clearance angle. A new analysis of the previously published data from the measurement of dynamic cutting force coefficients revealed that the drop in the stability is affected by changing the mutual phase of the dynamic cutting forces and tool vibration.

Keywords: chatter stability drop, turning, lower speed
 
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NUMERICAL AND EXPERIMENTAL DETERMINATION OF SPRINGBACK IN U-BENDING PROCESS

MM (Modern Machinery) Science Journal, December 2013
 

Miroslav Jurcisin1, Jan Slota1, Milan Dvorak2

1  TU of Kosice, Faculty of Mechanical Engineering, Department of Technologies and Materials, Kosice, Slovak Republic

2  BUT, Faculty of Mechanical Engineering, Department of Manufacturing Technology, Brno, Czech Republic

e-mail: miroslav.jurcisin@tuke.sk

Abstract
The most common problem in area of bending technology is problem of achieving accurate and repeatable bending angle. This problem is caused by elastic springback. Springback can be defined as an elastically-driven change of shape of the deformed part upon removal of external loads. This phenomenon is observed also in other sheet metal forming processes. Several technological parameters influence springback amount. In this paper were presented results for different bending curvature and its influence to the springback amount sprinback. Difference between springback amount caused by Bauschinger effect was also discussed. Process was also modelled in the static implicit finite element (FE) code - Autoform. In this paper were used two different materials - UHS and mild steel. Experimental and numerical results were compared and discussed.

Keywords: Springback, Bauschinger effect, bending, numerical simulation, Autoform

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AN UNCONVENTIONAL SOFTWARE ENVIRONMENT FOR FACTORY LAYOUT DESIGN AND AUTOMATED CONVERTER

MM (Modern Machinery) Science Journal, December 2013

Petr Horejsi, Jiri Polcar

UWB, Department of Industrial Engineering and Management, Faculty of Mechanical Engineering, Pilsen, Czech Republic

 
Abstract
The
development of a company layout is a crucial issue during Product Lifecycle Management. When introducing a new product or innovating the current onewhilst respecting the digital factory concept there is a need for stepping through more phases from a technical point of view: construction, technology and digital manufacturing design. This paper deals with the digital manufacturing design stage only - which consists mainly of the development of the manufacturing layout. The manufacturing design stage can be divided into: Rough plannin, Fine planning, Ergonomic Analyses and Discrete Simulation Validation [Kurkin 2010a].
All these stages can be supported by Virtual Reality hardware and software tools. This paper presents a method for producing simulations of factory design with a new self-developed procedure. The first version of an automatic convertor was also developed. This convertor can convert a layout designed with the aid of commercial off the shelf software visTableto a particular environment.
 
Keywords: Virtual Reality, visualization, Source Engine, visTable, manufacturing, factory layout
 
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INFLUENCE OF FLANK WEAR ON DECOMPOSITION OF CUTTING FORCES IN TURNING

MM (Modern Machinery) Science Journal, December 2013

Jaroslav Dubec, Miroslav Neslusan, Anna Micietova, Maria Cillikova

University of Zilina, Faculty of Mechanical Engineering, Department of Machining and Manufacturing Engineering, Zilina, Slovak Republic

 
Abstract
This paper deals with influence of flankwear on decomposition of cutting force in turning of roll bearing steel. The decomposition is carried out to evaluate the components of cutting force in the tool-chip as well as tool-workpiece interface. The decomposition enables evaluation of the shear and normal forces in the both interfaces. The results of experiments and the following calculations show that while conditions for chip separation in the tool-chip interface stays nearly untouched due to progressive development of fland wear, mechanical load of machined surface asssociated with components of cutting forces progressively increases with flank wear.
 
Keywords: cutting force, decomposition, fland wear, turning
 

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INFLUENCE OF SHIELDING GAS ON GMA WELDING OF Al ALLOYS

MM (Modern Machinery) Science Journal, December 2013

 

Ladislav Kolarik1, Karel Kovanda1, Marie Kolarikova1, Petr Vondrous1, Jaroslav Kopriva2

1  CTU in Prague, Faculty of Mechanical Engineering, Department of Manufacturing Technology, Prague, Czech Republic

2  Linde Gas a.s., Prague, Czech Republic


Abstract
The research is focused on influence of shielding gas on GMA welding process of precipitation hard enable Al alloys (6xxx and 7xxx). Pure Ar of different gas flow 0-35 l∙min-1, different Ar+He mixtures, up to 70 % He, active Ar+CO2 gases were used. The optimum Ar shielding gas flow was found to be 15 l∙min-1, where under this value porosity and over this value decrease of weld penetration have been observed. He content in Ar+He shielding gas mixtures is changing heat input and therefore weld shape. Increase of He content improves heat transfer efficiency, weld penetration, weld width etc. Influence of theoretically known properties of gases on welding process (e.g. ionization potential, thermal conductivity etc.) is quite complex, so experimentally researched influence of gases and their mixtures done in this research with exact values and practical results are valuable for praxis.
 
Keywords: welding, GMAW, Al Alloy, shielding gas, Ar, He, mixture
 

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