Bilgin Kaftanoğlu

An environmentally friendly method of cutting and forming of materials by boron nitride coated tools

To decrease the undesirable effects on global warming and environmental pollution, manufacturing techniques should aim to use less energy, generate less pollution to the environment and aim at higher performance in shaping and cutting materials. In this paper, a new coating technique is presented for cutting and forming tools so that they can withstand higher temperatures, preserve their surface quality and cutting edge longer and require minimum quantity of lubrication (MQL) and achieve a longer life. It is known that coolants used in manufacturing cause environmental problems and their processing raises the manufacturing cost. Therefore, MQL or dry cutting is preferred if the tool material can withstand the high temperatures. A new technology of boron nitride (BN) coating using a physical vapour deposition (PVD) system is developed. BN coatings are applied on cutting tools and forming dies. Experiments and industrial applications show an increase in tool life. MQL and manufacturing at higher temperatures can be used due to the stability of BN.

A Study on the Constitutive Equation Effects in the Fracture Initiation of AA5450 Sheets

Determination of the fracture initiation in the sheet metal forming applications can be achieved successfully using ductile fracture criteria (DFCs) and finite element codes together. In this study three different uncoupled, energy based ductile fracture criteria have been employed to predict the onset of the fracture in the AA5450 aluminum alloy sheets. Also, two different constitutive models namely, isotropic von-Mises and anisotropic Hill, have been implemented to the finite element code ABAQUS through VUMAT subroutine to investigate the effect of constitutive equations on the applicability of the utilized DFCs. It was shown that the constitutive model has significant influence on the estimation of the time and place of the fracture initiation in the sheets.

Wear resistance performance of boron nitride coatings on end milling cutters

For defence industry applications, the machining of ultra-high strength steels or aluminium with ballistic temper grades is a widely-used operation. Therefore, it is a great challenge to find an optimum solution for tool wear. In that sense, tool coatings provide various solutions for machining of hard materials or improving wear resistance. A cost-effective tool coating provides longer tool life, hence decreases the tool cost contribution in production. Boron nitride (BN) coating could be thought as a new generation coating method compared to titanium nitride (TiN), aluminium titanium nitride (AlTiN) or silicon aluminium oxy-nitride (SiAlON). BN coating material has a great strength, toughness and chemical stability whereas it has an important disadvantage of high intrinsic stress. In this industrial study, standard end mill cutters are coated with BN material by physical vapour deposition (PVD) method. The coated and uncoated milling tools are compared according to their wear resistance and the obtained workpiece surface roughness. First results of the study are presented in this paper.

On the fracture prediction of 304L stainless steel sheets utilizing different hardening models

Fracture prediction is one of the challenging problems in sheet metals. Forming limit curves at fracture (FLCF), as a tool to determine fracture in sheet metal processes, are obtained through the use of numerical analyses. As one of the approaches, the ductile fracture criteria (DFCs) represent the fracture initiation of the sheets formed by different loading histories. In this study, the effects of three different hardening models on different DFCs to predict the fracture for stainless steel 304L have been investigated. The results show that most of DFCs work better in the region ɛ2 0 where the stretching conditions are dominant, none of them could precisely estimate the fracture initiation.

Boron nitride coating of tools and dies to improve performance in manufacturing applications

A physical vapour deposition (PVD) system is developed to coat boron nitride (BN) films on tools, dies, and mechanical parts to improve hardness, to decrease wear, to reduce friction and to increase high temperature resistance. Various coatings applications on steel, stainless steel, aluminium, titanium and copper have shown good adhesion. Quality is checked by coating thickness, nanohardness, scratch testing, AFM, SEM and FTIR measurements. BN coating is also applied on specimens and tools which have been previously coated by titanium nitride (TiN). FTIR results show that different allotropes (polymorphs) of BN are produced by different coating parameters. From industrial tests, extended life and improved performance is obtained for tools and dies in manufacturing applications.

Investigation of Influence Parameters on Forming Limit Diagrams of Aluminum Alloy-AA2024

Sheet metal forming technology is the keyword for many industries such as aerospace, aeronautics and automobile industries. Customer expectations, quality and safety requirements and market competitions require sheet metal forming operations to be well analyzed before the process to fulfill all these requirements. In this study, combination of FEA (finite element analysis) and mechanical material characterization were used in order to improve sheet metal forming operations while considering cost and quality. On the material characterization side of the studies, simple uniaxial tensile tests were conducted to obtain anisotropy parameters and yield points along different directions and hydraulic bulge test (HBT) was performed to obtain plastic behavior of the material up to 0.7 strains. Deformation measurements were conducted using optical measurement system GOM-ARAMIS while a 60-ton hydraulic press; Zwick/Roell BUP600 was used to deform the sheet part AA2024-0 aluminum alloy. Effects of process parameters, which are initial material thickness, lubrication and punch speed, on sheet metal formability and forming limit diagrams (FLDs) were investigated. On the study of thickness effects, sheet metals those having 0.81mm, 1.27mm and 1.60mm thickness were tested. Punch velocities of 250mm/min, 500mm/min and 750mm/min were used to investigate effect of punch speed on formability of sheet metals. Finally, PTFE (Polytetrafluoroethylene), paraffin lubricated and dry conditions were presented to obtain friction effects. FE analyses were performed to simulate experiments and to obtain friction coefficients of different lubricants. Good correlations were observed between numerical simulations and experimental results.