Yusuf Usta | Gazi University (original) (raw)

Papers by Yusuf Usta

Hücresel imalat sistemi son yillarda yaygin olarak kullanilan ve parti bazindaki üretimlerde uygu... more Hücresel imalat sistemi son yillarda yaygin olarak kullanilan ve parti bazindaki üretimlerde uygulanan bir tekniktir. Fiziksel olarak bir araya kümelenmiş makinalardan oluşan bir hücrede üretim verimini, kaliteyi ve iş emniyetini artirmak, sikici işleri yorulmadan yaptirmak için robot kullanimi tercih edilmektedir. Bu çalişmada, en fazla on makinadan oluşan bir imalat hücresi ve bir tek robot olduğu kabul edilerek, en fazla on

mmfdergi.gazi.edu.tr

... Yusuf USTA, Ömer KELEŞ ve Yücel ERCAN Makina Mühendisliği Bölümü, Mühendislik-Mimarlık Fakült... more ... Yusuf USTA, Ömer KELEŞ ve Yücel ERCAN Makina Mühendisliği Bölümü, Mühendislik-Mimarlık Fakültesi,Gazi Üniversitesi, Maltepe 06570, Ankara, uyusuf@gazi.edu.tr ... Bunu sağlamak için ise, soğuk pistonda yatak bölgesinin daha küçük çapta imal edilmesi gerekmektedir. ...

Advanced Materials Research, 2012

ABSTRACT Parameters on a CO2 laser machine effects the variations on hole diameters. In this stud... more ABSTRACT Parameters on a CO2 laser machine effects the variations on hole diameters. In this study, a CO2 laser machine is used for drilling processes. Processing parameters are selected between 1.2-4 mm workpiece thickness, 2500-4000 W laser output power, -4 to 2 laser focus setting, 8-14 bar assisted gas pressure and 500-1200 Hz laser frequency. After the drilling process, with the diameter measurements, pictures were taken with an optic microscope then the effect of the processing parameters on hole diameter variations were investigated.

Journal of Power Sources, 2008

Journal of Micromechanics and Microengineering, 2009

Integrated and compact products necessitate the use of advanced thermal management systems with r... more Integrated and compact products necessitate the use of advanced thermal management systems with reduced footprint and cost as well as increased efficiency. Micro-scale, porous and modulated (i.e. channels, pyramids, etc) surfaces offer increased surface area for a given volume and lead to two-phase heat transfer conditions with efficiency enhancements up to 300%. Such surfaces made of copper powders were demonstrated to be quite effective by several researchers after they were produced in controlled lab environments. Similar surfaces made of high temperature resistant materials such as stainless steel, nickel and titanium can also be used in fuel processor, SOFC and PEM fuel cell applications as bipolar/interconnect plates. However, their fabrication under mass-production conditions for marketable and cost-effective products requires well-established process parameters. In this study, warm compaction of copper powders onto thin copper solid substrates was experimented with under different compaction pressure (15-50 MPa), temperature (350-500 • C) and surface geometry (flat, large and small channeled) parameters using a design of experiment (DOE) approach to determine the proper process conditions. Porosity and bonding strength of compacted samples were measured to characterize their feasibility for compact and/or micro-scale heat/mass transfer applications. Results showed that a minimum 350 • C temperature and 15 MPa pressure level is necessary to obtain sound porous and micro-channeled surface layers. It was also found that at higher pressure levels (50 MPa), fabrication of micro-scale surface structures is highly repeatable with enhanced bonding strength characteristics. DOE findings will be used to establish proper process conditions to produce such porous surfaces using a continuous roll compaction process in the future.

International Journal of Heat and Mass Transfer, 2009

A new fabrication method (hot-powder compaction) is developed to readily make 2-D and 3-D modulat... more A new fabrication method (hot-powder compaction) is developed to readily make 2-D and 3-D modulated coatings for enhanced pool-boiling performance. The modulated coatings are 2-D and 3-D stacks with different height, width, and pitch (modulation wavelength), and made with different particle diameters and porosities. The maximum measured critical heat flux (qCHF) of 2-D and 3-D modulated coatings are 3.3 and

Journal of Materials Engineering and Performance, 2007

In the present study laser cutting of composite structure, consisting of Kevlar laminate at the t... more In the present study laser cutting of composite structure, consisting of Kevlar laminate at the top and mild steel sheet at the bottom, is considered. The end product quality is assessed using the thermal cutting standards. To compare the end product quality of composite structure cuts, Kevlar laminate and mild steel sheet are cut using the same cutting parameters. The kerf widths for Kevlar laminate and mild steel sheet cuts are predicted from the analytical formulation based on the lump parameter analysis. It is found that the end product quality of composite structure cuts is lower than that corresponding to Kevlar laminate and mild steel sheet cuts.

Optics and Lasers in Engineering, 2008

In some applications, laser cutting of wedge surfaces cannot be avoided in sheet metal processing... more In some applications, laser cutting of wedge surfaces cannot be avoided in sheet metal processing and the quality of the end product defines the applicability of the laser-cutting process in such situations. In the present study, CO 2 laser cutting of the wedge surfaces as well as normal surfaces (normal to laser beam axis) is considered and the end product quality is assessed using the international standards for thermal cutting. The cut surfaces are examined by the optical microscopy and geometric features of the cut edges such as out of flatness and dross height are measured from the micrographs. A neural network is introduced to classify the striation patterns of the cut surfaces. It is found that the dross height and out of flatness are influenced significantly by the laser output power, particularly for wedge-cutting situation. Moreover, the cut quality improves at certain value of the laser power intensity.

Journal of Materials Processing Technology, 2006

CO 2 laser cutting of steel sheets is considered and influence of beam waist position relative to... more CO 2 laser cutting of steel sheets is considered and influence of beam waist position relative to the workpiece surface and the workpiece thickness on the striation formation is examined. The kerf width is modeled using a lump parameter analysis. The measurements are composed with the experimental findings. SEM and optical microscopy are conducted to examine the cutting surfaces. It is found that beam waist position has significant effect on the kerf size and as the workpiece thickness reduces, the relative location of beam waist position varies for the minimum kerf width. The microcracks are found in the resolidified material at the cutting surface, which is due to non-uniform and rapid cooling of the resolidified material at the surface.