Papers by Author: Ulvi Şeker

Abstract: MMCs components are mostly produced using near net shape manufacturing methods and are subsequently machined to the final dimensions and surface finishes. The MMCs consist of extremely hard reinforcing particles and pose considerable challenges due to the poor machinability and severe wear of the cutting tool. In this study, cutting performance of WC, CBN and PCD cutting tools were investigated with respect to surface roughness during machining of 10 wt % SiCp reinforced Al-Si alloy matrix composites produced by powder metallurgy (PM) method. Average surface roughness (Ra) corresponding to each machining condition was measured. After the machining process the worn insert tips were examined under the scanning electron microscope (SEM). Chip geometry and machined surface photographs have been taken by optical microscopy. The experimental results showed that surface roughness decreased with increasing cutting speed for all of cutting tool materials. The best surface integrity was occurred after the machining with PCD insert at the highest cutting speed employed.

Abstract: In this study, the machinability of the Cu matrix composites reinforced with 5, 10, 15 and 20 vol.% of Al2O3 particulates produced by powder metallurgy have been investigated. The effects of compaction pressure, sintering duration and volume fraction of reinforcing component on the surface roughness during machining of the considered composites, obtained by the appropriate Cu-Al2O3 powder mixtures cool die pressing at 500, respectively 700 MPa, and sintered at 800 °C for durations of 45 and 60 minutes in an argon atmosphere were determined. The machining tests were performed on a CNC machining centre, by means of samples face milling in dry conditions, at two different feed rates and four different cutting speeds, while the depth of cut was kept constant. As cutting tools have been adopted commercial grade (H13A) uncoated cemented carbide inserts manufactured by Sandvik Coromant with the geometry of TPKN1603 PP-R. After the machining tests, the surface roughness measurements clearly showed an increasing trend in surface roughness when the feed rate is increased from 300 mm/min to 400 mm/min for both sintering durations. Surface damages created on the machined surface through release from the matrix of particles negatively impact surface roughness. The most stable results in terms of surface roughness were obtained at 20% reinforcing ratio for 700 MPa compacting pressure and 60 minutes sintering duration.

Abstract: The objective of this paper is experimentally investigation of the effects of different chip breaker forms on the cutting forces according to various cutting parameters. AISI 1050 workpiece material, most used material in the manufacturing industry, and SNMG 120408R inserts and PSBNR 2525M12 tool holder have 75° approaching angle according to ISO 3685 are used in the experiments. Seven groups chip breaker form were used in the tests. The chip breaker forms are the coated inserts MA, SA, MS, GH and standard, and the uncoated inserts MS and standard. These inserts are Mitsubishi UC 6010 and UTI20T grade; correspond to ISO P30 and P15 grade, respectively. Machining tests were carried out by using five levels of cutting speeds (150, 200, 250, 300, 350 m/min), three levels of feed rate (0.15, 0.25, 0.35 mm/rev) and two levels of depth of cut (1.6, 2.5 mm). Cutting forces were measured using Kistler dynamometer. The test results show that the highest cutting force values were measured on SA, GH, MA forms, respectively. Complex chip breaker forms cause the increase of the cutting forces. Although the cutting forces on the uncoated inserts were partly small in light cutting conditions, it has increased on the uncoated inserts in heavy cutting conditions compared to coated inserts.

Abstract: In this paper, a mathematical model has been developed for the cutting tool stresses in machining of nickel-based super alloy Inconel 718 used in aircraft and spacecraft industries, nuclear power systems and steam generators etc. necessitating oxidation and corrosion resistance, high temperature and strength. The cutting forces were measured by a series of experimental measurements and stress distributions on the cutting tool were analyzed by means of the finite element method using Ansys software. The mathematical modeling process of the compressive stresses in x, y and z directions was carried out with multiple regression analysis regarding to Ansys stress results depending on the cutting forces and the chip–tool contact area. It is found that model results had good agreement with the Ansys stress results.