Theses supervised by Doç. Dr. İsmail Lazoğlu
10 theses · Koç University
Minyatür ve vücuda yerleştirilebilir bir kalp pompasının sol karıncık destek sistemi olarak geliştirilmesi: Santrifüj Türk kalbi
Heart disease is one of the most common, unexpected and number one cause of death globally; according to world health organization, approximately 17.5 million people died because of cardiovascular heart disease in 2005 which represents the 30 % of all of the deaths worldwide. In Turkey, similar situation also occurs; 55% of the total deaths is because of the heart failure problems. According to the Europe Heart Health Research, Turkey is the European leader in the number of heart failures for the ages of less than 50. In Turkey, every year approximately 500,000 patients have heart failure and 2000 to 3000 of them need urgent heart transplantation. Unfortunately, due to lack of donors, only about a few operations can be done every year.During the long waiting time for a healthy donor heart, an artificial heart, mainly a ventricular assist device is currently the only hope and possible solution for the patients. Artificial heart pumps are known to be the best solutions for bridge-to-transplant, bridge-to-recovery and final medical solution for the patients who suffer from heart failures that result from the overfilling of the blood vessels of heart.There are various ventricular assist devices produced in the developed countries. It is imported and used in about 20 patients in Turkey. Costs of LVAD systems are very high and not affordable by many patients in Turkey. The aim of this thesis is to develop a new ventricular assist device in Turkey. The VAD system being developed is named as ?Heart Turcica?. The development process of the Heart Turcica LVAD system of five main parts: CAD (Computer Aided Design), CFD (Computational Fluid Dynamics) analyses, CAM (Computer Aided Manufacturing), precision production by Computer Numerical Control (CNC) machines and performance testing. The developed Heart Turcica LVAD system consists of a centrifugal pump, control unit and peripheral equipments. The pressure rise of the heart pump, flow rates and rotational speeds are controlled and monitored in the experiments.Heart Turcica Centrifugal is designed and manufactured from Titanium alloy to be biocompatible with the blood tests in the hospital. In this thesis, the design process of the heart pump, the performance curves of several designs, and the results of in-vitro experiments carried out are presented.
Açık mimariye sahip yeni bir hızlı prototpileme sisteminin geliştirilmesi
Rapid Prototyping (RP) is a crucial technology in order to reduce the product development time. Today this technology is not only used for prototyping in product development but also manufacturing of small volume products and rapid tooling for some special cases. Moreover, beside the production industry, it is used in a wide range of areas from art to medicine. RP technology enables 3D model designed by using a computer aided design (CAD) program to be manufactured layer-by-layer. This advanced technology allows users to save significant amount of time over the conventional manufacturing methods. Many different RP methods have been developed in the last two decades and well known ones are stereolithography (SL), selective laser sintering (SLS), laminated object manufacturing (LOM) and fused deposition modeling (FDM). A wide range of materials including ceramics, polymers and metals can be used for production with these methods. In addition, living cells can also be used to create tissues with RP technology.In this thesis, a novel open architecture rapid prototyping system is developed including all its hardware as well as its software. The hardware includes a 3-axis machine that is precisely controlled by a PC via a servo system. Since the system is open architecture, various tool path generation algorithms developed in-house can be implemented. Three different slicing and path generation software are created. In the developed software, the operator can generate tool paths manually as well as using stereolithography files (STL file) or cutter location source files (CLS file) as inputs. The STL or CLS files for any part can be obtained from any commercially available solid model based CAD/CAM programs. The developed software processes 3D CAD data and generates electronic signals to drive the servo system. Moreover, a new rapid prototyping robot dispensing (RPBOD) unit is developed and integrated to the system. Various 3D parts produced by this new open architecture RP system are also presented.
Bir sol karıncık destek aygıtının tasarımı: Heart Turcica Centrifugal
Left ventricular assist devices (LVADs) are highly demanded in fighting against cardiovascular diseases which are statistically number one cause of death. In this respect, Heart Turcica Centrifugal (HTC) that is composed of a continuous centrifugal blood pump (CBP) is purposed to be developed. In development of such a device, design phase is highly challenging due to both mechanical and medical constraints such as need of small-size, high efficiency, biocompatibility. In order to satisfy the entailed design features, a regular flow within the pump is inevitable. Since the flow behavior is mainly governed by the geometry of the pump, the design tools utilized in determining the values of geometric design parameters were investigated. Design tools included One-dimensional (1-D) design procedure, Computational Fluid Dynamics (CFD) analyses, and trial and error method. In the investigation design tools, Computer Aided Design, Engineering, and Manufacturing (CAD/CAE/CAM) tools were utilized. 1-D design procedure was found to be unable to provide assistance to design since operating conditions of CBPs fall out of the valid range of the theory. CFD analyses were found to be incapable to assist the design by means of determining the values of geometric design parameters because the tool couldn?t predict the experimentally measured hydraulic performance of many designs. In contrast, trial and error method initiated with an inspiration from the findings of previous studies was quite successful in designing a CBP. An initial pump, Model 3, was manufactured with values of geometric design parameters adjusted with respect to the previous findings in literature. With respect to the experimental results of Model 3, Model 4 was manufactured with change of control parameter, impeller outer diameter, in accordance with the affinity laws. Model 4 achieved required operating conditions (5 L/min flow rate against a pressure difference of 100 mm-Hg) at a rotational speed of 3000 rpm. Further flow analyses of the pump were conducted with CFD analyses after validating the tool with successful prediction of experimentally measured hydraulic performance. Analyses of shear stress and velocity vectors pointed no risks of hemolysis or thrombogenicity. The proposed design methodology was, thus, successfully applied and yielded satisfactory results.
Kompresör valf yapraklarının darbe yorulması özelliklerinin incelenmesi
A unique automated impact fatigue test system has been designed and produced, which enables to carry out impact fatigue tests of the compressor valve leaves under the desired impact velocities. The test system serves investigations on the impact fatigue characteristics with the ability of crack detection and as the subsequent step of terminating the test system. The crack detection technique incorporates a microphone and a data acquisition system with a non-contact actuation. The impact fatigue experiments were performed on hardened and tempered carbon flapper valve strip steel Sandvik 20C, martensitic stainless chromium steel alloyed with molybdenum Sandvik 7C27Mo2 and Sandvik Hiflex®.The impact fatigue life was determined for various impact velocities. The influence of temperature on the impact fatigue life of Sandvik 20C was investigated in the designed temperature control cabin. Cold-worked edges of the valve leaves were sharpened due to the blanking operation of the valve leaves. Therefore, a tumbling operation is performed in order to round the sharp edges, remove the small manufacturing defects and introduce compressive residual stresses. The edge radius of the specimens was characterized and tumbling duration was correlated with the impact fatigue life. In addition, asymmetrical impact behavior due to the variation in working condition of compressor and the designs of other components were examined. Microscopic and metallographic observations were carried out. It was observed that the impact fatigue failure originated at the edge of the valve leaves on the contact surface of valve leaf and vale plate. The crack propagation results were also presented. The introduced test system and methodology guides the design optimization of valve leaves in terms of compressor performance due to energy consumption and lifetime of the valve leaf.
Heart turcica centrifugal sol karıncık destek sisteminin in vitro kan testleri için geliştirilmesi
Patients need heart transplantation in order to recover from heart related diseases but there is shortage of donor. Left ventricular assist devices (LVADs) are developed for patients that are in the late stages of cardiovascular diseases. Heart Turcica Centrifugal (HTC) is the first centrifugal LVAD that is being developed in Turkey. In the previous stages of the development, HTC was brought to the stage of blood tests in order to determine its hemolytic performance. This thesis covers the development process of HTC for in vitro blood tests. First prototype of HTC was manufactured of biocompatible Ti-6Al-4V ELI for the in vitro blood tests. However, the driver magnets on the bottom of the impeller were not biocompatible, so a solution had to be developed. The first approach was to coat these magnet surfaces with biocompatible coatings such as Diamond Like Carbon (DLC) coatings. Those coating failed to solve the problem. In order to solve the problem a design modification has been made. Impeller of HTC was manufactured from two components, which encapsulated driver magnets and prevented their blood contact. HTC could be subjected to in vitro blood testing for hemolytic performance. During in vitro blood test ASTM International standards F1830 and F1841 will be used. A test loop with proper equipment will be prepared and HTC will be connected to this setup for the in vitro blood testing. According to the ASTM F1841, Normalized Index of Hemolysis (N.I.H.) will be calculated in every hour for test duration of 6 hours.
Dinamik omurga implantının geliştirilmesi ve l3-l4 segmentinin sonlu elemanlar yöntemi ile modellenmesi
Low back pain due to disc degeneration is a worldwide major health problem at any age, but especially at an elderly age. In the treatment of low back pain, dynamic stabilization may provide a more physiologic alternative to fusion. In this study, initial model of dynamic implant was developed that limit abnormal motion at the segment while preserves the motion within normal physiological limits. The effects of design parameters to strength and flexibility of the implant were investigated. Initial design was improved to final design that builds balance between flexibility and strength.Finite element model of an intact L3-L4 lumbar segment was developed. Load sharing characteristic of implant and effect of implant to segmental range of motion are two main criteria in evaluation of the newly developed implant. Finite element analysis were performed to investigate effects of newly developed implant to the segmental range of motion and load sharing characteristics in lateral bending, flexion, extension, and axial rotation. In this study, intact L3-L4 model and four types of screw-implant systems were investigated. These systems were rigid screw-rigid rod system, rigid screw-dynamic implant system, polyaxial screw-rigid rod system, and polyaxial screw dynamic implant system.The polyaxial screw-dynamic implant system exhibits the best results for range of motion and load sharing characteristics within four stabilization systems. The reduction of motion for the polyaxial screw-dynamic implant system in all loading is minimum within four stabilization systems. This stabilization system shares load with the intervertebral disc and the facet joints. The rigid screw-rigid implant system greatly reduces the motion in all loading. Performances of other two stabilization systems in range of motion and load sharing are lying between the polyaxial screw-dynamic implant system and the rigid screw-rigid implant system.
Serbest yüzey geometrili parçalarin 5 eksen küresel frezelenmesinde kesme kuvvetlerinin modellenmesi
5-axis milling processes are used widely in various industries such as aerospace, die-mold and biomedical industries where surface quality and integrity is important and the production tolerances are very tight. Therefore, improving surface quality and integrity without sacrificing productivity is crucial in these industries. Improvements in CAD/CAM, cutting tool and the machine tool technologies allow the production of high precision parts with less cycle times. In order to obtain desired quality and productivity, process parameters such as feedrate, spindle speed, axial and radial depth of cut have to be selected appropriately. In general, these parameters are selected conservatively, most of the time arbitrarily, in order to prevent workpiece, cutter or the machine to be damaged. Consequently, this selection criterion is based on engineering expertise or trial and error methods. Therefore virtual machining simulation for milling processes is an increasing demand before the production of the free-form surfaces.In this thesis, virtual machining simulation model for the simulation of cutting forces in 5-axis ball-end milling of free-form surfaces is presented.5-axis milling kinematics differs from the 3-axis milling. For this reason, modeling of 5-axis machine tool kinematics is introduced and a generic post-processor with variable feedrate is developed. A virtual machine simulation model, which is capable of simulating machine tool movements from the NC code, is also presented.Cutting forces in machining is determined by extracting the Cutter-Workpiece Engagement (CWE) from the in-process workpiece. A discrete method (Three-Orthogonal Dexelfield) of obtaining CWE maps for 5-axis ball-end milling is developed. The results of the Three-Orthogonal Dexelfield method is compared with the solid-modeler based CWE calculation method.A cutting force prediction model for 5-axis ball-end milling is developed. Cutting force modeling is performed in the fixed coordinate frame (for table type dynamometer) and in the rotating coordinate frame (rotating coordinate dynamometer). A modular approach is developed where different cutter and workpiece geometries and tool motions can be incorporated into the model without additional analysis. Several validation tests are presented in the study and these validation tests demonstrate that presented cutter-workpiece engagement model is accurate and force predictions are in good agreement with the measured data.
Doku mühendisliğindeki yapı iskelet üretimi için açık mimari sistem
In this thesis, two open architecture rapid prototyping systems are described. One of them was designed and manufactured in previous work by Erdem Cerit and his colleagues. Other system was developed in this work. Both systems were developed in the Manufacturing and Automation Research Center at Koc¸ University. Both of the systems are 3 axis machines. First generation rapid prototyping (RP) system has three servo motors and one step motor. In the second generation RP system four step motors are used to actuate the system. Since the systems are open architecture, various tool path generation algorithms developed in-house can be implemented. In this work precise algorithms were developed and implemented to both of the systems. Developed programs enable production of parts without using any CAD or CAM software. Hollow spheres and 3 dimensional scaffolds can be manufactured on first generation RP system. Other two algorithms which were implemented on the other system allow operator to fabricate equilateral quadrilaterals as well as scaffolds with different dimensions. The developed programs for both of the systems process input data and generates electronic signals to drive the motors. Various 3D parts produced by both systems are also presented. Finally, polymeric scaffolds fabricated by using old RP system were cell cultured in vitro to determine if they could be used for tissue engineering applications. It was shown that scaffold material is not toxic and cells can attach and proliferate on it.
Oblik kesme işleminin ısıl modellenmesi
Machining processes such as turning, milling, drilling, grinding etc. are the most widespread processes for producing final shapes of the discrete parts. In today?s competitive manufacturing environment, increasing productivity without sacrificing from part quality is an obligation. Considering machining from this point of view, physics based modelling of machining process and optimization of process parameters gain importance.The aim of this thesis is to develop a novel temperature prediction model that is applicable to oblique cutting processes in variable cutting conditions. Thesis consists of two main parts. In first part mechanics of oblique cutting and mechanics of turning process is presented. Orthogonal to oblique transformation procedure is used in mechanical analysis. Mechanical and geometric outputs of first part are utilized in thermal model as simulation inputs. In second part of the thesis, thermal modelling approach is introduced. A finite difference method based approach is followed in modelling of cutting temperatures. Oblique cutting process model is applied to prediction of turning temperatures by splitting turning geometry in to oblique cutting segments. This block by block modelling approach allows representing a complex problem with simpler subparts. Then, tool, chip and workpiece temperatures are calculated.Predicted temperature values are validated by using the data available in literature. Simulation results showed that average temperatures on rake face are in acceptable agreement with experimental results. Proposed solution method can be utilized in selecting optimum processing parameters, tool geometry and tool material in order to avoid excessive tool temperatures.
Hibrid ve açık mimari lazer iş istasyonu geliştirilmesi
The overall goal of this research was to develop a laser workstation which is capable oflaser machining (laser drilling, laser cutting and laser marking) and direct (SLS) armedwith a fundamental understanding of the underlying physics behind it. The knowledgegained from experimental (with technological demonstration) and analytical work isessential for machine design, process development and control.