Prof. Dr. Ömer Eyercioğlu danışmanlığındaki tezler

Effects of local heating on formability of advanced high strength steel in U-bending operation

New grades of steel with high strength are being developed within the steel industry, of which, the steel of martensitic structure that has come to light recently with low ductility that is considered as the main concern in sheet bending operation. Indeed, bending has been researched extensively over the years since the application of bent parts varies widely. Yet, similar bending techniques are used to obtain the bent shapes of most ferrous and non-ferrous metals. In this study, a developed method was introduced to enhance the technique for bending the martensitic steel by heating the bending zone, bending in die, then cooling in air. A finite element model was built and validated by experiments to bend a sheet of MS1500 with a thickness of 2 mm into U shape at temperatures ranged from RT to 750°C. Optimal temperature distribution in the sheet was achieved, however, the percentage of martensite decomposing was increased with the temperature elevation resulted in decreases in the hardness of the bending zone. Likewise, the bending load and the springback were highly impacted by the bending temperature. Lastly, sheets with thicknesses of 1, 1.5, and 2 mm were studied using the built FEM to predict the springback, maximum load, and damage.

Noktasal dövmenin sonlu elemanlar modellemesi

Peen Forming is a type of controlled deformation that can be managed through residual stress for a workpiece forming process. This process is typically applied using metallic, ceramic, or laser shots called impact. The main principle is the same for all peening methods. Instead of others, the Needle Peen Forming (NPF) has preferable properties in respect to optimizing the process and high energy efficiency. This research aims to create an experimental setup to define the effects of NPF on the different thicknesses and, different indentation depths of SAE1070 steel Almen strip type A and type C under different working pressures and, to compare the experimental setup with the FE analysis model. The saturation points and the arc heights of strips were exposed to 6 different indentation depth ratios under 4 different pressures. The plastic deformations on the Z-axis ( arc heights ) of workpieces were quantified by a comparator probe that assembled a CNC milling machine's head. A maximum 5.7% difference in arc height was observed between the results of FE modeling and experimental studies. The presented NPF methodology with one needle by multiple impacts proves possible to estimate the last concavity and arc height of sheet metal surface profile. The results prove the convexity of the workpieces can manage by changing the compressed stress at the center of the impact.

Distortion analysis in large-scale additive manufacturing using finite element method

The mechanical properties and deformations of materials produced in large-scale additive manufacturing with different mixing ratios were investigated on the produced samples in this thesis. In the parts produced by additive manufacturing, residual stresses occur on the part due to the transition from liquid to solid. Residual stresses cause unwanted deformation. Shape changes are more prominent in parts produced on a large scale, and this brings a significant limitation in production. In order to overcome these limitations, samples were produced using the homogenization technique of fiber orientations in 15%, 10%, 5%, and 0% carbon fiber-reinforced Acrylonitrile Butadiene Styrene (ABS) by weight. Experimentally, the amount of distortion of the parts modeled according to these carbon fiber ratios was examined, the cooling times were followed, and the results were compared by finite element analyses. In addition, the flexural bending strengths of the samples were investigated by bending tests in accordance with the ASTM D790 standard. The finite element analysis results show 10-20% higher distortion than experimental ones. The maximum flexural strength was obtained for a 5% carbon fiber reinforced specimen among all specimens. The porosity formation for the specimens having more amounts of carbon fibers (10%-15%) reduced the flexural strength According to the results from FEA, pure ABS has the highest distortion whereas 10% ABS-CF has the least distortion.

Yapay kalça ekleminin femur gövdesinin dövmesinin sonlu elemanlar analizleri

Nowadays, total hip arthroplasty is increasing, and an improved artificial hip joint system becomes more needed. The femoral stem is a critical part of the system that upholds the most of stress resulting from the human body weight and movement. Many casting and forming methods are used in the manufacturing of the femoral stem and hot forging is one of the forming processes used to produce titanium-based femoral stem. The effect of the different forging temperatures on the forging of the femoral stem is studied in this thesis and two preforms are used to conduct the final step of the forging. The numerical study was conducted using finite element modeling for an isothermal hot forging for temperatures ranging from (700 ℃ to 1000 ℃). In the study, analyses were conducted to measure the press load and the mapping of the effective stress in the forged part, and the die-filling rate was evaluated. It was observed that the model provided a reliable forged product.

Finite element analysis of enclosed die forging of axisymmetric parts

In this thesis, the finite element analysis of enclosed die forging of axisymmetric parts is studied. Prediction of the exact behavior of enclosed die forging process is becoming increasingly essential and it also important to optimize the process design to reduce the required load and consumed energy. In this study, evaluation of forging load and metal flow for H-shape part by using various punch/counter-punch movements and various preforms are presented. By using a finite element analysis (FEA), uni-directional forging and bi-directional loading conditions for two types of preforms (upset and extrusion mode of deformation) are compared in terms of forging load, deformation energy and metal flow under different friction conditions. The effects of rib angle and hub thickness of H-shape forgings on the forging load and energy are also shown. The experimental work is carried out by using a modeling material (plasticine) for verification. The results show that the forging load asymptotically increases at the final stage of the forging where the corner filling of the die cavity. The maximum forging load is considerably reduced by using the bi-directional step loading (divided flow), therefore, the usage of servo-driven presses are very effective. The material flow in bi-directional forging of the H-shape is symmetrical while the flow in uni-directional forging is non-symmetrical. The non-uniform material flow increasing the deformation resistance and friction load. Key Words: FEM, enclosed die forging, divided flow, bi-directional loading

Analysis of warm forming of locally heated sheet metals by using finite element analysis

Automotive industry uses stainless steels for place where needed corrosion resistance and aluminum or magnesium alloys to reduce weight of chassis. High mechanical properties of these materials are reasons for preference however low formability of these materials in the ambient temperature creates manufacturing problems. In this study, enhancement of bending ability of a stainless steel and a magnesium alloy by local heating was investigated. The specimens were bent in V-bending die by using a servo-press at room temperature. Load and deformation rate were determined during forming process. Final shapes were measured by Coordinate Measuring Machine (CMM) and springback ratios were determined. Same procedures were conducted with locally heating (heating the region of deformation) and the results were compared with cold forming. It was observed that locally heating the bending area was adequate to give form the workpiece and this result was verified with FEM. The changing of the thickness on the bending area was also determined for cold and locally heated specimens. Keywords: Locally Heating, Formability, Stainless Steel, Magnesium Alloy, FEM.

Evaluation of cutting surface quality in high speed blanking process

Blanking process holds a crucial point in metal forming industry. The main goal in blanking is to achieve the best surface quality on the blanked parts while spending minimum energy. In this study the surface quality, cutting load and cutting energy of the workpieces were investigated under three different speeds (0.1 m/s, 1 m/s and 10 m/s) with respect to the clearance, material thickness and thickness to die diameter ratios. Five different clearances (1%, 3%, 5.%, 10.0% and 20.0%) were used to blank 2 mm, 3 mm and 4 mm thick workpieces made of AISI 304 stainless steel under four different ratios (t/Dm=1/5, t/Dm=1/10, t/Dm=1/30, t/Dm=1/50). Both experimental and FEM studies were accomplished. Results showed that increasing punch speed improves the surface quality and best surface quality was achieved at 10 m/s by reaching lowest surface roughness values. Another important contribution is the thickness to die diameter ratio and found out that energy, surface quality and related clearance values change according to the workpiece diameters that are neglected in the literature which only considers the thickness of workpiece. The total energy increases due to increasing punch speed, thickness and thickness to die diameter ratios. Clearance between 3% and 5% is found to be optimal value range for AISI 304 stainless steel when considered all investigated parameters.

Precision forging of asymmetric spur gear

The use of asymmetric gear tooth profile can be considered as a creative and innovative solution for many power transmission applications where gear wheels often rotate in only one direction. However, the production of the asymmetric gear profile by the conventional thread cutting method is dependent on the cutting tool design and the machining process. Recent studies in this area have shown that asymmetric profiles designed independently from the cutting tool are more efficient. In precision gear forging, on the other hand, the final tooth profile is determined by the die geometry, and therefore the limitations of the cutting tool can be eliminated totally. The precision forging of asymmetric spur gear was studied in this thesis and the design criteria for the asymmetric spur gear die were presented. For this purpose, upper bound energy analyses (UBEA) and finite elements (FE) simulations of the gear forging process were carried out to determine the forging load and die stresses. The gear tooth profile modifications of the die required for the dimensional accuracy of the forged gear were evaluated. The UBEA and FEA results were compared with the experimental studies. The study shows that precision forging is a feasible method for the manufacturing of asymmetric spur gears and the method eliminates the limitations of the tooth profile of gear cutting or generation methods. However, the design of the forging die is critical in the success of the process. The design criteria presented in the study can be used successfully.

Hybrid additive manufacturing by shaped metal deposition

In this thesis, a study on Shaped Metal Deposition (SMD) technique which is one of additive manufacturing methods was presented. The study was related to experimental investigation and creation of Hybrid Additive Manufacturing (Hybrid AM) by using SMD machine. In the Hybrid AM method, instead of removing the material, products are manufactured by adding a layer upon layer in order to the material has a near net or net shape of the full geometry. Thus, the final shape of the products can be produced by using less material, and hybrid parts can be easily produced by this method. Hybrid AM can produce fully functional assemblies without any assembly operation. However, Hybrid AM describes multi-operational or multi-functional additive manufacturing systems. In industry, the increasing tendency in applications of Hybrid AM brings up the challenge of improving novel methods for the manufacturing of new or hybrid parts. A special care is essential for the intended manufacturing for SMD to get the output at its optimum. In this study, a prototype hybrid SMD system with using pulsed TIG-Wire-Arc technique was designed and constructed. The constructed SMD system has three drivers on x, y and z axis and an additional rotary driver (fourth axis). The Hybrid AM machine was designed and constructed in such a way that the material can be deposited on an existing object e.g. a rod, pipe, a profile or any 3D surfaces. This may reduce production time if a primitive profile is used as the substrate. By this way spiral shaped features or twisted blade shapes can be added on cylindrical parts. The temperature distribution, overhang angle, microstructure and hardness measurements of the printed parts that are produced by this system, were investigated experimentally. Key Words: Hybrid Additive Manufacturing, Shaped Metal Deposition, TIG-Wire Technique.

Abrasive flow machining of asymmetric spur gear forging die

Abrasive Flow Machining (AFM) is a relatively novel and non-usual surface finishing process that is performed by the movement of abrasive media through the surface. Conventional surface finishing operations are limited to regular geometries as circular, rectangular or flat shapes. With the help of the flowability of media, AFM is not limited by simple geometries especially for internal shapes like forging and extrusion dies. In this study, AFM was carried out for finishing the asymmetric spur gear precision forging die. A mathematical model was derived to obtain material removal with respect to the number of AFM cycles. CFD analysis has been used to predict the flow characteristics of the flowing media and the stresses exerted on the die surface. The material removal depth (i.e. dimensional change) along the gear tooth profile was investigated by using two AFM models; circular- and gear-shaped mandrel models. The white layer formed after the WEDM process was successfully removed by AFM. The resulting surface roughness values are in between polishing and super-finishing ranges. The experimental results are in agreement with the presented mathematical model. The mathematical model is suitable for both circular- and gear-shaped mandrel models. Although circular-shaped mandrel is simple and economical, the use of gear-shaped mandrel results in a more uniform surface finish and a higher amount of material removal. Due to the amount of material removal depth is non-uniform through the tooth profile, some amount of machining allowance must be considered during tool path generation for WEDM cutting.

Design and manufacturing of asymmetric spur gear forging die

Asymmetric gears have some advantageous in one directional motion. But, due to the profile geometry, the production with the conventional cutting method limits the design of the profile. Recent studies in this area have shown that asymmetric profiles designed independently from the cutting tool are more efficient. Therefore, in this study, a precision forging die of an asymmetric spur gear was designed and the design criteria were presented. Because the die is exposed to high loads and tensions during forging in a short period of time, a single ring shrink fit assembly was proposed. A design procedure for determination for the dimensions of the die components and the amount of interference was developed. The tooth profile deviations of the die due to shrink fit and the forging load of the die were also investigated. Software was developed to generate corrected tooth profile due to the above-mentioned deviations. The results predicted by the software were validated by finite element analyses. A gear die measurement system was developed based on image processing and software was integrated to automatically measure the dimensions of the spur gears. An asymmetric spur gear forging die was designed and manufactured using the presented criteria. The dimensions of the die were measured by the developed image processing system and CMM. The CMM measurements and the image processing algorithm results are in good agreement. The results show that the developed inspection system can be used for asymmetric gear measurements with the advantages of less time requirements.

Evaluation of metal flow precision forging of axisymmetric parts

Design and construction of a compact high energy rate forming (HERF) hammer

High speed forming is receiving increasing attention due to high rate of production, smaller-size equipment, improved quality of the products and economic reasons. It is also preferred to manufacture parts which cannot be produced by other methods because of size and material characteristics. However, high speed forming requires specially designed equipment and techniques. High Energy Rate Forming (HERF) hammers operate at forming speeds between 5 and 22 m/s.The aim of this study is to design and construct a compact prototype HERF hammer which uses two-cylinder internal combustion to produce forming energy and a mechanical re-cocking mechanism. Therefore, it can be considered as a new type of HERF hammer in the literature. It?s a compact prototype having a capacity of 100 J and 12 m/s forming speed. The performance characteristics of the HERF hammer were compared with conventional hydraulic and mechanical presses. For this purpose, forging and blanking operations were carried out on three different materials (aluminum, St37 and AISI 304) using these presses.The results of open die cylindrical forging operations show that the barreling effect is reduced by increasing punch speed. The blanking load and energy values for all of the materials under investigation were significantly reduced at HERF hammers. From the microstructural analyses of the blanked surfaces, formation of adiabatic shear band was observed at higher strain rates. The surface quality of the blanks are also much better at HERF hammers showing less dishing and lower surface roughness. The corrosion test results indicate that the resistance to corrosion of the blank surfaces increased with increasing punch speed.

Kaynak mikroyapisinin sonlu elelmanlar yöntemi kullanilarak modellenmesi

In the present study, arc welding of the AISI 1045 steel is modelled by using 2D-FEM for three types of welding groove; V, double V and U. The temperature distribution, microstructure, grain growth, and the hardness of the heat affected zone (HAZ) of the welding are simulated. The experimental work is carried out to validate the FE model. The very close value between the simulation and experimental results show that the FE model is very effective for predicting the microstructure, the phase transformation, the grain growth and the hardness. The effect of preheating temperature on the martensite formation is analysed. It is shown that 225oC, 300oC and 350oC pre-heatings eliminate completely the martensite formation for 12 mm thick, V, U and double V-shaped butt welding of AISI 1045 steel. Among the welding grooves, the V-shape is providing the lowest martensite formation and the lowest preheating temperature for martensite elimination.

Evaluation of multi-stage electro discharge machining (edm) parameters

Electrical discharge machining (EDM) is a well-established machining process for manufacturing geometrically complex and/or hard parts that are extremely difficult-to-machine by conventional machining processes. However, the process is a complex task due to the nonlinearities of the process parameters. In a whole EDM process, multi-stage machining is generally carried out from rough to finish for minimizing the machining time. In this thesis, the effects of the most important electrical parameters such as discharge current (I), pulse on time (Ton) and pulse off time (Toff) to material removal rate (MRR), electrode wear ratio (EWR), surface roughness (Ra) and average white layer thickness (AWLT) were experimentally investigated for different machining stages. The experimental data was modelled using artificial intelligence techniques and the alternative EDM parameter sets were generated by the help of these models. A multistage strategy and a computer program were developed to determine the required number of stages for minimum machining time. The resulting average white layer thickness of the previous stage was taken as a criterion to determine the machining depth. The machining depth and the corresponding parameters set in each stage according to the desired surface quality, volume and area of the workpiece can be defined by using the alternative EDM parameter sets which were generated by the models. The developed multi-stage EDM strategy and the computer program were experimentally verified.

Abrasive flow machining of edmed surfaces

Abrasive flow machining (AFM) is a novel technique having potential to provide high precision and economical means of finishing inaccessible areas and complex internal passages of hard, high strength, heat resistant alloys and die steels. The AFM process has been applied to improve the surface integrity of the parts processed by electro-discharge machining (EDM). During EDM process, rapid heating and cooling occur and they cause re-cast (white) layer which has micro-cracks, poor mechanical properties and irregular features on the workpiece surface. The effects of AFM process parameters (number of cycles, abrasive type, mesh size and concentration, workpiece material and hardness) on wire EDMed surfaces have been investigated in this study. A one-way and two-way machines were designed and constructed to carry out the experimental work. A polymer based abrasive media which acts as a deformable grinding tool for obtaining enhanced quality characteristics has been developed. A series of experimental studies were carried out on DIN 1.2379 cold work tool steel and titanium (grade 1) using SiC, Al2O3, B4C and garnet as abrasives with different mesh sizes and concentrations. The experimental results showed that the white layer formed during WEDM is successfully removed by AFM in a few cycles and the surface roughness of the rough-cut samples reaches to the finish-cut ones. Therefore, the pre-machining time and the cost may be reduced by eliminating finish cut in WEDM, if AFM is used as the post-finishing process. The surface roughness decreases with increasing number of cycles and the abrasive concentration. The resulting Ra values are comparable to the surface quality of those obtained from lapping and super-finishing. The material removal increases with increasing abrasive mesh size and the abrasive hardness. The experimental results also showed that the harder workpiece material has more surface improvement than the softer ones.