Çetin Karataş

Modelling of residual stresses in the shot peened material C-1020 by artificial neural network

This study consists of two cases: (i) The experimental analysis: Shot peening is a method to improve the resistance of metal pieces to fatigue by creating regions of residual stress. In this study, the residual stresses induced in steel specimen type C-1020 by applying various strengths of shot peening, are investigated using the electrochemical layer removal method. The best result is obtained using 0.26mmA peening strength and the stress encountered in the shot peened material is -276MPa, while the maximum residual stress obtained is -363MPa at a peening strength of 0.43mmA. (ii) The mathematical modelling analysis: The use of ANN has been proposed to determine the residual stresses based on various strengths of shot peening using results of experimental analysis. The back-propagation learning algorithm with two different variants and logistic sigmoid transfer function were used in the network. In order to train the neural network, limited experimental measurements were used as training and test data. The best fitting training data set was obtained with four neurons in the hidden layer, which made it possible to predict residual stress with accuracy at least as good as that of the experimental error, over the whole experimental range. After training, it was found the R^2 values are 0.996112 and 0.99896 for annealed before peening and shot peened only, respectively. Similarly, these values for testing data are 0.995858 and 0.999143, respectively. As seen from the results of mathematical modelling, the calculated residual stresses are obviously within acceptable uncertainties.

Diffusion Welding of Thick Components Fabricated by Inserted Powder Injection Molding

Abstract Powder injection molding consisting of four stages – feedstock preparation, injection, debinding and sintering – is a unique technique to produce small and complex metal or ceramic components in high quantity. One of the limitations of this method is the production of thick components, which arises from difficulties in de-binding stage. In this study, a novel method is presented to produce thick components with large sections by powder injection molding using preformed inserts in the injection stage. By using a wrought insert on which the feedstock is injected, the thickness of an injected section that needs to be debound, is decreased, while the whole thickness of the component is still large. The key point in this method is the amount of diffusion welding of the wrought insert and the injected feedstock to form an integrated component. 316L stainless steel has been used as material for both insert and feedstock. The effects of insert/component diameter ratio and the sintering atmosphere on diffusion welding have been studied. Finally, a defect-free thick component with a diameter of 20 mm is fabricated with a bonded area at the interface of the insert and injected section having shear strength up to 427 MPa.

Experimental and theoretical investigations of mouldability for feedstocks used in powder injection moulding

Experimental and theoretical analyses of mouldability for feedstocks used in powder injection moulding are performed. This study covers two main analyses. (i) The experimental analysis: the barrel temperature, injection pressure, and flow rate are factors for powder injection moulding (PIM). Powder-binder mixture used as feedstock in PIM requires a little more attention and sensitivity. Obtaining the balance among pressure, temperature, and especially flow rate is the most important aspect of undesirable conclusions such as powder-binder separation, sink marks, and cracks in moulded party structure. In this study, available feed-stocks used in PIM were injected in three different cavities which consist of zigzag form, constant cross-section, and stair form (in five different thicknesses) and their mouldability is measured. Because of the difference between material and binder, measured lengths were different. These were measured as 533 mm, 268 mm, 211 mm, and 150 mm in advanced materials trade marks Fe-2Ni, BASF firm Catamould A0-F, FN02, and 316L stainless steel, respectively. (ii) The theoretical analysis: the use of artificial neural network (ANN) has been proposed to determine the mouldability for feedstocks used in powder injection moulding using results of experimental analysis. The back-propagation learning algorithm with two different variants and logistic sigmoid transfer function were used in the network. In order to train the neural network, limited experimental measurements were used as training and test data. The best fitting training data set was obtained with three and four neurons in the hidden layer, which made it possible to predict yield length with accuracy at least as good as that of the experimental error, over the whole experimental range. After training, it was found that the R2 values are 0.999463, 0.999445, 0.999574, and 0.999593 for Fe-2Ni, BASF firm Catamould A0-F, FN02, and 316L stainless steel, respectively. Similarly, these values for testing data are 0.999129, 0.999666, 0.998612, and 0.997512, respectively. As seen from the results of mathematical modeling, the calculated yield lengths are obviously within acceptable uncertainties.

The impact of injection velocity on the defects in thick components fabricated by inserted metal injection molding

Abstract The initial stage of shaping a component in metal injection molding is the injection process. Any defects occurring in this stage are transferred to the subsequent stages, namely debinding and sintering. To investigate the jetting phenomenon in the current study, 316L stainless steel feedstock was exploited as the material for fabricating thick cylindrical specimens with a diameter of 20 mm. Regarding the aforementioned thick specimens, injection at the normal velocity of 15 cm3 s−1 resulted in critical defects, such as folding, weld lines and porosity. It was found that these defects were eliminated in the specimens injected at velocities as low as 1 cm3 s−1. Under such conditions, however, due to the increase in the injection time, the flow front rapidly solidifies with ensuing dramatic deterioration of component surface quality. Furthermore, the present study proposes a novel method, entitled inserted metal injection molding, with a double aim both for removing the jetting phenomenon and the c...

Reducing debinding time in thick components fabricated by powder injection molding

Abstract Of the five steps in powder injection molding, namely feedstock formulation, mixing, injection, debinding and sintering, the one which markedly demands more time is debinding. Studying the effect of specimen thickness on debinding time in the current study, 316L stainless steel feedstock was exploited as the material for fabrication cylindrical specimens with varying thicknesses ranging from 2 to 10 mm. The thicker the specimen, the more time-consuming the debinding is. In addition, a novel method has been presented to produce thick components with large sections by powder injection molding, using preformed inserts in the injection stage. By using a wrought insert on which the feedstock is injected, the thickness of the injected section in need of debinding decreased while the whole thickness of the component was still large. Finally, defect-free specimens with diameter of 20 mm have been fabricated using inserts with different sizes, which resulted in dramatic reduction of debinding time from several days to only some hours. Moreover, it revealed that the interface of the insert and injected section was bonded properly, reaching more than 400 MPa of shear strength, depending on insert/part diameter ratio.

Effect of heat treatment conditions and densities on residual stresses at hybrid (FLN2-4405) P/M steels

The characteristics of residual stresses occurring in PM steel based nickel (FLN2-4405) was investigated. Residual stresses were measured by electrochemical layer removal technique. The values and distributions of residual stresses occurring in PM steel processed under various densities (6.8, 7.05, 7.2 and 7.4 g/cm3) and heat treatment conditions (sintered at 2050 ºF, sintered at 2300 ºF, quenching-tempered, and sinter-hardened) were determined. In most of the experiments, tensile residual stresses were recorded on the surface of the samples. The residual stress distribution on the surface of the PM steels was found to be affected by the heat treatment conditions and density. The maximum values of residual stresses on the surface showed sinter hardened condition and a density of 7.4 g/cm3. The minimum level of recorded tensile residual stresses are150 MPa and its maximum level is 370 MPa.

Investigation of Sintering Behaviors of Steatite Parts Produced by Powder Injection Molding

In this study, the properties of sintered parts produced by Powder Injection Molding (PIM) from the feedstocks of steatite powders with water based binders were investigated. The steatite powder solid loading was 58 vol. %. The properties investigated were density, % size change, tensile and bending strengths. Sintering in a high temperature furnace at different temperatures, heating rates and sintering times have been carried out. Densities of sintered parts have been measured by using Archimedes’ principle. Maximum attained relative density was 96 % at 1275 °C sintering temperature, 5 °C/min heating rate and 3 hours sintering time. At this sintering condition, linear shrinkage was 17.6 %, tensile strength was 16.7 MPa and bending strength was 130.6 MPa.

Residual stresses in injection molded shape memory polymer parts

Shape memory polymers (SMPs) are materials which have shape memory effect (SME). SME is a property which has the ability to change shape when induced by a stimulator such as temperature, moisture, pH, electric current, magnetic field, light, etc. A process, known as programming, is applied to SMP parts in order to alter them from their permanent shape to their temporary shape. In this study we investigated effects of injection molding and programming processes on residual stresses in molded thermoplastic polyurethane shape memory polymer, experimentally. The residual stresses were measured by layer removal method. The study shows that injection molding and programming process conditions have significantly influence on residual stresses in molded shape memory polyurethane parts.

An Electrochemical Machining Device for Residual Stresses Measurement in PM Parts by Layer Removal Method

Residual stresses play an important role in the performance of materials and the components produced from them. All manufacturing processes introduce residual stresses. These stresses can have a positive effect, for example by increasing the fatigue limit in the case of compressive surface residual stresses. Layer removal by electrochemical machining (ECM) can be used for measurement of the residual stresses in the PM parts. The device removed the layers by aid of electrochemical machining for this purpose is designed and developed. The device setup for residual stress measurement is based to the changes on deformation quantity. Since ECM is a non-mechanical metal removal process, ECM is capable of machining any electrically-conductive material with attendant high removal rates, regardless of mechanical properties. In particular, the removal rate in ECM is independent of the hardness, the porosity and toughness of the PM parts being machined. The micro constituents in PM steels resulting from different processing routes exhibit different thermal and mechanical behavior. This will lead to the formation of residual stresses around these micro constituents. Here we give the results of the first work carried out on PM steels in relation to residual stress measurements by the electro-chemical layer removal technique. The device works as follows. As a layer of thickness is removed, a certain amount of stress is removed from the sample. Equilibrium is violated and the sample deforms elastically to compensate for the stress removed. This elastic deformation in the sample is measured by the linear displacement gauge. This gauge pushes on the end of sample and deformation is recorded by this gage. The linear gauge send a signal to a display and then to the data converter. As simultaneous, this signal sent to the computer from the data converter for further calculations by RS 232.