Post-heating Process Research Articles

Optimization of Printing Process Variables and the Effect of Post-Heat Treatments on the Mechanical Properties of Extruded Polylactic Acid-Aluminum Composites.

Polymer extrusions are employed in the fabrication of crucial parts for automotive, aerospace, and other mechanical applications. The use of fillers and microfibers is contributing to the advancement of material extrusion polymers. In order to enhance their mechanical characteristics, printed materials undergo a post-heating process utilizing microwaves. Specimens were fabricated using polylactic acid filaments containing 2 wt% aluminum. Two sets of specimens were fabricated and subjected to testing in order to evaluate the features of extruded specimens and specimens that underwent post-heating. In terms of mechanical performance, specimens subjected to post-heating exhibited superior results compared to specimens merely subjected to extrusion. The tensile, flexural, and Shore D hardness properties of the specimens exhibited improvements of 5.07, 6.16, and 1.32%, respectively, after being subjected to heating. Furthermore, the wear rate decreased by 13.58 percent. The results of the regression analysis indicate that the print angle and the air gap exhibit the greatest influence on the observed responses. The validation test outcomes exhibit a high level of concordance with the predicted findings. The mechanical and surface properties of components extruded with filler-added material are enhanced by subsequent heating.

Effect of in-situ post-heating on the microstructure and tensile performance of TiAl alloys produced via selective electron beam melting

Selective electron beam melting (SEBM) is an additive manufacturing technique commonly used to fabricate TiAl alloys. Changing the process parameters to adjust the alloy structure for enhanced mechanical performance is an effective means in this field. Herein, we investigated the effects of the in-situ post-heating process on the microstructure and tensile performance characteristics of SEBM Ti–48Al–2Cr–2Nb alloys. Two processes were designed: without and with post-heating after melting under identical melting process and total energy input conditions. The tensile strength of the samples with the post-heating process reached 707 ± 12 MPa and strain reached 1.8 ± 0.1%. Compared with the other process, the strain increases by 50%, and the strength decreases by 4.8%. This phenomenon was mainly caused by the more precipitation of γ-phase during the phase transformation of TiAl via an in-situ post-heating process. Even with the same energy input, different heating strategies still significantly affect the tensile performance of TiAl alloy, showing that post-heating is an effective way to improve mechanical properties of additive manufactured material.

Fabrication of continuous glass fiber-reinforced dual-cure epoxy composites via UV-assisted fused deposition modeling

This paper proposes an ultraviolet (UV)-assisted fused deposition modeling (FDM) method with a dual-curing process for fabricating continuous fiber-reinforced thermosetting polymer composites (CFRTPCs). The entire approach is based on the additive deposition of fused continuous glass fiber (CGF)/epoxy (EP) filaments, which are rapidly cooled upon exiting the printer nozzle to form a solid three-dimensional (3D) object. At the same time, UV irradiation is used to activate the photoinitiator and photosensitizer to pre-cure the extruded material. The final polymerization and crosslinking reactions are achieved using a post heat treatment. Herein, the UV absorption characteristics and post heating process of the dual-cure EP matrix were investigated to demonstrate the feasibility and generality of the proposed technique. Finally, 3D printed CGF/EP samples with a 43 ± 3 wt% fiber content exhibited a tensile strength and tensile modulus of 272.51 ± 5.12 MPa and 8.01 ± 0.45 GPa, respectively; flexural strength and flexural modulus of 299.36 ± 6.16 MPa and 8.35 ± 0.18 GPa, respectively; and interlaminar shear strength of 34.06 ± 0.83 MPa. The combination of UV irradiation and post heat treatment offers a rapid, feasible, and effective dual-cure solution for 3D printing of CFRTPCs, which could be a reliable fabrication method for the development of thermosetting composite systems used in various applications.

Microstructure and its hardness estimation of resistance spot weld of ultra-high strength steel sheets: development of resistance spot welding with pulsed current pattern for ultra-high strength steel sheets

ABSTRACT A new resistance spot welding process with ‘pulsed current post-heating pattern’ is developed for improving joint strength of ultra-high strength steel (UHSS) sheets. This post heating process consists of short-time high-current post-heating (pulsed current) and short-time cooling, which utilizes the phenomenon that the pulsed current reheats especially near the outer peripheral regions of the contact area of electrode/steel interfaces and faying interface of steel sheets. The strength improvement can be obtained owing to two effects; the reduction of solidification segregation in the nugget and the appropriate softening of the heat affected zone (HAZ). Toughness of the nugget increases with alleviating segregation of embrittling elements. Properly widened and softened HAZ would lead to large plastic deformation, which could reduce stress concentration at the edge of the nugget on the faying interface and prevent brittle fracture in the nugget during straining. This study aims to elucidate the microstructural change in the HAZ due to the pulsed post-heating current pattern and its effect on hardness profiles, and to propose an estimation method of HAZ hardness. 1180 MPa grade ultra-high strength steel sheet consisting of ferrite and martensite was used. Softened region was fairly widened with decreasing its minimum hardness when applying the pulsed current post heating. No significant difference was observed in the region where the maximum temperature is over Ac1 between with and without the pulsed current post heating pattern. This would be because the maximum temperature was the same in these regions even when applying the pulsed current. The HAZ was widened in the region where the maximum temperature was lower than Ac1. These regions have the same fractions of martensite and ferrite as the steel sheet before welding, but the martensite was much tempered when applying the pulsed current pattern. These tempered phenomena of the martensite can be well estimated using an accumulated tempering parameter for both tempering martensite and autotempering behaviour of martensite formed during cooling after welding.

Synthesis and application of new types of fluorinated oxetanes

Herein, a simple strategy is presented for the one-pot synthesis of fluorinated oxetanes based on the click reaction between fluorinated thiol and ene groups induced by UV radiation. The final fluorinated product was obtained within 10 min and with a nearly 99 % yield. The cationic ring-opening epoxy polymerization at varying concentrations of these fluorinated oxetanes was conducted using real-time Fourier transform infrared spectroscopy. Compared with traditional post-heating process, the pre-heating process showed higher efficiency and energy saving for the preparation of the final coating. The wettability and hardness of the so-prepared fluorinated coatings were thereafter evaluated. Due to the bicyclic rigid structure, the addition of only 2 mol% FNOX led to an increase in the water contact angle from 64° to 107° and a change in pencil hardness from HB to 4H. Furthermore, improved hardness significantly increased its wear resistance. After 50 abrasion test cycles, the coating retained good hydrophobicity. This synthetic route provides new insights into the potential industrial production of fluorinated coatings on a large scale and at a low cost.

Magnetic properties enhancement of hot-deformed NdFeB magnets by two different methods of CeNdCu diffusion

Two different ways were used to control the distribution of cerium for the enhancement of coercivity. One was by coating CeNdCu in the prepared magnet and annealing to make CeNdCu diffuse into the grain boundary to increase the coercivity, the other was by mixing CeNdCu with initial magnetic powders and then preparing the hot-deformed magnet. The SEM-EDS result indicates that cerium diffuses more easily into the main phase by the mixing way, while cerium is mainly distributed in the grain boundary via the coating way. The heat-treatment process may be one of the dominant influencing factors for the distribution of Ce. Multi-steps heat treatment in the mixing way, consisting of hot-pressing, hot-deforming and post heat process, easily introduces Ce into the main phase Nd2Fe14B, which forms the Ce2Fe14B shell resulting in the decrease of HA. But the coating way can ensure uniform dispersion of Ce in the grain boundary, which leads to the high coercivity.

Thermal Stability Change of Insoluble Sulfur by a Heat Treatment and Its Mechanism Study.

Insoluble sulfur (IS), used as a vulcanizing reagent of rubber, is prepared by the thermal ring-opening polymerization of sulfur (S8). Enhancing its thermal stability and content ratio (yield) is important for the industrial production of IS. The post-heating process at a high temperature of 70 or 90°C of the mixture of IS and S8 enhanced the thermal stability of IS and reduced the yield of IS. Further, the process at 30°C enhanced its thermal stability and maintained its yield. Since the thermal stability of IS is considered to be closely related to the chain length of polymer sulfur, a method for determining the chain length of IS was investigated by quantifying the amount of electron spin of radicals from sulfur, estimated from electron spin resonance (ESR) measurements. We confirmed that the long-period post-heating process at 30°C induced high thermal stability without reducing the yield of IS due to growth of the sulfur polymer chains.

One-step solution combustion synthesis and characterization of ZnFe2O4 and ZnFe1.6O4 nanoparticles

One-step solution combustion of ZnFe2O4 and ZnFe1.6O4 nanoparticles was represented. To obtain a better dispersion of nanoparticles with high specific surface area values, salt-assisted solution reaction was applied using KCl as a key criterion. Structure, chemical composition, microstructure, photoluminescence emissions, magnetic properties, and band gap of the samples were also studied. Results showed that ZnFe2O4 and ZnFe1.6O4 crystalline phases were synthesized in a one-step combustion reaction without any post-heating process requirement. The cation distributions amongst tetrahedral and octahedral sites in samples were estimated by modified Bertaut method using XRD data. Both stoichiometric and non-stoichiometric zinc ferrites had a partial reverse spinel structure with high degree of inversion. FTIR spectra demonstrated some bands associated with Fe–O and Zn–O bonds. Moreover, no unwanted impurity such as nitrate was detected in synthesized powders. Microstructure and nitrogen adsorption/desorption studies showed that the synthesized powders were mesoporous with high specific surface area, together with agglomerated nanoparticles. Magnetization curves showed that both ZnFe2O4 and ZnFe1.6O4 samples were superparamagnetic materials.

Controlling of resin impregnation and interfacial adhesion in carbon fiber/polycarbonate composites by a spray-coating of polymer on carbon fibers

To improve the interfacial properties between carbon fibers (CFs) and polycarbonate (PC) resin, the PC resin was pre-coated onto the CF surfaces by a spray-coating method, and a post-heating process was applied for ensuring uniformity of the coating layer. To further investigate the interfacial interactions between the CFs and the coating layers, the physically-adsorbed PC resins were removed from some coated CFs by washing with solvent. The results showed that the CF/PC interfacial adhesion properties could be related to the coating thickness (or the resin impregnation) and fiber-matrix interactions. For a PC coating layer thinner than 0.15 μm, the PC could not be fully-impregnated into the CF bundles, thus leading to inferior CF/PC interfacial properties and mechanical properties in the final composites; while for a coating layer with thickness ranging from 0.15 to 0.32 μm, it allowed formation of well-impregnated interfaces; if coupled with a further hot-pressing for strengthening the interfacial bonding interactions, both the CF/PC interfacial shear strength and mechanical properties for the corresponding composites were significantly enhanced. The interfacial interactions and reinforcing mechanisms for the CF/PC composites were schematically proposed.

Preparation of flame-retardant lignin-containing wood nanofibers using a high-consistency mechano-chemical pretreatment

Deep eutectic solvents (DESs) can be used as green media for lignocellulosic nanofiber production. However, typically, a high liquid-to-lignocellulose ratio is required (i.e. the consistencies of biomass are low, usually limited from 1 to 5 wt%), which greatly reduces the sustainability of DES use. In the present work, wood sawdust was first anionized using a reactive DES (formed from sulfamic acid and urea) at a high mass consistency (with gradually increased sawdust consistencies up to 60 wt%) in the pre-milling and post-heating processes. Anionic sawdust nanofibers (ASNFs) were then produced after mild nanofibrillation (two passes) using a microfluidizer. The processes of producing ASNFs were fast (1 h of pretreatment) and the ASNFs was obtained with high sulfate group contents (up to 3.1 mmol g−1). Besides, the ASNFs possessed a well-individualized structure with a homogeneous size distribution (3–5 nm in width). More importantly, films fabricated from ASNFs achieved strong flame resistance and good mechanical strength. Due to the presence of lignin, ASNF films were able to block over 90% of UV light (at a wavelength of 200–400 nm). The investigated functionalities of ASNFs led the lignocellulosic biomass residuals to be converted to high value-added bioproducts. Therefore, the reactive DES treatment combined with milling and heating process offers a practical and sustainable route for multi-functional biomaterial production, which can be potentially utilized, even at an industrial scale.

Fe7S8 Nanoparticles Anchored on Nitrogen-Doped Graphene Nanosheets as Anode Materials for High-Performance Sodium-Ion Batteries.

Despite high sodium storage capacity and better reversibility, metal sulfides suffer from relatively low conductivity and severe volume change as anode materials of sodium-ion batteries (SIBs). Introducing a conductive carbon matrix is an efficient method to enhance their sodium storage performance. Herein, we present iron sulfide (Fe7S8) nanoparticles anchored on nitrogen-doped graphene nanosheets fabricated through a combined strategy of solvothermal and postheating process. The as-prepared composite exhibits appealing cycling stability (a high discharge capacity of 393.1 mA h g-1 over 500 cycles at a current density of 400 mA g-1 and outstanding high-rate performance of 543 mA h g-1 even at 10 A g-1). Considering the excellent sodium storage performance, this composite is quite hopeful to become a potential candidate as anode materials for future SIBs.

Preparation of Sustained Release Tablet with Minimized Usage of Glyceryl Behenate Using Post-Heating Method.

The purpose of this study was to prepare sustained release (SR) matrix tablets using a direct compression incorporated with a post-heating process. Allopurinol was selected due to the water-soluble property and Compritol 888 ATO® (also known as glyceryl behenate) was used as an SR matrix-forming agent. The API, SR material, microcrystalline cellulose, and magnesium stearate (lubricant) were mixed and prepared into a tablet by a direct compression method. The compressed tablets were stored in a dry oven at four temperatures (60, 70, 80, and 90°C) and for three time periods (15, 30, 45min). The DSC and PXRD data indicated that the crystallinity of the API was not altered by the post-heating method. However, SEM images demonstrated that Compritol 888 ATO® was melted by the post-heating method, and that the melted Compritol 888 ATO® could form a strong matrix. This strong matrix led to the significant sustained release behavior of hydrophilic APIs. As little as 3mg of Compritol 888 ATO® (0.65% of total tablet weight), when heated at 80°C for 15min, showed sustained release over 10h. The post-heating method exerted a significant influence on lipid-based matrix tablets and allowed a reduction in the amount of material required for a water-soluble drug. This will also provide a valuable insight into lipid-based SR tablets and will allow their application to higher quality products and easier processing procedures.

Engineering Surface Vacancy to Stabilize High-Voltage Battery Cathodes

In this issue of Chem, Cao and co-workers report a stabilization strategy for high-voltage lithium-ion battery cathodes down to the atomic scale. Using LiNi0.5Mn1.5O4 as a model, the authors demonstrated a protocol for precisely modulating the interstitial lattice sites on the material surface, showing the promising capability to improve electrochemical cyclability.

High-Speed Growth of ZnO Nanorods in Preheating Condition Using Microwave-Assisted Growth Method.

In this study, we present the microwave-assisted growth (MAG) of ZnO nanorods (ZNRs) using a preheating hydrothermal method under tailored preheating and postheating growth conditions. The perimeters such as solution concentration, preheating time, and postheating time, were changed to optimize ZNR growth and the growth was carried out in a domestic 850 watt microwave oven. Preheated solution was utilized as an accelerator to increase the aspect ratio of the ZNRs and reduce the fabrication time. Because of a long fabrication time and limited length in the conventional MAG method, preheating condition was used for efficient growth of nanorods through homogeneous nucleation in the solution and then heterogeneous nucleation of the formed ZNRs on seeded substrate during postheating process. The nanostructures were characterized with scanning electron microscopy to look at the morphology and dimensions. Dimensions of ZNRs kept on increasing as the molar concentration went higher. Preheating time highly affected the morphology, dimensions, and aspect ratio of ZNRs and postheating time not only ensured the stability of ZNRs with substrate due to heterogeneous nucleation process but also influenced the morphology of ZNRs.

The Effect of Shot-Peening on Thermal Residual Stress around the Singular Point of Cu-Low Alloy Rail Steel in Welded Joints

A copper wire was welded to low-alloy rail steel by exothermic welding. There were pre-heating and post-heating processes before and after welding, respectively. Unfortunately, the cooling rate of temperature could be controlled in the post-heating process. The cooling rate of temperature was too fast because the ambient temperature was very low (-5 °C). After that, the large value of thermal residual stresses remained in the welding joint and led to failure. In the present study, a welded joint between copper and low-alloy rail steel was analyzed using finite element analysis (FEA). The singularity of thermal residual stresses in the welding joint was observed after post-heating processes. The intensity of stress singularity (Kqq) was estimated around a singular point of the welded joint by least-square method. The possibility of crack initiation was determined. Then, a shot-peening process was applied on the surface of the low-alloy rail steel near the singular point of the welded joint. A small particle of 3 mm diameter was shot to make it plastically deform on the low-alloy rail steel surface. The effect of the shot-peening on the singularity of thermal residual stresses around the singular point of the welding joint was determined and found that the value of singularities for the stress sqq profile were reduced and became steady.

Ag-migration effects on the metastable phase in CaCu3Ti4O12 capacitors

The silver migration effect into the metastable phase forms a micro-electric path, to enhance the relative dielectric permittivity of CaCu3Ti4O12 ceramics for electronic devices. Controlling the sintering time uniquely develops the metastable phase of as-sintered CaCu3Ti4O12 ceramics. A post-heating process that applies the migration of silver into the metastable phase increases the relative dielectric permittivity. At 1 kHz frequency, the relative dielectric permittivity at room temperature of the silver-migrated CaCu3Ti4O12 ceramics sintered for 2 h is 565.9 × 103, almost 52 times higher than that of the as-sintered CaCu3Ti4O12 ceramics. The selected area electron diffraction (SAED) patterns of the large and small grains were similar, but differed from those of the metastable region, including the grain boundary of the as-sintered CaCu3Ti4O12 ceramics sintered for 2 h by TEM technique. This phenomenon suggests that enabling Ag-migration into the metastable phase develops a micro-electric path that improves the relative dielectric permittivity of CaCu3Ti4O12 ceramics.

Improvement of the electrochemical properties of LiNi0.5Mn1.5O4 by controlling the heating atmosphere during synthesis

Abstract The heating atmosphere for LiNi 0.5 Mn 1.5 O 4 (LNMO) powder synthesis was controlled during part of the temperature elevation process to examine its effects. The heating profile was designed with two constant-temperature steps, and various atmospheres were introduced during the first (low-temperature) section. The electrochemical performance of LNMO could be controlled by applying an inert or reducing atmosphere during the first heating step. Optimized performance could be obtained by flowing Ar during the first step at 800 °C, which showed simultaneous improvement of the rate performance, room- and high-temperature cyclabilities, discharge capacity, and proportion of the high-voltage discharge relative to conventional synthesis in an oxidizing condition. The underlying mechanism was investigated by a first-principles simulation, which indicated that an inert or reducing atmosphere during the heating period induced disordered arrangement of Ni and Mn while controlling the loss of discharge capacity caused by the formation of impurity phases. This study investigated the effect of conditions during the temperature elevation period of the synthesis while previous research generally focused on the post-heating processes. The method is proposed as a new effective way to control the electrochemical performance of LNMO.

Polymer-Modified Carbon Nanotube Paper As an Efficient Current Collector in Li-S Batteries

Introduction Rechargeable batteries with high energy densities are highly demanded in our daily life and many commercial applications. Lithium-ion batteries have been successfully in the rechargeable battery market, but their energy densities are limited by the capacity of electrodes, particularly the cathodes such as LiCoO2, LiMn2O4, and LiFePO4. To further increase the energy density of rechargeable lithium batteries, alternative cathodes with high specific capacities, such as sulfur with a theoretical capacity of 1,672 mAh/g, are highly needed.1 Sulfur is also an environmental friendly material, which is an abundant element on earth and can be widely used for the future battery applications. Several challenges impede the application of rechargeable lithium-sulfur (Li-S) batteries. For instance, the dissolution and loss of intermediate polysulfide materials between the repeating charge and discharge processes result in rapid reduction of capacity and poor cycle life. To improve the cycling performance, a variety of approaches have been developed showing promising improvements. However, new approaches are still needed which can not only further improve the battery performance but also inspire more interest in the battery community. Lithium/dissolved polysulfide batteries using binder-free carbon nanotube (CNT) paper as a current collector have shown highly reversible cyclability with unprecedented capacities.2 LiNO3 additive in the electrolyte can form a passivation layer on the surface of lithium metal anode, which can reduce the reduction of lithium polysulfide on the anode side. However, prolonged cycle life (>100 cycles) cannot be obtained which is partially due to the loss of active material from the cathode. To overcome this issue, the current collector should be able to “hold” lithium polysulfides from migrating. We present here a strategy to modify CNT paper by a functional polymer to enhance the “holding” property of the current collector, which can eliminate the use of LiNO3 additive in the lithium/dissolved polysulfide batteries and improve cycle life. Experimental Polyvinylpyrrolidone (PVP) was selected as the functional polymer, which has been confirmed to have high affinity with lithium polysulfides and lithium sulfide.3 A solution (0.15 wt.%) of PVP in ethanol was added to a disc of a commercial CNT paper. Ethanol was evaporated by heating to render PVP-modified CNT paper, as shown in Fig. 1. To fabricate half cells, 20 µL of 0.25 M Li2S6/1 M LiCF3SO3 in dimethoxy ethane (DME)/1,3-dioxolane (DOL) (1:1 v/v) was added in the PVP-modified CNT paper as the cathode. Additional blank electrolyte was added in between the lithium metal anode and Celgard® separator. Results and Discussion PVP can be dissolved in ethanol, which can be easily removed during the post-heating process. The solution penetration allows uniform distribution of PVP in the CNT paper. After the modification process, PVP formed many small particles within the 3D CNT network and some thin films in the spaces among CNTs, as shown in Fig. 1. Without LiNO3 additive in the electrolyte, the cell can be discharged to 1.5 V without the reduction of LiNO3 at low potential. The cells show typical two distinguishable discharge voltage plateaus and two overlapped charge plateaus, which are similar to those with LiNO3 additive in the electrolyte.2 Fig. 2 shows the voltage profile of the cell in the 1st, 2nd and 50th cycle after initial charge to 3.0 V. Without LiNO3, the cell can be completely discharged to 1.5 V without a voltage slope meaning negligible side reactions in the discharge. With the PVP coating, diffusion of lithium polysulfides out of the cathode is significantly slowed down, which can be evidenced from the improved cycle life as shown in Fig. 3. The cell without PVP modification shows a rapid capacity decrease from 1,100 mAh/g to 200 mAh/g over 35 cycles. In contrast, the cell with PVP-modified CNT current collector, the cell maintains an average discharge capacity of 900 mAh/g over 50 cycles. The Coulombic efficiency was maintained at 82%. This study demonstrates that PVP can be an efficient binder holding lithium polysulfides from diffusion, which can significantly improve the battery cycling performance. References A. Manthiram, Y.-Z. Fu, and Y.-S. Su, J. Phys. Chem. Lett. 4, 1295 (2013).Y.-Z. Fu, Y.-S. Su, and A. Manthiram, Angew. Chem. Int. Ed. 52, 6930 (2013).Z.W. Seh, Q. Zhang, W. Li, G. Zheng, H. Yao, and Yi Cui, Chem. Sci. 4, 3673 (2013). Figure 1

Induction Assisted Hybrid-Welding Processes to Join Heavy-Walled Steel Components

In order to weld heavy-walled metal sheets (16mm and more) a hybrid process, that includes an electric arc and the laser beam, is frequently applied at present. Due to the high thermal conductivity of metals and the enormous temperature gradient between the laser-welded area and the not welded region around the bond, there is a great heat flow and the welded material is cooled down in very short time. This high decrease of temperature leads to decayed metallurgical qualities. In order to slow down the temperature drop, an inductive process is applied to the hybrid welding device. Because of the high thickness of the metal sheets both an inductive preheating and an inductive post-heating process are added. To configure an optimal design for the inductors the numerical simulation is used and especially the heat generation of the welding process has to be included in a physical realistic way.

Evaluation by FEM of the Influence of the Preheating and Post-Heating Treatments on Residual Stresses in Welding

During the last few years various experimental destructive and non-destructive methods were developed to evaluate residual stresses. However it is impossible to obtain a full residual stress distribution in welded structures by means of experimental methods. This disadvantage can be solved by means of computational analysis which allows to determine the whole stress and strain fields in complex structures. In this paper the temperature distribution and residual stresses were determined in a single-pass butt joint welded by GMAW (Gas Metal Arc Welding) process by finite element model (FEM). A 3D finite parametric element model has been carried out to analyze temperature distribution in butt weld joints and thermo-mechanical analyses were performed to evaluate resulting residual stresses. Temperature fields have been investigated by varying an initial preheating treatment. Moreover the technique of “element birth and death” was adopted to simulate the process of filler metal addition The high stresses were evaluated, with particular regard to fusion zone and heat affected zone. The influence of preheating and post-heating treatment on residual stresses was investigated. The residual stresses decrease when preheating temperature increases. The maximum value of longitudinal residual stresses without pre-heating can be reduced about 12% and 38% by using the preheating and post-heating process respectively.