• Transactions of Materials Processing
• /
• v.15 no.8 s.89
• /
• pp.609-614
• /
• 2006

Micro-alloyed steels(MA steels) for cold forging was developed to replace the usual quenched and tempered steel. MA steels have several advantages over the conventional quenched and tempered carbon steels. First of all, energy consumption could be lowered due to the elimination of spherodizing annealing and quenching/tempering heat treatment. Also, bending during quenching could be avoided when MA steels are applied for manufacturing of long fastener parts. However, larger amount of load is exerted on the dies compared than in the case of conventional mild steels, which might lead to the earlier fracture of dies, when MA forging steels are applied in forging practice. Therefore, die lift could be a critical factor to determine whether HA forging steels could be widely applied in cold forging practice. In the present study, authors have investigated the forging characteristics of non-heat treated micro-alloyed steel by using a series of experimental and numerical analyses. Firstly, microstructural features and its effect on the deformation behavior have been studied. Numerical analysis has been done on the forging of guide rod pin to investigate for the optimization of forging process and die stress prediction.

• Transactions of Materials Processing
• /
• v.12 no.8
• /
• pp.702-709
• /
• 2003

In the automotive industry hydroforming of sheet metal pairs have received special attention because materials for various sheet metal components of vehicles have changed into the high strength steel, aluminum, and titanium blank having low formability. Uniform deformation over the whole region is a main advantage in the sheet hydroforming process. Because upper and lower parts could be produced simultaneously with one tool, hydroforming of sheet metal pairs is competitive in reducing the lead-time and development cost. In this paper, the multi-stage hydroforming process of sheet pair is proposed in order to increase the formability of a structural part like the oil pan shape. The upper die for forming oil pan shape is divided into two parts which can move separately. By the finite element simulation, the design parameters such as geometry of the tool and detailed specification of hydraulic pump were calculated and verified. For the strict comparison of the proposed process, the blank holding force is kept to a constant value during deformation by hydraulic valve. The deformed shape and strain distribution of the manufactured parts with the proposed process are compared with the results of simulation. In the multi-stage hydroforming process, maximum thickness strain was improved by more than 30 percent.

• Transactions of Materials Processing
• /
• v.18 no.8
• /
• pp.607-616
• /
• 2009

There are three sub-processes associated with the assembly of the valve seat and cylinder head; heat fitting, cold fitting, and shrink fitting. In the heat fitting stage, the cylinder head is heated to a specified temperature and then squeezed toward the outer diameter of the valve seat. The cold fitting process cools the valve seat and safely squeezes it toward the inner diameter of cylinder head. However, these methods increased the installations & running cost and curtailed productivity. To address these problems, we analyzed the shrink fitting process using the contact pressure caused by fitting interference between the outer diameter of the valve seat and the inner diameter of the cylinder head. In this study, a closed form equation for predicting the contact pressure and fitting load is proposed. For quality control of the assembly line, principal factors of the shrink fitting process influenced in contact pressure were simulated by the FEM. Actual loads measured in the field showed good agreement with the results obtained by theoretical and finite element analysis.

• Transactions of Materials Processing
• /
• v.16 no.1 s.91
• /
• pp.20-24
• /
• 2007

Polypropylene substrate with hair-like nano features(aspect $ratio{\sim}10$) on the surface is fabricated by injection molding process. Pure aluminum plate is anodized to have nano pore array on the surface and used as a stamper for molding nano features, The size and the thickness of the stamper is $30mm{\times}30mm$ and 1mm. The fabricated pore is about 120nm in diameter and 1.5 um deep. For molding of a substrate with nano-hair type of surface features, the stamper is heated up over $150^{\circ}C$ before the filling stage and cooled down below $70^{\circ}C$ after filling to release the molded part. For heating the stamper, stamper itself is used as a heating element by applying electrical power directly to each end of the stamper. The stamper becomes cooled down without circulation of coolant such as water or oil. With this new stamper heating method, nano hairs with aspect ratio of about 10 was successfully injection molded. We also found the heating & cooling process of the stamper is good for releasing of molded nano-hairs.

• Transactions of Materials Processing
• /
• v.24 no.6
• /
• pp.411-417
• /
• 2015

The piston engine is an essential component in automobiles. Since the piston is used in a high temperature and high pressure environment, the piston needs to be manufactured to achieve high strength and high durability. In addition, cost reduction is also an important consideration. In conventional forging, an additional heat treatment after hot forging is necessary to ensure proper mechanical properties for heavy-duty engine pistons. The newly developed manufacturing method lowers production costs by saving manufacturing time and reduces energy consumption. The current paper describes the hot forging of an engine piston made from 38MnSiVS5 micro-alloyed steel using controlled cooling. The finite element analysis was used to check for possible problems and suitable press capacity. Hot forging experiments were then conducted on a 2500tons crank press to evaluate feasibility of the proposed material and process. To check the mechanical properties after hot forging, the forged specimens were tensile tested, and the microstructures were examined in order to compare the results with the conventionally forged material. The skirt region of the as-forged 38MnSiVS5 piston showed better material properties compared to the conventional material. In addition, the total production time was reduced by about 80% as compared to conventional forging.

• Transactions of Materials Processing
• /
• v.20 no.7
• /
• pp.504-511
• /
• 2011

The alkaline earth metal Ba has a relatively low melting point. Because of its significantly high affinity to oxygen, nitrogen and sulfur, it is highly functional as a steel refining agent. But Ba can adversely affect the properties of steel especially the workability, because it can form a variety of inclusions. So, understanding of these inclusions is needed for improvement of the properties of steel. Thus a fundamental study in the formation behavior of non-metallic inclusions in Ba added Hyper Duplex STS melts was investigated. The amount of Ba, holding time and temperature were considered as experimental variables. The number of non-metallic inclusions decreased and the large particle size of non-metallic inclusions increased as the amount of Ba increased. The number of non-metallic inclusions also decreased and the large particle size increased with increased holding times and temperatures of molten steel.

• Transactions of Materials Processing
• /
• v.23 no.4
• /
• pp.238-243
• /
• 2014

Recently, magnesium alloys have been widely used in the automotive, aerospace and electronics industries with the advantages of high specific strength, excellent machinability, high electrical conductivity, and high thermal conductivity. Deep drawn magnesium alloys not only meet the demands environmentally and the need for lighter products, but also can lead to remarkably improved productivity and more rapid qualification of the product The current study reports on a failure prediction procedure using finite element modeling (FEM) and a ductile fracture criterion and applies this procedure to the design of a deep drawing process. Critical damage values were determined from a series of uniaxial tensile tests and FEM simulations. They were then expressed as a function of strain rate and temperature. Based on the plastic deformation histories obtained from the FEM analyses of the warm drawing process and the critical damage value curves, the initiation time and location of fracture were predicted. The proposed method was applied to the process design for fabrication of a Mg automotive compressor case and verified with experimental results. The final results indicate that a Mg case part 39% lighter than an Al die casting part can be produced without any defects.

• Transactions of Materials Processing
• /
• v.23 no.4
• /
• pp.211-220
• /
• 2014

The outer race of a constant velocity (CV) joint having six inner ball grooves has traditionally been manufactured by multi-stage warm forging, which includes forward extrusion, upsetting, backward extrusions, necking, ironing and sizing, and machining. In the current study, a multi-stage cold forging process is examined and an assessment for replacing and modifying the conventional multi-stage warm forging is made. The proposed procedure is simplified to the backward extrusion of the conventional process, and the sizing and necking are combined into a single sizing-necking step. Thus, the forging surface of the six ball grooves can be obtained without additional machining. To verify the suitability of the proposed process, a 3-dimensional numerical simulation on each operation was performed. The forging loads were also predicted. In addition, a structural integrity evaluation for the tools was carried out. Based on the results, it is shown that the dimensional requirements of the outer race can be well met.

• Transactions of Materials Processing
• /
• v.26 no.1
• /
• pp.48-54
• /
• 2017

The dissolution and precipitation of Nb, which has been known as strong carbide-forming element, play a key role in controlling phase transformation kinetics of microalloyed steels. In this study, we analyzed both numerically and experimentally the precipitation behavior of Nb-microalloyed steel and its effect on the austenite decomposition during cooling. Nb precipitation in austenite matrix could be predicted by the thermo-kinetic software MatCalc, in which interfacial energy between precipitate and matrix is calculated. The simulated precipitation kinetics fairly well agrees with the experimental observations by TEM. Austenite decomposition, which is strongly affected by Nb precipitation during cooling, was measured by dilatometry and was modeled on the basis of a Johnson-Mehl-Avrami-Kolmorgorov(JMAK) equation. It was confirmed that the dissolved Nb delays the austenite decomposition, whereas, the precipitated Nb accelerates phase transformation during the austenite decomposition.

• Transactions of Materials Processing
• /
• v.27 no.3
• /
• pp.165-170
• /
• 2018

In order to increase the lifetimes of cold forging dies, insert rings are generally used. In this study, an insert ring and shrunk ring of the flange upsetting die were designed for the cold forging of an automotive wheel nut. The Stress distribution occurring in the die during forging was simulated using a commercial finite element analyzing program. The effects of the fitting interference and inclined angle of the insert ring on the compressive stress of the die inside were also investigated. The simulated data were compared with the real lifetimes of the forging dies. The maximum compressive stress acting on the edge of a forging die should have the most influence on die lifetime, an idea which could help develop the die design with the longest lifetime. The design of the most optimal forging die with the longest lifetime is made possible by analyzing the maximum inner pressure and principal stress between the shrunk ring and insert ring.