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This paper proposes a rolling machine that forms fine corrugated section patterns for thin sheets. A prototype of the machine was made and the performance of the machine was tested. As compared with press forming, rolling has the advantages of the high forming limit, the low forming reaction force, the easy control of the thin sheet's curve and high productivity. We confirmed these four advantages by using finite element analyses and the prototype rolling machine. Stainless steel sheets and titanium sheets, which were one of the materials with a low forming limit, were used. Firstly, the rolling showed a 1.3-times higher forming limit than the press forming in the case that a fine corrugated section pattern was formed in a stainless steel sheet of 22-mm square sizes. Secondly, the forming reaction force of the rolling was about one-twentieth of the press forming without coining, and the experimental results agreed with the finite element simulation.

A simple testing method is proposed in order to investigate ductile fracture in crashed automotive components made from advanced high strength steels. This type of fracture is prone to occur at spot-welded joints and flange edges. It is well known that the heat affected zone (HAZ) is a weak point in high strength steel due to the formation of annealed material around the spot-welded nugget, and the flange edge also has low ductility due to the damage caused by shearing. The proposed method is designed to simulate a ductile fracture which initiates from a spot-welded portion or a sheared edge in automotive components which are deformed in a crash event. Automotive steel sheets with a wide range of tensile strengths from 590MPa to 1470MPa are examined in order to investigate the effect of material strength on fracture behavior. The effects of material cutting methods, namely, machining and shearing, are also investigated.

In order to develop a new carburizing steel material that realizes an intermediate heat treatment-free process in parts manufacturing, the cold forgeability of the as-rolled steel and suppression of abnormal grain growth of austenite were studied. It was shown that adjustment of addition amount of Si, Mn and Cr, suppression of dynamic strain aging during cold forging, and an increase of ferrite fraction by controlled rolling contribute to the reduction of deformation resistance. However, Nb precipitation control by fully utilizing mill manufacturing processes was also necessary for suppression of abnormal grain growth of austenite. A new steel for carburizing was developed by integrating these technologies, making it possible to eliminate annealing before cold forging and normalizing before carburizing simultaneously. Thus, the developed steel is an important innovation in the parts manufacturing process.

The authors have developed a high-performance talc masterbatch (hereinafter HPTMB) to achieve sufficient flexural modulus and impact resistance at the same time using inexpensive conventional PP as a base resin. Highly compressed fine talc and elastomers were selected as the filler and the impact resistance improver by considering their dispersion in the molded parts. The mixing process was also optimized. In order to stabilize impact resistance after molding, several elastomers were selected based on molecular weights and melting points. The developed HPTMB showed excellent balanced properties for instrument panels using inexpensive conventional PP as a base resin. The HPTMB is applied to the instrument panel of a Mitsubishi mini car. This technology will enable us to reduce the material cost by consolidating automotive interior plastic materials as well as by using available conventional PP.

The application of tailored blanks to autobody parts has progressed because of its numerous advantages. The forming of tailored blanks has, however, a lot of technical problems. Among the problems, weld-line movement and formability deterioration are the most significant ones in case of deep drawing. The weld-line movement and formability change were examined experimentally as a function of weld-line location in square cup deep drawing. The weld-line movement of tailored blank consists of two sources. One is the geometrical reason, and the other is due to the hardening of weld bead. The formability of tailored blank is inferior to that of an original blank by the existence of hardened weld region. The mode of fracture changes from wall breakage to a fracture adjacent to punch radius when the weld-line was close to the punch corner.

With society demanding automobiles that provide higher fuel efficiency, safety of occupants in collisions and that at the end of their service life can be recycled with low environmental impact, the steel industry is tackling the needs of the automobile industry by developing ever-higher performance steel materials and simulation technologies that can demonstrate the performance of steel materials at the development stage without the need for costly prototype testing. In this paper, weight reduction of automobile body in Japan will be discussed. The main items will be as follows: (1) Development of Automobile Steel Sheets, (2) Materials for Automobile Bodies, (3) Materials and Technologies (Tailored Blanks, Hydroforming and Locally Quenching) for Reducing the Weight of Panels and Reinforcing members, (4) Future Prospects.

A resin cylinder head model was produced using a rapid prototype producing system. The resin model was used in the lost-wax casting process instead of a wax model. The casting molded by this method was as precise in both shape and dimensions as a casting produced using a metal mold. This paper describes the manufacturing process of cylinder head material using this method in detail.

A method of fatigue life prediction of spot welded joint under multi-axial loads has been developed by fatigue life estimation working groups in the committee on fatigue strength and structural reliability of JSAE. This method is based on the concept of nominal structural stress ( σ ns) proposed by Radaj and Rupp, and improved so that D value is not involved in stress calculation. The result of fatigue life estimation of actual vehicle with nominal structural stress which was calculated through newly developed method had very good correlation with the result of multi-axial loads fatigue test carried out with test piece including high strength steel.

New 440MPa class high-strength steel, which had high r-value(1.6) and elongation(38%), was applied to outer-panel for the first time in the world. In this development FEM simulation was carried out to clarify the necessary steel properties, and the production conditions in strip mill were established. 10-kg weight reduction was realized by using this steel.

In this paper the fatigue life of welded steel sheet structures is predicted by using FE-Fatigue, which is one of fatigue analysis software tools on the market, and these predicted results are evaluated by reference to corresponding experimental results. Also, we try to predict these structures by using two fatigue life prediction theories established by the JSAE fatigue and reliability committee to compare prediction results. It was confirmed that spot welds fatigue life predictions agree qualitatively with corresponding experimental results and arc welds fatigue life predictions are in good agreement with corresponding experimental results in cases where the SN curve database is modified appropriately.

The main operations for the manufacturing of auto parts are the cutting of the flange and the stamping. In order to perform accurate fatigue calculation it is necessary to have the material properties for each point of the structure. Usually, only the fatigue curve obtained on the flat sheet with polished edges is used because it represents the basic metal behaviour. The real edge quality decreases the fatigue limit while the hardening induced by the stamping increases it. To take these effects into account allows a better fatigue calculation of the structural part.

In order to examine the compatibility of improvement of crashworthiness with weight saving of automobiles by using high strength steel, a combination analysis of Finite Element Method and Dynamic Mechanical Properties has been established. Material properties used in this analysis have been measured by “one bar method” high velocity tensile tests, which can examine the deformation behavior of materials at a bend crush speed range (∼55km/h). It was confirmed that the strength of steel measured by one bar method was raised remarkably after press and hydro forming of high strength steels. It was also confirmed by FEM analysis and load drop test that absorbed energy of bend crush was improved by pre-strain effect. Further, we proved that absorbed energy of bend crush was also improved by appropriate design of thickness and the ratio of bend span and plate length. These effects are applicable to respective high strength steels.

The influence of tensile strength on fatigue strength and the effect of strengthening mechanism on fatigue notch factor were investigated into conventional mild steels, HSLA steels, DP steels and TRIP steels. The grade of studied steels was altered from 440MPa to 780MPa. Not only smooth fatigue specimens with side surface ground and smooth fatigue specimens with laser-cut side surface but also fatigue specimens with a pierced hole were prepared for each of steel sheets. Fatigue tests were conducted in an axial load method. These experiments made it clear that the fatigue limits of smooth specimen increase along the tensile strength approximately independent of strengthening mechanism but those of notched specimen do not necessarily increase along the tensile strength. Namely, fatigue limits of DP steels and TRIP steels with notch increase in proportion to tensile strength although those of HSLA steels with notch do not increase.

The newly developed sheet steel lightly coated with an organic composite is as follows. Zn-Ni alloy plated sheet steel with a coating weight of 30 g/m2 and average Ni concentration of 11.5 ∼12.0 % is chromated through electrolysis. The coating weight of chromate film is 50 ∼90 mg/m2 in Cr. Furthermore, emulsified olefin-acrylic acid copolymer resin mixed with colloidal silica of particle size 7 ∼8 nm applied to a thickness of 1.0 ∼1.8 μm. Olefin-acrylic acid copolymer resin and colloidal silica are mixed at the rate of 100 and 30 (parts by weight). It maintains excellent corrosion resistance even after forming, C-ED paint corrosion resistance and paint adhesion. Furthermore, it has excellent perforation resistance. The product has excellent weldability and is well suited to continuous forming, too.

As a demand for vehicles of higher functionality grows, automakers and material suppliers are devoting increasing efforts to develop technologies for greater safety, lighter weight, higher corrosion resistance, and enhanced quietness. The resin-sandwiched vibration damping steel sheet (VDSS), developed as a highly functional material for reducing vehicle vibration and noise, has been used for oil pans1) and compartment partitions2). First applied for a structural dash panel of the new Mazda 929, a Zn-Ni electroplated VDSS which allows direct electric welding has contributed to greater weight reduction as well as improved quietness.

Weight reduction of automobiles is one of the most highlighted subjects in automobile industry from the energy saving and clean environment points of view. A typical approach for the purpose is to use high strength steel sheets as well as optimizing designs and using low density materials. It is not, however, easy to apply high strength steel sheets to automotive panels because of their strict requirement for the shape-fixability although a high dent resistance is also required. Besides the use of bake hardening steels, two different high strength steel sheets, which are a continuously annealed extra-low carbon titanium-added IF steel and a low carbon TRIP steel which contains about six volume% of austenite, were assessed for the application to automotive panels in combination with a tension-controled press-forming technique and showed as good shape-fixability as a conventional box-annealed aluminum-killed DDQ steel sheet when high blank-holding-forces were applied.

Since galvannealed steel sheets (GA) are widely used for automobile body parts, they require excellent features such as press formability, resistant spot weldability and phosphatability. We have focused on improving the press formability of GA since the late 1990s, and have developed a new type of surface modified GA which has a lower friction coefficient than conventional GA. The developed surface modified GA based on mild steel is now used by all automakers in Japan, especially for those parts such as side panels that are difficult to form. This paper describes the features of the surface modified GA.

Sheet hydro-forming was applied to hydro-form a door outer panel using different steel grades. The effect of mechanical properties and the forming conditions on panel properties such as thickness profile and cross-sectional shape accuracy were investigated by both experimental sheet hydro-forming and FEM forming analysis. 590MPa T.S. steel grade was successfully formed with improved dent resistance compared to the conventional 340MPa T.S. steel grade. On the other hand, the results of the FEM forming process analysis showed that the pre-forming conditions were important in controlling the fracture formation during forming and to improve dent resistance, which successfully led to the best forming condition.

A new topology analysis method was developed to optimize part shapes and the configuration of automotive components. Only solid elements are used in the conventional topology optimization method. The key point of the new method is to embed solid elements in a model made of shell elements. In this study, stiffness optimizations were carried out for a simple cylindrical model, automotive floor model and full vehicle model. Specifically, optimized automotive components were a center tunnel, a side-sill and a joint linking a side-member and a cross-member, which are made of steel sheets and have rectangular cross sections. The results show that the newly-developed topology optimization method is valuable in the optimization of automotive components which are made of steel sheets and have rectangular cross sections.

In order to clarify the effect of design and materials of the hem as well as the climatic factors on perforation corrosion of the automobile doors, field car and laboratory investigation has been carried out Field car investigation revealed that corrosion of the hem can be minimized by using two side galvanized steel plus adhesives. The ratio of wet/dry environment was evaluated in laboratory on hemmed sample, and it was found that the design of the hem in conjunction with the various wet/dry ratio affected the corrosion rate differently.