The sub-frame is located on the lower body of a monocoque type vehicle and serves as an engine and suspension, and is an important object part that receives a lot of load. The existing press-type sub-frame has a large number of parts for assembling, which causes an increase in cost. Changing the machining form of this part from the existing press-type machining method to the hydro-forming machining method has the advantage of reducing the cost and weight at the same time due to the reduction of the process. Therefore, in this study, the purpose of this study is to change the design so that the sub-frame of the existing press type can be changed to the hydro-forming process method. To this end, we intend to present a design method by analyzing the effect on the rigidity of the sub-frame using the existing machining method through shape optimization analysis.

Hydro-forming technology is a technology that will replace the existing press-forming technology and is used in various industry range from automotive parts to electronic products. The advantage of this technology is that it has dramatically changed the existing processing method, and it can be said that the process reduction due to the reduction of parts, cost reduction, and high precision are mentioned. In this study, it is intended to present a design process using computer simulation by changing the sub-frame for automotive parts produced with the existing press forming technology to the hide-forming method. To this end, it is intended to use it as part design data by comparatively analyzing the cross-sectional shape and thickness reduction, which are the major factors necessary to determine the successful development of the developed parts.

In this study, stiffness evaluation was conducted on the main member, front cross member, and rear cross member, which are three components of sub-frame for SUVs (sports utility vehicles), through mode analysis. As for the design variables used in the analysis, the maximum frequency was examined by varying the width and height of each of the three parts into four types. Of course, the weight at this time is minimized, and the mode is set as a constraint that only bending occurs and no distortion occurs. As a result of the analysis, the member affecting the 1st mode was the rear cross member, and the member having the greatest influence on the 2nd mode was the front cross member. In addition, the member with the greatest influence on the 3rd mode appeared as the rear cross member, indicating that this part had the greatest effect on the bending stiffness.

The hydro-forming design process of the sub-frame side members was studied using a high strength steel of 440 MPa in tensile strength. In the part design stage of the side member, the cross section analysis and the overall process design of the part shape were done. In the detailed simulation results, the maximum thickness reduction rate due to hydro-forming was predicted to be 13% and this was predicted to be a safe level without cracking. The end curvature was reduced to increase the stiffness of the part to design more secure parts and two types of grooves were added to the cross section and compared. The thickness reduction rates of the narrow and wide were improved by 18.6% and 15.6%, respectively when the narrow and wide grooves were added.

Hydroforming is a forming technology in which a steel tube is fixed in a die and formed to fit a specified design shape by applying hydraulic pressure from inside the tube. In present study, the whole process of sub-frame side member development is presented by tube hydro-forming using steel material. At the part design stage, it requires feasibility study and process design aided by CAE (computer aided design) to confirm hydro-formability in details. Overall possibility of hydro-formable side member parts could be examined by cross sectional analyses. All the components is designed and formability is examined from the point of geometry and thinning. From the simulation results, the maximum thickness reduction rate is 55% after hydroforming. In order to improve this result, the feeding by 30 mm is applied to the both sides of the tube and the thickness reduction can be reduced from this management.

Recently, the use of tubes in the manufacturing of the automobile parts has increased and therefore many automotive manufactures have tried to use hydro-forming technology. The hydro-forming technology may cause many advantages to automotive applications in terms of better structural integrity of the parts, lower cost from fewer part count, material saving, weight reduction, lower spring-back, improved strength and durability and design flexibility. In this study, the whole process of sub-frame parts development by tube hydro-forming using steel material is presented. At the part design stage, it requires feasibility study and process design aided by CAE (computer aided design) to confirm hydro-formability in details. Overall possibility of hydro-formable sub-frame parts could be examined by cross sectional analyses. All the components of prototyping tools are designed and interference with press is examined from the point of geometry and thinning.

The latest weight reduction research of automotive industry and technology was improved. In this paper, we aim to evaluate the composite frame to manufacture the floor assembly of commercial vehicle. The design of subframe incorporated into the floor module was determined by FEM(Finite Element Method) simulation. The mechanical properties used for the simulations were obtained from the tests for samples of glass fiber/epoxy composites. We made two kinds of pultrusion products, one was aluminum profile, the other was unidirectional composites with aluminum profile. Based on the results from the simulation and bending test, the design of the subframe was finally determined prior to adoption of the commercial vehicle floor.

In commercial vehicle, sub-frame which equipped in main frame supporting dump deck and oil tanker. This is the main structure for all equipment which including joint function. Sub-frame is made by welding process, this susceptible to deform and crack by its longitudinal size. Also various kind of sub-frame make it difficult to standardization in manufacturing process and exclusive jig is not adapted yet. Frame size is over 6~8m and weight is more than 300kg this make re-work more difficult. If manufacturing company made precise sub-frame, this is not only convenient for customers but also save the company money by reducing the working time. In this study manufacture the sub-frame be suitable for its main function and develop exclusive welding jig for obtain checking fixture function as well.

Hydroforming is a forming technology in which a steel tube is set in a die and formed to fit a specified shape by applying hydraulic pressure from inside the tube while also applying force in the tube axial direction (axial feed). In present study, the whole process of automotive cross members simulation and development by hydroforming technology to apply high strength steel is covered. At the part design stage, it requires feasibility study and process design aided by CAE(Computer Aided Design) to confirm hydroformability in details. Overall possibility of hydroformable cross members parts could be examined by cross sectional analyses. Moreover, it is essential to ensure the formability of tube material on every forming step such as pre-bending, preforming and hydroforming. At the die design stage, all the components of prototyping tool are designed and interference with press is investigated from the point of geometry and thinning.