INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING Vol. 16, No. 9, pp. 1975-1981 AUGUST 2015 / 1975 © KSPE and Springer 2015 Forming Box-Shaped Ends in Circular Tubes Chin-Joo Tan 1,2,# , Judha Purbolaksono 1,2 , and Wen-Tong Chong 1 1 Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia 2 Centre of Advanced Manufacturing and Material Processing (AMMP Centre), Level 8, Engineering Tower, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia # Corresponding Author / E-mail: tancj1@yahoo.com, TEL: +603-79675237, FAX: +603-79675237 KEYWORDS: Balusters, Tube forming, End forming, Decorative columns, Box shape, Plastic reshaping This study is aimed to form a pair of axially displaced box-shaped ends from a circular tube. In this process, one tube end is first expanded into a circular section having a diameter equal to the diagonal length of the target square using a conical top circular die. A square punch having a conical bottom end and a tapered square die are then used to draw the expanded section into a square box. The side walls of the box are flattened at an ironing ratio of 15% corresponding to its initial wall thickness. The expansion and squaring processes are repeated at the opposite tube end. However, the tapered die in the final stage is oriented at 45 relative to the square punch and tube to form an axially displaced square section at the opposite end. Both the experiments and FE simulations were performed to evaluate this process. A pair of axially displaced box-shaped ends having small corner radii is successfully obtained from the experiment and the simulation. With the developed process, the design of steel balustrades is improved and similar to the precast or stone balustrades. Manuscript received: March 23, 2014 / Revised: February 12, 2015 / Accepted: May 28, 2015 1. Introduction Balusters are normally made of plasters, stones, woods and wrought irons. It is usually formed by a molding, carving or forging process. Although there are some steel balusters in the market, its designs are very simple i.e. either in straight round or square. Despite its stylish surface, the aesthetic quality of the stainless steel tube is not as good as the carved or the molded ones due to its simple shape. Hence, it is important to reshape the steel tube to improve its aesthetic value. Plastic reshaping of round tubes into different cross sections have been mainly performed by cold rolling, hydroforming and tube end forming process. In the cold rolling process, the round tubes are continuously passed through a series of flat idle rollers at reducing roll gap in each pass until the circular sections are completely reshaped into square sections. Kiuchi et al. 1-4 theoretically analyzed and optimized the reshaping process. Kiuchi and Feizhou 5 developed a simulation program based on 3D elastoplastic finite element method for the reshaping of round pipes into square and rectangular pipes. Naeini et al. 6 have designed roll profiles and pass-schedules for the reshaping of round tube into the pentagonal cross-section. Bayoumi 7 analytically solved the problem for the cold flattening of a round tube into an oblong shape by means of rolling process. Abrinia and Farahmand 8 solved the reshaping of a thick square tube from a round one based on the upper bound method. Bayoumi and Attia 9 presented an analytical solution and finite element simulation using the ABAQUS/ STANDARD and LS-DYNA to reshape a round tube into a square section through four flat rolls. However, reshaping by rolling produces only the continuous profile along the tube. It cannot form a tube having multiple cross sectional shapes. Hydroforming of a round tube inside a box-shaped die had been widely presented by others. Chen et al. 10 modeled hydroforming of a round tube inside a square die cavity with and without end feeding. Hwang and Altan 11 analyzed the plastic flow pattern for the expansion or crushing process of a round tube into a rectangular cross-section. The ratio of the corner radius of the square section to its initial wall thickness was 2.4. Kridli et al. 12 discussed the effect of strain hardening component and die corner radii on thickness distribution of hydroformed parts. Orban and Hu 13 developed an analytical model to determine the variation in the stresses and strains along the tube wall as the internal pressure increases to expand the circular tube into a NOMENCLATURE s 1 = Punch stroke in 1st stage s 3 = Punch stroke in 3rd stage DOI: 10.1007/s12541-015-0257-0 ISSN 2234-7593 (Print) / ISSN 2005-4602 (Online)