Cracking of Telescopic Front Fork Tube During Field Operation
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CASE HISTORY—PEER-REVIEWED
Cracking of Telescopic Front Fork Tube During Field Operation Arthita Dey • Sharmistha Dhara • Tanmay Bhttacharyya Sandip Bhattacharyya
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Submitted: 2 January 2013 / in revised form: 14 January 2013 / Published online: 13 April 2013 ASM International 2013
Abstract Telescopic front fork tube of the bike is manufactured by electrical resistance welding of pickled hot rolled strip followed by cold drawing. The fork undergoes cyclic loading during operation and is prone to crack along the weld. This paper presents the investigation of such a failure of fork at field. The investigation consists of visual inspection, chemical analysis, characterization of microstructure, and energy dispersive spectroscopy. The result of the analysis revealed that there was a pre-existing crack, known as hook crack, which lead to the cracking of the tube. The hook crack was slightly offset from the bond line, i.e., weld line between the edges of the cold drawn electrically welded seam. Metallographic examination exhibited that during field operation the pre-existing hook crack was surfaced out leading to crack in the pipe. Parallel separation/delamination due to upsetting of pipe edges during welding caused the ‘‘hook crack’’ formation. Keywords Electrical resistance welding Hook Delamination Manganese sulfide Upsetting of weld
Introduction Motorcycle fork connects a motorcycle’s front wheel and axle to its frame, typically via a pair of triple clamps. It typically incorporates the front suspension and front brake, and allows the bike to be steered via handlebars attached to the top clamp. This contains fork tubes which contain the suspension components (coil springs and damper) internally. The front fork tube is manufactured from structural A. Dey (&) S. Dhara T. Bhttacharyya S. Bhattacharyya Tata Steel, Scientific services, Jamshedpur, India e-mail: [email protected]
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grade steel and it attributes high strength, surface finish, ease of manipulation, and closer dimensional tolerance. Initially the coil is loaded on the lock side of double mandrel un-coiler (DMU) by a cantilever crane and the strap is being cut out manually, followed by straightening of the end of the coil material by pinch roll flattener, only the ends are levelled for coil end welding. Then the ends of the coils are welded by MIG welding procedure. Then the strips are accumulated vertically on a larger radius in continuous coil accumulator (CCA). Then the coil is pickled and pickled slit coils of 125 mm 9 3.80 mm dimension are fed at 400 tube mills for manufacturing tube of 41.28 9 3.80 mm dimension. The continuous strip coming out of stamping unit is formed to a tubular shape in tube mill. The forming of the strip is initiated by a special w-pass roll drive followed by four pairs of horizontal– vertical rollers. Ultimately fin-pass is used to precise the weld bead thickness. Continuous high frequency induction welding takes place and the tubular-shaped strip is properly formed into a tube. The high frequency weldin
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