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مطالعه فرآيند شكل دهي لوله هاي بزرگ با دستگاه اكسپندر و بررسي عوامل مؤثر در شكست ابزار

كارشناسي ارشد

مهندسي مكانيك گرايش ساخت و توليد

شهريور 1400

دكتر محمد صديقي

مهندسي مكانيك

1400/07/13

Investigation of the causes for tool failure in large pipe expander machine

9/22/2022 12:00:00 AM

In this thesis, the cold expansion forming process has been studied to investigate the causes for the failure in large pipe expander machine observed in Mahshahr Pipe Manufacturing Industry. The specific failure in the proposed subject happens in the tool segments made of AISI-D2 steel. After collecting the history data of the segments manufacturing process, four possibilities were taken into account regarding the failure: 1) stress concentration, 2) fatigue, 3) difficulties in heat treatment and 4) the undesirable electrical discharge machining (EDM) performed on the segments. In this research, firstly the metal forming simulation results showed that the stress state in segments during pipe expansion was quit low; so the fatigue was not the reason for the failure. Then, the analysis and simulation of time-temperature history of the segment during quenching showed a reduction in tool hardness. For this purpose, the cooling curves superimposed on the steel CCT diagram to predict the phase transformation and hardness. The reduction in the hardness affected the crack growth in the segment, but was not the main cause for the crack initiation. Finally, microscopic observations hinted to the more decisive role of the sharp cracks formed by poor EDM process on the surfaces of the failed segments. This conclusion clarified that inaccurate heat treatment and poor EDM process are the causes for the failure of the segments.

شكل دهي ، انبساط سرد لوله هاي بزرگ ، اكسپندر ، فولاد ابزار D2 ، شبيه سازي عددي ، ماشينكاري تخليه الكتريكي

Forming, Cold expansion of large pipes, Expander, D2 tool steel, Numerical simulation, Electrical discharge machining (EDM