Abstract




 
   

IJE TRANSACTIONS A: Basics Vol. 31, No. 7 (July 2018) 1123-1128    Article in Press

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  OVALITY AND BOW DEFECT OF PRE-PUNCHED SHEETS IN ROLL FORMING OF TRAPEZOIDAL SECTIONS
 
M. Safari and J. Joudaki
 
( Received: November 20, 2017 – Accepted in Revised Form: January 16, 2018 )
 
 

Abstract    Roll forming process is used for manufacturing sheet metal parts by successive bending and creating the final shape with gradual deformation. In this article, deformation of a pre-punched sheet due to the roll forming process was studied. Two main defects in the roll forming process are ovality of holes and bow defect. The ovality of the hole is influenced by the process parameters including sheet strength, thickness, initial hole diameter and distance of hole center to lateral edge. Due to the roll forming process, the sheet undesirably bent along longitudinal direction to a slight curved part which called bow defect. Also, the magnitude of product’s curvature along longitudinal direction (bow defect) was measured. The experimental tests were conducted on ASTM 230, 275 and 340 galvanized steels. The results showed that increase in the yield strength elongates the hole along rolling direction and shortened the hole perpendicular to rolling dimension. Therefore, the ovality of hole increases by increasing the yield strength. Also, similar trends were observed by increasing the thickness and the distance between hole center and lateral edge. The results showed that the bow defect decreases by increasing the material yield strength, while with increase in the sheet thickness, initial hole diameter and hole distance from lateral edge the bow defect was increased.

 

Keywords    Roll Forming; Hole Deformation; Process Parameters; Ovality; Bow Defect

 

چکیده    فرآیند شکل­دهی غلتکی یکی از فرآیندهای ساخت قطعات ورقی بوسیله خم کردن تدریجی ورق می باشد. در این مقاله به مطالعه تغییر شکل ورق با سوراخ­های اولیه در فرآیند شکل­دهی غلتکی پرداخته خواهد شد. دو عیب اصلی در فرآیند شکل­دهی غلتکی، عدم دایروی بودن (بیضوی بودن) سوراخ­ها و تاب برداشتن قطعه است. بیضوی شدن سوراخ­ها وابسته به پارامترهای فرآیند شامل استحکام تسلیم ورق، ضخامت، قطر اولیه سوراخ، فاصله سوراخ ها از یکدیگر و فاصله مرکز سوراخ تا لبه جانبی است. در اثر فرآیند شکل دهی فلتکی، ورق به شکل ناخواسته در راستای طولی خود خم شده و قطعه ای غیرتخت و دارای انحنا را ایجاد می کند که این عیب را تاب برداشتن می گویند. در این مقاله میزان ارتفاع خمیدگی اندازه­گیری شده است. آزمایش­های تجربی بر روی ورق گالوانیزه ASTM 230،275 و340 انجام شده است. نتایج نشان می­دهد که افزایش استحکام تسلیم باعث کشیدگی بیشتر سوراخ­ها در راستای نورد غلتکی و کاهش قطر سوراخ­ها در راستای عمود می­شود. لذا میزان بیضوی بودن سوراخ ها، با افزایش استحکام تسلیم ورق افزایش می­یابد. همچنین نتایج مشابهی با افزایش ضخامت و افزایش فاصله میان مرکز سوراخ و لبه جانبی نیز بدست می­آید. همچنین با افزایش استحکام تسلیم ورق، ارتفاع خمیدگی کاهش می یابد در حالی که با افزایش ضخامت ورق، قطر اولیه سوراخ ها و فاصله مرکز سوراخ تا لبه جانبی، میزان ارتفاع تاب برداشتن افزایش می یابد.

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