An experimental study on the examination of springback of sheet metals with several
thicknesses and properties in bending dies
Zafer Tekiner
Accepted 25 July 2003
Presented by Jared Moyer
September 22, 2004
Bending Background
•Used anciently-5000 BC•Utensils and jewelry
•A common shaping process today•Seams, flanges•Automotive-car bodies•Aircraft fuselages•Beverage can•Metal desks
Modern forms
Advantages
• Low cost
• Good strength
• Light weight
• Formability characteristics• no necking or tearing
• Versatile shapes
Disadvantages
• Cracking
• Springback– Sheets
– Rod
– Wire
– barsSB = (A’ – Ab’)/ Ab’
Reducing Springback
• Over bending part• Elevated temperatures• Bottoming the punch
• High-localized compressive stresses between the punch and die surface
• Stretch bending• Part is in tension while
being bent
Purpose of Paper
• Find a springback values – Bending die designers– Acceptable tolerances
• Experimental methods• Time
• Money
Test Set Up
• Several materials: Steel, Copper, Brass, Aluminum, Galvanized and stainless steels
• Dimensions: 25 mm x 50 mm• Different thicknesses: .5, .75 & 1.00 mm• Measured bending by optical profilometer (1 min)• Used four different methods • Results graphed by Microsoft Excel software
Forces Needed• Force Equations
– C = 1 + (4*T/W)
– P*v = C (B*T^2*dd*b-/W) x 10
Method 1
• Punch doesn’t touch die corners
• Gap thickness between punch and die equaled to sheet metal thickness
• Punched left for 20 sec.
• Repeated each material and thickness
Method 1 Results
Method 1 overall results
Method 2
• Punch on the sheet metal
• No maintaining load
Method 2 Results
Method 2 overall Results
Method 3 and 4• Method 3
– No gap between punch and die– Load left for 20 sec
• Method 4– No gap between punch and sheet metal– No holding load
• Results– Too complicated– Crushing material– Depth of descending punch not considered
Conclusions
• Changed with material and die
• Reduced by leaving loads
• Developed equations help produce more precise results
My conclusions
• Are the springback values valid with multiple bends?
• Experiments have been preformed
• Machinists use charts
References
• Fundamentals of Modern Manufacturing, Mikell P. Groover
• Manufacturing Engineering and Technology, Kalpakjan and Schmid
Questions