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