Lecture 4 : Design for Sheet Metal Forming Processes Notes | EduRev

: Lecture 4 : Design for Sheet Metal Forming Processes Notes | EduRev

 Page 1


 
 
 
 
 
 
 
 
Module 
3 
Selection of Manufacturing 
Processes 
Page 2


 
 
 
 
 
 
 
 
Module 
3 
Selection of Manufacturing 
Processes 
 
 
 
 
 
 
 
 
Lecture 
4 
Design for Sheet Metal 
Forming Processes 
Page 3


 
 
 
 
 
 
 
 
Module 
3 
Selection of Manufacturing 
Processes 
 
 
 
 
 
 
 
 
Lecture 
4 
Design for Sheet Metal 
Forming Processes 
Instructional objectives 
By the end of this lecture, the student will learn the principles of several sheet metal forming 
processes and measures to be taken during these process to avoid various defects. 
 
Sheet Metal Forming Processes 
Sheet metals are widely used for industrial and consumer parts because of its capacity for 
being bent and formed into intricate shapes. Sheet metal parts comprise a large fraction of 
automotive, agricultural machinery, and aircraft components as well as consumer appliances. 
Successful sheet metal forming operation depends on the selection of a material with 
adequate formability, appropriate tooling and design of part, the surface condition of the 
sheet material, proper lubricants, and the process conditions such as the speed of the forming 
operation, forces to be applied, etc. A numbers of sheet metal forming processes such as 
shearing, bending, stretch forming, deep drawing, stretch drawing, press forming, 
hydroforming etc. are available till date. Each process is used for specific purpose and the 
requisite shape of the final product.  
Shearing 
Irrespective of the size of the part to be produced, the first step involves cutting the sheet into 
appropriate shape by the process called shearing. Shearing is a generic term which includes 
stamping, blanking, punching etc. Figure 3.4.1 shows a schematic diagram of shearing. When 
a long strip is cut into narrower widths between rotary blades, it is called slitting. Blanking is 
the process where a contoured part is cut between a punch and die in a press. The same 
process is also used to remove the unwanted part of a sheet, but then the process is referred to 
punching. Similarly, nibbling, trimming are a few more examples of cutting process using the 
same principle of shearing process. 
 
 
 
 
 
 
Figure 3.4.1 Schematic set-up of shearing operation[1] 
 
Page 4


 
 
 
 
 
 
 
 
Module 
3 
Selection of Manufacturing 
Processes 
 
 
 
 
 
 
 
 
Lecture 
4 
Design for Sheet Metal 
Forming Processes 
Instructional objectives 
By the end of this lecture, the student will learn the principles of several sheet metal forming 
processes and measures to be taken during these process to avoid various defects. 
 
Sheet Metal Forming Processes 
Sheet metals are widely used for industrial and consumer parts because of its capacity for 
being bent and formed into intricate shapes. Sheet metal parts comprise a large fraction of 
automotive, agricultural machinery, and aircraft components as well as consumer appliances. 
Successful sheet metal forming operation depends on the selection of a material with 
adequate formability, appropriate tooling and design of part, the surface condition of the 
sheet material, proper lubricants, and the process conditions such as the speed of the forming 
operation, forces to be applied, etc. A numbers of sheet metal forming processes such as 
shearing, bending, stretch forming, deep drawing, stretch drawing, press forming, 
hydroforming etc. are available till date. Each process is used for specific purpose and the 
requisite shape of the final product.  
Shearing 
Irrespective of the size of the part to be produced, the first step involves cutting the sheet into 
appropriate shape by the process called shearing. Shearing is a generic term which includes 
stamping, blanking, punching etc. Figure 3.4.1 shows a schematic diagram of shearing. When 
a long strip is cut into narrower widths between rotary blades, it is called slitting. Blanking is 
the process where a contoured part is cut between a punch and die in a press. The same 
process is also used to remove the unwanted part of a sheet, but then the process is referred to 
punching. Similarly, nibbling, trimming are a few more examples of cutting process using the 
same principle of shearing process. 
 
 
 
 
 
 
Figure 3.4.1 Schematic set-up of shearing operation[1] 
 
Bending 
Bending is the operation of deforming a flat sheet around a straight axis where the neutral 
plane lies. It is a very common forming process for changing the sheets and plates into 
channel, drums, tanks, etc. Two different scheme of bending are shown in the figure 3.4.2. 
Spring back is a major problem during bending of sheets that occurs due to elastic recovery 
by the material causing a decrease in the bend angle once the pressure is removed. The 
springback can be minimized by introducing excess amount of bending so that the finished 
bending angle is the same after the elastic recovery. However, a careful estimate of the elastic 
recovery based on the mechanical behaviour of the sheet material is necessary to achieve the 
same. 
 
 
 
 
 
 
 
 
 
 
Figure 3.4.2 Schematic set-up of (a) air vee bending, and (b) die bending [3] 
 
Stretch Forming 
It is a method of producing contours in sheet metal. In a pure stretch forming process, the 
sheet is completely clamped on its circumference and the shape is developed entirely at the 
expense of the sheet thickness. Figure 3.4.3 presents a schematic set-up of stretch forming 
process. The die design for stretch forming is very crucial to avoid defects such as excessive 
thinning and tearing of the formed part. The stretch forming process is extensively used for 
producing complex contours in aircraft and automotive parts. 
 
 
 
 
(a) (b) 
Page 5


 
 
 
 
 
 
 
 
Module 
3 
Selection of Manufacturing 
Processes 
 
 
 
 
 
 
 
 
Lecture 
4 
Design for Sheet Metal 
Forming Processes 
Instructional objectives 
By the end of this lecture, the student will learn the principles of several sheet metal forming 
processes and measures to be taken during these process to avoid various defects. 
 
Sheet Metal Forming Processes 
Sheet metals are widely used for industrial and consumer parts because of its capacity for 
being bent and formed into intricate shapes. Sheet metal parts comprise a large fraction of 
automotive, agricultural machinery, and aircraft components as well as consumer appliances. 
Successful sheet metal forming operation depends on the selection of a material with 
adequate formability, appropriate tooling and design of part, the surface condition of the 
sheet material, proper lubricants, and the process conditions such as the speed of the forming 
operation, forces to be applied, etc. A numbers of sheet metal forming processes such as 
shearing, bending, stretch forming, deep drawing, stretch drawing, press forming, 
hydroforming etc. are available till date. Each process is used for specific purpose and the 
requisite shape of the final product.  
Shearing 
Irrespective of the size of the part to be produced, the first step involves cutting the sheet into 
appropriate shape by the process called shearing. Shearing is a generic term which includes 
stamping, blanking, punching etc. Figure 3.4.1 shows a schematic diagram of shearing. When 
a long strip is cut into narrower widths between rotary blades, it is called slitting. Blanking is 
the process where a contoured part is cut between a punch and die in a press. The same 
process is also used to remove the unwanted part of a sheet, but then the process is referred to 
punching. Similarly, nibbling, trimming are a few more examples of cutting process using the 
same principle of shearing process. 
 
 
 
 
 
 
Figure 3.4.1 Schematic set-up of shearing operation[1] 
 
Bending 
Bending is the operation of deforming a flat sheet around a straight axis where the neutral 
plane lies. It is a very common forming process for changing the sheets and plates into 
channel, drums, tanks, etc. Two different scheme of bending are shown in the figure 3.4.2. 
Spring back is a major problem during bending of sheets that occurs due to elastic recovery 
by the material causing a decrease in the bend angle once the pressure is removed. The 
springback can be minimized by introducing excess amount of bending so that the finished 
bending angle is the same after the elastic recovery. However, a careful estimate of the elastic 
recovery based on the mechanical behaviour of the sheet material is necessary to achieve the 
same. 
 
 
 
 
 
 
 
 
 
 
Figure 3.4.2 Schematic set-up of (a) air vee bending, and (b) die bending [3] 
 
Stretch Forming 
It is a method of producing contours in sheet metal. In a pure stretch forming process, the 
sheet is completely clamped on its circumference and the shape is developed entirely at the 
expense of the sheet thickness. Figure 3.4.3 presents a schematic set-up of stretch forming 
process. The die design for stretch forming is very crucial to avoid defects such as excessive 
thinning and tearing of the formed part. The stretch forming process is extensively used for 
producing complex contours in aircraft and automotive parts. 
 
 
 
 
(a) (b) 
 
 
 
 
 
 
 
 
 
Figure 3.4.3 Schematic illustration of typical stretch forming process [3] 
 
Deep Drawing 
Deep drawing is a sheet metal forming process in which a sheet metal blank is radially drawn 
into a forming die by the mechanical action of a punch. It is thus a shape transformation 
process with material retention. The process is considered "deep" drawing when the depth of 
the drawn part exceeds its diameter. This can be achieved by redrawing the part through a 
series of dies. 
 
 
 
 
 
 
 
 
 
Figure 3.4.4 Schematic outline of Deep Drawing Process [3] 
 
The metal flow during deep drawing is extensive and hence, requires careful administration 
to avoid tearing or fracture and wrinkle. Following are a few key issues affecting metal flow 
during deep drawing process and each of them should be considered when designing or 
troubleshooting sheet metal deep drawing stamping tools. 
 
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