Sheet Metalworking Flashcards
What is typical sheet metal thickness?
Between 0.4 mm and 6 mm. Above 6mm is referred to as a sheet
How are sheet metals usually formed?
Flat Rolling
What are the three major categories of sheet-metal processes?
Cutting
Bending
Drawing
Describe the shearing action involved in cutting f sheet metals
The punch comes down on the sheet metal and pushes it, causing plastic deformation. As the punch moves downwards penetration occurs to about 1/3 the thickness of the sheet; after which fracture is initiated and the two fracture lines meet leaving a clean cut.
What are the characteristics of a sheared edge of sheet metal?
At the top of the cut surface is a rollover where initial plastic deformation occurred. Just below is a relatively smooth region called the burnish. Beneath the burnish is the fracture zone which has a relatively rough surface. At the bottom of the edge is a burr, a sharp corner caused by elongation of the metal during final separation.
What are the three most important operations of cutting metal sheets in pressworking?
Shearing
Blanking
Punching
What is the difference between blanking and punching?
Blanking produces the desired shape object by cutting it out of a strip, the desired piece is called a blank. Punching creates a hole, the scrap piece left over is called the slug.
What tool is used for V-bending?
V-die
What tool is used for edge bending?
Wiping die
What is a limitation of edge bending?
Bending angle is limited to 90’
It is more costly and complicated than V-bending
What is springback?
When the bending pressure is removed at the end of the deformation operation, elastic energy remains in the bent part, causing it to recover partially toward its original shape. It is defined as the increase in included angle of the bent part relative to the included angle of the forming tool after the tool is removed.
How can springback be over come?
Overbending where the metal is bent further than the specified angle so it springs back to the correct size.
Bottoming, involves squeezing the part at the end of the stroke, thus plastically deforming the bending area.
What is used to prevent collapse of tubes during bending?
Special flexible mandrels are usually inserted into the tube prior to bending to support the walls during the operation.
What are the tube bending limits (with and without a mandrel) due to the flattening tendency
The minimum bend radius R that the tube can be bent is about 1.5 times the diameter D when a mandrel is used and 3.0 times D when no mandrel is used.
How is wall factor (WF) calculated?
Diameter D divided by wall thickness t. Higher values of WF increase the minimum bend radius.
