Flashcards in Chapter 19 Deck (33):
Sheet-metal products from "stamping" presses
A major sheet metal process used to separate large sheets into smaller pieces, to cut out part perimeters, and to make holes in parts.. Cutting is accomplished by a shearing action between two sharp cutting edges.
Define: Plastic Deformation/Rollover
When the upper cutting edge (the punch) begins to push into the work.
Rollover is the top of the curt surface and corresponds to the depression made by the punch in the work prior to cutting
As the punch moves compresses the sheet and cuts into the metal. This penetration zone is generally about one-third the thickness of the sheet..
Burnish is just below the rollover and is a relatively smooth region, resulting from penetration of the punch into the work before fracture
As the punch continues to travel into the work, "fracture" is initiated int he work at the two cutting edges. IF clearance is correct, the two fracture lines meet, resulting in a clean separation of the work into two pieces.
A sharp corner on the edge caused by elongation of the metal during final separation of the two pieces
Sheet-metal operations along a straight line between two cutting edges; typically used to cut large sheets into smaller sections for subsequent press-working operations
Machine=power shears/squaring shears
Define: Blanking vs Punching
Blanking- Involves cutting of the sheet metal along a closed outline in a single step to separate the piece from the surrounding stock (ex. square piece)
Punching- (similar to blanking) It produces a hole in a piece with a separate circular hole portion that is scrap, called a slug
The clearance "c" in a shearing operation is the distance between the punch and the die. Typically, c = 4-6% of sheet metal thickness (t).
c = Ac * t, where Ac (clearance allowance) is determined by metal.
Define: Cutoff vs. Parting
Cutoff: is a shearing operation in which blanks are separated from a sheet-metal strip by cutting the opposite sides of the part in sequence
Parting: involves cutting a sheet metal strip by a punch with two cutting edges that match the opposite sides of the blank
Involves the simultaneous punching of a pattern of holes in sheet metal. The hole pattern is usually for decorative purpose, or to allow passage of light or fluid.
Define: Notching vs. Semi-Notching
Notching: Involves cutting out a portion of metal from the side of the sheet or strip
Semi-notching: removes a portion of metal from the interior of the sheet and creates part of the blank outline but creating a cutoff line into the interior.
In sheet-metal work is defined as the straining of the metal around a straight axis. The metal on the inside of the neutral plain is compressed, while the metal on the outside of the neutral plane is stretched
Define: Edge vs. V-bending
Edge Bending: Involves cantilever loading of the sheet metal, while a force is applied to hold the base of the part against the die (high production operations)
V-Bending: Sheet metal bent between a V-shaped punch and die (low production operations)
Define: Bend Allowance
The estimated amount of stretching that occurs during bending.
Allowance = 2 * pi * (angle/360) * (R + K * t)
When bending pressure is removed at the end of the deformation operation, elastic energy remains in the the bent part, causing it to recover partially toward its original shape
Is a bending operation in which the edge of a sheet metal part is bent at a 90 degree angle to form a rim or flange
Involves bending the edge of the sheet over on itself in more than one bending step (done to eliminate the sharp edge on the piece, increase stiffness, and improve appearance
A related operation in which two sheet-metal edges are assembled together in two, hemmed regions.
Forms the edges of the part into a roll or curl. Done for the purpose of safety, strength, and aesthetics.
A Sheet metal forming operation performed by placing a piece of sheet metal over a die cavity and then pushing the metal into the opening with a punch. The blank must usually be held down flat against the die by a blankholder.
Due to the downward motion of the punch in a continuation of the metal flow caused by drawing, the walls of the cylinder are thinned
Define: Drawing Ratio
(or DR) is the ratio of blank diameter (Db) to punch diameter (Dp)
DR = Db/Dp
The piece that holds the blank flat against the die. The force applied by the blankholder is called the "holding force"
Define: Wrinkling (in flange or wall)
Defect of drawing in which a series of ridges form radially in the undrawn flange of the work part or in the vertical wall. These are a result of compressive buckling
Used to make cylindrical cup more uniform in wall thickness by drawing into a smaller circumference diameter after drawing into the original.
Used to create indentation in the sheet such as raised (or indented) lettering or strengthening of ribs. Similar to coining except that embossing dies possess matching cavity contours.
A combined cutting and bending or cutting and forming operation performed in one step to partially separate the metal from the sheet
Define: Compound vs. Progressive Die
Compound: Performs two operations at a single station, such as blanking and punching, or blanking and drawing
Progressive: Performs two or more operations on a sheet metal coil at two or more stations with each press stroke. The part is fabricated progressively
Define: Roll Bending
Is an operation in which (usually) large sheet-metal or plate-metal parts are formed into curved sections by means of rolls.
Define: Roll Forming
(or Contour Roll Forming) is a continuous bending process in which opposing rolls are used to produce long sections of formed shapes from coil and strip stock.
Bends metal around a moving circular axis to conform to the outside surface of the axisymmetric mandrel.