Transcript Document
Traditional Manufacturing Processes Casting Forming Sheet metal processing Powder- and Ceramics Processing Plastics processing Cutting Joining Surface treatment Sheet Metal Processes Raw material: sheets of metal, rectangular, large Raw material Processing: Rolling (anisotropic properties) Processes: Shearing Punching Bending Deep drawing Hydroforming Shearing A large scissors action, cutting the sheet along a straight line Main use: to cut large sheet into smaller sizes for making parts. Shearing • Shearing is a process for cutting sheet metal to size out of a larger stock such as roll stock. Shears are used as the preliminary step in preparing stock for stamping processes. • Material thickness ranges from 0.125 mm to 6.35 mm (0.005 to 0.250 in). The dimensional tolerance ranges from ±0.125 mm to ±1.5 mm (±0.005 to ±0.060 in). • The shearing process produces a shear edge burr, which can be minimized to less than 10% of the material thickness. The burr is a function of clearance between the punch and the die (which is nominally designed to be the material thickness), and the sharpness of the punch and the die. Blanking / Punching • Blanking and punching are similar sheet metal cutting operations that involve cutting the sheet metal along a closed outline. • If the part that is cut out is the desired product, the operation is called blanking and the product is called blank. If the remaining stock is the desired part, the operation is called punching. Blanking / Punching Cutting tool is a round/rectangular punch, that goes through a hole, or die of same shape F t X edge-length of punch X shear strength crack (failure in shear) t Punch piece cut away, or slug sheet die die clearance Punching Main uses: cutting holes in sheets; cutting sheet to required shape nesting of parts typical punched part Exercise: how to determine optimal nesting? Bending Body of Olympus E-300 camera component with multiple bending operations component with punching, bending, drawing operations [image source: dpreview.com] Typical bending operations and shapes (a) (b) Sheet metal bending Planning problem: what is the sequence in which we do the bending operations? Avoid: part-tool, part-part, part-machine interference Bending mechanics Bending Planning what is the length of blank we must use? Bend allowance, Lb = (R + kT) This section is under extension T = Sheet thickness Neutral axis L = Bend length This section is in compression Ideal case: k = 0.5 R = Bend radius Real cases: k = 0.33 ( R < 2T) ~~ k = 0.5 (R > 2T) Bending: cracking, anisotropic effects, Poisson effect Bending plastic deformation Engineering strain in bending = e = 1/( 1 + 2R/T) Bending disallow failure (cracking) limits on corner radius: bend radius ≥ 3T effect of anisotropic stock Poisson effect Exercise: how does anisotropic behavior affect planning? Bending: springback T Final R Rf Initial i i f How to handle springback: 3 R RY RY (a) Compensation: the metal is bent by a larger angle i 4 i 3 i 1 Rf ET ET (b) Coining the bend: at end of bend cycle, tool exerts large force, dwells coining: press down hard, wait, release Deep Drawing Tooling: similar to punching operation, Mechanics: similar to bending operation punch blank holder blank punch punch punch part die die (a) die die (b) (c) die (d) Examples of deep drawn parts Common applications: cooking pots, containers, … (e) Sheet metal parts with combination of operations Body of Olympus E-300 camera component with multiple bending operations component with punching, bending, drawing operations [image source: dpreview.com]