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20 A - SHEET METALWORKING: CUTTING AND BENDING


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Sheet metalworking
IN SHEET METAL WORKING STAMPING PRESSES CUT, BEND, DRAW CHEAP AND ACCURATE METAL SHEETS. Sheet metal working includes processes and equipment such as: [1] Cutting, [2] Bending, [3] Drawing, [4] Others sheet metal forming operations, [5] Dies and presses, [6] Sheet metal preformed not in presses, [7] Tube stock bending, the processes of sheet metal working produce a multitude of components from car bodies to airplane wings to office furniture, produce cheap and precise strong parts by using stamping presses and dies to produce metal sheets. >>> CuBeD ODd Not PoT: CUTTING, BENDING, DRAWING,,, OTHER, DIES,,, NOT_IN_PRESSES, TUBES
Stamping press
Press for stamping sheet metal parts.
Stamping die
Die for stamping sheet metal.
Stamping
Sheet metal product.
Major sheet metal processes
Major sheet metal processes are: [1] Cutting, [2] Bending, and [3] Drawing. >>> CBD: CUTTING BENDING DRAWS
CUTTING OPERATIONS
CUTTING EDGE PENETRATES, DEFORMS, AND FRACTURES VIRGIN SHEET, first deforming the work in a plastic manner, then compressing and penetrating deeper into the work, finally fracturing the sheet. >>> DeeP Fuck: DEFORM, PENETRATE, FRACTURE
Sheared profile
Sheared profile has four features: [1] Rollover - initial plastic deformation made by die, [2] Burnish - area of further penetration and deformation up to fractured zone, [3] Fractured zone - rough area of the fracture, [4] Burr - sharp metal elongation due to separation. >>> RiB FeeBle: ROLLOVER, BURNISH, FRACTURE, BURR.
Angular clearance
DIE MUST HAVE ANGULAR CLEARANCE, to allow clearing of the punched, cut, or blanked sheet parts to exit.
*Shearing, blanking, and punching
SHEARING, BLANKING, AND PUNCHING are the most common cutting operations. [1] Shearing - shears cut of a piece of metal, [2] Blanking - punch cuts blanks for further processing, [3] Punching - punch removes a slug, an unneeded portion of part. >>> SoB Cunt: SHEARING, BLANKING, PUNCHING
*Analysis of metal cutting
Sheet metal cutting parameters depend on the following factors: [1] Clearance between punch and die, [2] Stock thickness, [3] Metal type and strength, [4] Length of cut. >>> CuT MiLf: CLEARANCE, THICKNESS, METAL, LENGTH
Clearance
DISTANCE BETWEEN PUNCH AND DIE IN SHEARING OPERATION - too small and the fractures overlap, too big and the burr grows too big, for best results clearance should be: $$c = A_c t$$ $A_c$ - Clearance allowance - from 0.045 for aluminum to 0.075 for steel. $t$ - Stock thickness.
Cutting forces
CUTTING FORCES depend on: [1] Shear strength of metal - $\tau_{uts}$, [2] Thickness of the plate $t$, [3] Length to be cut $L$: $$F=\tau_{uts} \cdot tL$$ or if shear strength is unknown: $$F = 0.7 \cdot \sigma_{uts} \cdot tL$$
Shear angle
SHEAR ANGLE OF THE PUNCH THAT PENETRATES THE SHEET - if it's flat then the force is applied instantly, if the punch penetrates the sheet gradually due to a shear angle, then instantaneous force at any given moment is smaller, but the overall energy for the operation is the same.
*Other sheet metal cutting operations
Other sheet metal operations include: [1] Cutoff - sequentially cutting off bit after bit from a sheet without producing waste, [2] Parting - cutting off, quite often with two blades at a time, a set of blanks from a sheet, [3] Slotting - punching out an elongated slug, [4] Perforating - simultaneous punching out of holes, like for a fan grill, [5] Notching - removal of slots from sheet sides, [6] Seminotching - removal of internal sheet portions, [7] Trimming - removal of excess metal, [8] Shaving - finishing operation to get smooth and straight edges, [9] Fine blanking - blanking of sheet clamped between two dies. >>> CuPS PiNeS FiTS : CUTOFF, PARTING, SLOTTING,,, PERFORATING, NOTCHING, SEMINOTCHING, FINE_BLANKING, TRIMMING, SHAVING.
Cutoff
Punch cuts off blanks without producing waste.
Parting
TWO CUTTING EDGES ON A PUNCH PART OUT A BLANK, an operation to make some parts from a metal sheet, an operation that produces some left over waste.
Slotting
Punch makes a slot
Perforating
MACHINE MAKES MANY HOLES AT ONCE for decoration or ventilation.
Notching and seminotching
Punch removes notches from sheet.
Trimming
Wage slave trims off excess metal.
Shaving
SHAVING IS A PRECISE SHEARING OPERATION WITH SMALL CLEARANCES, performed to obtain accurate dimensions. WAGE SLAVE SHEARS SHEET TO ACCURATE DIMENSIONS.
Fine blanking
SLOW PUNCH BLANKS TRAPPED SHEET, the sheet clamped between two dies, the bottom one is a regular die, the top one has protruding teeth to hold the sheet in place for the fine operation. FINE TEETH HOLD FUTURE BLANK
BENDING OPERATIONS
BENDING OPERATIONS STRAIN THE METAL AROUND THE NEUTRAL PLANE, compressing the metal below it and stretching the metal above it, with most common bending operations being [1] V-Bending - punch bends metal in V-shaped die, and [2] Edge bending - holding sheet on one edge and bending on the other one at 90° or more. V AND EDGE BEND AND FORM
Analysis of bending
Analysis of bending of sheet with a thicnkess of $t$, width of $w$, bend radius $R$, and the angle at which it is bent $\alpha$ and it's complimentary angle $\alpha'$ determines [1] Bend allowance - at what radius can you bend the part, [2] Spring back - how much the sheet will "undbend" itself due to stored elastic energy, [3] Bending force - the force needed to bend the the sheet. >>> ASs Fuck: ALLOWANCE, SPRINGBACK, FORCE
Bend allowance
LENGTH OF BENT PORTION WITH THE ELONGATION OF NEUTRAL AXIS, a parameter determined to estimate the new part length, the new length of the part which results from bending the part, the new part length that occurs because the neutral axis moves from the middle of the part, its offset dependent on the bending radius, bend angle, material, and some other shit: $$A_{b}=2\pi\frac{\alpha}{360}\left(R+K_{ba}t\right)$$
K-factor
Deflection of neutral axis from middle during bending, a factor used in calculating bend allowance, usually around 0.33 for small radii and around 0.5 for big radii. $$\begin{array}{l} K_{ba}=\frac{neutral \, axis \, deflection} {sheet \, width}\\ if:\, R \leq2t \rightarrow K_{ba} \approx0.33 \\ if \, R \geq2t \rightarrow K_{ba}=0.5 \end{array}$$
Springback
AMOUNT BY WHICH PART INCLUDED ANGLE $\alpha '$ INCREASES BEYOND THE TOOL'S INCLUDED ANGLE $\alpha '_{t}$, the part springing back towards it's unbent shape, as if longing for the magical time when he was a flat and carefree piece of shit metal without a single thing to worry about, a phenomena overcame by [1] Overbending - bending a part a bit more, and [2] Bottoming - squeezing the part at the end of the stroke to deform it plastically. FREE THINKING SHEET SUBMITS TO OVERBENDING AND BOTTOMING. $$SB=\frac{\alpha'- \alpha'_{tool}}{ \alpha'_{tool}}$$
Bending force
Amount of force to bend sheet into shape: $$\begin{array}{c} F= \frac{K_{bf} \sigma_{uts}wt^{2}}{D} \\ {\scriptstyle V-bending: \,\, K_{bf} \approx1.33}\\ {\scriptstyle Edge \, Bending:\,\, K_{bf}=0.33}\end{array}$$ The equation is based on bending of simple beam in mechanics. $D$ - die opening dimension, $K_{bf}$ - constant accounting for different types of bending
*Other bending and forming operations
OTHER BENDING AND FORMING OPERATIONS include: [1] Flanging - bending edge of part at 90° to form rim or flange, [2] Hemming - bending edge of sheet over itself to increase stiffness, remove sharp edge, or to improve appearance, [3] Seaming - joining two sheets together by hemming them to each other, [4] Curling - forming of edge into roll or curl to increase strength or appearance of part, like in hinges and pans. [5] Channel bending - making channel in sheet, [6] U-Bending - like channel bending only with curved corners, [7] Air bending - bending sheet without die, [8] Offset bending - creates offsets, [9] Corrugating - press makes corrugated sheet, [10] Tube forming - gradually making a tube from shit. >>> FiSH CUC COAT: FLANGING, SEAMING, HEMMING,,, CURLING, U-BENDING, CHANNEL,,, CORRUGATING, OFFSET, AIR, TUBE
Flanging
PRESS BENDS EDGE AT 90°, forming a rim or a flange at straight or bent axis and improving stiffness of sheet. BENT FLANGE STIFFENS THIN SHEET.
Seaming
SHEET JOINS SHEET AND FORMS UNHOLY SEEM, the two hemms joined in unholy union that holds the abominable sheets together when a wage slaves joins them with a press and the will of the dark one.
Hemming
EDGE BENDS OVER ITSELF FORMING A HEMM, the machine goes a step beyond making a flange and bends it until it touches itself. NASTY SHEET TOUCHES ITSELF.
Curling
FORMING OF CURLED FLANGE, a curled flange to increase stiffness, enhance appearance, or serve a functional purpose like in a door hinge. CURLING FLANGE HOLDS MYSTERY DOOR.
U-bending
U-formed press makes bends a U-formed channel.
Channel bending
Press bends channel in sheet.
Corrugating
WAVY PRESS FORMS CORRUGATED ROOF COVERS, pressing down sheet into a corrugated die.
Offset bending
Machine bends offset into sheet.
Air bending
PUNCH BENDS SHEET IN AIR, the sheet resting on two supports, lacking a die to hold it, a simple and cheap process since you save money on not having a die.
Tube forming
Press forms sheet into tube.