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Handout 8 c1 Drawing Principle of the process Structure Process modeling Defects Design For Manufacturing (DFM) Process variation Metal forming

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Handout 8 c2 Bulk Drawing: Engineering Analysis 1. Introduction In the bulk deformation processes, drawing is an operation in which the cross section of a bar, rod, or wire is reduced by pulling it through a die opening, as shown in Figure 1.

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Handout 8 c3 Figure 1 here Has pulling force Has pushing force ExtrusionDrawing

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Handout 8 c4 Rolling process Torque (force) Power Velocity (productivity) Max draft Drawing process Pulling force Power Pulling velocity Max draft Bulk Drawing: Engineering Analysis 2. Objectives of the Analysis

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Handout 8 c5 3. Mechanics Phenomenon There is a tensile stress due to pulling force, but compression still plays a significant role since the metal is squeezed down as it passes through the die opening.

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Handout 8 c6 4. Parameters r: area reduction A0: initial area of work Af: final area d=D0-Df, draft Drawing stress Contact length Die angle Friction between work and die Force r=(A0-Af)/A0

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Handout 8 c7 5. Drawing stress, drawing force, power Accounts for inhomogeneous deformation

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Handout 8 c8 5. Drawing stress, drawing force, power

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Handout 8 c9 6. Limit of Drawing Allowable power Yield stress Maximum power < Allowable power of a drive system Maximum stress < Yield stress If not, material goes into plastic region & no “drawing” occurs, just “elongation” Entire reduction not done in a single pass (done in steps) - If done, as Reduction, draw stress also

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Handout 8 c10 Assumption: no friction, no strain hardening (n=0), no redundant work (perfectly plastic) 6. Finding Max draw stress & Max reduction (1 pass) Max. draw stress = Yield Strength Also, because (n=0)

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Handout 8 c11

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Handout 8 c12 Example Wire stock of initial diameter = in. is drawn through two dies each providing a 0.20 area reduction. The staring metal has a strength coefficient = 40,000 lb/in. 2 and a strain hardening exponent =0.15. Each die has an entrance angle of 12 o, and the coefficient of friction at the work-die interface is estimated to be The motors driving the capstans at the die exists can each deliver 1.50 hp at 90% efficiency. Determine the maximum possible speed of the wire as it exits the second die.

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Handout 8 c13

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Handout 8 c14

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Handout 8 c15 From this calculation, the velocity of the second die is the limiting velocity. That is to say, the velocity of the whole system should take 3.47 ft /s. As a result, 1.the first operation would have to be operated at well below its maximum possible speed; or 2.the second draw die could be powered by a higher horsepower motor; or 3.the reductions to achieve the two stages would be reallocated to achieve a higher reduction in the first drawing operation.

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