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# review2 - 2.008 Quiz 2 Review 2.008 Quiz 2 Review p.1/17...

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2.008 Quiz 2 Review 2.008 Quiz 2 Review p.1/17

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Quiz Topics Casting: V/SA vs. ( V/SA ) 2 Forming: Force, elastic v. plastic deformation. Process: shop,project,ﬂow,cell. Systems: L = λw Quality: C pk , SPC. Cost: allocations Layered Manufacturing MEMS Look this over! 2.008 Quiz 2 Review p.2/17

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Laser Cutting Problem A laser cutter cuts its material by evaporating the material along the cut line. In terms of the following variables: Quantity Variable Units Mass m grams Ambient Temperature t o K Melting Temperature t m K Boiling Temperature t b K Solid specific heat capacity c p J ( kG ) 1 K 1 Latent heat of fusion h f J ( kG ) 1 Liquid specific heat capacity c l J ( kG ) 1 K 1 Latent heat of vaporization h v J ( kG ) 1 K 1 Density ρ kg/m 3 Material thickness h m Radius of laser spot r m Power of the laser P W write a formula which describes how much energy per gram is required to vaporize a material. 2.008 Quiz 2 Review p.4/17
Laser Cutting Problem A laser cutter cuts its material by evaporating the material along the cut line. In terms of the following variables: Quantity Variable Units Mass m grams Ambient Temperature t o K Melting Temperature t m K Boiling Temperature t b K Solid specific heat capacity c p J ( kG ) 1 K 1 Latent heat of fusion h f J ( kG ) 1 Liquid specific heat capacity c l J ( kG ) 1 K 1 Latent heat of vaporization h v J ( kG ) 1 K 1 Density ρ kg/m 3 Material thickness h m Radius of laser spot r m Power of the laser P W write a formula which describes how much energy per gram is required to vaporize a material. E vaporize = m (( t m t o ) c p + h f + ( t b t m ) c l + h v ) 2.008 Quiz 2 Review p.4/17

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Laser Cutting The laser beam is focused onto a circle of radius r . Assume that all of the energy of the laser is all delivered to this circle, and that all of the energy is used in the cutting process (ie, there is no energy loss due to spectral absorption). Let ρ be the density of the material, and let h be the material thickness. Write an equation governing speed of cutting to the power of the laser, P . 2.008 Quiz 2 Review p.5/17
Laser Cutting The laser beam is focused onto a circle of radius r . Assume that all of the energy of the laser is all delivered to this circle, and that all of the energy is used in the cutting process (ie, there is no energy loss due to spectral absorption). Let ρ be the density of the material, and let h be the material thickness. Write an equation governing speed of cutting to the power of the laser, P . The laser’s energy, P , is delivered uniformly over an area of πr 2 . In order to cut through this material, a volume of πr 2 h mm 3 must be evaporated. This volume will require πr 2 hE vaporize Joules e = ρ of energy to vaporize. If P represents watts of laser power available, then P/e seconds are required for the laser to cut through the material. Since the laser can safely move 2 r during this

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