Estimation of your energy usage for the 2.810 car projectT. Gutowski, 12/05/061. IntroductionPlease use this guideline for estimating your energy usage for building your 2.810 cars. This is now a required section of your final project report1. The estimates here are a summary of the individual process reports provided by the environmental officers.2 Here we will summarize data for the most commonly used materials and processes for your 2.810 car projects. Any other materials and processes could be estimated based on your class handouts or you should contact the instructor or the TA. 2. MaterialsSince there often can be a range in values for the primary energy required for making materials, please use the values in Table 1 so that all reports are consistent.Table 1Material Density (g/cm3) Primary Energy (MJ/kg)Aluminum 2.7 270Polyethylene (injection molding)0.9 90ABS (Thermoforming) 1.2 95Steel 8.9 353. ProcessesManufacturing processes draw power when idling and then increase their power draw when processing parts (in operation). This is shown schematically in Figure 1. Some processes also have a warm-up period. Warm-up energy, and idle and operation power values are given in Table 2.Two pieces of equipment on the list require warm up. In these cases the warm-up power has been multiplied by the typical warm up times, so the values are given in total energy (MJ). Please notice also that all the numbers given in Table 2 have already been multiplied by one over the efficiency of the electrical grid (1/eff =3)and therefore are in terms of primary energy units. This allows direct comparison with the values obtained from the material usage.1 The environmental reporting requirements are given at the end of this handout.2 Matthew Branham (casting), Thor Eusner (Waterjet), Terry Gaige (Bridgeport CNC), Jonathan Hopkins (Rice manual lathe), Yixiong Kok (Thermoforming machine), Thomas Ligon (EZ-trac mill), and Robert Scaringe (Engel injection molding machine)1Figure 1 Power Vs time for a typical manufacturing processTable 2 Energy and Power (electrical X 3) for Mfg Processes in the LMP ShopSummary Warm-up (power x time) Idle (kW)x3 Operation (kW)x3Energy in MJ Power in kJ/s Power in kJ/sProcessManual Lathe 0.3 2.8Manual Mill 0.7 3.75CNC Mill 1.6 4.0Waterjet 0.6 27.6Thermoformer 9MJ 9.0 9.0Injection Molding 5MJ 15.3 15.34. ExamplesA. ThermoformingMaterial: each ABS sheets is 18” x 23” x 0.0625”, or45.72 cm x 58.42 cm x 0.159 cm = 425 cm3425 cm3 x 1.2 g/cm3 = 0.51 kgSay 10 sheets are used to make 8 carsTime (seconds)Power (kW)IdleOperation210 x 0.51kg x 95MJ/kg = 484.5 MJBe sure to include any additional waste.Process: say these shells are formed in 45 minutes after warm-upWarm-up = 9MJForming = 45 min x 60 sec/min x 9kJ/s = 24.3 MJForming energy is 9 + 24.3 = 33.3 MJTotal thermoforming energy = 484.5 + 33.3 = 518MJEnergy/car = 518/8 = 65 MJB. Injection MoldingMaterials: purging the machine to change color uses 0.1 kg of material. A rear wheel + runner = 21 g, front wheel + runner = 11g: so the four wheels needed per car = 64g, and for 8 cars this is 0.51 kg.Total material 0.1 kg + 0.51kg = 0.61 kg0.61kg x 90MJ/kg = 54.9 MJProcess: warm up is 5 MJ, say molding takes 1 hr and 20 minutes80 min x 60 sec/min x 15.3 kJ/s = 73.4 MJinjection molding for eight cars is 5MJ + 73.4 MJ = 78.4 MJTotal Energy = 54.9MJ + 78.4 MJ = 133.3 MJEnergy per car = 133/8 = 16.7 MJC. WaterjetMaterials; prototype chassis; 9in x 12in x 0.25in, (no waste) or22.86cm x 30.48cm x 0.635cm = 442 cm3, x 2.7 = 1.2kg, x 270 MJ/kg = 324MJThe material removed is the length of the cut x depth x kerf. This 42in x 0.25in x 0.03in, or 106.6cm x 0.635cm x 0.076cm = 1.37cm3, x 2.7 = 3.7 grams.The ratio of abrasive to material removed is about 150:1. So abrasive is 555g. (This information can also be gotten from the computer output.)If the energy to produce the abrasive is 5MJ/kg, this gives .555 x 5 = 2.8 MJ3Total material energy = 324 + 2.8 = 327MJProcess; cutting the perimeter of a 9” x 12” rectangle is 42 in, at 21ipm, this will take 2 minutes cutting time. In addition there are 45 minutes idle time. The process energy is 45 x 60 x 0.6 = 1.6 MJ; 2 x 60 x 27.6 = 3.3 MJTotal energy for one prototype is 327 + 1.6 + 3.3 = 332 MJ5. Sand CastingSand casting is a special case for us because it is not done in-house. The estimatesbelow are based upon comments from the foundry we use for 2.810, and other information. Materials: assuming secondary aluminum 0.7kg part x 16.7 MJ/kg = 11.7 MJProcess: For a small aluminum foundry we estimate the melting energy as(part + runner system wt)(CpT + H)(1/eff)(0.7kg + 0.5kg)(0.9 MJ/kg)(1/0.25) = 4.3 MJ this energy comes from oil.In addition we add 2 MJ per casting (for electricity use, this includes the x 3 factor), this gives, Total Energy =(11.7+ 2 + 4.3) X 8 = 144 MJEnergy per Car 18 MJEnvironmental reporting requirements; The 2.810 environmental reporting requirements have been reduced to just doing the energy used, similar to the estimates in this handout with the same level of detail. To do this you will need to report all materials used, and also the materials in you final car (weights in grams). You will also need to report how long you were on each machine in the shop (minutes). Please attempt to estimate what portion of the materials use and energy use was related to prototyping, and what portion was for
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