2.810 Car Project Injection Molding Machine: Energy Analysis Method Process: Injection Molding Machine: Engel EC88 2.810 Application: Construction of plastic rims for cars Summary The electric energy consumption of the injection molding machine is to be calculated using a highly simplified analysis. The machine operation is broken up into two regimes: 1. Warm-up: Control panel and heater on, hydraulic pump off 2. Operation/Idling: Control panel, heater, and hydraulic pump on. Additionally the total material used must be accounted for. Machine Analysis Warm-up The injection molding machine requires roughly 15 minutes to warm-up. Once this warm-up period is complete, the hydraulic pump is turned on and the machine can be operated. The average current during the warm-up period was measured to be 4 amps. Thus the warm-up energy usage can be calculated using the following equation: ()()AmpsVoltssTimeJEnergyupwarmupwarm4480××=−− To ensure uniform analysis between groups, a warm-up time of 15 minutes should be used. This may differ from your actual warm-up time as a result of the machine’s use history during. That is, if the machine was used immediately after another group, the required warm-up time would be very small. Thus the assumed warm-up time is to be used instead of your actual warm-up time. Operation/Idling It is important to note that the energy used during the plunging operation is about 20% higher than the idling energy consumption (hydraulic pump and heater on). However the plunging operation is quick and represents a small fraction of the time that the machine is in use. A much larger amount of time is spent with the machine idling during the part removal period. The energy consumption during the polymer filling period is roughly the same as that at idle. Note the polymer filling period refers to the build-up of polymer with the rotation of the piston-screw (this pushes the piston-screw backward). Thus to simplify the analysis, the time weighted average electric current was computed using anaverage time for the part removal process, and measured times for the plunge and fill operations along with measured electric current values for the plunging, filling, and idling operations. This average current is to be used with the total time that the machine is being operated (heater and hydraulic pump on). Thus the operating energy usage can be calculated using the following equation: ()()AmpsVoltssTimeJEnergyoperationoperation6.10480××= Total energy The total electrical energy used by the injection molding machine can be estimated: ()()()JEnergyJEnergyJEnergyoperationupwarmmoldinjection+=−− Material Usage In addition to the electric energy consumed by the machine, a large amount of energy is used to make the polymer pellets. The mass of polymer to be used in this calculation must include the mass of all the parts, the mass of all the scrap material (from runner/sprue) and the mass of the material purged from the system prior to making your parts. Note to allow a color change from the previous operation, any remaining died material must be purged from the system. The mass of this purged polymer will vary. Thus to provided for a uniform analysis, an average purge mass will be assumed. Based on Gerry Wentworth’s recommendation, an average purge mass of 1 kg is to be used in by all groups. Thus do NOT include the actual purge mass for your operation but instead use this assumed value. The energy required to make 1 kg of the polymer can be determined from the injection molding notes. Thus the operating energy usage can be calculated using the following equation: () ( )()()⎟⎠⎞⎜⎝⎛×+=+kgJEnergykgkgMassJEnergyrunnerspartsmaterial1 Tooling Costs For this analysis, the energy cost to machine the wheel plates is not included. These plates are shared by all the groups. However if new plates are machined to allow other components of the car to be injection molded, the energy consumption of the machining process needs to be included at some point in the energy
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