Processing
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PROCESSING PARAMETERS TEMPERATURES REQUIRED! MELT TEMPERATURE Bulk temperature of the melt at the point it enters the feed system (if modeled) or at the gate if feed system is not included TOOL TEMPERATURE Surface temperature of the mold at the beginning of the filling cycle after it has reached stabilized condition Hot Tip, Hot Drops, Heated Sprue Bushings or Hot Manifolds Temperatures of any heated elements in the feed system including method of heating (internal/external) FILLING PROFILE required! The filling profile describes the manner in which the injection rate is controlled from the time the ram begins to move forward until the cavity is completely filled and packing has not yet started. Typically this is not equivalent to the Injection High or Boost phase of the cycle. It is crucial to know when this portion of the cycle is to truly correlate analysis results to known physical outcomes. In most cases a constant ram velocity is used with a pressure control switch over at a predetermined pressure level. Normally the filling process is described to the analysis code using either a fill time or flow rate. The programs attempt to fill the tool using a constant flow rate which is 100% of the specified rate as input. A switch over to pressure control at a specified percentage of volume is used by default. (98% typ.) This switch over can also be specified by time. This shifts control of the injection speed from a constant flow rate to a constant pressure mode. This results in the actual fill time being slightly longer than the time input. The compressible nature thermoplastics (as much as 20% by volume) also results in a throughput of plastic into the cavity that exceeds the cavity volume itself. FILL TIME (seconds) Actual time beginning the instant the ram begins to move forward and ending when cavity is just filled (just beginning to pack). If a profiled injection is used. From this time, the analysis code calculated a total (average) volumetric flow rate that would be needed to fill the mold in that time. Remember that this time will include time to fill any feed system modeled (cold runner/drops). FLOW RATE (cubic inches/second or CC/Sec) The indicated flow rate, combined with the tool volume, result in an injection time. Remember that this volume will include any feed system modeled. A ram velocity setting can provide this information if the actual speed (in/sec), stroke (in), screw diameter(in) are known. The accuracy of this information is critical for the simulation to be relevant. PRESSURE If the filling is controlled by pressure, it is necessary to correlate the pressure indicated on the tool to the actual pressure that is present in the feed system. This usually requires knowing the compression ratio of the screw to determine the relationship between indicated pressures (hydraulic or back) and actual pressures inside the tool. CONSTANT PRESSURE MODE Switch over at Volume Switches to constant pressure mode at a % of shot volume (pressure specified as specific or % of maximum) Switch over at Time Switches to constant pressure mode at a specified time (pressure specified as specific or % of maximum) no Pressure control MACHINE LIMITS Maximum injection pressure Limits flow rate when pressure cap is reached CLAMP TONNAGE Limits flow rate when maximum clamping force is reached. Note that this value typically peaks during packing. If flashing has occurred, samples along with description of when and at what levels they were observed are very valuable. PROGRAMMED INJECTION SEQUENCE IF programmed (or profiled) injection sequences, if used, are described to the filling routines in any of three ways. %Flow Rate - %Volume A percentage of the nominal flow rate is specified for a percentage of the shot volume, allowing reduced flow rates for certain portions of the injection sequence. This will result in a longer fill time than specified unless, at user option, the flow rates are resealed to fit the indicated fill time. Time - Ram position Ram position at specific times relative to the initial position and moment ram begins to move forward. Ram diameter must be specified as well. Time - Ram position cubic spline Same as above, but more accurate. Fits a cubic spline through the time-position points to more closely model the actual ram motion when compared with the stepped nature of the preceding Time-Ram position method. PACKING REQUIRED TO MODEL FULL CYCLE! PACKING TIME/PRESSURE PROFILE Portion of cycle from time filling is done to moment gate freezes. This is described by pressure levels and duration that they are held for. As stated before, the program requires these numbers to indicate the actual pressure in the tool rather the hydraulic or back pressures indicated by the controls. Environment Temperature Environment Barometric Pressure TOTAL CYCLE COOLING TIME Additional time that mold remains closed after packing pressure is released. MOLD OPEN TIME
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