A key aspect of an effective flow analysis project is accurately simulating processes that have already be run. When troubleshooting problems, this is obviously crucial. When the analysis aim is optimizing an existing process, it is very useful to establish a baseline by using processes with know results. These replications of known phenomena are useful in extrapolating results from analysis data to their likely physical outcomes and serve to develop a basis for confidence in the predictions of the analytical models.
Certain information is mandatory, and can be determined in several different manners, while other information is useful, but not essential.
In general, the accuracy of the results, predictions and interpretations is directly proportional to the amount and quality of this foundation data. The following outlines the required and useful parameters and how to determine and represent them. The mandatory information will be note as such. While, in many cases, several options are presented and one may be sufficient, it can be assumed that all options would preferred.
CAVITY DIMENSIONS( at least one required)
The cavity dimensions can be represented in several ways. Ideally, this would include any scaling of the final product that would be added to compensate for shrinkage. In most cases nominal product dimensions are adequate and using them should impact the results noticeably. It is important to be consistent in how the cavity is represented when design changes are evaluated. Any one of the following can be used to describe the cavity physically.
When considering how best to describe the cavity, keep in mid that the FEM model used for flow analysis is a mesh of triangles representing the mid-plane surface of the cavity. Each triangle is assigned a thickness attribute that tells the analysis routines the local wall section in that area. One half of that thickness is added to each side of the triangles, resulting in wedges that approximated the cavity extents. For parts with thin wall sections (relative to overall dimensions) it is usually acceptable to use either inside or outside surfaces for most of the FEM model
1. PART OR CAVITY DETAIL PRINT(S)
Hard copy detail drawings should always be provided it available.
1. CAD MODEL
CAD models can be extremely useful. the following are listed in order of preference
1. Solid models using ACIS format
Provide model in .SAT file if possible
1. ACAD R13, Designer, or Mech Desktop
3. .SAT file from others including current versions of HP, Graftek.
1. Surface or Wireframe 3D Models
Should provide wireframe edges as well as surfaces, for IGES files it is helpful to separate the features by layers.
1. Moldflow surface model (.MFL)
2. IGES (w/ trimmed surfaces)
3. ACAD R13 AutoSurf
4. AutoSurf .MOD file
1. Other Solid models
3. AutoCAD AME
2. 2D or Wireframe (section cuts are very useful)
1. ACAD R10 or later
3. FEM MODEL
Shell Model representing mid-plane model can be very useful or totally useless depending on how it is made.
1. Moldflow .MFL file
2. Patran File
3. MSC Nastran Mesh
4. Ansys Mesh
5. SDRC Mesh
1. PRODUCT SAMPLE
strongly desired EVEN IF OTHER REPRESENTATIONS ARE PROVIDED
1. Production piece
A sample of a production component made using the processing and tooling to be evaluated
1. Production part from different tool or process
A part from another tool, process or material
if production sample is not available...
1. Injection molded
3. StereLithography or other Rapid prototype technology
4. other such as hand sculpted or cast
5. Similar product of same general configuration
1. FEED SYSTEM DIMENSIONS
Required for proper process simulation
1. TOOL PRINT(S)
Hard copy detail drawings should always be provided if available.
Should include runner centerlines, shapes, and dimensions.
1. SPRUE details
A detail drawing or, If a standard bushing is used, copy of a catalog page will suffice. If not available, a supplier and product number is OK.
1. Gate Details
Detail drawing with centerlines, shapes and dimensions.
1. Other Hardware Details such as Hot Manifolds, Heated drops or Valve Gates
2. RUNNER/SPRUE SAMPLE
DESIRED whether OR NOT drawings are provided
1. MOLD BASE DESCRIPTION
1. TOOL DRAWING
2. CATALOG NUMBER
3. CORE and CAVITY PLATE Extents
4. PLATE MATERIAL
1. Thermal Conductivity
3. Heat Capacity
1. 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
1. TOOL TEMPERATURE
Surface temperature of the mold at the beginning of the filling cycle after it has reached stabilized condition
1. 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)
1. FILLING PROFILE
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.
1. 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).
1. 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.
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.
1. CONSTANT PRESSURE MODE
1. Switch over at Volume
Switches to constant pressure mode at a % of shot volume (pressure specified as specific or % of maximum)
1. Switch over at Time
Switches to constant pressure mode at a specified time (pressure specified as specific or % of maximum)
1. no Pressure control
1. MACHINE LIMITS
1. Maximum injection pressure
Limits flow rate when pressure cap is reached
1. 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.
1. PROGRAMMED INJECTION SEQUENCE
IF programmed (or profiled) injection sequences, if used, are described to the filling routines in any of three ways.
1. %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.
1. 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.
1. 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.
REQUIRED TO MODEL FULL CYCLE!
1. 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.
1. Environment Temperature
2. Environment Barometric Pressure
1. TOTAL CYCLE
1. COOLING TIME
Additional time that mold remains closed after packing pressure is released.
1. MOLD OPEN TIME
1. MATERIAL CHARACTERIZATION*
1. MATERIAL SUPPLIER AND GRADE
2. THERMAL DATA
2. THERMAL CONDUCTIVITY
3. NO-FLOW TEMPERATURE
4. FREEZE TEMPERATURE
3. VISCOSITY DATA
4. PVT DATA (PRESSURE-VOLUME-TEMPERATURE)
5. RECOMMENDED PROCESSING LIMITS
1. MELT TEMPERATURE
2. TOOL TEMPERATURE
3. SHEAR RATES
4. SHEAR STRESS
2. PRESS CHARACTERISTICS
1. MAXIMUM TONNAGE
2. MAXIMUM PRESSURE
3. COMPRESSION RATIO
4. MAXIMUM FLOW RATE
5. REACTION TIME
3. PHYSICAL SAMPLES
1. PRODUCT SAMPLE
1. 'GOOD' SAMPLE
2. PROBLEM SAMPLE
3. SHORT SHOTS
2. RUNNER/SPRUE SAMPLE
1. 'GOOD' SAMPLE
2. SHORT SHOTS
4. OTHER VARIABLES
1. MATERIAL ADDITIVES
2. ENVIRONMENTAL VARIABLES