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Plastic Molding

Geometry or Cost Engine Changes that Could Impact Configured Digital Factories

The following changes might impact costing, even for Digital Factories that use earlier cost model versions.

  • Thickness Near Toroidal Surfaces (can impact process feasibility, routing, and design guidance): This release improves the algorithm used to determine part thickness for parts with toroidal surfaces, that is, parts with features that are shaped like a portion of a doughnut's surface. The previous release's algorithm was sometimes inaccurate regarding part thickness near such features. The change generally has a very minor impact on thickness values.

  • Flow Appraisal GCD: This release introduces the FlowAppraisal GCD. The properties of each FlowAppraisal GCD capture the results of a new three-dimensional material flow analysis. The presence of this new GCD has no cost impact for prior cost models, but may increase the GCD extraction time for a CAD model by around 9%. Cost models from prior releases do not use the results of the new three-dimensional analysis, and instead rely on a two-dimensional flow analysis that does not fully consider wall thickness variation.

    Note:

    Users of prior cost models can disable the extraction of FlowAppraisal GCDs by setting the site variable isFlowAppraisalEnabled to false.

    See also Required Clamping Force.

Bug Fixes or Small Improvements to Prior Cost Model Versions

The following changes might impact costing for Digital Factories that use earlier cost model versions.

  • NO IMPACT

Cost Model Changes that Do Not Affect Configured Digital Factories

The following changes do not affect costings with Digital Factories that use earlier cost model versions. The changes are available only in the latest cost model version.

  • Flow Analysis and Required Clamping Force (can impact machine selection, overhead costs, and tooling costs): This release improves the determination of required clamping force for a given part, leading to more accurate selection of the lowest-overhead machine that can produce the part. The change affects Injection Molding, Reaction Injection Molding, and Structural Foam Molding.

    In the previous release, aPriori analyzed material flow in two dimensions, based on the geometry of the projection of the part along the draw direction and based on a user-specified number of gates (1 by default). This release analyzes flow in three dimensions, based on the part's full, three-dimensional geometry, leading to a determination of the minimum required number of gates and a more accurate determination of the flow length.

    Info:

    Flow length is the maximum distance the melt must travel from a gate to the extremities of the mold cavity. Flow ratio is flow length divided by wall thickness, and is crucial in the determination of required clamping force.

    Note:

    To utilize this enhancement with a scenario cost in a previous version of aPriori, the scenario must be connected to the CAD file and geometry must be re-extracted.

    Note:

    You can disable the new three-dimensional flow analysis by setting the site variable isFlowAppraisalEnabled to false. In this case, the cost model will rely on a two-dimensional flow analysis that does not fully consider wall thickness variation.

    The results of the new flow analysis are extracted as FlowAppraisal GCDs, a new type of GCD introduced in this release. The properties of each FlowAppraisal GCD capture the results of an analysis based on the part's geometry, the current scenario's material and gating requirements, and a candidate gate distribution type (short side, long side, or free).

    As a result of this enhancement, in a set of test parts, required clamp force decreased by an average of around 40%. Because this sometimes caused selection of a lower-overhead machine, machine overhead rate decreased by an average of around 18% for parts with cold runner systems and about 13% for parts with hot runner systems. Fully-burdened cost decreased by an average of around 8% for parts with cold runner systems and around 3% for parts with hot runner systems. The impact of the enhancement is likely to be greatest for long, thin parts and parts made with low viscosity materials.

  • Material Property Flow Length Ratio: This release introduces the material property Flow Length Ratio, the material's maximum flow ratio. By default, the property influences the number of gates assumed for each cavity.

    For Injection Molding, this property places an upper bound on the feasible flow length for a given material and a given part. See Injection Molding Feasibility and Design Guidance, below.

    When you add a custom material, provide Flow Length Ratio values using the following guidelines:

    • If the new material’s Material Type already exists in the material table, use the Flow Length Ratio value provided for other materials of the same type.
    • If the new material’s Material Type does not already exist in the material table, use the Flow Length Ratio value for materials of a closely related Material Type.
    • If there is no closely related Material Type available, aPriori recommends using 150 as a reasonable conservative starting-point value corresponding to a high-viscosity material. If a material has no value for Flow Length Ratio, aPriori uses the value of the site variable flowLengthRatioDefault (150 by default). Note that the default for this site variable is a conservative value corresponding to a high-viscosity material and as such aPriori might underestimate the given material's ability to flow and overestimate the number of gates and clamp force required.

  • Flow Ratio Feasibility and Design Guidance: For Injection Molding, in starting point Digital Factories, the new material property Flow Length Ratio places an upper bound on feasible flow ratios. If a mold's flow ratio exceeds the material's Flow Length Ratio, there is a risk of a short shot condition, that is, the material might freeze before filling the entire mold, regardless of clamping force.

    The flow analysis determines the minimum number gates required to prevent the mold's flow ratio from exceeding the material's Flow Length Ratio. If no increase in the number of gates suffices to prevent the mold's flow ratio from exceeding the material's Flow Length Ratio, the process is considered infeasible, and the problem is noted in the Design Guidance tab.

    Note:

    You can disable this Injection Molding feasibility constraint by setting the cost model variable checkFlowRatioFeasibility to false.

    If you disable this feasibility constraint, the flow analysis determines the minimum number of gates required to prevent the mold's flow ratio from exceeding the material's Flow Length Ratio, and if no increase in the number of gates suffices to prevent the mold's flow ratio from exceeding the material's Flow Length Ratio, the number of gates is assumed to be the smallest number of gates such that any additional increase in the number of gates has a negligible effect on the flow ratio.

  • Minimum Number of Gates per Cavity: In the previous release, the setup option Minimum Number of Gates per Cavity allowed you to override the default minimum number of gates per cavity. In this release, Minimum Number of Gates per Cavity is purely informational in the Process Options Editor. If a scenario from a prior release includes an override of the default minimum number of gates, the override is ignored in this release. You can now override the default minimum number of gates by editing the value of the Number of Sites property of the Flow Appraisal GCD in the Geometric Cost Drivers pane.

  • Material Properties Injection Pressure Max and Injection Pressure Min (can impact machine selection and overhead costs): This release updates the values of the properties Injection Pressure Min and Injection Pressure Max in starting point Digital Factories for several Plastic Molding materials.

  • Injection Pressure and Clamping Force Calculations: In the previous release, cavity pressure and required clamping force calculations assumed the use of the material's maximum injection pressure. In this release, these calculations assume the use of the average of the material’s maximum and minimum injection pressure values.

    Note:

    You can direct aPriori to use the material's maximum injection pressure, as in the previous release, by setting the new setup option Maximum Material Injection Pressure to Material Recommended Max.

    Due to this change (together with other enhancements--see Flow Analysis and Required Clamping Force, above), estimates of cavity pressure and required clamping force generally decrease compared to the previous release. For some parts, this may result in selection of a smaller, lower-overhead machine.

  • Cavity Finish (impacts hard tooling cost): In the previous release, the Cavity Finish setup option allowed you to choose from among four finishing grades: A (High-Gloss), B (Semi-Gloss), C (Matte), and D (Textured). In this release, each of these four grades has been expanded into three sub-grades (1, 2, 3), so the setup option provides a choice among 12 finishing grades. The polishing hours associated with each grade have also been updated.

    As a result of this change, tool finishing costs will decrease somewhat for Grade C, increase somewhat for Grade A, and can increase or decrease for Grade B depending on cavity surface area. In general, parts with a higher surface area are expected to have a larger change in tool finishing cost.

    If a scenario from a prior release includes an override of the default cavity finish, this override is ignored in this release and the current default is used instead. The defaults are specified by the cost model variables defaultCavityFinishIM, defaultCavityFinishRIM, defaultCavityFinishSFM (SPI B3 - Normal Semi-Gloss in starting point Digital Factories).

  • Cavity Texture (impacts hard tooling cost): This release improves the estimation of mold texturing cost. The cost model now better accounts for the individual texturing processing steps and for the difference in processing steps between the Mold-Tech A standard and the other texturing standards. The cost model also now assumes that the pre-finishing rate increases over time for a mold with a large surface area, due to an assumed learning curve.

    As a result of these enhancements, mold texturing is now reduced to approximately 3% of total mold cost with default, starting point configurations; previously it was between 6% and 14%. In general, deeper textures are expected to have a larger change in texturing cost.

  • Hydraulic Slide Count (can impact mold assembly time and hard tooling cost): In the previous release, aPriori sometimes used an incorrect value for the number of hydraulic slides (side actions) required by a part. This release corrects the problem. As a result, tooling costs may change slightly for parts that have hydraulic slides or hydraulic ejectors. Hydraulic slides are required when the slide pin travel distance exceeds the machine opening stroke. Hydraulic ejectors are required for large-area core plates.

  • Mold and Gating Configuration Feasibility: This release strengthens the feasibility constraints for Injection Molding and Structural Foam Molding. Feasibility now fails for the following configuration:

    • Cold runner system
    • Center gate
    • 2-plate mold
    • Multiple cavities or multiple gates A cold runner system must have either a 3-plate mold, an edge gate configuration, or a single cavity with a single gate. As a result, some scenarios that previously costed successfully might now fail to cost.

  • Plasticizing Time for Injection Molding (can impact cycle time): In the previous release, the cost model did not account for plasticizing (which occurs in parallel with cooling). In this release, if the cooling time for a given part is exceeded by the plasticizing time for the next part's material, the cycle time for the given part now includes the extra time required for plasticizing to complete.

    This release introduces the machine property Plasticizing Rate, which specifies the machine's plasticizing rate for general purpose polystyrene. If the property is not populated, the cost model looks up the rate for general purpose polystyrene by machine clamp force in the lookup table plasticizingRateByClampForce. The rate is adjusted for the current material.

    This change rarely affects cycle time, since plasticizing time rarely exceeds cool time. Cycle time could increase with a thin-walled part that has a particularly short cooling time, with a part that uses a glass-filled material, or with a machine that has an insufficient injection barrel capacity.

  • Ejector Plate Time (impacts cycle time): This release improves the estimate of eject time (a component of cycle time) for Injection Molding, Reaction Injection Molding, and Structural Foam Molding. In the previous release, aPriori overestimated eject velocity and so underestimated eject time. Eject velocity was assumed to be the machine's maximum velocity (estimated based on the machine's dry cycle time and tie bar distances).

    In this release, by default, eject velocity is assumed to be 50% of the machine's maximum velocity. Administrators can customize this percentage with the cost model variable ejectorPercentMaxMachineVelocity (50 in starting point Digital Factories). The change results in a very small increase in cycle time, compared to the previous release.

    Note:

    You can restore the behavior of the previous release by setting the cost model variable ejectorPercentMaxMachineVelocity to 100.

    This release also introduces the cost model variable numEjectorCycles (1 in starting point Digital Factories) which allows you to specify that there are multiple ejector cycles, further increasing eject time if desired.

  • Material Regrind Allowance (can impact material cost): In the previous release, by default, regrind allowance (the percentage of melt consisting of reground material) was assumed to be specified by the cost model variable defaultRegrindAllowance (25% in starting point Digital Factories), regardless of the amount of available in-process regrind.

    In this release, the default regrind allowance is the percentage of in-process regrind available from runners and downstream scrap parts up to the value set by defaultRegrindAllowance, which represents the default design limit for the percentage of runners and scrap allowed with virgin material.

    As a result of this change, material cost might increase somewhat for some scenarios that have less in-process regrind available than the defaultRegrindAllowance. You can restore the behavior of the previous release for a particular scenario by setting Material Regrind Allowance to Max default design regrind allowable.