Moldflow Analysis Options

Fibre Orientation, Gas injection, Shrinkage Analysis, Over molding, Metal Inserts, In Mold Decoration and Core Shift.

Imtech have continually updated and expanded their plastics simulation tools and have a wide capability in the field of plastics injection moulding simulation:

Most options are available with basic FEA model types including, 3D tetrahedral, Mid-plane and Fusion / Dual Domain mesh formats.

Fibre Orientation

The Fiber-orientation flow analysis is used to predict the behavior of composite materials. While injection-molded fiber-reinforced thermoplastics constitute a major commercial application of short-fiber composite (a filler within a polymer matrix) materials, the modeling of the process is more complex than in other flow applications.

In injection-molded composites, the fiber alignment (or orientation) distributions show a layered nature, and are affected by the filling speed, the processing conditions and material behavior, plus the fiber aspect ratio and concentration. Without proper consideration of the fiber behavior, there is a tendency to significantly overestimate the orientation levels. The Moldflow fiber orientation model allows significantly improved orientation prediction accuracy over a range of materials and fiber contents.

Fibre / Polymer composite materials simulation:

Predict fiber orientation and thermo-mechanical property distributions in the molded part

Predict elastic modulus and average modulus in the flow and transverse-flow directions

Predict linear thermal expansion coefficient (LTEC) and average LTEC

Calculate Poisson's Ratio, a measure of the transverse contraction of a part compared to its length when exposed to tensile stress

Optimize filling pattern and fiber orientation to reduce shrinkage variations and part warpage

Increase part strength by inducing fiber orientation along load bearing part surfaces

Filler database: stores material data for the most common filler materials:

Glass fibers, Glass bead, Carbon fibers, Aramid fibers, Boron fibers, Metals, Minerals, Synthetics, Talc.

Fibre Orientation Results:

Average fiber orientation
Fiber orientation tensor
Fiber direction
Thermo-mechanical properties of the composite material
Shrinkage

Gas Injection

Gas-Assisted Injection Molding is a process where an inert gas is introduced at pressure, into the polymer melt stream at the end of the polymer injection phase. The gas injection displaces the molten polymer core ahead of the gas, into the as yet unfilled sections of the mold, and compensates for the effects of volumetric shrinkage, thus completing the filling and packing phases of the cycle and producing a hollow part.

Traditionally, injection molded components have been designed with a relatively constant wall thickness throughout the component. This design guideline helps to avoid major flaws or defects such as sink marks and warpage. However, apart from the simplest of parts, it is impossible to design a component where all sections are of identical thickness. These variations in wall thickness result in different sections of the part packing differently, which in turn means that there will be differentials in shrinkage throughout the molding and that subsequently distortion and sinkage can often occur in these situations.

Gas Injection Capability:

Gas injection allows cost effective production of components with:

• Thick section geometry.
• No sink marks.
• Minimal internal stresses.
• Reduced warpage.
• Low clamp pressures.

Evaluate the filling pattern with the influence of gas injection to aid in part design, gate placement, and process setup

Properly size gas channels for optimal filling and gas penetration

Determine the best gas channel layout to control gas penetration

Inject gas at any location or in multiple locations within the part or runner system

Inject gas through multiple gas pins simultaNeo™usly or at different times during the process

Detect areas of poor gas penetration or other problems

Determine the proper shot size to avoid gas "blowout"

Determine injection pressure and clamp force requirements for proper molding machine selection

Incorporate delay time prior to injecting gas allowing thin areas to solidify

Automatically determine gas pressure required to avoid short shots, melt-front hesitation, or burning

Determine final part weight after gas injection to help maximize material savings and minimize weight

Estimate the final wall thickness after gas penetration

Gas Injection Results:

Polymer fill pattern
Gas channel route during filling
Gas channel advancement during packing
Gas blow-through locations
Weld-line positions
Location of air traps
Gas penetration into thin wall sections (fingering)
Polymer wall/gas channel thickness
Gas and polymer pressure profiles during cycle
Clamp tonnage requirement

Shrinkage

Every part which is injection molded requires someone to select the dimensions to which the mold must be cut. In the past, many precision parts have required molds to be heavily modified so that tolerances can be met successfully. On some occasions, molds have been scrapped several times over, in order to achieve the required dimensions, incurring huge costs and significant delays in time to market for the product.

Because plastic parts shrink as they cool, it is essential to accurately account for this shrinkage in the design of the mold so that critical product tolerances can be met.

Shrinkage Simulation

Shrink enables you to determine an appropriate shrinkage allowance to use to cut the mold taking into account the shrinkage characteristics of the material being used to mold the part and the molding conditions.

The key features of the shrinkage analysis are:

• Calculation of a recommended shrinkage allowance.
• Graphical display indicating whether it is valid to apply this single shrinkage allowance value across the part.
• Optional definition of critical dimensions and their associated tolerances. Where critical dimensions are defined, the shrinkage analysis predicts whether the specified tolerances can be met if the recommended shrinkage allowance is used, included detailed dimensional and tolerance information resolved into X, Y and Z directions.

Shrinkage Analysis Results:

Shrinkage values along the x, y, and z axes
Dimension tolerances and confidence intervals
Shrinkage variation across the part
Error distribution for shrinkage allowances
Average shrinkage allowance
Dimensional accuracy report
Mold dimensions between any two points on the model

Over molding, Metal Inserts, In Mold Decoration and Core Shift.

In-mold labels are very thin inserts usually less than 1mm thick. Labels are applied to the mold before each injection cycle. The labels normally have different material properties can affect the flow and cooling behavior. An insert is a component that is placed into the mold before the injection phase and is anchored into the plastic part by being partially or wholly surrounded by the injected plastic. Typical inserts may have threads, may be electrically conductive, or may be a different plastic material.

Core Shift

Core Shift Analysis – Moldflow provides a unique multi-physics solution to simulate injection mold core shift, which is defined as the movement of a core caused by non-uniform pressure distribution during the filling and packing stages of the injection molding process. Core shift typically causes molded part wall thickness variation which can result in both structural and cosmetic defects.

Core shift can result in undesirable variations in wall thickness which will affect the final shape and mechanical performance of the part. The core shift simulation provides detailed information about the movement of the mold core and its interaction with the polymer flow process as the plastic is being injected. Designers can use this information to correct for the core shift phenomenon, for example, by modifying the design of the part, or adjusting process conditions such as the gate location or core/mold temperatures.