Autodesk Moldflow Insight AMI Resin Transfer Molding

Transcription

1 Autodesk Moldflow Insight 2012 AMI Resin Transfer Molding

2 Revision 1, 22 March This document contains Autodesk and third-party software license agreements/notices and/or additional terms and conditions for licensed third-party software components included within the product. These notices and/or additional terms and conditions are made a part of and incorporated by reference into the Autodesk Software License Agreement and/or the About included as part of the Help function within the software.

3 Contents Chapter 1 Resin Transfer Molding Chapter 2 RTM/SRIM analysis types and analysis technologies RTM/SRIM analysis types and analysis technologies Setting up a Resin Transfer Molding analysis RTM/SRIM analysis types and analysis technologies Process Settings Wizard dialog RTM/SRIM Settings Chapter 3 Preparing the model for Reactive Molding analysis Chapter 4 Preform surface Preform surface Porosity and permeability Preform surface Orientation Preform surface Preform Surface (Dual Domain) dialog Preform Surface (Midplane) dialog iii

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5 Resin Transfer Molding 1 Resin Transfer Molding (RTM) is a liquid composite molding process. Unlike materials used in RIM or SRIM processes, where the chemical reaction is activated by mixing the reactants, the chemical reaction for resins used in RTM are thermally activated by heat from the mold wall and fiber mat (preform). The reaction rate in RTM processes is typically much slower than that in SRIM, allowing a longer fill time at lower injection pressure. The RTM process RTM is a process for the manufacture of fiber-reinforced composites. The resulting light-weight, high strength parts are attractive for many applications. Examples are chairs, automobile parts and aircraft components. RTM is of interest to the aerospace industry because it promises cost savings and performance improvements over traditional methods. In the RTM process, dry fiber reinforcement, or fiber preform, is packed into a mold cavity which has the shape of the desired part. The mold is then closed and resin is injected under pressure into the mold where it impregnates the preform. After the fill cycle, the cure cycle begins, during which the mold is heated and resin polymerizes to become rigid plastic. Benefits of RTM The greatest benefit of RTM relative to other polymer composite manufacturing techniques is the separation of the injection and cure stages from the fiber preform stage. Liquid molding also enables high levels of microstructural control and part complexity compared with processes like injection molding and compression molding. Other benefits afforded by RTM include: Low capital investment. Good surface quality. Tooling flexibility. Large, complex shapes. Ribs, cores and inserts. Range of reinforcements. 1

6 RTM/SRIM analysis types and analysis technologies 2 The following table shows the available analysis technologies for an RTM/SRIM analysis type. Table 1: RTM/SRIM process and analysis types Analysis Type Analysis Technology Fill+Pack Runner Balance RTM/SRIM analysis types and analysis technologies There are steps that are required to set up a Resin Transfer Molding analysis. Setting up a Resin Transfer Molding analysis For an RTM or SRIM analysis, resin is forced to flow through a cavity in which reinforcing preform (also called fiber mat) is present. The fiber-mat, or preform reinforcement is positioned in the mold, and the mold is closed and heated under pressure. The mold is then opened and the part is removed. In order to run an RTM or SRIM analysis, you must specify a preform surface on the entire part. 1 In the Layers pane, deselect all layers except the layer containing the cavity elements. 2 Click Geometry tab > Selection panel > Select All to select the entire model. 3 Click Geometry tab > Properties panel > Assign. The Assign Property dialog appears. 4 Click New > Preform surface to assign the Preform surface property to all model elements. In the Preform Surface dialog, you can use the selected preform, edit the properties of the selected preform, or select a new preform. 5 Select the required preform for the analysis. If you click Select, you can search the supplied database for an appropriate preform to use. 2 RTM/SRIM analysis types and analysis technologies

7 6 Specify the required preform thickness option. 7 Specify the required preform orientation. 8 Click OK twice. RTM/SRIM analysis types and analysis technologies Use this dialog to specify settings for a Resin Transfer Molding analysis. Process Settings Wizard dialog RTM/SRIM Settings This page of the Process Settings Wizard, which can be accessed by clicking (Home tab > Molding Process Setup panel > Process Settings), is used to specify the Resin Transfer Molding (RTM) and Structural Reaction Injection Molding (SRIM) related process settings for the selected analysis sequence. NOTE: The RTM analysis will be used if you are analyzing a fiber-reinforced plastic. NOTE: Some of the items listed below may not be available on the current dialog. This is dependent on the mesh type, molding process and analysis sequence selected. Mold surface temperature Melt temperature Nominal injection time Melt initial conversion Curing time Machine pressure limit Intensification ratio The temperature of the mold at the plastic-metal interface, where the plastic touches the mold. The temperature of the molten plastic, or melt, as it starts to flow into the cavity. Enter the injection time that you would use with the injection unit for the process. Enter a value between -1 and 1 to specify the initial conversion (curing) level at the injection location. The time taken for a thermoset material to become sufficiently cross-linked from heating to form a solid and freeze. The maximum allowable hydraulic pressure that can be used on the injection molding machine. The ratio of the material pressure in front of the screw, compared to the oil pressure in the piston of the injection molding machine. RTM/SRIM analysis types and analysis technologies 3

8 Preconditioning analysis Specifies whether a preconditioning analysis should be performed. 4 RTM/SRIM analysis types and analysis technologies

9 Preparing the model for Reactive Molding analysis 3 There are modeling tasks required for a Microchip Encapsulation molding analysis, Reactive Molding analysis, and Underfill Encapsulation molding analysis. Compulsory modeling tasks In order to run a thermoset analysis, the following must be specified for your model: A meshed part model Injection location(s). Analysis setup options The following can be specified for your model: Porosity and permeability for a surface/element (for RTM/SRIM analyses). Runner dimension constraints (for a Runner Balance analysis). 5

10 Preform surface 4 Surface characturistics that impact on the analysis can be simulated. Preform surface Porosity and permeability In the RTM (Resin Transfer Molding) and SRIM (Structural Reaction Injection Molding) analyses, resin is forced to flow through a cavity in which reinforcing preform (also called fiber mat) is present. The flow type, characterized by the preform properties, may be isotropic or anisotropic depending on the preform structure. The resistance of a resin to flowing through the preform also depends on the resin properties and flow rate. When preparing an RTM or SRIM analysis, the preform data includes: Porosity and permeability. Orientation, if the preform is anisotropic. Preform porosity Porosity represents the packing density of the preform in the cavity. Porosity is defined as the ratio of the void volume to the cavity volume, before the cavity is filled with resin. The void volume is equal to the cavity volume minus the volume occupied by the fiber reinforcement. Preform permeability Permeability is the ability of a fluid to flow through a porous medium. The greater the permeability, the more easily the fluid flows through the medium. For RTM and SRIM processes, permeability depends on the network structure of the fiber mat. The in-plane and the transverse-to-flow structures of the fiber mat can be different, and can create different resistance to the flow. Transverse permeability is used to characterize the flow of autoclave composite processing. In-plane permeability is used to determine the flow resistance in RTM or SRIM, since these processes are often modeled with a two-dimensional flow due to the small ratio of the gap thickness to the plane dimension in many applications. Transverse permeability: 6 Preform surface

11 In-plane permeability: Using preform in a cavity with varying thickness Sometimes a preform is placed on areas with different thicknesses. A cavity with varying thickness, but reinforced with the same preform, can result in different porosity, and, therefore, permeability. To deal with this situation, specify the Reference thickness on which the preform properties were based. In the Properties tab of the Preform dialog, thickness is the reference thickness. If the cavity thickness at molding is different from the specified reference thickness, the Reactive Molding analysis automatically modifies the porosity and permeability. Preform surface Orientation In the RTM (Resin Transfer Molding) and SRIM (Structural Reaction Injection Molding) analyses, resin is forced to flow through a cavity in which reinforcing preform (also called fiber mat) is present. The flow type, characterized by the preform properties, may be isotropic or anisotropic depending on the preform structure. The resistance of a resin Preform surface 7

12 to flowing through the preform also depends on the resin properties and flow rate. When preparing an RTM or SRIM analysis, the preform data includes: Porosity and permeability. Orientation, if the preform is anisotropic. Isotropic preform Resin flowing through a preform with random structure produces a circular melt front. This flow pattern is known as isotropic flow. This kind of preform normally is made from randomly chopped fiber strands; it is known as an isotropic preform. Since the resin flow pattern does not depend on the direction of flow, there is no need to specify the preform orientation. For an isotropic fiber mat, the preform permeability in principal direction 1 is equal to the preform permeability in principal direction 2, and the preform cross permeability is zero. Therefore, in Autodesk Moldflow Insight, you do not need to specify the orientation of an isotropic preform. Anisotropic preform If the structure of a directionally stitched or woven preform is not uniform, it is known as an anisotropic preform. In terms of the pore-area distribution, the preform shows a maximum in one direction and a minimum in the direction at right angles to the first direction. When resin flows through such a preform, the flow in the direction of maximum pore area advances more quickly, because it encounters less flow resistance. If the pore-area distribution is smooth, the melt front is elliptical. The shape of the ellipse depends on the maximum and the minimum pore areas, which can be characterized by the permeability of the principal directions. The direction with the largest pore area, and thus the greatest permeability, is defined as Principal direction 1. Principal direction 1 corresponds to the major axis of the ellipse. The minor axis of the ellipse corresponds to principal direction 2, which is at right angles to principal direction 1 and has the smallest pore area and, thus, the smallest permeability. Schematic planar view of cavity, showing elliptic melt-front pattern for resin flowing through anisotropic preform: 8 Preform surface

13 Where: a is the resin inlet (gate) b is the minor axis c is the elliptic melt front d is the major axis e is the anisotropic fiber mat NOTE: For an anisotropic fiber mat, the preform permeability in principal direction 1 is different from the preform permeability in principal direction 2, and the preform cross permeability may or may not be zero. Therefore, in Autodesk Moldflow Insight, you need to specify the orientation (principal direction 1, the major axis) of an anisotropic preform. Preform surface Use this dialog to specify the properties of selected elements or regions of type in an RTM (Resin Transfer Molding) and SRIM (Structural Reaction Injection Molding) analysis. Preform Surface (Dual Domain) dialog The Preform Surface (Dual Domain) dialog is used to specify the properties of the selected Dual Domain elements or regions of type Preform surface (Dual Domain). The set of property values defined by the dialog are saved to a property set with the description shown in the Name box. In addition, you may be given the option to also apply the property values to related entities in the model. NOTE: Do not assume that there is only one orientation direction for the entire part. Areas such as vertical ribs may require you to specify a different fiber-mat preform orientation to the rest of the part. Preform surface 9

14 Preform Surface (Midplane) dialog The Preform Surface (Midplane)dialog is used to specify the properties of the selected Midplane elements or regions of type Preform surface (Midplane). The set of property values defined by the dialog are saved to a property set with the description shown in the Name box. In addition, you may be given the option to also apply the property values to related entities in the model. NOTE: Do not assume that there is only one orientation direction for the entire part. Areas such as vertical ribs may require you to specify a different fiber-mat preform orientation to the rest of the part. 10 Preform surface