PROCESS SIMULATION OF RTM AND VACUUM INFUSION

1- INTRODUCTION

The development phase of a new product to be manufactured can be many times a costly and lengthy process. In this context, it is possible to reduce the duration, costs and risks of this design phase by optimising the design process using process simulation tools. The use of these tools will provide the following advantages in the case of RTM and Vacuum Infusion techniques:

· Optimise part injection: optimise the number and position in the mould of runners, injection and venting ports. Eliminate the risk of dry spots and also reduce the injection time.

· Evaluation of the behaviour of the resin flow around part discontinuities due to changes in the thickness, presence of inserts or cores in sandwich structures, producing different permeability zones and sometimes filling problems.

· Assess the impact and variations in resin and fabric properties.

· Possibility of running many simulation cases in order to reduce the number and cost of injection experiments.

· Easy calibration of the tool by using the simulation as well as a simple strip injection experiment to define the permeability of the reinforcement lay-up in the product.

2- SIMULATION PROGRAMS DESCRIPTION

The commercial available RTM simulation programs are normally based on Finite element and Control Volume methods in order to solve the physical equations that govern the resin flow through a porous medium.

Regarding the part geometry it is possible usually to use the modeller of the simulation programs or to import 3D models in standard formats, like STL or DXF, obtained using other programs.

Regarding the mesh it is also possible to use the mesh generator included in the simulation programs or to import FEM meshes from other programs.

3- CASE STUDY

3.1. Objective

In this case study, it is going to be studied the influence of inserts in the injection process of the manufacturing of a composite panel using RTM technology. The presence of an insert in the RTM process can produce filling problems due to the discontinuities and different permeability zones.

The process simulation has been performed using the Õ 7 program and the results of this simulation have been validated with experimental tests

Picture 1. Zone X permeability> zone Y permeability

In order to carry out the simulation it is necessary to know the different permeability values of the different zones. In this context, it has been calculated the permeability of the different zones considering the changes in fibre content in each case.

3.2. Process parameters and materials

The materials that have been used for the manufacturing of the composite laminate are the following:

· Polyester resin

· Glass fibre mat

· Coloured additives to allow recording

· Stainless steel insert: 100x100 mm

· Insert thicknesses: 0,75; 1; 1,5 mm.

The process injection parameters used for the manufacturing of the panel are the following:

· Mould temp.: 30ºC

· Resin temp.: 20ºC

· Injection pressure: 0,5 Bar

· Vacuum pressure: 0,5 Bar

3.3. Different inserts configurations

The insert situation as well as the different relevant zones defined in the panel, are indicated in the next drawing.

In order to define the best insert design, 6 different insert configurations have been studied varying the insert thickness and position and fibre layers. These different insert configurations have been compared with the same panel situation but without insert.

3.4. Experimental validation

The simulation results have been validated by the recording of the experimental tests using a transparent mould. The relevant process injection instants have been defined:

Instant 0 - Is the moment when the resin front flow arrives to point A.

Instant 1- Is the moment when the resin arrives to points C and D.

Instant 2.- Is the moment when the resin arrives to point B

Instant 3.- Is the final state of the injection

The results of the experimental results are indicated below including the pictures of the resin flow at the relevant defined instants and for each of the 6 insert configurations:

SD-0 without insert:

SD-1:

SD-2:

SD-3:

SD-4:

SD-5:

SD-6:

3.5. Simulation results

In this chapter, the simulation results are included for each of the 6 insert configurations and also for the case without insert:

SD-0 without insert:

SD-1:

SD-2:

SD-3:

SD-4:

SD-5:

SD-6 upper:

SD-6 lower:

3.6. Conclusions

Comparing the experimental and the simulated results obtained, the following conclusions can be mentioned:

· The insert solutions defined as SD-3 or SD-4 are the most convenient to avoid injection filling problems as it can be concluded from the results obtained. In this case, the fibre content is more homogeneous due to the fact that the fibre layers have been eliminated where the insert has been placed.

· The behaviour obtained of the injection flow in the simulation is very close as the one obtained in the experimental results, which means that the simulation tool is really helpful to define the best insert configuration in this case.

· Regarding the injection times, the tool provides interesting qualitative information in terms of comparative values of the different solutions tested.

· Nevertheless, regarding the quantitative analysis, the injection times obtained in reality are higher that the ones obtained by simulation.

4- COMMERCIAL SIMULATION SOFTWARE

The following simulation software is commercially available for the process simulation of RTM and Vacuum Infusion:

RTM-Worx

POLYWORX

The Netherlands