Guia de seleccion de parámetros para configurarión de un preimpregando

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The following diagrams (Figure 2 and Figure 3) are of a typical epoxy, urethane, graphite foam, glass foam and ceramic foam block construction patterns with a steel base.

The following options are shown.

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Solid Construction and Hollow Construction

[pic 2]Tooling block cut and

bonded to the desired profile.

Master model surface can be inside and/or outside.

Steel base

Figure 3 Thick ‘Brick Wall’ Master Model Construction

Page 2 of 30 Chap ter 1 Manufacturing Master Models A1.fm

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[pic 3]Tooling Design Manual

- [pic 4]Master Model - Manufacturing Overview

When it comes to manufacturing the master there is no significant difference between the processes used.

Basically, layers of tooling block are cut and bonded together under vacuum pressure. Alternative clamping arrangements have been tried, but are not recommended for large or complex shapes. The shape, size and position of the blocks is derived either from the CAD model and/or from drawings prints.

Because a machining allowance is required, the master is always constructed slightly larger than its finished size. Obviously, the hollow master will use less tooling block material and will be lighter than the solid master, but it will generally take more time to construct and longer to vacuum bag when the composite mould tool is produced.

Similarly, with the ‘brickwork’ construction, it will generally take longer to construct. This is because the block needs to be cut and fitted to suit a curved profile. However, for a barrel or engine nacelle shaped master, it gives the most economical use of the tooling block. An added benefit is that, in certain circumstances, both the inside and outside faces can be machined for separate master model profiles.

Master models are normally built up in stages, typically two or three layers at a time. The number of layers that can be bonded at any one time is restricted by the working life of the adhesives used.

The sections of tooling block are cut to profile and dry fitted together, after which they are thoroughly degreased and allowed to dry. The specified adhesive is then mixed and applied with a trowel to all surfaces that will be bonded. A castellated scraper is then drawn over the surfaces to create ridges of adhesive.

The surfaces are then brought together and manual pressure applied until surplus adhesive is squeezed out of the joint. This process is repeated until all of the blocks for the stage are in place. The blocks are then vacuum bagged to provide additional/constant pressure while the adhesive cures.

The vacuum bag normally consists of a ply of peel ply - to absorb any additional adhesive from between the blocks, a breather felt - e.g. Airbleed 120, and a low temperature vacuum bag. The master is generally left overnight for the adhesive to cure, after which the process is repeated until the desired construction is achieved.