Autoclave process tooling

Resin flow and pressure distributions are among the most challenging aspects of the autoclave process cycle to model. Accounting for tooling and bagging variations, such as inner bag... 

Part heat-up rate during autoclave processing can dramatically influence final part quality. At least three variables can affect the autoclave heat-up rate for composite parts (1) tool material and design, (2) the actual placement of the tool within the autoclave, and (3) the autoclave cure cycle used. Recommendations for the design of an individual tool are fairly obvious and well understood in industry (e.g., thin tools heat faster than thick tools materials with a high thermal conductivity heat faster than those with lower thermal conductivity and tools with well-designed gas flow paths heat-up faster than those with restricted flow paths [e.g., tools... 

Heat transfer models are a powerful tool for developing autoclave process cycles. They are especially useful in aiding tool designers in choosing tooling materials, thicknesses, and thermocouple locations. Models can also be used to determine if a tooling concept would be detrimental in a specific position in the autoclave and the types of tools that should be processed together to optimize the cure cycle. 

Thermoset based composite laminates are generally produced bj Autoclave/Vacuum Degassing Lamination Process (38, 39). The characteristics of this inocess are shown in Fig. IS. In this process, pr eg plies of desired shape are laid up in a prescribed orientation to form a laminate. The laminate is covered with successive layers of an absorbent material (glass bleeder fabric), a fluminated film to prevent sticking, and, finally, with a vacuum bag. The mitire system is placed upon a smooth metal tool surface into an autoclave, vacuum is a Ued to the bag and the temperature is increased at a constant rate in order to promote the resin flow and polymerization. The autoclave process will be used along this section as a case study to describe the influence of the matrix characteristics on the processing behavior of hi performance conqmsites. 

At the end of a process q cle, the manufactured structure will typically be removed from the autoclave, still affixed to any process tooling, and allowed to cool to room temperature. At this point, depending on the case, large residual stresses might stiU exist between part and tooling, sometimes making separation quite difficult. Consequently, the stress state in the processed structure, and thus the residual deformation, will be quite different before and after tool removal. 

Although being a relatively old technology to process composites, the autoclave technique is still a matter of research. Besides the previously mentioned microwave development, research is being conducted to simulate the autoclave process and to derive models for time-based cost calculations [5,6]. In addition, efforts are being undertaken in the field of tooling and the effect of the tool on the part quality [7,8]. 

Kaushik V and Raghavan J (2010) Experimental study of tool-interaction during autoclave processing of thermoset polymer composite structures, Composites Part A 41 1210-1218,... 

The tool face is commonly the surface imparted to the outer surface of the composite and must be smooth, particularly for aerodynamic surfaces. The other surface frequently may be of lower finish quality and is imparted by the disposable or reusable vacuum bag. This surface can be improved by the use of a supplemental metal tool known as a caul plate. (Press curing, resin transfer molding, injection molding, and pultrusion require a fully closed or two-sided mold.) Figure 4.13 shows the basic components of the tooling for vacuum bag or autoclave processed components. Table 4.22 shows the function of each... 

Flat panels of uniform thickness are frequently bonded in heated platen presses. However, most bonded aerospace assemblies are contoured. For this reason, bonding is usually carried out in heated, pressurized autoclaves. In the autoclave process the assembly is supported by a tool of the required contour, wrapped with several layers of glass or polyester bleeder cloth, and then enclosed in a impermeable heat resistant bagging film. This layup is then placed inside a pressurized autoclave and the inside of the bag is vented either to the atmosphere or connected to a vacuum pump. The autoclave is then pressurized to the desired level by compressed air, nitrogen, or other relatively inert gas. 

First part qualification. First part qualification is a process performed the first time a new bonded assembly is manufactured or the first time a new tool is used to manufacture a bonded assembly. First part qualification provides assurance that all of the aspects that control bond assembly quality, such as the design dimensions, detail part manufacturing techniques, tool dimensions, layup procedures and autoclave cure cycle parameters are correct and will produce a bond assembly that meets the engineering requirements. 

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