Bonding, process control assembly

The Bonding Process. Before the actual assembly operation, the cleanliness of the shop and tools should be verified. The shop atmosphere should be controlled as closely as possible. Temperature in the range of 18 to 32°C and relative humidity from 20 to 65 percent are best for almost all bonding operations. All parts should be fitted together without adhesive or sealant to indicate possible production problems due to fit. The suitability of fit is established by either visual inspection or direct measurement with gauge or shim. It is desirable that the extremes in mechanical tolerances also be noted and that test specimens be made with the worst possible fit to ensure that the bonding process will always provide reliable joints. 

The tendency of porphyrins to form aggregates, and the structural control of the assembly formed can be directed by the help of axial binding in the case of metalloporphyrins. In this section we will first examine examples in which the axial bond formed is a coordination bond for which dissociation is still possible. The formation of reversible bonds in self-assembled processes is extremely important because it permits the use of combinatorial type approaches, and leaves the possibility of correcting errors that may have occurred during the assembly process. Such synthetic design features usually afford thermodynamically stable scaffolds instead of a more or less random assembling of the chromophores. 

In order to verify that the bonding process is under control, process control panels are frequently bonded along with the production assemblies and then tested to determine bond strength. Lap shear, metal peel, or sandwich peel panels are the type most frequently used for this purpose. 

Industrial processing of adhesives has made considerable progress from the crude processes of the past [1]. Unfortunately, one of the disadvantages of adhesive bonding as an assembly method is that a bond area cannot be inspected visually. Inspection must be carried out by two methods destructive and nondestructive. Destructive inspection may be carried out on process-control test specimens prepared from the same adherend and adhesive materials as used for the production parts. The process-control specimen, as the name implies, accompanies the production parts throughout the stages of cleaning, assembly, and cure. The adhesives and adherends are all assembled at the same time and cured in the same press or autoclave. 

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