Adhesive bonding automation

As to the first point mentioned above, cost-cutting steps have to be taken seriously. Increasing automation of the adhesive application is imperative. Adhesive bonding processes without extra pretreatment of joint surfaces and without using a primer but with... 

Adhesive bonding and welding are the most commonly used where a sealed or reinforced seam is required. They also offer value in that they can be used in high-speed, automated production processes. Examples of various applications for adhesive bonding or thermal welding are shown in Table 13.12. 

Recent advances have made radiation-curable laminating adhesives very attractive in terms of economics, automation, quality of adhesive bond and throughput, while offering distinct advantages with respect to both energy consumption and pollution control [4],... 

Nondestructive Testing (NDT, NDE, NDi, NDC) -Techniques used to examine the quality of adhesive bonds without causing damage to the item or bond. The terms NDT (Testing), NDE (Evaluation), NDI (inspection) and NDC (Characterisation) tend to be Interchangeable. Nondestructive inspection systems may be manual or automated to some extent. Whilst effective for finding defects in the bond, no method currently exists which allows a reliable, quantitative measure of bond strength. 

Flame treatment is widely used to prepare polyolefin surfaces for adhesive bonding, particularly in labelling operations. This method is purported to burn-off contaminants and weak boundary layers, and also produces surface oxidation. Although flame treatment can be readily automated on a container labelling line, it is very impractical for most product assembly operations. 

If a small number of components are required to be adhesively bonded, then it is most likely that the process will be manual in type as the cost of automation would not be justifiable. The beauty of adhesive bonding is that it is fully scalable enabling initial prototypes to be manually assembled, but as volumes increase more and more of the bonding operations can be automated. See Part G Manufacture for more information on manufacturing. 

Many of the loudspeakers assembled in North America make extensive use of adhesive bonding. Adhesives are used to bond the fabric to the cone, attach the cone to the speaker frame and secure the permanent magnet (Fig. 6.3). High production rates and good joint reliability, both easily achieved with automated adhesive dispensing, have made this... 

For many bonding applications a variety of adhesives can perform adequately. Hot melt adhesives are normally chosen where process speed is critical. Since hot melts have no carrier vehicle (solvent or water), and thicken rapidly as they cool, they are limited in their ability to (1) penetrate low porosity substrates or wet out very rough surfaces (2) cut through or imbibe surface contaminants and (3) wet out high thermal conductivity substrates (e.g. metals). Nonetheless, hot melts are increasingly the adhesive of choice in automated production environments because of their fast set speed. 

The crystallization kinetics defines the open time of the bond. For automated industrial processes, a fast crystallizing backbone, such as hexamethylene adipate, is often highly desirable. Once the bond line cools, crystallization can occur in less than 2 min. Thus, minimal time is needed to hold or clamp the substrates until fixturing strength is achieved. For specialty or non-automated processes, the PUD backbone might be based on a polyester polyol with slow crystallization kinetics. This gives the adhesive end user additional open time, after the adhesive has been activated, in which to make the bond. The crystallization kinetics for various waterborne dispersions were determined by Dormish and Witowski by following the Shore hardness. Open times of up to 40 min were measured [60]. 

JP 05311144 (Japanese) 1993 Heat-resistant adhesive compositions containing polyimide-siloxane block copolymers Ube Industries, Japan H Inoe, S Takabayashi, T Funakoshi, K Sonoyana Useful for Cu-clad laminates of printed circuit boards and tape-automated bonding with good flexibility and heat resistance Formulated compositions containing siloxane-imide block copolymers made from aromatic tetracarboxylic acids and aromatic diamines and aminosiloxanes... 

The total assembly time, from the applieation of the adhesive to entry into the hot press, ranges from 20 to 40 minutes. For part of that time the glue is exposed and can lose moisture rapidly. The viseosity of the glue and other adhesive characteristics change over time and the bonding strength after curing in the hot press is influenced by sueh factors. Automated layup minimizes open assembly and total assembly times. 

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