DESIGN FOR ASSEMBLY (PART 4)
In our final article on assembly methods we shall look at bonding.
Adhesive Bonding.
Advantages:
Aesthetic and design flexibility
Uniform stress distribution
Can join dissimilar materials
Can provide tight seal
Flexible adhesives can compensate for thermal expansion mismatches between
materials
Flexible adhesives can dampen vibration
Can be used with thin, flexible substrates
Provide electrical and thermal insulation
As with the materials themselves, adhesives can be affected by environmental factors and time. Unlike other fastening methods it can take time for the adhesively bonded joint to reach full strength.
Solvent Bonding. This method can only be used with certain types of thermoplastics and is mostly used with amorphous materials. This is more of a welding process whereby the solvent softens the surfaces of the two parts to be joined; they are then clamped together while the solvent evaporates.
This is a simple relatively inexpensive method but it does require the parts to be joined to have no warpage and be moulded to relatively tight tolerances.
Joint Types Joint designs tend to be variations of two main types – lap and butt. A lap joint is where two parts to be joined overlap whereas the butt involves the two parts to be joined end-to-end.
Both types of joints have variations that give improved performance. Lap joints may be stepped or bevelled and butt joints may have some form of strap applied over the joint. The use of a strap in this manner adds to the cost but can make for a design feature.
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