Fabrication and Composite Adhesives:  Which is Best for Your Next Project?

New developments in material engineering have provided technologically-advanced alternatives for gear materials. Multiple adhesives have been created to meet and exceed an engineer\’s process and performance needs.

Adhesives improve assembly and processing speed, as well as product durability and aesthetics. Their ability to be customized also provides a variety of benefits. Adhesives can be formulated with a range of different viscosities and made into tapes and films.

In addition, adhesives can be either applied through automation or installed manually. The two-part adhesive application can be fully automated by using a specially designed cartridge. At the touch of a button, adhesives are exactly mixed and dispensed. Engineers across many industries are looking toward automation because of the lower labor costs, increased consistency, and high quality.

In addition to meeting the demand for automation, adhesives continue to be developed toward trends in the industry. Low-odor adhesives have been designed to ensure safer and more comfortable work environments. Likewise, adhesives that do not use volatile organic solvents have been formulated to meet environmental and sustainability initiatives.

Since adhesives meet today’s standards in both design and efficiency, they can replace rivets and weld lines as a cost-effective and lightweight alternative.

Adhesive Benefits

Due to the specific materials needing to be bonded and temperature variations, manufacturers must consider the best adhesive for each application.

Materials with different coefficients of thermal expansion (CTE) contract and expand differently under temperature variations. Adhesives provide the perfect choice because mechanical fasteners do not allow expansion or contraction of joined materials during temperature variations without causing damage.

In addition, some adhesives have the flexibility to accommodate movements caused by thermal expansion of the substrates even after they have fully cured.  For those applications with protective coatings or paint, adhesives have the benefit of not requiring holes to be drilled into the metal parts, which can damage the surface and expose the metal underneath to the elements. As well as the physical damage to the application, damage done while joining composites leads to a waste of both time and money.

Besides being costly, drilling holes in composites cause the load-bearing stress to be concentrated entirely at the fastening point. This can lead to early failure. With the use of an adhesive bond, the load is balanced over the whole joint area, therefore distributing the load-bearing stress evenly throughout.

Bonding Dissimilar Materials and Composites

Projects that have dissimilar materials and composites are no longer best completed with metal fasteners. Metal fasteners require that engineers limit their options by only choosing certain materials or those with an increased thickness.  Adhesives, on the other hand, give engineers thinner and lighter material choices, which are a best-fit for today\’s manufacturing applications.

For example, sheet molding compound (SMC), plastics, or thinner-gauged aluminum and steel can be substituted in components where steel was once traditionally used. Using adhesives for thinner materials reduces costs and expands manufacturing options that are not available when restricted to using thick materials.

Adhesives also lower costs because of the increase in assembly productivity and efficiency. Using adhesives means no grinding off weld marks, no adding of sealant to make the design waterproof, and no straightening warped pieces.

Extensive surface preparation is often needed when one or more of the bonding materials is oily or has low surface energy.  The best solution in these circumstances is the use of special adhesives including polypropylene, polyethylene, thermoplastic polyolefin (TPO), polytetrafluoroethylene (PTFE), polybutylene terephthalate (PBT), polystyrene, ethylene propylene diene monomer (EPDM), rubber, and silicone. By choosing the correct adhesive for the substrate, engineers can avoid most or all of the tedious surface preparation.

Working with the adhesive supplier will allow the best adhesive and application method to be chosen for each project.

Challenges of Lightweighting

The need to reduce a product’s energy consumption and size, as well as decrease manufacturing costs, has led the push toward “lightweighting”, or taking the weight out of a product. Engineers encounter several design challenges that need to be considered when lightweighting products that have been fastened together with adhesives.  These challenges include:

Bonding to Lighter or Dissimilar Substrates:

A lighter weight substance usually creates an adhesion difficulty for engineers. This is most common when bonding two different materials. Bonding dissimilar substrates can also be a challenge because of their unique chemical properties. Adhesive tape, however, can allow the materials to bond while avoiding an electrochemical reaction that could cause corrosion.

Noiser Substrates:

Higher pitch and more vibrations, which creates noise of greater frequency, are generated with lightweight substances. This noise can cause the perception of lower quality and/or decreased safety in some applications. Sound damping materials can be used to decrease excessive pitch and vibrations.

• Weaker, More Flexible Substrates:  Products sometimes require reinforcement if they are weaker and more flexible in order to ensure stability and durability. Adhesive tapes can allow for reinforcement without unduly adding weight to the overall product.
• Heat and Flame Substrate Susceptibility:  Overall heat resistance or one-time protection from flames may be required for some applications. If this is the case, foil tapes can be used to provide the necessary safeguard.
• Substrate Visual Appearance:  The perception of  a reduction in quality can occur when attempting to lightweight by switching from metal to plastic. The solution can be found in bonding veneers, which can be added to substrates to enhance visual appeal.