It’s a common fallacy that you can’t join prepainted metal. The truth is that many manufacturers in a variety of industries join prepainted metal every day with great success.

It’s a common fallacy that you can’t join prepainted metal. The truth is that many manufacturers in a variety of industries join prepainted metal every day with great success. You can use adhesives, fasteners, welding applications and assembly techniques to join prepainted metal and retain a beautiful surface.

A Primer on Primer - When Welding Is the Only Answer

Manufacturers might not realize that weldable primers are available as part of the coil coating process. These primers can be welded without sacrificing product quality and provide a precleaned and treated alternative for post-painting operations that reduces inventory and cleaning costs.

Requirements for weldable primers vary depending on the welding process used, but for most processes, the main requirements are that the primer must conduct electricity and “burn back” evenly next to the weld area, and that it must not smoke excessively during welding, combust or produce harmful fumes. Your coil coater can provide advice on priming methods and product selection.

Key advantages of using weldable primers include:

• Better adherence
• Better corrosion resistance
• Better cosmetics: eliminate runs, bare spots, bubbles and dirt spots
• Consistent film thickness
• Lower paint usage and costs
• A faster process with no need for painting
• Reduced cleanup and environmental costs
• Decreased energy consumption
• Decreased labor
• No need for stamping oil (the coating acts as a lubricant)
• Reduced safety hazards
• The ability to specify chrome free primers and pretreatments

A Sticky Solution

Adhesive joints offer benefits such as smooth surfaces, clean contours and uniform stress distribution. Adhesives also can seal joints from a variety of elements. Prepainted metals can be bonded with the same adhesives used for uncoated metals, and joining prepainted metals with adhesives does not alter the properties of the metal or its coating. The finished product retains a stunning exterior appearance. Your coil coater and adhesive supplier can help specify an adhesive-compatible paint and help select the best adhesive for almost any application, including epoxies, urethanes, cyanocrilates, acrylics, anaerobics, hot melts and silicones.

Joining with adhesives provides creative solutions to some old manufacturing problems related to combining various joint types. Adhesives work well with stiffener joints, joggle joints, simple lap joints, double-butt and double-scarf joints, and even sheet metal corner joints (when used with simple supplementary attachments).

Going Nuts

Mechanical assembly with fasteners also works well with prepainted metals. Nuts, bolts and screws are cost-effective fasteners that offer design flexibility and allow for parts to be disassembled. Rivets are another choice that produce liquid-tight seals, are easily automated, and offer excellent shear and tensile strength.

A third and exciting option for mechanical assembly is the AKH FAS-NER system. A simple punch and die operation, the FAS-NER system automatically feeds, punches, inserts and locks self-piercing FAS-NERs to produce a solid joint in one high-cycle operation. The FAS-NER is directly inserted into prepainted metal without the need for pre-punched holes. This feature saves time and labor costs associated with tooling maintenance.

Sans Fasteners

There are also proven, highly repeatable methods requiring only conventional tooling to join prepaint mechanically without fasteners. Lock-and-seam, pierce-and-tab or stake, and clinching assembly methods can be employed with success. Lock-and-seam works well when disassembly is required and it keeps joint buildup to a minimum. Pierce-and-tab or stake is another conventional and low-cost solution that works well with prepaint. Clinching provides a neat, clean appearance, and it’s ideal for applications that require vibration resistance.

Lasers

For joint applications like butt welding that require fine or nearly invisible seams, lasers might be the answer. Joining prepaint with the precision of a laser creates little or no distortion to the coating at the point of contact and results in the least amount of discoloration and damage to the coating.

Before designing your next product, take a look at the possibilities offered by joining coated metal. Prepainted metal can be easily joined, helps streamline the manufacturing process, saves money and hassles in the plant, and provides a stellar finished product that is rust resistant with a tougher, more beautiful finish.