Direct comparison Gluing versus Welding: a clear favorite

Adhesives are experiencing a renaissance. In times of cost pressure and weight savings in favor of a reduced CO₂ footprint, every gram counts. In practice, however, welding is also used. However, gluing is becoming more prevalent, the advantages outweigh.

Already in the Stone Age, joining and creating durable and long-lasting connections played an important role. Spears and spearheads were joined with tree resins. Today, adhesives are ubiquitous in our daily lives and indispensable. With the beginning of the industrial age and the extraction of crude oil, modern adhesives were created, which were continuously developed and today provide stable connections in almost all industries. Parallel to the development of adhesives, other joining processes were established. Welding is today, alongside bonding, one of the central joining techniques. Both technologies are—with regard to DIN 8593—in direct competition and bonding is increasingly convincing users and scientists.

Bonding allows the connection of different materials with each other, for which there is no direct possibility of connection at first glance. Especially in multi-material applications, as used for example in the interior of vehicles, new combination possibilities arise. The connection of metals and plastics is basically also possible by welding, but only with a few very specific material combinations. In addition, bonding ensures an even distribution of stress, so that forces can be distributed more evenly and the connections can withstand higher loads overall. Weld seams, on the other hand, are rigid, prone to cracks, and less resistant to stress.

The preservation of the shape of the parts to be joined also represents a significant advantage of bonding. Neither screw holes nor the risk of material distortion due to locally high heat affect the characteristics of the component. If the joining process or the adhesive is to fulfil other tasks, such as bridging gaps or protecting against corrosion, welding seams reach their limits. Adhesives, on the other hand, offer various solutions and functions for these tasks.

Gluing is a special process

What bonding and welding have in common is that they are both defined as a special process according to ISO 9001. This means that the connection can only be tested retrospectively and by destructive testing. Non-destructive testing only provides indications of the properties of the connection, but without meaningful details. For this reason, it is important that the joining process itself is adequately monitored so that errors can be detected and corrected early. In the vast majority of cases, the failure of adhesive bonds is not due to the adhesive itself, but to its improper use. Incorrect handling and lack of expertise in processing are the most common sources of error. Comprehensive and practical employee and user training, such as that offered by adhesive manufacturers like Drei Bond, is therefore essential to achieve sustainable quality of the connections.

Despite the challenges in handling adhesives, key aspects advocate for their use. Not only the significant weight savings compared to the material requirements of welding seams make bonding appear advantageous, but also the considerably lower energy needs. Since the materials must be melted in welding, the total energy expended, measured by the force of the connection, is significantly higher than with adhesive bonds. Also, the total process energy incurred in bonding processes is much lower than in other joining methods. Thus, the CO₂ emissions for bonding processes, considered over the entire life cycle, are at about 0.0015 kilo-CO₂ equivalents while laser welding with 0.009 kilo-CO₂ equivalents or clinching with almost 0.006 kilo-CO₂ equivalents lead the comparison.

Adhesives as a central element of an overall system

In order to fully utilise the advantages of bonding, it is necessary to master the overall process. Christian Eicke, Managing Director of Munich-based Drei Bond GmbH, says: "A highly accurate consideration of the basic task, such as determining the strain on the joint, is just as important as the adhesive-friendly design of the components or the selection of the adhesive system. Other aspects, such as surface preparation and the metering technology to be used, must also be optimally matched to the adhesive. We offer all these coordination efforts, products and consulting services from a single source!" The metering technology used must be precisely adjusted to the specific properties of the respective adhesive, including viscosity or pot life, so that process times and quality requirements for the connection can be met.