Individual systems for automated glue dispensing

A perfect bond formed in seconds

Adhesive bonding has long since replaced traditional joining techniques such as welding and screwing in a multitude of applications. More and more customers these days look for automated solutions that are individually tailored to the specifics of their application. In these cases, the design of a suitable system concept must take a number of factors into account.

Increasing demands on dosing technology

In recent years we have seen the demands on metering and mixing technology increase notably. Particularly against the backdrop of “Industry 4.0“, it is no wonder that flexibility, efficiency and cost-effectiveness are now inextricably embedded among the key prerequisites for successful production. Add to this the ever advancing trends of automation and digitisation and the picture of the new challenges posed to the field of dosing technology starts taking shape. It is no longer the case that customers are looking for a simple dosing system. Rather, what they demand is a complete and automated solution that will readily integrate into their existing production process. On the one hand, their requirements vary greatly depending on the industry and application in question - for example, considerations of accuracy, material savings, cycle time, speed of handling, certification class or standards to be complied with often heavily influence the system design. On the other hand, a truly smart and comprehensive concept needs to cover more than the sole process of metering and mixing. It should also accommodate the associated peripheral tasks such as component pre- and post-treatment, conveying and handling, and last but not least, quality assurance.

Capturing short cycle times with an efficient system

Two robots alternately picking up components and moving them toward a gas flame. On the other side, another robot is lifting the finished components off the conveyor belt, depositing them in a shelf trolley. These robots are part of an automated dispensing system for the bonding of oven door components, built for the Polish appliance manufacturer Amica. The design of the system is one of a kind and has been carefully engineered around the specific needs of Amica’s application by the dosing technology manufacturer Dopag.

A key step in the design phase of this system was establishing the manufacturer’s requirements. The starting point here was the specification of the number of pieces that were to be produced within a certain time frame. Since the cycle times were very short, both the component handling and hardening processes had to be made much more efficient than in the previous set up; up until that point, the manufacturer had been using a system with little automation, where curing took place at room temperature. This proved inefficient in terms of space and time needed to process the components: 100 square meters were taken up by the curing process only. With the new bonding system, Amica is now looking at a much more efficient production in many different ways.

All production steps - from pre-treatment to bonding, curing and handling – are now integrated and laid out on circa 52 square meters. The large curing area has been effectively eliminated because the components come out of the new system already cured and ready for the next production stage. The conveyor technology is designed in such a way, as to make the components available at all times and to ensure a continuous production flow. All components can be added manually on an ongoing basis, thus avoiding downtime. The handling of the components is carried out by two robots working in parallel. To the left and the right of the glass pane storage rack there are sliding tables, from which the robots take the profiles. These serve for the attachment of inner panes and door hinges at a later stage. A conveyor belt system delivers the outer panes of the oven door from the storage rack to the bonding station. Here, an operator places the glass panes into the correct position for the bonding process.

Pre-treatment, application and bonding in a single move

Before the individual components are bonded, the profiles must first be pretreated with Pyrosil. This involves the application of a silicate coating onto the surface by means of a gas flame system. The adhesive applied onto the profiles immediately after this step adheres better following the pre-treatment, creating a lasting and secure bond between the two components. The complete Pyrosil pre-treatment process has been integrated into the new bonding unit with the advantage, that the processes of pre-treatment, adhesive application and joining all take place in a single, uninterrupted motion, deeming the intervention of an operator not only unnecessary but also impossible. This is essential because if the operator could access the component before the adhesive is applied, they could contaminate the surface, preventing a reliable adhesion of the material. As the result of the Pyrosil treatment is invisible to the eye, prevention of human interference is an effective way of ensuring the silicate layer has been applied successfully and the adhesive is going to be reactive.

Amica’s requirements were more complex than the assurance of a precise, reliable and reproducible application of an adhesive. Instead, their ideal bonding system had to additionally cover a full range of different applications. The appliance manufacturer uses a range of different glass pane and profile types, ending up with more than ten final product versions. The DOPAG vectomix metering and mixing system has been selected – among other reasons – for its ability to cater for this flexibility requirement. In this application, it is used to meter and mix a two-component silicone adhesive, and to apply it in a round bead form. Vectomix has been developed specifically for the processing of multi-component media. Featuring a modular design, it can be used in a wide range of applications. The material is supplied via a piston pump technology with two individual piston metering units interconnected by a mixing block. A plastic mixing tube is attached at the block outlet. As the material needs to be applied evenly in two different places, the volume flow of the mixing tube is divided in two, allowing the adhesive to be applied simultaneously and uniformly in both locations. The mixing ratio and discharge rate can be controlled via an integrated dosing computer.

A curing buffer saves time and space

In Amica’s previous set up, component curing was an extremely lengthy process, the infrastructure for which took up a large floor space. This is because it took place at room temperature. In order to accommodate the manufacturer’s wish for short cycle times and to avoid downtime, Dopag engineers have integrated a curing buffer with a Pater-Noster system into the new production concept. As part of this post-treatment facility, the freshly joined components pass through a heating chamber, after which they enter a cooling chamber. This speeds up the curing reaction inside the adhesive, allowing the manufacturer to produce the components in the shortest possible cycle time, while additionally saving a significant amount of floor space. Thanks to the new bonding system, a component is now manufactured and ready for further processing every 11.5 seconds. According to Dopag, the cycle time has been cut by 30 percent compared with the previous production method.

Customers expect comprehensive solutions

DOPAG’s observation is that more and more customers these days look for a complete solution for their automated application, be it bonding, sealing or potting. The resulting expectation is, that the system developer can offer not only a high level of competence in metering, mixing and dispensing technology, but also in custom-design machine construction. The optimum result is a turnkey dosing system which covers the entire component handling process, as well as material application including any necessary pre- and post-treatment. A detailed customer needs analysis is always the key here - without it, finding a solution that will bring the customer maximum benefit, while ensuring a successful production, is simply not conceivable.

Pre- and post-treatment: process steps

Pre-treatment in automated bonding applications:

  • Cleaning
  • Brushing
  • Priming
  • Plasma
  • Gas flame
  • Pyrosil (based on plasma or gas flame)
  • Corona

Post-treatment and quality assurance in automated bonding applications:

  • Curing systems: Infrared, ultraviolet (UV), medium frequency technology, continuous furnaces, buffer sections
  • Quality assurance: Volumetric measuring systems, verification of material application (position and quality), component quality assurance and measuring
  • Process data archiving, process visualisation: Data carriers (USB, flashcard), network, SCADA systems

Custom-built dispensing systems to automated bonding applications