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FEATURE


FASTENINGS & ADHESIVES


Simon Gibbs, technical sales executive at adhesives specialist


Intertronics, examines the importance of


considering adhesives early on in a project


A


dhesive bonding is a vital and challenging part of product design. Every application is different and establishing what works best


for your project will involve detailed discussions and testing.While consulting with an adhesives supplier early on will avoid complications later, manymanufacturers contact adhesives providers oncemost of the design work is done – once they have finalised and assessed bondline design, substrate selection, environmental resistance, and so on. However, with much of the design finalised, there will be a particular set of requirements the adhesive needs to meet. There may not be an adhesive that meets the criteria without major compromise, or a suitable adhesive may not be available in the specified packaging or quantities. If this is the case, the design may need to be changed. At Intertronics, we therefore recommend


contacting an adhesives specialist at a stage where the substrates and bondline geometry could still be changed.


PREVENTING FAILURE A small change to a design can have a big impact on the performance of the adhesive – tweaking one thing can mean an adhesive that previously passed the test now has the potential to fail. For example, something as simple as how the substrate is pre-treated or cleaned can lead to part failure. One common reason the bond fails testing at


the later stages of a project is that the prototype has been made differently, or using different materials, to the production parts. An example is if the prototype was done using one white plastic and then this was later changed to another. While it might be natural to expect the same result, the adhesive may no longer bond. Recently, for example, we supported a


customer bonding plastic LEDs to a plastic housing using a UV curing adhesive. The company then developed another version of the same product, which involved bonding the plastic LEDs to anodised aluminium instead. The new product did not pass the required testing, and the design had to be changed to incorporate a different adhesive. Another factor to consider when changing


the substrate is that many modern materials are formulated with specific properties where the benefits to the application – such as chemical resistance or UV blocking – are the same reason that makes the application challenging. For example, properties that make design engineers select polypropylene as a substrate (e.g. low surface energy, solvent


2


DON’T COME UNSTUCK WHEN SPECIFYING AN ADHESIVE


resistance, opaque), are the same properties that may make it more difficult to bond. As well as changing the substrate from


prototype to production, we sometimes see manufacturers change the adhesive. In some cases, design engineers will prototype their product using an adhesive they have available in the lab or which is already used in the factory for another application. They will then select a different adhesive for the production parts using data sheets, subsequentlymeeting a challenge when production has started and the specified material doesn’t pass functional tests. It is important to note that the data sheet may not always give the same insights as practical observations, experience and tests. In many cases, the data needs to be interpreted and extrapolated to fit with the individual scenario.


EXAMINING THE PROJECT Another possible hurdle is that the specified adhesive does not line up with the production team’s schedule. For example, many manufacturers request UV curing adhesives due to their ability to cure on-demand and in seconds, but the adhesive might not meet the functional requirements for the application in question. However, it is a challenge to simply swap one adhesive for another to meet a production-related challenge. One automotive customer, for example, was


using a two-part epoxy cured in an oven to bond parts. Months later, as the production cell was being finalised, the company swapped to a UV material because the epoxy’s cure time was too long. However, the same design bonded with a different adhesive didn’t pass any tests, and it was back to the drawing board on adhesive selection. A good adhesives supplier can speak to the


design engineer about the full complexity of the project, to establish the speed and long-term


2 DESIGN SOLUTIONS SEPTEMBER 2022


throughput requirements and make a recommendation for materials and dispensing technology to match. Similarly, if the supplier talks the design engineer through the return on investment (ROI) considerations upfront, they can save their production colleagues time by ensuring what they have specified is commercially and technically viable. For example, a supplier could explain how switching from a manual to an automated process could offer a good ROI, by resolving issues around validating the process, removing operator variance, and reducing the risk of operator RSI. A bonding process consists of the cost of amaterial purchase and the cost of processing it – often the latter is a bigger proportion of the overall cost.


MAKING THE RIGHT CHOICE By contacting an experienced adhesives supplier early in the project, you can receive advice on material selection, bondline design, and more. The supplier will need to provide all the information you need on the adhesive – including its chemistry, how it cures, and how it can be dispensed. For example, if you are dispensing a cyanoacrylate with a secondary UV curing mechanism, which dispensing technology should you use to avoid clogging? The supplier can also explain why amaterial


might work, using evidence from previous experience to advise on why it is a good selection, how it might be dispensed and cured, and to highlight any downsides or compromises. At Intertronics, we recognise the importance


of asking our customers the right questions, understanding the detail of each application, and giving honest answers.


Intertronics T: 01865 842842 www.intertronics.co.uk


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