In 2018, the New South Wales Government faced embarrassment after ordering $2 billion worth of new trains that were too wide for the tunnels. To solve the issue, the Government body managing the rail system was forced to relax its safety standards and modify ten tunnels so that the new trains could run. Similarly, many product designers find they need to make significant adjustments when they reach the production stage. Here Kevin Cook, technical manager of adhesives specialist Intertronics, discusses the benefits of designing with production in mind.
When a design engineer requires an adhesive to bond one substrate to another, they can save time, money and effort by designing with production in mind. During the design process, it is common to produce a prototype 3D model, using a variety of methods. The prototype will be tweaked, adjusted and improved until it matches form, fit and function requirements. However, if the designer hasn’t considered how the prototype will be scaled up into a saleable product, they could run into problems. The designer could be forced to adapt their product, or the environment the product is going into, for it to be functional.
Intertronics recommends that the design engineer thinks about moulding, bonding and dispensing from the outset. Working with an adhesives specialist early on paves the way for a project to be completed smoothly and without hold ups.
The designer should use the same substrate in the prototyping and testing of a product as will be used in production to ensure consistency. Considering adhesion from the outset can help the designer to make an appropriate substrate choice. If they do not, they may not be able to use their first choice of substrate, which can call for an entire redesign.
The designer must firstly consider how the joint will provide the right support for the structure, particularly if it is a structural component. An exposed or unsupported joint may be weak, regardless of whether an appropriate adhesive choice is made or not. The designer should also think about where the product will be manufactured, as for example a cyanoacrylate adhesive would not cure successfully in a cleanroom, as the humidity in the air would be too low.
The environment the product will operate in can also influence adhesive choice. If the product will be subject to a harsh environment such as salt water, or one with temperature fluctuations, the designer must ensure the adhesive and the substrate can withstand the conditions.
The adhesive must also be appropriate for the application. The designer must consider the properties of the adhesive. For example, some room temperature vulcanising (RTV) silicones have a corrosive by-product, which makes them unsuitable for use in the electronics industry.
Similarly, if the joint will be exposed to the end user, such as in a potting application, the designer must opt for an adhesive that is aesthetically pleasing as well as effective at performing its function of sealing, bonding and protecting.
As well as ensuring the substrate and adhesive are suitable for the conditions, they must also be suitable for use together — certain adhesives are better suited to plastic or metal and an appropriate substrate choice can bring the best out of an adhesive. Consider this example. A designer is planning to bond two pieces of acrylonitrile butadiene styrene (ABS) to each other with one adhesive, but later changes the substrate to be polyethylene. The new material will require a different choice of adhesive and will have different dispensing requirements, kickstarting a domino effect. The original production process can no longer be used and the designer must go back to the drawing board or use their second choice of material.
Bond line design is a critical consideration during the design process. For the product to be successful, the bond line must be accessible so that adhesive can be correctly dispensed. There are several common dispensing techniques available to designers, from simple time pressure dispensing or simple volumetric dispensing. This can be done manually, with a three-axis robot or for more complex applications, a six-axis robot. The designer must consider adhesive dispensing and whether it will be a manual, semi-automated or automated process to ensure they can use their first choice of equipment.
To make dispensing as easy as possible, the designer must ensure the bond line is not obscured behind another feature. To use a UV curing adhesive, the entire bond line must be visible. If it is not, the designer has ruled out a popular adhesive choice early on or must redesign the product so that the bond line is accessible.
If the bond line is difficult to access because it is obscured or requires a tight angle, it can require the designer to purchase a six-axis robot to dispense the adhesive, greatly increasing the costs of the project. Alternatively, in complex cases, the adhesive could be applied by hand, which increases the labour costs of the project and the risk of error.
Single part adhesives are easier to dispense and handle than mixed. By opting for a single part, UV curing adhesive, the part can be cured and finished rapidly — an easy process to automate. If the designer has opted for a two-part adhesive, it can be a little trickier. Two-part materials begin to gel and change in viscosity as soon as they are mixed. This means that simple time pressure dispensing techniques, which require the adhesive to be in a constant state, are unsuitable. The designer would require a different technique, such as volumetric dispensing, for the production to be successful.
Return on investment
Naturally, return on investment is an important consideration for any designer, who must think about what their budget will support when scaling up to production. This is not as simple as considering upfront cost; time, labour requirements and materials supply should be factored in too. Semi-automated or fully-automated solutions offer good return on investment as they can reduce operator variability and strain, reduce scrap and improve consistency.
For example, a UV curing adhesive offers manufacturers a quick and easy solution but is expensive in comparison with adhesives with other chemistries, such as two-part epoxies of polyurethanes. These alternatives may be cheaper to purchase per part, but more difficult to handle, taking up more labour time or requiring an investment in more costly dispensing techniques.
One of the biggest production considerations for a business when scaling up is time. The company must consider how long the product takes to assemble, factoring this against the time the product takes to gel or tax. The curing time of adhesives can vary from seconds to days. If work in progress (WIP) is an important factor during production, the manufacturer must take the curing time into account to ensure that WIP is not sat on a bench, unable to move forward, because of the curing process.
For other curing methods, there may be an additional investment cost, such as purchasing and operating an oven to cure the adhesive. This adds an additional investment cost, as well as increasing the business’s energy costs. Establishing whether this will be the case early on will protect the company from a nasty surprise when its energy bill arrives.
The New South Wales Government was left in a predicament after its trains were too big for the tunnels. Had operation been considered from the outset, perhaps this would not be the case. Intertronics works with designers at every stage from design to production to help you bring your product to market efficiently and without costly errors. To speak to an adhesives specialist, get in touch on 01865 842842.