Maximising efficiency is a key priority for manfacuturers in the defence sector. Automation of operations such as paint processing can often be a sound investment that will deliver significant cost savings.
Efficiency programs are commonplace in manufacturing and sustainment programs, particularly in the defence forces and supporting industries. The aim is to produce savings which could be redirected into other priority areas, such as purchasing new equipment or supporting ongoing operations. Understandably, it is extremely worthwhile to seek ways to make infinitesimal gains, even outside those obvious areas where ‘low hanging fruit’ paybacks have already been made, in order to streamline maintenance procedures.
One of the relatively under-explored areas where investment in automation can provide tangible value for money through potential reductions in costs is in paint processing and the rework of parts and capital equipment. When considering automation, there are some obvious savings in labour and material usage, but digging deeper, there are a myriad opportunities for a significant return on investment that may not be apparent to those who haven’t worked with robotic paint application equipment before.
These improvements include transfer efficiency gains, removal of operators from potentially hazardous environments, a reduction in the volatile organic compounds (VOCs) emitted from the process, film build optimisation, and a reduction in rework and repair rates. Exploration of each of these points in detail provides an understanding of where these gains can come from.
Transfer efficiency gains
Transfer efficiency refers to the amount of paint that goes onto the surface as a percentage of the overall amount of paint dispensed. Reducing waste at the point source of origin is the most important tool in reducing paint usage.
A typical manual air-assisted application can have a transfer efficiency of around 25%, depending on the shape and surface of the part. That is, for every litre of paint needed to get onto the part, four litres of paint are required. In the process, a huge amount of waste is generated – in this case, three litres. That atomised paint generally finds its way onto the grates, or into a filtration system; it is eventually cleaned off, or finds its way out the stack into the environment.
In comparison, a high-volume low-pressure spray gun can spray with a transfer efficiency of anywhere from 20% to 45%, again depending on the nature and shape of the part being sprayed. Still, this represents slightly over two litres of paint required to get one litre onto the part.
A gun, or air-atomised applicator, uses high-pressure or high-volume air impinging on the fluid to create atomised paint droplets. These droplets are shaped by the fan air into an elliptical spray pattern, which can be sprayed onto the part. Depending on the amount of paint required to be sprayed, the applicator can have one or more heads to accommodate for high fluid flows.
The advantages of an air-atomised gun are that the high-velocity paint particle can be used to drive coating into recessed areas. The downside of this is it can also cause a considerable amount of overspray, which is wasted paint.
Where robotics plays an influential role in increasing transfer efficiency is through electrostatic deposition of the paint. Electrostatic deposition depends on the ability to ground the parts and have a conductive substrate, or conductive coating over the substate. Electrostatics can be employed for either a bell or a gun application. A bell, or rotary atomiser, uses a mechanical shearing action to create the paint droplets. The atomiser spins at between 20,000rpm and 70,000rpm, and it is driven onto the part using shaping air. As the shaping air is increased, the pattern becomes smaller. The downside of the rotary bell applicator is its limited ability to get into recessed areas.
Advances in rotary atomiser technology have resulted in electrostatic applicators achieving transfer efficiencies upwards of 90%. That means that for every litre of paint that is needed on a given part, only 1.1 litres of paint are required. That amounts to 100 milliletres of paint wasted, versus the three litres lost during a regular hand-applied, air-atomised spray, with a huge impact on the emission of VOCs generated, the frequency of cleaning required from overspray, and of course the cost of the material itself.
In recent times, Automated Solutions Australia (ASA) has been involved in some case studies where customers have migrated from an automated high-volume, low-pressure (HVLP) gun application, to a rotary atomising solution. A project for one customer was driven by the fact that the surface area to be painted had increased, and the company was not able to get enough film build in these areas, so it looked into electrostatic rotary atomisers. Using advancements in technology, these rotary atomisers not only delivered the required film build, but also resulted in a 55% saving in paint usage per part. The customer was getting more paint onto the part, as per its requirements, but also saving an enormous amount of paint per part.
These savings aren’t always typical – sometimes they can be as low as 30%, depending on the complexity of the shape and the grounding of the part. However, the flow-on effects from applying more paint onto the surface where it is required and not onto the grates or into the atmosphere are significant. Typical yields from these systems are also very high – upwards of 85%, subject to the material, booth and oven metrics being held constant within process constraints.
By reducing waste at the point of origin, automation also offers reduced paint consumption, and in turn, reduced solvent usage and emissions. Indirectly, the reduction in the number of rejects and rework of parts also reduces material usage and general overall waste. Where parts may have been rejected due to inconsistent film thickness, robotic applications can provide a stable, consistent film thickness.
Removal of operators from potentially hazardous environments
Another factor to consider in the adoption of automation into a paint line is the materials being dispensed onto the substrate. The nature of a solvent or paint can be determined from its Material Safety Data Sheet (MSDS) – this will identify whether the product has a serious effect on the human respiratory system. Although operators can wear respirators and take breaks, the best way to avoid a problem is to eliminate it, by removing operators from these potentially dangerous environments.
Flexible automation is the simplest and easiest way to avoid manual pick-up for these parts. In parallel, automation offers opportunities for enhanced throughput, as robots handle difficult, repetitive tasks with ease, and often remove operators from dangerous environments – for example, spray painting and spraying of resins, lacquers and adhesives containing isocyanates.
In manufacturing, it is not unusual for unreacted or partially cured isocyanates to be present in the atmosphere after spraying. These may potentially be inhaled or come into contact with skin. Spray painters who use two-pack mix polyurethane paints are at high risk of exposure. Isocyanates like HDI used in paints are often also present as pre-polymers and polymeric isocyanates. Pre-polymers and polymeric isocyanates have the same health effects as free isocyanates when sprayed due to the generation of aerosols and overspray that may be inhaled.
According to Safe Work Australia, a person conducting a business or undertaking must ensure, so far as is reasonably practicable, that workers and other people are not exposed to health & safety risks arising from the business or undertaking. Robots provide an excellent mechanism for eliminating the risk associated with isocynate exposure.
Reduction in VOC emissions into the atmosphere
If you take automobile production as an example, a vehicle’s exterior finish represents less than 10% of its cost, but it is responsible for approximately 80% to 100% of the total VOCs emitted in the automotive production process (70% to 80% are from the spray booth, while another 10% to 20% are emitted through the drying oven). Waste reduction isn’t just limited to reduced paint usage and VOCs going out of the stack – it is also directly proportional to scrap rates due to quality improvements. Set correctly, a robot can be your best painter, on their best day, all day every day – optimising VOC reductions in manufacturing operations.
Optimisation of film build
A manual operation will often require “too much” paint in a certain area, in order to get paint into a specific area. While a manual operator may trigger on and off, robots have the capacity to alter fan and atomisation air profiles on the run, or bell speed and shaping air, depending on the type of applicator used. For this reason, film builds can be optimised. Programs can be written with specific overlaps, to minimise film build variations. It is not usual in a basecoat paint application for automation to be held to requirements for 16 microns, plus or –minus two microns. Film builds of this nature are required, specifically where the surface is being prepared specifically for radar detection avoidance. Manual painting applications struggle to compete with these exacting film build requirements.
Reduction in rework & repair rates
The consistent nature of robotic applications leads to a reduction in warranty recalls, claims and rejections. Rework due to manual error tends to be decreased, as the inconsistent reworks tend to diminish. The flow-on effect of this can often be reduced inspection requirements, assuming all process parameters are held constant (temperature, humidity, solids content of the paint, and so on). Flexible automation presents opportunities for improvements in quality, and particularly with part-to-part consistency through improvements in repeatability.
The combined synergy of these efficiency gains in lifecycle programs is that flexible automation can provide a significant return on investment. The overall return on investment must be considered when weighing up these factors to understand the true benefit of automating your paint line, and whether your company will innovate, or evaporate.