Today’s paint finishing arena is extremely competitive. While the revenue received from painting a part has dropped considerably, the requirement for meeting colour and film build specifications has tightened dramatically.
The world has become a far smaller operating environment, and customer’s demands have meant that manufacturers cannot afford to waste any paint, whether through rework or poor transfer efficiencies. Companies are being driven to adopt new technology through flexible automation, or face extinction. Automation presents opportunities for improvements in quality, and particularly with part to part consistency through improvements in quality and consistency. In parallel, automation offers opportunities for enhanced throughput, as robots handle difficult, repetitive tasks with ease, and often remove operators from dangerous environments. By reducing waste at the point source 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.
Robotic painting solutions are slightly different to regular robot applications, in so far as the robot must meet specific conditions for operating in a hazardous environment. Paint automation has several complicating parameters affecting the result, such as fluid viscosity, booth humidity and temperature that traditional robot programmers may not typically compensate for. Paint solutions can be fixed, or flexible (robotic). Fixed solutions have substantial limitations where a myriad of different parts are processed down a common line. In comparison to a robotised solution, fixed guns need to use additional paint in order to get the required surface coverage, and quite often require manual reinforcement. They also require more spray guns, which in turn uses more compressed air, paint, and has significantly higher maintenance requirements.
Flexible automation provides a far more adaptive solution, where any number of parts can be processed through the same booth, and an accurate gun-to-target distance can be achieved. Using a gun or rotary atomised, the paint can be distributed far more evenly – the same technology used in automotive finishing is now applied to the small component industry. The nature of the atomiser used is dependent on several factors, but none more so than the ability to electrostatically ground the parts and have a conductive substrate. 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.
In contrast, a bell, or rotary atomizer, uses a mechanical shearing action to create the paint droplets. The atomiser spins at between 20 and 70 krpm, 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 ability to get into recessed areas.
Advances in rotary atomiser technology have resulted in electrostatic applicators achieving transfer efficiencies upwards of 90%
These two atomisers are important when considering the transfer efficiency, and hence the paint waste generated, when comparing applications. Reducing waste at the point source of origin is the most important tool in reducing paint usage. A typical manual air-assisted application has 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, 3 litres. In comparison, a high volume low pressure spray gun can spray anywhere from 20 to 45%, again depending on the nature and shape of the part being sprayed. This would represent slightly over 2 litres of paint required to get 1 litre onto the part. Moving up, 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 needed on a given part, only need 1.1 litres of paint are required. That 100 mL of paint wasted, versus the 3 litres lost during a regular hand air atomised spray, represents a huge impact on emissions generated (volatile organic compounds), the frequency of cleaning required from overspray, and of course the cost of the material itself.
Though a vehicle’s exterior finish represents less than 10% of its cost, it is responsible for approximately 80 to 100% of the total volatile organic compounds (VOCs) emitted in the automotive production process
In recent times, ASA has been involved in some case studies, where customers have migrated from an automated HVLP gun application, to a rotary atomiser solution. The customer’s project was driven by the fact that their surface area had increased, and they weren’t able to get enough film build in these areas, so they looked to electrostatic rotary atomisers. Using advancements in technology, these rotary atomised delivered the required film build, AND a 55% saving in paint usage per part. So, not only was the customer getting more paint onto the part and meeting their requirements, they saved 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 getting more paint onto the parts that its required on, and not onto the grates or into the atmosphere are. Typical yields from these systems are also very high – upwards of 85%, subject to the material, booth and oven metrics being held constant.
Though a vehicle’s exterior finish represents less than 10% of its cost, it is responsible for approximately 80 to 100% of the total volatile organic compounds (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 the reduced paint usage, and VOC’s 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 his best day, all day, every day, if all else is held equal.
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.
Automating your paint line can be driven by many factors – quality and consistency, throughput improvements, reduction of waste and scrap, and eliminating manual operation in potentially hazardous environments. Flexible automation, in the form of robotics, is the adaptive solution for these situations, and can be modified for gun or rotary bell atomisers, depending on the nature of the products being sprayed, and whether they can be grounded for electrostatic charge. 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.