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Case Studies Of Industrial Robots

Robots in action can be found everywhere. Robot Manufacturers give examples of robot applications in different industries.

DÜRR, Germany - IFR Partner

Progress in robotic painting systems

 

Improved Performance and Reduced Complexity

It is becoming increasingly clear that a process which is technically feasible may not necessarily always represent the best solution. Reducing the complexity of painting systems is an important aspect of product development. In today's global market, it is increasingly important to have a comprehensive overview of all the relevant influential factors. Production robots must be able to function as well in emerging markets, such as India and China, as they do in the country where they were developed.

The latest robotic painting systems are highly technical solutions. Vehicles can be painted automatically both inside and out to an extremely high level of quality. Electrical isolation systems that allow water-based paints to be charged directly have been developed. As a result, vehicle interiors can also be painted using electrostatic systems. For many people, application efficiency is the ultimate standard for evaluating application systems. As a result of all the measures described above, this standard has become even more demanding. This is a positive development both for the environment and for the economy. However, as a result of all these new features, painting plants have, in some cases, become extremely complex. Highly trained staff are needed to operate and maintain them, which can present a problem, in particular in emerging countries. For this reason, developers must find ways in which to improve performance, while at the same time reducing complexity. The examples described below demonstrate that these two objectives are not mutually contradictory.

Reducing complexity

Much has already been said about robots on raised, travelling axes and about their benefits, including easy accessibility for external painting, simple, cost-effective installation in existing painting booths, smaller booth sizes and savings on operating costs. These robot systems are used not only for painting in stop-and-go processes, where a travelling axis is essential, but also in tracking plants where the vehicle body is moved uninterruptedly through the painting zone. In this case, the travelling axis is not needed. For this reason, the seventh robot axis was not included in one of the most recent large-scale orders supplied by Dürr. The result was a lower investment cost and, of course, a reduction in the complexity of the plant in a number of ways, including maintenance (for example, the lack of the high-maintenance trailing cable system) and simpler track programming. This type of approach is, of course, only possible with modular robot systems.

A robot station with fixed, overhead robots for external
painting using a tracking system.

 

Another example of this kind is the option of choosing a robotic hand with two rather than three axes for a high speed rotary atomiser with a symmetrical spray pattern. A hand of this kind has a much simpler structure and is lighter in weight. In addition, only two drive systems are needed for the robot instead of three.

 

Colour changer integrated into the atomiser

Application methods also offer a great deal of potential for increases in efficiency. One option is to reduce colour change losses. How can this be achieved when the colour changer is already installed very close to the atomiser? The answer is simple: the colour changer must be incorporated into the atomiser. This is the solution chosen for the EcoBell2 from Dürr which is widely used for painting bodywork. This atomiser, which is referred to as the EcoBell2 ICC, has an integrated colour changer (ICC) for up to seven colours. The paint lines are connected directly to the atomiser and each colour has a separate dosing pump.

These pumps therefore do not need to be cleaned. The individual dosing pumps are connected to the servo motor via switchable pneumatic couplings. As a result, only one pump motor is needed for the entire multi-pump system. If more than seven colours are required, an additional external colour changer can be used.

The new atomiser in use at Nissan in Barcelona.

 

The new atomiser with integrated colour changer (left) and external charging system.

 

Reducing paint loss by half

The ICC system results in only a slight increase in the complexity of the plant. This is relatively unimportant in comparison with the benefits that it brings, which are significant: a drastic reduction in paint and cleaning agent losses during colour changes. This relatively simple technology reduces paint losses to only 6 ml in the case of frequently used colours, per atomiser and colour change, instead of an average of 40 ml. This represents a reduction of 85% and the fall in the cleaning agent losses is within the same range. A quick calculation on the basis of this example will highlight the importance of the new technology. One base coat robot station with a total of eight robots will have a paint loss of around 320 ml using a conventional colour changing system. Based on a total paint quantity of 1040 ml for the vehicle (given an area of 9 m² to be painted, 25% volume solids and an application efficiency of 75%), this means a paint loss of more than 30%. Depending on the proportion of frequently used colours, this paint loss can be reduced by at least half, if not more. To compensate for this kind of loss by improving the application efficiency, an increase of 15% would be needed, and given the current very high standards this is no longer possible.

Colour change time reduced from 12 to 6 seconds

In addition, using ICC technology the colour change time can be reduced by half from 12 seconds to 6. This allows the cycle interval to be shortened, which results in an increase in capacity of around 5% or 30 vehicles per day (calculated  on the basis of 30 units per hour and a daily production period of 20 hours).

Improving the efficiency of interior painting

The third example involves developing the rotary atomiser for use in vehicle interiors. The introduction of rotary atomisers for interior painting resulted in an improvement in application efficiency when compared with pneumatic atomisers. However, when water-based paints are applied electrostatically, an electrical isolation system is needed, which involves a significant increase in complexity (and, of course, in cost). For this reason, many manufacturers have opted not to provide the charging system, which brings the application efficiency back down to the level of pneumatic atomisers.

The development of a new bell cup and a new shaping air ring allows the atomiser to be used in a different way and results in an easily focused spray jet. The new atomiser is part of Dürr's EcoBell range. It has been used on several projects and has produced an average improvement in application efficiency for interior painting of 15%. This significant increase means that the charging system and the accompanying electrical isolation system are no longer needed and therefore the system can be kept relatively simple.

The improvement in application efficiency not only significantly reduces the amount of paint used, but also has an important side effect. The plant remains much cleaner because of the reduction in overspray. This means that the cleaning intervals can be extended and therefore the capacity of the plant is increased.

The possibility of focusing the spray jet effectively allows the EcoBell 2 HD to be used in other areas, such as for painting plastic trim components. These generally have a complex shape and only a small area to be painted. A highly flexible spray jet which can be adjusted to the shape of the parts enables the paint to be applied efficiently.

The EcoBell2 HD used for interior painting with and without electrostatically charged paint.

 

The picture shows the tracks followed by the atomiser in the
engine compartment of a vehicle.

 

 

The new EcoBell 2 HD atomiser achieves a significantly higher
level of application efficiency when painting plastic trim parts.

 

Summary

These examples show how the efficiency of robot painting processes can be increased without making the plants more complex. The objective should be to use only the level of technology which is absolutely necessary. A quick calculation on the basis of a mid-range car body with an area of 9 m² to be painted and a daily output of around 1000 vehicles shows that an increase in the availability of the plant of only 1% reduces the cost per unit by around 3 euros. This includes only the impact of the increase in capacity and not the savings resulting from reduced maintenance.

 

Author:

Dr. Pavel Svejda
Dürr Systems
Bietigheim-Bissingen, Germany
Tel. +49 7142 78 2290
pavel.svejda@durr.com, www.durr.com

 

References:

Schumacher, H.: Progress in robotic painting.
Surcar 23rd International Conference on Automobile Body Finishing.
Cannes 2007.

Svejda, P.: Weniger Lackverbrauch und kürzere Taktzeiten (Reduction in paint consumption and shorter cycle times). JOT Journal für Oberflächentechnik, Vieweg Verlag, Volume 47, March 2007.

 

 

 

 



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