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Process Cleaning Magazine
© 2012
AMT-The Association For Manufacturing Technology
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PC FEATURE
The use of CO2 snow jet cleaning in the cleaning of plastic parts, such as fenders, offers economic and ecological benefits, compared to traditional wet cleaning. With a modular-based jet array, even complex geometries are reachable. Image Courtesy of acp
In the event of product changes or new components, standard cleaning units with a robot completely integrated into the system provide the opportunity for rapid process adaptation, with low input of resources, thanks to reprogramming. Image Courtesy of Dürr Ecoclean
In the case of batch processes, decentralized cleaning units, coordinated in terms of the spectrum of parts, the degree and type of soiling and the cleanliness requirements, usually provide a better cleaning result within a shorter time and with reduced logistics and handling resources. Image Courtesy of MAFAC
The basic model of the Process Control Unit Libelle monitors and analyzes the washing fluid, using an optical procedure, giving a signal when a change of bath is required. Image Courtesy of BvL
Cleaning receptacles, in which the parts can be rinsed around effectively from all sides by the cleaning medium, contribute to a better cleaning result and shorter process times, or higher throughput or longer bath usage times respectively. Image Courtesy of Metallform
This fully automatic evaluation system, using a microscope, scanning table, digital camera and PC system, enables the technical cleanliness of components to be analyzed and documented with regard to conformity to the norm ISO-DIN 16232. Image Courtesy of Leica Microsystems
The demand for higher performance, while simultaneously reducing weight, fuel consumption and the emission of pollutants, can only be fulfilled with components that match the most rigorous requirements and the most exacting tolerances. This is linked to a higher degree of sensitivity of components to impurities. Any dirt not removed can lead to expensive rejects, laborious follow-up work, restrictions in functionality that damage a company’s image, right through to vehicle failure in service. To fulfill the challenging requirements of component cleanliness with maximum economic effectiveness, the optimum coordination of cleaning strategies is essential.
Greater Flexibility
Within the automotive industry and its suppliers, a large number of versions of equipment for engines and transmissions, as well as ever-shortening product life cycles, necessitate a high degree of flexibility. This means that production equipment and machines must be able to be re-equipped and adapted in order, for instance, to suit engines with less cubic capacity. The production of cylinder heads, crankcases and gearbox housings, for instance, entails the use of processing centers that can be reprogrammed easily, thus enabling different versions of a workpiece to be produced. Frequently the parts, made in large production runs, are still cleaned in transfer units specifically arranged for a given component. Modern automatic cleaning solutions, using robots and integrated into the production line, offer a flexibility in the cleaning of parts that is appropriate to production needs. Integrated into the wet cell, the robot serves as the handling and processing system of the cleaning unit, precisely positioning the workpieces to guide them to the various treatments, such as spray cleaning, injection flood washing, high pressure burring and drying. Control is via a standard CNC system; the programming is via a user-friendly teach panel. This way, the unit’s operating personnel are in a position to program necessary adaptations to new or changed parts, rapidly and without problems.
These cleaning units, usually offered as standard modules, are compactly constructed; the media processing is integrated. Their space-saving mode of construction means that they take up much less production area than transfer units, while most of them also offer energy savings.
More Effective Batch Processes
Whether it is bulk material or products made in sets, wet chemical cleaning, using solvents or water-based cleaning agents in a batch process, is the procedure of choice for countless parts built into vehicles. The advantage of this type of cleaning is a high throughput in a relatively short time and, accordingly, a low proportion of the total manufacturing costs of a given workpiece. Frequently the cleaning process is carried out in central units. However there is no guarantee that the necessary degree of cleanliness is attained for all workpieces when simultaneously cleaning parts with different geometries, cleanliness requirements and/or levels of soiling (for instance cooling lubricant and polish dust), or those consisting of different materials. For an optimum cleaning result, in most cases it is advantageous to carry out the cleaning process decentrally, in separate units, coordinated according to the spectrum of parts, the degree and type of soiling and the cleanliness requirements. In most cases this also leads to a significant reduction in the resources expended on logistics and handling, because the cleaning units can be placed close to the production of the respective part.
A cleaning receptacle in which the parts are well rinsed by the cleaning medium from all sides is conducive to the process in all cases. This high level of accessibility also provides rewards in terms of the required drying time and lower level of carry-over of media, providing the opportunity of shorter cycle times or a higher throughput and longer bath usage times respectively.
Bath Supervision and Media Processing
Bath supervision and media processing also make substantial contributions to process-safe, economically efficient cleaning in the automotive sector. A variety of systems is available for the continuous monitoring of the cleaning baths. These calculate the cleaning capacity presently available in the process that is currently in progress; they either provide a consumption-dependent follow-up dosage automatically or they signal the need for a change of bath. New developments and product improvements in terms of filtration and processing systems open up opportunities for constantly higher separation rates and, thus, extended bath usage times.
Monitoring and Documentation
A continually growing quantity of components for the automotive sector requires the fulfillment of precisely defined stipulations regarding residual dirt. Due to the introduction of the ISO-DIS 16232 norm, Volumes 1 to 10 (VDA 19), “Road Vehicles—Cleanliness of Components of Fluid Circuits,” comprehensive standards were defined with regard to the approach and methods adopted for monitoring the cleanliness of particles. The objective of the directives is to be able to evaluate and compare the technical cleanliness of a component, by means of clear, unambiguously described paths and procedures for obtaining and analyzing particles.
For most of the relevant components, the proof of a particle’s properties cannot be provided directly on the product surface, simply due to its geometry. This necessitates a cleaning measure in which the particles are transferred into a fluid medium. The particles can be extracted from the component by means of spraying them away in a targeted manner, cleaning them off using ultrasound, rinsing them off and shaking the component.
A second step is to count, measure and characterize the particles obtained. This involves the use of various procedures with varying degrees of usefulness in drawing conclusions. The gravimetric method enables conclusions to be drawn about the monitored components’ level of cleanliness without giving information about the particles’ potential to cause damage. Manual analysis gives the opportunity to determine the sizes and distributions of particles (or, respectively, the largest particle) cleaned off the component, and, thus, to see whether the product conforms to certain specifications (e.g., no particle > 15 micrometers). In addition, automated microscopy with image processing creates the opportunity for conclusions on the damage potential of individual particles. The raster electron microscope provides information on the size and distribution of the particles found, as well as the chemical elements they contain. This enables deductions to be made about the origin and the damage potential of the particles. A further alternative is fluid particle counters, working on the basis of so-called extinction particle counters. With these automated systems, an ultrasound bath is used to clean the particles off the component being checked. After this, fluid samples are assessed according to a defined program setting. The cleaning industry offers special checking systems in various sizes and versions for each of these procedures.
The Functional Area
The selective cleaning of certain areas on the components (such as sealing areas, joining areas and adhesion areas, as well as laser weld areas) can lead to a huge savings in time and costs. Using the classic water-based or solvent-based solution in these cases would usually require investing a great deal of time and cost to bring the entire component up to the degree of cleanliness needed for the functional area. Here cleaning is carried out on a production-integrated basis, using CO2 snow jet, laser or plasma procedures.
Thanks to the limited-area cleaning effect and the compact jets, the CO2 snow jet procedure is also suitable for integration into assembly units. Here screw insertion, caulking processes or contact with uptake from the workpiece can similarly give rise to functionally-critical particle dirt. Until now, little attention has been given to this issue.
Alternative Procedures Save Costs
CO2 snow jet cleaning also offers advantages over traditional wet processes in terms of the cleaning of plastic assemblies (such as bumpers and mirror housings) prior to varnishing or coating. The cleaning process is dry, using environmentally neutral, liquid carbon dioxide, accelerated by compressed air and jet-sprayed onto the component to be cleaned. This is also a targeted means of reaching areas that are difficult to access. Whether in the form of particles or film, any dirt present is removed (in what is a sparing manner in material terms) by using mechanical, thermal and chemical properties. On average, the investment cost for such a cleaning system is as much as 50 percent below that of a conventional wet chemical system. The operating cost is as much as 30 percent lower on average. Because the cleaning process is dry, no energy-intensive drying is required. The cleaning equipment can also be integrated directly into the varnishing booth, thus saving space.
The same also applies to plasma cleaning, which offers a broad application spectrum because of the use of various reaction gases. This cleaning technology primarily comes into play in cases where later processes demand a very high level of degreasing. An additional effect of this procedure is a good preparation (for instance, simultaneous activation) of the surface for subsequent processes, including improvement of adhesion properties of adhesives and coatings. The plasma procedure is also suitable for applying coatings, such as those for corrosion protection.
Frequently a cleaning strategy that is coordinated to match requirements offers the opportunity to exploit optimization potential within the entire production chain, thus structuring production more efficiently. Yet this can only be effected using knowledge of the way the various cleaning technologies perform and the best possible way of using them.