Achieving Cleanliness Reliably And Efficiently

Component cleanliness is a quality criterion in the motor vehicle industry. Requirements are becoming stricter and stricter with each vehicle generation – with simultaneously increasing cost pressure. And thus for the automotive industry and its suppliers it’s becoming more and more important to exploit optimisation potential in the area of parts cleaning.

Global emphasis is being placed upon reducing CO2 emissions and fuel consumption, as well as increasing safety and comfort within the vehicle manufacturing industry. Downsized engines are in demand which run more efficiently with high power output, as are components that are capable of withstanding extreme loads and are distinguished by tight tolerances. However, this is only possible with high precision components – and this is associated with increased sensitivity to contamination. If they end up in the wrong place, even particles with sizes down to 500, 200 or even just 100 µm can cause damage and failure in the field. This is why, in the meantime, the automotive industry has started defining particle size distributions for certain parts in functional modules such as the power train, steering and brakes, for example no more than 1,000 particles between 100 and 200 µm, 500 particles between 200 and 400 µm etc. In order to fulfil and document these requirements, large investments in industrial parts cleaning technology are required in some cases. For example, based on calculations, the outlays required for cleaning technology which fulfils a specified requirement of “no particles larger than 1,000 µm” are two to three times higher than for systems in which cleaned parts are contaminated with larger particles.

Minimising Contamination

The issue of potential for economic optimisation in the parts cleaning process is pursued despite, or perhaps precisely due to the large investment sums involved in some cases. One approach is component design, because the geometry of the workpiece and the individual steps of the manufacturing process, for example turning, milling and assembly, as well as cleanability, are determined during the design stage. The latter usually plays no role at all, for which revenge is taken during the subsequent production process: The parts have corners, edges or drill holes from which particles and processing residues can only be removed with considerable effort, or not at all.

Due to the fact that material is removed during the course of chip-forming machining processes, contamination can never be entirely avoided. The quality of cooling lubricants and machining fluids influences the quantity of chips, burrs and particles on the workpieces. Suitable purification/filtration prevents previously washed away contamination from being returned to the component once again.

A special rinsing step with the tool in the machining centre – perhaps even with more finely purified fluid from a separate tank – can also make a contribution to reducing the number of chips. At first glance, this represents an additional expense. But it pays for itself later on in the manufacturing process thanks to shorter cleaning times and/or a longer bath service life, as well as better component quality. And residues which are removed after machining by means of mechanical pre-cleaning based on vibration, shaking, spinning or vacuum blasting the surfaces of the part do not place any unnecessary load on the cleaning agent.

In the case of multi-stage machining processes in metal forming and machining applications, intermediate cleaning steps prevent the accumulation of contamination, as well as any mixing or drying out of media on the workpieces.

Ideally Laid Out Cleaning Processes

Modern cleaning systems are capable of fulfilling even very high demands for component cleanliness – assuming the cleaning process has been ideally matched to the contamination to be removed, part geometry, the utilised material and the cleanliness specification to be complied with.

The limit value of “smaller than 1,000 µm” for components in engines and gearboxes can only be adhered to with a cleaning process which has been laid out specifically for the respective part. The current state-of-the-art makes use of a multi-stage procedure to this end. The workpieces are thus usually subjected to mechanical cleaning during the first step, which removes some of the adhering machining fluid. The second step involves immersion flooding: Water is injected into the cleaning chamber below the surface of the bath at a pressure of 10 to 15 bar. The resulting whirlpool effect rinses chips and contamination out of hollow spaces such as threaded blind holes. Water jet systems which are aimed at openings in the component, and lances which advance into holes, allow for optimised results within short periods of time. This applies as well to subsequent high-pressure cleaning or deburring. Rinsing is followed by a drying process.

Numerous engine and gearbox variants, as well as ever shorter product life cycles, necessitate a great deal of flexibility – even for individual part cleaning. This is accomplished by automated cleaning solutions with robots, which are integrated into the production line. Thanks to options provided for easy reprogramming, these assure levels of flexibility which are comparable to those offered by machining centres.

Large numbers of vehicle parts are cleaned in batch processes as individually positioned items or bulk goods. Single and multi-chamber systems which can be integrated into the production line are available for these cleaning tasks as well. A modular design with various interlinking options assures adaptability to specific requirements, as well as expandability in accordance with actual needs.

In addition to the utilised process technology and the medium, the container also has a great deal of influence on the results and the economic efficiency of the cleaning process. There are two primary questions in this respect: Are the parts in the container readily accessible from all sides for the medium and the washing mechanism? Is it possible to position the part within the container such that critical areas can be treated in a targeted fashion?

An additional requirement for efficient cleaning processes is the removal of loosened contamination from the cleaning bath so that it isn’t redeposited on the parts. In order to assure continuous particle removal, gentle but constant bath motion is necessary on the one hand, and effective filtration which is matched to the actual particle size is required on the other hand.