Boosting efficiency in engine production

By Niraj M Wanikar, Chief Editor, CNCTimes.com, 2014-06-04 15:42:33

Sustainability and resource efficiency are on everybody's lips. The automotive industry is investing billions into more fuel-efficient cars and alternative drive systems, including, needless to say, the development of ‘green’ manufacturing technology. Only rarely, however, will parts cleaning processes come in the focus of such efforts. Unjustly so – for the cleaning systems used in engine and transmission assembly can be enormous in size and are noted energy guzzlers.

Parts are treated with large amounts of heated cleaning media, the residue of which must then be removed again by drying. In addition, high-pressure deburring at 300 to 600 bar pressure causes heating of the work piece which will require cooling as a result. If the downstream process following the cleaning operation calls for a defined part temperature, still more energy must be expended on further part cooling. Such high-energy processes turn cleaning machines into a major power consumer.

Looking at the entire production line, it emerges that the handfuls of cleaning systems use almost as much energy as all machine tools taken together. Electric power costs account for between 90 and 95 per cent of the total energy bill.

Saving money through energy-optimised cleaning systems

In view of the above, OEM and tier 1 suppliers are in need of more energy-efficient equipment for cleaning engine and transmission parts such as, e.g., cylinder heads. At the same time, the continuous downsizing of engines calls for high levels of reliability and repeatability in meeting what may at times be ultra-exacting cleaning requirements – and within very short cycle times at that. In order to manage this balancing act, Dürr Ecoclean GmbH of Monschau has taken a good hard look at the machine concepts and robotised cells used in engine manufacturing to date.

This review has revealed significant improvement potentials which can be broken down into diverse individual steps. It goes without saying in this context that today's parts cleaning machines are equipped with energy-efficient drive systems. Efficiency-optimised EcoCFlex robotised cells can resolve more than 95% of the cleaning tasks encountered in engine and transmission building.

More efficient cleaning methods

Another building block is optimising the cleaning processes employed while maintaining or even improving cleaning quality. This approach is exemplified by injection flood washing, which conventionally used to be carried out at medium volume flow rates and high pressure. From extensive trials in which identical parts exhibiting the same degree of contamination were cleaned within the specified cycle time, it emerged that by increasing the flow rate by around 50% while significantly reducing pump pressure, pump power ratings could nevertheless be substantially reduced. Significant energy savings and improved cleaning results can be achieved in this manner.

The newly developed Water Knife directs the cleaning jet over the entire length of the part while keeping it focused on the areas to be cleaned. A key contributor towards such progress is Durr’s newly developed nozzle technology as embodied, e.g., in the WaterKnife system. Unlike the conventional round types, this nozzle directs the cleaning jet onto the treated surface in a focused manner over the entire part length.

Another new development is the so-called hybrid nozzle featuring a variable mixing chamber. With the aid of this innovative general-purpose nozzle, both high-pressure and low-pressure applications as well as injection flood washing can be performed flexibly at a single cleaning station. As a result, the non-productive times needed for moving the work piece around inside the robotised cell are reduced substantially. And although this benefit may not yield significant energy savings at first sight, efficiency gains are achieved through the reduction in cycle.

Design-to-part concept

All too often, cleaning systems today are still being designed on the "more is more" principle, i.e., aiming at all-round maximisation. Naturally, this also implies maximised energy consumption. With its "design to part" approach, Dürr Ecoclean pursues the strategy of reducing energy demand to a minimum by adopting part and task-specific designs for the various machine components such as, e.g., treatment stations, pumps and tanks. After all, it is common practice in engine and transmission building to make only very similar components on the same line.

One pre-condition for the above is that the cleaning system is of modular design and that the equipment manufacturer is prepared to keep suitable module sizes available. This, in turn, will ensure flexibility in adapting the system to changing objectives. Converting a machine for cleaning a different part, for instance, will set the owner back by an average 10 to 15% of the original investment in the case of a robotized cell but may cost as much as 50% in the case of a continuous-type cleaning system.

’Design-to-part’ approach of EcoCFlex minimising the energy demand by adopting part & task specific designs for various machine components.

Reduced exhaust air flows and temperatures

In order to prevent cleaning vapours from escaping into the environment, continuous-type cleaning systems are fitted with extraction systems at the inlet and outlet ends. Thus, energy is annihilated in no less than two ways. Firstly, heat is removed along with the vapours and must then be re-introduced into the process at high cost to ensure effective cleaning. Secondly, the extraction systems themselves need to be powered. Both factors are eliminated in a closed-loop system such as the robotized cells of our EcoCFlex series.

Here, further energy savings can be achieved via the option of reducing the cleaning media temperature, e.g., from 60 … 65 °C to 50 … 55 °C. This adjustment is supported by new and improved developments made available by the cleaning chemicals manufacturers.

VFD for motor speed control and intelligent software solutions

Dürr Ecoclean's energy saving approach also relies on the use of variable frequency drives (VFDs) for controlling high power consuming equipment in part-load operation. Pumps, for example, can thus be run at lower rpm during idling or low-output periods in order to minimise their power demand. To ensure that a VFD will not consume more energy than it saves, the Monschau-based equipment manufacturer thoroughly investigates its usefulness for every single unit.

Moreover, intelligent software solutions supplying power only upon demand (similar to the automatic start-stop systems used in today's cars) have been developed for both existing and new installations. These software tools ensure, for instance, that when the line is re-started after a production pause, the individual units will be powered up "as needed", as opposed to starting them up all at the same time. On the other hand, energy-intensive units such as vacuum pumps are automatically switched to standby mode after a certain interval during which no parts are available. It may also be determined via the software settings that the system shall start only when a suitable quantity of parts is available for cleaning.

Huge savings due to efficiency-optimised robotised cells

Dürr Ecoclean has implemented these individual features on its new efficiency-optimised, compact EcoCFlex series. Compared to previous systems, these robotised cells can save up to 25% of electricity costs. Their savings potential is even greater when measured against competitor equipment available in the marketplace. Here, the electric power consumption is up to two-thirds lower.

• Follow @CNCTimes