Lubricant reduction through precision dosing in metal forming production

A look into the tooling area of a high-speed stamping machine shows a roller lubricator providing the exact amount of required lubricant to the strip material using the installed precision metering unit.

Reliable and cost-reducing lubrication systems are a basic requirement for economical metal forming production. Increasing international competition, ever-higher cost pressure, and greater demand for health and environmental protections are putting process optimization to the test. Because of those external and internal performance forces, finding potential oil savings during the metal stamping process has been elevated to center stage.

In this context, minimum-quantity lubrication systems such as precision dosing systems are key to greater efficiency in production.

Precision Dosing, Explained

Precision dosing systems have been in practical use by many well-known metal forming companies worldwide for several years. The basic principle of minimum-quantity lubrication applies to the precision dosing concept. By also integrating high-precision metering pumps, lubricant application systems supply a constant amount of lubricant according to the principle of “as much as necessary but as little as possible.”

Not only does this save oil during application, it makes cost-intensive follow-up processes, such as degreasing the formed metal part, unnecessary.

Efficient Lubricant Delivery

Classic roller lubrication systems with metering using pressurized tanks and timing-controlled oil valves can have performance limits for manufacturing electrical contacts and components in a high-speed stamping environment. Settings have been too easily changeable and uncontrollable, making it very difficult—and sometimes unachievable—to apply the lowest possible dosing quantity.

As a result, spray chamber systems, which can distribute an oil film evenly on the material strip, were installed more frequently. Present-day spray chamber technology systems also can have some drawbacks, however. For physical reasons, the lubricant can never be applied at 100% of the set volume. To prevent oil mist and to recycle the overspray lubricant, vacuum and filter systems usually are necessary, depending on the application and the system. This adds maintenance and energy costs.

In the case of partially volatile (evaporating) lubricants, the recycled oil no longer corresponds to its original state because carrier substances evaporate. This recycled lubricant would change the tribological conditions in the tool.

Continuous, Consistent

Optimal application makes for more efficient production

Standard metering systems provide varying amounts of lubricant to the oil applicators, which are based on pulsing (see Figure 1). This means that to achieve an average amount of lubricant on the strip, a much larger amount of oil must be applied so that the material always has sufficient lubricant at its lowest points. This extra oil ends up on the material. Invariably, it runs off or gets squeezed out of the tool and therefore is wasted.

As a result of their need for higher productivity and economical, environmentally friendly processes, they require more from the applicator and lubricant. Stampers now demand exact and reproducible quantity settings in the nanoliter range for lubricating thin-strip metals with narrow bandwidths, especially for high-speed stamping processes.

Precision metering units with built-in micrometering pumps ensure that oil application systems provide the exact amount of lubricant continuously. The result is a more precise and reproducible lubricant application (see Figure 2).

The optimal coordination of the amount of oil applied with the amount of oil required by the process and the exact setting of the application amounts for each lubrication point have additional positive side effects. Ideally, cost-intensive, time-consuming downstream washing, drying, and degreasing processes can be eliminated.

A recent development has been exact dosing even on larger strip widths during high-speed punching processes up to 3,000 SPM. This has been particularly helpful in production with short feed lengths and minimal stroke heights, such as in electrical contact stampings.

Another positive outcome is material scrap reduction, increased tool life, a more precise forming of components, and elimination of hydraulic oil pockets in the tooling. These oil pockets can form if too much oil is on the strip and gets trapped between the strip and the tooling surface, creating an unwanted bubble on the production part.

Software

The installed visualization software on precision dosing units also can be used to display the exact consumption quantity. The documentation and printouts of consumption data provide important key information for process control and quality assurance. The software can document continuous improvement efforts as well. The data can be stored and recalled at any time.

The metering unit is equipped with an integrated OPC Unified Architecture (OPC UA is a machine-to-machine communication protocol for industrial automation developed by the OPC Foundation) interface for the Industry 4.0 age.

A precision dosing unit for forming oils can be combined easily with roller band lubricators, minimal-lubrication nozzles, and tool lubrication systems.

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