Minimum quantity lubrication

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The minimum quantity lubrication ( MMS ) or minimum quantity cooling lubrication ( MQL ) refers to the cooling of cutting processes with small amounts of cooling lubricants . An oil-air mixture is used here, which prevents the development of frictional heat through optimal lubrication. The remaining heat is dissipated via the tool and the chip . The coolant must be dosed reliably and fed to the tool. This must also be ensured with frequently changing, very different tools. Safe removal of chips from the machine is also important, and the escape of aerosol vapors must be avoided.

The process is a further development of the usual wet machining , in which the tools are literally flooded with cooling lubricant . A related discipline is dry machining , which completely dispenses with lubrication in metal cutting.

Machining processes that use less than 20 ml cooling lubricant per hour are defined as minimum quantity lubrication. It differs from conventional wet machining.

In the case of minimum quantity lubrication, the amount of cooling lubricant used is reduced to the amount actually required for lubrication and cooling using metering technology and is brought directly to the point of contact of the tool cutting edge under pressure or with compressed air .

technology

Depending on the machining conditions, MMS requires minimal to extensive changes to the machine tool and tool. Circular saws , band saws or lathes , for example, can easily be retrofitted with a system for MMS. In the area of high performance cutting , however, you need machines and tools specially designed for MQL.

The minimum quantity lubrication technology is divided into the following systems:

  • Systems with external MQL feed

In the case of the external feed, the minimum amount is fed to the tool or the active point through a nozzle installed in the machining area of ​​the machine tool .

  • Systems with internal MQL feed

The internal supply of the MQL medium, on the other hand, takes place through the work spindle, the tool holder and the tool right up to the cutting edge . This enables optimal wetting of the active partners at the surgical site. The group of MQL systems with internal feed is in turn divided into 1-channel and 2-channel MQL systems. With 1-channel systems the aerosol is premixed outside the spindle, with 2-channel systems directly in the spindle.

advantages

  • Financial benefits
    • The elimination of almost all supply and disposal technology for the cooling lubricant results in great savings potential.
    • Longer service lives can be expected with optimized processes.
    • In individual cases, the process duration can be reduced by up to 30% with optimal processes.
    • Costs for purchase, storage and transport as well as disposal of the cooling lubricant are greatly reduced or eliminated.
    • There is no need to check and maintain the coolant.
    • Depending on the application, complex subsequent processes for cleaning / washing the workpieces can be reduced or saved.
    • Dry shavings can be sold as recycling material, wet shavings must be disposed of as hazardous waste.
  • Environmental benefits
    • There are no environmentally harmful old emulsions.
    • Accidents caused by cooling lubricants leaking in large quantities are not possible.
  • Occupational safety
    • A dry machine environment reduces the risk of occupational accidents.
  • Health protection
    • Diseases caused by cooling lubricant (e.g. in the respiratory tract, skin diseases) are avoided. No evidence of dust exposure from machining with minimum quantity lubrication could be detected. There is no longer an occupational exposure limit for cooling lubricants . The earlier air limit values ​​are used as a guide for the assessment.

disadvantage

  • Depending on the constellation, there are high investments in retrofitting the machines.
  • Ongoing tool costs increase due to more expensive special tools when optimizing.
  • A very careful coordination of the workpiece, machine parameters, tool and lubrication is required. The necessary specialist knowledge is usually missing and has to be bought in.
  • Switching to minimum quantity lubrication does not make sense for all processes, machines and workpieces, so that the cooling lubricant supply in the company is usually still required.

Web links

Individual evidence

  1. ↑ German statutory accident insurance e. V. (DGUV): DGUV Information 213-723 - BG / BGIA recommendations for risk assessment in accordance with the Hazardous Substances Ordinance - minimum quantity lubrication in metal cutting. Retrieved October 30, 2019 .