Case Study

How lubricants can help in improving CNC machine performance

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Computer Numerical Control (CNC) machines automate the machine tools by means of computers executing pre-programmed sequences of machine control commands. This is in contrast to machines that are manually controlled by hand wheels or levers, or mechanically automated by cams alone. Any particular component might require the use of a number of different tools – drills, saws, etc. – modern machines often combine multiple tools into a single ‘cell’. In other installations, a number of different machines are used with an external controller and human or robotic operators that move the component from machine to machine.

Companies specialising in producing nuts and bolts, complex gear sets or high precision valves, pay high emphases on efficient functioning of the components of their computer-controlled cutting machines for long term profitability. Lubrication plays an integral role in reducing friction between critical rotating and moving machine components, which then translates into equipment durability, longevity and continued uptime.

To help ensure that the machine runs smoothly, it is important to choose a combination of high-quality metal working lubricants such as slideway oils, water soluble cutting fluids and neat cutting oils.

Slideway Oils
Poorly formulated slideway oils may not separate readily from aqueous coolants. This results in the formation of ‘tramp oil’ which compromises the effectiveness of the coolant by shortening its effective life and adversely altering cutting performance. Tramp oil can also lead to bacterial growth resulting in foul odour, short service life and potential health as well as safety concerns.

To identify high performance slideway oils, maintenance professionals should seek out products such as Mobil Vactra Oil Numbered Series of slideway oils with the following performance characteristics:
• Exceptional coolant separability which enhances the performance and life of water based metal working fluids, outstanding frictional properties which enable increased machine accuracy and reduced chatter, and stick-slip.
• Mobil Vactra Oil No.2 is a premium-quality ExxonMobil slideway lubricants specifically designed to meet the requirements for accuracy, aqueous coolant separability, and equipment protection of precision machine tools.

Water soluble cutting fluids
To optimise productivity it is very important to choose technology-leading aqueous coolants. The highest performing coolants can reduce maintenance requirements by resisting biological attack thereby extend batch life. Ease of maintenance needs to be balanced with performance as well as protecting the CNC machine components from corrosion and sticky deposits. In addition, the fluids should meet the latest health and safety regulations, be easy to monitor and maintain in service. Collectively, these properties will help deliver long service life, excellent cutting performance and reduced maintenance downtime.

The new Mobilcut series from ExxonMobil, comprises of milky emulsions, high performance micro-emulsions and a fully synthetic grinding fluid. The high performance, long life semi-synthetic cutting fluids in particular have been designed to meet the wide variety of applications and operations found in medium to small sized CNC machines.

Mobilcut 250 is a high performance semi-synthetic fluid formulated to enhance performance when machining aluminium and aluminium alloys and where low staining potential is important on sensitive components. Containing high levels of lubricity agents, it provides high machining performance of carbon and alloy steels and yellow metals.

Neat Cutting Oils
Neat or straight cutting oils are used in applications which are beyond the typical performance profile of aqueous coolants, such as tapping and threading of high alloy steels. They improve machining in high speed automated machining centres through outstanding cutting performance, reduced tool wear and enhanced surface finish. Ideally they should be light coloured to allow clear visibility of the workpiece; have low misting characteristics to help workplace safety and product usage; and are chlorine free to support environmental concerns, while balancing with a high degree of lubricity and machining performance.

Specially designed to meet the increasing demands of today’s sophisticated machining centres, tooling trends and health and safety regulations, Mobilmet series of cutting oils and the new series of Mobilgrind grinding oils from ExxonMobil have been developed for applications where excellent surface finish, high precision machining and improved productivity are the primary objectives.

Spindle Oils
Spindle oils are used for high speed spindle bearings and equipment where high speeds and fine clearances are involved. It provides exceptional lubrication of close-tolerance bearings which helps keep the bearings running cool and helps maintain the precision required by many of today’s critical machine equipment. These are designed for spindle bearings, they exhibit the required properties to function as low pressure hydraulic and circulating oils as long as the proper viscosity is selected. This feature helps minimise inventory costs and reduce the potential for product misapplication.

The Mobil Velocite oils are premium performance products primarily designed for the lubrication of high-speed spindles in machine tools. They are also used in some critical hydraulic, circulation systems and air line oilers where the appropriate viscosity grade is selected.

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