For well over a century before the advent of Dry Machining technology manufacturers have used various forms of metalworking fluids (MWF’s) to
improve the performance of metal working processes such as machining, grinding and forming. Coolants, which are oil-based, water-based or oil/water emulsions, are necessary for removal of the extreme heat generated during manufacturing operations. Unfortunately, the majority of the MWF systems in use today, while a necessary evil, are expensive, ineffective and carry high risk from an employee health and safety perspective. While coolant/lubricant systems are a critical part of manufacturing processes, there has been little technical advancement in the area coolants or dry machining technology for dry coolants beyond incremental improvement of existing systems.
Current State of the Art
Currently the major approaches to coolant systems fall into a few categories; dry machining or Green Manufacturing (no coolant system), flood coolants, Minimum Quantity Lubrication (MQL) and gas based systems.
With the exception of grey cast iron and some aluminum alloys, dry machining is costly and inefficient and is largely restricted to applications where the use of flood coolants is impractical (such as rail grinding) or more costly than usual. Also applications such as the machining of some medical alloys, such as titanium preclude the use of flood coolants or oils for cleanliness.
Flood coolants are by far the most commonly used heat removal and lubricity systems in manufacturing with an annual U.S. market of $1B for the coolants alone. Treatment chemicals, filter media and fluid handling systems are almost as much again. The problems and shortcomings of flood based systems are well documented. They are costly, with maintenance and disposal costs each costing about as much, or more, than the original purchase price. Several major manufacturers have determined that flood coolants and associated infrastructure account for 15% or more of finished part cost, often exceeding the cutting tool cost per part. Furthermore, the current oil/water emulsions currently in use are an inherent tradeoff between cooling and lubricity – more of one leads to less of the other. Finally, the toxicity and health dangers of current metalworking fluids are well documented with a very high incidence of specific types of cancers and other health issues among machinists and machine operators.
MQL dry machining systems using a spray mixture of air-oil have been are fully developed for both spray and through spindle applications. Large automotive manufacturers that embrace Green Manufacturing such as Ford now have installed over 900 machining centers used for high volume production of cylinder blocks, heads and transmission cases. Significant lifecycle cost savings over flood systems have been demonstrated for MQL. However, the major drawback of MQL dry maching is that the inherent lack of cooling capacity limits its applications to cases where the machining operation is largely limited by lubricity and not heat removal. In applications where both lubrication and cooling are required, CO2 MQL dry machining provides a perfect solution of frozen ice particles and oil mist.
Impact & Benefits of MQL Dry Machining
- Cost Reduction – The cost of fluid disposal systems, filters, air handeling, etc are eliminated.
- Tool Cost Reduction – Both MQL and CO2 MQL will extend tool life via enhanced cooling and lubrication.
- Metal Removal Rate – Faster MRR are possible due to tool life improvement, can trade off tool life vs. feed rate for better productivity.
- Capital cost reduction – elimination od plant coolant systems, treatment costs, electricity for pumps and air cleaners
- Health and Safety – No biocides or toxicity components on people, on the floor or in the air.
- Environmental – Both MQL and CO2 MQL are Green and the CO2 used is captured and repurposed from other industrial processes