Metalworking fluids make up about 6 percent or 2.4 million metric tons of global demand for finished lubricants, with about a 40/60 split between neat oils and water-miscible fluids, according to Nynas, which makes naphthenic base oils that go into metalworking fluids, greases and industrial lubricants. On the water-miscible side, the breakdown includes conventional soluble oils (coolants) with 70 percent of the total; semi-synthetic fluids with 18 percent; and synthetic fluids (12 percent).

Indestructible or Unworkable?

Modern materials deliver practically indestructible parts but come with a dilemma, Norrby remarked at the conference, which took place in September in Warsaw, Poland. How to machine them to final shape at a reasonable cost per part? he asked. Different types of material need different metalworking fluid solutions to address machining challenges. We have fully hardened steels that are tougher, gummier and tend to work-harden very rapidly. Also, there are hard powder-metals and sintered materials that can give extensive tool wear, which are usually dry machined.

Norrby also pointed to the difficulty of machining heat-resistant superalloys such as Inconel (containing nickel and chromium), Waspaloy (also nickel-based) and titanium 6AI4V, as well as bi-metals that have hard materials in select wear areas surrounded by or mixed with softer alloys. Superalloys work-harden so rapidly that after one or two passes, they may be so hard that subsequent passes can deform the piece, the tool or both.

To manage these challenging metallurgies, high thermal-stress machining operations such as cutting, broaching and milling will require the cooling and lubricity supplied by either soluble or neat oils. For some materials, such as the superalloy Inconel, machining speed must be reduced to minimize work hardening, Norrby said, while chip breaking and cooling should be addressed by high-pressure metalworking fluid delivery; that helps reduce tool wear and increase tool life.

The Nynas executive also sees many metalworking shops trying out minimum quantity lubrication (MQL) as a first step on the path toward fluid-free operation. MQL is a process of applying very small quantities of high lubricity oil mixed with air at the precise point of contact between the tool and the workpiece, Norrby explained. It can provide micro-lubrication for near-dry machining, it reduces or eliminates problems associated with thermal shocking of the machine piece, and it also reduces [workplace] mist and spray, providing more acceptability when used on unenclosed machines. He added, Minimum quantity lubrication cutting fluids can be classed as low-emission lubricants.

Layer by Layer

Another rising challenge to metalworking fluid volumes is 3D printing technology. This is a process in which material is not removed but added, and built up in layers. Powdered titanium, for example, can be loaded into a 3D printer, then deposited in successive layers via an electron beam to achieve a near-perfect part; only minor machining is needed then to reach the desired trim or finish.

In metalworking circles, 3D printing often is called additive manufacturing, a term which is unrelated to lubricant additives, Norrby commented. In additive manufacturing, material is added, not removed, so thats why no removal fluids are necessary.

In what has traditionally been metalworking territory, 3D printing is commercially viable for replacing very complex cast products. Also, it is extensively used for prototyping, design of models and short, one-off series. To say the least, this leads to establishing a new aspect in manufacturing, Norrby emphasized.

Among those adopting 3D printing are aerospace manufacturers like Airbus and Lockheed. For its forthcoming 777X airplane, Boeing was able to 3D-print the solid wing trim, a 17.5-by-5.5 foot structure weighing 1,650 pounds. A component that size and complex would have needed three months to build using traditional methods; the 3D version required just 30 hours-and zero metalworking fluid. Siemens announced in February that it will 3D print high-pressure gas turbine blades, and many others are climbing on board, too.

Regulations and MWF

Of course, traditional manufacturing processes are not going to vanish overnight, but traditional metalworking fluids face another sort of pressure: regulations that limit or bar some longstanding chemistries. This started in the European Union with the REACH (Registration, Evaluation and Authorization of CHemicals) legislation introduced in stages since 2006, Norrby said, and the Biocidal Product Regulation (BPR), which took force in 2013.

The main worries for metalworking fluid formulators under REACH and BPR are the high costs of testing and registration of chemical and biocidal components, and disappearance of many specialty chemicals and chemistries that are too costly to test and register, Norrby said.

One additional difficulty with REACH, besides the cost and unavailability of chemicals, is the dwindling time that companies have to comply under the regulations strict timeline. The final substance registration date, for chemicals produced in volumes less than 1 ton per year, is June 1, 2018, Norrby reminded. Time is running out. Huge numbers of small-volume chemicals remain to be registered, about 8,000, of approximately 50,000 chemicals registered so far.

For its part, BPR made a huge impact on the slate of available biocides. Whereas in 1999 approximately 100 different biocides were on the market, Norrby related, only 25 are available now, from just 11 suppliers; very few biocides are available from more than two sources, Nynas found, which makes the long-term outlook somewhat unpredictable.

The number of utilizable chemicals is dwindling fast, and about half of the remaining are formaldehyde-releasing agents. Legislative limits on free formaldehyde [exposures] are far above those encountered in metalworking fluid formulations, but the legislation still induces hesitation in the market, Norrby observed. Some end users are categorically rejecting such biocides, making it even tougher to keep water-miscible fluids from deteriorating.

He added: As biocides are required for metalworking fluid emulsions, the long-term availability of accessible and affordable biocides will be key to the future usage and market of soluble oils. Bio-stability is most critical in soluble (that is, high water content) metalworking fluids.

The EU Watch List

European regulators meanwhile are scrutinizing three additional high-toxicity metals and chemicals that affect the use of metalworking fluids: lead, boron and chlorine.

Lead is a component of many alloys, where even at small percentages it greatly eases machinability. Amongst other benefits, lead acts as a chip breaker and lubricant, which provides manufacturing and performance benefits, precise tolerance in tiny components and excellent sliding characteristic. If removed from the market, it can affect the machinability of bronze and steel parts, Norrby said.

Boric acid is used in fluids as a pH buffer to inhibit growth of microorganisms, and as a corrosion inhibitor and anti-staining agent on ferrous material, but in late 2010, free boric acid (not the salt) was classified as toxic to reproduction. As end users become more averse to boric compounds, formulators must find suitable alternatives that are not as costly as those alternatives already established, Norrby said.

Chlorine is found in many synthetic, oil-free formulations, usually in the form of medium-chain and long-chain chlorinated paraffins (MCCP and LCCP). Although shunned in the EU, these popular extreme-pressure agents remain on the market in the United States and elsewhere. Now the U.S. Environmental Protection Agency has targeted them, clouding their long-term prospects.

Alternative chemicals for medium-chain and long-chain chlorinated paraffins are boundary lubricity additives such as esters, phosphorous and sulfur based additives, and overbased calcium sulfonates, the last being similar [to chlorine] but without giving identical results, Norrby said. In the U.S., he sees many synthetic formulations being replaced by semi-synthetic (oil containing) formulations.

Looking ahead, he anticipates three drivers-biocide restriction, minimum quantity lubrication and dry machining-putting pressure mainly on coolants, the soluble oils that make up 70 percent of water-miscible fluids.

Because of this, the Swedish refiner is confident that neat oils could increase their share in the global market, because they provide crucial lubricity and tool wear control. This need [for neat oils] will remain on the market as long as metal is being worked, he concluded.