Choosing the Right Coolant for your Industrial Metal Cutting Operation

September 15, 2014 / Cost Management, cost per cut, customer delivery, LIT, operator training, preventative maintenance, productivity, quality, ROI

For many managers, metalworking fluids are just another line item on a long list of tooling expenses. Similarly, operators often see them as just one more box on their daily PM checklist. This type of mentality often leads manufacturers to question whether or not they really need coolants at all. Do they really offer a true ROI, or are coolants just another necessary evil?

As any metal-cutting expert can attest, metalworking fluids are a critical part of the metal-cutting process. This is especially true if your goal is optimization. As an article from Production Machining states, manufacturers should view coolants as an asset or, better yet, a “liquid tool.”

Here are just a few benefits metalworking fluids bring to the cutting process:

Provide cooling for the work piece and tool by minimizing thermal stressing and brittle hardening of the tool bit
Remove chips from the cutting zone
Provide better surface integrity
Provide lubrication between tool and work piece
Prolong the life of the tool
Prevent corrosion of the work piece and tool
Prevent built-up edge (BUE)

All of these bullet points boil down to two bottom-line implications—quality and cost. As this white paper explains, failure to maintain proper coolant levels can lead to decreased blade life and premature and uneven wear of band wheels. Both of these issues can lead to increased maintenance and tooling costs, unplanned downtime, poor quality, increased scrap and rework, missed delivery dates, unhappy customers, and so on.

In the metal-cutting world, there are several different methods for applying coolants, as well as different coolant types. Flood coolants are the most widely used because, in most cases, they provide the best lubrication and cooling for work pieces. There are also spray, wax stick, and drip applications, but for the purposes of this article, the focus will be on flood coolants.

There are four different types of flood coolants, each have their own unique set of uses, advantages, and disadvantages. Like any other metal-cutting tool, choosing the right coolant plays a key role in achieving efficiency. To help industrial metal-cutting organizations make the right choice for their cutting operations, the LENOX Institute of Technology (LIT) provides the following overview:

Straight Oils. This type of lubricant is 100% oil and does not contain any water. It is mostly used to cut high alloys and other difficult-to-cut materials. Benefits include excellent lubricity, good rust protection and sump life, and easy maintenance. Drawbacks include poor heat dissipation, increased risk of fire, and hard-to-clean work pieces.

Soluble Oils. This is the most popular type of coolant and is used in light- to heavy-duty operations working with both non-ferrous and ferrous metals. It contains a mixture of water and oil, combining the lubricity of cutting oils with the cooling ability and economy of water. Benefits include good lubrication, improved cooling capability, and good rust protection. It also resists emulsification of greases and sideways oil. Disadvantages may include increased maintenance costs and susceptibility to rust problems, bacterial growth, oil contamination, and evaporation losses.

Semi-Synthetics. This coolant is synthetic-based but also contains oil (5 to 30%) and water. A “hybrid” of both soluble and synthetic fluids, it can be used in a wide variety of applications and is suitable for large cross-sections and cast-iron applications. Benefits include versatility, good microbial control, corrosion control, cooling, and lubrication. Other benefits include resistance to rancidity, easy maintenance, and long service life. On the downside, water hardness can affect stability and may cause misting, foaming, and dermatitis. This type of coolant may also emulsify oils and form residues.

Synthetics. These fluids are transparent, detergent-like compounds that contain no oil content. Considered to be the “cleanest” coolant type, synthetics are said to offer the best heat reduction, good corrosion control, and a longer sump life than all other coolant types. They can be used on a wide range of machining operations and are suitable for large cross sections. On the downside, they can lead to rust on the machine interior and may cause misting, foaming, and dermatitis. Because they lack oil, they also have reduced lubrication compared to other coolant types.