How many times a day do you come across something made out of metal? Think of all the metal parts in the structure of your home. Think of the metal handles you pull when you open your bathroom cabinet drawers or the the door knobs you turn when you close the door. Think of all the appliances you use in your kitchen and all the metal parts they are made of. Think of all the metal parts in the car you drive or the millions of metal parts in every commercial airplane when you fly. The grand majority of these metal parts for all these types of products are machined, which means they are cut to shape. Even those that are cast or molded usually undergo some secondary machining operation to finish the part. Despite increased usage of plastics (of which many are also machined) and composite materials and despite the advances in additive manufacturing processes and 3D printing, machining is still used to make the vast majority of metal parts in all high volume industries.
How are these metal parts machined? The tools that cut into metal must be physically harder than the metals being machined. These tools are often on automated machines e.g. CNC (Computer Numeric Control) that are driven by code fed in through a computer program in which the part has been designed. As the cutting tool carves into the part being machined, a constant stream of fluid is needed to be streamed at the surface of contact between the two. This fluid serves two main purposes: cooling and lubricating.
Why does the cutting surface needed to be cooled? As the tool carves into the metal part (which is either rotating on a lathe, moved around on a mill, or being drilled), there is a tremendous amount of heat generated through friction. This heat translates into temperature increases at the cutting surface which changes the control and accuracy of the cut. A constant stream of coolant channels the heat to the fluid and helps limit these temperature increases. Why does the cutting surface need to be lubricated? The friction resulting from metal on metal contact creates high forces that are imparted upon the cut part and the tool. These forces can cause damage to the part and to the cutting tools. In addition, since the cutting tools are made of a special hardened alloys, they are often expensive and their replacement comprises one of the primary running costs of these machines. Besides the direct damage these forces create, they also cause heat generation. Applying a lubricant can decrease the magnitude of these forces and therefore the amount of heat also being generated.
For nearly the past century, the primary cutting fluid used in high speed machining operations is an emulsification of oil and water. These fluids currently have the following challenges:
1. Since they are recirculated, they must be constantly monitored for pH or contaminants which can either adversely affect the function of the fluid or create damage in the cutting process.
2. Because the types of oil used in the emulsification are organic, they often become contaminated with bacteria. Since the types of bacteria that contaminate these oils can double as quickly as every 30 minutes, they can quickly turn the cutting fluid rancid, and accelerate corrosion on the surface of the parts being cut.
3. The fluids need to filtered and cleaned of any metal particulate on a regular basis.
4. After a certain amount of time or utility, the fluids need to be disposed in specific manners consistent with the composition of the fluid, the EPA, and local regulations.
5. These emulsified coolants inevitably produce an aerosol that makes human contact and have been shown in many large studies to create respiratory and skin ailments in machining workers.
In comes Fusion, a company founded and spun out by Professor Steven Skerlos, an authority on metal machining and Director of Sustainability Education Programs in the College of Engineering at the University of Michigan.
Fusion has developed and patented a simple and elegant technology which puts Carbon Dioxide in a supercritical state between a liquid and gaseous phase and uses it in place of standard machining fluids. Their supercritical CO2 results in more effective cooling which can allow for faster metal machining translating in greater throughput and productivity. Because it dissipates into Carbon Dioxide gas, there is no processing and disposal needed for the fluid resulting in a more cost effective coolant. Since it dissipates into carbon dioxide, it is clean and does not create a health hazard to factory workers. And since the Carbon Dioxide gas that is sourced for Fusion’s technology is captured before emission and recycled for use as a metal working fluid, it does not add to the environmental carbon footprint.
Fusion’s technology is a great fit for us since it is a material-based technology that is elegant in its simplicity and has a material impact on industrial productivity, environmental cleanliness, and worker’s health. We are glad to join their “revolution” they are leading in the machining industry.