The pressures of maintaining tighter and tighter tolerances and finishes on machining processes have forced engine rebuilders to stay on the cutting edge in all aspects of engine building. In order to produce the best performing engines with tight tolerances and finishes, CNC machines require cutting fluids to perform at the highest levels.
You might think a fluid is a fluid is a fluid, but you’d be wrong. Fluids used for cutting processes today have different chemical makeups, are used for different materials, and are different for certain machines or processes. Using the right fluid for the right application is just as important as any other aspect of rebuilding an engine. Here are some key things to note about cutting fluids the next time you’re honing or boring a block.
You might be asking, with today’s advanced CNC machines, why are fluids even needed? Well, back during the origins of cylinder honing, it was actually in many cases done dry. However, it wasn’t long before people realized there were better ways to do it. Today, there are numerous types of fluids available depending on your application and process, and the advancements within these fluids allow for excellent cutting.
The biggest reason these fluids are necessary is lubricity, which is the measure of the reduction in friction and wear by a lubricant. Without lubricity, the material you’re cutting could chip, get too hot and crack, or wear down your abrasive much too fast. The shavings you create can also get stuck on your work piece and in the block itself allowing for bigger problems down the road.
“Honing fluid not only cools the part you are honing thus creating less bore distortion, but it acts as a lubricant while the abrasive is cutting the material you are honing,” says Ed Kiebler of Rottler Manufacturing. “It would be impossible to hone some materials without the cooling and lubrication factors of a coolant or honing fluid. It also helps flush away tiny chips that could damage the surface finish that piston rings ride on. As the demand for better finishes and more precise finishes has increased, so has the need for cutting fluids. It would be virtually impossible to obtain the finishes required by ring manufacturers without a top quality fluid.”
Fluids today help significantly increase tool life and surface finish while providing excellent heat dissipation and chip evacuation. This allows metal to flow and not adhere to the tools, which favors increased speeds, feeds, and depths of cuts, resulting in improved productivity.
“Increased tool life enables engine builders to not only improve their tool usage but also improve their cutting speeds, their cutting times, and their accuracy,” says Mike Ditzel, performance racing product specialist for Hangsterfers Laboratories. “It’s very important when machining that you have a straight, round, consistent finish, and consistent size that you’re leaving for the hone. That’s what makes or breaks that operation. You want to start off right to minimize your issues down the road when you’re honing.”
Lubricity is also important when we look at the movement from conventional abrasives to super abrasives. These fluids keep the bond system from interacting with the work piece.
“Oftentimes that interaction revolves around electrochemical interactions that lead to what we call rewelding or pick up that gets on the abrasive,” says Scott Alcock, product manager of abrasives, tools and cutting fluids for Sunnen. “It’s where a piece of the wall has embedded or interacted with the stone in such a way as to stick to the stone.”
For those reasons, lubricity and continuing to keep the stones clean and cutting efficiently are the primary factors for utilizing fluids during cutting.
The cutting fluids in today’s marketplace can be broken down into several groups. Mineral-based coolants like honing oil and cutting oils, water-based synthetic and semi-synthetic coolants for both honing and boring, and water-soluble coolants and cutting fluids.
“We prefer water-based coolants because of the ability of water to absorb heat from the point of contact and carry it away,” Kiebler says. “Thus, after honing a cylinder it is still cool to the touch and you have no cool down effect. The cylinder and block doesn’t heat up causing the cylinder to shrink and the operator to have to re-hone to size after the cylinder has cooled.”
In general, water-based coolants are easier to dispose of as well, and are easier on the operator and on your cleaning systems.
“Once upon a time, the industry used mineral-based honing and cutting fluids with more sulfur in them to help with lubricity,” Kiebler says. “Today, water-based honing and cutting fluids have proven to be easy on the environment and on operator’s skin and noses. Water-based fluids also have rust inhibitors to prevent blocks from rusting and anti-bacterial properties to prevent fungus from growing in the coolant tanks.”
While the movement to water-based fluids has allowed for a much wider range of coolants, oil-based fluids still work well today.
“Oil is still our primary go-to coolant because it has the most lubricity,” Alcock says. “We always try to lead people towards an oil base if possible, whether it be petroleum, ester or a vegetable base. That kind of product has a lot of lubricity. It has, with the additives in it, the ability to keep pick up from becoming a problem. Ester-based or vegetable-based products have two big downsides and a couple upsides. The downsides are generally the cost and the fact that they do not last as long. They’re more prone to oxidation or going rancid, whereas a petroleum oil is generally not going to oxidize in our lifetime. The upsides of the vegetable and the ester base tend to be slightly higher lubricity at almost any viscosity. They also tend to be more likely to stick to the wall of the work piece, and the benefit there is that you keep that lubricity right where you want it.”
While petroleum oils offer benefits to the cutting process, they can be hard to sell or get your hands on in various parts of the country due to them being volatile organic compounds (VOCs). This parallels a trend toward safer products in general when it comes to cutting fluids.
“Years ago, a lot of the technologies were functional, but down and dirty and maybe not as cautious to the environment or the human body,” Ditzel says. “Today’s vegetable-based technologies are free of boron, chlorine, formaldehyde, secondary amines and other substances of very high concern. That’s what is different about today’s technology, being conscious of these ingredients with our environment, health and safety in mind.”
Cutting fluids today also have extreme pressure additives that push the product above and beyond in terms of performance, replacing previous ingredients without compromise.
The other thing to consider when selecting a cutting fluid is what type of abrasive you’re using. Depending on the hones – CBN honing stones, diamond, aluminum oxide, silicone carbide – you want to pay attention to make sure you have a compatible lubricant.
“There are copper-containing materials and some aluminums which stain depending on the cutting fluid, and specifically whatever anti-galling agents that you have in there, because sometimes they’re fairly aggressive and can actually attach to the work piece and cause a little bit of corrosion,” Alcock says. “We add anti-staining agents to keep that from happening, but it certainly is possible. In cast iron, most people use the semi-synthetic, and if you’re doing aluminum, you’re probably going to use the full synthetic.”
As many of these fluids are multi-functional, the biggest differences in similar fluids will be seen in viscosity.
“That depends on how aggressive you are and how much material you’re moving,” Ditzel says. “A lot of it is a personal preference too when it comes to a viscosity. It depends on the machine and the pressure.”
Boring and Honing
While many fluids are multi-functional, cutting fluids for boring or machining do have differences from those used in honing. Honing is a unique operation and needs certain amounts of lubricity and the point of contact with the material being honed and the abrasive. A lack of lubricity or too much of a good thing will cause all sorts of problems.
“The wrong fluids can cause excessive abrasive wear causing your cost of honing to double or triple,” Kiebler says. “They can also cause an abrasive or honing stone to glaze or quit cutting due to too much lubricity.”
Typically, in most cases, when you shift over to honing you’re using straight oils as your cutting fluid, and the differences there is what you’re trying to achieve when honing.
“You’re looking for a lubricant that will cool and flush the fines from the work piece while lubricating the abrasive tool,” Ditzel says. “You’re trying to accomplish a lot of things at once. There are a variety of viscosities depending on the application and whether you’re rough honing or finish honing, or depending on where you are in the process and the finish you’re looking for.”
In the racing world, they are honing aluminum blocks with sleeves. In the standard automotive world, it’s a lot of cast iron. The right fluids depend on the material and the application.
Filtration is Key
Once you’ve met all these other requirements, filtration is the key to maintaining size and finish as those metal fines contaminate your fluid. It doesn’t matter how good or how right it is if you don’t keep it clean. You’re going to shoot yourself in the foot without filtration.
“Newer machines are all equipped with usually a minimum of two stage filters and some three,” Ditzel says. “It’s important when you have a used machine or you’re switching oils that the machines are cleaned out properly. If you’re going to switch from one lubricant to another it’s very important that that machine is flushed properly. It’s not something that you just want to empty and fill because you’re going to have a lot of fines and a lot of residues in hard-to-get-to areas. If you have high-pressure pumps you have to clean those pumps out because they’re holding gallons of fluid in them themselves.”
Hangsterfers has a product called Ozonic 203 that is especially good for machine tool flushing where machines have an existing lubricant that could be stained, varnished, or oxidized and needs to be replaced.
“That’s something I do if I call on somebody who’s going to switch to my product or another one of mine or a competitors product,” he says. “I’ll always treat it as if I need to get it restored to a new condition. It’s important to clean in between switching from one product to another.
Houston, We Have a Problem
In keeping with the theme of tight tolerances and finishes, mistakes won’t be accepted by your engine customer. However, we’re all human and mistakes happen. During a cutting process it is imperative that the operator knows the operation and the signs of something going wrong.
“Most of the issues are really quite clear when they happen,” Alcock says. “The sound of the operation changes. The surface finish that they’re trying to achieve changes. Whether they can continue to keep it cutting under the normal operating parameters. All of that changes and changes relatively quickly, so operators would notice it almost immediately. It is a sign of a set up that’s not particularly good when that happens. It’s not a common thing because most of the people who have been doing this for a while know the parameters they need to maintain. But certainly a cutting fluid that does not have the lubricity, doesn’t have the anti-galling agents in it – those types of coolants could be more prone to pick up or rewelding.”
If pick up or rewelding does occur during your machining process, you’re going to start creating big scratches in the bore.
“That’s a case where either you didn’t have the volume to flush the chips out or you didn’t have a coolant that had enough anti-galling agents in it or high enough lubricity, or it could be that you were pushing the abrasive either way too hard or way too lightly,” Alcock says.
Either case will actually generate the same problem, which is that the bond in the abrasive gets too close to the wall of the work piece, and when there’s no space between the wall of the work piece and where the bond is, that doesn’t allow for chips to get through, so they just stick.
“Those are cases where you will have to go through a little bit of troubleshooting to say, ‘Did I have the wrong coolant or the wrong volume? Did I have the wrong parameters for how fast I was trying to feed into the wall?’” he says. “Those are all things that you just have to troubleshoot to figure out which problem was actually existing.”
There are other problems that can arise when you start to generate a lot of heat. That’s an indication that you’re lacking lubricity.
“If it’s a water base you want to up the concentration,” he says. “If it’s an oil base you may have something where the oil has broken down or it was too low of viscosity to begin with.”
Assuming someone knows what they’re doing and has done a good hone in the past, there’s really little chance that they wouldn’t recognize an issue is present. However, causing the stone to wear down too fast is a hard issue to recognize.
“In the automotive world, the people who see that are going to be the production engine remanufacturers (PER),” Alcock says. “Many of the custom engine builders and racing folks don’t actually go through enough abrasive to notice that it’s wearing any faster. Those folks are looking for the catastrophic failures whereas the PER is more concerned about how many dollars of abrasives they’re buying compared to how much the coolant costs. They’re going to look for that lowest cost per part.”
As you can see, a fluid isn’t just a fluid. There are a lot of different scenarios and things to consider when choosing your cutting fluids. Make sure you’re identifying what is most important to you and the engine results you’re trying to get. Happy honing!
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