Cutting Fluid: The “Invisible Hero” in Cylinder Block and Head Machining

In the production workshop of cylinder blocks and heads, when CNC machines run at high speed, a transparent or milky – white liquid continuously sprays between the cutting tool and the workpiece. This is cutting fluid. It may seem ordinary, but it is an “invisible hero” that ensures the machining accuracy and efficiency of cylinder blocks and heads. Without it, the oil passages of aluminum alloy cylinder blocks might be extremely rough, the mating surfaces of cast iron cylinder heads would be covered with scratches, and cutting tools would quickly become useless due to overheating. Therefore, cutting fluid plays a crucial role and is indispensable.

During the machining of cylinder blocks and heads, the friction between the cutting tool and the workpiece is extremely fast. For example, when milling the mating surface of a cylinder head, the rotational speed of the cutting tool can reach more than 3000 revolutions per minute, and the local temperature can instantly soar to 600°C. High temperatures can soften the cutting edge of the tool and cause the workpiece to deform due to heat. Cutting fluid, through continuous spraying, uses water – based liquid to quickly absorb heat, and at the same time, a small amount of evaporation takes away excess heat, stably controlling the temperature below 150°C, thus protecting the accuracy of the tool and the workpiece.

When machining deep oil passages in cylinder blocks, the cutting tool is prone to “jamming” due to high frictional resistance. The lubricating components in the cutting fluid will form an oil film, changing dry friction to wet friction, and reducing the friction coefficient from 0.3 to below 0.05. This not only makes the roughness of the machined hole wall meet the standard (from Ra6.3 to Ra1.6), but also extends the service life of the tool by 3 – 5 times. A tool that originally became useless after machining 20 cylinder heads can machine more than 100.

If the aluminum chips and cast iron powder generated during machining remain, they will scratch the workpiece or cause “repeated cutting”. Cutting fluid flushes the workpiece and the cutting tool like a water flow, carrying the chips into the filtration system. Especially, it can flush out the fine debris deep in the oil passages of the cylinder block, avoiding affecting subsequent machining.

After machining, cylinder blocks and heads need to be stored and are prone to oxidation and rust when exposed to the air. The rust – proof components in the cutting fluid will form a micron – level protective film, allowing aluminum alloy cylinder blocks to be stored for 72 hours without oxidation and cast iron cylinder heads to be stored for 120 hours without rust, preparing them for assembly.

Cutting fluid is a “compound solution” with multiple components working together. The base fluid accounts for 80% – 95%. Water – soluble cutting fluid is based on water and is suitable for aluminum alloy machining; oil – soluble cutting fluid is mainly based on mineral oil and is suitable for cast iron. Lubricants account for 5% – 15%. Synthetic esters have strong stability and are not easy to decompose at high temperatures, so they are the current mainstream. Rust inhibitors account for 2% – 5%, and there are special types for ferrous metals (such as phosphate esters) and non – ferrous metals (such as benzotriazole) to avoid material corrosion. Preservatives account for 0.1% – 0.5%, inhibiting the growth of bacteria and extending the service life of cutting fluid to 3 – 6 months. Defoamers only account for 0.01% – 0.1%, preventing foam from affecting the spraying effect.

Moreover, cutting fluid is “custom – made”. Water – soluble cutting fluid with low corrosion and high lubrication is used for machining aluminum alloy cylinder blocks; for cast iron cylinder heads, a type with high rust protection and strong cleaning ability is selected. When rough milling, the focus is on cooling, so the water content is high; when fine boring oil passages, the focus is on lubrication, so the proportion of lubricants is increased. It is precisely this precise adaptation that makes cutting fluid an indispensable aid in the machining of cylinder blocks and heads.