Metalworking fluid — whether a soluble oil emulsion, a semi-synthetic, or a fully synthetic coolant — performs several critical functions simultaneously at the cutting zone: cooling the tool and workpiece, lubricating the cutting action, flushing away chips, and protecting the machined surfaces from corrosion. Its ability to do all of these effectively depends on one thing: being mixed to the correct concentration. Too dilute, and the lubricating and corrosion protection performance degrades. Too concentrated, and the fluid is wasteful, potentially corrosive to non-ferrous materials, and irritating to operator skin. Getting the concentration consistently right, at every machine, every time a sump is filled, is where most CNC operations fail.
Why Manual Mixing Is Unreliable
The conventional approach to coolant preparation is manual: an operator measures a volume of concentrate, adds it to a volume of water in the sump or a mixing bucket, and uses a refractometer to check the resulting concentration. In principle, this produces a correctly mixed fluid. In practice, it produces highly variable results.
The first source of variation is measurement error. Operators under production pressure estimate rather than measure. The concentrate volume is poured by eye. The ratio varies between operators, between shifts, and between one filling and the next.
The second source of variation is the mixing order. Metalworking fluid emulsions must be prepared by adding concentrate to water — not water to concentrate — to form a stable emulsion. Reversing this order produces a concentrate-in-water emulsion rather than an oil-in-water emulsion, which has different stability, appearance, and performance characteristics. This error is common and difficult to detect by visual inspection alone.
The third source of variation is top-up practice. As sumps are used, water evaporates and the concentration of the remaining fluid increases. Top-up with plain water lowers the concentration; top-up with mixed fluid of the nominal concentration restores it. In practice, top-up practice is inconsistent, and the concentration in working sumps often bears little relationship to the nominal target concentration.
The Consequences of Incorrect Concentration
Under-concentration — fluid that is too dilute — reduces lubrication performance at the cutting zone, increasing tool wear rates and surface roughness on the machined workpiece. It also reduces the corrosion inhibitor concentration, allowing rust to form on machined surfaces, the sump, and the machine guarding. Most significantly, under-concentrated fluid is more susceptible to bacterial contamination. Metalworking fluid sumps are warm, nutrient-rich environments that support bacterial growth rapidly when the biocide and pH buffer concentrations fall below effective levels. A contaminated sump produces odour, reduces fluid life, and creates a skin contact hazard for operators.
Over-concentration — fluid that is too rich — wastes concentrate cost, which is significant when multiplied across multiple machines and frequent top-up events. At very high concentrations, some metalworking fluids become corrosive to aluminium and magnesium alloys. Foam generation increases. Residues on machined parts become more difficult to clean. Operator skin contact with over-concentrated fluid increases dermatitis risk.
Inline Proportional Dosing as the Solution
The Dosatron inline proportional dosing unit eliminates manual mixing variability by automating the concentrate-to-water ratio at the point of mixing. The unit installs in the water supply line feeding the sump or mixing station. As water flows through the Dosatron, it draws a fixed proportion of concentrate from a stock container and injects it directly into the water flow. The ratio is determined by the Dosatron’s setting and is maintained proportionally regardless of the water flow rate — whether the sump is being filled quickly or slowly, the concentration in the mixed fluid is the same.
Because the Dosatron is water-powered, it requires no electricity, no pump controller, and no operator measurement. The operator opens the water supply, the Dosatron doses the concentrate automatically, and the correctly mixed fluid fills the sump. There is no separate concentrate addition step, no risk of reversed mixing order, and no opportunity for measurement error.
For CNC machining operations in Malaysia running multiple machines with different coolant requirements, a Dosatron can be configured for each machine’s nominal concentration — different models cover different ratio ranges — providing consistent, correctly mixed coolant at every sump without the variability and operator dependency of manual mixing.
To discuss Dosatron sizing for your coolant concentration requirements and sump volumes, contact us at info@autoflotechnology.com.