Cutting Fluid System Dynamics: Modeling and Control
 
 

Aleksandar J. Filipovic | MS | 1998

If not treated prior to their disposal, industrial fluids have a deleterious effect on the environment. Treating these fluids is costly, and the resulting waste water affluent still may negatively impact the environment. Replenishing disposed fluids also incurs significant expense. One approach to reduce environmental impact and also lower fluid purchasing costs is to increase the time between fluid disposal events, i.e., increase the fluid life cycle.
 

This work is focused on increasing the life cycle of the cutting fluids by improving its maintenance strategy. An attempt was done on modeling and understanding the cutting fluid system dynamics. Cutting fluid data collected at the Ford Motor Company's transmission plant at Livonia were used in this research. Obtained data describe daily measures of the system properties and corresponding amount of additives used during the year 1996 in 27 different machining systems.

The dynamics of pH and oil concentration, as the most important fluid characteristics, and caustic and added oil, as corresponding additives, were modeled. Data Dependent Systems modeling theory was used as a mathematical tool. One input - one output Extended Auto-Regressive Moving Average models for pH - caustic as well as oil concentration - oil additions relations were developed. These models were used for understanding the dynamics involved into the system. It was recognized in all four modeled systems that pH decays faster than oil concentration. Also, it was seen that the pH of a small system decays slower than the pH of a large system.
 

In addition, two input - two output models that describe the relations of all four investigated parameters were generated. These models were used for generating the new maintenance policy. Theory of the Linear Quadratic Regulator was used for computing the optimal feedback gain matrix that generates the appropriate amount of inputs for reducing the variance of the measured system properties. It was assumed that the reduced variance of oil concentration will protect the oil molecule chains to be catastrophically destroyed. Also, the reduction in pH variance will maintain the mixture stability by preventing the additions of large amounts of caustic.
 

Both real maintenance policy and the proposed one were simulated for four different fluid systems. The simulation results showed that the significant reduction in the variances of the fluid measurements as well as reduction in the amount of additives was achieved. Therefore, this methodology can be used as a new way of looking, modeling, and controlling the cutting fluid systems. In addition, the similar procedure should be applied on any other environmentally related problem whose dynamics can be described by collecting the historical data.

If you have any comments or suggestions please e-mail jwsuther@mtu.edu.