Investigated via a series of finite-element (FE) process simulations is the effect of diverse process variables on some selected nondimensional parameters characterizing the thermomechanical behavior of the strip in hot-strip rolling. Then, on the basis of these parameters an on-line model is derived for the precise prediction of roll force and roll power. The prediction accuracy of the proposed model is examined through comparison with predictions from a FE process model and also with measurements.
General, dimensionless expressions are derived for the parameters describing the thermo-mechanical behavior of the roll-strip system, on the basis of the boundary value problem associated with hot strip rolling. Then, it is shown that, by conducting process simulation with an integrated finite element process model, the dimensionless expressions may be transformed into various on-line models which may be applied to precision process set-up and control. The validity of the proposed approach is examined through comparison with predictions from finite element process simulation.KEY WORDS: finite element method; thermo-mechanical behavior; effective strain; non-dimensional analysis; hot strip rolling. (7) where DTϭT 2 ϪT 1 . Note that V 2 and T 2 may be precisely predicted from the FE process model described previously. It is to be noted that FЈ and PЈ represent the theoretical minimum (or very close to the theoretical minimum) of roll force and roll power, respectively, in the context of the assumed distribution of strip temperatures in the bite zone. Dimensionless Expressions for the Process ParametersLet us consider a 2-D boundary value problem for the analysis of the rigid-plastic deformation of the strip, with the process geometry given in (18) where K, C 1 , C 2 , are constants that possess the same unit as s , T, and ē , respectively. Note that C 1 and C 2 are introduced since s is governed by non-dimensional T and ē , and therefore, their values may be chosen arbitrarily. In the present investigation, C 1 ϭ1°C and C 2 ϭ1 rad/s are assumed.Let us define the average values of the flow stress for the hypothetical mode of rolling, as follows: Selecting xϭCs 0j , where C is a prescribed constant, it follows from Eqs. (17) and (24) that˜˜,˜, Vol. 45 (2005) where N S represents ē, ė /w, s/w, as well as V ĩ /Rw. Now, let us consider the boundary value problem for the analysis of heat transfer in the strip, with the process geometry given in Fig. 2. • energy balance equation: (39) where Ñ s represents all the basic non-dimensional fields, which are, ē, ē˜/w, s, s 0j , and T/T 1 .It may be deduced from Eq. (39) that any, reasonably selected, dimensionless parameters that describe the thermomechanical behavior of the strip should, in general, be influenced by eight independent dimensionless parameters appearing in the right hand side of Eq. (39). Note that all of them represent design variables (variables to be prescribed by an engineer), except b˜3, since q s is unknown.For the work roll, the boundary value problem associated with the steady-state thermal behavior of the roll may be given, with the definition sketch shown in (42) Assuming a uniform roll cooling system (water is uniformly sprayed on the entire roll surface, except the roll-strip interface), it may be deduced from the boundary value problem that (43), which involves nine variables, may be reduced to a dimensionless form with five independent dimensionless variables, since four independent units (temperature, force, length, and time) are identified ...
Investigated via a series of finite element process simulation is the effect of diverse process variables on some selected non-dimensional parameters characterizing the thermo-mechanical behavior of the strip in hot strip rolling. Then, on the basis of these parameters an on-line model is derived for the precise prediction of roll force and roll power. The prediction accuracy of the proposed model is examined through comparison with predictions from a finite element process model. KEY WORDS: hot strip rolling; roll force; roll power; on-line model; finite element process model.
The milling of highly flexible workpieces, such as thin-walled structures used in turbine blades, aerospace equipment, and jet engine compressors, requires vibration compensation to improve the quality of the workpiece surface. Vibration can be reduced by selecting appropriate cutting parameters. However, this approach reduces system productivity. This paper presents an active workpiece holder that controls the vibration of general computer numerical control machine tools. The proposed holder, which comprises a flexible guide mechanism, driver, and sensor, measures vibration and actively controls it using piezoactuators. A high-rigidity flexure mechanism was designed for the holder, and finite element method simulation and modal analysis were performed. Finally, the proposed system was fabricated, and experimental verification indicated that the system reduced vibration. The surface quality obtained using the controlled system was ∼50% better than that obtained using the uncontrolled system.
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