An analytical design method for milling cutters with nonconstant pitch to increase stability, part 1: Theory

Chatter vibrations result in reduced productivity, poor surface finish and decreased cutting tool life. Milling cutters with nonconstant pitch angles can be very effective in improving stability against chatter. In this paper, an analytical stability model and a design method are presented for nonconstant pitch cutters. An explicit relation is obtained between the stability limit and the pitch variation which leads to a simple equation for determination of optimal pitch angles. A certain pitch variation is effective for limited frequency and speed ranges which are also predicted by the model. The improved stability, productivity and surface finish are demonstrated by several examples in the second part of the paper

Machining stability and machine tool dynamics

Machining is a common manufacturing process in industry due to its high flexibility and ability to produce parts which excellent quality. The productivity and quality in machining operations can be limited by several process constraints one of which is the self-excited chatter vibrations. Under certain conditions, the process may become unstable yielding oscillations with high amplitudes which result in poor surface finish and damage to the cutting tool, part and the machine tool itself. Stability analysis of the dynamic cutting process can be used to determine chatter-free machining conditions with high material removal rate. Since chatter is a result of the dynamic interactions between the process and the structures both cutting and machine tool dynamics are important elements of the stability analysis. In this paper, methods developed for stability analysis of cutting processes and machine tool dynamics will be presented. Implications of these methods in the selection of process parameters and machine tool design will be also discussed with example applications

An analytical design method for milling cutters with nonconstant pitch to increase stability, part 2: Application

Chatter stability in milling can be improved significantly using variable pitch cutters. The pitch angles can be optimized for certain chatter frequency and spindle speed ranges using the analytical method presented in the first part of this two-part paper. In this part, the improvement of productivity and surface finish are demonstrated in three example applications. It is shown that chatter stability can be improved significantly even at slow cutting speeds by properly designing the pitch angles. A roughing example demonstrates substantially reduced peak milling forces which allows higher material removal rate

Analytical models for high performance milling. Part II: process dynamics and stability

Chatter is one of the most important limitations on the productivity of milling process. In order to avoid the poor surface quality and potential machine damage due to chatter, the material removal rate is usually reduced. The analysis and modeling of chatter is complicated due to the time varying dynamics of milling chatter which can be avoided without sacricing the productivity by using analytical methods presented in this paper

Plant genetic reseources: effective utilization

Characterizing better understanding the genome organization and differentiating identity of genotypes based on their morphology and genome characteristics are vital determinants in their commercialization, management of germplasm repositories, and genetic conservation. Morphoagronomic characterization of plants is not always feasible or sometimes labor intensive. Employing chloroplast, mitochondrial, and nuclear genome diversity using molecular biology tools will enhance the effectiveness and efficiency of revealing identity differences between genotypes. Using organelle and nuclear genome diversity can also answer a broad range of genetic, evolutionary relationships, and ecological questions

Analytical models for high performance milling. Part I: cutting forces, structural deformations and tolerance integrity

Milling is one of the most common manufacturing processes in industry. Despite recent advances in machining technology, productivity in milling is usually reduced due to the process limitations such as high cutting forces and stability. If milling conditions are not selected properly, the process may result in violations of machine limitations and part quality, or reduced productivity. The usual practice in machining operations is to use experience-based selection of cutting parameters which may not yield optimum conditions. In this two-part paper, milling force, part and tool deection, form error and stability models are presented. These methods can be used to check the process constraints as well as optimal selection of the cutting conditions for high performance milling. The use of the models in optimizing the process variables such as feed, depth of cut and spindle speed are demonstrated by simulations and experiments

Analytical modeling of chatter stability in turning and boring operations - Part II: Experimental verification

In this part of the paper series, chatter experiments are conducted in order to verify the proposed stability models presented in the first part (Ozlu, E., and Budak, E., 2007, ASME J. Manuf. Sci. Eng., 129(4), pp. 726–732). Turning and boring chatter experiments are conducted for the cases where the tool or the workpiece is the most flexible component of the cutting system. In addition, chatter experiments demonstrating the effect of the insert nose radius on the stability limit are presented. Satisfactory agreement is observed between the analytical predictions and the experimental results

Optimization of 5-Axis milling processes based on the process models with application to airfoil machining

5-axis milling is widely used in machining of complex surfaces such as airfoils. Improper selection of machining parameters may cause low productivity and undesired results during machining. There are several constraints such as available power and torque, chatter stability, tool breakage etc. In order to respect such constraints proper machining parameters should be determined. In this paper, methodologies for improving 5-axis milling processes are presented. Selection of machining parameters is performed using process simulations. The developed methodologies are presented on an example airfoil

Thermomechanical modeling of orthogonal cutting including the effect of stick-slide regions on the rake face

An orthogonal cutting model including the primary and secondary shear zones is pre-sented in this study. The primary shear zone is modeled by a thermomechanical model where the rake contact is represented by two regions of respectively sticking and sliding friction. The model is compared with experimental results in terms of shear stress, shear angle, and cutting force predictions. Overall a good agreement is observed

Experimental analysis and modeling of orthogonal cutting using material and friction models

In this study, a process model for orthogonal cutting processes is proposed. The model involves the primary and secondary deformation zones. The primary shear zone is modeled by a Johnson-Cook constitutive relationship and a shear plane having constant thickness. The secondary deformation zone is modeled semi-analytically, where the coefficient of friction is calibrated experimentally. The cutting forces predicted using the calibrated sliding friction coefficients are in good agreement with the measurements. The experimental investigation of sliding friction coefficients also show promising results for the proposed model, which is still under development