Effect of cutting conditions and tool geometry on process damping in machining

Process damping can be a significant source of enhanced stability in metal cutting operations especially at low cutting speeds. However, it is usually ignored in stability analysis since models and methods on prediction and identification of process damping are very limited. In this study, the effects of cutting conditions and tool geometry on process stability in turning and milling are investigated. The previously developed models by the authors are used in simulations to demonstrate conditions for increased process damping, and thus chatter stability. Some representative cases are presented and verified by experimental data and conclusions are derived

Robots in machining

Robotic machining centers offer diverse advantages: large operation reach with large reorientation capability, and a low cost, to name a few. Many challenges have slowed down the adoption or sometimes inhibited the use of robots for machining tasks. This paper deals with the current usage and status of robots in machining, as well as the necessary modelling and identification for enabling optimization, process planning and process control. Recent research addressing deburring, milling, incremental forming, polishing or thin wall machining is presented. We discuss various processes in which robots need to deal with significant process forces while fulfilling their machining task

Use of inverse stability solutions for identification of uncertainties in the dynamics of machining processes

Research on dynamics and stability of machining operations has attracted considerable attention. Currently, most studies focus on the forward solution of dynamics and stability in which material properties and the frequency response function at the tool tip are known to predict stable cutting conditions. However, the forward solution may fail to perform accurately in cases wherein the aforementioned information is partially known or varies based on the process conditions, or could involve several uncertainties in the dynamics. Under these circumstances, inverse stability solutions are immensely useful to identify the amount of variation in the effective damping or stiffness acting on the machining system. In this paper, the inverse stability solutions and their use for such purposes are discussed through relevant examples and case studies. Specific areas include identification of process damping at low cutting speeds and variations in spindle dynamics at high rotational speeds

Smart tool path generation for 5-axis ball-end milling of sculptured surfaces using process models

Efficient 5-axis milling of free form surfaces required smart parameter selection and tool path generation approaches. Current computer-aided manufacturing (CAM) technology offers limited flexibility and assistance for such purposes, where purely geometrical issues are considered. Consequently, the generated tool path may be off the high-performance milling parameters. In 5-axis milling, the efficient process parameter set usually vary along the tool path due to varying engagement conditions because of inherent reasons. In this paper, a novel approach is proposed for identification of efficient surface milling parameters according to the variation of cutting forces and stability along the tool path, and then continuously implementation of these parameters for smart tool path generation, obeying the geometrical requirements. The proposed approach is applied on representative cases relevant to industrial applications to demonstrate the benefits. It is shown that, use of process simulations in tool path planning and generation offers significant benefits in decreasing the total cycle time in 5-axis milling

Stability optimal selection of stock shape and tool axis in finishing of thin-wall parts

In 5-axis milling of thin-wall parts, flexibility of the in-process-workpiece (IPW) governs static and dynamic deflections. Thus, the stock shape left around the part and the tool axis are crucial for stability. This paper presents a methodology for selection of stock shape and tool axis for improved stability. Constant stock finishing is compared to variable stock, where a novel tool path generation approach is used to achieve the desired semi-finish shape. Effect of stock shape on IPW structure is simulated in FEM and benefits are shown. The proposed method is experimentally verified on case studies

Identification and modeling of process damping in milling

In this study, a practical identification method for process damping is presented for milling, and the information obtained from identification is used for modeling purposes. In the proposed approach, the process-damping coefficients in x and y directions are identified directly from the experimental stability limits. Then, they are used in identification of the indentation constant through energy balance formulation. The identified indentation constant is further used in modeling of process damping and estimation of stability limit for different cutting conditions and tool geometries. Milling tools with two different types of flank geometries, namely, planar and cylindrical, are considered in this study. The predictions are verified by time-domain simulations and experimental results. It is shown that the presented method can be used for identification and modeling of process damping in milling to determine chatter-free cutting depths at relatively low cutting speeds

The evaluation of pulmonary function and blood gas analysis in patients submitted to laparoscopic versus open nephrectomy.

The aim of this study was to assess the early postoperative pulmonary function and arterial blood gases in patients who have undergone open versus laparoscopic nephrectomy