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

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

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

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

Kinematic based selection of the workpiece location in robotic milling

The use of industrial robots in milling applications exhibits several issues such as low accuracy, low structural rigidity and kinematic singularities etc. The inverse kinematic solution of the robot i.e. positions and motion of the axes, strictly depends on the workpiece location with respect to the robot base. Therefore, workpiece placement is crucial for improved robotic milling applications. In this paper, the effect of workpiece location in robotic milling is investigated considering the robot kinematics. The investigation criterion is selected as the movement of the robot axes. It is aimed to minimize the total movement of either all axes or selected the axis responsible of the most accuracy errors. Kinematic simulations are performed on a representative milling tool path and results are discussed

Analytical methods for increased productivity in five-axis ball-end milling

Five-axis ball-end milling is a technology that many industries such as aerospace, automotive and die/mould employ for complex surface machining. Cutting forces, form errors and chatter vibrations are among the most important limitations in five-axis ball-end milling. Since they are generally not calculated beforehand, machining a product with five-axis ball-end milling may involve iterations on the machine tool due to process problems. In order to eliminate this, process models can be used. An analytical methodology is presented in this paper for modelling of five-axis ball-end milling. The method includes process models, and an interface between process models and CAM software. Process models for cutting force, form error and chatter stability predictions are used in the process planning stage to predict potential problems beforehand, and optimise machining conditions. The process models are presented and verified by experimental tests. The presented method is implemented in a simulation software, and applied in machining of industrial parts where productivity increase for example cases is demonstrated

Generalized cutting force model in multi-axis milling using a new engagement boundary determination approach

Simulation of cutting processes provides valuable insight into machining applications which have complex mechanics. In this paper, a generalized cutting force model is proposed for multi-axis milling operations. In the proposed model, the cutting tool envelope is defined either as revolution of a multi-segmented curve or using seven-parameter milling tool definition. The engagement between the cutting tool envelope and workpiece is calculated using a new, robust, and fast approach based on projective geometry. Exact chip thickness expression is used to simulate cutting kinematics for all types of edge geometries, such as serrated, variable pitch, and variable helix cutting flutes. The performance of the method proposed for determination of engagement boundaries is discussed through calculation time studies under several conditions. The predictions are verified and discussed through cutting experiments, conducted at multi-axis machining conditions using various cutting tool geometries