Process simulation for 5-axis machining using generalized milling tool geometries

Multi-axis machining (especially 5-axis machining) is widely used in precision machining for automotive, aerospace and die-mold manufacturing. The goal in precision machining is to increase production while meeting high part quality needs which can be achieved through decision of appropriate process parameters considering machine tool constraints (such as power and torque), chatter-free operations and part quality. In order to predict and decide on optimal process parameters, simulation models are used. In the literature, individual tool geometries for multi-axis machining are examined in detailed with different modeling approaches to simulate cutting forces. In this study, a general numerical model for 5-axis machining is proposed covering all possible tool geometries. Tool envelope is extracted from CAD data, and helical flutes points are represented in cylindrical coordinates. Equal parallel slicing method is utilized to find cutter engagement boundaries (CEB) determining cutting region of the tool surface. for each axial level in the tool axis direction. For each level uncut chip thickness value is found and total forces are calculated by summing force values for each point along the cutting flutes. For arbitrary cases forces are simulated and obtained results are experimentally verified

Mechanical and dynamical process model for general milling tools in multi-axis machining

Multi-axis milling operations are widely used in many industries such as aerospace, automotive and die-mold for machining intricate sculptured surfaces. The most important aspects in machining operations are the dimensional integrity, surface quality and productivity. Process models are employed in order to predict feasible and proper process conditions without relying on empirical methods based on trial and error cutting and adaptation of previous experiences. However, previously developed process models are often case specific where the model can only be employed for some particular milling tools or they are not applicable for multi-axis operations. In many cases, custom tools with intricate profile geometries are compatible with the surface profile to be machined. On the other hand, for more robust and stable cutting operations, tools with wavy cutting edge profiles and varying geometric edge distributions are utilized. In this thesis, a complete numerical mechanic and dynamic process model is proposed where the tool is modeled as a point cloud in the cylindrical coordinates along the tool axis. The tool geometry is extracted from CAD data enabling to form a model for any custom tool. In addition, the variation in the cutting edge geometry, where serrated and variable helix/pitch cutting edges can be adapted for any milling tool is taken into account. The cutting engagement boundaries are identified numerically using a Boolean intersection scheme. Moreover, a Z-mapping algorithm is integrated in the proposed multi-axis mechanistic force model to predict cutting forces for a continuous process. As for the multi-axis milling dynamics, previous single-frequency stability models are extended to encompass all possible tool geometries taking the time delay variation introduced by irregular cutting edge geometries. The proposed model is experimentally verified with different tool geometries investigating cutting forces and also predicting the stable cutting conditions

Machining strategy development in 5-axis milling operations using process models

Increased productivity and part quality can be achieved by selecting machining strategies and conditions properly. At one extreme very high speed and feed rate with small depth of cut can be used for high productivity whereas deep cuts accompanied with slow speeds and feeds may also provide increased material removal rates in some cases. In this study, it is shown that process models are useful tools to simulate and compare alternative strategies for machining of a part. 5-axis milling of turbine engine compressors made out of titanium alloys is used as the case study where strategies such as flank milling (deep cuts), point milling (light cuts) and stripe milling (medium depths) are compared in terms of process time by considering chatter stability, surface finish and tool deflections

Machining strategy development and parameter selection in 5-axis milling based on process simulations

In modern machining applications, with the developments in computer aided manufacturing (CAM) technology, predictive modeling of milling operations has gained momentum. However, there is still a big gap between CAM technology and process modeling which limits their use in machining strategy development and parameter selection. In this paper, an approach is proposed for use of process models and simulation tools in this direction. Cutting force and stability simulations are used in identification of feasible regions of cutting parameters and comparison of machining strategies for productivity. Cutting force simulation throughout a toolpath is performed through extended Z-mapping approach, where a previously developed generalized cutting force model is utilized. Stability diagrams are generated in frequency domain. Dynamic programming (DP) approach is adapted for machining strategy comparison, which takes into account several constraint curves such as chatter stability, cutting torque, spindle power, tool deflection, and surface roughness. The proposed approach applied on a case study to demonstrate the use of process models in machining strategy and parameter selection in 5-axis milling

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

Increasing productivity in die machining through process modelling

Die manufacturing is a very critical part of the overall production chain in many industries. Depending on shape and size of a die, machining time can be very time consuming. Furthermore, since usually one die is manufactured, the chance for testing is very limited. Machining processes in die manufacturing can be limited by many factors. Process models can be used in order to select process conditions which will yield the required quality in the shortest possible time. In this study, force, tool deflection and chatter models are developed for different materials and tool geometries used in an automotive die shop. Tool geometries are modelled and frequency response functions (FRFs) are measured for different combinations of machine tools and cutting tools for the chatter stability analyses. Using the developed models, process parameters are modified and their effects on productivity are demonstrated