Complex Workpiece Geometries Research Articles

Predicting cutting forces in 5-axis milling of sculptured surfaces directly from a CAM tool path

The present work is motivated by the fact that for predicting the cutting forces which arise under various cutting conditions, workpiece-tool pairs, machining depths and tool orientation, numerical methods are slower and less efficient than analytical methods. In addition, recent developments in Computer Assisted Machining (CAM) techniques have enabled analytical methods to be applied even with complex workpiece geometry. The method developed in this paper is both practical and inexpensive. It is based on an analytical method using only few approximations and uses the toolpath file as the main information source for the machined surface. This method takes into account both tool position and orientation in a 5-axis finishing milling process with ball-end cutter, independent of the machining parameters and the couple of tool-workpiece materials. However, this calculation must be supplemented by a mechanistic approach in order to obtain results equivalent to those of the experiment. The result is a model which is implemented in a program allowing the visualization of the cutting forces along a given path. The program is easy to apply in practical cases with the possibility of implementing it in a machining software.

Flexible telemanipulation based handy robot teaching on tape masking with complex geometry

Abstract Traditional robot teaching methods are cumbersome, tedious and difficult to scale for high-mix low-volume applications. The tape masking, a common process for surface protection before plasma spraying, spray painting and shot peening, is one of those domains where robotic automation lacks flexibility and reliability due to the complexity in task. Fortunately, it is still within the grasps of human-robot collaborative systems. This work presents a telemanipulation-based robot teaching framework that is able to let the robot manipulator cope with the taping tasks with complex workpiece geometries. The proposed framework allows quick calibration, variable motion mapping, and indexing so that the operators can easily set up and guide the robotic taping system to cover the tapes onto the layers and grooves of different workpieces. This framework enables the operators to change the motion mapping scale for both large-scale guidance and fine motion dexterous manipulation. Meanwhile, an indexing function makes it possible for the operators to re-map their poses from the edges of their comfortable regions. A portable VR system is applied in the telemanipulation system. With its six DoF motion precisely measured in real-time, the proposed motion remapping algorithms enable the operators to directly guide the robot in their selected scales. Experimental results show that the proposed framework facilitates robot programming on the manipulation of the complex workpieces that have multi-layer surfaces and grooves in between. It also reduces the teaching time comparing to other methods. This system and method improve teaching efficiency and convenience, which has potential value to be deployed in manufacturing.

Effect of the Relative Velocity Between Electrodes in High Speed Wire EDM (HSWEDM)

High Speed Wire EDM (HSWEDM) is a technology that differs from conventional wire EDM in many aspects like polarity, pulse duration, discharge formation, working medium, wire material and speed. The comparably high relative velocity between the wire and the workpiece is one of the key characteristics of HSWEDM. Its main effect lies in improved flushing that allows high cutting rates to be achieved by this technology. In this study, discharge locations and cutting speeds were determined. Additionally, traces of single discharges on the workpiece surface were measured using a profilometer. Results show that flushing effects tend to vary significantly depending on the wire direction of the (vertically) reciprocating wire. Also, by mapping the number of discharges, considerable differences of the machining efficiency were found within complex workpiece geometries. However, the high wire velocity also affects the formation of the discharges as (other than in conventional wire EDM) relative motion during a discharge cannot be neglected. Additionally, indications of electrochemical material removal could be observed.

Modeling and simulation of industrial waterjet stripping for complex geometries

Industrial waterjet stripping/cleaning is a prime example of a dull, dirty, dangerous manufacturing process that is ripe for automation, yet it remains a manual task in most instances due to complex workpiece geometry and/or low-volume, high-mix production. Recently developed automated tool trajectory planning algorithms and collaborative path planning frameworks offer a potential solution but are of limited use without corresponding process models and simulation tools to evaluate toolpath quality. Existing process models do not consider the spray impingement angle or the cumulative effect of successive tool passes—both of which are inevitable when spraying geometries that possess concave and/or discontinuous features. This research proposes a novel process model that includes impingement angle and accounts for the cumulative, ablative nature of the process. It also develops a simulation algorithm that applies this model to complex geometries while considering shading effects caused by protrusions and overhangs. Model parameters are determined via a design of experiments approach and nonlinear regression, and verification experiments on complex test parts show good agreement between predicted and measured results. Paired with the aforementioned trajectory planning tools, this research represents a complete robotic process planning solution for waterjet stripping/cleaning of complex parts in high-mix, low-volume manufacturing.

A novel command generation paradigm for production machine systems

Abstract This paper presents a new command generation technique titled VEPRO for computer controlled production machinery. In this method, the tool trajectory is described by a high-level scripting language that enables parametric representations of complex work-piece geometries. The interpreted script is then employed to generate the interpolation data required to compute a tool trajectory that is subjected to a number of kinematic constraints. A real-time interpolator is employed to provide the position commands required by each motion controller in a synchronous fashion. As a proof of concept, the proposed method is emulated on a PC using Python scripting language. The performance of the paradigm is rigorously assessed via two test cases involving different manufacturing techniques (e.g. pocket milling and 3D printing). Through the experimental results, the paper illustrates that the technique, which lends itself for real-time hardware implementation, exhibits satisfactory performance for all intensive purposes and that the method is technically feasible for a wide spectrum of manufacturing applications and systems.

Efficient Simulation of Nonlinear Heat Transfer during Thermal Spraying of Complex Workpieces

The quality of coatings, produced by thermal spraying processes, considerably decreases with the occurrence of higher residual stresses, which are especially pronounced for complex workpiece geometries. To understand the occurring effects and to aid in the planning of coating processes, simulations of the highly transient energy flux of the HVOF spray gun into the substrate are of great value. In this article, a software framework for the simulation of nonlinear heat transfer during (HVOF) thermal spraying is presented. One part of this framework employs an efficient GPU-based simulation algorithm to compute the time-dependent input boundary conditions for a spray gun that moves along a complex workpiece of arbitrary shape. The other part employs a finite-element model for a rigid heat conductor adhering to the computed boundary conditions. The model is derived from the fundamental equations of continuum thermodynamics where nonlinear temperature-depending heat conduction is assumed.<

The influence of the microstructure of hardened tool steel workpiece on the wear of PCBN cutting tools

Due to the recent developments of advanced cutting tool materials in the superbarasive family, such as cubic boron nitride (CBN) tools, the interest in cutting hardened steels has increased significantly. High flexibility and ability to manufacture complex workpiece geometry in one set up is the main advantage of hard turning compared to grinding. The focus of this study is to investigate the performance and wear behavior of CBN tools in finish, dry turning of four different hardened steels, treated to the same hardness R c = 54. The following four materials were machined: X155CrMoV 12 cold work steel (AISI D2), X38CrMoV5 (AISI H11) hot work steel, 35NiCrMo16 hot work steel and 100Cr6 bearing steel (AISI 52100). A large variation in tool wear rate was observed in the machining of these steels. The tool flank grooves have been correlated to the microstructure of these steels, namely the presence of various carbides. The chip study reveals that there is presence of different amounts of white layers in machining these steels.

A Fast Analytical Method to Compute Optimum Stiffness of Fixturing Locators

Machining fixtures are used to rigidly hold and support workpieces during machining. The quality of the machined part directly depends on the combined stiffness of the workpiece and the fixture. Low fixture stiffness causes poor quality parts, while large fixture stiffness causes the fixtures to be expensive and cumbersome. Finite element models can be used to optimize the fixture stiffness; however these techniques are computationally expensive for complex workpiece geometries. This paper develops a fast analytical method for optimizing fixture locator stiffnesses for workpieces that are more rigid than the fixture elements. The developed methodology is validated through finite element simulations and experiments.

An Enhanced Cutting Force Model for Face Milling With Variable Cutter Feed Motion and Complex Workpiece Geometry

An enhanced model for the prediction of static cutting forces in face milling is presented. The key features of the model include the ability to handle complex work-piece geometry, two-dimensional cutter feed paths, multiple pass machining, and effects of machine set-up errors. A two-dimensional boundary representation scheme is used to describe the workpiece geometry which may contain holes, slots, and other complex geometrical features. Variable cutter feed paths are represented by a combination of linear and circular arcs. In view of this and the complex workpiece geometry, a new algorithm for cutter-workpiece engagement determination is developed. Several sources of machine set-up error such as spindle and cutter axis tilt, and cutter center offset runout are modeled and their individual as well as combined effects on key machining process variables such as the axial and the radial depth of cut illustrated. Results of model verification experiments are reported for different workpiece geometry and cutter feed paths. A comparison of the predicted and measured forces shows good agreement.

Dynamic simulation and neural network compliance control of an intelligent forging center

Automation of forging processes is important for both safety and efficiency in today's advanced manufacturing operations. This work supports the development of an Intelligent Open Die Forging System which will integrate state-of-the-art modelling techniques, automatic die selection and sequencing, full system dynamic simulation, automatic machine programming and coordination, and sensor-based process control to enable the production of more general and complex workpiece geometries than are achievable using current forging methods. Effective automation of this open die forging system requires the coordination and control of the major system components: press, robot, and furnace. In particular, forces exerted on the robot through its manipulation of the workpiece during forging must be minimized to avoid damage to the manipulator mechanism. In this paper, the application of neural networks for compliance control of the forging robot to minimize these forces is investigated. Effectiveness of the neural network-based compliance control module is evaluated through a full dynamic system simulation, which will later form a central part of the complete Intelligent Forging System. Dynamic simulation of the robot is achieved using an efficient O(N) recursive algorithm, while material flow of the workpiece is modeled with a finite element approach. Simulation and timing results for the complete processing system for a specific open die forging example are presented.

EDM-Future Steps towards the Machining of Ceramics

Abstract As a thermal machining process, Electro-Discharge Machining (EDM) provides a means of machining ceramic materials, irrespective of their hardness and strength, provided that their electrical conductivity values are of the order of 0.01 S/cm (100 Ω*cm), as is sometimes the case with engineering ceramics. EDM achieves high removal rates as compared with traditional techniques for the machining of these materials. The lack of correlation between the cutting rate, the surface roughness and the physical material parameters confirms that the removal mechanisms for machining conductive ceramics differ from those involved in metal machining. In order to ensure process stability, the grain structure evinced by the ceramic must be as fine and homogeneous as possible. The complex workpiece geometries and high accuracy to shape and size attainable with electro-discharge machining particularly favour its use in toolmaking.

New Technique for Monitoring Nitrogen Ion Implantation Dose

A new dosimetry technique for use in industrial nitrogen ion implantation is described. This relies on colour changes induced in anodized tantalum. Visual inspection of these dosimeters, by comparison with a set of calibrated standards, provides an accuracy of around ±20% over the range 1 × 1017-5 × 1017 nitrogen ions cm −2. Scope exists for more accurate use of the system by means of commercial colour analysis equipment. However, even as it stands, the material has been shown by field trials to be a useful accessory to commercial nitrogen ion implantation, i.e. for verifying applied dose, especially with complex workpiece geometries, and for evaluating implanter performance.