Tool Path Parameters Research Articles

An integrated framework for optimizing sculptured surface CNC tool paths based on direct software object evaluation and viral intelligence

Two critical objectives in sculptured surface tool path optimization are machining accuracy and process efficiency. The former objective is characterized as the combined effect of chord error and scallop height, known as surface machining error, whilst the latter may be reflected by the number of cutting tool locations constituting the tool path. These objectives are entirely depended on the values to be selected for computing tool paths under a given cutting strategy and preset tolerance. In order to determine optimal tool path parameters that will simultaneously satisfy the trade-off incurred between these objectives, a novel; generic and unbiased environment integrated with a virus-evolutionary heuristic for intelligent tool path optimization is presented. The proposed environment has been developed using the open architecture of a cutting edge CAM system whilst it deploys a set of interactive functions to straightforwardly assess criteria without the formal knowledge of any objective function; but directly from computer-aided manufacturing attributes; fully responsible to formulate efficient tool paths. A utility based on weighted summation for multi-objective optimization has been introduced to capture the direct output of globally optimized tool paths avoiding this way problem oversimplification and statistical errors that mathematical relations involve. Results have been rigorously validated both computationally and experimentally with the aid of a benchmark sculptured part that has been previously tested by several noticeable research contributions. Based on the quality of research outputs it is shown that the proposed framework for optimizing sculptured surface CNC tool paths may gain a prominent role for further extending the capabilities of current industrial strategies and be the flagship of allied; not-yet industrially interfaced approaches for deploying similar software integration tools to transfer significant results to production.

Part accuracy improvement in two point incremental forming with a partial die using a model predictive control algorithm

As a flexible forming technology, Incremental Sheet Forming (ISF) is a promising alternative to traditional sheet forming processes in small-batch or customised production but suffers from low part accuracy in terms of its application in the industry. The ISF toolpath has direct influences on the geometric accuracy of the formed part since the part is formed by a simple tool following the toolpath. Based on the basic structure of a simple Model Predictive Control (MPC) algorithm designed for Single Point Incremental Forming (SPIF) in our previous work Lu et al. (2015) [1] that only dealt with the toolpath correction in the vertical direction, an enhanced MPC algorithm has been developed specially for Two Point Incremental Forming (TPIF) with a partial die in this work. The enhanced control algorithm is able to correct the toolpath in both the vertical and horizontal directions. In the newly-added horizontal control module, intensive profile points in the evenly distributed radial directions of the horizontal section were used to estimate the horizontal error distribution along the horizontal sectional profile during the forming process. The toolpath correction was performed through properly adjusting the toolpath in two directions based on the optimised toolpath parameters at each step. A case study for forming a non-axisymmetric shape was conducted to experimentally validate the developed toolpath correction strategy. Experiment results indicate that the two-directional toolpath correction approach contributes to part accuracy improvement in TPIF compared with the typical TPIF process that is without toolpath correction.

A New Methodology of Finding Optimal Toolpath and Tooling Strategies for Robotic-Assisted Arthroplasty

Robotic total hip arthroplasty is a procedure in which a milling operation is performed on the femur followed by insertion of a prosthetic implant. Although surgeons operate the robots, they do not control the choice of robotic tools and cutting strategies of the robot. Toolpath parameters, such as feedrate, tool geometry, and spindle speeds, govern the cutting forces of the robot. This research covers a methodological approach for finding optimal parameters such that cutting forces and surgical times are reduced. Many different types of orthopedic surgical burs were retrofitted into an advanced computer numerically controlled (CNC) machine, and the characteristics of each tool were evaluated. A simulation cutting model was then developed to find the parameters that could remove the most material in the fastest amount of time without violating any of the safety constraints of surgery. The new methodology proposed not only finds the theoretical optimal parameters but also expedites the process of finding sufficient parameters for orthopedic surgery.

Stability contour maps with barrel cutters considering the tool orientation

The geometry of rotary aircraft engine components is usually defined by thin mechanical elements and complex surfaces that are only achievable by 5-axis machining due to either limited access or the design itself. Such thin-walled characteristics make these components susceptible to vibrations while machining and usually require careful manipulation of the toolpath parameters to minimize cutting forces and vibration. Moreover, the tool suppliers’ approach leans towards the feature-build design of cutter geometry to increase the productivity and quality of a machined surface. Some examples of those recent improvements for rotary aircraft engine components are barrel-shaped tools that attempt to increase the contact radius on the tool-part interface to minimize step-over while conserving the scallop height to meet roughness tolerances. This research aims to fill a gap in the current literature by proposing a stability model for barrel-shaped tools. Stability contour maps make use of a mechanistic dynamic force model for barrel-shaped tools. The force model is also capable of including tool runout and orientation angles, tilt and lead, as named in most CAM software. By simulating dynamic forces on the time domain, a contour map is presented to address unstable vibrations. Since forced vibrations and surface location error (SLE) may also appear when milling aircraft parts, SLE and surface roughness are also determined. Finally, given the complexity and number of parameters, validation of the stability maps is performed through experimental chatter tests using a thin wall component.

Optimisation of tool path for wood machining on CNC machines

Peripheral pocket or contour milling in wood machining, using flat end milling tool, can be performed with different tool paths. Technology designers of multi axis CNC wood machining use their experience and intuition to choose some of the options offered by CAM systems that determine the final shape of tool path, thus the generated tool path largely depend on individual judgment. Minimum cutting force, maximum dynamic stability of the process and minimum tool wear are achieved, or some other technological requirements are met, by using optimal tool path. Tool path optimisation is based on analysis of possible tool paths and determination of cutting parameters which are dependable of chosen tool path and are affecting the main wood processing factors. Axial and radial depth of cut, engagement angle, feed and feed rate profile are identified as key parameters dependable of tool path, and their values and variations along the tool path influence the cutting speed, tool wear and cutting force. Knowledge of values and changes of those key machining parameters along the tool path is necessary for simulation and monitoring of the main cutting factors during the wood machining process. NC code transformation methodology and generation of tool path parameters necessary for calculating all elements needed for tool movement simulation from given NC programs are shown. Blank and tool mathematical description are used with tool movement information for simulation of wood machining process. Simulation of cutting parameters and their variation along the tool path, presented in this paper, can be used as bases for development of methodology for choosing the most adequate tool path for wood machining of given contour considering minimum cutting force and cutting force variation, minimum tool wear, maximum productivity or some other criteria.

Analytical prediction of formed geometry in multi-stage single point incremental forming

Single Point Incremental Forming (SPIF) is a die-less forming process that can be economically used for low volume production of sheet metal components. One of the limitations of SPIF is the maximum wall angle that can be formed in a single stage. To overcome this limitation, Multi-stage Single Point Incremental Forming (MSPIF) is used to form components with large wall angles. When the tool is moved from out-to-in during any stage, material present ahead of it (towards the centre of the component) moves down rigidly. If this rigid body displacement is not considered during tool path generation for MSPIF, it leads to stepped/unwanted features. Predicting the component geometry after each stage helps in monitoring the shape being developed and in turn is useful in designing intermediate stages to form required final geometry with desired accuracy. In the present work, a simple methodology is proposed to predict rigid body displacement based on tool path and process parameters (tool diameter, incremental depth, sheet thickness) used. Tool and sheet deflections due to forming force are also considered to predict final geometry of the component. Proposed methodology is validated by comparing predicted profiles with experimentally measured profiles of high wall angle axisymmetric components formed using different materials and sheet thicknesses. Predicted profiles are in good agreement with experimental results.

Influence of Machine Hammer Peening on the Tribology of Sheet Forming

The recently developed machine hammer peening process is used at the die shop of the Mercedes-Benz plant in Sindelfingen in order to replace manual surface finish of deep drawing dies. The goal of the process is surface roughness reduction after milling to ensure the tribological properties, which are necessary for the sheet metal forming process. Using machine hammer peening it is also possible to create defined surface structures that may be employed to influence local friction conditions and therewith overcome current limitations of the forming process. To take advantage of the surface structuring capabilities it is necessary to understand how to create defined surface structures using machine hammer peening and how the created structures affect friction and material flow behavior. In this work an approach is presented to describe the interaction of milling and machine hammer peening parameters on the created topography by wave theory. Especially the influence of tool path parameters of milling and consecutive machine hammer peening is investigated. The results, which are calculated using wave theory, are verified by FEM simulations and real experiments. In addition, suitable process parameters for machine hammer peening are derived from the obtained results, as they are used at the Mercedes-Benz die shop today.

Modeling and Experimental Study on the Material Removal in the Velocity-dwell-mode Polishing Process

With the demand of improving the form accuracy of free-form surface by computer-controlled polishing, a theoretical investigation is presented on the material removal for the velocity-dwell-mode polishing process. Especially, the material removal profile as the sub-aperture tool polishes at the path corner is modeled. The material removal profile perpendicular to the polishing path can be calculated by integrating the wear index, the polished depth at unit length of polishing path, along the tool path in the contact region. The effects of the straight path and arc path on the polished profile at the bisector of the path arc angle are discussed in different cases. On the basis above, the polished profile at the path corner is modeled and a series of experiments are conducted to verify the proposed model. According to the experimental results, the material removal at the path corner is uneven, and the path radius and arc angle both affect the material removal profile during the velocity-dwell-mode polishing. The proposed model is potentially useful for the planning of tool path and process parameters in the polishing process.

Kinematic nonlinearity analysis in hexapod machine tools: Symmetry and regional accuracy of workspace

The kinematic nonlinearity of hexapod machine tools is the source of an error which requires special consideration during toolpath planning and command generation. Analytical formulation for such an error is presented in this paper. The presented formulation can also be employed in optimal toolpath planning and workpiece setup. The effects of toolpath parameters such as the length, orientation, and the location of the toolpath together with the upper platform travel speed are considered in this investigation. Toolpaths are categorized based on their orientation into vertical toolpaths, horizontal–horizontal toolpaths, horizontal–vertical toolpaths, horizontal-inclined toolpaths, and inclined toolpaths. Variation of the kinematic nonlinearity error and the regional accuracy of the machine's workspace are presented in this paper. Workspace symmetry is studied and it is shown that one-sixth of the machine's workspace can represent the whole workspace. Eventually, the presented formulation and the effect of parameters are experimentally verified.

Evaluation of Geometric Accuracy and Thickness Variation in Incremental Sheet Forming Process

Abstract The aim of this study is to evaluate dimensional conformity and thickness variation of a pyramid geometry obtained by negative single point incremental sheet forming. DC04 mild steel, which has been widely used in automotive and numerous applications due to high formability, was used for experimental investigations. Dimensional accuracy of whole geometry and surface roughness are investigated under the influence of toolpath parameters such as tool diameter, feed rate and vertical step down. In this paper, geometric accuracy and thickness are evaluated by production tolerances of conventional methods and results show that thickness reduction of formed sheet and geometrical deviation of side faces are out of tolerance for all cases.

Rapid optical surface figuring using reactive atom plasma

In the context of large optics figure correction, the reactive atom plasma (RAP) process constitutes a fast and unique solution for ultra-precise surface figuring. The RAP process combines high material removal rates with the advantages of non-contact machining methods. The RAP technology is based on an inductively coupled plasma torch that produces a sub-aperture near-Gaussian etching footprint, with material removal repeatability at nanometre level. A large-scale RAP figuring facility, Helios 1200, has been developed in the Precision Engineering Centre at Cranfield University to optimize and apply the RAP technology on metre-sized optical surfaces. In this paper, the first examples of figure correction carried out with Helios 1200 are reported. These experimental results were achieved over 100 and 140 mm diameter areas by means of in-house developed timedwell figuring techniques and a dedicated tool motion path. In particular, classical de-convolution techniques were adapted to the non-linear nature of the etching rate in order to derive velocity maps, while the tool-path algorithm was designed to induce a homogeneous temperature distribution on the process surface. Still, surface temperature raises are known to increase the rate of material chemical etching. Therefore, as a form of heat effects compensation, the adapted tool-path algorithm was combined with an iterative figuring procedure in order to assure faster process convergence. This promptly enabled the realization of figure error corrections down to λ/40 rms. High overall rates of convergence between 78 and 89% were attained within a maximum of three iterations. The mean processing times per iterative step were 6.6 minutes over the 140 mm diameter areas, thus confirming the potentiality of RAP as large surface figuring technique. Applied to metre-class optics, the method should then deliver comparable levels of form accuracy within less than ten hours processing time. The scope of the work presented included both investigation and verification of the effects of tool-path parameters, as well as of the modified de-convolution method. The validated figuring procedure can be progressively scaled up to medium and large optical surfaces. The surface texture after plasma machining was characterized. Some deterioration of surface roughness was observed.

Solid Modeling Methods and Wire-Cutting Process Simulation of Non-Circular Gears

Non-circular pitch curves is not a circle, the design and simulation of non-circular are complexity and difficulty. Based on the design theory and wire cutting theory of non-circular gears, main introducing to create parameter model of third-order non-circular gear based on Pro/E drawing module. Using Pro/E manufacturing module cut third-order non-circular gear by line. Include using Pro/E creates third-order gear machining tool path, set tool and process parameters, process simulation tool process of post-processing analysis and generate post-processing procedures which NC machine tool need. And analyzing the results of processing, then shows that the solid modeling methods and cutting process simulation are correct and highly precision, solve the difficult problem about non-circular gear solid modeling and machining simulation.

Improving trochoidal tool paths generation and implementation using process constraints modelling

With the emergence of high dynamic machine tools equipped with performing NC controllers, new types of strategies have risen to meet the demands associated to high-speed milling process. Among them, trochoidal tool paths are applied in rough machining applications. In this paper several improvements for their implementation are proposed. First, maximal radial depth of cut calculation according to tool path parameterization is made. Two interpolation models are tested and compared. The aim is to select the best tool path parameters according to the process constraints. Then, improved tool path generation for pocket milling applications is proposed. An experimental study is performed to validate the proposed approach and study the efficiency of trochoidal tool path implementation for pocket milling applications. The impact of the dynamics of the machine tool is evaluated in particular. The work presented here leads consequently to enhancement of implementation of trochoidal tool paths according to process constraints.

Virtual manufacturing of milling operations with multiple tool paths

Virtual manufacturing (visualisation and animation of a manufacturing process) provides the user with visual feed back in order to understand relations between the data in the process plan. The paper presents a framework, a procedure and an object-oriented prototype for virtual manufacturing of milling processes. A visualisation model is generated through three steps: geometric model, kinematic model and animation model. In the first step, geometric model, the feature geometry is analysed and corresponding tool path patterns are generated, and initial and final work piece geometry computed using stock and feature geometric models. Kinematic model is generated by segmentation of end milling processing time into intervals for each tool path segment and identification of part/tool engagement and disengagement relations. The third step, animation model, creates objects necessary for virtual manufacturing of the process in virtual 3D world. The user-friendly prototype has been implemented in Java using Java3d API. The user is able to experiment with different values of the tool path parameters and visually inspect results in order to select the most suitable ones.

Milling error prediction and compensation in machining of low-rigidity parts

The paper reports on a new integrated methodology for modelling and prediction of surface errors caused by deflection during machining of low-rigidity components. The proposed approach is based on identifying and modelling key processing characteristics that influence part deflection, predicting the workpiece deflection through an adaptive flexible theoretical force-FEA deflection model and providing an input for downstream decision making on error compensation. A new analytical flexible force model suitable for static machining error prediction of low-rigidity components is proposed. The model is based on an extended perfect plastic layer model integrated with a FE model for prediction of part deflection. At each computational step, the flexible force is calculated by taking into account the changes of the immersion angles of the engaged teeth. The material removal process at any infinitesimal segment of the milling cutter teeth is considered as oblique cutting, for which the cutting force is calculated using an orthogonal–oblique transformation. This study aims to increase the understanding of the causes of poor geometric accuracy by considering the impact of the machining forces on the deflection of thin-wall structures. The reported work is a part of an ongoing research for developing an adaptive machining planning environment for surface error modelling and prediction and selection of process and tool path parameters for rapid machining of complex low-rigidity high-accuracy parts.

Force and deflection modelling in milling of low-rigidity complex parts

To remain competitive, high-quality high-value manufacturers constantly seek to improve their product quality and to reduce cost and lead times by producing ‘right first time’ machined components. Producing the right profile in such parts increasingly depends on specialised CAM packages for defining appropriate cutting strategies and tool paths. Despite the significant developments in NC simulation and verification there are still gaps between the theoretically predicted surfaces and the measured surfaces due to a relatively small percentage of machining error types that could be detected and interpreted by the existing software systems. The paper reports on a virtual environment for simulation and prediction of the deflection of thin-walled parts during machining. It aims to increase the understanding of the causes of poor geometric accuracy by considering the impact of the machining forces on the deflection of thin-walled structures. The proposed approach is based on identifying and modelling of key processing characteristics that influence part deflection, modelling of the material removal process using “voxels”, and predicting and correcting the deflection of the parts. The decision making is based on a novel integrated environment using CAD and finite element analysis tools. The reported work is part of an ongoing research on developing an adaptive machining planning environment for modelling, prediction, and selection of process and tool path parameters for rapid machining of complex low-rigidity high-accuracy parts.

Towards deflection prediction and compensation in machining of low-rigidity parts

Producing the right profile in machining low-rigidity complex parts increasingly depends on specialized computer aided manufacture (CAM) packages for defining appropriate cutting strategies and tool paths. Despite the significant developments in numerically controlled (NC) simulation and verification there are still gaps between the theoretically predicted surfaces and the measured surfaces owing to a relatively small percentage of machining error types that could be detected and interpreted by the existing software systems. This paper reports on a new methodology for simulation and prediction of the deflection of thin wall parts during machining. It aims to increase the understanding of the causes of poor geometric accuracy by considering the impact of the machining forces on the deflection of thin-walled structures. The proposed approach is based on identifying and modelling key processing characteristics that influence part deflection, modelling the material removal process using ‘voxels’ and predicting and correcting the deflection of the parts. The reported work is part of ongoing research on developing an adaptive machining planning environment for modelling, prediction and selection of process and tool path parameters for rapid machining of complex low-rigidity high-accuracy parts.

Times and costs analysis for sheet-metal cutting processes in an integrated CAD/CAM system

The aim of the present article is to develop a detailed time and cost analysis for process planning sheet-metal operations. A special computer module for determining the times and costs in sheet-metal operations has been developed and integrated in a CAD/CAM system which incorporates modules for nesting, toolpath generation, post-processing, etc. The special module allows all the geometrical and technological data from other modules in the CAD/CAM system (e.g. cutting conditions, toolpath parameters, types of material, cutting gases, etc.) required for the cost and time analysis to be automatically included without the need to manually enter the data in the module. This program can also be used as a 'stand alone' module, it has been developed with a graphic programming language (AutoLISP). Case studies are presented to highlight the benefits of using the program during practice.