Rigid Tool Research Articles

Feeling machines for online detection and compensation of tool deflection in milling

In milling, the tool deflection negatively affects the accuracy of the workpiece geometry. Feeling machines with force sensing capabilities represent a promising enabler to detect and to compensate the deflection-related machining failures in real time. This paper gives an overview about current applications of feeling machine tools and developments of monitoring and compensation systems for tool deflection. At first, a method to integrate strain sensors within rigid machine tool structures is introduced. Secondly, the prototypical application within commercial milling centres is presented. Finally, two compensation strategies for tool deflection via feed- and position-based control are discussed and experimentally evaluated.

Research on Liquid Forming Process of Nickel Superalloys Thin Sheet Metals

AbstractThe paper presents the study of drawability of thin sheet metals made of a nickel superalloy Inconel type. The manufacturing process of axisymmetric cup – cone and a closed section profile in the form of a circular tube were designed and analyzed. In both cases, working fluid-oil was used in place of the rigid tools. The process of forming liquid is currently the only alternative method for obtaining complex shapes, coatings, and especially if we do it with high-strength materials. In the case of nickel superalloys the search for efficient methods to manufacture of the shaped shell is one of the most considerable problems in aircraft industry [1-5]. However, the automotive industries have the same problem with so-called advanced high-strength steels (AHSS). Due to this, both industrial problems have been examined and the emphasis have been put on the process of liquid forming (hydroforming). The study includes physical tests and the corresponding numerical simulations performed, using the software Eta/Dynaform 5.9. Numerical analysis of the qualitative and quantitative forecasting enables the formability of materials with complex and unusual characteristics of the mechanical properties and forming technology. It has been found that only the computer aided design based on physical and numerical modeling, makes efficient plastic processing possible using a method of hydroforming. Drawability evaluation based on the determination of the mechanical properties of complex characteristics is an indispensable element of this design in the best practice of industrial manufacturing products made of thin sheet metals.

Planning, guidance, and quality assurance of pelvic screw placement using deformable image registration

Percutaneous pelvic screw placement is challenging due to narrow bone corridors surrounded by vulnerable structures and difficult visual interpretation of complex anatomical shapes in 2D x-ray projection images. To address these challenges, a system for planning, guidance, and quality assurance (QA) is presented, providing functionality analogous to surgical navigation, but based on robust 3D–2D image registration techniques using fluoroscopy images already acquired in routine workflow. Two novel aspects of the system are investigated: automatic planning of pelvic screw trajectories and the ability to account for deformation of surgical devices (K-wire deflection).Atlas-based registration is used to calculate a patient-specific plan of screw trajectories in preoperative CT. 3D–2D registration aligns the patient to CT within the projective geometry of intraoperative fluoroscopy. Deformable known-component registration (dKC-Reg) localizes the surgical device, and the combination of plan and device location is used to provide guidance and QA. A leave-one-out analysis evaluated the accuracy of automatic planning, and a cadaver experiment compared the accuracy of dKC-Reg to rigid approaches (e.g. optical tracking).Surgical plans conformed within the bone cortex by 3–4 mm for the narrowest corridor (superior pubic ramus) and >5 mm for the widest corridor (tear drop). The dKC-Reg algorithm localized the K-wire tip within 1.1 mm and 1.4° and was consistently more accurate than rigid-body tracking (errors up to 9 mm).The system was shown to automatically compute reliable screw trajectories and accurately localize deformed surgical devices (K-wires). Such capability could improve guidance and QA in orthopaedic surgery, where workflow is impeded by manual planning, conventional tool trackers add complexity and cost, rigid tool assumptions are often inaccurate, and qualitative interpretation of complex anatomy from 2D projections is prone to trial-and-error with extended fluoroscopy time.

Evaluating the factors influencing the friction behavior of paperboard during the deep drawing process

Deep drawing of paperboard with rigid tools and immediate compression has only a small presence in the market for secondary packaging solutions due to a lack of understanding of the physical relations that occur during the forming process. As with other processes that deal with interactions between two solids in contact, the control of the factors that affect friction is important due to friction’s impact on runnability and process reliability. A new friction measurement device was developed to evaluate the factors influencing the friction behavior of paperboard such as under the specific conditions of the deep drawing process, which differ from the standard friction testing methods. The tribocharging of the contacting surfaces, generated during sliding friction, was determined to be a major influence on the dynamic coefficient of friction between paperboard and metal. The same effect could be examined during the deep drawing process. With increased contact temperature due to the heating of the tools, the coefficient of friction decreased significantly, but it remained constant after reaching a certain charging state after several repetitions. Consequently, to avoid ruptures of the wall during the forming process, tools that are in contact with the paperboard should be heated.

Influence of tool elasticity on process forces and joint properties during clinching with rotational tool movement

Clinching as a joining method for sheet metal components offers various advantages. Therefore, the process optimization using finite element simulations is continuously increasing. For translational clinching, the use of rigid tools results in a good prediction of process forces and joint properties. In case of roller clinching, the lateral forces acting on the punch lead to significant elastic tool deformation during the process. This paper focuses on the effects of the tool elasticity on the joining forces, the tool deformation and the joint formation during roller clinching. The results are obtained using the finite element tool Abaqus. To evaluate whether higher simulation costs in form of elastic tools are necessary, the obtained clinchpoints are compared to experimental data.

Generation of segmental chips in metal cutting modeled with the PFEM

The Particle Finite Element Method, a lagrangian finite element method based on a continuous Delaunay re-triangulation of the domain, is used to study machining of Ti6Al4V. In this work the method is revised and applied to study the influence of the cutting speed on the cutting force and the chip formation process. A parametric methodology for the detection and treatment of the rigid tool contact is presented. The adaptive insertion and removal of particles are developed and employed in order to sidestep the difficulties associated with mesh distortion, shear localization as well as for resolving the fine-scale features of the solution. The performance of PFEM is studied with a set of different two-dimensional orthogonal cutting tests. It is shown that, despite its Lagrangian nature, the proposed combined finite element-particle method is well suited for large deformation metal cutting problems with continuous chip and serrated chip formation.

A New Control Architecture for Stable and Transparent Haptic Feedback of Interactive Simulation

This paper proposes a new control architecture for stable and transparent haptic rendering of interactive simulation involving a rigid tool and deformable objects. The traditional direct and proxy-based haptic rendering schemes are analyzed for the absolute stability, and transmit impedance employing the well-known bilateral control architecture frequently used in the field of teleoperation systems. An equivalent impedance is conveyed in the proposed control scheme to the haptic device instead of the contact force between the virtual tool and the object. The trade-off problem between the absolute stability and the transmitted impedance is resolved by computing the haptic feedback using the equivalent impedance. The proposed rendering scheme shows higher transparency than the conventional haptic rendering methods while maintaining the absolute stability.

Introduction of elastic die deformations in sheet metal forming simulations

Simulations of sheet metal forming (SMF) with finite element models (FE-models) for stamped parts in the car industry are useful for detecting and solving forming problems. However, there are several issues that are challenging to analyze. Virtual tryout and analyzes of stamping dies in running production are two important cases where many of these challenging issues are present. Elastic deformations of dies and press lines and a physically based friction model is often missing when these types of cases are analyzed. To address this, this research aims to develop a method wherein the results of two separate FE-models are combined to enable SMF simulations with the inclusion of elastic tool and press deformations. The two FE-models are one SMF model with two-dimensional (2D) rigid tool surfaces and one structural model of the die and press. The structural model can predict surface shapes and pressure distributions for a loaded stamping die. It can also visualize relatively large and unexpected deformations of the die structure. The recommended method of transferring the deformations from the structural model to the 2D surfaces is through an FE technique called submodeling. The subsequent SMF simulations show that the method for calculating and using the deformed surfaces together with the TriboForm friction model yields a result that matches measured draw-in and strains. It is verified that the ability to virtually deform a die and include the resulting geometry in forming simulations is of high importance. It can be used for the virtual tryout and optimization of new dies or analyses of existing dies in running production. It is suggested that future research focus on a more efficient and automated workflow. More experimental data and simulations are also needed to verify the assumptions made for the simulation models. This will enable the method to be adopted in a reliable way for standard SMF simulations.

Optical anisotropy in micromechanically rolled carbon nanotube forest

The bulk appearance of arrays of vertically aligned carbon nanotubes (VACNT arrays or CNT forests) is dark as they absorb most of the incident light. In this paper, two postprocessing techniques have been described where the CNT forest can be patterned by selective bending of the tips of the nanotubes using a rigid cylindrical tool. A tungsten tool was used to bend the vertical structure of CNTs with predefined parameters in two different ways as stated above: bending using the bottom surface of the tool (micromechanical bending (M2B)) and rolling using the side of the tool (micromechanical rolling (M2R)). The processed zone was investigated using a Field Emission Scanning Electron Microscope (FESEM) and optical setup to reveal the surface morphology and optical characteristics of the patterned CNTs on the substrate. Interestingly, the polarized optical reflection from the micromechanical rolled (M2R) sample was found to be significantly influenced by the rotation of the sample. It was observed that, if the polarization of the light is parallel to the alignment of the CNTs, the reflectance is at least 2 x higher than for the perpendicular direction. Furthermore, the reflectance varied almost linearly with good repeatability (~10%) as the processed CNT forest sample was rotated from 0° to 90°.[Figure not available: see fulltext.].

Understanding the requirements of self-expandable stents for heart valve replacement: Radial force, hoop force and equilibrium

A proper interpretation of the forces developed during stent crimping and deployment is of paramount importance for a better understanding of the requirements for successful heart valve replacement. The present study combines experimental and computational methods to assess the performance of a nitinol stent for tissue-engineered heart valve implantation. To validate the stent model, the mechanical response to parallel plate compression and radial crimping was evaluated experimentally. Finite element simulations showed good agreement with the experimental findings. The computational models were further used to determine the hoop force on the stent and radial force on a rigid tool during crimping and self-expansion. In addition, stent deployment against ovine and human pulmonary arteries was simulated to determine the hoop force on the stent-artery system and the equilibrium diameter for different degrees of oversizing.

Improving smoothing efficiency of rigid conformal polishing tool using time-dependent smoothing evaluation model

A rigid conformal (RC) lap can smooth mid-spatial-frequency (MSF) errors, which are naturally smaller than the tool size, while still removing large-scale errors in a short time. However, the RC-lap smoothing efficiency performance is poorer than expected, and existing smoothing models cannot explicitly specify the methods to improve this efficiency. We presented an explicit time-dependent smoothing evaluation model that contained specific smoothing parameters directly derived from the parametric smoothing model and the Preston equation. Based on the time-dependent model, we proposed a strategy to improve the RC-lap smoothing efficiency, which incorporated the theoretical model, tool optimization, and efficiency limit determination. Two sets of smoothing experiments were performed to demonstrate the smoothing efficiency achieved using the time-dependent smoothing model. A high, theory-like tool influence function and a limiting tool speed of 300 RPM were o

Rotational abrasive finishing (RAF); novel design for micro/nanofinishing

Traditional finishing techniques, including grinding, honing, and lapping have several disadvantages and limitations due to their solid and rigid tools with complex geometries. To overcome these limitations, modern techniques known as nanofinishing techniques are introduced. This paper presents a new micro/nanofinishing technique used in different industries, especially high-tech industries like aerospace, military applications, and auto-making industry. This technique is called rotational abrasive finishing (RAF) method. In this technique, the medium inside the cylindrical workpiece is rotated using a bladed stirring axis. The medium hits against the surface of the workpiece while rotating in the opposite direction. In this way, material removal and finishing operation are achieved. In order to avoid medium discharge, two caps, one in upper side and one in the bottom side of workpiece, are used. RAF technique makes it possible to reduce surface roughness and achieve roughness in nanometer scales so that on our test workpiece roughness was reduced from 0.283 to 88 nm, indicating 70% improvement in surface quality by applying 20 min machining duration. It was practically proved that RAF is a fast, efficient, and cost-effective finishing technique for different products by which it is possible to achieve ultra-precise surface quality at nanometeric scales.

Investigation of new tool design for incremental profile forming

Abstract Incremental Profile Forming (IPF) is a highly flexible and versatile process for the manufacture of tubular parts with variable cross-section design along the centre-line of the tube. Within an incremental approach multiple forming tools with arbitrary geometries indent into the tube and move along predefined tool paths to deform the desired tubular shape. Since rigid forming tools are used, a sliding friction contact between tool and workpiece exists leading to several process limits. On the one hand tearing occurs in the forming zone due to high tensile stresses near the contact area between tool and workpiece. On the other hand the workpiece properties in terms of surface quality decrease due to wear. Unlike incremental sheet forming processes, where the workpiece surface area is under contact load twice (assuming a 50 % side overlap between subsequent tool paths), the deformed surface areas in IPF experience several repetitive contact loads leading to comparatively higher occurrence of wear. In order to improve surface qualities as well as to lower the loads in near contact regions by the reduction of friction, novel tool designs for IPF are introduced which allow a smoother transition of the material flow into the forming region. Besides a rigid tool, a roller-based tool is designed for substituting the conventional sliding friction by a rolling friction mode. Within experimental studies the influence of the tool shape as well as the rolling friction condition was examined. Comparative analyses show that the process forces are decreased by the use of the new tool designs leading to higher formability in IPF since a higher radial tool infeed is achievable. For the analysis of the component loads e.g. contact stresses and corresponding distributions in the contact region between workpiece and forming tool a numerical model is developed. A significant reduction of process limiting tensile stresses in contact near regions could be proven. Beside the reduction of process forces an improvement of the surface quality as well as a more accurate geometry of the workpiece were achieved by the use of the new tool designs.

Too Sharp for its Own Good – Tool Edge Deformation Mechanisms in the Initial Stages of Metal Cutting

Metal cutting simulations have become an important part of cutting tool design and the research in the field in general. One of the most important aspects of modeling is the accuracy of the tool geometry. 3D microscopy is used for measuring the tool edge radius with good accuracy. However, especially with sharp tools, i.e. small tool edge radii, the measurements, no matter how accurate, are not much of a use, since the initial wear, or deformation is so fast in the first 1-30seconds into the cutting, that the tool geometry is significantly different than the one measured from the new tool. The average tool life is often set to 15minutes. Therefore, the cutting simulations that only predict the tool behavior in the first seconds of its lifetime are not very useful in predicting the process variables throughout the tool life. Simulations with creep and elastic-plastic material model however, can predict the initial deformation of the tool. This tool shape can be then used in rigid tool model to predict the process variables in the steady wear region of the tool life. This paper presents simulation model for predicting the initial tool edge deformation for WC-10%Co tool while machining AISI 304 stainless steel. The novelty in this approach is the simultaneous coupled calculation of contact surface temperature and stress and change of the tool shape.

An Experimental Investigation on the Effect of Nanopowder for Micro-Wire Electro Discharge Machining of Gold Coated Silicon

Micro Wire Electro Discharge Machining (μ-WEDM) is a type of electro-discharge machining (EDM) process where the wire is used instead of a rigid tool. It is a reliable and precise machining process, which is commonly used to produce various complex structural shapes for a wide range of industrial applications. However, to machine a semiconductor material of high resistivity like silicon (Si) requires more advanced processing to produce larger electrical sparks during the μ-WEDM operation. Current (μ-WEDM) technology is not enough to realize a stable machining environment for Si. In this research, a new type of μ-WEDM process for Si machining was investigated. At first, Si was temporarily coated with gold and then nanopowder mixed dielectric medium was used for the WEDMing process. The main purpose of this work is to investigate the effects of different nanopowder concentrations on two important response factors such as material removal rate (MRR) and spark gap (SG). In this regard, the μ-WEDMing of gold coated silicon was carried out in pure dielectric EDM oil and also in three different concentrations (0.1g/L,1g/L,2g/L) of nanopowder mixed dielectric oil to conduct an initial study with the aim to achieve better machining accuracy and stability. Based on the experimental investigations, the MRR were found to be increased on average minimum ∼ 1% to maximum ∼ 33% respectively for different carbon concentrations, as compared to machining in the pure dielectric medium. The spark gap was also observed to be increased by a significant margin on average of ∼ 2% to up to ∼ 159% than without using any nanopowder concentration, correspondingly.

Deep Learning for Surface Material Classification Using Haptic and Visual Information

When a user scratches a hand-held rigid tool across an object surface, an acceleration signal can be captured, which carries relevant information about the surface material properties. More importantly, such haptic acceleration signals can be used together with surface images to jointly recognize the surface material. In this paper, we present a novel deep learning method dealing with the surface material classification problem based on a fully convolutional network, which takes the aforementioned acceleration signal and a corresponding image of the surface texture as inputs. Compared to the existing surface material classification solutions which rely on a careful design of hand-crafted features, our method automatically extracts discriminative features utilizing advanced deep learning methodologies. Experiments performed on the TUM surface material database demonstrate that our method achieves state-of-the-art classification accuracy robustly and efficiently.

Small petal tools performance for parabolizing optical surfaces.

Small rigid petal tools, driven by a traditional polishing machine, were used to parabolize 20 mirrors 14 cm in diameter and 192 cm of curvature radius. Small rigid circular tools (SCTs), driven manually, were used to parabolize another 20 identical surfaces. A Ronchi test with a square grid was used to evaluate the performance of both techniques. If small rigid petal tools are used, the surface quality, the reproducibility in the production process, and the time spent required to generate the surfaces are markedly better than using SCTs.

Plastic deformation of a wedge by a sliding punch

We present a self-similar solution of the problem of deformation of an ideally plastic wedge by a sliding punch with regard to contact friction; such a solution generalizes the well-known solutions of the problem of wedge penetration into a plastic half-space and of compression of an ideally plastic wedge by a plane punch. The problem is of interest for modeling the processes of plastic deformation of rough surfaces of metal pieces by a rigid tool.

Numerical analysis on the elastic deformation of the tools in sheet metal forming processes

The forming tools are commonly assumed as rigid in the finite element simulation of sheet metal forming processes. This assumption allows to simplify the numerical model and, subsequently, reduce the required computational cost. Nevertheless, the elastic deformation of the tools can influence considerably the material flow, specifically the distribution of the blank-holder pressure over the flange area. This study presents the finite element analysis of the reverse deep drawing of a cylindrical cup, where the forming tools are modelled either as rigid or as deformable bodies. Additionally, the numerical results are compared with the experimental ones, in order to assess the accuracy of the proposed finite element model. Considering the elastic deformation of the tools, the numerical results are in better agreement with the experimental measurements, namely the cup wall thickness distribution. On the other hand, the computational time of the simulation increases significantly in comparison with the classical approach (rigid tools).

Sensitivity analysis on ram speed of a direct extrusion process model using a porthole die through CEL method

In this paper, a tube extrusion process by finite element was analyzed, using coupled Eulerian-Lagrangian method (CEL) due to the severe deformation that material presents and thereby avoids distortion of the mesh and adaptive meshing used in Lagrangian models, in order to obtain stress distribution, strains, extrusion force, and flow material behavior. Four isothermal models were performed by modifying the sensitivity of ram speed using discrete rigid tools with general contact option to simulate the interaction between them; 7005 aluminum was considered as the material to be extruded. In order to reduce high computational time application, speed was increased to observe its influence on the results, in other words the variations between the models. As a consequence of this analysis, it was found that while the kinetic energy does not exceed 5 to 10 % of whole internal energy, material flow behavior and stress level are not affected.