Tool Forces Research Articles

Single Point Incremental Forming to increase material knowledge and production flexibility

Nowadays, manufactured pieces can be divided into two groups: mass production and production of low volume number of parts. Within the second group (prototyping or small batch production), an emerging solution relies on Incremental Sheet Forming or ISF.ISF refers to processes where the plastic deformation occurs by repeated contact with a relatively small tool. More specifically, many publications over the past decade investigate Single Point Incremental Forming (SPIF) where the final shape is determined only by the tool movement. This manufacturing process is characterized by the forming of sheets by means of a CNC controlled generic tool stylus, with the sheets clamped by means of a non-workpiece-specific clamping system and in absence of a partial or a full die. The advantage is no tooling requirements and often enhanced formability, however it poses a challenge in term of process control and accuracy assurance. Note that the most commonly used materials in incremental forming are aluminum and steel alloys however other alloys are also used especially for medical industry applications, such as cobalt and chromium alloys, stainless steel and titanium alloys. Some scientists have applied incremental forming on PVC plates and other on sandwich panels composed of propylene with mild steel and aluminum metallic foams with aluminum sheet metal. Micro incremental forming of thin foils has also been developed.Starting from the scattering of the results of Finite Element (FE) simulations, when one tries to predict the tool force (see SPIF benchmark of 2014 Numisheet conference), we will see how SPIF and even micro SPIF (process applied on thin metallic sheet with a few grains within the thickness) allow investigating the material behavior. This lecture will focus on the identification of constitutive laws, on the SPIF forming mechanisms and formability as well as the failure mechanism. Different hypotheses have been proposed to explain SPIF formability, they will be listed however the lecture will be more focused on the use of SPIF to identify material parameters of well-chosen constitutive law. Results of FE simulations with damage models will be investigated to better understand the relation between the particular stress and strain states in the material during SPIF and the material degradation leading to localization or fracture.Last but not least, as industrial world does not wait that academic scientists provide a deep and total understanding on how it works, to use interesting processes, the lecture will review some applications. Examples in fields as different as automotive guard, engine heat shield, gas turbine, electronic sensor, shower basin, medical component (patient-fitted organic shapes) and architecture demonstrate that the integration of SPIF within the industry is more and more a reality.Note that this plenary lecture is the result of the research performed by the author in the University of Liege (Belgium) and in Aveiro (Portugal) with the team of R. de Souza during PhD theses of C. Henrard, J. Sena and C. Guzman and different research projects. It is also a synthesis of the knowledge gathered during her interactions with many research teams such as the ones of J.R. Duflou from KU Leuven in Belgium, J. Cao from Northwestern University in USA, M. Bambach in BTU Cottbus-Senftenberg in Germany, J. Jeswiet from Queen's University, Kingston, Canada who are currently working together on a state-of-the-art paper. The micro SPIF knowledge relies on contacts with S. Thibaud from the University of Franche Comte.

Performance of AlTiN- and diamond-coated carbide tools in dry high-speed milling of electro discharge machining graphite

Electrodes made of graphite material are widely used for electro discharge machining. The performance of physical vapor deposition AlTiN and chemical vapor deposition diamond-coated carbide end-milling tools in dry high-speed milling of electro discharge machining graphite was investigated, also adopting an uncoated one as a comparison. The quality of as-deposited diamond film was evaluated by Raman spectroscopy. The adhesion between the coating and the substrate was assessed by indentation test. The tool life and wear mechanism of the milling tools, the cutting forces during tests, as well as the roughness of processed surfaces were systematically studied. It is found that the diamond coating has lower adhesion than the AlTiN coating under the same load. Coating delamination and chipping, irregularly zigzag side flank wear, concave structure on the cutting edge are primary wear patterns for the diamond-coated tool. While different primary wear patterns, including uniform polishing abrasive flank wear and crater rake wear, are observed on the AlTiN-coated tool. Besides, the total cutting force of the diamond-coated tool is larger than that of the AlTiN-coated tool when the diamond-coated tool side flank wear value reaches 0.06 mm, attributed to the different wear patterns. Another notable result is clarified that the chipping of the diamond coating can cause significant increment in the feed force, radial force and worked surface roughness.

PATEX

Patterns play a central role in 2D graphic design. A critical step in the design of patterns is evaluating multiple design alternatives. Exploring these alternatives with existing tools is challenging because most tools force users to work with a single fixed representation of the pattern that encodes a specific set of geometric relationships between pattern elements. However, for most patterns, there are many different interpretations of its regularity that correspond to different design variations. The exponential nature of this variation space makes the problem of finding all variations intractable. We present a method called PATEX to characterize and efficiently identify distinct and valid pattern variations, allowing users to directly navigate the variation space. Technically, we propose a novel linear approximation to handle the complexity of the problem and efficiently enumerate suitable pattern variations under proposed element movements. We also present two pattern editing interfaces that expose the detected pattern variations as suggested edits to the user. We show a diverse collection of pattern edits and variations created with PATEX. The results from our user study indicate that our suggested variations can be useful and inspirational for typical pattern editing tasks.

Analytical and Empirical Modeling of Wear and Forces of CBN Tool in Hard Turning - A Review

Machining of steel material having hardness above 45 HRC (Hardness–Rockwell C) is referred as a hard turning. There are numerous models which should be scrutinized and implemented to gain optimum performance of hard turning. Various models in hard turning by cubic boron nitride tool have been reviewed, in attempt to utilize appropriate empirical and analytical models. Validation of steady state flank and crater wear model, Usui’s wear model, forces due to oblique cutting theory, extended Lee and Shaffer’s force model, chip formation and progressive flank wear have been depicted in this review paper. Effort has been made to understand the relationship between tool wear and tool force based on the different cutting conditions and tool geometries so that appropriate model can be used according to user requirement in hard turning.

Application of Self-Made Dynamometer in Measuring Tool Forces in Friction Stir Welding Process

In this paper, the dynamometer for measuring the forces of the tool in FSW process was designed. The design principle of the dynamometer was adopted octagonal ring deformation to get the forces in FSW process. The design dynamometer was calibrated, the result showed the linearity and cross sensitivity of the dynamometer in allowed range, the worked reliable of the dynamometer was good. It can be used to measure the forces in FSW process.

Influence of tool material on mechanical and microstructural properties of friction stir welded 316L austenitic stainless steel butt joints

In the present research, the influence of friction stir welding (FSW) tool material on the mechanical and microstructural properties of friction stir (FS) welded 316L stainless steel butt joints is investigated. FS welds were produced using two different tungsten based FSW tools having identical tool shoulder and pin profiles. In both the cases, the FSW experimental runs were carried out using tool rotational speed of 600rpm, welding speed of 45mm/min, axial force of 11kN and tool tilt angle of 1.5°. The results of the study show that the joints produced using the tungsten lanthanum oxide tool are having superior mechanical and microstructural properties when compared to the joints produced using tungsten heavy alloy tool. Furthermore, the tool degradation study by mass loss and photographic techniques suggests that the tungsten lanthanum oxide tool is more prone to degradation by plastic deformation, whereas the tungsten heavy alloy tool is more prone to degradation by wear.

Systematic handling of missing data in complex study designs – experiences from the Health 2000 and 2011 Surveys

ABSTRACTWe present a systematic approach to the practical and comprehensive handling of missing data motivated by our experiences of analyzing longitudinal survey data. We consider the Health 2000 and 2011 Surveys (BRIF8901) where increased non-response and non-participation from 2000 to 2011 was a major issue. The model assumptions involved in the complex sampling design, repeated measurements design, non-participation mechanisms and associations are presented graphically using methodology previously defined as a causal model with design, i.e. a functional causal model extended with the study design. This tool forces the statistician to make the study design and the missing-data mechanism explicit. Using the systematic approach, the sampling probabilities and the participation probabilities can be considered separately. This is beneficial when the performance of missing-data methods are to be compared. Using data from Health 2000 and 2011 Surveys and from national registries, it was found that multiple imputation removed almost all differences between full sample and estimated prevalences. The inverse probability weighting removed more than half and the doubly robust method 60% of the differences. These findings are encouraging since decreasing participation rates are a major problem in population surveys worldwide.

Prediction of fatigue life of welding tool in friction stir welding of AA6061-T6

Computational fluid dynamics model is proposed for the calculation of tool forces in friction stir welding of AA6061-T6. Then, a finite element model is established to calculate the fatigue stress of the welding tool. Damage accumulation method and KBM multiaxial fatigue formulation are used to predict the fatigue life of the welding tool. Results indicate that the fatigue stresses on the tool pin are in tension at the front side and in compression at the rear side. Fatigue life of the welding tool can be increased with the increase of the rotation speed and can be decreased with the increase of the transverse speed. Both the increase of the shoulder diameter and the pin diameter can lead to the increase of the fatigue life of the welding tool.

The effect of in-process cooling conditions on temperature, force, wear resistance, microstructural, and mechanical properties of friction stir processed A356

This paper focused on the effect of in-process cooling conditions (coolants and flow rate) on the temperature history, the tool applied forces, wear resistance, mechanical, and microstructural properties of friction stir processing (FSP) of Al–Si aluminum alloy. FSP was carried out using different compressed air and water coolants with different flow rates. The FSP tool force was measured experimentally using an especially designed load measuring system. Optical microscopy was used to probe the microstructures of the FSPed samples. The results showed that the Si particles size significantly decreases with increasing in-process cooling rate. Mechanical properties of each FSPed sample were also determined using hardness tests. Finally wear tests were conducted using a pin-on-disk tribometer.

Effects of Some Process Parameters on the Impulse Force in Single Pulsed EDM

Electrical discharge machining (EDM) gets the advantage of less cutting force. However, a transient force named the impulse force exists in the machining process. The impulse force has effects on the efficiency, stability and accuracy of EDM. The peak current plays a major role in the impulse force, which has been studied and verified. However, the effects of other process parameters on the impulse force are lack of systematically study. Five single-factor experiments adopting different dielectric medium, polarity, gap width, tool geometry, and immersion depth, were designed and carried out. The single pulsed power source used in the experiments had constant discharge durations by detecting and shutting discharge current, which made the experiments to get rid of the randomness of discharge durations and be accurate. However, the vibration characteristics of the force sensor were changed by the dielectric medium, the fixture and the electrode weight, which made the measure of the impulse force to be complicated. The force balance method was simplified and adopted to acquire the maximum impulse force. It was found that these machining parameters had effects on the impulse force. There was little impulse force when the dielectric medium was air. The impulse force of positive polarity was a little higher than that of negative polarity. The impulse force of sphere tools was larger than that of needle tools. The increasing of gap width or immersion depth enlarged the impulse force. Moreover, the gap width had effects on the crater diameter while the depth of immersion did not. It is verified that these process parameters affected the impulse force by their effects on the bubble.

Investigation of the effect of friction stir processing parameters on temperature and forces of Al–Si aluminum alloys

Temperature and forces in friction stir processing (FSP) induced by process input parameters play a critical role in successful welding. In this investigation, the effect of the process parameters on the axial and longitudinal forces and temperature history of the process were investigated. The temperature distribution during the FSP was determined by placing thermocouples in the workpiece and measuring the temperature during the process. The tool forces were investigated experimentally using an especially designed load measuring system. The pin shape, rotational speed and traverse speed were the parameters taken into consideration. It was observed that increase in tool traverse speed or decrease in rotational speed leads to increase in both tool axial and longitudinal forces.

Enhancement of process capabilities in electrically-assisted double sided incremental forming

Electrically-assisted incremental sheet forming (E-ISF) is an effective method to improve formability by introducing the electric current in ISF process. This method is particularly useful for production of lightweight ‘hard-to-form’ materials such as magnesium and titanium alloys. However, the use of electricity and heat may also lead to side effects to formed components, such as unacceptable surface finish. In this work, an improved E-DSIF process has been developed by combining the electrically-assisted forming technology, the double sided incremental forming (DSIF) and a newly designed slave tool force control device to ensure stable tool-sheet contact. Different types of forming tools and toolpath strategies are explored to improve surface finish and geometrical accuracy by using a customized DSIF machine. AZ31B magnesium alloy sheets are formed into a truncated cone shape to verify the proposed E-DSIF process. In the investigation, the causes of rough surface finish are investigated in detail, and the surface finish is refined by improving the contact condition at tool-sheet interface. In addition, a hybrid toolpath strategy is proposed to further enhance the geometrical accuracy. The results demonstrate that the two challenging issues, surface finish and geometrical accuracy, could be improved by using the enhanced technologies of E-DSIF.

Study on the dynamic coupling characteristics of 3PTT-2R numerical control serial–parallel machine based on singular constraints and position coupling factors

The dynamic coupling problem for the self-designed “3 parallel ∪ 2 series” mixed-type numerical control machine tool is studied based on the singular constraints and position coupling factors in order to ensure that the machine can have better dynamic characteristics and a higher quality of parts during the process of machining complex surface. This article puts forward a method based on singular constraints and the coupling factor. A whole dynamic coupling model of series and parallel mechanism is established and the coupling factors are determined. Numerical and parameter simulations of mechanism are analyzed and the real working space is obtained. And this article takes the simulation of the process of machining complex part and the force of the machine tool. The simulation results show that the established dynamics model is credible and reliable on the basis of considering singular constraints and position coupling factors. It is proved that the simulation data can correspond to the established model and the situation of force and kinematic suits the working mechanism. The cutting experiment of complex surface parts was took and the machine tool was run more smoothly and faster than the conventional machine tools. The velocity of the machine is regular and circular and there are no kinematic singularity data on the machine’s trajectory. The trajectory of the tool is in the working space completely and the accuracy of the part is good. The surface roughness results show that the kinematics accuracy of the machine tool is good. The interference fringe results show that the force of the machine tool is uniform. As there is no singular coupled vibration and collision, it is proved that the theoretical analysis is correct. The dynamics model of 3PTT serial and parallel mechanism is complete in this article. And the working space of the mechanism is obtained on the base of analysis of the singular constraints and position coupling factors. The article has carried out the dynamic simulation and processing experimental verification. Not only the method and process of this article was solved by dynamics coupling problem of 3PTT-2R numerical control machine tool actively, real-time and effectively, but also it was laid a foundation for accurate control of numerical control machine tools.

Analysis of hard turning process: thermal aspects

In manufacturing sector, hard turning has emerged as a vital machining process for cutting hardened steels. Besides many advantages of hard turning operations, one has to implement to achieve close tolerances in terms of surface finish, high product quality, reduced machining time, low operating cost and environmental friendly characteristics. In the study, three dimensional (3D) computer aided engineering (CAE) based simulation of hard turning by using commercial software DEFORM 3D has been compared to the experimental results of stresses, temperatures and tool forces in machining of AISI D3 and AISI H13 steel using mixed ceramic inserts (CC6050). In the following analysis, orthogonal cutting models are proposed, considering several processing parameters such as cutting speed, feed and depth of cut. An exhaustive friction modelling at the tool-work interface is carried out. Work material flow around the cutting edge is carefully modelled with adaptive re-meshing simulation capability of DEFORM 3D. The process simulations are performed at constant feed rate (0.075 mm/r) and cutting speed (155 m/min), and analysis is focused on stresses, forces and temperatures generated during the process of machining. Close agreement is observed between the CAE simulation and experimental values.

Tool path generation and optimization method for pocket flank milling of aircraft structural parts based on the constraints of cutting force and dynamic characteristics of machine tools

The cutting force and vibration will be increased dramatically due to the sharp change of cutting engagement angle during the process of pocket flank milling for aircraft structural parts. And the sharp change of the curvature of tool path curves of pocket corner brings higher requirements for the performance of dynamic characteristics of the machine tool, while the machining quality of the surface will be affected heavily once the dynamic characteristics of the machine tool cannot meet the machining dynamic characteristics requirements. It is very important to consider the constraints of cutting force and dynamic characteristics of the machine tool during tool path generation. However, it is a contradictory problem to satisfy the requirement proposed by the two constraints on tool path, and it is not easy to compromise the two constraints. In order to address the difficult issue mentioned above, a new tool path generation and optimization method for pocket flank milling is proposed. The essential idea of this paper is the combination strategy of corner-looping milling and clothoid curve transition, where the contradictory requirement of the above two constraints can be compromised and optimized. The machining experiment results show that the conditions of cutting force can be improved, vibration during the process of machining can be reduce, as well as the machining quality of the surface is improved.

Modeling of a virtual grinding wheel based on random distribution of multi-grains and simulation of machine-process interaction

The interaction of the machine-process in grinding frequently brings unpredictable results to the quality of the prod- ucts and processing stability. This paper presents a multi-grains grinding model to simulate the precision grinding process of cemented carbide inserts. The interaction between the grinding process and machine tool is then investigated based on the pro- posed grinding model. First, the real topography of the grinding wheel is simulated. Based on the assumption of spacing distri- bution of multi-grains and the virtual grid method, the hexahedron abrasive grains are randomly distributed on the surface of the virtual grinding wheel and the postures of abrasive grains are randomly allocated. Second, the grinding model is built by import- ing the virtual grinding wheel model into Deform-3D software, and the grinding force values are obtained by simulation. The validity of the proposed grinding model is verified by experiments. Then, the interaction coupling simulation of the machine tool structure and grinding process is built to investigate the interaction mechanism. The simulations reveal that remarkable interac- tive effects exist between the deformation of the grinding wheel of the machine tool and grinding force. The finite element method (FEM) coupling simulation method proposed in this paper can be used to predict the machine-process interaction.

Boolean Satisfiability Solvers and Their Applications in Model Checking

Boolean satisfiability (SAT)—the problem of determining whether there exists an assignment satisfying a given Boolean formula—is a fundamental intractable problem in computer science. SAT has many applications in electronic design automation (EDA), notably in synthesis and verification. Consequently, SAT has received much attention from the EDA community, who developed algorithms that have had a significant impact on the performance of SAT solvers. EDA researchers introduced techniques such as conflict-driven clause learning, novel branching heuristics, and efficient unit propagation. These techniques form the basis of all modern SAT solvers. Using these ideas, contemporary SAT solvers can often handle practical instances with millions of variables and constraints. The continuing advances of SAT solvers are the driving force of modern model checking tools, which are used to check the correctness of hardware designs. Contemporary automated verification techniques such as bounded model checking, proof-based abstraction, interpolation-based model checking, and IC3 have in common that they are all based on SAT solvers and their extensions. In this paper, we trace the most important contributions made to modern SAT solvers by the EDA community, and discuss applications of SAT in hardware model checking.

Comprehensive error measurement and compensation method for equivalent cutting forces

To determine the error compensation for cutting forces with a machine tool, this paper proposes a comprehensive error compensation method that determines an equivalent cutting force. The loading system that applies this equivalent cutting force was designed to load a constant force that imitates the actual cutting force of a machine tool. The equivalent cutting force, when applied to the working table of the machine tool, induces an error that can be directly measured by a laser interferometer. Moreover, a stable measurement environment suitable for laser interferometer is configured. A comprehensive error compensation model of a three-axis computer numerical control (CNC) machine tool was developed using multi-body systems theory and homogeneous transformation matrices. Solutions for the error compensation model and parametric equation were automatically found using MATLAB, based on this model. The effectiveness of this compensation method has been confirmed by machining experiments. The experimental results show that this comprehensive error compensation of the equivalent cutting force can greatly improve machining accuracy.

Mechanochemically Active Soft Robots.

The functions of soft robotics are intimately tied to their form-channels and voids defined by an elastomeric superstructure that reversibly stores and releases mechanical energy to change shape, grip objects, and achieve complex motions. Here, we demonstrate that covalent polymer mechanochemistry provides a viable mechanism to convert the same mechanical potential energy used for actuation in soft robots into a mechanochromic, covalent chemical response. A bis-alkene functionalized spiropyran (SP) mechanophore is cured into a molded poly(dimethylsiloxane) (PDMS) soft robot walker and gripper. The stresses and strains necessary for SP activation are compatible with soft robot function. The color change associated with actuation suggests opportunities for not only new color changing or camouflaging strategies, but also the possibility for simultaneous activation of latent chemistry (e.g., release of small molecules, change in mechanical properties, activation of catalysts, etc.) in soft robots. In addition, mechanochromic stress mapping in a functional robotic device might provide a useful design and optimization tool, revealing spatial and temporal force evolution within the robot in a way that might be coupled to autonomous feedback loops that allow the robot to regulate its own activity. The demonstration motivates the simultaneous development of new combinations of mechanophores, materials, and soft, active devices for enhanced functionality.

Experimental study on the effects of clearance and clamping in steel sheet metal shearing

Shear cutting is common within several sheet metal industry processing steps, e.g. in cut to length lines, slitting lines, end cropping. Shearing is fast and cheap relative to competing cutting methods like laser and plasma cutting, but involves large forces on the equipment that increase with increased sheet material strength. Accurate shear experiments are a prerequisite to increase the knowledge of shearing parameters, improve industrial shearing, and provide data for validation of numerical shear models. Here, the two shear parameters clearance and clamp configuration, identified as important to the shear results, were studied in an experimental set-up with well defined tool movement and high measurability of tool position and force. In addition to force measurements, the sheared edge geometry was characterized. Steels of low, medium, and high strength were selected for the study. Throughout the experimental study, the shear tool penetration before fracture decreased with increased material strength. The required shear force decreased and the force attempting to separate the two shear tools increased when one side of the sheet was left unclamped and free to move. Further, the maximum shear force increased with decreased clearance. Clearance changes were small and moreover continuously measured during all shear experiments.