Small Corner Radii Research Articles

Impact of rubber block end-face corner radius on the friction coefficient between rubber blocks and a glass plate under dry and lubrication conditions

The friction between a glass plate and rubber blocks with different end-face corner radii was investigated. Under dry conditions, rubber blocks with a large end-face corner radius (r = 0.83 mm) exhibited greater friction coefficients than those with a small end-face corner radius (r = 0.11 mm). Conversely, friction coefficients for r = 0.11 mm were greater than those for r = 0.83 mm under lubrication conditions. Further, the friction coefficients for r = 0.11 mm increased as the sliding velocity and lubricant viscosity increased owing to the formation of the fluid-free gap at the contact interface.

Surface machining effect on material behavior of additive manufactured SUS 316L

Abstract Microstructural change of the additive manufactured (AMed) SUS 316 L part via surface machining and its effects on mechanical properties are analyzed. The laminated surface layer is formed with higher hardness and higher strength comparing to the inside due to the distortion of grains through repeated melting and rapid solidification. Through the microstructure analysis of inverse pole figure and grain boundary information maps on the surface before and after surface machining, we found out how the surface layer affects the material behavior. The surface machined simple-stepped-model (SSM) specimen showed an increase in deformation by about 5.6–8.9% compared to as-built one. Moreover, in the case of the additive manufactured SSM specimen with a small corner radius, the amount of deformation increased after machining. Therefore, we believe that when the design of mechanical parts that are manufactured by AM process should be considered the surface machining effect studied in this work.

Movable Die and Loading Path Design in Tube Hydroforming of Irregular Bellows

Manufacturing of irregular bellows with small corner radii and sharp angles is a challenge in tube hydroforming processes. Design of movable dies with an appropriate loading path is an alternative solution to obtain products with required geometrical and dimensional specifications. In this paper, a tube hydroforming process using a novel movable die design is developed to decrease the internal pressure and the maximal thinning ratio in the formed product. Two kinds of feeding types are proposed to make the maximal thinning ratio in the formed bellows as small as possible. A finite element simulation software “DEFORM 3D” is used to analyze the plastic deformation of the tube within the die cavity using the proposed movable die design. Forming windows for sound products using different feeding types are also investigated. Finally, tube hydroforming experiments of irregular bellows are conducted and experimental thickness distributions of the products are compared with the simulation results to validate the analytical modeling with the proposed movable die concept.

MESO-Scale Modeling of CFRP-Confined Concrete: Microplane-Based Approach

The present paper shows the results of three-dimensional (3D) meso-scale numerical simulations that were performed on unconfined and Carbon Fibre Reinforced Polymer (CFRP)-confined concrete specimens under uniaxial compression. The numerical results are compared with available experimental data. The meso-scale structure of concrete is composed by two phases, namely: the coarse aggregate and the mortar matrix. The presence of Interfacial Transition Zone (ITZ) is neglected. A simple generation procedure is used to randomly place the coarse aggregate inside the concrete specimens. The finite element code MASA is used to perform the three-dimensional (3D) Finite Element meso-scale simulations. The constitutive laws for mortar and epoxy resin are based on the microplane model, while an elastic-brittle behavior is assumed for the fibers. Aggregate in concrete is considered to be linear elastic. The adopted meso-scale model for concrete can realistically reproduce the mechanical behavior of both unconfined and CFRP-confined specimens. However, in the case of small corner radius, the effect of confinement predicted by the model is overestimated with respect to the experimental results. This is partially related to the simplifications introduced in the model in terms of aggregate volumetric fraction (10%) and aggregate size distribution. It is shown that a more detailed meso-scale model, which is characterized by 30% of the coarse aggregate and realistic aggregate size distribution, can better capture the interaction between the concrete heterogeneity and the confining effect provided by CFRP.

Experimental investigation on influence of engagement angle and tool geometry on plunge milling

Taking advantage of the superior cutter axial stiffness, plunge milling provides a higher material removal rate in rough milling for components with deep cavities. Tool wear depending on cutting parameters of radial cutting width, axial cutting depth, step interval, feedrate, and spindle speed has been studied by several researchers. For a more comprehensive understanding of the wear mechanism, this study investigates the influences of tool engagement angle and tool geometry on tool wear based on multiple sets of machining tests. The development of tool wear during plunge milling is monitored. Results show that tool wear of insert with large engagement angle mainly exists on minor edge, which is caused by increased tool deflection. When the radial distance equals to tool radius, optimal engagement angle can be achieved while considering both tool life and machining efficiency. The experimental results show that tool life of insert with rake angle of 22° is 6.5% higher than rake angle of 15°. Smaller corner radius has positive influences on tool life improvement. Surprisingly, tool life of insert without cutting edge chamfer is 3.6 times than insert with cutting edge chamfer. The best tool geometric parameters of plunge insert can then be identified among a variety of inserts. This work is useful for cutting tool producers and manufacturers to optimize tool geometry and machining parameters.

<b>Influence of different dielectrics fluids on the surface integrity of high speed steel

Machining by electrical discharges is a huge process for the machining of complex shapes in materials that are electrical conductors, in particular for those of high hardness, difficult to be machined by conventional processes. Its unique feature of using thermal energy to machine parts has been a distinctive advantage in the manufacture of moulds, dies, aerospace components, and surgical, and of course, it can be widely used in the industry of tooling in the manufacture of geometric features, such as, for example, cavities narrow and deep, grooves, thin-walled, and small corner radii. One of the materials that are widely machined by spark-erosion is the tool steel (ABNT M2, has good toughness, hardness and abrasion resistance being indicated for the manufacture of stamping dies. The present work describes experiments conducted on a modern machine eletroerosiva using the electrode-tool of electrolytic copper in the machining of parts from high-speed steel (ABNT M2 to investigate the effect of different fluid dielectric about the generation of microcracks and heat affected zone (HAZ). A review of the comparative shows that the surfaces machined with dielectric fluid “A” have low values in the length of the microcracks compared with the other fluids. In the meantime, the machined surfaces with the dielectric “B” have a lower density of microcracks.

Reduction of corner radius of cylindrical parts by magnetic force under various loading methods

To prevent small corner radius of cylindrical parts from cracking near the sheet bottom corner during deep drawing, a new method combining multidirection magnetic force electromagnetic forming and traditional stamping is proposed in this paper. First, a punch with an 8-mm corner radius is used to obtain a cylindrical part. Then, a coil-generated multidirection magnetic force is used to further deform the sheet corner radius and obtain a smaller corner radius. ANSYS/emag and ABAQUS/explicit software are used to calculate the multiphysical field coupling process in electromagnetic forming (EMF), and obtain accurate simulation data based on the experimental results. We found the following that the maximum thickness thinning ratio was 20% in the sheet corner region with an applied multidirection magnetic force in comparison to 33% if only a bulging coil was used.

Metal flow control during hot forming of square cups with local-thickened plates and varied friction conditions

Obtaining square cups with the radius at the bottom corner lower than the thickness of original plate via a single-step hot forming process is a challenge. In this paper, a processing way was proposed by combining local-thickened plate and friction control, to manufacture square cups with small corner radii. Through finite element (FE) simulations, the metal flow during hot forming of square cups was optimized by varying the shape of the local thickened section and adjusting the friction conditions at the interfaces between blank and tools. It was found that the filling ratio of the bottom corner can be significantly improved by increasing the friction coefficient at the interfaces between the blank and the upper punch, and that between the blank and the central zone of counter punch. The established flow dividing surface (FDS) model is capable for describing the variation of metal flow with the friction coefficients. Base on the simulation results, hot forming experiments were also carried out, and square cups with small radii of 2mm at the bottom corners were successfully manufactured.

Reliability of Al<sub>2</sub>O<sub>3</sub>/TiC Micro-Nano-Composite Ceramic Tool in the Machining of Stainless Steel

The cutting performance, failure mechanisms and reliability of Al2O3/TiC micro-nanocomposite ceramic tools with different geometry parameters in continuous machining of austenitic stainless steel were studied. The results showed that the largest metal removal amount was got at the cutting speed of 80 m/min, the feed rate of 0.15 mm/r and the cutting depth of 0.1 mm. The failure modes of the tool with small chamfering width and corner radius were mainly cutting edge fracture and tool materials peeling off, which was due to the subcritical crack growth. The life of the tool with small chamfering width and corner radius well followed the Gamma distribution.

Corner strengthening of square and rectangular concrete-filled FRP tubes

This paper presents the results of an experimental study that investigated the application of a corner strengthening technique to square and rectangular concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs). Effects of the strengthening technique were investigated through axial compression tests undertaken on a series of CFFT specimens having different corner radii and sectional aspect ratios. The results indicate that the compressive behavior of square and rectangular CFFTs can be improved through corner strengthening, which significantly reduces or completely eliminates temporary post-peak strength softening observed in some CFFTs. The results also indicate that the premature FRP rupture at corners due to stress concentrations can be prevented through sufficient strengthening of the specimen corners. It is found that increasing the amount of corner strengthening leads to an increase in the confinement effectiveness of CFFTs and results in a more uniform confining pressure distribution along specimen cross-section. It is also found that corner strengthening provides a more significant improvement in the compressive behavior of CFFTs with lower original confinement effectiveness caused by a smaller corner radius or a larger aspect ratio.

Residual Stresses and Surface Integrity of Ti-alloys During Finish Turning – Guidelines for Compressive Residual Stresses

Residual stresses (RS) induced by machining control a component's resistance to progressive failure. It is crucial to identify favorable cutting conditions that promote fatigue-inhibiting compressive RS while preserving other aspects of surface integrity. An extensive investigation was performed in the finish turning regime for two aerospace grade Ti-alloys, Ti-6Al-4V (Ti-64) and Ti-6Al-2Sn-4Zr-6Mo (Ti-6246). A comprehensive evaluation of surface integrity was carried out including RS, surface roughness, the near-surface microstructure, and hardness distribution. The behavior of RS and surface roughness was correlated to the cutting parameters. Within the investigated parameter range, RS were compressive in nature. High MRR conditions and small corner radii were found to promote larger compressive RS for both Ti-alloys. A conflict between RS and surface roughness was observed. While machining at high feed rates enhanced compressive RS, it was detrimental to surface finish. Guidelines were developed for the optimal selection of cutting parameters to achieve desired levels of RS and surface finish.

Forming box-shaped ends in circular tubes

This study is aimed to form a pair of axially displaced box-shaped ends from a circular tube. In this process, one tube end is first expanded into a circular section having a diameter equal to the diagonal length of the target square using a conical top circular die. A square punch having a conical bottom end and a tapered square die are then used to draw the expanded section into a square box. The side walls of the box are flattened at an ironing ratio of 15% corresponding to its initial wall thickness. The expansion and squaring processes are repeated at the opposite tube end. However, the tapered die in the final stage is oriented at 45 relative to the square punch and tube to form an axially displaced square section at the opposite end. Both the experiments and FE simulations were performed to evaluate this process. A pair of axially displaced box-shaped ends having small corner radii is successfully obtained from the experiment and the simulation. With the developed process, the design of steel balustrades is improved and similar to the precast or stone balustrades.

A new method for multi-pass single-point incremental forming of vertical wall square box with small corner radius

According to the sine law, a vertical wall square box cannot be formed by incremental forming with a single-pass process; or rather it must be created with multi-pass processes. It is found that successful forming not only depends on the forming half-apex angle θ of a conical box, but also on the corner radius r. The metal will pile up on the corner for a square box with a small corner radius when the tool paths are unreasonable. Therefore, the tool paths with a gradually reduced corner radius are adopted to overcome this problem. A vertical wall square box with a small corner radius is successfully created.

A Simple Procedure to Optimize Small Radius Rounded Corners Obtained From Schwarz–Christoffel Conformal Transformations

Both conformal mapping via Schwarz–Christoffel (SC) formulas and finite element methods (FEM) can provide accurate results in analyzing 2-D electric or magnetic fields. In the presence of curved boundaries with small radius of curvature, the first are normally constrained to introduce piecewise straight lines. The original contribution of this paper consists of presenting a reliable but simple procedure to smooth several sharp vertices of a polygonal boundary by the formula for rounded corners, and comparing the results with those obtained by replacing sharp corners with piecewise straight lines. Differences are perceived only in close proximity, and this quantitatively explains the similar results obtained from maps and from FEMs and provides reliable assessment of the obtainable results. Two approaches are followed. According to the first, sharp corner geometries are directly mapped into rounded corner ones, accepting small changes in the whole structure, and negligible only for small corner radii. According to the second, the simple optimization procedure of the SC prevertices allow us to match the original geometry in all details.

High Pressure Pneumatic Forming of Ti-3Al-2.5V Titanium Tubes in a Square Cross-Sectional Die

A new high strain rate forming process for titanium alloys is presented and named High Pressure Pneumatic Forming (HPPF), which might be applicable to form certain tubular components with irregular cross sections with high efficiency, both with respect to energy cost and time consumption. HPPF experiments were performed on Ti-3Al-2.5V titanium alloy tubes using a square cross-sectional die with a small corner radius. The effects of forming of pressure and temperature on the corner filling were investigated and the thickness distributions after the HPPF processes at various pressure levels are discussed. At the same time, the stress state, strain and strain rate distribution during the HPPF process were numerically analyzed by the finite element method. Microstructure evolution of the formed tubes was also analyzed by using electron back scattering diffraction (EBSD). Because of different stress states, the strain and strain rate are very different at different areas of the tube during the corner filling process, and consequently the microstructure of the formed component is affected to some degree. The results verified that HPPF is a potential technology to form titanium tubular components with complicated geometrical features with high efficiency.

End Formation of a Round Tube into a Square Section with Reduced Forming Loads

Low formation loads are desirable in metal stamping industries as it reduces the press capacity of the machine and the tooling cost. In the previous study, the author had successfully developed a 2-stage end formation process of a round tube into a square section having small corner radii. However, the formation load in this process increased linearly with the punch stroke in the 1st stage due to the continuous expansion of the tube end by the conical die. Hence, buckling and cracks occurred at the circular section and the bottom end of the square section respectively when the punch stroke was excessive. In this study, the author proposes a circular die having a conical bottom replacing the conical die for the expansion of the tube end. Although the formation load increases when the tube end is expanded at the conical bottom, the amount of increase becomes small when the tube end reaches the circular section of the die due to its constant diameter. At the circular section, the tube end curls and wraps over the die when the punch stroke is increased. In the 2nd stage, the squaring process is performed with a conical bottom square punch and a taper square die for the two different expanded tubes i.e. the one formed with the conical die and the one formed with the conical bottom circular die. Both Finite Element Method (FEM) simulation and experiment were performed to evaluate these two processes. The distribution of plastic strains, forming loads and product appearances are investigated. With the circular die, the maximum forming loads are successfully reduced by 20% and 33% in the 1st and the 2nd stages respectively in the experiment when compared to the ones formed with the conical die. No buckling and cracks are observed for the tube formed with the circular die.

Effect of Initial Position of the Counterpunch on T-Shape Hydroforming

The loading path is crucial to the quality of forming parts in the process of tube hydroforming. The counterpunch is usually used to control the protrusion height and also to control the evolution of thickness and avoid over thinning in T-shape hydroforming. In this study, the experiments of T-shape hydroforming are conducted, in which tubular material used is stainless steel and has an outer diameter of 103mm. A fuzzy logic-based load control algorithm is developed for optimizing the loading path, and four different initial positions of the counterpunch are designed to investigate its influence on wall-thinning and the corner radius at protrusion end. The results show that the minimum thinning can be obtained with an initial position of 12.5mm, while a smaller corner radius is obtained with an initial position of 37.5mm.

End formation of a round tube into a square section having small corner radii

Expansion and reduction are the two common end forming processes for tubes. In the tube end expansion process using a square punch, it is difficult to obtain a small corner radii due to the stretching of the tube around the punch corners. The wall thickness around the corners is small when compared to the side wall. Hence, a tube having a poor square look is formed. In this study, a 2-stage end expansion of a round tube end into a square section having an improved square look i.e. small corner radii and increase in wall thickness around corners is developed. In the 1st stage, the tube end is flared into a cone shape using a 30° conical die by axial compression. In the 2nd stage, the conical end of the tube is drawn through a taper square die using a conical bottom square punch, and a near square section is formed. A 15% ironing ratio is applied during the drawing process to flatten the side wall of the square. Experimental and FEM simulation were performed to evaluate and to verify the forming process. Although the height of the square section increases when the punch stroke at the 1st stage is increased. However, this increase is limited by the buckling of the pipe at the circular section of the thick blank tube. Since the conical end is drawn into a square section having different radial lengths, the bottom of the square section is uneven. The uneven bottom end is trimmed off in the later process. A square section having a maximum height of 32mm after trimming is successfully obtained from the experiment for the punch stroke, S=44mm using an API 5L tube.

Correlating surface roughness, tool wear and tool vibration in the milling process of hardened steel using long slender tools

High speed milling is an operation frequently used in finishing and semi-finishing of dies and molds. However, when it is necessary to produce molds with deep cavities and/or with small corner radius, long tools with small diameters are required. This represents a challenge for manufacturing professionals: how to minimize tool vibration using a tool with such low rigidity and obtain good workpiece surface quality and long tool lives. This paper attempts to answer this question. Milling experiments on hardened AISI H13 steel were carried out using integral and indexable insert tools with different tool overhangs and different diameters. Tool wear, workpiece surface roughness and cutting forces were measured and these parameters were correlated with the frequency response function (FRF) obtained with the tools fixed in the machine tool. The main conclusion of this study is that good workpiece surface roughness allied to long tool lives for long tools with small diameters can be achieved, provided the tooth passing frequency used in the milling process (and its harmonics) does not produce high FRF values.

Surface topography changes in aluminum alloy sheet during large plastic straining under cyclic pure bending

This study consists of the experimental assessment of the surface topography of aluminum alloy AA 6022 sheet during large cyclic tensile and compressive plastic straining such as those present in the flow through drawbeads and small corner radii. Uniaxial and cyclic bending tests were used to measure the effects of such strains on the substrate layers of the sheet. All testing was performed without tool contact to ensure surface roughness changes were exclusively the result of the straining evolution of the free outer layers. The three-dimensional average surface roughness (Sa) was measured using optical interferometry. Changes in Sa were evaluated for two sheet textures: mill finish (MF) and electro discharge texture (EDT), along longitudinal and transverse rolling directions. Texture pattern, test direction, and bending/unbending strain are all shown to be significant contributors to variations in Sa. The magnitude of the initial surface roughness was also an important factor of the resultant %Sa variation, ranging from 40% ΔSa for EDT, to approximately 350% ΔSa for MF. Unbending the sample to its flat state considerably altered the Sa, disturbing any monotonic Sa trend. This made it unfeasible to assess the effects of strain history on a formed part based only on Sa values. The non-linear relationship between Sa and strain was more significant at medium and large strains. Effects on Sa due to bending/unbending of the substrate layer presented in this study must be taken into account in the modeling of more complex phenomena involving tool radii contact and friction.