Rolling Tool Research Articles

Texture evolution and controlling of high-strength titanium alloy tube in cold pilgering for properties tailoring

Abstract As one of the preferred fabrication technologies for high-strength titanium alloy tubes, cold pilgering has unique advantages of large deformation, fine surface, and close dimensional tolerance since materials are incrementally experiencing compressive stress states dominated local loading throughout entire rolling process. However, both complex external loading history and low symmetric hexagonal close-packed (HCP) crystal structure induce heavy crystallographic reorientation of polycrystalline significantly influencing formability and performance of titanium tubular products. How to achieve a bespoken tailoring of texture related properties is still a challenge. Accordingly, taking high-strength Ti-3Al-2.5 V tubes as the case material, this study focuses on the tube texture evolution and the texture controlling guidelines for properties tailoring in cold pilgering. By coupling validated and verified three dimensional finite element (3D-FE) model and viscoplastic self-consistent (VPSC) crystal plasticity model, a macro-meso scaled computation platform is established to predict the inhomogeneous deformation flow and texture evolution during pilgering. Then the tube texture evolution characteristics along rolling process with three typical initial textures are investigated, and the correlation between texture evolution and spatial inhomogeneous deformation allocation is explored, in which the deformation history is fully featured by strain vector, viz., strain ratio α and equivalent plastic strain ee as well as ratios of wall thickness thinning to outer diameter reduction (total Q value and transient Q value). Taking the contractile strain ratio (CSR) as the most important indicator for evaluating the texture and properties, the effect of final texture features of the tube on its tensile mechanical properties is revealed, and then the texture controlling guidelines for properties tailoring of the tube are proposed. To obtain the desired near radial texture and the reasonable CSR, the different pass rolling specifications can be considerably designed to coordinate the spatial strain components based on reasonable range of total Q value and ee, then the rolling tools can be designed for further fine tuning of the transient Q value and strain ratio α.

The ways to ensure fatigue strength of cold-formed rebars. Foundry production and metallurgy

To ensure safe operation of buildings and structures from reinforced concrete, European norms set requirements for its fatigue strength (resistance). Tests are carried out with oscillation swing amplitude 2sa from 150–200 MPa. Rebar shall withstand from 1 to 2 mln. cycles.The analysis of causes which decrease the fatigue strength of cold-formed steel is made in the article. Fatigue strength is a lot affected by surface defects and stress concentrators. Filler transition in the point where transversal rib crosses a rebar body becomes as a rebar stress concentrator. To detect details of early breakage, analysis the condition of fracture in the area of thickened (marking) ribs was made. Sequence of rebar breakage was established as well as the initial point of a crack creation was detected. This fracture is characterized as a fatigue one, with clear zones of fatigue fracture having fine-grained surface and static fracture zone– the rest of section with fibrous structure. While applying a bar mark, smoothness of filler transition was disturbed in the crossing point where transversal rib crosses a rebar body, and this action caused decrease of fatigue strength of cold-formed rebar.The article describes research on development of requirements for rolling tools used in production of cold-formed rebars.Use of information given in this article during design, purchasing and manufacture of the equipment will allow to minimize factors which have negative influence on rebar’s fatigue test results.

Mechanization of forming and levelling of frame and casing parts

The machining of parts reinforced with ribs may lead to deformations expressed by two-axis bending and twisting. An effective method to eliminate such deviations is rolling, which unlike pressing, excludes cracking of aluminum alloys [1-3]. The developed set of manual rolling tool allows processing ribs and blades of a part to receive deformation in two planes. The development of levelling technology that includes mechanized rolling unit and software for automated calculation of process parameters of rolling seems quite promising.

Improving nanocutting surface quality by force-controlled rolling

Force-controlled rolling method which is a combination of rolling tool, force sensor and fast tool servo is proposed to realize real-time control of rolling force in surface modification process. Especially when the surface is complex, the rolling force can be changed dynamically based on the surface profile and the rolling path. Therefore, the machinability of soft material, such as lead (Pb), are easy to be modified by force-controlled rolling. After the soft and sticky workpiece, lead, is modified, the surface of it becomes hard enough to suppress the scratch of the chips, the formation of built-up edge, and the side flow of the workpiece material at the subsequent nanocutting process. Nanocutting of Pb mirrors validates the effectiveness of the force-controlled rolling method. Besides that, side flow region under the action of the tool edge and its evolution after the formation of build-up edge is investigated.

Numerical and experimental investigation on material flow in gear forced throughfeed rolling process

The cylindrical die forced throughfeed rolling process for gears was proposed to overcome an end-effect behavior of the standard radial-feed gear rolling process which can result in pitch variation and excessive axial end-flow. In the rolling process, the workpieces are pushed through the gap of the rolling tools to form the gear teeth. Understanding of material flow is important for grasping the cause of defect formation and improving the quality of formed gears. In this paper, the material flow behavior of the gear forced throughfeed rolling process was studied on the flow velocity and displacement of key locations by using finite element analysis (FEA). The experiment was also conducted and its blank was sliced to thin pieces, and the grid pattern (GP) was utilized to track the trajectory of flowing materials. The results show that the end-flow is located at the root rather than the tooth crest of the formed workpiece, because the compressive forces from rolling tool mainly take effect at the root of the formed workpiece. The asymmetry of circumferential flow displacements with respect to the gear teeth results in the asymmetrical flanks defect, and this is due to the meshing between teeth of rolling tool and workpiece. The local displacement in the radial direction is larger than that in the circumferential direction.

Hardness prediction of a cold rolled Nimonic 80A exhaust valve spindle

Purpose: of this paper is to predict the hardness of cold rolled exhausts valve spindle fabricated of Nimonic 80A via axisymmetric finite element analysis, compression testing, and hardness inspection. Design/methodology/approach: The stress-strain relationship of Nimonic 80A was obtained via compression testing with deformation ratios of 10%, 20%, and 30%. Hardness changes caused by the strain hardening effect were measured in cut specimens in both the axial and circumferential directions following compression testing. The effective strain at the measurement position was calculated via finite element analysis. The regression equation for hardness changes caused by work hardening was derived from analysed strain and inspected hardness. The cold-rolling deformation of an exhaust valve spindle was analysed using axisymmetric finite element analysis. Findings: The stress-strain relationship calculated from compression testing was well expressed using the Holloman equation and the strain-hardness relationship by strain hardening was successfully regressed using the shifted power law model for Nimonic 80A, Nickel-Chromium based super alloy. Research limitations/implications: This research focused hardness prediction of spindle after ring rolling operation for generating beneficial compressive surface residual stresses for enhancing fatigue life. Further research to quantify compressive residual stress after rolling shall be followed to increase fatigue life. Practical implications: The cold rolling process is a typical incremental forming method and should be analysed under three-dimensional conditions. However, it takes lots of time to solve incremental forming analysis. To predict hardness distribution after rolling in the manufacturing field, FE analysis was performed under two-dimensional axisymmetric conditions based on the assumption of no friction generated by the rolling tool. The deformed shapes and hardness distribution from the inspection quality standard and two-dimensional FE analysis showed very similar results. Simplified finite element analysis method for ring rolling process for local area could be very effective method in the industrial field. Originality/value: The stress-strain relationship and the hardness and strain relationship were derived by compression test and hardness measurement for compressed specimen for Nimonic 80A, Nickel-Chromium based super alloy. And simplified finite element analysis method was suggested to predict deformed shape and hardness distribution of locally cold rolled region and achieved similar result between FE analysis result and Quality standard. Suggested method would be very effective method to engine spindle manufacture to predict hardness of different size of product.

Performance investigation of magnetorheological finishing of rolls surface in cold rolling process

Cold rolling is one of the most vital manufacturing operation in the sheet metal industries. It produces controlled size and accurate thinner gauge components with a smooth surface. In cold rolling operation, the rolls are the most important component. If rolls surface gets finished at a greater level, a smooth surface on the final products can be achieved. This may improve functional performance for their practical use. To accomplish this requirement, the magnetorheological (MR) finishing process using rectangular-rotating tool core tip has been used to finish the external surface of the rolls. The process parameters such as roll workpiece rotation, tool feed, tool rotation, working gap and current intensity of the electromagnet and composition of MR polishing fluid are considered to investigate the performance of cold rolling rolls using the rectangular-rotating core tip-based MR finishing process. For effectively performing the MR finishing operation, the optimum process parameters are predicted by using the response surface methodology. These optimum parameters have been used to perform the MR finishing on the external surface of the industrial H13 die steel rolls as used in cold rolling process. The surface roughness gets reduced to 18 nm from the initial ground roughness value of 200 nm. After the MR finishing operation, the cold rolling rolls are tested its functional performance in the industry. The performance of the MR finished rolls surface is investigated as compared with the ground rolls surface. Experimentally and theoretically analyse the roll force, roll torque, and power consumption on use of before and after MR finished rolls surface in cold rolling operation. Almost all the performance parameters with MR finished rolls surface are found in favour of improvement in functional operation during its actual application in the cold rolling process.

Experimental Assessment of the Depth of the Deformed Layer in the Roller Burnishing Process

This paper presents the methods of experimental determining the depth of the plastically deformed top layer in the roller burnishing process. Precise determination of the depth of the plastically deformed layer is difficult due to slight deformation at the boundary of the plastic and elastic zone, the lack of visible changes in the microstructure, and minimal changes in microhardness. The article shows the method of original measurement method that consists in determining the thickness of the deformed layer using rings. The method involves the profilographometric measurements of the disconnected rings (samples) which are flat-faced in the package on the mandrel. The rings material deforms plastically in the surface layer causing wrapping of the end face of the ring in the direction of the rolling tool movement. After dismantling the ring pack, measurements were made on the face of each ring along radial directions, and the thickness of the deformed layer was observed on the microscope. The method was verified by microhardness measurements in the cross-section and cross-section of the ring. The results of deformation depth measurements were verified by finite-element-based numerical simulation.

Geometric design of the rolling tool for gear roll-forming process with axial-infeed

Roll-forming process is an innovative manufacturing technology for the near-net-shape production of high-performance gears. Outstanding surface quality, high material utilization rate and short process chain are the essential merits of this process. The geometry of rolling tool has a significant impact on its lifetime and the quality of formed gears. In this paper, analytical models with consideration of geometric parameters of rolling tools (cone angle, tooth depth and addendum modification coefficients) were proposed to investigate the forming force, root stress of rolling tool, rabbit ear defect and scratches on tooth flank. Then, an example was studied by using the proposed models, Finite Element Method (FEM) simulation and experiments. The results show that the optimized geometric design of rolling tool will not only reduce the deflection and root stress of rolling tool’s teeth, but also eliminates the scratches on tooth flank of the formed gear. Moreover, the positive addendum modification design of rolling tools also contributes to reduce the height of rabbit ear in the roll-forming process with axial-infeed.

Continuous roll forming including in-line welding and post-cut within an ALE formalism

Cold roll forming is a rather old process for which there is a renewed interest due to its capacity to form ultra high-strength steels. For the first time ever in the literature, the manufacturing chain involving both the continuous cold roll-forming process, the in-line welding operation for closed sections and the post-cut operation is numerically modelled. The first phase of this process sequence consists in computing the hopefully steady state configuration of the strip for the total length of the roll-forming mill, including the in-line welding phase. For addressing this problem, the Arbitrary Lagrangian Eulerian (ALE) formalism is used. Once the ALE steady state is reached, the computation is pursued with a second Lagrangian phase which is aimed at simulating the post-cut operation that releases the formed section from the rolling tools of the mill, enabling to determine the final geometry of the product. In this paper, the computational modelling framework employed within the in-house finite element code METAFOR is described. In particular, the proposed techniques — which are definitely original within an ALE formalism — for modelling the in-line welding operation and the post-cut operation are extensively detailed. The welding is considered with three different methods: (1) symmetry boundary conditions coupled with a well-suited node relocation procedure, (2) a closed mesh of the closed section coupled with a well-suited node relocation procedure, and (3) sticking elements based on a spring constitutive formulation. A set of simple numerical examples demonstrates the confidence in all the proposed modelling methods. Finally, these methods are successfully applied in the cases of two complex roll-forming mills of closed tubular sections.

Ball Burnishing Under High Velocities Using a New Rolling Tool Concept

Ball burnishing is a process used to smooth rough surfaces. For not rotational symmetric parts, the process is typically conducted on milling machines. Since it is an incremental process, it is relatively time consuming. Therefore, a rolling tool is developed, which superposes the rotation of the milling spindle with the feed of the machine to increase the rolling velocity. In order to achieve constant rolling forces, hydrostatic ball-burnishing tools are used. Within this work, the influence of this tool concept on the processing time as well as on the leveling of surface irregularities is investigated. This is achieved by a comparison with a conventional ball-burnishing process. Finally, the rotating tool is used to investigate the influence of high rolling speeds on the leveling of the surface. All experiments were carried out with thermally coated specimens. A model for calculating the strain rates at the roughness peaks during ball burnishing is derived. For the experiments carried out with the rotating rolling tool, rolling velocities of 50,000 mm/min were realized. Calculations with the developed model showed that this results in local strain rates at the roughness peaks of up to 1384 s−1. In addition, the flow stresses at the roughness peaks were calculated. Compared with quasi-static experiments, the flow stress drops to less than the half under high velocities. This results in a better leveling of the surface for rolling velocities between 10,000 mm/min and 25,000 mm/min. A further rise of the rolling speed increases the flow stress again and thereby reduces the possible leveling.

Surface integrity after internal load oriented multistage contact deep rolling

Mechanical treatment by deep rolling generates an improvement of the surface integrity by inducing compressive residual stress, strain hardening as well as a reduction of the surface roughness. The resulting material modification is based on the plastic deformation of surface and subsurface layers caused by the movement of a deep rolling tool across the workpiece surface under defined conditions in terms of rolling force, ball diameter and number of contacts. A correlation between the process parameters and the surface integrity to predict the modification in the workpiece is of limited validity. It is more useful to consider the internal load during the mechanical treatment in form of stress fields occurring during the process. This paper shows an approach to describe the internal load based on the hertzian stress in combination with the elastic model considering the multiple contacts in a deep rolling process. A defined variation of process parameters regarding the internal loads and the number of contacts was performed. It is shown that the correlation between internal loads and material modification (process signature) offers a good approximation to describe the surface integrity of workpieces after multistage contact in deep rolling processes. The description of material modification based on equivalent stress depth profiles enables the prediction of maximum of compressive residual stress after multistage deep rolling.

Residual stress and dislocation density development in single track deep rolled AISI 4140H steel

Plastic deformations induced by the rolling contact in the deep rolling process are the origin of the formation of residual stress fields and increased dislocation density in the material. The near surface material modification achieved through the process, like a compressive residual stress field, improved hardness and reduced surface roughness, give rise to improved component performance during operation. For a general understanding of the generated surface-near properties, an analysis of single tracks contributing to surface integrity is required. In the present study, a detailed investigation of the achieved residual stress state distribution as well as the local dislocation density of single processed tracks was performed through high spatial resolution X-ray diffraction analyses. Using two spherical deep rolling tools of 6 mm and 13 mm diameter, single tracks were processed with different parameters on samples of steel AISI 4140H. It could be observed that residual stress fields at the surface reach much larger lateral expansion than the plastically deformed track which can be determined by optical measurements, while a correlation with the dislocation density distribution was found. For the maximum dislocation density in the tracks, a correlation with the theoretical maximum equivalent stress was determined. Furthermore, a method to connect the measured dislocation density to the localized plastic strains during processing was applied to exemplary distributions.

On the pitch error in the initial stage of gear roll-forming with axial-infeed

Gear roll-forming process demonstrates an innovative energy-material saving and high efficiency forming technology for the powertrain gears. The pitch error in the initial stage has significant impact on the pitch deviation of the formed gears and the lifetime of the rolling tools. In this paper, an analytical model was proposed for predicting the pitch error with consideration of geometric relations and process parameters. Then, the impact factors related to the rolling tools, workpiece and process were analyzed based on the proposed model. To verify the model, Finite Element Method (FEM) simulations and experiments were conducted. The compared results show that the proposed model can well predict the pitch error in the initial stage. Moreover, the root causes of pitch error were revealed and its influence factors were also discussed. This research will lead theoretical foundation for reducing the pitch error in the gear roll-forming process.

Development of 3D modeling technology for manufacturing finned ribbons from heat-resistant steels

The process of shaping a workpiece by a tool using the rolling method is, from the geometric point of view, a process of interaction of two conjugate surfaces. The technology of rolling finned stainless steel ribbons is close to the technology of shaping details by cutting. However, the problems of its practical implementation in the well-known papers analyzing this issue are practically not considered. As a result of the analysis of conjugate surfaces profiling methods in relation to the problem, it was concluded that it seems urgent to develop a methodology for the formation of corrugated ribbon based on 3D modeling use. The implementation of this methodology includes the creation of solid models of the product and the tool, as well as computer simulation of their shaping processes using rolling method. So, at the first stage, a 3D model of finned ribbon was developed, which was then used to produce a profile of a rolling tool. The modeling of this profile was carried out on the basis of the proposed software package in the CAD environment. The created theoretical model of the tool profile was replaced from the technological point of view by a rectilinear profile. To carry out the analysis of the obtained results, the inverse shaping problem was solved - according to the corrected profile of the tool, real profile of the corrugated ribbon is obtained. Computer modeling of extruded volumes in the process of shaping was performed. The analysis of qualitative and quantitative parameters of the extruded volumes made it possible to give recommendations on setting the increment of the tool motion parameter. Based on the results of the studies, profile parameters of the roller are assigned for its practical implementation. The proposed methodology, based on 3D-modeling, allowed to develop a technology for manufacturing finned ribbons from heat-resistant steels by rolling with high productivity, accuracy and stability of the sizes obtained.

Prediction of Thread Rolling Tools Wear Resistance

This article describes a method developed to predict the wear resistance of thread rolling tools, which is based on the assumptions of the energy theory of wear applicable to solids. Through experiments, the authors defined the energy intensity of wear for the 30CrNiMo8 steel at room temperature and at 400°C and 800°C. Using the DEFORM-3D finite element simulation software, the authors established how the shear stresses changed along the length of the plastic zone and determined the friction work taking place on the contact surface in the area of maximum pressures. Calculations were performed to determine the expected life of thread rolling dies used in the manufacture of C22 steel screw spikes per GOST 809-71. The research was supported by RFBR (project № 16-38-00026).

ОПТИМИЗАЦИЯ ТЕХНОЛОГИИ ИЗГОТОВЛЕНИЯ ЦЕНТРОБЕЖНОЛИТЫХ ВАЛКОВ

This paper reports the sheet roll spun casting. It is shown that sheet rolls of required quality and with minimum production costs are manufactured through a method of spun casting on a machine with a vertical axis of a mould rotation. It is defined that at spun casting a more intensive foundry cooling occurs as a result of which a blank is characterized with a denser and more even structure of a working layer. It is revealed that the stability of such a process depends to a considerable degree upon a spin casting system functioning a significant property of which is a speed of rotation. In the paper there is analyzed a rotation speed influence upon a grain size, a quantitative ratio of structural constituents in a working layer composed of nickel-chromium cast iron and also upon the level of its properties. The analysis of the rotation speed influence of a casting mold upon a structure and a property level of a roll working surface was based on experimental investigations of foundries under industrial conditions. The microstructure (the size of primary grains, their composition) of products analyzed was estimated with the aid of a common metallographic procedure. On the basis of experiments carried out it is determined that even an insignificant increase (by 7%) of mould rotation speed during roll casting allows without expensive processing of liquid melt of a work-ing layer increasing its structure uniformity. As a result of this the level of its properties increases (hardness – by 3 units). Consequently, the increase of rolling tool efficiency is expected. The presented results of investigations are basic for works on servicing characteristics increase of spin-cast rolls.

Experimental Study on the Surface Densification of Fe-2Cu-0.6C Powder Metallurgy Material

The present work investigated the effects of rolling force (longitudinal feed) and spindle speed on surface performance of Fe-2Cu-0.6C powder metallurgy material. A newly self-designed rolling tool was used to densify the material's surface, and then the surface properties were measured. Results indicated that rolling force was the main effective parameter, and spindle speed was the secondary one. A densified depth and a surface hardness of 335 µm and 320 HV0.1 were obtained by using a rolling force of 2800 N and a spindle speed of 360 r/min. The tensile strength was improved by 75%. The tensile fracture had mixed-rupture characteristics of dimples and tear ridge. In the surface layer, the ferrite was stretched and refined. The pearlite was deformed and oriented along the rolling direction. The lamellar spacing close to the surface was reduced. It played a significant role in enhancing the strength of material.

ВИРТУАЛЬНОЕ МОДЕЛИРОВАНИЕ ЦЕНТРОБЕЖНОГО ЛИТЬЯ ВАЛКОВ

The work is devoted to the virtual simulation of a sheet roll working layer formation at a technological stage “casting-solidification”. To form a virtual model of a roller mould pouring and foundry solidification there was used a computer modeling system (CMS) which included initial and boundary conditions for a roller mould pouring process with highalloy cast iron in the field of centrifugal force action. The distribution of a metal working layer along an inner surface of a rotating mould at different technological parameters: mass of highalloy cast iron, its density, temperature and pouring velocity, temperature of metal and non-metal parts of a mould at the initial point of time, modes of rotation and conditions of mould cooling and others were investigated. It is established that under the influence of centrifugal forces a free surface of liquid melt obtains a parabolic form. The influence of basic technological parameters upon the vertex position of a paraboloid of revolution of highalloy liquid melt z0 is revealed. It is shown in the paper that it stipulates for the unevenness of a working layer value along a roller barrel. As a result of computations it is obtained that the value of a working layer at lower flanks of barrels is higher than that of upper sides. The average value of such an exceeding makes 0.012 m. As a result of a simulation analysis of a foundry formation process at different technological parameters it is determined that the distance increase between the vertex of a paraboloid of revolution and the metal area investigated raises the working layer evenness along a roller barrel 3.6 times. Hence, the increase of capacity for work of a rolling tool is expected. The results of investigations presented are basic for the works for the increase of centrifugal roller servicing characteristic increase.

FE-simulation of the Presta joining process for assembled camshafts - local widening of shafts through rolling

Considerable weight benefits and the option to combine various steel alloys of the single parts are the major advantages of assembled over conventional camshafts. The Presta joining process is the leading manufacturing method of assembled camshafts in the global market. The process is divided into two substeps. At first, the outer diameter of the shaft is widened with a profile oriented orthogonal to the shaft axis at the intended cam seat. At this position the shaft is subsequently joined with a cam with an internal profile oriented parallel to the shaft axis. As a result, these perpendicular profiles form a tight fit due to plastic deformations. Consequently the simulation of the manufacturing process has to start with the simulation of the rolling of the shaft. The resulting profile requested in this step is axisymmetric, but the arrangement of tools is not. Thus a three-dimensional model is required, which is presented in this work. Furthermore, the infeed of the rolling tool is unknown and controlled by the stiffness of the holders of the rolling tool. This work shows the modeling of this behavior. To predict realistic results for the underlying process, the use of precise material models is essential in order to take several hardening mechanisms into account. However, the use of complex material models implies additional effort, which is shown in this work.