Cold Heading Process Research Articles

Dynamic characteristics and optimization research on PVDF piezoelectric film force sensor for steel ball cold heading machine

According to cold heading process with overloaded craft, high-impact dynamic real-time measurement requirements, this paper presents researches on dynamic characteristics and optimization of PVDF piezoelectric film force sensor for steel ball cold heading forming quality monitoring, through the combination method of mechanism analysis, mathematical modeling, numerical simulation and experimental validation. The motivation and strategic objectives are to breakthrough dynamic time-varying impacting load measuring fundamental technologies in steel ball forging process. The structure of piezoelectric film force sensor is proposed. The theoretical calculation formula of natural frequency is deduced and calculated by using MATLAB software. The mechanical performance analysis on dynamic model and structural optimization simulation by FEM is carried out. In order to study the validity of the proposed method, a prototype of the sensor is fabricated. The static and dynamic calibration devices are designed to realize calibration experiments on the fabricated PVDF piezoelectric film force sensor. The differences among experimental value, simulation value and the theoretical value are given. The nonlinear error of the fabricated sensor is 0.197%. The sensor’s first order natural frequency value is 5238 Hz. It is proved that the PVDF piezoelectric film force sensor has superior dynamic performance and high accuracy for measuring deformation in steel ball. The paper will provide important scientific basis and technical foundation to achieve superior performance steel ball.

粉末冶金与冷镦加工Fe-36Ni合金及其微波器件的性能研究

粉末冶金与冷镦加工Fe-36Ni合金及其微波器件的性能研究

Towards a Fracture Energy Based Approach for Wear Prediction of WC-Co Tools in Industrial Cold Heading Process

Tools sustainability and reliability is a key axis for economic competitiveness of companies in the field of cold heading of steels. This durability is currently limited by the damage occurring at the contact surfaces.The main objective of this study is to propose an energy based approach to understand the mechanisms of deterioration of the WC-Co carbide tools.Firstly a finite element simulation of an industrial cold heading process is run in order to identify the contact condition at the tool workpiece interface. Main results are the stress, strain and temperature distributions in the near surface of the tools. A particular attention is paid to the location of critical areas that may limit the tool life.Jointly, characterizations of the morphology of the worn surfaces are performed. SEM observations added to EDS and roughness measurements are done from midlife to end of life of industrial tools. Friction tests are performed with the Upsetting-Sliding Test involving contactors extracted from real worn tools to identify friction coefficients in order to provide the evolution of the friction coefficient according to the wear state of the tools. Finally, the correlation between the numerical analysis and the experimental measurement is discussed to attest to the relevance of the energy fracture based model to explain the deterioration of the tribological conditions.

On-line spheroidization process of medium-carbon low-alloyed cold heading steel

Conventionally manufactured 35CrMo cold heading steel must undergo spheroidization annealing before the cold heading process. In this paper, different types of deformation processes with various controlled cooling periods were operated to achieve on-line spheroidal cementite using the Gleeble-3500 simulation technique. According to the measured dynamic ferrite transformation temperature (Ad3), the deformation could be divided into two types: low temperature deformation at 810 and 780°C; “deformation-induced ferrite transformation” (DIFT) deformation at 750 and 720°C. Compared with the low temperature deformation, the DIFT deformation followed by accelerated cooling to 680°C is beneficial for the formation of spheroidal cementite. Samples subjected to both the low-temperature deformation and DIFT deformation can obtain granular bainite by accelerated cooling to 640°C; the latter may contribute to the formation of a fine dispersion of secondary constituents. Granular bainite can transform into globular pearlite rapidly during subcritical annealing, and the more the disperse phase, the more homogeneously distributed globular cementite can be obtained.

Design and Analysis of Force Sensor for Condition Monitoring System of Ball Cold Heading Forming

In order to solve the forming defects in the steel ball cold heading process, a novel force sensor which chooses the PVDF piezoelectric films as force-sensing elements is designed. The advantages and disadvantages of piezoelectric force sensor on measurement of the cold heading force are compared with existing force sensors. By using FEM, sensor’s linearity and the structure size are analyzed. Compared with the traditional sensor, this structure is more reasonable. The presented PVDF piezoelectric force sensor has wide frequency range, good dynamic performance, and can realize dynamic measurement.

Research on on-line monitoring technology for steel ball's forming process based on load signal analysis method

This paper presents a novel on-line monitoring technology to obtain forming quality in steel ball's forming process based on load signal analysis method, in order to reveal the bottom die's load characteristic in initial cold heading forging process of steel balls. A mechanical model of the cold header producing process is established and analyzed by using finite element method. The maximum cold heading force is calculated. The results prove that the monitoring on the cold heading process with upsetting force is reasonable and feasible. The forming defects are inflected on the three feature points of the bottom die signals, which are the initial point, infection point, and peak point. A novel PVDF piezoelectric force sensor which is simple on construction and convenient on installation is designed. The sensitivity of the PVDF force sensor is calculated. The characteristics of PVDF force sensor are analyzed by FEM. The PVDF piezoelectric force sensor is fabricated to acquire the actual load signals in the cold heading process, and calibrated by a special device. The measuring system of on-line monitoring is built. The characteristics of the actual signals recognized by learning and identification algorithm are in consistence with simulation results. Identification of actual signals shows that the timing difference values of all feature points for qualified products are not exceed ±6ms, and amplitude difference values are less than ±3%. The calibration and application experiments show that PVDF force sensor has good static and dynamic performances, and is competent at dynamic measuring on upsetting force. It greatly improves automatic level and machining precision. Equipment capacity factor with damages identification method depends on grade of steel has been improved to 90%.

Experimental and finite element simulation study of the adiabatic shear band phenomenon in cold heading process

This paper presents the outcomes of a comprehensive experimental, metallurgical and finite element (FE) simulation study to characterize the development of adiabatic shear band (ASB) phenomenon in steel cold heading (CH) process. The main objective of this work is to investigate the complex interplay of different process and material parameters on the ASB development stages inside the cold headed parts.In this work, the drop weight compression test (DWCT) was selected to simulate the CH process impact loads on specimens machined from 1038 steel and 1018 steel. Series of DWCTs were performed under different impact loading conditions. The goal of these tests is to achieve different deformation levels and introduce ASBs at different stages.To reach a full understanding of this complex phenomenon, the FE simulation analysis was used to support the metallurgical examination of the DWCT specimens. The FE analysis provided important details about the changes of different material and process parameters at the critical zones inside the ASBs.This study confirmed that the ASB is mainly a thermo-mechanically controlled phenomenon. The ASBs develop in three stages: homogeneous plastic strain, inhomogeneous plastic strain, and strain localization. The ASB development stage depends mainly on the status of the competition between the work hardening and the thermal and geometrical softening mechanisms inside the bands. The domination of the softening mechanisms at advanced levels of deformation triggers a self-catalytic strain localization and material strength degradation process that leads to failure inside the band.In general, the metallurgical and finite element analysis investigation revealed that under impact loads, three ASBs can develop simultaneously inside the cold headed parts; lower, upper and central ASBs. As the deformation continues; the development of the lower and upper bands slows down and contributes in the rapid development of the adjacent central ASB. This study confirmed that the ASB has a canonical structure which leads to an ASB that can experience different development stages along the same band simultaneously.This study proved that the shape and the type of ASBs in cold headed parts depend highly on material's properties. The metallurgical and finite element analysis revealed that the higher the strength of the tested steel, the easier to form a narrow ASB that reaches the localization stage at low deformation levels. In contrast, ductile steels experience wider ASBs when subjected to the same deformation levels. These bands require higher levels of deformation to reach the localization stage in comparison to higher strength steels.

Influence of strain rate and adiabatic heating on the deformation behavior of cold heading steels

In the cold heading process of metals, strain rates in complex parts can vary considerably and locally reach very high values. Therefore, when considering the material's deformation behavior, both the transient hardening at high strain rates as well as softening due to adiabatic heating should be accounted for. In this work, a purely phenomenological model based on experiments performed at strain rates in the range of 10 −3–10 4 s −1 at temperatures extending from −150 to 800 °C was devised and used in finite element simulations of the cold heading process. The model separates yielding, including both the upper and lower yield point, from strain hardening, which typically depend on strain rate in a different way due to the adiabatic thermal softening effects at higher strains. The simulation results show good agreement with the high strain rate cold heading results obtained using a direct impact Hopkinson split bar technique.

Effect of Corner Radius and Friction Parameters on the Optimization of the Cold Forging Die Design

Finite element (FE) method is extensively employed in solving linear and non-linear problems and widely used particularly in analyzing a forming process. It enables the analysis on internal properties such as stress effective, forming load, metal flow and deformation to be performed, in which results in an increase on the performance of forging process. Heading process which is often performed in conjunction with other cold forging process has been simulated by FE-code DEFORMTM F3 v6.0. The numerical results were analyzed to evaluate the effect of the fillet size and the friction value on the cold heading process. It was found that the heading process provided good precision and productivity as the size of fillet was increased; due to intensification of the metal flow to infuse the die cavity. On the other hand, the friction value also played an important role in governing the reaction force between workpiece and punch in the process.

Internal ductile failure mechanisms in steel cold heading process

The occurrence of internal ductile failure in cold-headed products presents a major obstacle in the fast expanding cold heading (CH) industry. This internal failure may lead to catastrophic brittle fracture under tensile loads despite the ductile nature of the material. Comprehensive testing and investigation methodologies were used to this work to reveal the complicated interplay of process and material parameters contributing in the initiation and propagation of internal ductile failure in six CH quality AISI steel grades. The metallurgical and microscopic investigations showed that internal ductile failure occurs progressively by void nucleation and growth mechanisms with increasing plastic strain inside the highly localized adiabatic shear bands (ASBs). The void nucleation occurs by decohesion at second-phase particles, inclusion–matrix interfaces, grain boundaries and by particle or inclusion cracking. Therefore, the number and morphology of any inclusions and second-phase particles are key factors in material formability. The metallurgical investigations showed that under compressive loading conditions, the nature of the metal flow pattern promotes different rates of material flow around the inclusions and stringers which supports decohesion and void nucleation since the early stages of deformation. At advanced stages of deformation, the metal flow pattern contributes to the ASB localization in supporting void growth and coalescence along the band leading to narrow void sheets. All tested materials in this work experienced ductile failure by void nucleation and coalescence, forming cracks along the ASBs. The ductile failure of each material was the result of the contribution of all the mechanisms of void nucleation at the inclusion–matrix interface, second phase–matrix interface and at the grain boundaries. However, the level of contribution of each mechanism in the final ductile failure varied depending on material properties and their microstructure.

A Workability Criterion for the Transformed Adiabatic Shear Band Phenomena during Cold Heading of 1038 Steel

A criterion for predicting the workability limits for internal britde failure was developed for cold heading of 1038 steel. The criterion considers internal defects caused by microstructural changes generated by adiabatic shear. This transformation is termed the transformed adiabatic shear band (TASB) phenomena. The defect that develops is the formation ofbritde martensite as a result ofthe temperature rise and fall inside the adiabatic shear band (ASB). In this work, the material is considered to have a TASB defect when the temperature inside the ASB exceeds the phase transformation temperature (AC3). The empirical formulas provided by Andrews[1] were used to determine transformation temperatures. Microhardness testing and etching with 2% Nital and Le Pera etchants were performed on the sectioned specimens to locate and study the TASB. In order to simulate the cold heading process, a drop weight compression test was used and modeled with finite-element analysis (implemented within ABAQUS/Explicit).

Experimental evaluation method for determination of friction characteristics and performance of cold heading coatings

An experimental method was designed to evaluate wire coatings for the cold-heading process. Coatings are employed to increase material formability and to reduce wear on tooling. Typically, evaluation of frictional properties proves to be difficult because of problems instrumenting machine tooling and both the complexity and number of stages in the forming process. The proposed test is a cold extrusion process utilizing a selected trapped-forward extrusion die, where load versus stroke data is collected. Three different coating ratings are generated based upon maximum extrusion force, standard deviation of the force, and the characteristic shape of the extrusion curve. Coating performance interpretations for the curve characteristics are discussed.

DIFFERENT APPROACHES IN MULTIPLE-CRITERIA OPTIMIZATION USING THE TAGUCHI METHOD: A CASE STUDY IN A COLD HEADING PROCESS

Real life engineering problems usually require the satisfaction of different, potentially conflicting criteria. Design optimization, on the other hand, based on the conventional Taguchi method cannot accommodate more than one response. However, by the use of the overall evaluation criterion approach, the method can be applied to multiple-criteria optimization problems. This paper presents the use of different utility function methods as well as a multiple attribute decision-making model in the multiple-criteria optimization of a cold heading process. Different aspects of each method are discussed and compared.

Application of artificial neural network and Taguchi method to preform design in metal forming considering workability

This study describes a new method of perform design in muti-stage metal forming processes considering workability limited by ductile fracture. The finite element simulation combined with ductile fracture criterion has been performed in order to predict ductile fracture. The artificial neural network using the Taguchi method has been implemented for minimizing objective functions relevant to the forming process. The combinations of design parameters used in finite element simulation are selected by orthogonal array in statistical design of experiments. The orthogonal array and the result of simulation are used as train data for artificial neural networks. The cold heading process is taken as an example of designing preforms which do not form any fracture in the finished product. The results of analysis to validate the proposed design method are presented.

Methodology of preform design considering workability in metal forming by the artificial neural network and Taguchi method

Abstract This study describes a new method of preform design in multi-stage metal forming processes considering workability limited by ductile fracture. The finite element simulation combined with ductile fracture criterion has been carried out in order to predict ductile fracture. The artificial neural network (ANN) using Taguchi method has been implemented for minimizing objective functions relevant to the forming process. The combinations of design parameters used in finite element simulation are selected by an orthogonal array in a statistical design of experiments. The orthogonal array and the results of simulation are used as training data of ANN. A cold heading process is taken as an example of designing a preform which does not form any fracture in the finished product. The results of analysis to validate the proposed design method are presented.

A study of optimum die-design in the heading process with two blows. Part 1: Experimental study

The conventional cold-heading process for the production of a bolt-shaped product involves two or three blows. The strength of a bolt-shaped product produced by multi-blow heading depends on the mechanical properties of the material and on the working conditions of the heading process such as the corner radius of the necked portion of the product, the pre-forming die angle and the reduction in height during pre-forming. The effects of the corner radius of the necked portion and the die angle in pre-forming on the internal state of the product, such as the shape of the deformed zone, the hardness distribution and the fracture strength, of a product produced by double-blow cold heading have been investigated experimentally. A rigid-plastic finite-element program has been coded and the program vindicated by comparison of its predictions with the results of experimentation. The results are summarized as follows: (1) The corner radius of the necked portion of the product is a significant factor not only for fracture strength but also for the internal state of the product. (2) The die angle of the pre-forming die also affects the internal state, the shape of the head and the forming load, but its effect on the fracture strength is not remarkable. (3) The effects of the above two factors are not independent of each other. (4) The rigid-plastic finite-element code can provide accurate information on double-blow cold heading.

Adaptive 2D finite element simulation of metal forming processes

AbstractThe development and integration of available current methods and the development of new methods for an adaptive finite element analysis of metal forming processes are presented. The analysis includes large‐strain, elastic–plastic, and thermal effects. Many numerical methods such as mesh generation, simulation of the contact between the workpiece and tool and die, and optimization of the finite element mesh are integrated and incorporated. In addition, an algorithm is developed which can detect certain severely distorted elements where the area of integration is approaching zero. The advantage of correcting these regions of locally distorted elements is demonstrated. These numerical methods are implemented in a finite element program developed for simulating metal forming processes, with the emphasis on automating the analysis. Examples include an axisymmetric stress simulation of a coldheading process, a plane strain simulation of an extrusion process and a plane strain simulation of orthogonal metal cutting, all with noticeable thermal effects. The orthogonal cutting forces and feed forces calculated are compared with two sets of experimental data, with good agreement.

Finite-element analysis of a five-stage cold-heading process

An elastic—plastic finite-element analysis of a five-stage cold-heading operation is presented. This gives accurate prediction of the external shapes produced, and of the internal distortion. The method can be used to optimise preform routes with respect to maximum forces, homogeneity of the product and process costs in terms of number of stages and inter-annealing requirements.