Warm Forging Process Research Articles

Initial holding time dependent warm deformation and post-ageing precipitation in an AA7075-T4 aluminum alloy

• Warm deformation at 180 ℃ significantly enhances the formability of AA7075-T4 alloy. • The through-process microstructure evolution during warm compression is revealed. • Initial soaking of 10−30 s benefits the balance of warm-deformability and post-ageing. • A TTP sketch considering the reversion of clusters and reprecipitation is proposed. Process parameters such as soaking time and forming temperature are critical for the isothermal warm forming performance and post-form mechanical properties. The isothermal warm forging process of AA7075-T4 aluminum alloy has been simulated through the warm compression at 180 ℃. The warm deformation schedule including fast heating and short-term initial holding is found to be advantageous for enhancing the formability of high-strength AA7075-T4 alloy due to the reduced flow strength and significantly increased ductility. As revealed by differential scanning calorimetry and transmission electron microscopy, the natural ageing clusters quickly dissolve, then the GP zones and even η'/η 2 phases form during initial holding at 180 ℃ for 4 min. The optimum balance of warm-deformability and subsequent age hardening potential at 120 ℃ is obtained with an initial holding for less than 30 s, by restricting the growth of coarsening precipitates before isothermal warm deformation. The warm compression induced dislocations are largely retained during post-ageing, accelerating the hardening kinetics and promoting the formation of a high density of η'/η 2 precipitates in the peak-aged sample. Through considering the reversion of natural ageing clusters and solutes reprecipitation during the initial holding and post-ageing, a temperature-time-property sketch is proposed to explain the relationship between the warm deformation temperature, initial holding time and the obtained hardness for the AA7075-T4 alloy. This study could guide the optimization of warm forming process and is fruitful for establishing an accurate microstructure-based model for the warm deformation of AA7075-T4 aluminum alloy.

Preform Optimization of Functional Bevel Gear for Warm Forging Processes

Optimizing the design of the preform shapes used in warm forging processes is important for improving quality and reducing cost. The main objective of this study was to optimize the design of a preform shape for a bevel gear to obtain a good product and to improve the efficiency of the warm forging process. Quality parameters included in the fitness function were form-filling, preform volume, and complexity. First, basic principles pertaining to the cross sections, thickness, and concave radius of a bevel gear preform were applied in conjunction with certain theoretical expressions and empirical methods to produce an initial preform shape and initial geometry. Subsequently, mathematical evaluation models of the fitness function were generated to optimize the preform shape. Finally, a genetic algorithm was applied to solve the multi-objective optimization problem, and the best solution was determined considering the accuracy of the results, within the close proximity set generated by the multi-objective genetic algorithm optimization. The optimal preform shape was decreased in weight by approximately 8% and its flash dimensions were decreased by about 5% compared to the initial preform shape. This research is expected to improve the efficiency of fabricating bevel gears by means of warm forging processes.

Simulation and Experiment of Manufacturing Process for Structural Aluminum Parts with Hard to Plastic Forming

A process comprising a hot extrusion process and a warm forging process was designed to form an umbrella-shaped aluminum structural component with a high degree of difficulty for the plastic forming method. A circular cylindrical part was extruded with a hot extrusion process, and then an embossing part was produced with a warm forging process. The formability and the maximum load required for forming were then determined using a forming analysis program. The hot extrusion process was executed at 450 °C under the extrusion speed at 6 mm/s, while the warm forging process was executed at 260 °C under the forging speed at 150 mm/s. The simulation results showed that the load required for hot extrusion was 1019 ton, while the load required for the warm forging was 534 ton. The umbrella-shaped part was manufactured by using a 1600 ton capacity press. The graphite lubricant was coated on the mold as well as the material. A forming experiment was performed under the same condition with the simulation condition. The portion where extrusion was done became elliptical with the α-Al phase elongated towards extrusion direction. Whereas, the α-Al phase became circular in the forged portion. The tensile strength value was found as 345 MPa, while elongation rate was 12%. Meanwhile, Vickers hardness value at the extruded portion was 105 HV, and it was 110 HV at the forged portion.

Deformation mechanism of forging tool for multi-stage forming of deep groove ball bearing

In this study, two design configurations routinely adopted in actual mass production for deep groove ball bearing rings of multi-stage warm forging process are investigated numerically and experimentally. The deformation mechanism, forging defects, microstructures, and compositions analysis are the main focus of this study. For type A design with a stepped configuration, inner and outer rings are automatically pierced and separated in the multi-step forging machine. On the other hand, for the type B geometry, additional step is required by the customized milling machine. For type A design, the main issue encountered during actual forging process is the inadequate material filling at the upper corner radius and folding defects at the transition area of inner wall of forgings. For type B design, the material flow is unsatisfactorily directed and lower outer radius is insufficiently filled. Therefore, variations of forging parameters include billet weight, punch/knock out pin geometry and the effect of lubricating fluid is systematically investigated. In addition, the finite element method has been performed and compared with the actual forging experiments. In summary, the modification of tooling design, dimension variation of billet weight, and the forging temperature difference as impacted by the lubricating fluid, which are identified as the three major factors of the forging integrity and stability of the mass production process. The results are particularly useful for the advanced tooling design and contribute largely to minimize the tool failure and the integrity of the bearing forged.

Micro-voids quantification for damage prediction in warm forging of biocompatible alloys using 3D X-ray CT and RVE approach

This study aims to quantify the three-dimensional (3D) micro-voids for damage prediction in warm forging through non-destructive X-ray computed tomography (CT) and RVE approach. Typical biocompatible alloys, i.e., stainless steel 316 L (SS316L) and titanium alloy Ti-6Al-4V, were used as specimen materials in warm-forging a medical implant, i.e., a basal thumb implant. X-ray CT scanning was performed for both the preforms and forged components. Volumetric CT images were then reconstructed and the 3D micro-void distribution and evolution inside the materials were detected and analysed quantitatively. Furthermore, three typical local strain regions, i.e., the small tensile strain region (STSR), small compressive strain region (SCSR) and large compressive strain region (LCSR), were established as the 3D representative volume element (RVE) models for both SS316L and Ti-6Al-4V preforms. The spatial location, size and volume of each micro-void were obtained from defect analysis of the 3D CT images and considered explicitly for subsequent damage prediction. An improved thermo-mechanical coupled micromechanics-based damage (micro-damage) model, which considered the variation of volume fraction of micro-voids (VFMVs), was implemented into finite element (FE) package ABAQUS for localized damage prediction of the RVE models. The damage distributions of the RVE models at different strain levels were visualized and identified. Finally, the localized damage evolutions at both compressive and tensile deformations were predicted and found to match quite well with the findings acquired from CT scanning. Thus, the application of non-destructive X-ray CT measurement of micro-voids, incorporating the RVE approach, was able to play a significant role leading to a more reliable damage prediction in the warm forging process.

Preform Optimization for Bevel Gear of Warm Forging Process

Preform design is an important aspect in consideration of the improvement of quality and reduction of cost in warm forging process. Bevel gear being a key component of drive mechanisms in automotive industry requires lot of attention to its complex shape design optimization. A multi-objective optimization problem in designing preforms of warm forging for bevel gear by using genetic algorithm is solved and presented in this paper. The main objective of this study is to design an optimal preform part, which can get a better quality and the reliable preform shape systematically and theoretically.

X-ray CT assisted damage identification in warm forging

This study aims to identify the 3-dimensional interactions of micro-voids evolution before and after warm-forging a typical titanium alloy component by employing a micro-focus X-ray CT system so as to achieve a more accurate micro-void location and distribution as critical data input for damage prediction in warm forging. A specific forging tool was designed for warm-forging the component. Serval local regions that represented different strain levels were established as representative volume element models for the Ti-6Al-4V preform, in which, the micro-void distributions were obtained directly from the X-ray CT images. Furthermore, the micro-void evolutions of the corresponding representative volume element models were analyzed from the forged component. Thus, the damage evolution, i.e., the variation of void volume fraction, in the warm forging process was identified.

Strain Evolution in Cold-Warm Forged Steel Components Studied by Means of EBSD Technique.

Electron BackScatter Diffraction (EBSD) in conjunction with Field-Emission Environmental Scanning Electron Microscopy (FEG-ESEM) has been used to evaluate the microstructural and local plastic strain evolution in different alloys (AISI 1005, AISI 304L and Duplex 2205) deformed by a single-stage cold and warm forging process. The present work is aimed to describe the different behavior of the austenite and ferrite during plastic deformation as a function of different forging temperatures. Several topological EBSD maps have been measured on the deformed and undeformed states. Then, image quality factor, distributions of the grain size and misorientation have been analyzed in detail. In the austenitic stainless steel, the γ-phase has been found to harden more easily, then α-phase and γ-phase in AISI 1005 and in duplex stainless steel, sequentially. Compared to the high fraction of continuous dynamic recrystallized austenitic zones observed in stainless steels samples forged at low temperatures, the austenitic microstructure of samples forged at higher temperatures, 600–700 °C, has been found to be mainly characterized by large and elongated grains with some colonies of fine nearly-equiaxed grains attributed to discontinuous dynamic recrystallization.

Pinning effect of strain induced Nb(C,N) on case hardening steel under warm forging conditions

The effectiveness of Nb in retarding dynamic recrystallization (DRX) during warm forging process (700∘C–900 ∘C) and its dependence on the process parameters(ε,ε˙,T), which are the definers of formation conditions and morphology of the strain induced Nb(C,N), were studied. Due to its capacity of interaction with the austenite phase through solute drag and precipitate pinning effects, Nb is an important variable in the production of high-strength low-alloy steel (HSLA). However, the effectiveness of Nb as austenite conditioner is strictly dependent on its correct manipulation within each manufacturing step of finished or semi-finished products. Computer simulation of the precipitation kinetics of a forging steel 0.03wt. pct. Nb was performed in order to design a thermomechanical processing route based on the time-temperature-precipitation diagram (TTP), thereby ensuring high precipitate phase fraction in short processing time. Characterization of the steel mechanical behavior and its dependence with the formation of Nb(C,N) was done through flow stress curves analysis, the relaxation rate for the microalloyed steel is remarkably lower than for the Nb free steel being a typical stress plateau (carbonitride formation) and a peak stress (recrystallization) respectively observed. Transmission electron microscopy (TEM) was performed in order to characterize the distribution, geometry and dimension of Nb(C,N) generated by different processing routes at different process stages. The solubilization capacity of the adopted and computational designed austenitizing process was also experimentally analyzed. The energy-dispersive X-ray spectroscopy (EDX) method was used in the characterization of the precipitates chemical composition, allowing the identification of Ti-rich precipitation remnants of the austenitizing process and the absence of the element in the Nb(C,N) formed during deformation (strain induced precipitates). The strain, strain rate, temperature and isothermal holding time contribution upon the formation of precipitates were evaluated separately which reveals that it is so important as the processing temperature, the strain rate regime play decisive role in the formation of the particles. In addition, the strain rate dependency of strain induced Nb-precipitates formation at optimal processing temperature was indirectly confirmed by the capacity of the formed precipitates in hinder the static recrystallization (SRX) progress under relaxation tests.The strain induced precipitation formed at optimal processing conditions have circular geometry and size below 10nm, causing high precipitate pinning effect observed in the conditioning of austenite phase by hindering the DRX under warm forging condition.

A Novel Technology on Unfilled Corner Occurred in Gear Two-Step Warm Forging Process

Based on the geometric feature of back gear with double bosses, a new two-step warm forging process before cold precision forging was developed to reduce the number of process and the overall cost of manufacture. However, after the new process being conducted, unfilled corners were found at the bottom profile of all teeth. Two different methods were adopted to solve the issue but the results were unsatisfied. In order to solve the issue, a rigid plastic FE model was established to simulate the process. The velocity, stress and strain fields were investigated. In the mean time the metal flow rules were discussed along with experimental results. Through expanding the radial wave shape by means of a groove established in die and a qualified forge piece was achieved finally.

Numerical analysis and experimental validation on multi-stage warm forging process of deep groove ball bearing—a modified punch geometry with microstructure and defect analysis

In this study, a multi-stage warm forging process for making bearing rings is numerically and experimentally investigated. The aim of the study is to determine the crucial station of the finishing forging process such that the tool wear is prolonged and tool fracture should be minimized. In addition, in order to ensure the appropriateness of the suggested modification, a 3-dimensional finite element simulation on each sequence is performed and carefully compared with experimental investigations. Numerical simulation results indicate that the redesigned upper punch geometry, radius (R2) of the finishing forging process, demonstrate drastically different deformation rates (the effective strain/effective stress distribution) and material flow patterns, as compared with chamfer (C2) counterpart. Accuracy of the numerical models has been verified by comparing with experimental measurements. In addition, the numerically and experimentally validated process includes the detailed tooling design and dimension variation, which are of great importance in maintaining the overall structural integrity of the forging die/punch and thus, the stability of the whole process. Concerning on the waste ratio comparison, the method-used steel rods are as raw materials, and the IR/OR ring form is given by hot/warm forging and sequential cold rolling processes, and the waste ratio decreases to ~9 %. Finally, it is shown that the multi-stage warm forging process in this study could be successfully applied to the high-quantity production (10,000 pieces/h) of the IR/OR of the deep groove ball bearing with the stability and structural integrity of the whole process.

Static strength test with as-forged control-arm in automobile with Mg-Al-Sn-Zn alloy

This paper mainly concerns application of the Mg-Al-Sn-Zn alloy to the control-arm of an automobile with warm-forging process since Mg-Al-Sn-Zn alloy (ATZ842) exhibits enhanced strengths in tension and compression as well as the improved YR reaching 1.0. In order to validate the Mg control-arm, two wrought Mg alloys such as AZ80 (Mg–7.45wt% Al–0.38wt% Zn) and ATZ842 (Mg–7.59wt% Al–3.96wt% Sn–1.94wt% Zn) alloy have been produced with casting and extrusion processes, which have been applied to warm-forging of the Mg control-arm. As-forged two Mg control-arms with AZ80 and ATZ842 alloys have been evaluated with the static strength test to measure the maximum reaction force under the quasi-static compressive deformation. It is highly recommended to adopt the ATZ842 control-arm forged at 250°C since it does not only have comparably high reaction force in the static strength test, but also demonstrates fine grain structure if the abnormal grain growth is suppressed during the warm-forging process.

Warm forging of an aluminium alloy for the differential case in an automobile transmission

This paper presents a warm-forging process for the manufacture of an aluminium alloy differential case in an automobile, which has usually been produced from ductile cast iron. In order to replace the conventional ductile cast iron with a lightweight material in the differential case, aluminium alloy 6082 is utilized in the proposed warm-forging process, which is then analysed by numerical simulations using DEFORM-3D. Experimental warm forging using aluminium alloy 6082 was conducted in a 1600 tonf press shop to evaluate the proposed design in the die and the punch as well as the forgeability of the aluminium alloy differential case. The as-forged aluminium alloy differential case not only provides a net shape but also has a crack-free volume internally, while reducing the total weight by about 40% based on the proposed design.

Quality Cost Analysis of Typical Forging Based on SPC and DEA Model

In order to control the quality costs of forgings efficiently and ensure the optimization of enterprise production value input and benefit output, using piston, output shaft and other typical forgings as application objects, choosing cold and warm forging process instead of the former single hot forging or cold forging process, reinforcing Statistical Process Control (SPC) of processing quality and appropriately distributing quality failure cost and quality assurance cost in order to efficiently match the total cost of quality, quality process capacity index and production program so that the stability of forging quality can be improved. Using Data Envelopment Analysis (DEA) to contrast and analysis the quality cost data of new process and old process, of which the result shows that the technical input and benefit output of new process accord with mass production requirements in the prior period of enterprise industrialization.

Tool design and experimental verification for multi-stage cold forging process of the outer race

The outer race of constant velocity joints with six inner ball grooves has conventionally been produced using a multi-stage warm forging process, which consists of 9 operations such as billet cutting, forward extrusion, upsetting, backward extrusions, necking, ironing, sizing, and machining. In this study, a multi-stage cold forging process derived from process assessment to replace the traditional warm forging is presented. Detaily, both backward extrusions of the conventional one are redesigned as one operation, and the necking, ironing and sizing are combined into a single necking-ironing-sizing process, thus the proposed cold forging consists of 6 operations. To solve the tool interference in the combined necking-ironing-sizing process, and to facilitate extraction of the forged workpiece from the die cavity, a solid groove punch for shaping the inner ball grooves is redesigned with six-segmentalized grooving knives. Numerical simulation of each sequence is performed to ensure the appropriateness of the suggested process, and the structural integrity is also evaluated. Experimental investigations are carried out using SCr420H billet material. It is shown that this multi-stage cold forging process could be applied to the mass production of the outer race, with the dimensional variation of under 2.0% between the required and the forged geometries.

Mg scroll forging with AZ80 under warm forming condition

This paper proposes the net-shape forging process for the magnesium (Mg) scroll which is a device for compressing air or a refrigerant in air-conditioning equipment or an automobile supercharger. Mg scrolls make it possible to reduce the total weight of the scroll compressor noticeably by replacing the aluminum scroll in the compressor fields. In order to manufacture the sound scroll with uniform wrap height, the optimum back-pressure is applied to the Mg scroll forging, which is calibrated from the finite element analysis using DEFORM-3D. It is concluded that dimensional accuracy of the final product of the Mg scroll is comparably good since the all wraps are extruded more than the minimum machining line. It is also noted that the experimental and simulation results are able to be the best agreement with consideration of the texture evolution and DRX of the Mg alloy during the warm forging process.

Process Simplification of Multi-Stage Forging for the Outer Race of a CV Joint

Constant velocity (CV) joint with six inner ball grooves has been conventionally produced by a multi-stage warm forging process that includes forward extrusion, upsetting, backward extrusions, necking, ironing, and sizing. In this study, multi-stage cold forging is presented with four simplified stages of forward extrusion, modified upsetting, backward extrusion, and combined necking–ironing–sizing. A three-dimensional numerical simulation is performed to ensure the appropriateness of the proposed process, and experimental investigations are carried out using spheroidized and phosphophyllite-coated SCr420H billet material. It is shown that the proposed multi-stage cold forging process could be successfully applied to the production of the outer race.

Enhancement of the microstructure and mechanical properties in as-forged Mg–8Al–0.5Zn alloy using T5 heat treatment

This paper mainly concerns about the effect of T5 heat treatment on the microstructure and mechanical properties of the as-extruded as well as as-forged Mg–8Al–0.5Zn alloy which was produced by the warm forging process for the Mg tie-rod at the temperature of 523K. In the as-forged microstructure, rate of hardness increase from the initial to the peak hardness is substantially slow compared with the as-extruded since it already has a large amount of the precipitates in the warm forging process, which reduces the rate of precipitate hardening. Both types of precipitates such as the discontinuous lamellar- and continuous particle-types are favored simultaneously with the increase of aging time even though it is aged at the lower temperature of 450K.

Multi-stage cold forging and experimental investigation for the outer race of constant velocity joints

As an important load-supporting automobile part that transmits torque between the transmission and the driven wheel, the outer race of CV (constant velocity) joints with six inner ball grooves has been conventionally produced by the multi-stage warm forging processes, which involves several operations including forward extrusion, upsetting, backward extrusions, sizing and necking, as well as additional machining. There is still no choice but to produce the complex shaped components other than by this warm forging process. As an alternative, multi-stage cold forging process is presented to replace these traditional warm forging. The multi-stage cold forging procedure is first considered through a process assessment regarding the traditional multi-stage warm forging one. Then, the process is simplified and redesigned as one operation to produce the forged outer race and the backward extrusions of the traditional process, and the sizing and necking are also combined into a single sizing-necking process. In addition, to ensure the appropriateness of the suggested process with respect to deformation behavior, a 3-dimensional finite element simulation on each sequence is performed, and experimental investigations are also carried out using SCr420H as the initial billet material. Finally, a comparative investigation of the process duration between the traditional multi-stage warm forging and the suggested multi-stage cold forging is presented. It is shown that the multi-stage cold forging process in this study could be successfully applied to the mass production of the outer race of the CV joints with the appreciably reduced processing duration for the machining process on the inner ball groove.

Numerical Simulation Research on Warm Forging Process for Spur Gear with Large Module Based on Floating Die Method

The warm forging process of spur gear with large module using floating die set was studied in the paper. The influence of process parameters such as billet temperature, web position, web thickness, frictional factor on the filling of die cavity and forging load were investigated by finite element method. It was concluded that the corner filling of gear can be improved by using free floating die. The forging load decreased with the increase of billet temperature or the decrease of frictional factor. The best web position for die cavity filling was that the web was located in the middle of the forged part.