Cold Forging Process Research Articles

A comparative analysis of hot and cold flashless forging of a stepped shaft using vertically-parted dies

Flashless forging is classified as a precise metal forming technology. The main advantages of this technology are the reduction of the flash allowance and the shortening of the manufacturing time by eliminating the flash trimming operation. The article presents the process of one-step forging of a stepped shaft made of aluminum with the use of split dies. The process was carried out in cold and hot metal-forming conditions. The forging process was analyzed numerically using the Simufact Forming 15.0 software. The geometrical parameters of the obtained product were analyzed, and the distribution of effective strain, temperature, and the standardized cracking criterion was determined. The process force parameters were also determined. Numerical tests were verified in real conditions with the use of a specially designed device for forging in vertical split dies. Comparison of hot and cold forging in vertical split dies is presented. The comparative analysis results have demonstrated that the hot forging process has more advantages than the cold forging process. The hot forging process ensures higher accuracy of forged parts.

Machine Learning Acoustic Emission Based Monitoring of Cold Forging for Smart Manufacturing: A Review

Cold forging is a high-speed forming technique used to shape metals at near room temperature. and it allows high-rate production of high strength metal-based products in a consistent and cost-effective manner. However, cold forming processes are characterized by complex material deformation dynamics which makes product quality control difficult to achieve. There is no well defined mathematical model that governs the interactions between a cold forming process, material properties, and final product quality. The goal of this work is to provide a review for the state of research in the field of using acoustic emission (AE) technology in monitoring cold forging process. The integration of AE with machine learning (ML) algorithms to monitor the quality is also reviewed and discussed. It is realized that this promising technology didn’t receive the deserving attention for its implementation in cold forging and that more work is needed.

Further Development of Wear Calculation and Wear Reduction in Cold Forging Processes

Tools are of strategic importance for industrial manufacturing processes. Their behaviour has a great influence on the productivity of the process and the quality of the product. A material saving and efficient technique for processing metallic workpieces is cold forging. One major challenge of this production method is the handling of high contact normal stresses in the tool contact, which can lead to severe tool wear. To investigate promising approaches for understanding wear modelling and wear reduction a demonstrator process based on the first stage of a total five-staged cold forging process for the manufacturing of a bolt anchor is considered in the scope of this research. This work aims at the further development of a numerical wear calculation based on an adapted Archard model in order to be able to realistically predict the tool wear in cold forging processes. Therefore, the material characterization of the used workpiece material as well as an investigation of the worn tool dies takes place to validate a numerical wear calculation model. Furthermore, this research addresses a reduction in wear by identifying critical areas and changing the inlet geometry of the investigated demonstrator tool die. This way, conclusions can be drawn about the wear sensitivity during numerical process design, and particularly critical areas can be geometrically modified in terms of the design.

A study on using cold forging process to manufacture bush

This work studied on the feasibility to produce agricultural bush parts using cold forging followed by machining to replace existing processes of piercing operation followed by shaving had been studied. Short tool life of the shaving punch is a major problem for existing processes. From this work, it was found that the maximum force required for cold forging operation is similar to that used on the existing process. Therefore same facility can be employed for a proposed method. A proper selection of billet size was necessary not only to obtain specific shape of final part, but also to yield maximum rate of material utilization. Another factor influencing the process was material flow constraint by cold forging die design. The design with highly constrained would lead to high stress introduced to the part. It is recommended to use forging die design with allow more of free material flow which is expected to improve tool life.

Adapted tool design for the cold forging of gears from non-ferrous and light metals

Due to growing competitive pressure within the manufacturing sector, there have been increasing attempts to establish resource saving production methods in gear manufacturing within recent years. Cold forging offers the potential—in addition to a high material and energy efficiency—to produce gears with an excellent surface quality, increased hardness as well as a load adapted fiber orientation. With regard to the wide range of applications there is a broad demand for gear materials, ranging from high-strength steels to non-ferrous and light metals. The flow behavior of the material has a significant influence on the cold forging process. Therefore, no consistent process result is achieved when forming different materials. Challenges exist due to deficient die filling and poor resulting geometrical accuracy. In this contribution, material-specific challenges during the full forward extrusion of gears from non-ferrous and light metals have been identified and suitable tool-sided measures were derived. A validated numerical process model was used to determine the underlying mechanisms of action and to verify the derived measures. A reduced yield stress leads to inflow formation, insufficient die filling, and low achievable strain hardening, as well as gearing accuracy. The tool-sided measures achieved a significant increase of resulting die filling and gearing accuracy as well as the mechanical properties. That provides the basis for the production of ready-to-use gears from various metal materials.

Multi-Stage Cold Forging Process for Manufacturing a High-Strength One-Body Input Shaft.

A multi-stage cold forging process was developed and complemented with finite element analysis (FEA) to manufacture a high-strength one-body input shaft with a long length body and no separate parts. FEA showed that the one-body input shaft was manufactured without any defects or fractures. Experiments, such as tensile, hardness, torsion, and fatigue tests, and microstructural characterization, were performed to compare the properties of the input shaft produced by the proposed method with those produced using the machining process. The ultimate tensile strength showed a 50% increase and the torque showed a 100 Nm increase, confirming that the input shaft manufactured using the proposed process is superior to that processed using the machining process. Thus, this study provides a proof-of-concept for the design and development of a multi-stage cold forging process to manufacture a one-body input shaft with improved mechanical properties and material recovery rate.

Automatic Multi-Stage Cold Forging of an SUS304 Ball-Stud with a Hexagonal Hole at One End.

SUS304 stainless steel is characterized by combined tensile and compression testing, with an emphasis on flow stress at higher strain and temperature. The plastic deformation behavior of SUS304 from room temperature to 400 °C is examined and a general approach is used to express flow stress as a closed-form function of strain, strain rate, and temperature; this is optimal when the strain is high, especially during automatic multi-stage cold forging. The fitted flow stress is subjected to elastothermoviscoplastic finite element analysis (FEA) of an automatic multi-stage cold forging process for an SUS304 ball-stud. The importance of the thermal effect during cold forging, in terms of high material strength and good strain-hardening, is revealed by comparing the forming load, die wear and die stress predictions of non-isothermal and isothermal FEAs. The experiments have shown that the predictions of isothermal FEA are not feasible because of the high predicted effective stress on the weakest part of the die.

Fully Coupled Finite Element Analysis of an Automatic Multi-Stage Cold Forging Process

In this paper, non-isothermal analysis of an automatic multi-stage cold forging process of a ball-stud is conducted using a new material model which is a closed form function of strain, temperature and strain rate covering low and warm temperatures for high-strength stainless steel SUS304. An assembled die structural analysis scheme is employed for revealing the detailed die stresses, which is of great importance for process and die design for metal forming of the materials with high strengths. Die elastic deformation is dealt with to predict final geometries of material with higher accuracy. A complete analysis model is proposed to be used for optimal design of process and die designs in automatic multi-stage cold forging of high-strength materials.

Multistage Cold Forging Process Design of Al6082 Considering Forming Limit

Multistage Cold Forging Process Design of Al6082 Considering Forming Limit

A Combined Cold Extrusion for a Drive Shaft: A Parametric Study on Tool Geometry.

Parametric investigations related to shoulder angle on tool geometry for a combined cold extrusion of a drive shaft, which consisted of spur gear and internal spline structures, were conducted through three-dimensional FE (finite element) simulations. The drive shaft was required to be about 92.00 mm for the face width of the top land on the spur gear part and roughly 22.70 mm for the groove depth of the internal spline section. AISI 1035 carbon steel material with a diameter of 50.00 mm and a length of 121.00 mm was spheroidized and annealed, then used as the initial billet material. A preform as an intermediate workpiece was adopted to avoid the excessive accumulation of plastic deformation during the combined cold extrusion. Accordingly, the cold forging process involves two extrusion operations such as a forward extrusion and a combined extrusion for the preform and the drive shaft. As the main geometric parameters influencing the dimensional quality and the deformed configuration of the final product, the two shoulder angles of θ1 and θ2 for the preform forging and the combined extrusion were both considered to be appropriate at 30°, 45°, and 60°, respectively. Using nine geometric parameter combinations, three-dimensional finite element simulations were performed, and these were used to evaluate the deformed features and the geometric compatibilities on the spur gear structure and the internal spline feature. Based on these comparative evaluations using the numerically simulated results, it is shown that the dimensional requirements of the target shape can be satisfied with the shoulder angle combination of (45°, 45°) for (θ1, θ2).

A cold forging process for producing thin-walled hollow balls from tube using a plastic insert

This paper investigates a cold forging process for producing hollow balls made of an aluminium alloy. The forging with an outside diameter of 30 mm is formed from a tube section with a 2-mm wall thickness. Preliminary tests have shown that in traditional die forging, the use of a billet with such a small relative thickness not only limits the range of applicable geometric parameters but also causes buckling. The authors propose to solve this problem by using an additional tool that has an active effect on the inner surface of the workpiece, and thus makes it possible to control the forging process conditions. The tool is a plastic insert, i.e., an additional flexible core made of a low-melting alloy. Theoretical and experimental results presented in this paper provide a considerable insight into the cold forging process for thin-walled hollow balls. The effects of the plastic insert geometry and dimensions on the forging process are also examined. A solution is proposed to ensure that the forged part meets all requirements.

Evaluation of friction using double cup and spike forging test for dry-in-place coating and forming oils

The friction characteristics of lubricants were evaluated using the double cup and spike forging tests. Friction calibration curves, i.e., plots of cup height ratio vs. punch stroke and spike height vs. punch stroke, were established through finite element (FE) simulations considering various friction factor values. The friction factor of the lubricants was determined by matching the relationships of the cup height ratio and spike height with the punch stroke obtained from experiments to those obtained from the FE simulations. Under the lubricating condition of dry-in-place coating with forming oil, the results showed that different tribo-testing methods yielded different friction factors. The friction factor determined was applied in the FE simulation of a cold forging process of a claw pole.

A proposed Common Single-Die Exchange Technique (C-SDET) to enhance production of pulleys

The success in developing a metal forming process is relied heavily on the design of a preform to reduce the final forming load at the final step. The design of the preform is considered a big burden of a process designer. Currently, the automotive companies try to design components which can cover a wide range of car models, but only changing a few dimensions to accommodate different models. However, each product is still considered a single product during the process design. Therefore, if only one preform can cover a variety of products, the process design could speed-up and gain more benefits in the production. In this research, a technique to design preform for various product models was proposed. The aim of this technique is to develop generalized common preforms by utilizing the same part configuration/shape but different dimensions in some areas to reduce the number of preform and process design time. This technique is composed of two steps: (a) classification of product groups and (b) determination of the common tool for producing the common parts. This technique was applied to the cold forging process to produce various models of automotive pulleys. The results show that the number of preforms was reduced by almost 70%, and the die changeover time was approximately saved by 75 min per shift (8 h/shift), and the capacity was gained by 1800 pieces per shift without generating any product defects.

Finite element analysis with experimental validation of crack initiation in valve housing

The paper reports that the study on crack analysis of valve housing, manufactured by cold forging process. It is reported that during the cold forging, frequent undue cracks are observed on the outer edges of the component. A detailed study was undertaken to analyses the micro structural defects in the forging process of a specimen. Scanning Electron Microscope (SEM) is performed on the component to understand its physical and chemical properties. To overcome the defects, the material geometry, and manufacturing process were optimized considering different constraints such as, manufacturing feasibility and cost. The computational modeling used to analyze the finite element analysis and optimize techniques. Also, the surface irregularities present on the die material, due to manual machining process is suggested to be rectified with the help of high accuracy automated machining centers. Results shows that the aforementioned defects occurred in the valve housing are completely eliminated and the material properties are enhanced for the expected life during end application.

A Study on Microstructural Evolution in Cold Rotary Forged Nickel-Superalloys: C263 and Inconel 718

C263 and Inconel 718 are precipitation hardenable nickel-superalloys widely used in different sections of a gas turbine engine dependent on their strength and temperature capability. Cold rotary forging is an effective route for manufacturing axisymmetric components with significantly higher material utilisation as compared to machining from conventional hot forgings. This paper presents a study on how C263, an alloy system strengthened by γ’, and Inconel 718, an alloy system strengthened by γ” and δ, deform during the cold rotary forging process and how their microstructures evolve. The two alloys exhibit maximum formability in solution-annealed condition. In this study, both C263 and Inconel 718 were annealed before the cold rotary forging operation. Parts with a 90° bend flange were successfully cold rotary forged from tubular preforms with a wall thickness of 6 mm. For both the alloys, the cold rotary forged parts exhibit significant differences in material properties from the undeformed sections to the most deformed section (i.e. the flanges). Post-forging heat-treatments are required to impart the desired material properties throughout the part. Therefore, appropriate annealing and aging treatments were identified for each of the two alloys. These heat-treatments led to uniform material properties for both deformed and undeformed sections of the cold rotary forged flanges in case of both the alloys.

Analysis of the stress state in non-axially symmetrical cold forging dies

Conventionally, reinforcement systems are used to decrease tensile stresses in axially symmetrical cold forging dies. The increasing complexity of parts due to lightweight design leading to higher functional integration causes the necessity of producing non-axially symmetrical parts, for which there is insufficient knowledge about the adequate application of reinforcement systems. To gain understanding about the stress distribution for non-axially symmetrical dies, a cold forging process for producing elliptical parts is introduced and numerically described. The simulation model is validated in a test set up with strain gauges, which are used to measure the strains on the die and reinforcement ring. Subsequently, the process is analysed regarding the location, direction and magnitude of the resulting prestresses and maximum stresses. Based on the findings, a classification of areas for non-circular symmetrical cold forging tools is introduced. The compressive area is subjected to increasingly high contact pressures by the workpiece. This leads to compressive radial stresses and radial displacements. The high displacements induce a bending effect, which causes tangential stresses in the tensile area. The gained process understanding is used to propose measures for improving the stress state in cold forging dies for asymmetrical parts by locally strengthening the reinforcement system.

Evaluation of strength of stainless steel bolt without heat treatment considering Bauschinger effect during manufacturing process

Abstract Isotropic hardening models for elastic-plastic materials are often used to simulate cold forging processes, although it cannot represent the Bauschinger effect. However, the Bauschinger effect must be considered for precise simulation of the strength in service of cold-forged components without heat treatment, as well as their geometry. A cold-forged bolt made of stainless steel is a typical example. In this report, finite element analysis of the forming process and the strength was performed for two multi-stage cold forging processes of non-heat-treated stainless steel bolts. The Yoshida-Uemori model was used as a kinematic hardening model that takes into consideration the Bauschinger effect of a material. The Yoshida-Uemori model was modified so that they can represent the strain hardening behavior in a large strain region appropriately for applying the model to cold forging process. As a result, it was possible to account for the Bauschinger effect during the forming process. Moreover, it was possible to estimate the difference in strength between the isotropic and kinematic hardening models by analysis of the tensile test results. Furthermore, the impact of the forming process on the strength of the cold-forged bolt was also evaluated.

Development of Preform for Simulation of Cold Forging Process of A V8 Engine Camshaft Free from Flash & Under-Filling

Finite Element Method based techniques apply to a wide spectrum of engineering applications including manufacturing. The flexibility to achieve optimized results by simulations adds another dimension to process-development. The efficiency due to simulation is enhanced many folds for developing desired components by reducing the cost as well as time. This paper investigates cold forging process to be adopted to produce camshafts with a target to minimize flash as well as under filling. These two factors being major problems encountered when cold forging is to be adopted for complex shaped products. The current work is primarily concerned with the development of an optimized preform design for a V8 engine camshaft. The work involved the Solid modeling of the camshaft on AutoCAD and further analyzing the developed model through finite element analysis using Deform 3D. The analysis involved understanding of metal flow, volumetric analysis and die stresses in the forging process. The materials considered for the work-piece and the dies are AISI 8620 and AISI-H-26 respectively. The sample camshaft was taken from a standard Dodge Challenger V8 engine. 10 different cases are analyzed to find out the best possible scenario. It is fund that the stress level for the developed model was very much within the design limit of the material.

Effect of Lubrication and Forging Load on Surface Roughness, Residual Stress, and Deformation of Cold Forging Tools

Cold forging is a metal forming that which uses localized compressive force at room temperature. During the cold forging process, the tool is subjected to extremely high loads and abrasive wear. Lubrication plays an important role in cold forging to improve product quality and tool life by preventing direct metallic contact. Surface roughness and residual stress also greatly affects the service life of a tool. In this study, variations in surface roughness, residual stress, and specimen deformation with the number of cold forging cycles were investigated under different forging conditions. Specimens that were made of heat-treated SKH51 (59–61 HRC), a high-speed tool steel with a polished working surface, were used. The specimens were subjected to an upsetting process. Compressive residual stress, surface roughness, and specimen deformation showed a positive relationship with the number of forging cycles up to a certain limit and became almost constant in most of the forging conditions. A larger change in residual stress and surface roughness was observed at the center of the specimens in all the forging conditions. The effect of the magnitude of the forging load on the above discussed parameters is large when compared to the effect of the lubrication conditions.

Analysis of single-operation cold forging of a hollow ball from a tubular billet

The article reports the results of an experimental and theoretical study of a single-stage cold forging process. This process was used to produce hollow balls with an outside diameter of 30 mm, with two central openings. The forgings were made from tubular aluminum alloy billets with wall thicknesses of 3 mm and 4 mm. The other dimensions of the billets (outer diameter and height) were varied, always making sure that the volume of the forging remained constant. The results of the study were discussed with a special focus on forming conditions, quality of the forging, potential limitations of the process, and the impact of billet dimensions (also expressed as non-dimensional slenderness ratios) on the conditions of the forming process.