Split-Plot I-Optimal Design Optimisation of Combined Oil-Based and Friction Stir Rotation-Assisted Heating in SPIF of Ti-6Al-4V Titanium Alloy Sheet under Variable Oil Pressure

The aim of this paper is to determine the optimal input parameters for the process in order to ensure the maximum formable wall angle is obtained in a conical frustum with a varying wall angle fabricated using Single Point Incremental Forming (SPIF). The test material was 0.8-mm-thick Ti-6Al-4V titanium alloy sheets, and the test used a tungsten carbide tool with a rounded tip with a radius of 4 mm. Complete workpieces were heated using hot oil with a temperature of about 200 °C, and in addition, the high rotation speed of the forming tool generated an amount of friction heat. The input parameters were tool rotational speed, feed rate, step size, and tool rotation direction. Various oil pressures were used to improve both the accuracy of the components formed and the friction heating process. On the basis of calculations performed by means of the response surface methodology, split-plot I-optimal design responses were obtained by means of polynomial regression models. Models were fitted using REstricted Maximum Likelihood (REML), and p-values are derived using the Kenward–Roger approximation. Observation of the fracture surface of Ti-6Al-4V drawpieces showed that the destruction is as a result of ductile fracture mode. Tool rotational speed and step size are the most significant factors that affect the axial force, followed by feed rate. It was also found that step size is the most significant factor that affects the in-plane SPIF force.

Lubricant Evaluation Technique for Single Point Incremental Forming Process

Single-point Incremental Forming (SPIF) is highly flexible dieless forming process suitable for a small batch production. The higher the feed rate and tool rotational speed, the higher the production rate will be. Therefore, the selection of the suitable lubricant is a key important factor to maintain the formability of the material when increasing the feed rate and tool rotational speed. This paper proposes the technique to evaluate and later on select the proper lubricant for these conditions. This technique was divided into two phases; 1) screening, and 2) stabilization. The screening phase is a quick method for preliminary selection of the lubricants. The stabilizing phase is a step to evaluate reliability as well as ensure efficiency of the lubricant throughout the process, because of the significant increase of the forming temperature which affects directly to the performance of the lubricant. Two types of lubricants, namely solid (Graphite) and liquid (Callington Calform NF-206) lubricants mixed with the base oil (coconut oil) at different ratios were tested. The cold rolled hot-dipped zinc-coated steel sheet with thickness of 0.176 mm. and wall angles of 45, 50, 55 and 60 degrees with the depth of each wall angle of 5 mm were used. During the screening phase, the fifteen mixtures firstly were tested by using the achieved maximum wall angles without fracture as a criterion. Later on, the lubricant mixtures which could successfully form at the wall angle of 60 degrees with the forming depth of 20 mm would be tested in the stabilization phase to evaluate the formability and the forming temperature. The results showed that during the screening phase 11 lubricants could perform successfully, while the stabilization phase with the wall angle of 60 degrees only 3 lubricants could successfully form the workpiece. Therefore, this evaluation technique could help to evaluate and, for later on, be a criterion to select the select lubricant.

A Comparative Investigation of Conventional and Hammering-Assisted Incremental Sheet Forming Processes for AA1050 H14 Sheets

Incremental Sheet Forming (ISF) is emerging as one of the popular dieless forming processes for the small-sized batch production of sheet metal components. However, the parts formed by the ISF process suffer from poor surface finish, geometric inaccuracy, and non-uniform thinning, which leads to poor part characteristics. Hammering, on the other hand, plays an important role in relieving residual stresses, and thus enhances the material properties through a change in grain structure. A few studies based on shot peening, one of the types of hammering operation, revealed that shot peening can produce nanostructure surfaces with different characteristics. This paper introduces a novel process, named the Incremental Sheet Hammering (ISH) process, i.e., integration of incremental sheet forming (ISF) process and hammering to improve the efficacy of the ISF process. Controlled hammering in the ISF process causes an alternating motion at the tool-sheet interface in the local deformation zone. This motion leads to enhanced material flow and subsequent improvement in the surface finish. Typical toolpath strategies are incorporated to impart the tool movement. The mechanics of the process is further explored through explicit-dynamic numerical models and experimental investigations on 1 mm thick AA1050 sheets. The varying wall angle truncated cone (VWATC) and constant wall angle truncated cone (CWATC) test geometries are identified to compare the ISF and ISH processes. The results indicate that the formability is improved in terms of wall angle, forming depth and forming limits. Further, ISF and ISH processes are compared based on the numerical and experimental results. The indicative statistical analysis is performed which shows that the ISH process would lead to an overall 10.99% improvement in the quality of the parts primarily in the surface finish and forming forces.

Reduction of Die Wear and Structural Defects of Railway Screw Spike Heads Estimated by FEM

Railway spike screws are manufactured by hot forging on a massive scale, due to each kilometer of railway track needing 8600 spike screws. These components have a low market value, so the head must be formed in a single die stroke. The service life of the dies is directly related to the amount of energy required to form a single screw. The existing standard for spike screws specifies only the required tolerances for the head dimensions, particularly the angle of the hub faces and the radius of agreement of the hub with the cap. Both geometrical variables of the head and process conditions (as-received material diameter and flash thickness) are critical parameters in spike production. This work focuses on minimizing the energy required for forming the head of a railway spike screw by computational simulation. The variables with the highest degree of incidence on the energy, forging load, and filling of the die are ordered statistically. The results show that flash thickness is the variable with the most significant influence on forming energy and forming load, as well as on die filling. Specifically, the minimum forming energy was obtained for combining of a hub wall angle of 1.3° an as-received material diameter of 23.54 mm and a flash thickness of 2.25 mm. Flash thickness generates a lack of filling at the top vertices of the hub, although this defect does not affect the functionality of the part or its serviceability. Finally, the wear is mainly concentrated on the die splice radii, where the highest contact pressure is concentrated according to the computational simulation results.

Study On The Single Point Incremental Sheet Forming of AISI 321 Variable Wall Angle Geometry

For rapid prototyping, design validation and small batch productions process with low tooling cost is preferred. Single Point Incremental Forming (SPIF) is a die-less sheet metal forming process which requires only low cost forming tool driven by CNC machine in a toolpath to form required geometry at room temperature from sheet blank clamped in a low cost and low stiffness clamping system. In this study, effect of process parameters such as tool radius, feed rate and lubrication are considered on the formability of the truncated profile of AISI 321 Variable Wall Geometry (VWA). Set parameters conditions with 2 level layers are optimized using numerical and statistical approach. Experimentation on the same setup is carried out by selecting the most, least and mid favorable solutions optimized on the basis of forming forces and stresses in the sheet. Geometrical accuracy, sheet thinning, and forming forces are compared analytically, numerically and experimentally addressing the inadequacy of analytically models for Variable Wall Angle Geometries.

Investigation of Process Parameters in High-Speed Die-less Water Jet Spin-Forming of Copper Sheets

A new forming method called high speed water jet spin-forming was developed. This new forming method is a combination of water jet incremental forming and sheet metal spinning without any mandrel. The forming speed has been significantly increased by spinning of the sheet using a lathe machine. The effects of the forming parameters such as water jet pressure, rotation speed and relative water jet diameter on formability and surface quality of deformed copper parts were investigated. The experimental results indicate that the water jet pressure and the sheet rotation speed have a significant effect on the final depth, wall angle, and surface smoothness. It was also concluded that the final depth exponentially increases as the sheet rotational speed reduced. In addition, when the water jet pressure is low, sheet rational speed does not play a significant role in the final depth of the specimen. Furthermore, it has been determined from the results that high water jet pressure plays an important role in improving the surface quality and wrinkling at different rotational speeds, and as the pressure is increased, the wrinkling decreases and thus the surface quality is improved.

Numerical Investigation of an Axisymmetric Model Scramjet Assisted with Cavity of Different Aft Wall Angles

An axisymmetric model scramjet assisted with cavity flameholder is numerically investigated. Three-dimensional Reynolds-averaged Navier-Stokes simulation is carried out to reveal the fuel mixing and combustion characteristics. The simulation results show reasonable agreements with experimental data. The analysis indicates that the axisymmetric and rectangular scramjet has some similarities to the cavity shear layer in the nonreacting flow field. The configuration of the cavity shear layer changes hugely due to the significant chemical reaction and heat release in the reacting flow field. Typically, two more configurations with different cavity aft wall angles are compared with the experimental configuration to optimize the configuration of the cavity. When the cavity aft wall angle is small, the cavity shear layer bends to the cavity floor and more fuel enters into and stays in the cavity, which results in poor fuel mixing performance. With the increase of the aft wall angle, the fuel distributes more uniformly and the fuel mixing efficiency improves. In the reacting flow field, the volume of the cavity full of hot products and free radicals increases while the interaction between the cavity and main flow decreases with the increase of the aft wall angle. The improved combustion efficiency shows that larger cavity volume weighs more than reduced interaction between the cavity and main flow. The combustion is more violent in the case with a larger aft wall angle. Therefore, a proper increase of the aft wall angle is beneficial to the performance of cavity-assisted axisymmetric scramjet when designing the cavity flameholder.

Finite Element Analysis of Springback of High-Strength Metal SCGA1180DUB While U-Channeling, According to Wall Angle and Die Radius

Springback is a problem as important as tearing or thinning, while forming high-strength sheets. Springback is an undesirable situation and it is the form difference between the desired form of a part in theory and the form obtained due to mechanical characteristics and process inputs of the material after die forming. It affects operations in shearing, punching or bending dies in subsequent operations in forming die sets. If the part is not within the desired tolerance range, it creates problems during assembly. In order for cost effective production plans for automotive parts to be made, suitable sheet forming simulations are needed. Waste of time and failures during die construction are minimized by defining accurate parameters by finite element analyses and minimizing periods of trial-and-error. In this study, the material SCGA1180DUB in sheet thickness of 0.8 mm from multi-phase steel sheet group was U-channeled, using Autoform sheet forming analysis program, according to appropriate process conditions having wall angles of 7°,10°,12° and die radius values of R3, R5, R8 and the springback values were estimated. The results obtained were compared through the finite element program and suitable wall angle and die radius values for the material SCGA1180DUB for forming advanced high-strength sheets were determined. As the die radii increased at the same wall angles, the amount of spring back increased significantly. In particular, due to high yield and tensile strength of multi-phase high strength sheet, springback values were observed to be high. Negative springbacks were observed in the roof of the part. In the same die radii, under the same process conditions, as wall angles increase, springback values decreased. In the literature, it is interesting that there are few studies regarding forming, springback of high-strength sheets SCGA1180DUB. This study will contribute to the literature. Autoform program was used for Finite Element Analysis.