Nickel-Based Slag-Remelted Superalloy for Ti-Alloys Isothermal Forging Die-Tool

The work purpose is to evaluate the application of nickel-based CrNi73CuBeTeAl superalloy (tungsten-free), made by electroslag remelting as a die tool material for isothermal forming. Isothermal deformation was simulated by tests for high-temperature cyclic creep. The specimens with high and × in plan dimensions (both parallel and perpendicular to the ingots central axis) were cut from the bottom, top and central zone, near the lateral surface and in the ingots central axis area. The tests were performed at 900, 940 and 980 °C constant temperature with 100, 200 and 300 MPa cyclic pressure in 0.02, 0.2 and 2.0 mm/s velocities range corresponded to 10-3-10-1 1/s strain rates. Such tools application field is compressor blades Ti-forgings die forging and sizing with ε = 1.0-3.0% residual upsetting deformation of dies during operation. It is shown that the die life can be extended to 400-700 loading cycles at 850-950 °C operating temperature and pressure up to 150 MPa.

A New Path Planning Strategy Based on Level Set Function for Layered Fabrication Processes

In this paper, a new equidistant offset filling theory based on level set function and corresponding numerical solving algorithm based on dynamic finite difference method were proposed. Firstly, the closed curve is defined as the zero-value contour of level set function. Then, the level set equation, a partial differential equation, has been built to get the level set function, and a dynamic finite difference method has been proposed to solve the level set function. Secondly, three types of cross-sections which are simple polygon, multi-island polygon and multi-hole polygon were used to test the equidistant offset filling effect of the algorithm. The test results show that the proposed theory and algorithm in this paper can well deal with the equidistant filling problem of these cross-sections. In addition, any complex section can be equidistant offset filled by the algorithm proposed in this paper, and the calculation cost is significantly related to the number of offsets, but not directly related to the section complexity. Finally, the remanufacturing of a typical crankshaft hot forging die proves that the algorithm proposed in this paper can effectively complete the remanufacturing repair of this kind of forging die. The surface of the die is smooth, and there are no defects such as porosity and slag inclusion after machining. Compared with the new die, the manufacturing cost can be saved more than 50%, and the efficiency of die manufacturing can be improved more than 60%. This is due to the machining allowance of the die after additive manufacturing is very small, and it can be quickly repaired on site.

Filling Path Planning and Polygon Operations for Wire Arc Additive Manufacturing Process

To improve the service life of hot forging die, the additive manufacturing algorithm and additive manufacturing device for die remanufacturing are developed. Firstly, a compound filling algorithm in which the inner zone is filled by linear scanning and the outer contour is filled by offsetting is developed in order to solve the problems encountered in filling path planning for wire arc additive manufacturing (WAAM) like staircase effect at marginal division, degenerated edge at outer contour, programming difficulty, and so forth. Meanwhile, the attitude control algorithm of welding gun is proposed to control the angle between welding gun and welding path so as to improve the welding forming quality. Secondly, the high-temperature and low-temperature wear resistances of Fe-based and Ni-based alloy are tested. The results show that Ni-based alloy has higher high-temperature wear resistance. Finally, a disabled crankshaft hot forging die is selected for application test and the results show that, using the techniques discussed in this paper, welding materials can be saved by more than 50% and machining cost can be saved by more than 60%. In addition, the surface of automatic-repaired die is smooth without oxidation, collapse, and other defects after forging 3000 times, which is much better than that of manual-repaired die.

Adjusting Mechanical Properties of Forging Dies Produced by Ausforming

Due to high thermo-mechanical loads, tools used in hot forming operations need a high resistance to different damage phenomena, such as deformation, cracking and abrasion. They are exposed to cyclic thermo-mechanical stress conditions, which leads to tool failure and subsequent tool replacement during cost-intensive production interruptions. To increase wear resistance, forging tools can be produced in the metastable austenite area. Forming of steel below the recrystallisation temperature, also known as “ausforming”, offers the possibility to increase strength without affecting ductile properties. This is due to grain refinement during forming. In this study, the thermo-mechanical treatment ausforming will be used to form the final contour of forging dies. For this purpose, an analogy study was performed where a cup-preform is ausformed, which represents the inner contour of a highly mechanically loaded forging die. It is investigated to what extent a fine-grained microstructure generated in the last forming stage can be achieved and how it influences the tool’s performance. The hot-working tool steel X37CrMoV5-1 (AISI H11) was used as workpiece material. To achieve optimal properties, process routes with tempering temperatures from 300 °C to 500 °C and global true plastic strains of φ = 0.25 and φ = 0.45 were examined. The results were evaluated by pulsation tests, metallographic analysis and hardness measurements of the formed parts. Optimal ausforming parameters were derived to produce a high performance forging die.

A Path Generation Method for Wire and Arc Additive Remanufacturing of Complex Hot-forging Dies

Wire and arc additive remanufacturing (WAAR) technology has become a new solution for hot-forging dies repair and remanufacturing. In this study, a path generation method is proposed for WAAR of hot-forging dies. At first, a WAAR process of the hot-forging die is presented, and considering the characteristics of large welding heat input and complex 3D digital model, the hybrid path planning strategy is confirmed as an appropriate strategy for WAAR. The developed hybrid path generation method for WAAR consists of three main steps: determinate the direction of the scan line; divide and fill the internal area; and connect the sub-paths. the relatively optimal scanning direction is determined by calculating the length and inclination angle of each line segment in the contour lines, which reduces the possibility of sharp angles. The internal region is divided based on the location of the selected extreme points, and the path space is adjusted to avoid the occurrence of the underfilled phenomenon. At the stage of sub-paths connection, some criteria are proposed to reduce the number of sub-paths. At last, a planar deposition experiment and the WAAR process of four damaged hot-forging dies are carried out to validate the effectiveness and robustness of the proposed method.

Research on Gradient Additive Remanufacturing of Ultra-large Hot Forging Die Based on Automatic Wire Arc Additive Manufacturing Technology

In this paper, an automatic WAAM technology are proposed to realize the gradient additive remanufacturing of ultra-large hot forging dies. Firstly, a vertical additive manufacturing strategy and a normal additive manufacturing strategy are proposed to meet different additive manufacturing demands. Secondly, the basic principle of layering design of ultra-large hot forging dies is developed, and the wear resistance of Ni-based, Co-based and Fe-based alloys at room temperature and high temperature is analyzed. The Co-based alloy has the best high temperature wear resistance, which can be used on the surface of the hot forging die to strengthen the die. In order to control the forming quality of additive manufacturing, the relationship between welding parameters and weld shape was discussed, and the reverse system of welding process parameters was built. Finally, a typical aviation ultra-large hot forging die is selected as the research object. According to different stress and temperature distribution in different regions of the ultra-large hot forging die in service, materials with different properties are used in corresponding regions to improve the service life of the die, reduce the remanufacturing costs and improve the remanufacturing efficiency. The experimental results show that the service life of the hot forging die repaired by the automatic gradient function WAAM technology is significantly increased, the material is reduced by more than 50% and the production efficiency is increased by more than 50%.