August 2019 Volume 1

FORGING RESEARCH

hollow shaft based on differential heating will be analyzed with the aid of numerical modeling. The candidate parts to be explored for this process will include axle shafts, main shafts, pinion gear shafts and lay-shafts. To enhance power density of the shaft, the shaft is made hollow so that non-functional material is removed. In the development stage, system design, laboratory scale prototyping, and economic evaluation and validation are carried out. The main activities in the testing stage, include building of the tooling that will be integrated into an existing forging press, conducting trial runs for several shafts, and quality evaluation of the forged hollow shafts. The specific objectives for each stage are as follow. I. Investigation Stage • Develop a differential heating based forging process that can be used to produce a variety of power transmission shafts such as the axle shaft, main shaft and pinion gear shaft. • Investigate the metal flow patterns of the proposed forging sequence and evaluate the process in terms of the formability, the forming load and the geometric quality of the shaft using FEM simulations. II. Development Stage • Develop a laboratory-scale test setup for demonstrating the feasibility of the differential heating based forging process for making hollow shafts. • Produce the laboratory-scale hollow shafts models using the proposed process. • Investigate how to mitigate the strain concentration in the product by improving the induction heating scheme. • Design a preliminary system for large scale field trial with focus on establishing important parameters for forging of hollow axle shafts. 1.3. Approaches FEM is used to evaluate the proposed forging process. The finite element analysis software DEFORM2D is used. The process is applied to various hollow shafts, such as the axle shaft, the main shaft, the pinion gear shaft and the lay-shaft. Induction heating scheme is developed with the aid of analytical and numerical simulations. ANSYS and the induction heating module of DEFORM2D are used for numerical simulations. The results from the induction heating simulations are used as a guide for specifying the size of the induction heater needed for the experiments. The tooling is fabricated by using machining facilities available at NCSU such as Wire EDM, CNC lathe, and milling machines. Other operations that could not be done at NCSU such as heat treatment of dies are subcontracted to outside vendors. 1.4. Report Organization A brief introduction featuring various techniques for producing hollow shafts is given in Chapter 1. Objectives of the study and

methodologies adopted are also discussed in this chapter. A new forging sequence for manufacturing of hollow shafts is discussed in Chapter 2.This new forging sequence is based on differential heating of tubular blank. The discussion in this chapter include, material flow patterns and feasibility of the process to produce hollow axle shaft evaluated by numerical simulations. In Chapter 3, an ironing stage is added to the proposed process for the axle shaft to increase wall thickness uniformity. The bottom die of the upsetting operation is optimized to eliminate difficulties in fabricating long dies. In Chapter 4, application of the proposed process is extended to the main shaft. The metal flow pattern and feasibility of this process are studied by numerical simulations. Effects of the inner diameter on the process feasibility are investigated. In Chapter 5, dies used in the proposed process for the main shaft are redesigned to facilitate formation of a sizable flange from a thin walled tubular stock. The wall thickening problem during the upsetting operation is addressed. In Chapter 5, the proposed forging process is combined with tube extrusion to fabricate hollow pinion gear shafts. The metal flow pattern and feasibility of this hybrid process are studied with the aid of numerical simulations. In Chapter 6, the proposed process is adapted to produce two types of layshafts. One having two flanges at the end of the shaft whereas the other has two flanges at the middle of the shaft. Their feasibility is evaluated based on formability and forming load. In Chapter 7, a preliminary lab scale experiment is carried out to demonstrate the potential of the proposed process for producing hollow shafts. Chapter 8 discusses important process parameters for the field trial experiments of axle shaft to be carried out at Mid-West Forge. Major conclusions of the study are presented in Chapter 9. Appendix I discuses analytical and numerical calculations to estimate process parameters for induction heating. CHAPTER 2 Development and Evaluation of the Forging Process for Hollow Axle Shaft 2.1. Introduction The axle shaft is a narrow, pole-like part with a flange at the end that connects a wheel to the gears in the differential. It transmits torque from the differential to the wheel and, in some cases, bears the weight of the vehicle [10]. Figure 2-1 shows typical axle shafts. The axle shafts are generally made as solid steel components and weights around 20 kg. The drivetrain for heavy duty vehicles has typically 2-4 axle shafts depending on the rear axle configuration, making it an attractive target for weight reduction studies. A more cost effective process techniques for hollow axle shafts must be developed for mass production. To this end, focus of the chapter is to develop a new forging process to produce hollow axle shaft using forging presses and tools that are currently used to manufacture solid shafts. The final hollow axle shaft in this case is composed of a solid

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