August 2019 Volume 1

FORGING RESEARCH

Chapter 1 Introduction, Objectives and Approach 1.1. Introduction Lightweighting is being actively researched worldwide. The motivation to reduce the weight of a vehicle is largely driven by government regulations. For example, the fuel mileage requirement for cars in the US will increase to 35 mpg in 2020 [1]. For heavy duty trucks, the US is expected to cut carbon pollution by 17% from 2005 levels by 2020 [2]. The power train for cars and trucks carries a significant percentage of the total weight of a vehicle. For example, the power train in Classes 1–3 accounts for 36% of the total weight, whereas in Class 8 the power train accounts for 48% as shown in Figure 1-1. The majority of power transmission systems used in the automotive, aerospace, maritime, and other industries employ solid shafts. Because many of power transmission components are forged, light weight power transmission components should be of particular interest to the forging industry. Previous reports have shown that making traditional solid power-train shafts hollow or bimetallic has the potential to significantly reduce the weight of heavy duty vehicles and enhance fuel economy [1]. Although there are different ways that hollow shafts could be produced (e.g., machining), to meet the demand in the above-mentioned industries, any newmanufacturing process must meet the following criteria: mass production potential, short cycle time, structural integrity, and cost effectiveness. The hollow shafts are currently manufactured by rotary swaging, flow forming, spinning extrusion combined with the cross rolling, tube hydroforming, extrusion combined with the deep drilling, extrusion followed by friction wielding, etc. These processes are illustrated in Figure 1-2.

Figure 1-1: Weight Distribution of HDVs (class 8) [1] Rotary swaging is an incremental cold forming process for rods and tubular components. Rotary swaging can reduce the diameter and form the steps on the workpiece with radial oscillating dies. There are two types of rotary swaging. Radial forging, shown in Figure 1-2 a, moves the workpiece in axial direction through oscillating dies to reduce its diameter by a small amount. The other method called the plunging method, shown in Figure 1-2 b, is able to reduce diameter between two ends of the workpiece by closing a set of radially oscillating dies. Rotary swaging has all the advantages of cold forging, such as work hardening, tight tolerance and good surface finish. However, both processes require specialized forming machines, which may be costly. Upset swaging or axial radial forming, illustrated in Figure 1-2 c, is a special form of rotary swaging, which increases the wall thickness at the target region by heating the region and upsetting the work-piece. Although upset swaging has high flexibility for shaping the exterior and manipulating the wall thickness of the part, the high equipment cost and low production rate limit its application [3][4].

a. Radial Forging [3]

b. Plunge Method [3]

c. Upset Swaging

d. Flow Forming

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