August 2019 Volume 1

FORGING RESEARCH

The formability of the process is evaluated by the effective strain distribution of the final part. Figure 2-12 shows that the flange has larger effective strain than the tubular body.The maximum effective strain of 6.478, occurs in the center of the flange. This strain is acceptable for hot forming operation and thus from a material flow aspect the process is achievable and worthy of further examination. Besides the formability, attention is also paid to the forming load curve as it reflects the feasibility of the process. As is shown in Figure 2-13, the forming load of the upsetting operation increases slowly before the stroke reaches 68mmand then steeply increases.The steep increase is caused by deformation of the warm material. Maximum forming load of the upsetting operation is 201 tons. Figure 2-14 shows the forming load in the flanging operation increase slowly at the beginning and soars at the end. It also shows the forming load during the flange operation reaches a maximum of 847 tons, at a stroke of 349 mm, that is, when the flange thickness is reduced to the product design dimension of 25 mm. Because final machining operation will be carried out after the forging process to improve dimensional and geometric accuracy, the final forged shaft should have a slightly thicker flange than the product design to reserve machining allowance. Therefore, the maximum forming load during the flanging operation is 677 tons which occurs at the stroke

of 346 mm, if the machining allowance on the flange thickness is set at 3 mm. A forging press of 677 tons capacity will be needed at the flanging stage. Because the deformed volume is, for all intents and purposes, solid, the forming load should be close to that exerted on a press when conventional solid shafts are forged. The differential heating based process is good at maintaining a uniform wall thickness in axial direction. The majority of the tubular body is subjected to effective stress below 228 MPa and small regions exhibit effective stress of 598.8 MPa. It is found out that stress of the foregoing two magnitudes are less than or slightly more than the yield strength of AISI4140. Therefore, wall thickness of vast majority of the tubular body must be uniform along the axis. This is shown by distribution of the normalized wall thickness deviation which is defined as , where t 0 is the wall thickness of the initial tube, Δt is the tolerance (difference between the wall thickness of the final part and that of the initial tube), r is the radial coordinates of nodes along the inner boundary of the workpiece, OD is the outer diameter and ID is the inner diameter of the initial tube. Figure 2-15 shows 92.25% of the tubular body has a normalized wall thickness deviation less than 5% which is equal to 0.79mm. ∆ t = OD - 2r t 0 OD - ID

Figure 2-13: Forming Load Curve for the Upsetting Operation

Figure 2-14: Forming Load Curve for the Flanging Operation

FIA MAGAZINE | August 2019 58