Material flow control in plunge micro rotary swaging

Abstract

In rotary swaging, the material flow is not fully controlled by closure of the forming dies. This is especially noticeable in plunge rotary swaging of rod, where the workpiece is positioned into the forming zone und processed locally. As result, an uncontrolled elongation of the workpiece in axial direction takes place and an axial position shift of the workpiece relative to the dies occurs. This is a special challenge in production of linked micro parts, where single parts are interconnected in order to enable the handling as a strip and thereby a roll-to-roll production. The axial shift influences not only the subsequent positioning of neighbouring parts, but also the final geometry of the currently processed part. The presented investigation analyses the material flow during plunge micro rotary swaging on basis of in-process measurements of the workpiece shift on both sides of the forming zone as well as with the help of contour measurements of the processed parts. It is shown that the measured shift is strongly influenced by the workpiece clamping and fixation and that it can be controlled by applying low axial forces to the workpiece on one or both sides of the forming zone. Further, the geometry of the workpiece can be affected by these measures.

Micro Forming Processes

“…Figure 2.19 shows the final diameters after a reduction of rods from AISI 304 steel with an initial diameter of d 0 = 1.0 mm using a die set with a nominal diameter of d nom = 0.75 mm and a calibration zone of l cal = 20 mm. For low feed rates (v f < 4 mm/s), d 1 is constant over the workpiece length and close to d nom [Mou18a]. At high feed rates, however, the diameter evolves over the workpiece axis z'.…”

“…In order to control the material flow against the axial feed direction and thus prevent process limitations like bending or even breaking, a spring-loaded clamping device for the workpiece was developed [Mou18a]. The clamping device allows an axial evasion of the workpiece.…”

“…The stroke was h T = 0.3 mm and different radial feed rates v r were used. Furthermore, different IEs made of thermoplastic polyurethane with three different hardness grades were tested (low hardness = ILH; middle hardness = IMH and high hardness = IHH) [Mou18a]. For the reduction without IE, a maximum radial feed rate of v r = 0.34 mm/s could be applied before flashes or breaks occurred.…”

“…Three methods to improve the rotary swaging in the micro range based on the material flow control are presented. In infeed swaging a higher axial feed rate is enabled by using an adjusted workpiece clamping [Mou18a]. In plunge rotary swaging the application of an elastic tube prevents flash formation [Mou15b,Mou15b] and with the application of external axial forces the part geometry can be controlled [Mou18b].…”

Process Design

“…It could be shown that the effect on the part geometry can be more or less significant depending on the machine parameters. As shown in [Mou18], a convenient control of the applied forces or a compensation of the elongation improves the forming results and enables the production of symmetrical parts without defects.…”