**2.1. System specification and design of die assembly**

Developed micro-drawing die assembly is devised to improve the handling characteristics of tiny blank and to enhance the positioning accuracy of central axis of drawing process. A blanking-drawing process, which combines the blanking and drawing, is adopted and tool set is designed. The schematic illustration of micro-blanking-drawing process is shown in Fig.3. The tool of drawing die combined with the blanking punch is able to form directly from the blanking material to drawing micro-cup. In addition, blank holder force during the process is not applied for better reproducibility of the experiment. Instead of the blank holder, the constant gap between the drawing die and the blank holder is designed.

Fig.4 shows the appearance of designed micro-deep drawing die assembly. The die assembly is designed to compact palm-size with around 10cm square. Blanking punchdrawing die is mounted on the upper die, while the blanking die and the drawing punch is set up to the lower die. Furthermore, in order to measure the forming load during the process, the micro-compression load cell (TC-SR50N, TEAC Co.), which has the rating capacity of 50N, is aligned directly below the drawing punch of the lower die.

**Figure 3.** Schematic illustration of micro sequential blanking-drawing process

114 Metal Forming – Process, Tools, Design

further high precision forming process design.

micro-deep drawing experimental system.

Die/ tool set

**Figure 2.** Appearance of micro deep drawing experimental system

**2.1. System specification and design of die assembly** 

characterization of tribological behaviour under dry friction is a pressing need for the

In view of the significant importance of tribology in micro-sheet metal forming, this chapter creates an overview of the effect of surface topography of tools and workpieces on microsheet formability. Starting with an introduction of the newly developed micro-deep drawing experimental system and that of a finite element simulation model with surface asperities, the impact of surface topography on the tiny micro-scale forming behaviour is discussed.

The experimental system for micro-deep drawing is newly developed with a goal for highly accurate forming operation with a good reproducibility in experimental results. The system consists of (a) micro-drawing die assembly, (b) desktop size miniature press machine, (c) control panel and (d) compact feeding device. Fig. 2 shows the appearance of developed

Bar feed device

Developed micro-drawing die assembly is devised to improve the handling characteristics of tiny blank and to enhance the positioning accuracy of central axis of drawing process. A blanking-drawing process, which combines the blanking and drawing, is adopted and tool set is designed. The schematic illustration of micro-blanking-drawing process is shown in Fig.3. The tool of drawing die combined with the blanking punch is able to form directly from the blanking material to drawing micro-cup. In addition, blank holder force during the process is not applied for better reproducibility of the experiment. Instead of the blank

holder, the constant gap between the drawing die and the blank holder is designed.

Control panel

Control PC

Servo screw motor

Amplifier

Safety switch

**2. Development of micro-deep drawing experimental system** 

**Figure 4.** Appearance of designed micro drawing die assembly (a) micro compression load-cell, (b) micro drawing die assembly, (c) tool set of micro sequential blanking-drawing process

The micro-drawing die assembly is mounted on the desktop size miniature press machine (MS-50M, Seki Co.), which is custom-designed for the micro deep drawing experiment by Seki Corporation. The press machine is driven with a servomotor, which has a high motion resolution of 400nm and a maximum instantaneous velocity of 28mm/s. The motion control is based on the high precision digital displacement sensor (GT2 Keyence Co.) mounted on the press machine. In addition, a variety of press ram motion can be realized by developed controlling program, such as linear or S-curve acceleration and deceleration, inching motion at bottom dead point and motion stop at several displacement for input time length.

Impact of Surface Topography of Tools and Materials in Micro-Sheet Metal Forming 117

**Figure 6.** Appearance of drawn microcups on a forefinger and its SEM image

**Phosphor bronze Stainless steel**

**Pure titanium**

**Figure 7.** Appearance of drawn microcups with good reproducibility in three different materials,

phosphor bronze, stainless steel, and pure titanium

Moreover, the compact feeding device is newly developed for the miniature press machine. By using this device, the coiled material of metal foils can be progressively supplied during the process and the continuous transition of the forming behaviour, such as wear of tools, would be able to track in the experiment.
