Masahiro Sasada

Development of micro-piercing system with punch-damage monitoring function

Abstract This report discusses the results of a study on a new system which meets today’s requirements. In particular, the aim was to construct a system which can pierce small holes in green sheets and other thin foil for IC Industry and detect abnormalities like punch damage and clogging by scrap. A piezoelectric element and magnifying mechanism to enlarge its displacement were used for the drive to achieve high-speed piercing and controllability. The piercing unit is composed of piezoelectric elements and magnification mechanism to configure an electrical–mechanical system. The behaviour of the punch tip represents the changes in the electrical system. This suggests that by observing the driving current and voltage waveform of the piezoelectric element, it is possible to detect abnormalities during piercing. These results indicate the successful development of the aimed micro-piercing system with punch-damage detection function.

Burr-Free Microblanking Using Piezoelectric Actuator

Burr-free blanking requirements are strong; however, the thinner the product, the more difficult the burr-free blanking will be, due mainly to the control of the punch penetration depth. In this study the principle of accompanying burr-free blanking problems, and the driving mechanism of methods for realizing burr-free blanking of foil were realized. The conditions for realizing successful burr-free blanking are the clearance of step I and punch penetration depth. Use of the piezoelectric actuator element and the design method for this was proposed as the punch drive mechanism. Good results were obtained by using this press machine for burr-free blanking of 50 μm copper foil.

Study on pilot hole deformation by punching

Abstract Progressive die has some forming stages. The feeding of sheet material is necessary to obtain a forming product. In general, the sheet material used in the forming process is located using a pilot pin and pilot hole. It is important for keeping feeding accuracy that the deformation of the pilot hole is decreased in the punching stage of progressive die forming. In this paper, the deformation of a pilot hole by punching is discussed on the basis of the results of an experiment. A pilot hole and pilot pin were deformed by punching under various experimental conditions in this study. The deformation of the pilot hole and pilot pin decreased with increasing distance between the punch and pilot hole. Increasing the distance between the pilot pin and punch was effective for decreasing the dimensional changes of the pilot hole and the deflection of the pilot pin. The material flow in the lateral direction was observed using indentations produced by a micro-Vickers hardness testing machine. The material flow decreased with increasing distance from the punch. It is concluded that the material flow is useful data for deciding the positions of the pilot hole and pilot pin.

Investigation of the Relationship between Material Flow and Rollover in Double-Sided Shearing Using Image Processing

Shearing is the cutting of a sheet material with a punch and a die. The cut surface obtained by shearing is composed of rollover, a sheared surface, a fracture surface and burr. It has been reported that rollover is formed by the insufficiency of material and material flow in the lateral direction. However, the rollover in the sheet material on the die and that in the sheet material under the punch have not been evaluated individually in previous studies. In this report, the relationship between the material flow and the formation of rollover in the sheet material on the die is discussed on the basis of experimental results obtained by image processing. The relationship between the material flow and the formation of rollover in the sheet material under the punch also is discussed. Double-sided shearing with a counter punch was carried out. The deformation of the sheet material was observed through reinforced glass using a high-speed CCD camera. The image processing was carried out to investigate the material flow. The results were as follows. When the clearance is small, the material flow in the clearance is toward the sheet material on the die. When the clearance is large, the material flow in the clearance is toward the sheet material under the punch. The area of rollover in the sheet material on the die is equal to the sum of the amount of material flow in the clearance and that in the lateral direction. On the other hand, the area of rollover in the sheet material under the punch is equal to the sum of the amount of material flow in the lateral direction under the punch, that in the clearance and the insufficiency of material. These findings are useful for considering the relationship between the material flow and the formation of rollover in the case that the rollover in the sheet material on the die and that in the sheet material under the punch are evaluated individually.

Influence of Constraint of Material on Shearing Characteristics

In shearing, the crack occurrence may be controlled by elevating a hydrostatic pressure of a material near tool cutting edges. Since hydrostatic pressure is affected by constraint of material, the influence of constraint on shearing characteristics was investigated by the experiments and FEM analysis. The results of this study clarified the followings. The smooth sheared surface of blanked product is increased by constraint of material. When the material is tightly constrained, crack earlier occurs at the material near punch cutting edge than that of die cutting edge. This tendency agrees with the magnitude of hydrostatic pressure at punch and die cutting edges. It is confirmed that the constraint of material prevents cracks by adequate controlling of material flow aiming the hydrostatic pressure rise. It is also confirmed that the dishing of product is affected by the condition of the constraint.

Study on Crack Initiation from Small Holes of One-Piece Brake Disks for Motorcycles : How Braking Torque Directly Affects the Crack Initiation?

Cyclic braking tests at extreme conditions were carried out using large one-piece brake disks having some small holes in their flange. When the number of braking cycles was beyond 300, some tiny cracks occurring around holes were found. They grew in the radial direction of brake disks. In order to examine whether braking torque is a driving force for crack initiation or not, the time interval was altered 10 times longer than the previous braking decreased when the braking interval was extended. The crack length also decreased. An alternative test at the same braking torque condition was also conducted while the disk surface temperature was always kept lower than 40°C. In this case, no cracks were observed after 300 cycles of braking. This results indicates that the braking torque itself does have little direct effect on crack initiation.

Micro-metal-forming technology using specially designed microtool

The authors have been carrying out investigations on the fabrication of micro-tools such as medical devices. Until now, demands for higher productivity of micro tools have been overcome by applying molding technologies. On the other hand, demands for higher shape freedom have been satisfied by the use of cutting technologies. Generally, machining processes using the end mill are applied for creating complicated shapes. However, the minimum size of an ordinary end mill is about 0.1 mm, and grooves smaller than this size cannot be machined. In the previous report, the authors proposed a special oblique-cut mill. This tool has a very simple shape made by diagonally cutting a cylindrical tool material. It can be made even more miniature easily. However, in return for the simplification of the tool fabrication process, the cutting performance drops. To avoid this, optimum cutting conditions must be selected. In this study, the appropriate cutting conditions were reviewed based on the measurement results of the cutting force. At the same time, 3D shapes were also created using the special oblique-cut mill.