Effect of Convex Sheared Punch Geometry on Cutting Force of Ultra-High-Strength Steel

Abstract

Extremely high strength of the ultra-high-strength steels leads to increased load factors on the tooling machines and punching tools. This experimental study examines how much convex punch geometry affects cutting forces when punching ultra-high-strength steels. Tools used in punching tests were four different convex sheared rooftop punches and one conventional flat end punch, to which rooftop punches were compared to. The material in punching tests was ultra-high-strength steel Ruukki Optim 960 QC, with a thickness of 4 mm. The test material in punching tests was sheared with rooftop punches and a flat end punch and occurred cutting forces were measured. The qualities of punched holes were evaluated visually and the roundness measurements were also performed. The results show that the cutting forces of Optim 960 QC can be reduced radically with optimal convex punch geometry. With using 14-degree shear angle of the punch end, the cutting forces reduced up to 57 % compared to forces of the conventional flat end tool. However, largest tested shear angles caused several negative effects on the cutting quality of the holes and therefore they are not suitable in all applications. Punching tests proved that the cutting clearance had no appreciable effect on cutting forces when punching ultra-high-strength steel. Instead there was a noticeable effect on the quality of the punched hole, especially when large shear angles were used.

Experimental Examination of Effects of Punch Angle and Clearance on Shearing Force and Estimation of Shearing Force Using Fuzzy Logic

“…Besides, clearance negatively affects blanking/piercing force. In addition, increased clearance values reduce the quality of the product [5,6]. Choi et al [7] studied the effects of the clearance and the inclined angle of the die on the sheared edge characteristics of the trimmed DP980.…”

Estimation of the perforation force for polymer composite conveyor belts taking into consideration the shape of the piercing punch

“…Having analyzed the available literature, it is clearly visible that metal sheet punching has been widely researched [7][8][9][10][11][12][13][14][15][16][17][18] and there is a lot of information about the influence of the geometrical features of the piercing punch and die [7,12,18] as well as process parameters [15,16] on perforation force and quality of the holes. However, it is very hard to find research papers about punching the polymer composite structures.…”

“…In convex tools face surfaces are tilted at a desired angle to its axis. There are three main convex punch profiles: V-shaped chamfered punch [8,13,24], single sheared punch [19,22,24,25], and punch with a conical pilot [19]. The main principle of operation for convex tools is to fracture the structure of the material in order to soften it before the closed contour cutting appears or even divide the cutting on the circumference of the hole in order to minimize the length of the cutting edge, which does the cutting work at one time.…”

The Experimental Investigation of Punching of the AM60 and AZ61 Magnesium Alloy Sheets by Using Varied Punch Shapes

“…The blanking forces were reduced approximately 80 % by using the 16° angled punch. Besides, cutting forces can be reduced significantly by using the convex punch geometry (Kutuniva et al, 2012). The blanking of magnesium alloy sheets at room temperature results in sheared edge defects such as microcracks, loose particles, and a jagged-plus-curved fracture profile.…”