# Improvement of the Method for Fixing a Punch in the Punch Holder
## 1 Introduction  
Part designers are eager for improvements in the performance of tools, particularly in terms of fatigue but also with regard to the finish of the part obtained. The production of any part requires cutting at some point and one of the most widely used manufacturing methods is punching, a process which is required in, for example, the production of flat springs necessary in many industrial sectors, such as the automotive, aeronautical, electronics, and micromechanical industries, etc. The punching tools that manufacture flat springs from stainless steel sheets bend and cut the material. Unfortunately, during production, the punches gradually wear out and sometimes break suddenly, resulting in a significant shortfall after about 3000 cycles, since changing the tool after a fracture requires at least two hours of work. The fracturing of the tool has been studied by many authors and many parameters that influence tool wear and fracture have been explored with the aim of finding a way to ensure sufficient tool lifespan. For instance, a study by [PERSON] [1] showed the effect of the clearance between the punch and die and pointed out that the optimal clearance is equal to 10% of the thickness of the metal sheet. [PERSON] [2] and [PERSON] [3] claimed that, by increasing the contact pressure between the sheet and the tool, too little clearance increases the cutting force required and causes rapid tool wear. In addition, [PERSON] et al. [4], [PERSON] [5], and [PERSON] et al. [6] studied the effect of the punch corner radius in reducing the stress on the edges, thereby counteracting edge chipping. A study conducted by [PERSON] [7] also showed the effect of the punch angle on the shearing force. When a punch angle is used, the required penetration depth is increased for the punch-out operation to be fully completed and this increase in the required penetration depth may lead to accelerated wear on the punch tool. Several factors linked to the cutting process have been discussed. [PERSON] et al. [8] studied the effect of the cutting speed of the punch, showing that the cutting force increases with the speed of the tool and, therefore, increases the punch wear. The influence of temperature on the behavior of the material used in cutting is also very important [9]. [PERSON], cited in [PERSON] et al. [10], presents the influence of temperature rise on the maximum cutting force. [PERSON] and [PERSON] [11] studied the effect of the hardness of the steel. They performed a set of low-speed and high-speed cutting tests that showed that the cutting force increases with the hardness. Many experimental studies [12; 13; 14] showed the different factors affecting the punch wear and, in a study conducted by [PERSON] et al. [15], the spring back effect was elaborated on, showing that, without pressure on the holder, it is possible to have severe abrasive wear on the punching pin surface prior to stripping failure. He [16] and [PERSON] and [PERSON] [17] studied the different types of fracture that could occur and put forward potential solutions to minimize their effects. Finally, [PERSON] [18] studied the evolution of the burr during blanking. The appearance of the cut edges was examined by means of a topographic survey in order to monitor their evolution. The studies conducted so far do not, however, explore the influence of how the punch is fixed to the punch holder. The work presented below is based on an industrial case where a punch dedicated to the manufacturing of connectors made of stainless steel shows a premature break at the level of the pins holding it. The main issue that will be resolved is the determination of the optimal fixture, thereby avoiding the high constraints causing the tools to break. Different approaches are discussed and studied in order to achieve a significant reduction in the stresses on the tools. The punching tool is improved by changing the geometry of the cutting edge, changing the way the punch is fixed, and avoiding the use of eccentric pins.