# Induction of Highly Dynamic Shock Waves in
## 1 Introduction  
Current research work aims to describe production steps independently of the process using the so-called process signature, which summarizes all interactions between material and process [1; 2]. This new way of looking at and describing should enable the processing of materials in an even more targeted way, so that they can be optimally adapted to the respective requirements. The basic prerequisite for this is an exact understanding of the individual manufacturing processes. In this context, the cutting process with a defined cutting edge, as it occurs during turning and milling, is considered in this article. In order to understand chip formation and chip breakage, it is particularly important to determine the relationship between the loads acting on the material during machining and the changes remaining in the material afterwards. The loads in terms of the strains can be quantified during the production process by means of speckle photography [3; 4]. With this method, the surface to be measured is illuminated with a laser and the evaluation areas in the speckle images taken with the camera--before and during the occurrence of the deformation--are correlated with each other [5; 6]. From the correlated image sections, local displacements can be calculated, whose theoretical resolutions are limited only by [PERSON]'s uncertainty relation [7]. Due to the availability of compact diode lasers with a short-pulse length ofless than 1 ns and pulse energies of more than 20 uJ, it is possible to integrate the measuring system into the machining area of machine tools and to investigate dynamic manufacturing processes with tool speeds of, for instance, more than vc = 10 \(\frac{m}{s}\)[8]. However, the measuring of the remaining modifications (plastic deformations), which are ten times weaker in relation to the loads (elastic + plastic deformations), has been proven difficult so far, especially in processes with multiple stresses due to recurring loads and cyclic machining processes (e.g., milling). The modifications remaining in the material surface layer after the last tool intervention are usually inhomogeneous [8]. In extreme cases, the periodic fluctuations of the modification also occur under continuous cutting conditions (as in the turning process) and correlate with undesired chatter marks on the surface, which can be seen in Figure 1.  
The properties of the chatter marks, such as periodicity and amplitude, are influenced by the resonance behavior of the complex manufacturing system [9]. A causal trigger in the continuous process can be the disturbance of the system due to the effect of chip breakage or chip formation depending on the workpiece condition [10]. The chip formation and chip breakage were investigated theoretically by means of finite element method (FEM) simulations, compared with high speed videos and discussed with the relationship to the process stability and the surface quality produced [11]. When researching chip separation and chatter mark formation, mainly the resonance and vibration behavior of the machine tool and the workpiece are considered. Induced workpiece vibrations and dynamic strain states are difficult to determine so far, therefore these effects are currently not included in the investigations. In this respect, it is also not known how the remaining modifications in the form of periodic fluctuations of the strain [8] are related to chip formation or chip breakage. However, it is probable that both the chip breakage and the penetration of the tool at the beginning of the chip formation generate a shock wave, which propagates through the material at the speed of sound. The open scientific questions therefore are:  
* Are dynamic processes in the workpiece stimulated during machining and is the lifetime of these shock waves long enough to cause feedback in processes with multiple loads (such as milling)? * Can the excited workpiece states be measured with the aid of speckle photography?