Optimizing Force Distribution in Deep Drawing Tools Using SMA High Load Actuators

In this paper a novel approach to manipulate the force distribution in deep drawing tools using high load SMA actuators is presented. Nowadays, deep drawing is one of the most used processes for metal forming. It is used to form flat sheet metal efficient and precisely into complex, three-dimensional shapes and is widely used in many industries. However, on one hand ever-increasing demands on the process by increasingly complex geometries, smaller tolerances, and novel materials pushing the processes to the limits of their stability. On the other hand, the issue of the complex installation of a new or used tool becomes increasingly important. Here, the lack of automation makes this complex installation process labor-intensive and costly. Today, well-trained specialists with extensive experience are indispensable for the fine adjustment of the force distribution in deep drawing tools. However, growing scarcity of specialist, e. g. due to demographic change, not only increases the cost pressure, but also the risk of this technology. For these reasons, it is necessary to automate the fine adjustment of deep drawing tools, or more precisely, their force distribution.
For this automation, an actuator-array which introduces different micro-deformations into the tool and changes the stiffness distribution is required. High load actuators based on thermal shape memory alloys (SMAs) are ideal for this task. Unlike competing technologies, they offer a small installation space, sufficient forces, low costs, and a simple control. SMA high load actuators can, not only, statically optimize the press force distribution during fine adjustment processes, minimizing costs and time, but also enable dynamically compensation for fluctuating process parameters from stroke to stroke, effectively preventing the production of reject parts.
The approach presented in this paper is the integration of high load SMA actuators into the blank holder to create an adaptive pressure pad. In this study, an array of sixteen high load SMA actuators was integrated into the blank holder of a benchmark deep drawing tool to reduce the influence of process variations and speed up fine adjustment processes. The shape memory components (SMCs) of the actuators were additively manufactured from a Ni45.0Ti50.0Cu5.0 alloy using laser powder bed fusion (PBF-LB/M). The better degradation properties, smaller thermal hysteresis, and more stable phase transformation temperatures (PTTs) of these SMCs compared to conventionally manufactured SMCs are exploited for high-load SMA actuators. Each actuator is capable of exerting forces up to 5 kN and deformations up to 180 μm. Within the scope of this study, the successful integration of high-load SMA actuators into a deep drawing tool for a sample application is achieved with minimal installation space, utilization of forces in the kN range, and without the need for additional supply media such as hydraulic aggregates or complex amplifier technology. Finally, a simple control system for the actuator array is presented.