Design methods for novel, energy-efficient, closed phase change actuators with high action of force

Short introduction

The aim of this project is to create the basis for the economic production of forming manufactured phase change actuators (PCA). Compact paraffin wax actuators are planned, whose housings completely enclose the expanding material. When heated from the solid to the liquid phase, paraffin wax is subject to an increase in volume of 15 percent and more. The high volume expansion and the low compressibility of the paraffin core generate high pressure in the sealed housings. This leads to a stroke movement of the actuator or the application of a positioning force.

Motivation & Objectives

Production processes are necessarily associated with fluctuations. These can be divided into two areas. On the one hand, high-frequency fluctuations of the process properties, which are caused, for example, by stochastic influences or changes in the tribological system. A closed loop control is a typical countermeasure here. On the other hand, low-frequency system influences occur, caused, for example, by thermal environmental influences or wear on the machine itself. For correction, high actuating forces with comparatively small travel ranges are particularly necessary. This is where the integration of the PCA (Figure [1]) comes in. Two variants are possible, firstly a passive activation concept can be used. Here the necessary activation energy is supplied by the environment and a tailor-made compensation of thermal influences can be achieved. The second variant includes an integrated heating (e.g. by printed electronics) in the actuator, which generates the actuating energy. After the desired actuating movement, the stroke or actuating force achieved is maintained via an integrated self-locking wedge gear. This enables long-term energy-efficient compensation of system wear.

The objective of the project is to develop design methods for an actuator design and a combined forming and joining production. Subsequently, the qualification for the described applications as well as the development of the self-locking wedge gear will follow.

Figure 1: Basic structure of the phase change actuator in forming production

Approach

Within the framework of the completed first project phase of the four-year overall project, the functional verification of the actuator concept was fully achieved. Extensive numerical investigations allowed design guidelines to be derived and an optimal actuator design to be defined. Furthermore, the influences of various modifications were identified. In the next step, a production chain was created which combines efficient forming technology methods with the powerful laser processing centre for cutting and joining. In addition, a process window for the demanding laser welding process has been derived at the laser machining center. The characterization of the resulting demonstrators fully demonstrates the functionality of the actuators (Figure [2]). In the final step, the applicability of the PCA for the motivated cases could be shown by means of active and passive demonstrators.

Figure 2: Actuator characterization regarding force (a), displacement (b) and numerical investigation of the housing load (c)

The second project phase serves the further qualification of the PCA for the purpose of functional enhancement and optimization. One objective is the development of a model-based approach for the generation of tailor-made actuator characteristics. The addressed parameter field comprises the actuating force, the stroke and the active temperature range. For this purpose geometrical adjustments of the housing, structures integrated into the housing and paraffin additives or mixtures are investigated. Further objectives of the second project phase are the implementation of an integrated activation concept, the thermal decoupling of different zones in the actuator and a transfer of the concept to other actuator geometries, such as a circular ring shape (Figure [3]).

Figure 3: Prototypes of the expansion actuators in circular form and in circular ring form

Acknowledgement

The Institute of Production Engineering and Forming Machines thanks the German Research Foundation (DFG) for its support in carrying out this project (GR 1818/65-1).