Fabrication of plastic parts is an important scope of application for various branches of industry. This does not only concern manufacturing of end products but also production of sample parts in small lot sizes. Currently, most plastic parts are injection-molded. Consequently, it is first necessary to produce appropiate moldings, for example by milling of metal. This is very time-consuming on one hand and uneconomical concerning costs for production in small lot sizes on the other hand. Furthermore, the variety of forms is restricted considerably which is a clear disadvantage concerning the production of prototypes or spare parts. The use of a free-forming droplet generator for producing plastic parts can provide remedy.
The patented principle of the printing process used in this approach is to produce droplets of liquified plastic in a preparation unit. Sequential discharge of these droplets builds a part in the installation space by solidifying of the droplets into balls. Since each 3D printing process needs its own data preprocessing, this article presents its fundamentals. STL data is used as input data and allows almost any kind of geometry. In general, a typical workflow for processing STL data is as follows: slicing volume data in order to gain contours that form 2D boarders, offsetting contours for a true to scale building process, filling of slices dependent on (offset) contours and generation of machine-code (g-code) that can be executed by the 3D printer in order to build an accurate and high-quality part.
The model used in this approach is based on the droplets produced by the machine. A more detailed description of all the process-specific invidual steps from slicing up to g-code generation is presented within the scope of this paper. The continual development of custom-made algorithms based on process-specific models and parameters has resulted in the generation of g-code that could be executed on a 3D plastic polymer printer based on droplet generation for the first time. The resulting sample parts are very appealing.
In conclusion, the results have shown that the whole production process can be a significant benefit especially for rapid prototyping of sample parts or spare parts.