A Batch Tracing System for Thermochemical Finishing Processes Enables New Services for Quality Management

Manufacturing processes in the area of thermochemical treatment of work pieces impose lots of challenges due to the rough environment. High temperatures and the use of chemicals are aggravating conditions of salt bath nitrocarburizing processes, which are used to improve the wear resistance, the fatigue strength, and the corrosion resistance of components made from steel, cast iron, and sintered iron materials. The process is composed of preheating, nitrocarburizing, oxidizing, and multilevel cleaning. These stages are passed through consecutively, for what customer orders are combined in batches. It is an example of a discontinuous production which is characterized by a material flow which is interrupted in time. In this context a batch is an amount of pieces which form a whole and are processed together and therefore exhibit identical attributes with regard to the manufacturing process and the product quality. At present, the implementation of batch tracing mechanisms is difficult or impossible due to the harsh environment (hazardous chemicals, high temperatures …). As a consequence, wrong assignments of the finished pieces to the customers may occur while a possibility of documentation of the parameters concerning the manufacturing process is desirable. Several of the following reasons for the enhanced deployment of batch tracing thus apply: request of customers for security and information about the origin of the products (customer pull), new laws and regulations (regulatory push), availability of innovative communication and information technology (technology push), and increase in efficiency and advance of process reliability (industry pull). In this paper, we discuss batch tracing by means of intelligent RFID technology (radio frequency identification), which involves connections to sensors for measurements of ambient parameters. Information obtained by the RFID system such as the beginning and the length of stay of the batches in the different stages is merged with the temperatures delivered by the plant equipment. Thus identifying and determination of the position of the batches is achievable throughout the entire procedure. This allows the company to offer new supplementary services to the customers and to design the process in a more flexible way like prioritizing time-critical orders. In order to prove the technical feasibility of batch tracing in the field of thermochemical treatment two test cases are described: The first one is for gathering information about the functioning of the installed RFID system, the other one is the realization of the operational process in a simplified form.