This study is about the construction of a smart factory for aircraft parts, dealing with the overall factory establishment process from design to operation.
The targeted factory is expected to mainly produce 32 wing ribs of an aircraft, while each of them is 6 m long at maximum, 100 kg in finished part weight, and 4 tons in raw material weight. They are also experiencing the manufacturing processes of machining, deburring, and inspections as well.
As the required time for each process is heavily dependent on the size and the shape of the specific parts, it is practically not an easy task to manufacture them in a so-called “flow production”. In order to economically produce those parts. it is far vital to secure an autonomously decentralized automated factory based on FMS (Flexible Manufacturing System). In consideration of the fact that the required 5-axis machine tools are quite expensive, the study also aims to keep their average operation rate at 90 %.
One of the indispensable ingredients in the study corresponds to the introduction of the concept of TOC-DBR (Theory of Constraints- Drum-Buffer-Rope). The machining process which corresponds to the constraint process (CP) is set to be on three shifts for 24 hours, followed by non-constraint processes (NCP) with two shifts for 16 hours. Two buffers are placed before the CP and after the NCP, respectively, to absorb fluctuations of processing time. An additional buffer is provided between the CP and the NCP in order to overcome the mismatch between two different shifts.
A scheme of systematic procedure is hired to build the resulting smart factory. The factory-building procedure consists of the several phases, that is, factory designing, development and integration so that tasks of what-to-do and those outputs are defined in each relevant phase.
In the phase of designing, the concept of TOC-DBR is applied to the layout of the plant. Through the delicate simulation, the location and size of buffers are determined, and the capacity of the resources are then verified. In the phase of development, the study focuses on developing the methodology of decentralization and autonomous control for different types of material handling and processing equipment, and assigning intellectual tasks to the individual machines and software systems. In the phase of integration with the equipment installed, the software operation modules are furtherly developed, and the individual equipment is connected so as to complete a smart factory. In the meantime, operation rules are established, and improvements are continuously made in order to stabilize the factory.
The study has revealed that it can be a cornerstone of paving a way to the successful establishment of an autonomously decentralized smart factory, where the FMS, inspection and logistics equipment and operating systems are all integrated organically like a single system so that the factory workers are mainly in charge of simple setup and equipment monitoring.
According to the result of operating the factory during the first one year after its foundation, the 5-axis machining equipment indicated the figure of 85.8% as its utilization ratio. The difference of 4.2% from the original goal of 90% in the design phase was disclosed to be from equipment breakdowns, software errors, and workers’mistakes. Later, the target goal could be achieved by improved operational logics, stabilized equipment and intensified monitoring activities.
It is meaningful to refer to the evaluation results for the factory done by Korea Smart Factory Promotion Group, which is “Middle Level 2”, the highest development level that can be attained by the current utilizable technologies.
The study on the overall building procedure for a smart factory is expected to provide a guideline and insight for building smart factories in industry, and contribute to relevant researches especially for integration and standardization issues for smart factories in academia.