The idea of producing a 3 dimensional object layer by layer came about long before the development of ideas around additive manufacturing. The first concept patented can perhaps be traced back to Peacock for his patented laminated horse shoes in 1902. Half a century later in 1952, Kojima demonstrated the benefits of layer manufacturing processes. A number of additional patents and demonstrations took placed in the time period of 60--80 s that further solidified the idea of producing a 3 dimensional object using a layer wide approach and in the meantime set the stage for introduction and development of processes based on this principle to produce physical prototypes.
Yang, L., Hsu, K., Baughman, B., Godfrey, D., Medina, F., Menon, M., & Wiener, S. (2017). Introduction to Additive Manufacturing (pp. 1–31). https://doi.org/10.1007/978-3-319-55128-9_1