(221h) Using a Finite Element Method to Simulate Structural Defect Initiation during Tablet Compression Due to Punch-Die Misalignment

Tablets are the most common pharmaceutical dosage form due to their customizability, stability, precision dosing capability and cost-effective manufacturing. A critical step in the tableting process is powder compression. Ideally, the resulting powder compact should exhibit adequate strength to withstand the later phases of the tableting process, including film coating and packaging, without incurring structural defects. Tablet capping is a typical structural defect that could occur due to poor formulation properties, incorrect mechanical configuration of the tablet press and tooling etc.

Techniques like Discrete Element Method (DEM) and Finite Element Method (FEM) have become useful in studying powder compression kinetics and mechanics, thereby enabling accurate failure predictions. DEM captures the behavior of individual powder particles, interaction between them and their behavior under an applied load to predict its strength [1]. While DEM more accurately represents particle dynamics, FEM offers superior scalability due to its ability to model distribution of mechanical behavior by integrating complex material models [2] and multi-physics interactions [3]. More recently, FEM using constitutive material models, which capture volumetric reduction and non-linear powder densification, have been employed to provide a mechanistic understanding of tablet failure mechanisms [4, 5].

Existing literature predominantly examine the factors contributing to tablet defects during and post powder compression. The results obtained from these modeling techniques provide guidance for optimization of manufacturing operating parameters and powder formulation [6]. Despite having the right powder formulation and manufacturing operating parameters, a tablet’s structural integrity can still be compromised due to external factors such as deviations in equipment assembly and design. For example, misalignment between the upper and lower punches during their installation on the tablet press machine could result in critical tablet defects like capping.

This work uses FEM with a density dependent Drucker Prager Cap (DPC) plasticity model to study the effects of punch misalignment on a tablet’s structural integrity. The mechanical and physical behavior distributions identify locations in the tablet that are most susceptible to defect initiation. The likelihood of tablet defects arising from these locations could be increased due to other external deformation forces acting on the tablets during the downstream operations of storage, transfer, coating, packaging etc.

Tablet press tooling (punches and dies) are often disassembled and assembled during routine manufacturing due to cleaning and maintenance. This work demonstrates the importance of adhering to the right protocol during assembly of the tablet press tooling followed by inspecting and verifying that the installation is correct.

References:

1. Siiriä, S. M., Antikainen, O., Heinämäki, J., & Yliruusi, J. (2011). 3D simulation of internal tablet strength during tableting. AAPS Pharmscitech, 12, 593-603.
2. Partheniadis, I., Terzi, V., & Nikolakakis, I. (2022). Finite element analysis and modeling in pharmaceutical tableting. Pharmaceutics, 14(3), 673.
3. Krok, A., Garcia-Trinanes, P., Peciar, M., & Wu, C. Y. (2016). Finite element analysis of thermomechanical behaviour of powders during tabletting. Chemical Engineering Research and Design, 110, 141-151.
4. Baroutaji, A., Lenihan, S., & Bryan, K. (2017). Combination of finite element method and Drucker‐Prager Cap material model for simulation of pharmaceutical tableting process. Materialwissenschaft und Werkstofftechnik, 48(11), 1133-1145.
5. Sinha, T., Bharadwaj, R., Curtis, J. S., Hancock, B. C., & Wassgren, C. (2010). Finite element analysis of pharmaceutical tablet compaction using a density dependent material plasticity model. Powder Technology, 202(1-3), 46-54.
6. Han, L. H., Elliott, J. A., Bentham, A. C., Mills, A., Amidon, G. E., & Hancock, B. C. (2008). A modified Drucker-Prager Cap model for die compaction simulation of pharmaceutical powders. International Journal of Solids and Structures, 45(10), 3088-3106.