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Tablet design using CAD software

23rd January 2018


Fig 1. A 3D model of an exotic shape table
3D Printed tablets
TabletCad user interface
Generated drawing with critical info
FEA stress plot of multi-tip tooling

The advent of modern computer aided design (CAD) 3D-modelling software packages has revolutionised many design and manufacturing industries. These modelling and analysis programs have become so cost-effective, even mid-size and small companies can afford to use them in everyday operations. In addition to reducing time-to-market and the need and cost of multiple prototypes, these software packages allow the designer to quickly gather critical engineering information and perform complex analysis much more easily and quickly than ever before. These CAD technologies are used throughout the tablet design and tool manufacturing industries for a multitude of purposes.

The initial benefit of 3D CAD modelling in the tablet design process is the ability to model and view the tablet prototype or tablet design in three dimensions (as in the example in Fig. 1). This not only helps the designer better visualise the final product but can also help catch geometric anomalies or irregularities that would go unnoticed if designing in 2D and which might cause problems in actual tablet production. Having a 3D CAD model also allows for far easier and faster creation of manufacturing drawings and CNC programs, which speeds up the production process.

Most 3D CAD software packages can also be used with 3D printers. With the decreased cost and increased availability of accurate 3D printers, this means that 3D tablet models can be printed for marketing/customer approval of a proposed design. This eliminates the need to manufacture physical tooling and compress actual formulation just to see and approve a specific design (Fig.2). These time-saving steps can considerably decrease time to market for a new product.

Employing 3D CAD to the tablet design phase can also provide the engineering and product development teams with critical information quickly. Although the shape and cup of a tablet may not look that complicated, the long-hand mathematics for attaining total volume and surface area involves surface and volumetric integrals. These calculations are quite lengthy and time-consuming. CAD software can quickly and easily analyse the geometry of the model to calculate important data including surface area, volume and density, just to name a few. This information can speed the product development process by helping the product development teams quickly evaluate properties such as the surface area-to-volume ratios and density (both of which affect dissolution profiles). As dimensions and geometries of a 3D model can be easily altered, this allows for quick comparisons of many different designs and allows for predictions to be made based on the surface area and volume change of each design.

The ability to quickly gather information from the 3D model is incredibly helpful in the development of new tablets. This is especially true for dose proportional products where surface area-to-volume ratios are critical to establishing equivalent dissolution profiles for multiple dosages that are all compressed from a common blend.

The benefits and accuracy of CAD software can also be incorporated into web-based interfaces. Natoli Engineering’s TabletCAD is an example of a web-based interface that allows those unfamiliar with CAD modelling to enter a few parameters relative to the tablet dimensions to design their own tablet quickly and easily (Fig.3). These design parameters are then used to create a 3D model and drawing complete with all critical information (Fig. 4).

This quick, web-based parametric modelling is beneficial when studying multiple tablet designs. The user can easily identify the surface area-to-volume ratios to predict dissolution rates or even evaluate different bisect designs and bisect depth to help solve splitting issues common with scored tablets. Additionally, having information such as cup volume and die bore cross-sectional area can speed up everyday calculations such as fill depth requirements to achieve a specific weight. Finally, because the web-based interface creates a real 3D model, it offers real-time geometry validation, which, as mentioned above, will eliminate impossible geometric conditions. This can help mitigate production issues and related delays by catching mathematical errors before the tooling has even entered the first steps of manufacturing.

Importing tablet and models

Another major benefit of 3D modelling in relation to tablet design is the ability to import the 3D tablet and resulting tool models directly into finite element analysis (FEA) software.

These FEA software packages work with most CAD software to use the 3D geometry combined with defined material properties and set-up parameters. This provides the ability to simulate real-world service conditions and examine a wide range of complex physics and engineering solutions. This information is helpful in creating complex tooling designs where the maximum force rating is not based on the cup geometry alone, such as multi-tip or core-rod tooling (Fig. 5). This process is also helpful in establishing compression force ratings for unusual/exotic shaped tablets for which there are no established formulae (Fig. 6).

The use of CAD and FEA software together allows for more accurate maximum compression force ratings than before, especially for complex tablet designs where old-fashioned hand calculations were not possible.

Using 3D CAD software in the tablet design process offers a number of advantages. Not only does it save time by simplifying tedious calculations, it also provides a means to verify complex geometry and catch errors that may have gone unnoticed using ‘pen and paper’ 2D methods. In addition, 3D modelling helps engineering and R&D teams by providing a means to evaluate multiple designs quickly and decrease potential downtime by increasing accuracy of the tooling and preventing tooling failures through the use of FEA. The 3D models can also be used for 3D renderings or 3D printed tablets to help marketing departments and others better visualise the final product, which reduces the time and cost associated with producing prototype tablets
for approval.

Kevin Queensen is responsible for mechanical engineering and technical service support at Natoli Engineering.

www.natoli.com





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