Developments in Tooling Inspections and Technology

Inspecting punches and dies can be time-consuming and costly for tablet manufacturers. Advances in technology, however, have greatly improved in-process inspections. The author examines improvements in equipment and computer software for in-process tool inspections.
May 01, 2008
Volume 2008 Supplement, Issue 2

Tablet-tooling inspections present many challenges. Inspecting punches and dies can be time-consuming and costly for tablet manufacturers. Sometimes the cost is prohibitive and leads to cutbacks in the frequency of inspections or even eliminates them entirely. This situation is unfortunate because the quality of the tablet is determined in large part by the quality of the tooling. Every aspect of tablet production may be set up and run perfectly, yet if the tooling is of poor quality, the tablet quality will suffer. The only way to truly determine that tooling conforms to allowable specifications is to inspect the tooling for defects and excessive wear. Inspection data represent an additional challenge of the tool-inspection process. Often, inspection results are recorded on paper stored in a file and never seen again. Improvements in equipment and computer-software technology, however, have helped to make in-process tooling inspections more efficient and productive for tablet manufacturers (1, 2).

Tooling inspections by tablet manufacturers

A misconception is that the tablet manufacturer needs to conduct in-process tooling inspections in the same manner that a tool manufacturer conducts them. The tooling manufacturer must inspect all dimensions to ensure that the tools were manufactured to industry standards. The tablet manufacturer, however, does not need to inspect all punch dimensions and can concentrate on a few critical dimensions. Once dimensions have been confirmed during the tool-manufacturing process, only a few key wear points are of concern. For the most part, in-process inspections performed by the tablet manufacturer should be limited to the working length of the punch and cup depth as these two dimensions have the greatest impact on tablet quality (see Figures 1–3). The remaining dimensions, such as barrel diameter, tip dimensions, and overall length, are not critical because they do not change often or are difficult, if not impossible, to inspect accurately and consistently.

Punch working-length dimension. Measuring the working-length of a new punch is different than measuring the same dimension of a worn punch during an in-process inspection. Unlike other dimensions, the working-length tolerance applies to each punch only in relation to the other tools within the set. Working length is graded on a curve. For example, if new tools are designed to have a working length of 5.230 in. with a tolerance range of 0.002 in. (i.e. ± 0.001 in.), the analysis of new tools simply requires that each punch have a working length of at least 5.229 in. but not greater than 5.231 in. Worn tools, however, can wear to a length that is less than 5.229 in. as long as they all are within the 0.002 in. range. The key point to consider is the total range of 0.002 in. provided by a working-length tolerance of ± 0.001 in.

Continuing the example, although working lengths of 5.228, 5.227, and 5.226 in. are below the lower limit of 5.229 in. for a new tool, these dimensions are still within the 0.002 in. range of each other. Manually calculating which tools are within each other's specific tolerance range and at what working length can be difficult and time-consuming. Using a computer with the proper software, however, can make the process much easier. Moreover, using the first punch as the basis for comparison and simply comparing the measurements of the remaining punches with the first is not recommended as the condition of the first punch is not always certain. After completing an entire inspection, it would be unfortunate for the tablet manufacturer to discover that the first punch was the most severely worn, but was used as the comparative basis for the entire tool set.

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