Vision-system and digital technology
Vision-system technology and digital photography make the practice of taking pictures of punches during inspection more common.
A digital photo of a suspected issue with a particular punch can be saved as an electronic file. The electronic file can be
linked to inspection records, attached to an email, or forwarded to the tablet manufacturer's management team or to the tool
supplier for analysis. This process allows other interested parties access to the same view of the punch as the tooling technician
Technology has yet to provide a cost-effective solution for die inspections. As with punches, the tablet manufacturer does
not need to focus on every dimension of a die in the same manner as the tool manufacturer. The crucial wear points on a die
are the inner diameter (I.D.) and the inner surface area of the die wall (known as the die bore). Measuring the I.D. of a
round die is relatively easy; it is the nonround or oblong-shaped die bore that presents a problem. Measuring an oblong die
bore requires the measurement of both the minor and major axis. Determining the center line of each of the minor and major
axis is difficult to do accurately and consistently. Failure to correctly measure each axis could result in an incorrect measurement.
Another key wear point of a die is the location inside the die bore where tablet compression takes place. This location is
often referred to as the wear ring. Any occurrence of a wear ring may indicate that the die is unacceptable for continued
use. The most common inspection method is to "bore sight" through the die bore with a bright light on the far side. Any visual
ring indicates dimensional wear. Further inspection of a wear ring using a sensitive deviation indicator may help determine
the functionality of the die. Although inspecting a wear ring can require a certain amount of equipment setup, depending on
the extent of variation of each die bore, the depth within the wear ring can be measured with a bore gauge. The primary method
for inspecting dies, however, is to conduct a visual inspection that diligently looks for damage in the form of nicks, cracks,
and abrasions on the outer walls and wear rings within the die bore.
Measuring tip diameters
Because measuring the tip diameter of a worn punch can be difficult, this dimension is not recommended for in-process inspections.
Measuring the tip diameter of new punches is relatively easy, but the tip diameter of a worn punch is difficult to measure
accurately and consistently. Typical punch tip wear occurs only at the leading edge of the tip (see Figure 6), so conventional
contact-measuring devices are ineffective. Using a micrometer on the tip straight will often fail to capture the diameter
of the outermost edge of the tip (see Figure 7). Because the amount of wear can be difficult to see with the naked eye, an
inspector may be left with a false sense of accuracy. This situation is typically not a problem for new tools because they
are not worn. The tip-diameter dimension is another example of a measurement that is included in the inspection by a tool
manufacturer but excluded from the in-process inspection by a tablet manufacturer. Various imaging equipment such as optical
comparators and digital-measuring systems are available to assist with viewing and measuring this dimension.
Figure 6: (FIGURE COURTESY OF THE AUTHOR)
Electronic audit and security
Electronic-audit and security features should be built into any tool-management database to prevent the loss or corruption
of data. An electronic audit is the function of recording data as they existed prior to any modification or deletion. Referring
to previous audit data records can be helpful if any data are modified inadvertently or otherwise altered.
Figure 7: (FIGURE COURTESY OF THE AUTHOR)