Three Advances in Mold Measurement

As any mold’s integrity is paramount to output quality and success, this is where measurement machines play a critical role. Shops use these machines to verify a mold’s accuracy or the finished product created by the mold. For example, the accuracy demanded by manufacturers of medical equipment and tools, such as gears, syringes, tubing and bands, requires the mold builder to check both the mold and the output. Certain measurement machines are ideal for quality checking a finished product like lumens and tubing, while others are more appropriate for measuring the mold itself.  

Typically, a shop uses a coordinate measurement machine (CMM) with an attached laser or contact probe to inspect one half of the mold, paying particular attention to the surface where the two mold halves come together. The users also inspect the surface finish with the addition of a surface finish unit. Although vision machines and CMMs are the most commonly used, there are newer technologies for mold and mold output measurement.

1. Points From Focus—Camera-Created 3D Scans

One of these is points from focus (PFF) technology, which uses the camera from a vision machine to create a 3D scan of a part. PFF technology offer less expensive, faster measurement. Unlike a laser or sensor, this technology uses a camera to capture an image with no additional hardware from which the user creates a 3D scan.

The PFF technology is particularly useful when it comes to molding plastics. Concerns around the parting line’s size and the risk of flash can result in a mismatch in the alignment of the two molded halves. PFF can capture a good quality scan of the parting line, measuring its size and identifying any undesirable abnormalities. This technology is also useful for threads that screw a needle into a syringe because the user can conduct a scan that provides a closer look at the threaded contour.

Mold measurement is also an ideal application for PFF technology, which can be used to scan a mold for a high-resolution image of the mold’s features and contour. Seeing any potential flaws in creating a mold enables a user to fix a mold before creating parts, saving time and money.

2. Small-Diameter Probing Machine

A micro-scanning probe machine with accuracies down to 0.8 microns is another recent measurement technology. This type of vision measuring system uses a scanning probe with a ball diameter as small as 125 microns, making this technology ideal for inspecting parts with small features or contours. For example, a camera on a vision machine can scan a contact lens and its mold with high precision, but a microprobe can scan the mold surface for minuscule differences in surface contour that a camera could not measure. The same is true for plastic and metal gears in all applications, including medical. A microprobe permits a user to measure microform deviations in a mold and finished product. The camera provides perfect positioning for the probe’s placement while also making highly accurate overall measurements.

This probe process takes longer because vision measurements are nearly instant, while a probe must physically contact the part and scan. However, having a probe and vision measurement in the same machine saves time since both sensors are combined. The scanning probe does not have to rotate to take multiple measurements like on a CMM with a laser to provide the same contour and profile measurements.

Another benefit of a micro-scanning probe machine is how it handles shine compared to a laser. The probe touches what it measures, making optical interference a moot point, which is well suited for clear plastics, metal and other reflective surfaces.