Advanced-Manufacturing technology guide

How to accurately inspect micromolded parts

Tools such as coordinate-measuring machines and optical comparators are widely used to inspect parts. But how are components such as complex micromolded parts checked? CMM touch probes are often too big to capture data on small features. And optical sensors only provide 2D profiles of features. Further, fixturing small parts can be difficult, forcing micromolders to inspect the mold instead of the part. But this approach assumes that pressure, temperature, shot size, and dwell time have no bearing on part quality. When it comes to micromolded parts, these assumptions are incorrect.

A better approach comes from a patented process called crosssectional scanning (CSS) from CGI Inspection in Eden Prairie, Minn. It captures complete 3D data sets, eliminating judgment calls about parts being in or out of spec. It also lets users measure internal dimensions of micromolded parts.

Here’s how CSS works. A molded part is encased in a slow-curing plastic resin. The “potted” part is placed in the 2.50 × 1.75 × 3.50-in. work envelope of CGI’s Pearl-700 desktop machine. The Pearl slices ultrathin (0.001 or 0.002-in.) layers from the part. As each layer is cut off, the machine’s optical scanner captures the newly exposed profile at a resolution of about How to accurately inspect micromolded parts 1 million pixels/sq in. Cutting and imaging repeats until the part is consumed.

The machine processes the 2D images into a 3D point cloud that fully describes the component’s shape. The point cloud goes into the software, where it is digitally located in a user-defined orientation. The software captures all critical dimensions along precisely defined reference planes.

The Pearl-700 lets micromolders inspect features that are visible or buried in the part. In one case, the machine inspected a micromolded medical device with an internal channel that narrowed from 0.012 to 0.008 in. and had walls with thicknesses down to 0.0006 in. CSS simultaneously scanned a part from each of the mold’s eight cavities with little additional time or labor.

Portable laser tracker measures large volumes accurately

To work properly and turn out quality parts, machines in power plants and manufacturing facilities such as routers, lathes, and vertical or horizontal mills need alignment. Rolls, stamping presses, and large drivelines

also require alignment. Traditional alignment devices include granite blocks, machinist levels, and optics such as borescopes. But a quicker and more-precise method comes from portable CMM laser trackers from Faro Technologies Inc., Lake Mary, Fla. The laser trackers are well suited to the 3D, high-accuracy, large-volume measurements and alignments involved in leveling machine tools.

How do laser trackers typically work? They send a laser beam to what’s called a spherically mounted retroreflector (SMR), also known as a “target,” held against the object being measured. Light reflects off the target and back to the tracker where it hits a distance meter. The Faro Laser Tracker ION, for instance, uses a laser interferometer to measure distance, which is repeatable to 10 microns, and two precision angular encoders to measure the zenith and azimuth angles. This lets the ION measure in 3D to better than 0.001 in. Software converts the polar coordinates to rectangular coordinates and handles the precise measurement of many different geometric shapes. Users can check the shapes against user-definable datum for parallelism and concentricity.