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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.
To align or “remap” a machine tool, for example, technicians level the machine bed. They move the SMR along the bed, stopping at certain points — for instance, on top of each jacking screw, capture the point, and adjust the bed height. Or, technicians might capture a set of points along the bed and adjust the height later.
To ensure the machine is plumb and square, technicians place the target in what’s called a “pin nest” in the machining center’s spindle, chuck, or quill. (Plumb is defined as true to a vertical plane. When a plumb object intersects with a level object to create a 90° angle, the objects are known as square.)
To perform a full, 3D volumetric check of a machine tool, technicians zero-out an X, Y, Z-coordinate axis on one end of the machine tool. They attach the target to a “magnetic drift nest” which has been glued to the ram, move the machine through its volume, and collect the data, resulting in a grid of points. The X, Y, Z data shows deviations in all of the axes.
Laser trackers can also perform in-process part inspection; final part inspection and QA; inspection of molds and dies, and reverse engineering. Some trackers, such as the ION, can measure accurately over hundreds of feet, are traceable back to NIST standards, and can be fully verified for accuracy in the field.
Rapid image analysis allows for “invisible” welds
Researchers at the Fraunhofer Institute for Physical Measurement Techniques IPM in Germany have just turned carmaker dreams into reality by designing a technique that welds door panels to car frames so welds are only visible on one side. In what’s called “controlled partial penetration welding,” a laser penetrates to the bottom sheet, without damaging its surface, while the resultant weld meets strength requirements. Until now, such welds were not possible because there was no way to see — and, therefore, control — what was happening to the bottom sheet during welding.
“Key to the technique is our proprietary camera that generates temperature images,” says Andreas Blug, project manager at Fraunhofer. “The images show the hot region where the laser burns into the metal and causes it to melt. When the bottom of the melt pool reaches the gap between the upper and lower sheets, the conduction of heat is interrupted and it’s possible to see the cooler point, called the ‘Full penetration hole.’” Knowing the hole’s depth, the software adjusts the laser output accordingly.
“The welding technique is closed-loop controlled,” Blug explains. “The camera is what makes this possible. It is based on cellular neural networks, a type of parallel computing in which tiny processors look at each individual pixel. All processors work simultaneously, speeding up the analysis of the images to 14,000 images/second. This compares with the typical analysis rate of only 1,000 to 2,000 images/second.”
Think “fourslide” instead of metal stampings from China
According to Fourslide Spring and Stamping Inc., Bristol, Conn., if you’re buying metal stampings from overseas locations such as China, chances are you’re also buying into drawbacks such as long lead times, sketchy communications, expensive tooling, and the inability to stamp individual parts with complex shapes. Many U. S. manufacturers are finding that “fourslide” metal forming is a less-expensive and more-flexible option that can slash inventory investments with JIT deliveries from a domestic supplier. Fourslide production uses a series of relatively inexpensive tools that make parts in volumes of even a few thousand at an affordable cost.
The fourslide process uses a sequence of stamping and forming operations on a single workstation. It can make multiple bends, radii, angles greater than 90°, dimples, and other features to create precision metal stampings, flat springs, wire forms, contacts, and other complex shapes.
Fourslide works with materials including metal wire and flat strips of stainless steel, beryllium copper, phosphor bronze, brass, and high carbon steel, as well as electroless nickel, gold, silver, and zinc finishes.
Software helps medical molder meet standards
To meet the strict requirements of medical molding, Polymer Conversions Inc. (PCI), Orchard Park, N. Y., acquired software that monitors injection molding, rather than just counts parts. Medical molding involves lengthy product-development phases and lots of clinical trials. It also requires good recordkeeping and part traceability.
After researching different software suppliers, PCI went with Shotscope from Husky Injection Molding Systems Ltd., Ontario, Canada. Shotscope helps medical manufacturers collect and report on production and process statistics at both the machine and plant levels.
The software also provides real-time monitoring and mold-flow analysis, letting users simplify reporting, improve data flow, and coordinate more-efficient plant scheduling. Companies can look at data immediately, handy in making changes quickly for less scrap and part variability.
Shotscope lets PCI perform the qualification, documentation, and traceability needed to comply with FDA regulations. The software verifies that part parameters are correct and validates production to support compliance. For example, the software captures data from each injection cycle on every part, keeping detailed records to validate that the right decisions are being made. “This level of traceability is critical because health-care companies demand that suppliers verify the exact conditions and environment under which a part was manufactured,” says a PCI spokesperson.
The software helps PCI adhere to ISO 13485, an international standard that validates a qualitymanagement system’s capability to provide medical devices and related services that consistently meet customer and regulatory requirements.
PCI plans to upgrade to Husky’s next-generation Shotscope NX software. In addition to process and production monitoring, the new software provides more detail about the amount of energy used in an injectionmolding facility. And improved bar coding reduces paper pushing on the floor. PCI also plans to use the software with its enterprise resource planning program to eliminate manual tracking.