So how do you do mould verification? Do you use a laser scanner to measurepart dimensions? Look under a microscope? Perhaps you use the tried andtrue calipers and do it the old fashioned way. And just how do you getthose critical inside dimensions? Have you thought about being a littlemore destructive? You may wish you had, because there's a way to absolutelydestroy parts in order to bring them to life, verify moulds, create prototypes,and build CNC tool paths.

Susan Lovelace, supervisor, material and process conformance at CherryElectrical Products in Waukegan, Illinois, USA, was looking for a "betterway to use solid models to verify part quality." Cherry moulds snapaction switches, auto switches, gas discharge and gas plasma displays,and keyboards. The part in question is a switch housing moulded from GE'sValox thermoplastic polyester, about 1.3 by 2.5 cm with 100 or so criticaldimensions that had to be measured and verified to approve the mould. Inthe past, Cherry relied heavily on 2-D drawings, but they didn't producethe desired results. "We just couldn't get all of the dimensions weneeded," Lovelace said.

Debra Kinder was in a similar predicament. She's the senior qualityengineer at Siemens-Furnas Controls in Batavia, Illinois, USA, a manufacturerof motor controls and pressure switches. Its tool verification processwas taking up to three weeks. Using mostly calipers and gauges, Kinderwas trying to measure parts that were mostly nongeometric - lots of smoothlines, and sweeping curves - with few sharp corners and edges.

Lovelace and Kinder both tracked down Steve Gaspardo, owner of Gaspardo& Assoc., who has a way of not only measuring and verifying outsidedimensions, but inside surfaces as well. It appears to be as effectiveas it is destructive; and it takes only a week.

"It's basically a 3-D Xerox machine." That's Dan Falvey,design engineer, reverse engineer, rapid prototyper, and CAD/CAM expert.He's talking about the ACSS (Automated Cross Sectional Scanning) RE1000,the device Gaspardo uses to capture, map, and digitize solid part geometry.Although Gaspardo says mould verification provides the bulk of his work,he points out that the ACSS can be used in all stages of moulding, includingreverse engineering, ongoing mould verification, and rapid tooling.

The ACSS works like this: You take your part or product, either freshout of the mould or newly prototyped or just sculpted, and totally encaseit in a block of epoxy so that every corner, every undercut is filled,with no voids. The epoxy needs to be a colour that contrasts with the partcolour. Then mount the block on the aluminum base of the ACSS mill table.

The ACSS uses a fly cutter to machine away thin layers of the epoxyencased part - layer thicknesses can range from .013 to .254 mm. Aftereach layer is shaved off, an optical scanner captures the exposed surfaceof the part and saves the data to a file. With each successive layer itcaptures every corner, edge, slope, angle, and dimple in the part.

The downside is that when the process is done the part is destroyed.But the ACSS has a complete catalogue of the part that is accurate, Gaspardosays, to within .025 mm. This captured data can be rendered in a pointcloud, scaled up, scaled down, imported into a 3-D CAD package, outputas an STL file for prototyping, or exported as an NC tool path to builda mould.

If it is used for mould verification, the device can also read andanalyze the dimensions of the digitized part, comparing them to those ofthe master. It then generates a colour-coded 3-D image indicating wherethe part is out of spec in relation to the master.

Noting how typically difficult it is to get a moulded part into a database,Falvey says the ACSS system has several advantages over contemporary laser-basedscanning systems. The first is that the end result is one digitized filethat provides both external and internal dimensions. Falvey says most laser-basedscanners provide multiple files that must be "patched" togetherto form a complete image; and laser-based systems do not provide internalgeometry.

Falvey also cites errors introduced by laser shadows, scan inaccuracies,and multipass inaccuracies. Because ACSS uses a layered scanning process,he says, the margin for error is greatly reduced. Falvey notes that undercuts,especially on anatomical figures, which are often a difficult hurdle forlaser-based scanners, are easily mapped and digitized with ACSS.

The primary limitation of the ACSS, Gaspardo says, is size. The millingtable can accommodate parts that fit within a volume 30.5 by 27 by 20.3cm. This naturally eliminates larger parts and products, at least on themould verification side. However, for design and prototyping, Falvey saysthat because the ACSS generates CAD files, any scale of a product can bedigitized and then scaled up or down, depending upon the application. Falveyacknowledges industry-wide hesitation to scale up electronic files, butsays, "I've not seen any scale-up problems to date."

The ACSS requires significant computer power. That is, the data producedby the scanner is not the kind that can be copied to a floppy disk on alow-end PC. Gaspardo says that depending upon how thick the milled layersare, the scanner can produce densities up to 600 dpi. When converted toa point cloud, the density doubles, producing files, Gaspardo says, rangingfrom 5 to 60 Mb in size. To accommodate such very large files, Gaspardouses a workstation PC with 2.2 Gb of storage and a Zip drive to manipulateand move data. He says he uses Pro-E for most of his CAD work.

In the end, as Kinder at Siemens-Furnas Controls points out, every dimensionof the part is electronically filed. "It allows us to store partswithout storing them," she says. This comes in handy, she says, whentwo years from now she wants to know exactly what the first part out ofthe mould looked like - compared to the 200,000th. Says Gaspardo, "Onceyou have the data and bring it into a software package, the possibilitiesare endless."

Falvey points out another application that is not really the most obvious,but may prove just as useful; some of the hardest parts to measure arethose with assembled pieces. He points out that the ACSS could be usedto analyze parts that snap together in order to look particularly at thecontact points, part-to-part stress, and deformations.

Though the technology the ACSS provides may cost a little more up front,Kinder and Falvey point out that the savings in time more than compensates.Gaspardo says he turns around all of his scanning and analysis within fivebusiness days, whether it's generating an STL file, colour mapping, orcreating a CAD file. Kinder says mould verification that used to take threeweeks now takes one. "This way is more expensive than traditionalmethods, but sometimes time is more valuable than money," she adds.

Gaspardo says costs are comparable with laser scanning systems andvary depending upon the volume of the part when it's encased in the epoxy,the depth of the cut (which dictates total milling time), and the typeof analysis required. Gaspardo says a typical mould verification analysisranges from US$ 2,500 to US$ 3,500.

Contact Information: Gaspardo & Assoc. Mr. SteveGaspardo 227 Oswalt Ave. Batavia, Illinois 60510, USA Phone: (1) 630-761-8800Fax: (1) 630-761-8802 www.gaspardo.com