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BACK TO BASICS STAYING SHARP • STAYING SHARP • STAYING SHARP • STAYIN Flat lapping basics

BY DR. LAROUX K. GILLESPIE materials such as abrasive pastes or rolled into a flat metal or composite fine flourlike abrasive suspended in lapping disc. The individual abrasive apping is a grinding process for a liquid medium. For traditional flat grains protrude above the surface and Lpolishing or accurately finishing lapping, slurry or paste compounds perform the lapping. During process- a workpiece surface by abrasion using with loose abrasive are pressed or ing, parts are continuously rotated and pushed down with a small weight over the lapping disc. Lapping produces highly parallel and fine-finish components without introducing stresses and heat damage. This results in longer part surface life with improved sealing capability. Lap- ping effectiveness is a function of the lapping disc material, force between the part and lapping disc, abrasive ma- terial, abrasive size, cutting velocity and carrier fluid. Flat lapping requires the workpiece to be rotated over the abrasive-laden master lap in ever changing patterns. This rotary motion with different paths provides uniform abrasion of the lap and workpiece and ensures part flatness. Lapping removes less than 0.0005" of stock to provide flatness to 0.000001", parallelism to 0.00001" and surface roughness values as fine

as 0.6μin. Ra. The disc material is softer than the workpiece so that the abrasive embeds in the disc and not the workpiece. Hard lapping discs cut slowly and impart dull finishes. If a cast iron lapping disc wears at 1 μm/min. for each 0.01mm3 removed from a part, cold-rolled steel discs will wear at 1.27 μm/min. and copper discs at 2.62 μm/min. While copper lapping discs wear faster, they also cut faster. The carrier fluid serves to: „ Form a hydrodynamic film be- tween the workpiece and lapping disc to avoid direct contact between the two solid surfaces. „ Pick up and transport abrasive grains to the active cutting area. „ Guarantee a homogeneous grain distribution. „ Cool and lubricate the disc and workpiece. The carrier, or vehicle, fluids used include water-based gel, oil, water- AYING SHARP • STAYING SHARP • STAYING SHARP • STAYING SHARP • STAYING SHARP • STAYING

pulls the grains away from the work- turing engineer, writer and past qual- Abrasive-embedding tool piece. The mrr is directly proportional ity-assurance manager with a 40-year to path velocity and pressure as long history of precision part production as the pressure is below the workpiece and research. He is the author of 11 material-dependent critical pressure. books on deburring and 200 techni- Lap cal reports and articles on precision About the Author machining. He can be e-mailed at Embedded grit Loose grit Dr. LaRoux K. Gillespie is a manufac- [email protected].

Metallographic Polishing by Mechanical Methods by Leonard E. Samuels For traditional flat lapping, slurry or paste compounds with loose abrasive are pressed or rolled into a flat metal or composite lapping disc.

soluble oil, benzene and alcohol. Water-based gels are increasingly se- lected because of their cleaning ability and ease of waste removal. Additives are used in some solutions to reduce surface tension and to prevent packing of abrasive grains. Fluid viscosity can be regulated with additives. Highly viscous fluids impart finer surface finishes, but they reduce metal-removal rates. Less viscous, or easier flowing, carriers are suited for high-speed applications. The lubricat- ing function prevents scoring of the work and caking of the abrasive. Silicon-carbide abrasive is used for lapping hardened materials, aluminum oxide for softer materials and diamond for precision work. (See the table on page 24.) Abrasives with grains larger than 5μm are used for removing metal when lapping, while smaller sizes perform polishing. The variation in grain sizes affects the mrr and surface finish. The number of active grains increases with a decreasing standard deviation. Be- cause more grains are cutting, the mrr is faster. Abrasive is added in ratios of about 1:3 or 1:4 to the carrier liquid to make slurry. Diamond is applied in amounts of about 10 carats per liter for lapping glass and ceramic materials. Path velocity—as opposed to ma- chine spindle velocity—and the pres- sure between the part and lapping disc are the two primary variables once the lapping abrasive and carrier fluid are chosen. At path velocities above 150 m/min., aquaplaning occurs, which BACK TO BASICS STAYING SHARP • STAYING SHARP • STAYING SHARP • STAYIN

Typical lapping combinations. (See article beginning on p. 22) Abrasive Carrier Workpiece Comments

180- to 800-grit silicon carbide Oil or water-based gel Hardened steel For normal lapping

1,000-grit Al2O3 Oil or water-based gel Steel For high luster and cutting

1,200-grit Al2O3 Oil or water-based gel Steel For high luster and polishing

180- to 1,200-grit Al2O3 Oil or water-based gel Nonferrous metals, soft steel and stainless steel

700-grit Al2O3 Oil or water-based gel Glass and ceramic For cutting

900-grit Al2O3 Oil or water-based gel Glass and ceramic For fi nishing Diamond Oil Steel Precision lapping of all types of dies and molds and polishing of optical, ceramic and electronic components

Diamond Water-soluble oil Steel Polishing of tools and dies prior to CVD or PVD nitride coating; there is no impregnation by the compound into the substrate prior to coating PART TIME STAYING SHARP • STAYING SHARP • STAYING SHARP • STAYING SHAR Learning fast

BY BILL KENNEDY, eliminated. CONTRIBUTING EDITOR Torkay noted that 7075 T6 aluminum or engineering students, intercol- is stronger than Flegiate competition can go beyond cast 1080 steel, as games played with balls, sticks measured in kips and pucks. Future engi- per square inch. “The neers, for example, use yield strength of 7075 is carbon fiber, alumi- about 75 ksi; for the 1080 num, steel and com- steel it’s about 60 ksi,” he puter chips to compete said. The aluminum, however, in the Society of Au- lacks the steel’s surface hard- tomotive Engineers’ ness. The solution was hard an- Formula SAE (FSAE) odizing the aluminum part after racing series. For nearly machining. Torkay said the hard- 30 years SAE has spon- ness is still lower than steel but noted sored and regulated that “we are not driving the car for competitions between 100,000 miles.” teams of undergraduate When the team machines its and graduate engineering own parts, “anything we can do students to design, build by hand, we do in-house,” Torkay and race small open-wheel said. The college’s shop has two cars. The teams face perfor- lathes, four vertical mills and one mance tests for acceleration horizontal mill—all manual. As a re- and endurance, but they are also sult, the team outsources jobs that re-

scored on other key skills, such as quire CNC machining, and much of

cost control and design presentation. the powertrain machining time was FSAE’s most restrictive rules in- donated by Z Manufacturing Inc., La Pomona volve components that affect driver Verne, Calif. Poly

safety, such as frames. Teams build Cal The shop programmed the roughly their cars using commercially avail- This one-of-a-kind housing for the 4½"-long × 4"-dia. housing in Master- able parts, modified versions of exist- Torsen differential of the Cal Poly cam Version 9. The first set of opera- ing components or unique parts that Pomona Formula SAE racer, shown tions took place on a Femco WNCL-35 they make themselves. For example, before hard anodizing and with two of CNC lathe. The 6"-dia. workpiece was the FSAE team from California State three gear sets in place, was machined rough and contour turned at 1,000 to from 7075 T6 aluminum. Polytechnic University (Cal Poly Po- 2,400 sfm, with feed rates of 0.01 ipr mona) machined its own housing for minum to reduce weight. “A lot of for roughing and 0.007 ipr for contour- the gears that make up the car’s Torsen this competition is about keeping the ing. Holes measuring 1" in diameter (torque-sensing) slip-limiting differ- weight down,” he said. were drilled at 1,000 rpm and a 0.012- ential. The differential proportions JTEKT Torsen supplies a drawing ipr feed. The operations on the lathe torque between driven wheels to man- with each differential, and Torkay used took about 8 minutes. age traction and maximize available that as the basis for a SolidWorks CAD “On the CNC lathe, they turned it to horsepower. model of the new housing, incorporat- the appropriate size, and then put it on Torsen patent holder JTEKT Torsen ing specific changes for the racecar. “I the mill and machined out the spaces North America Inc., Rochester, N.Y., translated them into CAD, tightened for the gears,” Torkay said. The dif- produces—at a discount price for most of the tolerances and made a ferential consists of three separate gear FSAE teams—a “university special” couple changes here and there,” he sets spaced 120° apart in the housing. version of its differential, housed in a said. For example, the original dif- Z Manufacturing reproduced that spac- 1080 steel casting. However, Dustin ferential, based on an Audi unit, is ing on an Akira-Seiki SV-1000 3-axis Torkay, the Cal Poly Pomona team’s driven by a spline shaft. The racecar mill by machining flats in scrap areas design captain, said the team made features a chain drive via a sprocket, on the sides of the housing at 120° its own housing from 7075 T6 alu- so the splines in the housing can be intervals. Gripped in a vise, the flats PART TIME STAYING SHARP • STAYING SHARP • STAYING SHARP • STAYING SHAR enabled the shop to accurately index and 15 to 50 ipm. Drills from 0.136" the wear surfaces,” Torkay said. the housing between operations and to 0.3906" in diameter generally ran at Weighing only about 450 lbs., a generate the correct spacing. 3,000 rpm. The mill work took about four-cylinder Suzuki GSXR 600 mo- Thirty-four operations took place on 25 minutes. torcycle engine powers the car, putting the mill, including milling, contouring, When the part returned to the Cal Poly about 85 hp to the rear wheels. The drilling, reaming and tapping. Endmill Pomona shop, “we measured everything high power-to-weight ratio is “a lot of diameters ranged from ǩ" to 1", and out, made sure everything was in spec, fun,” Torkay said. the tools were run at 100 to 800 sfm and then sent it to get hard anodized on In addition to building cars with sparkling performance, the teams must also hone more prosaic skills. Cost control is what makes engineering a profession rather than simply an art. Expenditures are totaled using SAE-developed standardized lists of typical material, machining and other costs. At a theoretical production vol- ume of 1,000 units, the cars must cost $25,000 or less. As the cost moves down from the limit, a team scores higher. “Usually, making a lot of your own parts decreases the costs,” Torkay said. “For example, we made our own wheel shells, which took quite a bit off the cost of the car. We went from a $19,500 car last year to $13,800 this year.” The teams are also scored on formal design presentations made to a panel of industry professionals, including engineers from major automakers. “They know their stuff,” Torkay said. “You can’t trick them too much. Some of them are alumni, so they know how the cars are built.” An undergraduate majoring in me- chanical engineering, Torkay said building the cars has given him ex- cellent background in hands-on shop skills such as welding and machining. “Pretty much everything I know I learned here,” he said. In addition, he said all the team members “really get a lot out of FSAE, everything from learning about people to going out and getting sponsorships. It’s something I’ll never forget.” For more information about Cal Poly Pomona’s FSAE team, visit www.csu pomona.edu/~fsae or call (805) 405- 4678. For more information about Z Manufacturing Inc., visit www.zmanu facturinginc.com or call (800) 643- 7265. For more about Formula SAE, visit students.sae.org/competitions/ formulaseries. GET WITH THE PROGRAM STAYING SHARP • STAYING SHARP • STAYING SHAR

‘Paper CAD’ In the days before CAD, drafting any drafting. was done on paper. Parts were de- For the most part, that’s still being signed and drawn, and then copies of done. The difference is the shop now BY BILL FANE the drawings were sent to the shop to receives CAD files via e-mail or from have the parts made. Sometimes the a file server. This is much faster and arts manufacturers now have a way shop marked the drawings to indicate more efficient, but the process presents Pto electronically view and mark errors or to suggest improvements, a problem. The shop may need to buy CAD drawings without having to buy and the shop sent those versions back one or more copies of pricey CAD copies of expensive CAD software. to the originator. The shop seldom did programs just to view, print and mark files. In addition to its usual DWG for- mat, AutoCAD from Autodesk Inc., San Rafael, Calif., is able to publish a drawing in a read-only format called DWF. Autodesk originally called DWF its Drawing Web Format, but now re- fers to it as Design Web Format. It is a simpler format that was originally intended to allow users to post draw- ings to Web pages. DWF files download much faster when recipients access them for view- ing and printing using a free viewer supplied with AutoCAD. It is also available at www.autodesk.com/dwf viewer, but don’t download it yet! There is a better option. Autodesk used to sell a program that included capabilities beyond the generic viewer. Recently, the com- pany renamed that program Autodesk Design Review and is offering it free at www.autodesk.com/designreview. This is the one for general shop use. Autodesk Design Review opens DWF files and allows users to zoom, pan, freeze and thaw layers, and print all or portions of the drawing, but it will not permit editing of the under- lying drawing. This should make a shop’s customers happy because they can send design information without exposing their design content. Another big advantage to DWF files is that they are smaller than DWG files and, thus, easier to e-mail. How much smaller? Typical DWF files are about one-quarter the size of their parent DWG files. Autodesk Design Review has added functionality compared to DWF Viewer or DWG TrueView, both of which are available for free downloading. The latter two enable viewing and printing of DWG and DWF files, but Autodesk H ARP • STAYING SHARP • STAYING SHARP • STAYING SHARP • STAYING SHARP • STAYING SHARP

Design Review lets you add red marks marked it up, users can send it to the most standard Windows applications. to the DWF file. shop or back to the originator. The As a result, a single DWF file can Autodesk Design Review also lets originator can open the original DWG contain AutoCAD drawings, Word you add lines, rectangles, ellipses, file and import mark-ups from the documents and Excel spreadsheets— freehand scribbles, text and callout DWF. If a user clicks on a mark-up in all the documentation necessary to clouds and tags. You can measure a list, then AutoCAD automatically produce something, including the approximate distances and areas, and zooms to the applicable location in the drawings, the process specifications add approximate dimensions. I say drawing. and the work orders. “approximate” because DWF files do A DWF file is effectively “electronic No matter if you are at a small job not extend to as many decimal places paper.” You can view, review, mark, shop or the toolroom of a large manu- as the 14 or so used by AutoCAD. scribble on, make copies of and return facturer, you can make good use of In addition, DWF files use the it to its creator like a piece of paper Autodesk Design Review. It is often units setting from the original draw- without access to a copy of AutoCAD. said that “you get what you pay for,” ing, so an actual dimension of As indicated earlier, DWF files are but in this case it is worth considerably 3.5021373973" might display as 3.5". virtual pieces of paper, so AutoCAD more than its free price. q The dimensions may not be exact, but creates them through its plot com- they will match the values shown in the mand. The user selects the DWF6e About the Author original drawing. Plot.pc3 plotter in AutoCAD, supplies Bill Fane is a former product engi- Autodesk Design Review includes a file name and out it comes. neering manager, a current instructor several predefined rubber-stamp anno- A cunning bit is that a single DWF of mechanical design at the British tations, such as approved, rejected and file is not limited to containing a single Columbia Institute of Technology and preliminary, and allows users to create drawing. It can contain multiple sheets, an active member of the Vancouver custom ones. from multiple drawing files. A DWF AutoCAD Users Society. He can be e- Having reviewed a drawing and file can also contain files created by mailed at [email protected].

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