Concentric engineering

Author CTE Staff
Published
August 01,2009 - 12:00pm

In addition to handling prototype and production machining, R.E.F. Precision Products LLC, Deer Park, N.Y., provides engineering and productivity consulting services. “You give me what you are looking for, and I’ll engineer it to make it as cost competitive as possible,” said Co-owner Rob Fleece, whose background is in mechanical engineering. In some cases, R.E.F. Precision’s engineering expertise not only helps controls costs, but enables the shop to make difficult-to-machine parts.



When R.E.F. Precision Products manufactured this 8 "-long, 35⁄8 "-dia., 6061 aluminum heat sink for a computer-chip-making machine, it consolidated critical machining steps on one CNC lathe to assure concentricity of the part’s ID and OD. Image courtesy of R.E.F. Precision.


One example was an 8 "-long, 3⅝ "-dia., 6061 aluminum heat sink for a machine that makes computer chips. To permit rapid heat transfer, the part has 36 delicate cooling fins and interior walls as thin as 0.020 ". Because of the thin walls, concentricity between the part’s ID and OD was crucial. “If you don’t have dead concentricity, sometimes you’ll get a leak and a bad part,” Fleece said.

R.E.F. Precision’s customer attempted to make prototypes of the heat sink, but six out of 10 failed leak testing at 1,200 psi. According to Fleece, the problem was in the customer’s machining process, in which chucking and rechucking the part diminished its ability to maintain concentricity.

As a result, Fleece devised a process that produced all critical dimensions in one chucking. He began with 3.75 "-dia., 1 "-thick-wall tubing. The tubing was cut 1 " longer than the finished part, so “I had something to hold onto,” he said. He clamped one end of the tubing in a chuck on a Hitachi Seiki CNC lathe and faced the other end with a Sandvik Coromant grade-1025, CNMGP 431 coated carbide insert.

Then he bored the ID to a 0.001 "/ -0.000 " tolerance with a Kennametal grade-KC5010, coated carbide insert held in a 1 "-dia., solid-carbide boring bar. Because the bore went to the back of the part and thereby might amplify tool vibration, Fleece ran the tool at a relatively low 750 rpm and took three passes, with the first two at a 0.012-ipr feed rate. The feed had to be heavy enough, he said, to produce enough force to minimize chatter. The last pass, at a 0.020 " DOC, produced a 0.001 "-undersize bore. The boring tool ran at 0.006 ipr. The lighter feed was acceptable for the last pass, “because I was going to hone it to final size and I wasn’t as concerned about the finish,” Fleece said. The bore’s final ID is 1.912 ".

Once boring was completed, Fleece inserted a 0.001 "-undersize plug into the bore and pushed it against the chuck with an arbor on a center clamped in the machine’s tailstock. That enhanced rigidity for subsequent operations. “It almost became like a solid piece again,” Fleece said.

Next, the CNMGP insert roughed and finished the part’s OD to 3.380 ", up to a shoulder at the part’s chuck end. “With the positive-rake insert, I was able to get a really nice finish,” Fleece said. Then he cut a 2.030 "-dia., 1.312 "-wide groove at the front of the part with an ¼ "-wide Allied Machine deep-grooving tool.

Each cooling fin is 0.030 " thick and separated by 0.100 "-wide × 0.460 "-deep grooves. Fleece tried a number of tooling alternatives to create the fins and found his Seco cutoff tool worked best. He custom ground both sides of a 0.120 "-wide cutoff insert to produce a 0.100 "-wide tool.

He plunged the tool straight in at 400 sfm and 0.005 ipr to a depth of 0.200 " for all 36 fins, returned for another 0.200 "-deep pass for every one and finished each fin with a 0.060 "-DOC final pass. When trying to cut a fin in a single pass, Fleece said the 0.030 "-thick walls started to push away, so he machined them in steps. Initially, Fleece reground the insert once or twice to get the proper clearance, and “once we got the insert perfect it just worked.” R.E.F. ran 100-part batches, and one cutoff insert typically would last for an entire run.

After the fins were completed, Fleece backed off the machine’s center, removed the plug and applied the grooving tool to cut off the part. For that operation, he ran the tool at the same 0.006-ipr feed rate but at a 150-sfm cutting speed to minimize vibration and impart a fine surface finish.

Fleece said when the part came off the lathe, “Everything was concentric and perpendicular, because it was all made at once.” Manual finishing included minimal deburring and treatment with Scotch-Brite pads to clean the fins.

The part was then moved to a Bridgeport 760 vertical machining center, where it was clamped on an expanding arbor. Four 0.212 "-dia. holes, later to be fitted with press-in clinching screws, were drilled in the flange on the front of the part. Then the flange edges were squared with an endmill. Finally, the part was flipped, clamped again on the arbor and four clearance holes were drilled to accept 0.440 "-dia. screws. Milling and turning consumed 22 minutes.

The finished heat sink has an S-shaped connecting tube welded near its base. R.E.F. Precision turned a simple bushing-shaped part to be welded in the middle of the “S” between two pieces of tubing. R.E.F. Precision also engineered a fixture that positioned the tubing parts, bushing and heat sink for welding, which was outsourced. CTE

For more information about R.E.F. Precision Products LLC, call (631) 242-4471 or visit www.refprecisionproducts.com.

Related Glossary Terms

  • arbor

    arbor

    Shaft used for rotary support in machining applications. In grinding, the spindle for mounting the wheel; in milling and other cutting operations, the shaft for mounting the cutter.

  • boring

    boring

    Enlarging a hole that already has been drilled or cored. Generally, it is an operation of truing the previously drilled hole with a single-point, lathe-type tool. Boring is essentially internal turning, in that usually a single-point cutting tool forms the internal shape. Some tools are available with two cutting edges to balance cutting forces.

  • boring bar

    boring bar

    Essentially a cantilever beam that holds one or more cutting tools in position during a boring operation. Can be held stationary and moved axially while the workpiece revolves around it, or revolved and moved axially while the workpiece is held stationary, or a combination of these actions. Installed on milling, drilling and boring machines, as well as lathes and machining centers.

  • bushing

    bushing

    Cylindrical sleeve, typically made from high-grade tool steel, inserted into a jig fixture to guide cutting tools. There are three main types: renewable, used in liners that in turn are installed in the jig; press-fit, installed directly in the jig for short production runs; and liner (or master), installed permanently in a jig to receive renewable bushing.

  • chatter

    chatter

    Condition of vibration involving the machine, workpiece and cutting tool. Once this condition arises, it is often self-sustaining until the problem is corrected. Chatter can be identified when lines or grooves appear at regular intervals in the workpiece. These lines or grooves are caused by the teeth of the cutter as they vibrate in and out of the workpiece and their spacing depends on the frequency of vibration.

  • chuck

    chuck

    Workholding device that affixes to a mill, lathe or drill-press spindle. It holds a tool or workpiece by one end, allowing it to be rotated. May also be fitted to the machine table to hold a workpiece. Two or more adjustable jaws actually hold the tool or part. May be actuated manually, pneumatically, hydraulically or electrically. See collet.

  • clearance

    clearance

    Space provided behind a tool’s land or relief to prevent rubbing and subsequent premature deterioration of the tool. See land; relief.

  • computer numerical control ( CNC)

    computer numerical control ( CNC)

    Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.

  • cutoff

    cutoff

    Step that prepares a slug, blank or other workpiece for machining or other processing by separating it from the original stock. Performed on lathes, chucking machines, automatic screw machines and other turning machines. Also performed on milling machines, machining centers with slitting saws and sawing machines with cold (circular) saws, hacksaws, bandsaws or abrasive cutoff saws. See saw, sawing machine; turning.

  • cutting speed

    cutting speed

    Tangential velocity on the surface of the tool or workpiece at the cutting interface. The formula for cutting speed (sfm) is tool diameter 5 0.26 5 spindle speed (rpm). The formula for feed per tooth (fpt) is table feed (ipm)/number of flutes/spindle speed (rpm). The formula for spindle speed (rpm) is cutting speed (sfm) 5 3.82/tool diameter. The formula for table feed (ipm) is feed per tooth (ftp) 5 number of tool flutes 5 spindle speed (rpm).

  • endmill

    endmill

    Milling cutter held by its shank that cuts on its periphery and, if so configured, on its free end. Takes a variety of shapes (single- and double-end, roughing, ballnose and cup-end) and sizes (stub, medium, long and extra-long). Also comes with differing numbers of flutes.

  • feed

    feed

    Rate of change of position of the tool as a whole, relative to the workpiece while cutting.

  • fixture

    fixture

    Device, often made in-house, that holds a specific workpiece. See jig; modular fixturing.

  • gang cutting ( milling)

    gang cutting ( milling)

    Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.

  • grooving

    grooving

    Machining grooves and shallow channels. Example: grooving ball-bearing raceways. Typically performed by tools that are capable of light cuts at high feed rates. Imparts high-quality finish.

  • inner diameter ( ID)

    inner diameter ( ID)

    Dimension that defines the inside diameter of a cavity or hole. See OD, outer diameter.

  • lathe

    lathe

    Turning machine capable of sawing, milling, grinding, gear-cutting, drilling, reaming, boring, threading, facing, chamfering, grooving, knurling, spinning, parting, necking, taper-cutting, and cam- and eccentric-cutting, as well as step- and straight-turning. Comes in a variety of forms, ranging from manual to semiautomatic to fully automatic, with major types being engine lathes, turning and contouring lathes, turret lathes and numerical-control lathes. The engine lathe consists of a headstock and spindle, tailstock, bed, carriage (complete with apron) and cross slides. Features include gear- (speed) and feed-selector levers, toolpost, compound rest, lead screw and reversing lead screw, threading dial and rapid-traverse lever. Special lathe types include through-the-spindle, camshaft and crankshaft, brake drum and rotor, spinning and gun-barrel machines. Toolroom and bench lathes are used for precision work; the former for tool-and-die work and similar tasks, the latter for small workpieces (instruments, watches), normally without a power feed. Models are typically designated according to their “swing,” or the largest-diameter workpiece that can be rotated; bed length, or the distance between centers; and horsepower generated. See turning machine.

  • machining center

    machining center

    CNC machine tool capable of drilling, reaming, tapping, milling and boring. Normally comes with an automatic toolchanger. See automatic toolchanger.

  • milling

    milling

    Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.

  • outer diameter ( OD)

    outer diameter ( OD)

    Dimension that defines the exterior diameter of a cylindrical or round part. See ID, inner diameter.

  • tolerance

    tolerance

    Minimum and maximum amount a workpiece dimension is allowed to vary from a set standard and still be acceptable.

  • turning

    turning

    Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.

Author

CTE magazine staff
847-498-9100

News items authored by Cutting Tool Engineering have been written or edited by the editors of Cutting Tool Engineering magazine. The reports represent material submitted to CTE by outside authors, and edited by CTE editors for style and accuracy.