There’s more than one way to machine a part. The trick is to match the part’s complexity and volume requirements with an optimal production process. As a leading single-source contract manufacturer, Plouse Precision Manufacturing, Harrisburg, Pa., can choose from a wide range of production alternatives. The company’s capabilities include metal stamping, CNC machining, assembly, fabrication, grinding, wire EDM and welding. Part volumes range from single-digit prototypes to production runs of a few thousand. Such a diversified mix of capabilities and part volumes prompts careful consideration of processes and strategies to maximize accuracy and efficiency.
A good example was an approximately 1½ "×1¼ "×½ " squared-off, U-shaped aluminum bracket Plouse machined for a medical equipment manufacturer. Lot size was about 300.
The bracket featured milling, drilling and tapping on six sides, which would require a minimum of five fixturings to complete on a horizontal machining center. For significantly higher-volume part runs, the HMC would have been a wise choice, as parts for subsequent operations would be set up while the prior ones ran nonstop.
However, for this relatively small part run, Plouse determined that the most efficient method was to perform the operations in a continual sequence on a multitask lathe. The Mori Seiki NL-2000SY machine chosen for the job has driven tools and, in addition to turning, the machine can mill, drill and tap in both the Z and X axes. The machine’s Y- and C-axis motion capability permits machining of off-axis features, and the option of feeding bar stock through the chuck minimizes load time.
The machine enabled Plouse to write one program, setup once and machine the part complete, eliminating refixturing time and the possibility of setup errors between operations.
Working from a customer-provided print, Plouse drew the part in SolidWorks and programmed it in Mastercam. The workpiece material, 36 "-long bars of 2 "-dia. extruded 6061-T6 round bar stock, was fed into the machine through the chuck about 2 " at a time. “When most people see the part, they think rectangular bar stock,” said Darryl Smith, the company’s engineering services manager. “But it’s round.”
In the first and only turning operation, Plouse faced and rough-turned the bar’s OD to a diameter of 1.660 ". In the next operation, a ½ "-dia., 3-flute, solid-carbide endmill in a live toolholder approached the chuck in the Z-axis and milled and squared the round bar to 1.580 " wide × 0.500 " thick × 1.375 " long (from the free end to where it attached to the bar stock) at a speed of 3,200 rpm and a 40-ipm feed rate. Smith said the parameters were the maximum possible without generating chatter.
Courtesy of B. Kennedy
Plouse Precision Manufacturing machined this 1½ "×1¼ "×½ " aluminum bracket for a medical equipment application from a round bar of extruded aluminum.
Next, a 5⁄64 "-dia. HSS drill, applied in the X-axis at 4,500 rpm, made two holes on one side of the part, which then were tapped by a 2-56 UNC-2b thread form tap at 600 rpm. A 0.25 "-dia., solid-carbide endmill, run at 4,500 rpm and an 8-ipm feed, then plunged and interpolated a 0.25 "-dia. hole in the same side of the part. Smith said the endmill diameter could match that of the hole it made because the endmills run undersized. Then the part was rotated 180° and the endmill made an identical hole in the other side.
“On this lathe, it’s like having a 4th axis, because you can index the chuck around and stop it wherever you want,” Smith said. He noted that the tolerance on the two 0.250 "-dia. holes was 0.002 " to 0.000 " and “if we were to drill them, we would also have to ream them. Whereas we just dropped in with an endmill, and it only took a second to buzz around them.”
Next, with a live tool in the Z-axis, a 0.375 "-dia. center-cutting endmill plunged and interpolated a 0.375 "-dia. axial hole in the center of the bracket, running at 2,000 rpm and 5 ipm. A C-axis move enabled a 0.089 "-dia. hole to be drilled beside the 0.375 "-dia. hole, which was tapped with a 4-40 UNC-2b thread.
Next, the central 1.4 "× 1.3 " pocket of the U shape was milled through with a 0.25 "-dia. endmill run at 4,500 rpm and 23 ipm. The same tool then created chamfers and steps on the part at 5,500 rpm and 30 ipm.
At this point in the process, Smith said, “The opening of the U was still attached to the bar, but we had a finished part machined on the end.” He added that the key difficulty in producing this part on the lathe was determining how to remove the finished part from the slug it was attached to without damaging the part.
Plouse achieved that using a 1.00 "-dia., 0.033 "-thick slitting cutter run at 1,500 rpm. “We just went in and nipped both ends off, and it was a done deal,” Smith said. “It dropped into a parts catcher and was brought out to the operator.” Deburring was the final process.
Total part cycle time was about 6 minutes. “The critical issue in making the part was not that it was so difficult to manufacture, but why we chose to do what we did,” Smith said. CTE
For more information about Plouse Precision Manufacturing, call (888) 473-3606 or visit www.plousemanufacturing.com.
Related Glossary Terms
- 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.
- 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.
- electrical-discharge machining ( EDM)
electrical-discharge machining ( EDM)
Process that vaporizes conductive materials by controlled application of pulsed electrical current that flows between a workpiece and electrode (tool) in a dielectric fluid. Permits machining shapes to tight accuracies without the internal stresses conventional machining often generates. Useful in diemaking.
- 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.
- gang cutting ( milling)
gang cutting ( milling)
Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.
- gang cutting ( milling)2
gang cutting ( milling)
Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.
- grinding
grinding
Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.
- high-speed steels ( HSS)
high-speed steels ( HSS)
Available in two major types: tungsten high-speed steels (designated by letter T having tungsten as the principal alloying element) and molybdenum high-speed steels (designated by letter M having molybdenum as the principal alloying element). The type T high-speed steels containing cobalt have higher wear resistance and greater red (hot) hardness, withstanding cutting temperature up to 1,100º F (590º C). The type T steels are used to fabricate metalcutting tools (milling cutters, drills, reamers and taps), woodworking tools, various types of punches and dies, ball and roller bearings. The type M steels are used for cutting tools and various types of dies.
- inches per minute ( ipm)
inches per minute ( ipm)
Value that refers to how far the workpiece or cutter advances linearly in 1 minute, defined as: ipm = ipt 5 number of effective teeth 5 rpm. Also known as the table feed or machine feed.
- 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.
- milling machine ( mill)
milling machine ( mill)
Runs endmills and arbor-mounted milling cutters. Features include a head with a spindle that drives the cutters; a column, knee and table that provide motion in the three Cartesian axes; and a base that supports the components and houses the cutting-fluid pump and reservoir. The work is mounted on the table and fed into the rotating cutter or endmill to accomplish the milling steps; vertical milling machines also feed endmills into the work by means of a spindle-mounted quill. Models range from small manual machines to big bed-type and duplex mills. All take one of three basic forms: vertical, horizontal or convertible horizontal/vertical. Vertical machines may be knee-type (the table is mounted on a knee that can be elevated) or bed-type (the table is securely supported and only moves horizontally). In general, horizontal machines are bigger and more powerful, while vertical machines are lighter but more versatile and easier to set up and operate.
- outer diameter ( OD)
outer diameter ( OD)
Dimension that defines the exterior diameter of a cylindrical or round part. See ID, inner diameter.
- tap
tap
Cylindrical tool that cuts internal threads and has flutes to remove chips and carry tapping fluid to the point of cut. Normally used on a drill press or tapping machine but also may be operated manually. See tapping.
- tapping
tapping
Machining operation in which a tap, with teeth on its periphery, cuts internal threads in a predrilled hole having a smaller diameter than the tap diameter. Threads are formed by a combined rotary and axial-relative motion between tap and workpiece. See tap.
- tolerance
tolerance
Minimum and maximum amount a workpiece dimension is allowed to vary from a set standard and still be acceptable.
- toolholder
toolholder
Secures a cutting tool during a machining operation. Basic types include block, cartridge, chuck, collet, fixed, modular, quick-change and rotating.
- 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.
- wire EDM
wire EDM
Process similar to ram electrical-discharge machining except a small-diameter copper or brass wire is used as a traveling electrode. Usually used in conjunction with a CNC and only works when a part is to be cut completely through. A common analogy is wire electrical-discharge machining is like an ultraprecise, electrical, contour-sawing operation.
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