Shop Solutions: CNC Machining Energizes Manufacturer
Greg G. Wright & Sons LLC (Cincinnati) traces its history back to its founding in 1860 as a pioneer in manufacturing engraved steel blocks, custom tags and plates, and metal stampings.
As a US manufacturer, Carl Fries, president and CEO, is a realist and a fighter, who believes that there are opportunities for the shop that employs newer technology and higher quality technology.
"I think technology will open doors that have previously been closed. The name of the game is speed—to be able to process your parts as fast as possible at the highest level of quality. If you're not doing that, it's only a matter of time before you're done," Fries says.
Today's Wright & Sons occupies 34,000 ft2 (3179 m2) and employs some 20 operators and tool and die craftsmen—three with more than 40 years and many others with 20-plus years on the Greg G. Wright & Sons team. When Fries took over the company, there were two divisions, which he combined.
"When I stepped in, the company was very near death, and I had to breathe new life into it. I got rid of 25 to 35 manual machines and about 30,000 lb [13,608 kg] of scrap. It was ridiculous. There was a single small CNC router to make patterns, but not a single computer-aided machine tool in the shop. My first purchase was a CNC EDM sinker to engrave tools. At the time, engraving was our primary market. My background was CNC turning and milling, and I knew that eventually I'd move the company in that direction in a major fashion."
That is precisely what he did, investing in CNC turning and milling equipment to position the company to be competitive in an increasingly global market. He sold off manual machines, replacing them with CNC machines, many of which were used but in good shape.
Then, too, Fries realized he had to move away from Wright & Son's traditional target markets of engraving and metal stamping. To do that, he signed up with two Internet matching services to get his name and capabilities out before a broader audience and emphasize his focus on CNC turning and milling. He has mixed feelings about the Internet experience, and thinks it's still hard to replace face-to-face, palm-to-palm relationships, especially when working on large dollar and time-commitment jobs.
"For example, we've been working on a special project for CompX Fort [River Grove, IL]," Fries says. "We turn a ring on a Hardinge Quest Super Precision, roll-mark it, and then EDM a cut. The final EDM work is be done by a third party. Our customer uses a pneumatic air cylinder to spread the ring open to put a thick key on it.
"We've paid CompX Fort a visit to show them samples of the job, and they've been very pleased. This is a $50,000 contract, and they don't come around all that often to a $2–$3 million company. If this relationship blossoms, there are quite a few other parts we could be making for them. And we're working face-to-face. For me there's a certain comfort in that, as unfounded as many may think that is today," he says.
Right now, Fries says, the focus, short and long term, is getting Wright & Sons up to speed on CNC—CNC turning, CNC milling, and CNC Swiss turning. Evidence of this is a new Hardinge (Elmira, NY) Bridgeport 760XP3 VMC. "We got the 760 about four months ago when we started getting more and larger contracts for precision milling work," Fries says.
"Our existing VMC just couldn't keep pace. Granted, it's 14 years old, and technology has changed considerably in a decade and a half. But when we decided to expand our milling capacity we went with whom I knew best: Bridgeport and Hardinge. And before we really had the 760 set up and running, we ordered a second 760, which should be here anytime now."
What drove the order for the first Bridgeport 760XP3 was the awarding of a sizeable order for precision gas flanges for commercial jet engines.
"We run these parts chucked face up in a vise, four at a time," explains Gary Foster, tool-room manager. "Cycle time is roughly 28 min. The material is 410 stainless. The tolerance on the overall height is ±0.001" [0.25 mm] and ±0.005" [0.13 mm] or ±0.0010± (0.13 mm) on the shoulder. The Fanuc 18i MB handles all the interpolation of the holes, the large center hole and the perimeter holes, the face milling and radii. When the top face is finished, the part is turned over and refixtured in an adjacent vise on the table, face down, where the bottom is fly-cut to assure proper part thickness."
After the parts are fly-cut, they're placed on a fixture 20 at a time for finish grinding of the backside, which brings the part into final finish dimension. "This is the only operation that isn't done on the 760," Foster says. "In the past there were a number of secondary operations to finish this part. Now, this is the only one, this light grinding to bring the thickness into spec."
All 11 tools that are needed are in the 30-tool ATC. "Between the control and the ATC we've got a cycle time of 28 min, whereas the previous method took twice that long," Foster says. "The 290 psi [2 MPa] through-spindle coolant feature makes a real difference. We can take a flat-bottom drill at a rate of 4 ipm [106.6 mm/min] and pop the center hole through the stainless in 7 sec. Without the through-spindle coolant, we couldn't do that. It would heat up so quickly that the tool would burn into the material.
"Further, it keeps the holes, angles, and other characteristics free of chips, making the cutting zone easy to see and helping to move the chips into the swarf removal system, which separates chips from coolant," Foster says.
What sets the Bridgeport 760XP3 apart from its competition is an array of milling characteristics, says Fries. For one thing, the 25-hp (18.6-kW), 12,000-rpm spindle is not only powerful but is massive and offers rigidity and radial stiffness.
Fries points out that the table rides on twin ballscrews (X and Y axes). "Instead of having a single nut at an end, the 760 has two nuts at either end, and the lead nuts on the two ballscrews are enormous, which makes a huge difference. Plus, the precision of the grinding that has been done on the two ballscrews is unsurpassed," Fries says.
When he wants to machine 1500 lb (680 kg) of stainless (which he had to do for a recent order), Fries wants to make sure the 35.4 x 23.6" (899 x 599-mm) table and axis movement will permit the 760 to machine the job accurately. Axis travels are 29.9 x 24 x 24" (759 x 610 x 610 mm) X, Y, Z with rapid rates of 1690 ipm 43 m/min (X, Y) and 36 m/min (Z).
Other features that make the 760 stand out include the C-frame casting itself and the ribbing in the sides. "The casting weighs 14,300 lb [6486 kg], and while bigger isn't always better, the way this casting is built with all the ribbing and structural integrity," says Fries, "you can tell that care, design, engineering and structural analysis have gone into the 760 casting. This makes a huge difference. Our previous machine weighed half as much and raised all kinds of questions as to what we could run on it and what would push the weight limit."
The requirements for machining today include holding tolerances in Inconel, titanium, stainless, and a group of alloys many of which have their own range of machineability difficulties. "You want to have all the energy the spindle is producing be absorbed into your casting and not into your workpiece," Fries says. "That's the importance of a rigid base."
The global competitive environment has changed dramatically. Fries says, "The Chinese didn't have the technology to compete before. They're acquiring it now and getting better at using it all the time. A shop here that's in operation today and has been for the past 20 or 30 years is saying, well, the equipment that we have on our shop floor has always worked, it makes the parts, we hold the tolerances, then why invest in new machinery?
"Because you can't sit around and let things happen. You've got to be proactive. You're going to see more and more work returning to this country, true. At the same time you're going to see more and more shops go out of business because they're not employing the latest technology. They're not willing to make the investment. So, there's a thinning of the herd, and somehow they can't understand why."
Fries asks a number of rhetorical questions: "You've got to ask yourself if you're going to make money, or if you're going to make money with an eye on the future so you can keep the business going? Are you going to create a vehicle through business to provide for you and your family for generations?
"I believe I'm just a caretaker of this company. I'm the first outsider to own and operate Greg Wright & Sons. They started off making stencils and marking devices. We still make marking devices of some sort in one form or another. We still do what we did 145 years ago. I've built on that with the CNC technology—two Bridgeport 760 XP3s in a matter on months, and more to come. Yet, someone was here before me and someone will be after me. I'm only a caretaker. Yes, I own a good portion of the company, but I'm only a blink of the eye. I've been here for four years. What am I going to do to make this business more profitable going into the future?
"One thing I'm going to do is continue to invest in the best technology, and then I'm going to fight. I'm going to fight to win jobs that are coming back from China, and I'm going to fight to win those that might go to China. I'm not going to wait for someone else to do it. Who? It's my future. Mine."
Testing Tiny Targets for Big Results
ABTech Inc. (Swanzey, NH) is a supplier of precision-motion systems with an extensive background in the design and manufacturing of air bearings and oil hydrostatic bearings for geometry measurement systems and ultraprecision diamond machining and grinding equipment.
The development of small hydrogen targets to test thermonuclear ignition is like a science in itself requiring highly accurate targets, explains Kenneth D. Abbott, AB Tech owner. His company has manufactured the custom air-bearing motion system that builds those targets.
The new custom machine from AB Tech that is now in place at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL; Livermore, CA) has recently passed inspection to begin its work.
LLNL at the University of California employs 8000 and is federally funded to do research in a variety of areas, including nuclear power, national defense, and the environment. The NIF lab is currently on track to house the world's largest laser that will involve 192 individual laser beams that will be repeatedly trained onto high precision tiny hydrogen targets.
With the new hydrogen targets, NIF's experiments promise to produce temperatures and densities like those of the Sun or in an exploding nuclear weapon. These experiments will help scientists sustain confidence in the nuclear energy, without doing actual nuclear weapons testing (stopped in the US during the 1970s), as well as produce additional benefits in basic science and fusion energy research.
With each test, a double shell implosion target will be placed in a 30' (9.1-m) diam chamber with the laser beams fired simultaneously to explode it, demonstrating thermonuclear ignition. Its output will be measured for use in a variety of ways.
The manufactured hydrogen targets themselves use capsules of fusion fuel and are heated to thermonuclear ignition. The targets are made of silica-based inner sphere; the manufacturing requirements for surface finish and shell concentricity of the targets are essential to successful explosion. The shell halves are assembled on ABTech's custom five-axis air-bearing assembly station in order to achieve acceptable concentricity.
Weighing about 150 lb (68 kg), this air-bearing machine system includes mechanical arms that can slide, without friction, into position, with accuracy of up to 0.000004" (0.0002 mm). "Each target is 0.028" [0.71 mm], smaller than the top of a ballpoint pen," says Abbott.
The overall components of this unique machine include three linear air bearings and two rotary air bearings, a motion controller, host PC, and application software. The system is capable of positioning the target shell halves to locations within 0.1µm. "The only way this is now possible is with the use of today's ultraprecise linear scales for use on the linear slides," explains Abbott, "and because of the strict accuracies required in NIF's specifications, our only choice was the extremely high accuracy LIP 481 scales from Heidenhain Corp. [Schaumburg, IL]. It's really amazing what they can accomplish today."
The Heidenhain LIP scales are exposed linear encoders that are characterized by high accuracy together with small measuring steps as small as 0.005µm, depending on the model. Their measuring standard is a phase grating applied to a substrate of glass, and they are typically used in the highest precision machines such as diamond lathes for optical components, facing lathes for magnetic storage disks, and measuring microscopes and semiconductor equipment machines.
The ABTech air-bearing system at NIF includes three of these ultraprecise Heidenhain scales, one on each of the X, Y, Z-linear axes. The entire system is completed with a high-resolution camera and surgical microscope that provides views of the mating components.
The new system's bearings produce a thin film of air similar to the layer of air that allows a puck to move smoothly across an air hockey table. Precision manufacturing takes place from there.
"This ABTech machine is a significant improvement from what NIF was using to develop early stage targets," says Abbott. "Our project is a complicated device, having taken about eight months to develop. Because of the high accuracies, it was crucial that we received assistance from the Heidenhain representative. His highly technical expertise was instrumental in helping us with the installation alignments. This machine is now truly like no other," Abbott says.
Tackling Tough Machining Tasks
Twin-screw extrusion machines can run for months and even years mixing ingredients, additives, and binding agents, using heat (sometimes) and pressure to form compounds into desired shapes for the cosmetics, pet food, PVC pipe, wood composite, and plastics industries. More explosive applications involve blending explosive elements for the energetics industry for air bag deployment, military armaments, and solid-rocket fuels.
Operation of these systems is relatively simple—ingredients are fed to the machine, typically from overhead hoppers, and into twin-barrel chambers, where dual, side-by-side agitators, with screw-like thread geometries, provide the mixing action and continuously applied force to feed the material to and through the extrusion die.
Optimum performance of the extrusion process, however, depends on a correct application of parameters such as temperature, torque and corresponding RPM, placement of screw sections, plus rotational direction and screw alignment parameters, barrel design and sizing, stages of venting and degassing, along with setting mixing rates and formulations for the compounding materials.
Few of these elements are more critical than the precision of the agitator screw shafts. For more than 30 years, CIGNYS and its Advanced Manufacturing Product Group (Saginaw, MI) has used its machining expertise and process knowledge to provide extruder screws, barrels, driveshafts, and coupling components to the extruder industry.
In addition to its work providing extrusion-tooling units, modules, and a diverse range of services including turnkey solutions for retooling, refurbishing, and enhancing the performance of extruder lines, the Advanced Manufacturing Product Group of CIGNYS offers ball nut and ballscrew fabrication and contract machining. Other products and services from CIGNYS are materials handling equipment, military products and aviation ground support equipment, special machines and test stands, and prototype stamping and tooling.
The manufacturing challenge posed by agitator screw shafts involves the difficulties of machining tough materials, size impediments, operating specifications and dimensional tolerances, and multiple, complex geometries in a single project.
"Given the abrasive nature of the materials used in the extrusion process—because much of it is mixing bulk powders, strengtheners, or binding ingredients—the tooling materials selected are usually highly wear resistant," explains Dave Bosley, VP of the Advanced Manufacturing Product Group.
"Then, too, there are the needs for food preparation equipment to maintain high sanitary levels and frequent cleaning. Many of the elements we produce are made from pre-hardened 4340 aircraft-type high-strength alloy, or D2 tool steel along with CPM 9V and 10V alloys, tungsten carbides, high-nickel-content materials such as Inconel and Hastelloy, and a wide assortment of stainless steels including 300 and 400 series and precipitation hardening [17-4PH] materials," Bosley points out.
This range of materials offer excellent durability and long service in the extrusion process, but each also features distinctive machining characteristics that can play havoc with machines, tooling, and final dimensions.
Agitator shafts incorporate complex shapes to perform properly. For example, a small extrusion machine designed to produce prototype drug doses and pills uses two small conical and solid-piece agitator shafts about 8" (203.2-mm) long. The drive end of each shaft measures about 3/4" (19-mm) diam and tapers to 1/4" (6.4-mm) diam, and features a variable-pitch dimension as well as tapering outside, root, and pitch diameters of the thread-like form.
The component design called for 4340 alloy material with a core hardness of RC 28-32 that was ion-nitrided. The fit and function-positioning dimension of the shafts provides a clearance between the two of 0.015 to 0.020" (0.38–0.51 mm) that is fully intermeshing along their entire length when mounted and operating in the machine. All diameters of the shafts and their respective total indicator reading inspections had to be held to within ±0.0025" (±0.064-mm) tolerance.
The extruder OEM was having difficulty producing the conical agitator shafts and maintaining the correct clearance. CIGNYS consulted with an academic mathematician to formulate the points along the conical profile of the thread. Once these pitch points and calculations were established, CIGNYS was able to generate the toolpath program necessary to produce the conical variable-pitch profile.
To produce the part, CIGNYS first used a ram-style EDM system to cut the internal spline for the shaft's drive coupling, establishing a reference point for consistent orientation during subsequent machining steps. Then each thread profile was machined on a VMC featuring an added horizontal rotary table and fourth axis control. "We made 20 pieces total in a relatively short period of time," says Bosley, "but we were able to produce the part as it was designed, and to meet the pharmaceutical firm's requirements. It was one of our more unique challenges, one that few even thought could be produced."
The driveshaft is the next critical element of extrusion tooling systems. They typically consist of a spline, flatted, keyed, or possibly hexagon-shaped drive form on which screw flights or elements are mounted. The problem encountered with many of these components is also seen in how extrusion machines are often designated by agitator shaft length-to-diameter ratio. Common shaft diameters may range from 20 to 100 mm and lengths can typically measure 30, 40 to 50 times the diameter, resulting in shafts of less than 1" (25.4-mm) diam yet measuring from 5 to 10' (1.5–3-m) long or longer.
For CIGNYS, this means shafts usually require indicator readings of between 0.005 and 0.010" (0.13–0.25 mm) over the entire length of the piece. "When the two shafts are assembled in the machine," notes Bosley, "the straightness of each is critical to keep the thread profiles from rubbing against each other, and to maintain alignment and prevent wearing on the barrel walls. It's also important that the shafts retain their torsional straightness so the screw elements are always properly oriented and synchronized to their opposite element on the other shaft."
Through metallurgical studies and working experience, CIGNYS has developed the critical steps from stress-relieving through control of heat-treating conditions, straightening operations, plus the sequence of machining and grinding steps, and the fixturing systems necessary to produce shafts that are straight, and shafts that will remain straight, keeping the agitator screw running true," Bosley explains.
The most important component for tooling the extrusion machine is the thread profile of the agitator shafts, and in cases where a separate driveshaft is used, these profiles are often referred to as elements or, when the geometry/profile changes, as flights. The size, lead, and pitch characteristics of the profile—there are approximately ten different basic screw element configurations available and virtually infinite variations—along with speed, feed, and torque determine the mix consistency and thoroughness. Then, the placement of screw elements, plus rotational directions and screw alignment parameters, stages of venting, degassing, and pumping are also governed by the profile elements.
Over the years, CIGNYS has developed extruder-specific mathematical calculations and algorithms for element construction. They have become established subroutines within its CNC equipment, programmed modeling that results in proprietary component geometries, functional toolpath generation, and fast production of parts. At the same time, CIGNYS has employed sophisticated CAD and engineering analysis programs that facilitate the crossover of technologies and designs, providing 3-D renderings of the complex screw geometries, virtual performance testing, and design verification of components prior to cutting metal.
Part of the process of producing elements, including thread profiles, profiles with interrupted cuts, wiper elements that clean the barrel sides, vent elements that release built-up gases from the barrel chambers, and paddle sections that stir and mix ingredients, is to make sure the ends are ground flat and parallel and to certain size restrictions, so as not to alter the accumulated profile orientations of multiple flights. Also, the flatness and parallelism assure that, when the elements are drawn up and tightened on the shaft, that the shaft is not skewed out of alignment.
Bosley points to one element design in particular, a combination wiper and venting geometry that was especially difficult to machine. "The screw profile included a fin-like thread crest; that is, it was only attached to the main body of the element at a single point, the balance floated in air," he says. "The concept was to provide a little resiliency so that as the fin contacted the barrel wall to wipe the sides clean, it would be pliant to avoid wear. The gap in the design acts as the vent, allowing gases to escape. Of course, machining this feature was also a challenge for the same reason. Put a tool to the piece and it tended to give, so minimal depths of cut were the rule."
The solid shaft is the most complex of the tooling systems, comprising drive shaft and screw agitation geometry all machined from one piece. The solid shaft configuration combines all of the challenges of extrusion tooling machining in one setting, with tough materials, complex, multiple geometries, positioning and orientation, material pre-conditioning, and fit tolerances.
A solid shaft, made from 17-4 PH or other stainless alloy is ideal for applications involving food preparation, as there are no cavities, cracks, or crevices to be contaminated, and the solid shaft is easier to remove and clean in most instances. Solid units are also desirable when working in the energetics industries, because the elimination of multiple, assembled parts reduces the risk of friction and sparks that could lead to hazardous conditions.
"The single-piece shaft will usually have multiple geometries," Bosley remarks, "transitioning from one standard thread profile, to paddles for mixing where materials are introduced to the process, then back to a different thread profile for pushing the blended materials along the barrel, another series of paddles, possible interrupted-cut thread forms, a series of low-profile threads where material is pumped out of the barrel to the die, plus reverse threads that prevent materials from bypassing process stages."
"One of the most difficult steps in the solid-shaft process is designing the various transition geometries, especially between thread and paddles, to prevent materials from clogging up the introduction of additional ingredients, and make sure backpressure does not keep materials from moving forward."
This article was first published in the April 2007 edition of Manufacturing Engineering magazine.