- Published on Monday, 04 August 2014 14:27
- Written by Mike Finn
The valve landscape has changed over the past few decades—instead of über-high volumes of simple valves, many buyers and makers of valves are increasingly aiming for low-to-medium volumes of complex, high-precision valves made from exotic materials. That’s because the number of applications presenting new, more difficult challenges has increased in fields ranging from oil and gas to food processing and chemicals to fossil and nuclear power. As valve requirements have broadened, the need for better machine tool capabilities has increased.
Inflexible, single-process equipment is pretty much out altogether these days. In its place are advanced machine tools with multi-tasking, 5-axis and done-in-one set-up processing capabilities (see “The Evolution of Machining”). These machines provide the agility to quickly change over from one part family to the next; the strength, repeatability and precision to meet current valve machining requirements; and the automation to increase productivity. But most importantly, with today’s advanced machine tool technology, manufacturers can now produce the highest quality valves possible in the shortest amount of time. Plus, with the technology, they can significantly lower cost per part and thus pass savings on to customers.
Of the advanced machine tool technologies now available, some of the most predominant for small-to-medium-sized valve production include multi-tasking machines configured with twin turning spindles and twin tool turrets (plus a fourth or “Y”-axis capability), and machines that combine a turning spindle with a tilting fifth or “B”-axis milling spindle. For processing of larger valves, shops look for multi-tasking capabilities that can cut big part features requiring both inner diameter (ID) and outer diameter (OD) work in single workpiece clampings.
TWIN SPINDLE/TWIN TURRET
Twin turning spindle/twin tool turret multi-tasking machines (Figures 1 and 2) are well suited for medium to large valve components that require 5-axis machining. These machines permit shops to change jobs over in a matter of minutes as opposed to days. Additionally, they provide the flexibility to quickly adjust for varying part volumes, switch from one job to the next and squeeze in those frequently occurring hot emergency jobs.
Machines with Y-axis capabilities can perform off-centerline machining and complete valve parts in single setups that employ milling, turning, drilling, boring and tapping.
Twin turning spindles can be programmed to operate together or separately, allowing a single valve part to be machined on all its surfaces through a coordinated hand-off between the two spindles. Alternately, two different valve components can be machined simultaneously on one machine.
The tool turrets on these machines typically hold a variety of different cutting tools including fixed (lathe) and rotating (milling/drilling) tools. Multiple tool turrets can operate independently or together on the same part, providing the capability to machine two different features simultaneously or to use balanced machining strategies (Figure 3).
In balanced cutting operations, tools from the upper and lower turrets work together on the same valve part feature for rough and finish turning, rough and finish milling, or opposed feature drilling, tapping or boring. In cases where the part configuration permits, balanced machining significantly increases metal removal rates and shortens cycle times.
For valve manufacturing company Richards Industries in Cincinnati, OH, the versatility of multi-tasking machines allows quick changeovers from one part family to the next.
A larger tool magazine capacity compared to single-process (single spindle, single turret) equipment enables use of redundant tooling that significantly reduces machine changeover times for the company. The machine’s single-setup, part-processing capability makes it possible for Richards—and other manufacturers using this type of machinery—to hold very tight tolerances and provide high-quality parts in the shortest turnaround times possible.
TURNING SPINDLE/B-AXIS MILLING SPINDLE
In contrast to a twin spindle, twin turret multi-tasking machine, a machine with both a turning spindle and B-axis swiveling milling spindle combines the capabilities of a high-powered turning center with those of a full-function machining center.
Such machines may have a milling spindle with Y-axis travel and B-axis rotation that deliver full 5-axis machining capability. With them, a shop can easily process round parts, non-round workpieces and highly contoured sculptured parts. These machines can hold as many as 72 or more tools, speeding changeovers via short tool change times.
A machine that features two turning spindles and a milling spindle allows for done-in-one operations. It can handle all processes from raw material input through final machining, providing dramatic reductions in lead times and improving workpiece accuracy by eliminating multiple setups.
For Conval Inc., a valve manufacturing company in Somers, CT, twin turning spindle/B-axis milling spindle multi-tasking machine tool technology provides the versatility to process a wide variety of part types and materials on one machine. The shop’s various types of valve components are no longer pigeonholed on one particular machine or manufacturing cell because the multi-tasking machine can process any of the shop’s components.
The goal at Conval is to get parts through as fast as possible without jeopardizing quality, and multi-tasking machine technology makes that possible. The shop goes from one job to the next between five and eight times per day with job lot sizes varying anywhere from one to 10 pieces.
TRENDING TOWARD BARSTOCK
Advanced technology for loading of raw workpiece materials also enhances process flexibility. Some machines are equipped with bar feeders—devices that move a continuous bar of part material directly through the machine chuck where it is cut off and machined into individual components.
Feeders typically can accommodate bars up to about 3 inches in diameter. For larger-diameter components, bulk work material must be cut outside the machine into blanks that are loaded and clamped in the chuck one piece at a time. For additional flexibility, some machines are equipped to perform both chuck and bar work. Such machines give shops the ability to machine smaller parts from bar-fed work material and also handle large components made from individually-loaded blanks that are in some cases over a foot in diameter.
As multi-tasking machines become more prevalent, many machine users have realized that pairing the machines with bar feeders can create stand-alone, self-contained automated systems that further enhance output and machine utilization. At the same time, producing as many parts as possible from bar stock reduces material costs because less material is machined away. This is especially beneficial for valve shops working with expensive materials such as 316 stainless, F22 alloy steel, Inconel, Nitronic 50 and others. Plus, time and manpower needed to cut and deburr blanks for each job are eliminated.
Many valve manufacturers machine all their valve bonnets, bushings and other specialty internal components out of bar stock. This makes multi-tasking machines that handle larger-diameter bar stock desirable because a maximum number of components can be made at one time.
Today’s bar loaders are engineered to automatically feed out material the required distance from the chuck to minimize bar remnants. Furthermore, chuck pressure management systems can change automatically according to part programs to accommodate a wide variety of workpieces. Such systems maintain not only the set chuck pressure per workpiece, but also produce the same pressure when changing material.
LARGE VALVE COMPONENTS
In addition to dealing with tough part materials, stringent testing requirements and extremely high-quality standards, valve manufacturers such as Emerson Process Management, Marshalltown, IA, also face the challenge of producing large-size valve components. Valve body diameters of 40 inches and bigger with extremely complex features, produced in small (one-off) lot sizes, are common at Emerson.
At the same time, no matter the size of the valve, the shop’s varied workload requires versatility and flexibility to transition from one type of valve to another as quickly as possible. These demands make it essential to clamp and move a part only one time, if possible.
A good way to generate turned features on very big, cumbersome valve parts is to keep them clamped and stationary, letting the cutting tool move around them. A stand-alone valve body production center (See lead-in photo, page 14) that can finish most of the valve and other large part machining operations in one clamping can contribute to maintenance of tight tolerances. In addition, the machine can be integrated with horizontal machining centers and other production equipment to form a fully automated system that provides 100% complete done-in-one valve manufacturing.
Advanced machine tools can produce part features and surface finishes that are specific to the fluid-handling industries. For valve bodies and other large workpieces requiring turned features, the machines can efficiently generate spiral-groove “phonographic” finishes on flange surfaces and cut tapered bores, internal and external grooves, concave surfaces, and other specialized valve details.
For processing large valves, today’s advanced multi-tasking machine technology basically fuses together the capabilities of a horizontal machining center with those of a vertical turning center. The result is a machine that performs turning and milling for done-in-one processing of big, heavy, difficult-to-handle valve components.
C-axis rotary machine tables can make workpiece positioning and turning operations possible, while powerful and rigid milling spindles offer B-axis tilt from -30 to 120 degrees to accommodate both rotating (milling and drilling) tools as well as static ones for turning. Tool storage capacities can range from 40 to close to 350 tools. Two-pallet changers represent another way to enhance part-processing versatility.
Today’s valve users demand the highest quality valves at the lowest possible prices. To meet those demands, valve manufacturers need to produce components as quickly as possible without jeopardizing overall valve quality. At the same time, the manufacturers must control prices while maintaining profitability. All of this is a tall order that today’s advanced machine tools can help to fulfill.