High-Precision Single Stroke Honing® process produces <2 micron cylindricity in bores up to 10X longer than diameter
Sunnen Products Company has a quantum improvement in a key manufacturing process for cast-iron hydraulic valve bodies using a precision single pass process that achieves cylindricity/straightness under 2 microns in bores up to 10 times longer than diameter.

Developed in Europe to meet leak-free requirements for high-pressure hydraulic systems, Sunnen’s high-precision Single Stroke Honing® process is much more accurate than anything previously achievable for long, small-diameter, cast iron hydraulic valve bodies.
“Mobile equipment hydraulic systems manufacturers established this cylindricity specification to reduce internal leaks and achieve higher valve performance,” said Phil Hanna, Product Manager, Sunnen. “The precise fit between the sliding spool and valve body maintains the internal seal in this area. Precision cylindricity and straightness in this bore ensures uniform clearance between the moving parts from top to bottom in the valve, allowing free movement of the spool, without leakage around it.”
The Single Stroke Honing process sizes and finishes a bore with a series of progressively larger diamond plated tools adjusted to a pre-set diameter. Single Stroke Honing tools rotate while passing through the bore one time and then withdrawing. The Sunnen VSS-2 machine’s servo-controlled column feed provides flexibility with adjustable speed and various feed profiles, such as pecking, short stroke, dwell, etc. Column feed and spindle speed can be varied throughout a cycle using the machine control.
Single Stroke Honing tools consist of a tapered arbor with an expandable diamond-plated abrasive sleeve mated to it. The external profile of the abrasive sleeve is designed for the application. Single-pass honing is ideally suited for solid bore parts with bore L/D (length-to-diameter ratio) of 1:1 or less. Parts with much larger length to bore ratio can be honed under certain circumstances. Bores that have interruptions allow better chip flushing and reduce the cutting load on the abrasive sleeve.  In the case of cast iron valve bodies, bore L/D ratios of 10 or greater can be single-pass honed with great success.
“Single-pass honing is a stable, high-production process that can achieve one micron cylindricity in a short bore – one with L/D less than one – assuming the part has a sufficiently rigid wall,” explained Hanna. “However, as the bore length increases, it becomes more difficult  tends to follow the bore. On cast iron valve bodies with L/D of 10, the standard process has typically produced five microns cylindricity under optimum conditions. Sunnen’s high-precision Single Stroke honing process takes this to two microns cylindricity or less. And with a tool life that can be 60,000 to 80,000 parts, the process is economical. A typical part suitable for this process might have a 16 mm bore, over 160 mm long, with 11 lands. This type of part can now be honed to less than two microns cylindricity, less than two microns straightness and one micron roundness.”
The Single Stroke process utilizes a combination of proprietary tool processing, tool holding, workpiece fixturing and process parameters, without any penalty on cycle time. It is already in use by manufacturers of hydraulic valves in Turkey, Italy, Germany, Switzerland, Brazil, Sweden and the U.S.
The VSS-2 Series Single Stroke Honing® machine
Sunnen offers the Single Stroke Honing process on four different VSS-2 Series models that incorporate up to six spindles to progressively size and finish part bores. The machines are ideal for precision sizing of bores 3.9 - 50 mm (0.149 - 2.0”) diameter in stamped parts, hydraulic valve bodies, gears and sprockets, parking pawls, rocker arms, turbocharger housings and similar parts. Ideal materials include cast iron, powdered metals, ceramic, glass, graphite and other free-cutting materials.
The VSS-2 spindles are factory aligned independently for precision centering over the tooling plate to produce better bore geometry than possible when using an “average” alignment for all the spindles. The VSS-2 utilizes a spindle carriage with a 724 mm (28.5”) travel and up to 105 mm/sec (250 ipm) carriage speed for increased flexibility with a wide variety of parts and tooling combinations. The servo-powered column feed system provides process flexibility and is hand-wheel-controlled for easy set up. A Siemens PLC control provides optimum process control and easy program setups.
The menu-driven touchscreen control allows the column feed and spindle speed to be easily varied throughout the cycle. Process flexibility is enhanced by the use of six available profiles, including pecking, short stroke and dwell, which are easily added to a setup. Up to 500 setups can be stored. Additional I/O and memory are standard for integration with auxiliary equipment, such as robots or part loaders.
The VSS-2 Series 2 is available in four models – the 46 (four-station, six-spindle), the 64 (six-station, four-spindle), the 84 (eight-station, four-spindle) and the 86 (eight-station, 6-spindle) – to meet various mid- to high- production needs. Spacing between spindles is 205 mm (8.10”). The 7.5 kW (10 hp) spindle drive provides a speed range of 100-2250 rpm.
When properly applied, the Single Stroke Honing process is a quick, cost-effective method to get a precise bore size, geometry and surface finish. Single-pass bore sizing is also appropriate for splined bores or long L/D ratios if cross holes or other interruptions are present to allow chip flushing.
Sunnen offers a range of single-pass plated-diamond tooling for the VSS-2 for precise, accurate and consistent bore sizing. The machine is covered by a 3-year warranty and Sunnen is the complete solution provider for this machine, including: fixturing, tooling, coolants/coolant systems and automated part load/unload. More than 380 VSS-2 machines have been delivered since 2000.

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