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Sunnen Introduces High-Precision Single Stroke Honing

Posted: 05/10/2014 04:05:48   Edited: 05/10/2014 04:05:48  Clicks: 1684
Sunnen Company introduces a quantum improvement in a key manufacturing process for cast-iron hydraulic valve bodies using a precision Single Stroke Honing? 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, the High-Precision Single Stroke Honing process is almost 200% more accurate than anything previously achievable for long, small-diameter, tandem bores.
 
"European mobile equipment hydraulic systems established this cylindricity specification to reduce internal leaks and achieve higher valve performance," said Juerg Huber, Managing Director, Sunnen AG. "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." 
 
Single Stroke Honing is a single-pass process that sizes and finishes a bore with a series of progressively larger super abrasive tools adjusted to a pre-set diameter. Single Stroke Honing tools rotate while passing through the bore one time and then withdrawing. The machine's servo-controlled stroking system 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.
 
The Single Stroke Honing tool consists of a tapered arbor with an expandable diamond-plated abrasive sleeve mated to it. The external profile of the sleeve is designed for the application. Single-pass honing is ideally suited for solid bore parts with L/D (length/diameter) 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 load on the abrasive sleeve.  In the case of cast iron valve bodies, bore length-to-diameter 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 Huber. "However, as the bore length increases, it becomes more difficult to achieve good straightness and cylindricity. Among other reasons, the honing tool's sizing land 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. High-Precision Single Stroke honing 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 High-Precision Single Stroke process utilizes a combination of proprietary tool processing, tool holding, work piece 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.
 
When properly applied, Single Stroke Honing is a quick, cost-effective method to get a precise bore size, geometry and surface finish. Parts made of cast iron, powdered metals, ceramic, glass, graphite and other free cutting materials are ideal for the process. 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. 
 

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