A process that achieves tight tolerances while boring cast iron hydraulic valve bodies and fabricated parts of other materials is being offered by Sunnen Products Co., based in St. Louis.
The process, High-Precision Single-Stroke Honing, reportedly achieves cylindricity in cast iron valves of 2 microns or smaller when used for small-diameter bores with length-to-diameter (L/D) ratios of 10:1. Cylindricity in short bores with L/D ratios of less than 1 is down to 1 micron.
Cylindricity is a function of the roundness, straightness, and taper of a bore. Perfect cylindricity means that all points of a bored surface are equidistant from a common axis. Cylindricity is measured as the allowable difference in radius of two coaxial cylinders that encompass all data of a bore. Hence the lower the measurement, the closer it is to perfect cylindricity.
Bore sizes suitable for the process are typically 16 mm (0.62 in) in diameter and 160 mm (6.3 in) in length or longer, with 11 lands.
The degree of bore control in Sunnen's process reportedly makes it far more accurate than most competitive systems, which typically achieve cylindricity of 5 microns in bores with 10:1 L/D ratios, the company says.
The process, which runs on the three models in the company's VSS-2 Series honing machines, was developed in Germany by parent firm Sunnen AG to meet European leak-free specifications for mobile hydraulic systems.
Bores are sized and finished with the company's Single-Stroke Honing Tools. Each has a tapered arbor and a tapered abrasive sleeve on the body that progressively enlarges the bore as it passes through a part.
The standard tools are A-Types in bore diameters of 5.9 to 26.4 mm (0.23 to 1.04 in). Custom A-Type versions come in larger diameters: 3.78 to 100 mm (0.149 to 4 in).
High-Precision Single-Stroke Honing from Sunnen achieves tight bore control in valves and other parts with special tapered tools.
At the top end are HPH (High-Production Helix)-Type tools, which are diamond plated. These come in standard sizes of 6.35 to 25 mm (0.25 to 0.99 in) and custom versions of 3.78 to 25 mm diameters (0.149 to 4.0 in).
Tool life averages 60,000 to 80,000 parts, Sunnen says, which increases process economy.
Features of the VSS-2 Series machines include servo-controlled stroking, adjustable speeds - including variable speeds within boring cycles - and different feed profiles such as short stroke, dwell, and pecking.
The model types are VSS-284, with eight stations and four spindles; 286, with eight stations and six spindles; and 264, six stations and four spindles.
Each spindle is independently aligned for precision centering over the tooling plates. Spindle carriages have 724-mm (28.5-in) strokes and stroking speeds of up to 105 mm/s (250 ipm). The space between spindles is 190 mm (7.48 in). Spindle drives are equipped with 10-hp motors and generate 100 to 2,500 rpm.
The touchscreen control on each machine stores more than 100 setups.
The machines have stainless steel interior work areas and are designed for minimal maintenance. Other features include vertical positions that can be rapidly set up with the servo motor and ball-screw feed-control system, fast rotary worktable indexing and column traverse times to increase productivity, and a polymer concrete base for high rigidity.
VSS-2 Series machines are compact, taking up only 90 by 60 in of floor space. The units can be set up for optional functions, such as double indexing for increased production and custom loading and unloading actions. Automation is a capability, through integration of two-axis and multi-axis robots for 24/7 operations.
In addition to making cast iron hydraulic valves, High-Precision Single-Stroke honing can be used to precision size bores in gears and sprockets, rocker arms, turbocharger housings, and similar parts fabricated of powdered metals, ceramic, graphite, and even glass.
Sunnen will display its technology and process at the International Manufacturing Technology Show (IMTS), stand N7400, in Chicago, Sept. 8-13.
VSS-2 Series honing machines have multiple spindles and workstations for boring operations. Credit: Sunnen Products Co.