Sunnen’s new controlled-force tool-feed with its existing controlled-rate feed system. The two different modes allow the user to select the better option to suit the workpiece geometry, material and tool type/size. Typically, a production honing process is set up to use an abrasive tool with a combination of grit size and bond opti- mized for specific part conditions. Tool expansion to achieve the desired results and final size is programmed based on rate of time. However, when a batch of parts comes in with a different heat treatment, distortion or a size variation, the opera- tor must intervene because the tool may expand too quickly and be damaged. In the opposite case with a softer-than-normal or oversize workpiece, the tool will still expand at its programmed rate, when it might have been able to expand faster to reduce cycle time. Expansion at too slow a rate may also result in glazing of the honing stones, which won’t self-dress if the cutting force is too low. Typically, the operator tweaks a rate-feed system periodically to compensate for these variables. By servo-controlling the force in the tool feed system, however, the machine can sense and compensate for these variables. The controlled-force feature, which works in concert with the machine’s standard rate-feed system, functions like cruise control to maintain the optimum cutting load on the honing abrasive throughout a cycle, regardless of the incoming part’s hardness, geometry or size variation. Waltz’s new SV-1015 vertical CNC honing machine has a single 5-hp (3.7-kW) AC spindle with 10-hp (7.5-kW) servo-stroking system and X-Y air bearing table. The operator loads the workpiece in a dedicated fixture that uses the part’s kid- ney slot as a locating feature. After each bore, the table indexes 90° to an Etamic air gaging station where the necessary readings are taken and stored. If the bore passes inspection, the table moves the part to a robot that indexes it for the next bore, duplicating this routine eight times to complete a part. A fixed-position master set ring inside the machine’s work envelope ensures correct gage calibration for current environmental conditions.
Based on measurements taken by the air gage (shown), the honing tool is automatically adjusted to maintain a precise diameter. Com- pensations for taper, barrel-shape or bell-mouth conditions can also be made.
“On a recent project with an allowable bore tolerance of 0.000240" [0.006 mm], we easily held a tolerance range of 0.000060" [0.001524 mm]—that’s 25% of the total allowable tolerance, and we tripled the previous production rate, while reducing the labor component by 80% so the operator can do other work in the cell,” said Waltz. “We know from reinspecting the parts on our CMMs that the results correlate well. The process capability and data reporting features in the machine have been a great advantage to us and our customers, allowing that data to be downloaded to a spread sheet or SPC software. ME
For more information from Sunnen Products Co., go to
www.sunnen.com, or phone 800-325-3670.
December 2013 |
ManufacturingEngineeringMedia.com 67
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