Original Date: 07/13/1992
Revision Date: 01/18/2007
Best Practice : Rotary Forging Process and Associated Heat Treatment
Watervliet Arsenal (WVA) has implemented a rotary forge and heat treating system resulting in notable process time savings, improved forging straightness, minimized wall variation, and enhanced process control. The Arsenal manufactures 105mm, 120mm, and 155mm cannon tubes. Conventional cylindrical forgings previously were purchased to produce these gun tubes. This process began with a solid cast ingot which was rough-shaped on an open-die hot forging press, rough-bored, and machined on the outside diameter to near-net shape. The production and subsequent machining of the conventionally produced forgings was costly and involved significant processing time.
With the rotary forge process, a bored and turned pre-form is heated in the induction pre-heat furnace for approximately one hour to the forging temperature of 2000 degrees Fahrenheit. A transfer car is used to place the pre-form in the rotary forge. A push-type chuck aligns the pre-form and places a mandrel through the center of the pre-form to control the extrusion of the inside diameter. The four radial hammers, each capable of applying 1,000 tons, are CNC controlled and can accept up to 22-inch diameter billets. The rotary forging process requires approximately 12 to 15 minutes.
After forging, the tubes are cooled to room temperature then the deformed tube ends are removed in a hot cut-off saw. The horizontal Selas heat treatment furnace sends the tubes through the 12-zone austenitizing furnace on rollers which provides continuous rotating of the tubes to improve straightness. The tubes are radially spray-quenched inside and outside and sent on to the tempering furnace. This heat treating system is capable of accepting tubes up to 315 inches in length.
The rotary forge operation is a major electrical power consumer at the Arsenal. A power consumption analysis determined that the monthly billing was based on the peak consumption rate at any point during the billing period. The analysis showed that the major peaks or spike usage periods that formed the billing base occurred during operation of the rotary forge. Consequently, the rotary forge now operates on an as needed basis to minimize its power consumption being added to the normal operational load. This simple change in operational philosophy has produced a significant savings to the Arsenal.
In the years that the rotary forge and heat treatment system have been operational, several upgrades have been incorporated. Improvements such as the installation of the CNC system and the replacement of the induction pre-heating system have provided for a source of cost-effective, high quality forgings.
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