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HEADING HINTS: ABOUT COLD HEADING
Carpenter Technology Corporation, whose Specialty Alloys Operations produces hundreds of stainless steels and specialty alloys, published the booklet 'Heading Hints – A Guide to Cold Forming Specialty Alloys' to suggest proper cold-forming fabrication techniques. Heading Basics Cold heading is a cold forming process that essentially involves applying force with a punch to the end of a metal blank contained in a die. The force must exceed the metal’s elastic limit (yield strength) to cause plastic flow. You might consider cold heading a forging operation without heat. Heading, which includes upsetting and extruding, is often performed in conjunction with other cold forming operations such as sizing, piercing, trimming, thread rolling, blank rolling and pointing. Heading is a metalworking process that goes back before the turn of the 20th century and for many years was used only to produce simple fasteners. Today heading is a high-speed, automated and multi-station operation that is capable of producing not only increasingly complex metal fasteners economically, but a growing variety of other components, including some that are asymmetrical. Combined with this dramatic improvement in heading equipment is the ability to successfully cold form parts from tougher metals, including stainless steels and high temperature alloys. Advantages of Cold Heading Heading differs considerably from machining where material is actually cut away to form a finished part. In heading, scrap occurs in secondary operations, such as trimming. The intention is not for heading to replace machining. There are many cases - very complex parts, larger parts or low production requirements - where machining is more economical, and some materials cannot be headed. Today, heading and cold forming allows more economical and faster production of many fasteners and other parts that previously could only be made with machining. Why Cold Heading Is Increasing Fasteners represent the single largest category of headed parts produced. Today, the multi-billion-dollar domestic fastener industry manufactures some 260 billion fasteners from a variety of materials. Manufacturers head and cold form a wide range of components - from spark plugs to axles. Cold heading and forming technologies continue to expand and improve. Recent Developments in Cold Heading/Forming Heading and cold forming machinery is much more advanced. For example, modern machines have five or more dies and features to allow the production of both long and short parts. One adjustment changes the cutter, feed stroke, transfer and kickout timing functions. CNC control gives the operator instant access to production data. Quick-change setups allow both punch and die components to be set up and adjusted off-line, so valuable production time is not wasted. Multi-station headers that perform a combination of upsetting, extruding and other cold forming operations have also significantly increased heading production rates and capabilities. Increasing metallurgical knowledge enables the heading and cold forming of tougher materials. Specialty alloy producers can more closely control the analysis and manufacture of grades to provide greater corrosion resistance and strength in headed parts. Where good cold forming qualities and consistent performance are desired, it is now possible to have certain AISI grades made within controlled analysis limits to improve cold formability and subsequent secondary machining operations. In other cases, analyses that have been modified for cold forming provide a means for the economical production of certain fastener designs. Tougher tool steels extend the life of heading dies. Specialty alloys producers must be able to provide alloys that are versatile enough to meet fabrication operations that call for both heading and machining. Finally, other heading practices, such as warm and hot heading, can extend the forming limits to include many superalloys. The second installment of this six-part series on heading basics will outline the heading process and define knockout pin specifics.
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