This is the fifth in a six-part series on heading basics. This installment outlines the types of heading machines.

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. Request a free copy of "Heading Hints."

Many types of heading machines are available and they combine standard and special tooling to carry out a variety of heading and cold forming operations and sequences. Some weigh as much as 500,000 pounds and have seven die stations. Since only so much metal can be formed in one blow, the number of dies and wire diameter acceptance range are usually used to describe machine types. Typical measurements cover wire diameter, blank length and heading force.

Specifications for a typical solid-die header may be:

Max. Diameter Wire = 1/4" (Force available at cut-off knife for shearing).

Max. Shank Length = 2" (Approximately 8 times wire diameter).

Max. Wire Cut-off Length = 3-1/8" (About 12 times rated wire diameter).

Max. Pieces per Minute = 125 (Optimum machine rotation speed).

Max. Heading Capacity = 50 tons (Force required to upset a carriage bolt of the rated wire diameter wire, in this case 1/4").

Machine specs tend to be conservative. It is best to discuss questions about machine capabilities, or which type of header to purchase, with the manufacturer.

Heading machines are divided into two basic types, crank and toggle headers (Figure 1). The toggle type, the older version, provides a mechanical advantage and gives two forward strokes per machine revolution. The crank machine is capable of one blow per revolution. Neither is considered to be more advantageous. The toggle type is used to produce simpler parts, while the crank version, which is more prevalent today, is used for more complex forming.

There are several fundamental and critical points for proper heading machine setup. These include:

Material Selection: Regardless of the wire, adequate records are essential. Careful documentation includes writing down the lot number, heat number, wire condition and previous results. Save the original wire tag and apply it to any coil remainder.

Feeding: Properly sized feed rolls are important, yet often overlooked. With the wrong size rolls, several problems can occur. Galling may result during the heading stage with out-of-round wire; wire surface can be scratched; and slippage, resulting in short feeds, often comes with improper machine timing and tool alignment. The latter also means excessive tool breakage.

Quill: Good quill design calls for complete elimination of obstructions in the I.D. Sharp corners should be avoided. The inside bearing surface is usually just large enough to permit the wire to fit easily without being "sloppy." Excessive I.D. clearance will create a poor shearing action that results in a burr on the cut-off blank. This, in turn, causes problems in the heading stage.

Shearing: To produce consistent cleanly cut blanks, the cut-off knife should be made from a highly wear-resistant steel. Carpenter No. 610® alloy, a high-carbon, high-chrome tool steel, has been used in such applications.

Wire Stop Nib: The nib should have a hard, square contact surface to provide for maximum wear resistance without causing burr formation.

These are the common machines available:

Single-Stroke: Has one die, one punch. These are used to make simple parts that can be formed in one blow. Ball headers are a variation of this type. Production rates up to 600 parts per minute are possible.

Single-Die, Double-Stroke: Considered the most versatile and widely used machine. It includes one die, two punches, and produces most screw blanks and other fasteners. Wire capacity ranges up to 3/4"’ diameter. Production up to 450 parts per minute. Some double-stroke headers are custom designed for tubular rivet production.

Three Blow, Two Die: Includes two dies and three punches, and has the same basic design as the double-stroke header. It offers an added advantage of extruding or upsetting in the first die, with double-blow heading, or heading and trimming in the second die. It’s used to produce large-head small-shank fasteners, or parts requiring trapped extrusion and upsetting. It’s also excellent for making stepped-diameter parts where transfer between dies would be difficult.

Progressive or Multi-Station: These are equipped with as many as seven die stations; most are two- to five-die machines with an identical number of punches. A simple transfer mechanism moves workpieces from the cutter through successive dies. Multiple upsetting blows, combined with extruding, piercing and trimming, make these machines ideal for long shank parts production. They can accommodate materials up to an inch in diameter with under-the-head parts lengths of up to nine inches.

Boltmakers: These are three- and four-die headers that combine heading, trimming, pointing and threading in the same machine. Materials up to 1-1/2" in diameter are used, and production rates vary up to 300 pieces per minute. Boltmakers produce completely finished hexagonal and socket capscrews, as well as a number of other special threaded parts.

Cold Nut Formers: Standard or special nuts are run on this machine with five die stations. A simple transfer mechanism rotates the blanks end-for-end between successive dies, which allows for working of the metal on both sides to produce high quality nut blanks. Center plugs are easily reclaimable, so there is very little material waste. Nuts an inch or larger are run on this machine.

Cold Formers: Four, five or six die stations and a variety of transfer mechanisms make these the most versatile heading machines. Forming operations for making odd-shaped parts can be combined on this one machine. They are set up to feed wire, bar or blanks, and can form metal cold or warm. Materials in the 2" diameter and larger range can be run. Multiple upsetting blows combined with extruding, piercing and trimming operations make cold formers ideal for producing long shank or specially designed components.

All the above machines have five basic operations—upsetting, extruding (forward and backward), trimming and piercing. Other related operations like swaging, coining or embossing can also be performed. Since all heading machines include a predetermined number of die stations or operations, the design of parts must match equipment capabilities.