a tool for producing a screw thread by plastic deformation without chip removal. Threadrolling tools include plane thread-rolling dies, thread-rolling rolls, thread-rolling rolls with arched or ring-shaped dies (rarely used), and thread-rolling heads.
Plane thread-rolling dies are used in thread-rolling machines for thread rolling with a precision of class 2. Each unit consists of a mobile and a stationary die. The working face of the die contains intake, calibrating, and output parts long enough to ensure several full revolutions of the blank, which press and calibrate a full thread profile on the blank.
In terms of pitch and angle of thread profile, it is possible to produce thread of greater precision with rolls than with dies; there is also less surface roughness. The diameter of the roll exceeds by several times the diameter of the thread being rolled. Thread-rolling rolls are supplied in sets of two for use in automatic thread-rolling machines with interaxial distances of 130–230 mm (type A) and 90–135 mm (type B). Thread rolling on rod blanks employs rolling dies of type NP, whereas type NPT is used for thin-walled pipes. Rolling is done by means of lathes, turret lathes, drills, bolt-threading machines, and special semiautomatic and automatic machines; sometimes it is done manually. These operations lead to a thread of class 2 precision and a surface roughness of class 6–7. The die design makes it possible to control the position of the thread-rolling rolls, which permits thread of the same pitch to be rolled onto parts of varying diameters.
Thread-rolling heads roll metric thread 4–52 mm in diameter (type VNGN), trapezoidal thread (VNGN-trap.), metric thread 2–4 mm in diameter (VNGK), and thread for thin-walled pipes (VNGT). When the heads are equipped with special rolls, taper thread may be produced. Compared to thread-cutting heads, thread-rolling heads increase labor productivity by a factor of 5, increase thread strength, ensure a high level of precision (to classes 2–3), and decrease surface roughness (to classes 7–9).
REFERENCEChetverikov, S. S. Metallorezhushchie instrumenty, 5th ed. Moscow, 1965.
A. A. SHISHKIN