When parts are produced in larger quantities, single point threading’s versatility is less beneficial. This is because, in order to maximize effective tool life, single point inserts are processed with a limited depth of cut with multiple passes needed to cut to the thread’s full depth. The time needed to take these multiple passes can create a bottleneck. Additional passes may also be taken to deburr the thread, requiring more machine tool time or a secondary operation outside the machine. Although CNC is bringing down the total threading cycle times by making non cutting functions more efficient, these time savings are negated by the added time it takes to single point the thread. Thread rolling on the other hand, produces threads in one pass, reducing expensive CNC machining time.
In addition to doing more work on one machine in less time, thread rolling has many technical advantages over single point threading. Instead of cutting or shearing the material as is the case of single point threading, thread rolling cold forms the profile to be produced. In this process, the component material is stressed beyond its yield point, being deformed plastically, and thus permanently. A hardened die made from tool steel or HSS displaces the material along the contours of the thread profile, plastically deforming the material into the final form. The workpiece material is stressed beyond its yield point, which causes it to flow and conform to the mirror image of the die’s profile.
Rolling process is recommended when threads are required with superior tensile, shear, and fatigue strength. Other processes like turning, milling and grinding remove material to produce the thread form, but thread rolling displaces the material with hardened steel dies. Rolling dies typically have a hardness between a range of RC 58-63 and there is a specific set of dies for each thread size and each thread form.
Static tensile tests on parts formed through thread rolling show overall increases in strength of about 30 percent.
Fatigue strength is improved by 50-75 percent.
Tests on bolts first heat-treated to a hardness of 35-40 Rockwell C and subsequently rolled show even greater fatigue strength.
High benefits of Thread rolling process are:
✓ Lower costs
✓ Increased production
✓ Faster lead times
✓ Superior quality and accuracy:
○ Stronger threads
○ Improved finish
○ More accurate profile
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