During the thread rolling process, a hard die is pressed onto a rotating workpiece that is attached to the thread rolling machine. The thread rolling machine gradually increases the force that is applied to the workpiece. This force rolls the thread profile from the hard die onto the attached blank. The material on the blank is displaced to form the roots of the thread and the displaced material flows outward.
Both of these metalcutting processes are used to remove material to create the desired thread geometry. This illustration shows the difference in grain flow between a rolled thread, left, and a cut thread, right. Additional tensile strength and improved surface finish are inherent by-products of the thread rolling process. To produce a spiral strip helical wrap-on fin tube, the machine 30 comprises a tube guide 81 which is free to rotate in block 82 (see FIG. 9). The tube guide 81 has an angular face to match the angle of the pressure roll 83. The fin strip coil 84 (see FIGS. 1 and 2) is resting on coil stand 85 and is free to unwind.
Loop chain 41 wraps around sprockets 52 to form a drive system for shaft 60 and shaft 61. When motor 32 is running and transmission 34 is in gear, the drive train heretofore described will power the shaft 55, shaft 60 and shaft 61. Mounted on shaft 55, shaft 60 and shaft 61, are universal joint drives 92, which are attached at the opposite end to the arbors 70 (see FIG. 4). Arbors 70 are held in place by the arbor blocks 44 and the arbors 70 are free to rotate. Mounted on the arbors 70 are the discs 71 which do the finning and are held in place by nut 72 (see FIGS. 6 and 11). The arbor blocks 44 are bolted to the sliding jaws of the chuck 42.
The strip advances toward the tube, pulled by the pressure roll pressing the strip against the powered spinning tube guide. The formed base of the “L” strip lies on the upper outer edge of the pressure roll prior to wrapping around the tube. To produce a threaded rod, the transmission is shifted to the forward direction associated with the making of finned tubes and the smoothed driving wheels or finning discs are changed to cylindrical dies for rolling threads. The dies are set to the desired depth by closing the chuck on the adjusting screw, thus moving the arbor blocks down. The motor will drive the three cylindrical dies in a rotating motion. The stock to be threaded is fed into the dies and the dies which are set on a helical angle and rotating will grab the stock and feed it through the dies producing a threaded rod, tube or bar.
Because the blank material is plastically deformed by pressure in the thread rolling process, it should have a minimum elongation of 5 percent and a maximum tensile strength of 246,000 psi. While the initial costs of all three types of thread rolling systems are higher than single point threading systems, the long – term costs are lower due to longer tool life and substantially shorter machining times. Although initial cost savings may be a more tangible benefit, customers must consider the techincal and economic advantages offered by thread rolling in the long term. FETTE Thread rolling heads/ attachments can be used on almost any type of machine tool, including CNC automatic lathes, basic engine lathes, rotary transfer machines, and machining centers. Thread rolling creates a tremendous amount of heat very quickly.
Mics with such anvils are usually called “thread mics” or “pitch mics” . Users who lack thread mics rely instead on the “3-wire method”, which involves placing 3 short pieces of wire of known diameter into the valleys of the thread and then measuring from wire to wire with standard anvils. A conversion factor is then multiplied with the measured value to infer a measurement of the thread’s pitch diameter. Tables of these conversion factors were established many decades ago for all standard thread sizes, so today a user need only take the measurement and then perform the table lookup . The 3-wire method is also used when high precision is needed to inspect a specific diameter, commonly the pitch diameter, or on specialty threads such as multi-start or when the thread angle is not 60°.
All the advantages of cold forming are embodied by MEGA THREAD ROLLING MACHINES, such as uninterrupted grain flow material and surface consolidation, bright surface finish and substantial saving in production times. 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.
Every thread form, shape, and size has a unique set of dies which are typically ground from heat treated tool steel (typically Rockwell C 58-62) and procured, rather than made in-house. Profimach provides high precision two and three dies spline and thread rolling machines. We deliver very robust machines for cold rolling of high tensile materials such as 12.9 steel, titanium, inconel and other exotic alloys. The machines are supplied with Manual, PLC, NC or CNC controls for a quick machine set up and simple use. A simple but good designed hydraulic system allows a shorter cycle time and less mainte