Thread Rolling Machine Product

Overview

A thread rolling machine forms threads without cutting. A cylindrical blank is squeezed between two hardened Cylindrical Thread Die rolls whose surfaces carry a mirror image of the thread; under radial forces of 100-300 kN the blank material yields and flows, sinking into the die grooves to form the roots and extruding outward to form the crests. No chip is produced. The displaced grain structure follows the thread contour instead of being cut through, which raises fatigue strength of the finished thread by 30-70 % over a machined equivalent, and the cold-worked flanks come out smoother (Ra 0.2-0.4 µm) and harder than the parent metal. Essentially every high-volume bolt, wheel stud, and aerospace fastener is roll-threaded.

The blank is sized to the thread's pitch diameter, not its outside diameter, because rolling conserves volume: material squeezed below the pitch line reappears above it. For an M12×1.75 thread the blank is ground or drawn to about 10.86 mm. Blank tolerance is the first quality lever — a few hundredths oversize and the dies overfill and flake the crests.

Machine structure

The force loop runs through the Frame Casting, a closed cast frame of several tonnes proportioned so full rolling force stretches it only micrometres; any elasticity here shows up as pitch-diameter scatter. One die turns on the Fixed Die Spindle, whose Die Spindle Shaft runs in heavy Spindle Roller Bearing pairs that carry the rolling load continuously. The opposite die is on the Moving Die Spindle, mounted in a Slide Head guided by the frame's Slide Ways.

Both dies are driven, in the same direction and at the same speed, by the Spindle Drive Train: one Main Drive Motor through the Reduction Gearbox and a matched Timing Gear Set set that locks their angular phase. An articulated Articulated Drive Shaft keeps the moving spindle driven across its travel. Phase matters because the two dies must present their thread starts so the helix one die forms is continued, not crossed, by the other; "die match" is set at installation with the Axial Die Adjuster and verified on a test blank — mismatched dies cut each other's work and produce a drunken thread.

Hydraulic infeed

In infeed (plunge) rolling, the Hydraulic Infeed System drives the moving die radially into the blank. The Hydraulic Power Unit supplies 21 MPa to the Infeed Cylinder, metered by a Proportional Servo Valve following a programmed profile: rapid approach, controlled penetration over several blank revolutions (too fast overloads the die crests; typical penetration is spread over 15-30 revolutions), a dwell of 2-5 revolutions at full depth to round out the thread form, then retract. Two Pressure Sensor transducers close the force loop and trip the cycle if force runs outside the recipe window — the standard protection against a double-fed blank, which would otherwise shatter a die. A Positive Stop dead stop arrests the slide at final pitch diameter so part size repeats independent of oil temperature, with the Hydraulic Accumulator smoothing the pressure spike at die contact.

Through-feed rolling covers parts longer than the dies: the dies are dressed with a lead-in taper and skewed slightly so they screw the work axially past themselves, producing threaded rod of unlimited length.

Work support

The blank is not chucked. It rests on the Work Rest Blade, a carbide-faced blade held by the Rest Blade Holder between the dies, positioned by the Blade Height Adjuster so the blank center sits 0.1-0.3 mm below the die center line. Blade height is the second quality lever: too high and the blank climbs and chatters, too low and lead error creeps in. Blanks arrive along the Blank Guide from a bowl feeder or are placed by hand against the Foot Pedal cycle.

Control and consumables

The PLC Controller stores per-part recipes — force, ramp, dwell revolutions, die speed — presented on the LCD Panel HMI, and the Cycle Counter tracks pieces per die set against a replacement schedule. Dies are the principal consumable: ground tool-steel rolls at 58-62 HRC costing a few hundred to a few thousand dollars per pair, amortized over 10⁵-10⁶ parts. Flood lubrication from the Nozzle Bar with EP rolling oil, filtered by the Rolling Oil Filter, keeps fines out of the contact — embedded particles print into every subsequent flank. Cycle times of a few seconds per part and the absence of chips, with material savings of 15-20 % over cut threads from the smaller blank, are what make rolling the default threading process at volume.