Thread Rolling

Thread rolling is the preferred method for producing strong, smooth, precise, and uniform external thread forms. Thread rolling is different from other types of threading processes like cutting, grinding, and chasing.

Thread rolling is a cold forging process that can be performed on any ductile metal. The forming process can be used to produce other special forms, such as knurls. For the best quality threads, the process is performed on precision centerless ground blanks. The blank diameter of a rolled thread is at the pitch diameter, a theoretical point between the major diameter and minor diameter.



Cylindrical Roll ThreadingThread Rolling Inc. produces rolled threads on a wide variety of parts. Often, rolled threads are required by design because of their superior tensile, shear, and fatigue strength. Other processes remove material to produce the thread form, but thread rolling displaces the material with hardened steel dies. These dies typically have a hardness between a range of Rc58-Rc63 and there is a specific set of dies for each thread size and each thread form. The dies have the reverse for of the finished thread.

The result of moving the material grains (molecules) into the shape of the thread rather than weakening it by removing material, is that the grains become denser at the critical parts of the thread, especially in the root and on the flank below the pitch diameter. This effect improves the quality of the thread form. Additionally, the burnishing action of the steel dies produces an excellent (better than Ra32) micro-finish. The superior finish improves assembly between external and internal threads and reduces wear between mating components, thereby extending their life. A smooth finish is another advantage that roll threaded components have over other threaded components.

Roll Threading

Process: In-feed Roll Threading
Thread types: 60º thread form/machine screw type threads/pipe threads
Forms: UNR, UNF, UNC, UNJ, UNJF, UNJC (classes 1A, 2A, 3A, 5A)
Metric forms: ISO and DIN (classes 6g and 4g6g)
Minimum size: .078 inch (2mm)
Maximum diameter: 2.500 inch (63mm)
Pitches: Coarse, Fine, Extra Fine
Material Hardness: Cold rolling to Rc45 depending on material type and size
Notes: Flight Safety Threads, System 22/23, QSLM, right and left hand
Volume: 1 piece to 100,000 pieces

Thread Inspection

We maintain a large inventory of calibrated thread gauges and inspect threads to both industry and customer standards. Typical industry specifications include AS8879, MIL-S-7742, Handbook H28, and ANSI specifications. Since our focus is on precision threads, we inspect all threads with indicating type variable gauging and maintain a wide range of English standard and metric thread gauges to cover the full spectrum of common and special sizes. Thread ring gauges are used for reference, but indicating gauging is necessary to adequately measure proper thread functionality.

Centerless Grinding for Thread Rolling

Though threads can be rolled on turned, screw machined, or headed parts; a final sizing process is often preferable. The highest quality threads are produced from the highest quality blanks. Centerless grinding of the pre-roll thread diameter (pitch diameter) is one of the most important steps in the process of rolling high precision threads. Centerless grinding permits us to develop the correct pitch diameter prior to roll thread and control the diameter within .0004 inch. (10 microns). Roundness is controlled within .000050 inch (1.25 microns), concentricity is ensured, and the grinding process provides a diameter with an excellent surface finish prior to thread rolling. Typically, customers supply their machined components at a specified oversized diameter and we centerless grind the finished diameter as part of our multi-step process to produce the highest quality rolled threads.

We also have the capability to provide centerless grinding services for threaded and non-threaded components.

Process: In-feed and thru-feed
Minimum in-feed diameter: .020 inch (.5mm)
Maximum in-feed diameter: 6.00 inch (150mm)
Maximum in-feed length: 4.00 inch (100mm)
Maximum thru-feed diameter: 4.00 inch (100mm)
Maximum thru feed length: 24.00 inches (600mm)
Volume: 1 piece to 20,000 pieces
Material hardness: Up to Rc65

Thread Laboratory

We operate an in-house metallurgical laboratory for the metallographic examination of rolled threads. Certain aerospace, military, and commercial specifications require that rolled threads be inspected for external and internal defects in the root, flanks, and crests. Examples of defects include over-laps, cracks, seams, craters, notches, folds, roughness, and oxide scale. We offer a turnkey thread rolling service that includes metallographic thread examination when required. The metallographic examination of threaded parts is a destructive testing procedure, so sampling is done per specification. Thread samples are longitudinally bisected, cleaned, mounted, ground, and polished to produce a metallographic specimen suitable for the inspection process. Prior to examination, the sample is etched to reveal the microstructure of the thread. This microstructure is characterized by the composition of individual grains of material (molecules) arranged in flowlines, which are denser at the critical parts of the thread, including the root and the flankbelow the pitch diameter. The inspection process includes the microscopic examination of each thread at up to 500X. Each thread is checked for proper grain flow, defects, and other non-conformances. The appropriate test reports and certification are produced when required.

Customer Approvals: All AS Specifications (e.g. AS7460, AS7466), Kaman Aerospace KPS 547, Pratt & Whitney Aircraft PWA 96

Knurling

The same equipment used for thread rolling is used for high quality roll knurling. Typically, we help customers design their components to accommodate rolled knurls, and then we form the knurl with a value-added process.

Knurling is typically used to provide a uniform sure grip on an otherwise smooth surface. Knurled finishes for handles and grips are essential characteristics for tooling and components in a variety of industries, but especially important for surgical and other medical tooling and devices. We produce some of the finest knurled finishes in industry. Rolled knurls are superior in finish, form, and dimensional consistency to knurls formed by cutting or bump rolling on lathes and screw machines. Also, knurled components are used for metal parts that are molded into plastic or pressed into other metal components. The uniformly rough surface prevents slippage under stress.

Process: In-feed Roll Knurling
Knurl Types: Circular and Diametral Pitch
Circular: Straight, Diagonal, Diamond (Male and Female)
Pitches (teeth per inch): 12, 16, 20, 25, 30, 35, 40, 50, 80, special
Diametral: Straight and Diagonal
Diametral Pitches (DP): 64, 96, 128, 160, special
Minimum Size: .040 inch (1mm)
Maximum Diameter: 1.500 inch (38mm)
Material Hardness: Knurling to Rc42 depending on material type and size
Volume: 10 piece to 100,000 pieces

Raw Materials

Thread Rolling Inc. has experience roll threading and roll knurling parts made from a diverse range of metals.

Alloy Steel
Stainless Steel (300 Series, 400 series, etc.)
Carbon Steel
Aluminum
Titanium
Greek Ascoloy®
13-8MO
15-5PH
17-4PH
Inconel®
600/625/718
Stellite®
Invar®
Kovar®
Monel®
Hastelloy®
A-286®
L-605®
Custom 455®
MP159®
MP35N®
Nitronic 60®
Waspaloy®
René 41®
Tool Steel
Maraging Steel
Copper
Beryllium Copper
Brass