Controlled Deep Rolling of External Thread Root Radii

FX-90 is a mechanical single-roller tool developed for the controlled deep rolling of thread root radii in external threads. In threaded connections, fatigue cracks most commonly initiate at stress concentration points located at the thread root. FX-90 creates controlled plastic deformation in this critical area, generating permanent compressive residual stresses beneath the surface, helping to reduce micro-notch effects and improve the fatigue strength of the thread root region.

The rolling force is generated through the mechanical spring system inside the tool body and transferred to the thread root area via the roller. During the process, the roller follows the thread profile and produces precise and controlled deformation at the root radius. The roller geometry is selected according to the thread root radius and application requirements.

FX-90 enables deep rolling of external threaded components directly within the machine’s threading cycle. This allows the process, under suitable process conditions, to be completed in the same setup immediately after turning or threading operations. This approach increases process reliability while improving productivity by reducing the need for additional operations.

Especially in safety-critical applications such as heavily loaded threaded connections, press spindles, hydraulic connections, oilfield equipment, and mechanical press columns, FX-90 provides an effective solution for achieving more reliable and longer-lasting threaded connections.

Applications

FX-90 is used in components where the fatigue strength of external thread root radii is critical. It provides an effective solution for improving process reliability and component life in external threaded connections operating under dynamic loads, tensile-compressive loads, bending, torsion, or fluctuating stresses.

Main Application Areas:

• External threaded lead screws
• Tie rods for press and injection molding machines
• Hydraulic pistons and connection components
• Mechanical press columns
• Threaded connections used in oilfield equipment
• External threaded fastening components exposed to high loads
• Large-diameter or safety-critical external threaded components
• Applications where fatigue crack initiation is concentrated at the thread root

FX-90 acts directly on the root radius of external threads. Unlike conventional surface polishing or surface finishing methods, it focuses specifically on the critical geometric area that determines the fatigue performance of the component.

Features

• Developed for deep rolling of thread root radii in external threads
• Mechanical single-roller deep rolling tool design
• Suitable for operation within the threading cycle
• Can be used on CNC and conventional lathes
• Suitable for both right-hand and left-hand threads without conversion
• Designed for operation in both rotational directions
• Axially movable roller structure helps compensate for minor positioning deviations
• Roller angle is designed to automatically adapt to different thread pitches
• Roller selection can be matched to the thread root radius of the workpiece
• Rolling force can be monitored via the dial indicator mounted on the tool
• Spring-supported tool body ensures controlled and repeatable force transmission
• Enables deep rolling in the same setup after turning or threading operations

Advantages

FX-90 strengthens one of the most critical regions in threaded connections — the thread root — in a controlled manner. As a result, not only the surface but also the subsurface region of the component is mechanically improved.

Key Advantages:

• Helps increase fatigue strength in external threads
• Reduces the risk of crack initiation in the thread root area
• Generates permanent compressive residual stresses beneath the surface
• Reduces micro-notch effects in the thread root region
• Contributes to extended component service life
• Easily integrated into production since processing can be performed in the same setup
• Can reduce the need for additional operations and part handling
• Suitable for CNC and conventional lathes
• Flexible use for both right-hand and left-hand threads
• Controlled rolling force provides repeatable process quality
• Wide application range thanks to the roller structure adapting to different thread pitches
• Helps improve reliability in heavily loaded external threaded connections

During the deep rolling process, compressive residual stresses are generated in the thread root region, the material is strengthened through cold working effects, and surface micro-notches are reduced. These three effects play a key role in improving the durability of threaded connections operating under fluctuating loads.

Tool Structure

The FX-90 Deep Rolling Tool consists of a tool shank, spring-supported tool body, roller carrier head, rolling roller, roller holder, dial indicator, and connection elements. The spring system inside the tool body enables controlled generation of the rolling force. This force is transferred to the thread root radius through the tool body and roller carrier.

The roller holder is connected to the elastic section of the tool body. The roller follows the thread profile and creates controlled plastic deformation at the thread root radius. The roller structure of the FX-90 is capable of angular movement to adapt to different thread pitches. This feature provides ease of use for different thread pitches as well as right-hand and left-hand threads.

The dial indicator included in the standard version indirectly displays the spring force. The operator can monitor the rolling force through this indicator and make necessary adjustments during the process. The tool can also be configured for special applications with different roller diameters, different thread root radii, and various tool shank connections.

Processing Parameters

For deep rolling with FX-90, the process parameters should be determined according to the workpiece material, yield strength, thread dimensions, thread root radius, workpiece diameter, and the desired process effect.

With the correct roller selection, proper rolling force, and controlled process application, FX-90 provides a powerful deep rolling solution that helps improve fatigue strength in external threaded connections while being easy to integrate into production processes.