The LMT Fette Tangential Rolling System T18F-T27F is a specialized tool designed for chipless thread forming, offering significant advantages in economic viability and efficiency. This system operates on the plunge method, where the rolling head moves laterally onto a rotating workpiece, forming the thread within a few rotations before retracting. This cold-forming process ensures an uninterrupted flow of fibers within the thread profile, preventing notch effects and resulting in threads with high fatigue strength, wear resistance, and corrosion resistance.
Function Description:
The core of the system is the rolling head, available in T18F and T27F sizes, which houses a set of two synchronized thread rolls. These rolls, driven by the workpiece's rotation via a gear unit, form the thread profile. The system is particularly suited for rolling threads in front of or behind a shoulder, especially for short threads where the thread length is limited by the maximum roll width. It can produce various profiles, including threads behind a shoulder, extremely short threads, threads with very short run-outs (approx. 1 x pitch), tapered threads, knurling profiles as per DIN 82, burnishing, and other forms. The rolling head can be installed on any machine tool equipped with automatic feed motion, using a rolling head holder adapted to the machine's tool holder (e.g., T-slot, parallel shank, prisma, or square mount).
Important Technical Specifications:
The tangential rolling heads cover a working range of up to 64 mm.
For parallel threads:
- T18F: Workpiece major diameter from 2 mm (5/64 inch) to 30 mm (1 3/16 inch), max pitch 2 mm (12 threads/inch), max roll width 21.5 mm (0.8465 inch).
- T27F: Workpiece major diameter from 2 mm (5/64 inch) to 42 mm (1 5/8 inch), max pitch 2.5 mm (10 threads/inch), max roll width 31 mm (1.2205 inch).
For tapered threads, the system supports standards like DIN 158, DIN 2999, DIN 3858, and ANSI B 1.20.1 NPT/NPTF, with specific ranges for metric and Whitworth profiles.
The system is suitable for metallic materials with a breaking elongation A ≥ 7% and a tensile strength Rm not exceeding approximately 1000 N/mm² (145,000 Pa), or up to 1700 N/mm² (246,000 Pa) for very small forming volumes. Suitable materials include structural and case-hardening steels, stainless steels, and heat-treated steels up to approx. 1600 N/mm² (232,000 Pa), as well as soft brass, copper, light metals, and ferritic castings. Brittle materials like gray cast iron, hard brass alloys, and hardened materials are not suitable.
The maximum rollable thread length L is estimated based on tensile strength, major diameter d, and thread pitch P, with formulas provided for different tensile strength ranges.
The blank diameter
da for the thread to be rolled is typically d2 - 0.3 mm (pitch diameter minus 0.3 mm).
Recommended rolling speed v is 20–60 m/min, with up to 100 m/min possible for specific applications. A minimum speed of 20 m/min is crucial for material flow.
The number of workpiece rotations nw should be between 10 and 35, depending on rolling head size, thread pitch, thread length, and material tensile strength.
The tangential force FT required for rolling is calculated based on material constant, thread length, pitch, and number of starts on the roll.
The rolling time tr is a function of working feed time and dwell time, calculated based on spindle RPM or rolling speed.
Usage Features:
The system is designed for ease of use, requiring only a short training period for cost-effective production.
- Roll Selection and Labeling: Each thread size requires a set of two distinct thread rolls, labeled 1 and 2. Rolls are marked with thread size, code number, ID number, and a unique set number to prevent mixing.
- Setting Gauge: A dedicated setting gauge is used to precisely adjust the distance between the thread rolls (equivalent to the minor diameter
d3 of the thread) and to set the transverse stroke length. The rolling head size and consecutive number of the setting gauge must match those of the thread rolls.
- Assembly and Installation:
- Gear Settings: The synchronous operation of the gear unit must be checked by ensuring the driving claws of the pinion engage correctly with a steel reference gauge.
- Thread Roll Insertion: Thread rolls have a defined position, with specific markings (1 and 2) on the rolls and the rolling head arms to ensure correct orientation towards the workpiece. Molybdenum sulfide grease should be applied to the roll hole and carbide axis for optimal frictional behavior.
- Axial Rolling Clearance: This is adjusted after mounting the rolls by loosening a clamping screw, rotating a bushing, and then retightening. A maximum clearance of 0.05 mm (0.002 inch) is critical, especially for fine threads, to prevent chip formation.
- Distance Between Axes: Adjusted using set screws until the setting gauge fits exactly between the rolls, ensuring symmetrical opening/closing of the hinge.
- Workpiece Preparation: Workpieces must be pre-machined and chamfered immediately before rolling to ensure optimum true-running. An undercut as per DIN 76-A is recommended. The blank diameter
da is critical and must be maintained within a tolerance of ± 0.015 mm (0.0005 inch). Larger chamfers reduce tool life.
- Pendulum Clearance: The rolling head is inserted into the holder at a slightly inclined angle, allowing the first roll to touch the workpiece, and then centering the head during rolling. This clearance is achieved either with a spring-loaded bolt and stop bolt or a spring steel sheet, adjusted to approx. 0.5 mm (0.02 inch).
- First Rolling Process: Always use the calculated working feed (machine tool set to 100%) and never reduce RPM or operate in single-block mode. The goal is a "non-formed" thread tooth (Tooth 1 in Figure 22) for stability, avoiding over-forming (Tooth 3) which reduces roll tool life.
- Tapered Threads: Special considerations for setting the distance between axes and traverse paths are necessary, using the setting gauge at the largest roll diameter and ensuring the gauge touches the workpiece at the reference plane of the tapered thread.
- Knurling and Burnishing: Requires a special tangential rolling head or modification of an existing one with a kit (spacer and bushing) to replace driving grooves. The blank diameter
dA for burnishing/knurling should be within ± 0.015 mm (0.0006 inch) of the desired finished size.
Maintenance Features:
Regular cleaning, maintenance, and servicing are essential for proper function and extended tool life.
- Weekly (recommended daily):
- Remove rolling head from holder, clean chips, and reinsert.
- Check and adjust axial rolling clearance (max. 0.05 mm | 0.002 inch).
- Loosen cap screws, pull out axis, remove thread rolls, clean rolls, axis, washer, and bushing, apply molybdenum sulfide grease, and reinsert.
- Check washer (ET-15) for even wear; replace if thickness differs by > 0.05 mm (0.02 inch) between washers, or if thickness is less than 0.45 mm (0.018 inch) for T18F, or less than 0.6 mm (0.024 inch) for T27F.
- Weekly: Lubricate synchronous gear via nipples or connect to central lubrication system.
- Every three months/after long non-use:
- Disassemble the complete tool, remove contamination/chips, and lubricate all parts during reassembly.
- Visually inspect all parts for run-in marks, especially the axis (ET-3) in carbide bushings, gears in tooth flanks, pinion (ET-8) in driving cams, and hinge parts in the washer region (ET-15). If substantial wear (> 0.05 mm | 0.002 inch) is found, parts should be replaced or reworked. Alternatively, the rolling head can be sent to LMT Fette for inspection.
- Wear Parts: Key wear parts include washers (ET-15), spindles (ET-3), pinions (ET-8), gears (ET-10, ET-11, ET-12), and bushings (ET-13). It is recommended to keep a supply of these parts.
- Coolants and Lubricants: Sufficient supply of clean coolant (emulsions 1:10 to 1:20, or low-viscosity cutting oils) is necessary to dissipate heat and minimize wear. Coolant must be free of chips and particles. The rolling head should ideally be connected to the machine tool's central lubrication/cooling system.
The manual emphasizes safety, providing clear warnings and instructions for handling, transport, storage, and disposal of the tool and its components. It also offers comprehensive service information, including hotlines, maintenance and repair services, engineering support, and training seminars.
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