What are the selection criteria and usage techniques for follow-up tool holders when processing seamless steel pipe fittings

First, what are the core criteria for selecting follow-up tool holders in seamless steel pipe fitting processing?

1. Selection Based on the Structural Parameters of Seamless Steel Pipe Fittings

(1) Pipe Diameter Compatibility: The opening and closing range of the follow-up tool holder's support claws must cover the pipe diameter. Adjustable opening and closing structures are preferred to ensure close contact with the outer diameter of steel pipes of different specifications. For reducing pipes, replaceable support claws can be used, with a fit of≥90%.

(2) Length-to-Diameter Ratio Matching of Seamless Steel Pipe Fittings: When the length-to-diameter ratio of the fitting is >10, a multi-claw linkage follow-up tool holder should be selected to evenly distribute the support force; when the length-to-diameter ratio is ≤10, a simple double-claw follow-up tool holder can be selected, balancing flexibility and stability. For bent fittings, a rotatable follow-up tool holder should be selected, with the support claws adaptively adjusting their angle along the curved surface of the fitting.

(3) Wall Thickness Compatibility of Seamless Steel Pipe Fittings: Thin-walled fittings require flexible support, follow-tool holders with polyurethane or nylon support claws, and a contact pressure ≤5MPa to avoid damaging the pipe wall; thick-walled fittings can use rigid support, follow-tool holders with carbide support claws to improve vibration resistance.

2. Tooling Selection Based on Machining Center and Seamless Steel Pipe Fittings

(1) Installation Method Matching of Seamless Steel Pipe Fittings: Vertical machining centers should prioritize side-mounted follow-tool holders, fixed to the worktable via T-slots; horizontal machining centers should use top-mounted or linked follow-tool holders, connected to the main frame of the tooling via standardized interfaces, with a repeatability error ≤±0.02mm.

(2) Power Selection for Seamless Steel Pipe Fittings: Manual follow-tool holders are suitable for small-batch processing with an adjustment accuracy of ±0.01mm; large-batch automated processing requires hydraulic/pneumatic driven follow-tool holders, which can be linked with the tooling clamping mechanism to achieve adaptive adjustment of support force, with a response time ≤0.5s.

(3) Compatibility Requirements for Seamless Steel Pipe Fittings: The follower post must avoid the tool path and provide a coolant channel to prevent interference with chip removal. Modular follower posts are preferred, allowing for quick changes in support claw type to accommodate different machining features such as threads and stepped holes.

Second, Key Techniques for Using Follower Posts in Seamless Steel Pipe Fitting Machining

1. How to Install and Position Seamless Steel Pipe Fittings for Machining and Adjustment

(1) Reference Alignment: During installation, ensure the coaxiality between the center of the follower post support claw and the pipe axis is ≤0.015mm. This can be checked and adjusted using a dial indicator. Use the tooling positioning pin or plate as a reference to fine-tune the front-to-back and left-to-right positions of the follower post to prevent the support point from deviating from the pipe's center of gravity.

(2) Support Claw Adjustment: The contact between the support claw and the outer circle of the seamless steel pipe fitting must be uniform. The contact area of a single support claw should be ≥20mm² to avoid point contact leading to localized stress concentration. During adjustment, manually rotate the pipe fitting to feel the uniformity of support resistance; there should be no jamming or loosening.

(3) Pre-tightening force control: Adjust the pre-tightening force according to the material of the seamless steel pipe fitting: 3-8MPa for stainless steel fittings, 8-15MPa for alloy steel fittings, and 10- 20MPa for carbon steel fittings. Excessive pre-tightening force can easily cause deformation of the seamless steel pipe fitting, while insufficient pre-tightening force cannot suppress vibration. Real-time monitoring can be achieved through pressure sensors.

2. Optimization operations during the processing of seamless steel pipe fittings

(1) Segmented support strategy: For ultra-long seamless steel pipe fittings, adopt "multi-point segmented support," setting a follower tool every 500-800mm. The follower tool closer to the processing area receives priority force, while the follower tool further away assists in preventing slippage, effectively reducing deflection deformation.

(2) Dynamic adjustment techniques: If vibration occurs during processing, gradually increase the support force, or replace it with arc-shaped support claws to increase the contact area; if indentations are found on the surface of the fitting, immediately reduce the pre-tightening force and replace it with flexible support claws.

(3) Coordination with Tooling: The follower post must be linked with the auxiliary support pin of the tooling. Before processing, the middle of the pipe fitting should be pre-supported by the pin, and then the follower post should be adjusted to clamp, avoiding excessive force on a single support point. For multi-branched pipe fittings, the follower post support point should avoid the branching parts, select the straight section of the pipe fitting, and cooperate with the anti-torsion limit block to restrict rotation.

3. Maintenance and Precision Maintenance of Seamless Steel Pipe Fittings

(1) Regular Lubrication: Apply high-temperature grease weekly to the sliding guide rails of the support claws, adjusting screws, etc., to prevent wear from causing a decrease in adjustment accuracy. The lubrication cycle can be adjusted according to the processing intensity.

(2) Replacement of Wearing Support Claws: When the wear on the contact surface of the support claw is >0.1mm, replace the support claw or repair the contact surface in time to avoid a decrease in positioning accuracy due to poor contact. Flexible support claws need to be checked for material aging regularly and replaced immediately after aging.

(3) Precision Calibration: Monthly calibration of the coaxiality and support stability of the tool holder using a standard mandrel. If the deviation exceeds ±0.02mm, compensation is made by adjusting the screw or shims to ensure long-term accuracy.

Third, a typical application scenario optimization case of seamless steel pipe fitting processing

Taking the processing of DN80 stainless steel slender pipe with a length-to-diameter ratio of 15 as an example, it is necessary to process the outer diameter thread and the end step, with a dimensional tolerance of ±0.03mm:

(1) Selection: Use a 3-jaw hydraulic linkage follower tool holder, with polyurethane support claws, an opening and closing range of 60-100mm, and suitable for pipe diameter.

(2) Usage tips: During installation, use the tool positioning pin as the reference, calibrate the coaxiality between the support claw and the pipe fitting axis to ≤0.01mm, and set the preload to 6MPa; when processing threads, keep a 50mm gap between the follower tool holder and the tool, and move synchronously with the processing progress to suppress vibration;

(3) Effect: After processing, the straightness of the pipe fitting is ≤0.02mm/m, the thread pitch error is ≤0.015mm, there are no indentations on the surface, the processing efficiency is increased by 30% compared with no follower tool holder, and the scrap rate is reduced from 2.2% to 0.5%.