Aero Engine Turbine Disc Tongue And Groove Broaching Solution

Introduction

The turbine disc is one of the core components in thermal engines such as aero engines and gas turbines, and is a key component of the turbine rotor. The turbine blade is fixed on the edge of the turbine disc, and the high-temperature and high-pressure gas impact blade makes it rotate, driving the turbine disc to rotate, converting the thermal energy of the gas into mechanical energy, driving the compressor and other accessories to work, and is the core carrier of engine power transmission.
The turbine disc is made of a superalloy, such as the nickel-based alloy Inconel 718, which has excellent high temperature resistance, creep resistance, and oxidation resistance.
The broaching process of turbine disc tongue and groove is a key precision machining technique in aero engine and gas turbine manufacturing, used to machine the tongue and groove (or tenon) on which the turbine blades are mounted on the turbine disc.

1.Core Objective of the Plan

This solution aims at the core requirements of tongue and groove broaching in aero engine turbine discs, clarifying the following four major goals to ensure that the machining quality and efficiency meet aviation manufacturing standards:

1. Accuracy up to standard: the dimensional tolerance of the tongue and groove is controlled within ±0.005mm, the contour is ≤0.01mm, the surface roughness Ra≤0.8μm, the transition fillet of the tongue and groove edge (R0.4~R0.6) is smooth and consistent, and the shape and position tolerance (parallelism, perpendicularity) meets the design requirements, and there are no burrs, cracks and other defects;
2. Efficiency improvement: Compared with traditional hydraulic broaching, the processing efficiency is increased by more than 30%, and the processing cycle of the whole circumference of the single turbine disc is controlled within a reasonable range, which adapts to the needs of mass production and can achieve 24-hour non-stop machining.
3. Stability guarantee: the tool life is increased by more than 50%, there is no obvious vibration, knife punching, interference and other abnormalities during the processing process, and the batch processing pass rate ≥ 99.5%, effectively reducing the scrap rate of parts;
4. Compatibility and adaptation: It can be compatible with the processing of turbine discs of different specifications and different tongue and groove types (longitudinal tree shape, dovetail shape), taking into account the broaching needs of complex structure turbine discs such as thin walls and semi-closed cavities, and has the ability to flexibly adjust.

2.Machining challenges of turbo disc tenon slots

1. The processing accuracy of Hangfa’s parts is extremely demanding

• Tongue and groove profile accuracy: The tongue and groove profile of dovetail tongue/fir tree type is required to be ≤ 0.015mm, and the straightness of the side wall needs to be guaranteed to be 0.005mm/m
• Position tolerance: 80-120 tongues and grooves evenly distributed around the periphery, the cumulative indexing error takes ≤ 20 arcseconds

2. The turbine disc material is special (stainless steel, superalloy, titanium alloy, etc.), which is difficult to process

• Difficult to cut superalloys: Inconel 718/nickel-based alloy (tensile strength ≥ 1400MPa) is commonly used in turbine discs, which has a significant tendency to work hardening, and the tool is prone to diffusion wear and crescent wear
• Dissimilar material composite structure: Some new turbine discs use metal matrix composites (MMC) to enhance hardness to accelerate tool chipping

3. High requirements for dynamic stability, anti-vibration and burr suppression in the machining process

• Long overhang machining vibration: The cutter bar suspension has a diameter ratio of ≥ 10:1 during deep grooving machining, which is prone to cause chatter and cause surface ripple (Ra>0.8μm)
• Machining heat: Continuous broaching generates an instantaneous high temperature of 400-600°C, resulting in an over-deviation of the local thermal expansion of the workpiece
• Burr Suppression: The burr height of the tongue and groove edge is ≤ 5μm, which has unique requirements for tool edge design

3.Implementation of Core Turning and Milling Process

Adopting the core process idea of “step-by-step broaching, precise temperature control, dynamic vibration prevention, and real-time detection”, broaching is implemented in stages, focusing on controlling the three key factors of machining deformation, cutting heat, and tool wear to ensure processing quality and efficiency. According to the processing needs, two process modes of CNC high-speed side broaching or electrolytic broaching can be selected to adapt to the tongue and groove processing of turbine discs with different structure and precision requirements.

3.1 Optimized clamping positioning

The “three-point positioning + flexible clamping” scheme is used to avoid the deformation of the workpiece caused by clamping stress and ensure the positioning accuracy:

1. Positioning reference: take the inner hole and end face of the turbine disc as the positioning reference, use the positioning pin and the positioning disc to achieve three-point positioning, and the positioning accuracy ≤ 0.001mm; The positioning surface needs to be ground in advance, and the surface roughness Ra≤ 0.2μm to avoid positioning errors;
2. Clamping method: The flexible clamping mechanism is adopted, and flexible gaskets (such as polyurethane gaskets) are added to the thin-walled and easily deformed parts, and the clamping force is controlled at 5~8MPa, and the clamping force is evenly distributed to avoid the deformation of the turbine disc caused by local stress concentration. After clamping, use a dial indicator to detect the runout of the workpiece, the runout is ≤ 0.002mm, and if it is unqualified, it will be re-clamped.
3. Auxiliary support: For semi-closed cavities and deep cavity turbine discs, adjustable auxiliary supports are set inside the cavity to improve the rigidity of the workpiece and reduce vibration and deformation during broaching.

3.2 Step-by-step broaching process implementation

According to the steps of “grooving→ rough drawing→ fine drawing→ edge smoothing”, broaching is carried out step by step, and the accuracy is tested after each step of processing, and the parameters are adjusted in time to ensure the processing quality:

1. Step 1: Slotting processing (1st~7th grooving knife). The CNC high-speed side broaching machine is adopted, the broaching speed is controlled at 1m/min, the feed rate is matched with the tooth lift, and the tongue and groove prototype is gradually opened, and 70%~80% of the machining allowance is removed; During the processing process, high-pressure cooling is turned on, and the cooling oil is accurately sprayed into the cutting area, taking away the cutting heat and assisting chip evacuation. After each grooving knife is completed, the opening size and depth of the tongue and groove are checked to ensure that it meets the intermediate requirements and avoid uneven subsequent machining allowances.
2. Step 2: Roughing (8th~12th rough broaching knives). The groating speed is maintained at 1m/min, and the tongue and groove profile, bottom structure and top arc of the tooth are gradually trimmed, and 90% of the remaining allowance is removed. Focus on controlling the cutting resistance to avoid tool overload, and after each rough broach is processed, the contour of the tongue and groove (≤0.03mm) is detected, and the broaching parameters are fine-tuned in time.
3. Step 3: Finishing (13th~14th broaching). The broaching speed is adjusted to 1~1.5m/min, and the tooth lift is reduced to 0~0.025mm. During the finishing drawing process, the cooling temperature (20±2°C) is strictly controlled to avoid deformation of the workpiece caused by cutting heat; After the completion of fine drawing, the dimensional tolerance, contour and surface roughness of the tongue and groove need to meet the preliminary standards;
4. Step 4: Edge finishing. The automatic chamfering machine is adopted, equipped with a special chamfering milling cutter and the polishing brush of the machine tool polishing unit, according to the CNC program trajectory, the four-axis linkage milling of the tongue and groove edge fillet (R0.4~R0.6), the milling cutter speed n=25000r/min, the feed rate f=600mm/min, and the cutting depth ap=0.1mm; Then use diamond coarse and fine polishing brushes to round and polish the edges to ensure that the edges are smooth and smooth, and the surface roughness Ra≤0.8μm, which does not affect the surface and dimensional accuracy of the tongue and groove after broaching.

3.3 Key process parameter control

Combine material characteristics and tool parameters to optimize broaching process parameters and dynamically adjust to ensure machining stability:

1. Broaching speed: rough drawing speed 1m/min, finishing drawing speed 1~1.5m/min, to avoid too high cutting heat, aggravated tool wear, or too slow speed affecting the processing efficiency;
2. Cooling parameters: using special cutting oil (suitable for superalloy processing, with good lubricity, cooling and chip evacuation), cooling pressure 0.8~1.2MPa, cooling flow rate 15~20L/min, cooling temperature controlled at 20±2°C, real-time monitoring through temperature control system to avoid deformation of workpiece caused by cutting heat;
3. Vibration control: set up a damping vibration damping device between the broaching shaft and the worktable to reduce the vibration of the equipment; During the processing process, the vibration frequency is monitored in real time (controlled at 50~100Hz), and when the vibration exceeds the standard, the broaching speed is automatically reduced and the feed is adjusted to avoid vibration causing vibration on the surface of the tongue and groove or tool chipping;
4. Chip evacuation control: The combination of high-pressure spraying + spiral chip evacuation is adopted, the spraying direction is accurately aligned with the cutting area, and the chips are flushed away from the tongue and groove and the tool in time to avoid scratches and jamming caused by chip residue. Regularly clean the chip removal system to ensure smooth chip evacuation.

4.Quality Inspection and Defect Prevention

Process inspection

After the completion of each process of grooving, rough drawing, fine drawing, and edge finishing, targeted testing is carried out to adjust the processing parameters in time:

1. Slotting process: detect the deviation of the tongue and groove opening size, depth and position, and use calipers and depth rulers to detect, and the deviation is controlled within ±0.01mm;
2. Roughing process: detect the tongue and groove profile, tooth bottom size, tooth top arc size, use projector and dial indicator to detect, the contour ≤ 0.03mm;
3. Finishing process: Detect the dimensional tolerance, contour and surface roughness of the tongue and groove, use coordinate measuring instrument and roughness meter to detect, the dimensional tolerance is within ±0.005mm, the contour is ≤ 0.01mm, and the Ra≤ is 0.8μm;
4. Edge finishing process: detect the size and smoothness of the tongue and groove edge, use fillet gauge and microscope to detect, fill the corner R0.4~R0.6, no burrs, no sharp corners.

Common Defect Prevention Measures

For the four common defects that may occur in broaching processing: machining deformation, surface scratches, tool chipping, and tongue and groove size deviation, targeted prevention and control measures should be formulated to avoid risks in advance:

1. Processing deformation: optimize the clamping method, use flexible clamping and auxiliary support to control the clamping force; Strictly control the cooling temperature to avoid deformation of the workpiece caused by cutting heat; Differentiated tooth lift is used to gradually remove the allowance and reduce cutting stress. After the processing is completed, the workpiece is placed in a constant temperature environment (20±2°C) to cool to room temperature, and then tested and subsequently processed;
2. Surface scratches: ensure timely discharge of chips, optimize chip evacuation systems, and avoid chip residues scratching the surface; Use high-quality cutting oil to improve lubricity and reduce friction and scratches between tools and workpieces; Regularly inspect the cutting edge of the tool to avoid scratches caused by wear and crumbling of the cutting edge;
3. Tool chipping: optimize tool geometry parameters to improve edge strength; control broaching speed and feed to avoid tool overload; Regularly detect the wear of the tool, and replace or sharpen it in time when the wear of the tool reaches 0.01mm; the sharpened tool needs to be detected and degaussed before it can be reused;
4. Tongue and groove size deviation: Regularly calibrate equipment accuracy and tool accuracy to avoid equipment and tool deviation leading to unqualified dimensions; Optimize broaching parameters, dynamically adjust broaching speed and feed rate; Strengthen process detection, adjust parameters in time after each step of processing to avoid deviation accumulation.

5.Major breakthrough in domestically produced tenon and groove planing equipment

• Independent research and development of core technologies: The key core technologies are independent and reliable, breaking through foreign technical barriers and realizing the technical subseveration of domestic equipment for turbine wheel tongue and groove processing in many fields such as large aircraft, fighter jets, aircraft carriers, submarines, and large hydropower stations.
• Heavy-duty shock suppression technology: The particularity of turbine disc materials (stainless steel, superalloy, titanium alloy, etc.) and the requirements of tongue and groove surface processing quality make the tongue and groove broaching machine have extremely high requirements for vibration suppression in the broaching process±.
• New structure of C-shaped cradle: adopts a double-lead worm gear structure, which can adjust the clearance according to the actual needs of C-axis indexing; In addition, we have subverted the traditional simple hard rail structure and adopted a new guide rail combination form, which not only increases the contact area and contact rigidity of the guide rail, but also has better arc guide positioning accuracy to ensure dynamic rigidity during broaching.
• Ø2500mm ultra-large diameter turbine disc: Successfully developed the tongue and groove of broachable Ø 2500mm ultra-large diameter turbine disc, which is also the largest CNC tongue and groove broaching machine in the world.
• High-speed broaching technology (40% efficiency improvement): The optimized Z-axis broaching main motion can achieve high-speed broaching of 60m/min, and the efficiency of tongue and groove broaching can be improved by 40%.
• Fully automatic intelligent tool magazine: The fully automatic intelligent tool magazine matched with the broaching machine operating system intelligent process package can realize the automatic tool box replacement according to the progress of the broaching process during the broaching process, without manual intervention in the whole process. It ensures the continuity of broaching and the stability of accuracy, and reduces the strength and safety risks of manual operation.

Epilogue

The core difficulties of tongue and groove broaching in aero engine turbine discs are the processing characteristics of difficult-to-cut materials, the deformation control caused by complex structures, and the balance between high precision and high efficiency. This solution effectively solves various pain points in traditional broaching through accurate machining object analysis, high-performance equipment selection and debugging, optimized tool design and preparation, scientific step-by-step broaching process implementation, full-process quality inspection and defect prevention and control, and perfect post-guarantee system, and realizes the unity of high precision, high efficiency, high stability and low cost of tongue and groove machining.

The turbo disc is the “power heart” of the engine, and its performance directly determines the engine’s thrust, life and fuel efficiency. With advancements in materials science and manufacturing technology, turbine discs are moving towards lighter, stronger, and more resistant to high temperatures.