Cutting Tool Improvements in Pantograph Tube Machining Processes

The processing of pipe components is a crucial factor that impacts the performance of the pantograph. A 3mm thick seamless aluminum tube is chosen as the base material for processing. By analyzing the manufacturing process of the connecting pipe, as well as developing tooling fixtures and selecting and enhancing tools, we can improve both the processing efficiency and product quality of the connecting pipe. This approach helps to resolve production bottlenecks and ensures a smooth, rhythmic production flow on the assembly line.

 

PART 01 Preface
The pantograph is an essential component in high-speed rail systems, locomotives, and urban rail vehicles. The upper frame, which is welded to the connecting pipe, is a crucial part of the pantograph. It is mounted on top of the locomotive and must withstand various environmental challenges such as wind, frost, rain, and snow during high-speed operation. This ensures that it maintains sufficient strength, rigidity, environmental stability, and longevity.

The primary function of the pantograph is to draw electricity from the overhead contact network, providing the power necessary for the vehicle’s operation. The pantograph operates in three states: raised, held, and lowered. The reliability and stability of this component directly impact the overall performance and dependability of high-speed rail systems, locomotives, and urban rail vehicles. The upper frame, welded to the connecting pipe, plays a vital role in assembly. The connecting pipe is also welded to a reducer. Key aspects such as geometric tolerance, the angular positioning of the keyway, and the bevel angle and symmetry of the groove are critical for the proper positioning and connection of the upper frame. Therefore, the processing quality of the connecting pipe significantly affects the performance of the pantograph, which in turn influences the smooth operation of high-speed rail, locomotives, and urban rail vehicles.

 

Part 02 Parts Analysis and Processing Difficulties

The connecting pipe is a thin-walled aluminum alloy pipe with a diameter of 60 mm. Its structure is depicted in Figure 1, while the actual component is shown in Figure 2. The processing difficulties related to this component are as follows:

 

 

1) When machining symmetrical 41° bevels, controlling clamping deformation, machining deformation, and tool vibration can be challenging.

 

2) Maintaining the correct relationship between the symmetrical machining positions of both closed and open keyways, along with the keyway angle and the position of the bevel, is also difficult.

 

3) The connecting pipe has a wall thickness of 3mm, which classifies it as a thin-walled pipe fitting. During the clamping process of the bevel in a vise, excessive tool overhang can lead to vibrations in the workpiece. Different cutting and clamping methods may result in issues such as insufficient rigidity in the machining system, poor surface roughness, and deviations in machining size.

 

4) While machining the 6.5mm wide keyway, the drill tip is often prone to slipping and struggles to maintain stable centering on the top arc surface of the workpiece. The cutting force can cause the tool to develop built-up edge in a high-temperature environment, leading to uneven cutting, chipping of the milling cutter, and deformation of the keyway. Ensuring the correct positional dimensions and radial angle relationships between the slots poses challenges, creating production bottlenecks for batch processing. Thus, technical breakthroughs are urgently needed.

 

PART 03 Inclined surface processing route

Figure 3 illustrates the clamping method used for the clamping plate. It features two inclined surfaces at a 41° angle, connected by a pipe. The original process employs a 41° boring machine clamp to shape these inclined surfaces. The bolts of the clamping plate are secured and pressed against the arc surface. A φ30mm extended end mill is chosen for the machining. However, this process presents several issues, including long clamping times, low efficiency, and the potential for the workpiece to rotate, resulting in angular displacement that can compromise production safety.

 

The CNC milling method is employed to address the challenges associated with the bevel milling process at a 41° angle, ensuring precise control over size, angle, safety, and product quality. These thin-walled pipe fittings are made of aluminum alloy. When machining two 41° bevels on φ60mm pipe fittings, a φ30mm extended end mill is utilized. However, due to the large cutting forces and the extended tool length, vibrations can easily occur, causing the sharp corners of the bevels to deform under the cutting force.

 

Figure 4 illustrates the clamping method for CNC milling. Initially, clamping was achieved using a clamping plate bolt. The primary force acting on the pipe fittings during machining was the clamping force. However, due to the impact of the cutting force, the product would rotate during processing, leading to displacement that negatively affected the machining quality. To improve this, a pair of diameter pipe combination clamps were designed specifically for the φ60mm aluminum alloy thin-walled pipe fittings. These clamps ensure that the arc surface of the clamp block makes contact with the arc surface of the pipe fitting, allowing for effective wrapping and clamping of the workpiece during bevel processing. The advantages of this new clamping method include improved stability and enhanced quality of the machined bevels.

 

 

1) This method effectively prevents pipe fittings from being deformed by clamping forces, resulting in smoother processing.

2) An overall clamping method is used to ensure that the workpiece is clamped evenly, which effectively resists deformation during machining caused by variations in milling forces.

3) The inclined surface is clamped and formed in one step, ensuring accuracy in both angle and symmetry.

4) The vise jaws on both sides apply direct pressure to simplify the clamping method and accurately position the workpiece.

5) This approach significantly improves processing efficiency and product quality.

During processing, it is noted that, due to the varying lengths of the blanks, a margin needs to be left on the right side. Consequently, during rough processing, the right inclined surface will be milled using the reverse method, while the left inclined surface will be milled using the forward method. In fine processing, the right inclined surface will be milled forward, and the left inclined surface will be milled in reverse. The primary purpose of this approach is to prevent excessive machining and avoid overcutting or gnawing during the processing of the inclined surfaces.

In finishing, the cutting allowance for the reverse milled workpiece decreases from thick to thin, while for the forward milled workpiece, it increases from thin to thick. This combined forward and reverse milling process is designed to prevent deformation of the thin-walled tube caused by changes in cutting forces.

 

PART 04 Keyway processing process route

Figure 5 illustrates the grinding of the milling cutter’s cutting edge alongside the finished pipe fittings. When machining closed and open keyways, the aluminum alloy workpiece experiences significant deformation. During high-speed processing, the cutting temperatures are elevated, leading to faster tool wear due to the heat generated. As a result, frequent sharpening and tool replacement are necessary, which negatively impacts processing efficiency and increases tool costs.

 

 

Eight keyways need to be processed on the connecting pipe, each with specific angle requirements. The universal dividing head, identified as T11160A, is used for clamping. Based on the drawing specifications, the following analyses are necessary:

1. How to ensure the correct positional relationship between the bevel and the keyway.
2. How to establish the angle relationship between the bevel and the keyway.
3. The position and size requirements for the keyways.

 

PART 05 Processing method

5.1 Positioning method of bevel and keyway

When clamping the pipe fitting, position the end of the processed bevel on the connecting pipe and align it in the clamping direction of the dividing head for angle positioning. The three screw holes in the dividing head are primarily used to support the bevel, aligning the bevel angle of the pipe fitting with the screw hole as a rough reference for positioning. The clamping setup for the dividing head is illustrated in Figure 6. The dividing head should clamp the end of the connecting pipe that requires processing, using the machine tool worktable as the reference plane. A right-angle ruler is used to ensure that the bevel is vertically positioned at exactly 90 degrees, fitting flush against the right angle edge of the ruler. After analyzing the workpiece and fixture, the processing method involves first working clockwise, then counterclockwise. This approach helps eliminate any processing gaps in the dividing head and ensures the radial angle of the processing position is accurate.

 

 

5.2 Comparative analysis and optimization of tools

The process for using a keyway cutter is illustrated in Figure 7. After thorough verification, it has been determined that a φ6.5 mm keyway cutter is necessary for the operation. The cutting edge of the keyway cutter is specially ground to form the main cutting edge of the keyway bottom tooth into a drill tip shape. Since the thickness of the keyway in the pipe is only 3 mm, the keyway milling cutter should first drill a hole through the bottom of the pipe, and then the keyway can be milled. This method ensures adequate tool rigidity during processing. The following outlines the steps and analysis involved in this procedure.

 

- When processing thin-walled pipe fittings, the keyway milling cutter experiences force at the center, where the chip groove is shallow. Due to the softness of the aluminum alloy material during aluminum milling, it is prone to sticking. To prevent the keyway milling cutter from becoming deformed due to excess pressure, it should be ground into a drill tip shape for effective processing.

- For milling the pipe surface with a keyway cutter, a circular arc interpolation feed method is used. However, this method can lead to instability in centering, resulting in uneven forces on the keyway milling cutter. This uneven force can cause a misalignment of the radial angle position of the keyway, which may result in ineffective processing.

- Prior to keyway processing, it is beneficial to grind the tool into a drill tip shape to facilitate easy centering. This will help ensure the accurate positioning of the radial angle of the keyway. Using an integrated drilling and milling composite processing method helps reduce tool change time, enhances processing efficiency, and ensures product quality. This approach allows the same milling cutter to first drill the bottom hole and then directly mill the keyway.

- The keyway milling cutter should be ground into a drill tip shape, and a chip groove should be created to effectively prevent sticking.

- During processing, the method changes from milling to drilling, ensuring stable centering.

- After the composite tool drills the bottom hole, it directly proceeds to mill the 3mm deep keyway, making the process both convenient and efficient.

 

5.3 Solution to the processing problem of thin-walled pipe parts

During processing, the thin wall of the pipe is impacted by the cutting force, which can cause the groove width to deform and lead to opening and shrinking issues. This ultimately affects product quality. After conducting multiple verifications, we decided to use a φ6.5mm keyway milling cutter. By implementing a reasonable cutting parameter ratio, we can effectively control the deformation of the opening keyway and enhance processing stability. The optimized cutting parameters are detailed in Table 1.

 

After optimization, the adjusted cutting parameters ensured both processing efficiency and quality, effectively addressing the challenges associated with manufacturing thin-walled pipe parts.

 

PART 6: Fixture Production and Tool Improvement

- By refining the CNC manufacturing process, we boosted processing efficiency while ensuring the verticality, position, coaxiality, and parallelism of both the groove and bevel.

- The production of a clamp block effectively prevented deformation of the pipe fittings during bevel machining. This fixture made clamping firmer and simpler, making it more suitable for large-scale production and significantly enhancing efficiency.

- The capabilities of the machine tool were expanded, fully resolving the production challenges associated with the bottleneck process.

- Grinding the keyway tool minimized tool change time and improved processing efficiency. We used a φ6.5mm keyway tool to grind the cutting edge, which was shaped into a drill bit. This keyway tool features a short cutting edge, high strength, and stable centering. The enhancements made to the tool significantly decreased both tool change and installation time, reduced tool costs, and improved tool utilization and processing efficiency.

 

PART 07 Comparison before and after tool improvement

By improving tools, we can provide accurate benchmarks for positioning and orientation in subsequent processes, ensuring that the processing and welding meet necessary requirements. Selecting the appropriate spindle speed and feed rate enhances the processing accuracy of each part. Using a homemade clamp for workpiece fastening not only ensures reliable clamping and quick positioning but also reduces tooling production costs, shortens the production cycle, guarantees product quality, and increases production efficiency. By carefully selecting processing parameters, we can minimize deformation, enhance the quality of the processed parts, and improve overall production efficiency. The annual output of connecting pipes from 2019 to 2022 is illustrated in Figure 8.

 

PART 08 Conclusion

By enhancing the processing methods and tools for the pantograph connection tube and applying these improvements to the production of various pipe components, we can increase processing efficiency. This approach meets the production requirements of the process line while ensuring the stability and longevity of the product, ultimately creating added value.

 

 

If you want to know more or inquiry, please feel free to contact info@anebon.com

At Anebon, we firmly believe in “Customer First, High-Quality Always”. With over 12 years of experience in the industry, we have been working closely with our clients to provide them with efficient and specialized services for custom CNC machined parts, and die-casting parts.