Abstract:
The spiral bevel gear, serving as a transmission device, primarily functions in the transmission between non-parallel axes, exhibiting strong load-bearing capacity and smooth transmission capabilities. The manufacturing of spiral bevel gear relies heavily on numerical control (NC) milling machines. However, during the machining process, constraints from the size and installation conditions of NC milling machines have hindered significant improvements in the processing specifications and accuracy of spiral bevel gear. Currently, research focuses on the worm gear NC milling process based on the generating method. However, this process still exhibits certain deficiencies, including large machining errors, long processing cycles, low efficiency, and poor interchangeability of the processed gears. To address these issues, this paper proposes an optimized design based on traditional spiral bevel gear machining processes by introducing automatic programming. The research aims to develop an automatic programming and machining process for spiral bevel gear NC milling machines, achieving high-precision and high-efficiency automated machining of spiral bevel gear.
Keywords: spiral bevel gear; numerical control; automatic programming; gear machining process
1. Introduction
Spiral bevel gear is crucial components in mechanical transmission systems, particularly in applications requiring non-parallel axis transmission. They offer significant advantages such as high load capacity, smooth transmission, and compact structure. However, the precision and efficiency of spiral bevel gear machining are critical factors affecting their performance and reliability. Traditional machining methods often suffer from issues such as large machining errors, long processing cycles, and low efficiency, which limit the wide application of spiral bevel gear.
With the rapid development of numerical control technology and automatic programming technology, it is feasible to improve the machining accuracy and efficiency of spiral bevel gear through automatic programming and NC machining. This paper proposes a research on automatic programming and machining process for spiral bevel gear NC milling machines, aiming to provide a theoretical and practical basis for improving the machining quality and efficiency of spiral bevel gear.
2. Automatic Programming and Machining Process for Spiral Bevel Gear NC Milling Machine
2.1 Design of Cutting Parameters for Spiral Bevel Gear NC Milling Machine
The design of cutting parameters is crucial during the milling process of spiral bevel gear using NC milling machines, playing a significant role in subsequent automatic programming and machining. Cutting parameters are divided into controllable and uncontrollable parameters.
Among the controllable cutting parameters, the cutting speed and the number of tool passes of the NC milling machine are included. The cutting speed of the NC milling machine refers to the rotational movement of the hob around its own axis, with the calculation formula as follows:
v=n⋅d0
where n is the rotational speed of the hob of the NC milling machine, and d0 is the outer diameter of the hob. There are certain differences in the cutting speeds corresponding to different spiral bevel gear module numbers, as shown in Table 1.
| Table 1: Corresponding Cutting Speeds of NC Milling Machine for Different Spiral Bevel Gear Module Numbers |
|---|
| Module Number |
| ≤10 |
| >10 |
According to Table 1, the cutting speed of the NC milling machine should be set within the required range for different module numbers. When changes occur in the number of hob heads or hob manufacturing accuracy, the cutting speed of the milling machine should be adjusted accordingly based on the actual changes. For the setting of the number of tool passes on the NC milling machine, it should be set according to the spiral bevel gear machining efficiency requirements. If there are no special requirements for machining efficiency, a single-pass machining method of the NC milling machine can be adopted.
2.2 Tool Path Planning for Spiral Bevel Gear NC Milling Machine
After designing the cutting parameters for the spiral bevel gear NC milling machine, the tool path for the NC milling machine should be planned. Before planning the tool path, a suitable cutting method should be selected. Then, the tool path route of the milling machine should be determined. The starting point coordinates of the milling machine tool are denoted as (x0, z0), which can be set to any value according to the operating conditions of the NC milling machine. The coordinates of the contact point between the milling machine tool and the spiral bevel gear workpiece are denoted as (x2, z2).
Due to the thread structure of the milling machine tool’s cutting edge, there is a certain rise angle during the machining process. Therefore, the installation deflection angle θ of the milling machine tool is set. The shape of the tool in the vertical plane is mostly elliptical.
The installation deflection angle θ is crucial as it affects the engagement of the tool with the workpiece, influencing both the cutting efficiency and the surface quality of the spiral bevel gear. This angle must be carefully calculated and set to ensure optimal machining results. The elliptical shape of the tool in the vertical plane further complicates the tool path planning, as it necessitates precise control over the tool’s orientation and movement to maintain consistent contact with the workpiece surface.
To plan the tool path, the first step is to establish the mathematical model of the spiral bevel gear’s tooth surface. This model should take into account the gear’s geometry, including its pitch, spiral angle, and tooth thickness. Based on this model, the coordinates of the desired tooth profile can be computed, which will serve as a reference for the tool path planning.
Next, the tool path is generated by calculating the necessary movements of the milling machine’s tool relative to the workpiece. This involves determining the feed rates, cutting depths, and tool orientations at each point along the path. The tool path should be designed to ensure that the entire tooth surface is machined uniformly, with minimal deviation from the desired profile.
In addition to the geometric considerations, the tool path planning must also account for the dynamic aspects of the machining process. This includes factors such as tool wear, cutting forces, and machine vibrations, which can all affect the final quality of the gear. To mitigate these effects, adjustments to the tool path may be necessary, such as varying the cutting speed or feed rate in certain areas.
Once the tool path is planned, it is typically programmed into the NC milling machine’s control system using a suitable CAM (Computer-Aided Manufacturing) software. This software allows for precise control over the machine’s movements, ensuring that the tool follows the planned path accurately.
Finally, before commencing full-scale production, it is essential to conduct test runs and inspections to verify the accuracy and quality of the machined spiral bevel gear. Any necessary adjustments to the tool path or cutting parameters should be made based on these test results to ensure consistent and high-quality output from the NC milling machine.