Abstract: In order to meet the high quality and high standards of product production, it is necessary to consider the requirements of the product on the gear shaper and improve the precision and quality of gear processing, thereby bringing better economic benefits. The hydraulic system serves as the main motion drive of the CNC gear shaper, effectively improving the quick return characteristics of the original crank connecting rod system. The hydraulic drive can realize the stepless speed regulation function, and the output torque is relatively large, which expands the range of tool speed change in the gear shaper. During the working process, there will be no mechanical accidents such as torque imbalance caused by the tool stopping. The requirements for cutting force, length, and stability of large-scale gear shapers are constantly increasing, necessitating improvements in the design of the hydraulic drive system for CNC gear shapers. This article briefly analyzes the hydraulic main drive system and design of a large-scale CNC gear shaper.
1. Introduction
With the continuous development of the machining industry, the precision requirements for mechanical components have been continuously raised. High-precision machining equipment is also an important demand object in modern industrial production. By utilizing numerical control technology, the automation and intelligence of machining can be improved, and machining errors can be reduced. CNC machines have gradually replaced traditional machining equipment. The tool post structure of small and medium-sized CNC gear shapers mainly includes a tool shaft, a slider, worm gears, and worm wheels. However, in large-scale CNC gear shapers, the current structure faces issues such as relatively slow cutting speeds at the tool entry and exit points and relatively low force in the middle section, making it difficult to meet market demands. By employing a hydraulic main drive system, the problem of cutting large gears in large-scale CNC gear shapers can be effectively addressed.
2. Analysis of the Motion Principle of CNC Gear Shaper
The gear shaper primarily adopts the generating method to achieve its shaping principle. It uses a specialized gear shaper cutter to process gears. This cutter and the gear have the same shape, and the teeth of the cutter can form a cutting edge to cut mechanical parts. During this process, the cutter moves reciprocally along the axis of the workpiece, ultimately achieving the cutting function. After multiple gapless movements between the cutter and the workpiece, the outer contour of the gear is formed on the surface of the workpiece. The cutting motion characteristics of a CNC gear shaper are the same as those of a traditional gear shaper. The main components include the main motion, generating motion, and cutting-in motion. The main motion is the reciprocal linear motion of the gear shaper cutter along its axis, indicated by the number of reciprocations formed by the gear shaper cutter. The generating motion occurs during the gear shaping process, where the gear shaper cutter needs to maintain a meshing motion relationship with the gear blank similar to that of a cylindrical gear. When the cutter rotates through one tooth, the workpiece also rotates through one tooth. The cutting-in motion mainly involves the gradual feeding of the gear shaper cutter into the full tooth depth during gear shaping. However, excessive tool engagement can damage the cutter and workpiece. Therefore, in actual operation, the gear shaper cutter gradually cuts in. For the workpiece, the gear shaper cutter exhibits radial cutting-in motion. The numerical control device controls the entire movement process of the cutter from the tool point to the cutting-in point, gradually cutting in until the full tooth depth is reached. After the workpiece rotates one full circle, all teeth are cut, which is referred to as one cutting-in operation. In practical work, due to the relatively large full tooth depth or the hardness of the workpiece, secondary or tertiary cutting-in operations can also be adopted. The proportion of the cutting-in operations needs to be comprehensively judged based on the cutter material, full tooth depth dimensions, angles, and workpiece material.
Table 1: Key Components and Their Functions in CNC Gear Shaper
| Component | Function |
|---|---|
| Gear shaper cutter | Forms the cutting edge to cut mechanical parts |
| Workpiece | The object to be processed to form the gear contour |
| Tool shaft | Supports and drives the gear shaper cutter |
| Slider | Converts the rotational motion of the crank into reciprocal motion |
| Worm gears/worm wheels | Provides the necessary reduction ratio and torque transmission |
3. Functional Requirement Analysis of CNC Gear Shaper System
3.1 Stroke Length
According to market demand, the maximum cutting stroke length is currently 600mm, with an effective reciprocal stroke of 650mm. The minimum cutting stroke length is 60mm, and the minimum reciprocal stroke length is 100mm.
3.2 Maximum Cutting Force
Based on literature research and analysis, when the tool module is 20 and the feed depth is 15mm, the maximum cutting area per stroke is 11.61mm². This cutting area can also be used as a cutting parameter for the machine tool. The preset maximum shear stress of the workpiece can be set to 3137MPa, and the cutting force is 36.42kN.
3.3 Cutting Speed Design
The hydraulic cylinder piston rod affects the areas of the upper and lower oil chambers of the oil cylinder. Based on this characteristic, the time ratio between the downward cutting motion and the upward return motion of the tool shaft can be adjusted to minimize its impact. According to the ratio of the oil chamber cross-sectional areas, the cross-sectional area is gradually adjusted to be close to a 1:2 ratio with the time ratio, while ensuring that the CNC gear shaper meets the stroke motion with a downward and upward time ratio of 2:1. Considering the friction characteristics of the oil cylinder piston, the maximum continuous reciprocal motion speed is set to 28m/min. Based on the analysis of machining characteristics, the gear shaping cutting speed is maintained at 10m/min, with a maximum upward speed of 25m/min and a maximum downward speed of 12.5m/min.
3.4 Other Functional Requirements
The system needs to balance the weight of the tool shaft and slider connected to the piston rod, which totals 800kg. The oil cylinder piston reciprocates between any two points at the highest and lowest points. Therefore, the piston can stop at any set position. Both the rodded and unrodded chambers of the oil cylinder have pressure sensors, and the hydraulic system ensures the function of the slide-down stop valve. The resolution of the position sensor built into the oil cylinder can be 0.005mm.
4. Motion Scheme Design Based on Hydraulic Drive for CNC Gear Shaper
During the motion scheme design process, it is imperative to comprehensively consider whether the motion of the CNC gear shaper can meet product requirements. At the same time, comparisons should be made between the CNC gear shaper and traditional gear shapers in terms of footprint and economy. The motion of the gear shaper cutter and gear blank is primarily accomplished by specific workpieces and tools, which involves the allocation of motion functions within the gear shaper. Although this is unrelated to the control method of the gear shaper itself, it is closely linked to the overall layout of the gear shaper.
4.1 Selection and Design of Motion Schemes
The CNC gear shaper primarily adopts a crank-slider mechanism, where a servo motor drives the crank to rotate continuously through a gear transmission. When the connecting rod transfers power to the slider, the gear shaper cutter undergoes reciprocating motion up and down, ultimately forming the main motion for gear shaping. In the crank-slider mechanism, the length of the crank affects the stroke length of the slider, while the length of the connecting rod influences the positioning of the slider. To more precisely control the motion speed of the slider, simulation analysis can be conducted using ADAMS software to measure the velocity changes of the slider at different positions.
Since the slider’s moving speed varies within a certain cycle, to ensure uniform gear shaping speed, the speed near the trough or peak of the speed curve can be selected during speed measurement and used as the cutting speed curve during gear shaping. To improve the quality of gear shaping, researchers have adopted a double crank-slider six-bar mechanism, which better realizes the main motion of the gear shaper and optimizes motion performance through simulation-based optimization of bar lengths.
4.2 Motion Function Allocation and Layout
The motion functions of the gear shaper primarily include main motion, generating motion, and cutting-in motion. In the design of the main motion scheme, consideration must be given to how hydraulic drive can achieve reciprocating motion of the gear shaper cutter and ensure steplessly adjustable motion speed. At the same time, the stroke should enable slow motion to allow accurate stopping at any position.
For generating motion and cutting-in motion, they need to be integrated with the main motion scheme and the final motion scheme should be drawn based on the overall layout of the gear shaper. The rotation of the gear shaper’s spindle mainly involves components such as couplings and worm gear reducers, while the rotation of the workpiece is achieved through mechanisms such as reducers and couplings. The workpiece rotates with the drive of the worm gear on the workbench to meet the requirements of generating motion. This is primarily controlled by the control system.
To cut out the entire tooth, radial feed of the workpiece is required. This can be achieved by a servo motor reducer, ball screw, and other mechanisms to drive the workbench for radial feed.
4.3 Key Technical Specifications and Performance Optimization
The main technical specifications of the CNC gear shaper can be referenced based on those of the Y51160 gear shaper. However, it should be noted that the maximum processing diameter of the CNC gear shaper is typically smaller than that of mechanical gear shapers, mainly because large-diameter internal gears are more suitable for processing with CNC milling machines. The maximum processing tooth width of the CNC gear shaper can be increased to 380mm, with a maximum module of 16mm. The reciprocating stroke rate of the cutter can be set to 10-60 strokes per minute, the radial feed rate to 0-500 mm/min, and the workbench’s rapid traverse speed to 1 revolution per minute.
When optimizing system performance, factors such as the design size, working pressure, and load capacity of the hydraulic cylinder need to be comprehensively considered. Additionally, the material, structure, size, and bearing capacity of the spindle should be checked to ensure they meet usage requirements. Through reasonable motion scheme design and performance optimization, better solutions can be provided for cutting large and precision gears, improving the processing accuracy and efficiency of the gear shaper.