1. Introduction
In the fields of automotive manufacturing and aerospace, there are strict requirements for the space and quality occupied by components. Aluminum alloy, with its good plasticity, high strength, and lightweight characteristics, is widely used in these fields. The worm gear housing, a core component of the worm gear in automotive transmissions, has complex structures and high precision requirements. This article discusses the single-piece processing technology of a representative servo worm gear housing part, providing practical basis for processing such parts.
2. Part Characteristics and Dimension Analysis
| Characteristic | Details | Importance |
|---|---|---|
| Shape | Irregular, with circular cavity and thin-walled structure near the end face, and small holes and grooves on the end face | Affects clamping |
| Dimension Precision | – Center distance between worm gear and worm hole: 54.0±0.025 – Worm gear hole diameter and position precision: Φ97-0.05, Φ96.6-0.05, with 0.05 tolerance – Worm hole diameter and position precision: Φ47H7, Φ30H7 with 0.02 coaxiality tolerance | Affects assembly and operation |
3. Processing Difficulties
| Difficulty | Description | Impact |
|---|---|---|
| Irregular Shape | Difficult to clamp and position directly with ordinary fixtures | Affects machining accuracy |
| Complex Cavity | Thin-walled structure near the end face, prone to deformation, chatter, and clamping deformation | Affects part quality |
| High Precision | High precision requirements for worm gear and worm holes and their spatial positions | Difficult to achieve precision |
| Material Property | LY12 high-strength hard aluminum, with good machinability but prone to sticking and deforming | Affects machining process |
4. Part Processing Scheme
| Scheme | Process Steps | Advantages | Disadvantages |
|---|---|---|---|
| 1 | – Rough machining on a three-axis vertical machining center – Finish machining of the turbine face and side step on a four-axis (with rotary table) machine using a process cylinder – Machining the worm hole on a four-axis machine using a mandrel fixture with the turbine hole as the positioning reference | Fewer processes, high precision for hole machining | Poor clamping rigidity, increased fixture manufacturing difficulty, and possible impact on machining accuracy during fixture installation |
5. Fixture Design and Error Analysis
5.1 Fixture Design
- For the finish machining of the worm hole and flange face, a mandrel and a four-axis indexing chuck are used.
- To ensure the center distance between the worm gear and worm holes, an auxiliary mandrel is installed after machining the worm gear hole for secondary positioning and clamping.
5.2 Positioning Error Calculation
- The commonly used method for calculating positioning error is the synthesis method, where the positioning error (ΔD) is the sum of the datum non-coincidence error (ΔB) and the datum displacement error (ΔY), i.e.,ΔD=ΔY+ΔB .
- When the mandrel is coordinate with the worm gear hole, the location error is calculated as follows:
- Given the worm gear face bearing hole diameter of and the mandrel diameter of , and the center distance between the worm gear and worm holes is .
- Since the design datum and process datum coincide when using the worm gear hole as the location, .
- By controlling the worm gear hole size and improving the mandrel size precision, the location error is calculated as mm, which is less than one-third of the workpiece size tolerance ( mm), meeting the processing requirements.
6. Part Processing Difficulty Analysis
6.1 Worm Gear Hole Processing
- On a four-axis machine, use a dividing head to clamp the outer circle of the process block, with the center of the process block end face as the coordinate origin and the worm gear end face leveled as the A-axis zero point.
- Machine the tool to 2 mm below the worm center, and use the three-jaw chuck of the dividing head to clamp the outer circle of the process block as a programming check body to avoid interference between the tool and the chuck claws. Leave a machining allowance of 0.2 mm.
- For the finish machining of the worm gear hole, since the and hole diameters of the worm gear face are used for assembling the worm gear and bearing, and the dimensional and positional tolerances of the stepped holes are within 0.05, the coaxiality of the stepped holes and the size precision control of each step hole are the key points. Adopt one-time clamping to ensure the positional precision and use the boring machining method to ensure the size precision of each hole. Remove the process block after completion.
6.2 Worm Hole Processing
- As shown in Figure 3, install the flange face part with the hole of the worm gear as the定位, use a diamond pin for rotation定位, and take the flange face on the upper surface of the part as the A0 surface.
- After assembling the mandrel with the worm gear hole, clamp the mandrel as the installation定位基准 and level it to ensure the relative position of the worm hole.
- Use a medium-sized wave blade cutter to machine each step hole of the worm, leaving a margin of 0.2 mm. After finish machining all grooves and the outer circle, use a boring cutter to finish bore the worm hole, such as boring the hole, hole, and hole to size.
- The boring machining of the worm gear hole and worm hole is an important means for part processing. Considering factors such as part size precision, surface roughness, tool vibration, and thin-walled deformation during machining, conduct multiple cutting tests and optimize processing parameters before machining to ensure smooth processing. The optimized boring parameters are shown in Table 1.
7. Part Processing Result Analysis
| Basic Dimension | Tolerance Range | CMM Measurement Value | Conformance |
|---|---|---|---|
| Center Distance 54.0 | 54.01 | Conforms | |
| Worm Gear Hole 96.6H7 | 0.030/0 | 96.62 | Conforms |
| Bearing Hole 55 | -0.042/-0.072 | 54.95 | Conforms |
| 47H7 | 0.025/0 | 47.015 | Conforms |
| 30H7 | 0.021/0 | 30.01 | Conforms |
| 89 | -0.03/-0.065 | 88.96 | Conforms |
The measurement results show that all dimensions of the worm gear part are within the tolerance range, effectively solving the problems of the worm gear and worm center distance positional precision and thin-walled deformation.
8. Conclusion
For the processing of this type of worm gear housing part, it is necessary to focus on the center distance between the worm gear and worm holes. Use multi-axis machines to reduce processes and ensure the relative position and size precision of machining elements. Each process must strictly follow the process steps and set the machining depth, tool change position, and tool parameters. Proficiency in using CAD/CAM software and using arc transitions in tool path programming can improve efficiency and reduce losses. Future optimization can be achieved by introducing finite element analysis for part clamping and processing.