Machining Solutions for Complex Automotive Transmission Components

Background Introduction

In automotive parts development, the transmission is a key component of the drivetrain. It has a complex structure, high precision requirements, and strict assembly fit, which makes the manufacturing process challenging. In this case study, we will share a high-precision CNC-machined prototype of the transmission part.

This transmission prototype accurately replicated the complex geometry and ensured efficient integration with internal parts. It also laid a strong foundation for future testing and mass production.

Compare Different Processes of Transmission Part Manufacturing

The mass production of transmission components are usually done through die casting. However, traditional mold making takes a long time and costs a lot. If there are design changes, the mold often needs to be redone, leading to wasted time and resources. That’s why, in the early design stage, metal 3D printing or CNC machining is used to make prototypes for testing and design improvement.

Compared to 3D printing, CNC machining has some key advantages. It can use the same metal materials as mass production (like aluminum or magnesium alloys). It also provides strength, assembly precision, and a surface finish that is closer to the final product. This makes testing results more reliable.

Part Structure Analysis

Let’s take a look at the 3D and 2D drawings to better understand this part’s structure and precision requirements.

1. Complex Outer Geometry

The transmission part is a shell-type part with an irregular outer shape and many curved surfaces. It also has multiple assembly surfaces and machining areas spread across the part. The vertical walls have draft angles, showing that the design is made for future die casting production.

2. Lightweight Design and Chip Considerations

To reduce weight, the transmission prototype has large hollow sections. This makes it harder to remove chips during machining. Chips can easily accumulate, which lowers machining efficiency and affects surface quality.

3. Requirements of Precision Holes

The transmission part is not only a structural support but also a high-precision assembly platform. Some surfaces require a very smooth finish (Ra 1.6 μm), and many functional precision holes must be machined accurately.

For example, the ⌀22 mm (H6) hole for the engine shaft bearing and the ⌀22 mm (H7) hole for the gear shaft bearing shown in the 2D drawing are critical bearing seats. The inner and outer rings of the bearings must fit tightly. Too loose or too tight will cause issues such as vibration, noise, overheating, or early failure.

Optimized Machining Approach and Solution

To address the complexity of this transmission component, we carefully evaluated machining approaches to balance accuracy, efficiency, and setup time.

Machining Method Selection

Given the part’s complex geometry and multiple machining surfaces, we considered two options:

• Option 1: Use a 3-axis machine with multiple repositionings (flips) to complete all machining operations.
• Option 2: Combine 3-axis rough machining with 5-axis finishing for precision features.

Although the order quantity was small, many mounting holes demanded high accuracy. Frequent flipping in Option 1 would increase setup time and risk positioning errors, potentially compromising precision.

Therefore, we chose Option 2:

The 3-axis machine was used to rough out the outer surfaces and leave allowance at the critical hole areas. Then, a 5-axis CNC machine completed the complex features and precision holes inaccessible to 3-axis CNC machining. This approach minimized repositionings, improved setup repeatability, and enhanced overall accuracy.

High-Precision Hole Machining

The transmission part includes numerous bearing holes that require tight tolerances. These holes were a key focus of the part machining. To ensure their precision, we employed fine boring techniques for the final finishing of these critical features.

Surface Finish Requirements on Assembly Faces

Assembly surfaces of the transmission part must achieve a surface roughness of Ra 1.6 μm without scratches or marks, as any damage can affect assembly fit and function. During rough machining, clamping, and handling, we placed special focus on protecting these areas.

To mitigate this risk, we designed custom fixtures and deliberately left an extra allowance on these surfaces. After completing all other machining operations, a final finishing pass removed the excess material, ensuring a high-quality surface.

Practical Chip Evacuation Solutions

To solve the chip evacuation challenge, we used a combination of internal and external machining methods.

• Internal High-Pressure Coolant Flushing: Coolant was delivered directly through the spindle to the cutting zone, flushing chips out of deep holes.
• External Vacuum Extraction: A vacuum system surrounded the machining area, suctioning fine chips and debris that the coolant flow could not remove effectively.

This dual approach greatly improved chip removal, leading to better machining efficiency and surface finish.

Inspection and Quality Confirmation

After machining, a thorough pre-shipment quality inspection was conducted to verify that all dimensions and tolerances met the required standards. This process included the use of CMMs, go/no-go gauges, surface roughness testers, and detailed visual checks to ensure every detail was precise and flawless.

Inspection reports and detailed product photos were then shared with the customer for final approval. The customer expressed satisfaction with the quality, and the parts were delivered smoothly without issues.

Customer Commitment and Technical Support

WayKen is dedicated to delivering high-quality, precision-engineered custom solutions tailored to our customers’ needs. From prototype development to mass production, we provide full technical support and quality assurance throughout the process.

If you have CNC machining requirements, please don’t hesitate to contact us. We look forward to partnering with you to bring your projects from concept to reality successfully.