Automotive Turbocharger Housing Prototypes: High-Precision CNC Alternative for Complex Sand Casting Parts

Customer Background

A multinational automotive parts supplier needed to develop metal prototypes for the validation of a new turbocharger. The original process used sand casting, which took as long as six weeks, and each design change required a new mold, seriously slowing down the engine matching project. The customer wanted a method for making metal prototypes without molds that could deliver quickly.

Challenges

• Complex Geometry: The turbocharger housing includes multiple complex features such as spiral flow channels, flange mounting surfaces, and sensor interfaces, with an internal flow channel surface roughness requirement of Ra3.2.
• Strict Material Requirements: It requires high-temperature resistant cast iron alloy (close to GGG40), capable of withstanding thermal shock of up to 850°C at the exhaust end.
• Precision Requirements: Flange surface flatness of 0.05mm, installation hole position accuracy of ±0.1mm, and the gap with the turbine impeller must be controlled within 0.2mm.
• Time Pressure: The customer had only 15 days left and had to obtain a metal prototype that was ready for assembly testing.

Solution

Yiruida Technology completed DFM analysis within 24 hours and proposed an innovative solution:

• Process Route: Abandoning the casting approach, we used five-axis CNC machining for full-body milling. Considering the high hardness of cast iron material and the large cutting force, we selected ceramic end mills and a high-pressure internal cooling strategy.
• Machining Strategy: The housing was split into three independent parts (inlet side, scroll body, and outlet side), which were machined separately and then assembled using precision locating pins and bolts. The internal flow channels were finished with ball-end mills and polished manually with polishing wheels.
• Post-processing: All flange surfaces were machined to Ra1.6, and high-temperature anti-seize agents were applied to the assembly surfaces. A pressure test was conducted on the housing to ensure no leakage.
• Quality Inspection: All critical dimensions were inspected using a coordinate measuring machine, and a full-size report was provided.

Results

• Delivered two complete turbocharger housing metal prototypes on day 12 (originally planned for day 15), which were assembled onto the engine test bench.
• Passed a 600-hour high-temperature cycle test without deformation or cracking.
• Due to the absence of mold costs, the customer's design iteration costs were significantly reduced. They carried out two more rounds of modifications, and each time they received the new prototype within a week.
• The customer incorporated this "CNC direct machining of complex housings" method into their internal rapid development guidelines for early verification of other casting-type products.

"Yiruida achieved what seemed almost impossible by using CNC to machine complex flow channel housings, allowing us to complete all performance validations before tooling."