Precision CNC Turning Techniques for Large Titanium Alloy Casings

To address the challenges associated with cutting thin-walled casings made from Ti6Al4V titanium alloy, we analyze the structural and dimensional requirements of the components. By developing a well-structured process route and a CNC program, and by selecting appropriate tools, cutting parameters, and fixtures, we can ensure the machining accuracy of these parts. This approach serves as a valuable reference for CNC turning of such thin-walled components.

 

# 01 Introduction

Ti6Al4V titanium alloy is known for its high strength, low density, excellent heat resistance, and corrosion resistance. It is widely utilized in aerospace, automotive, and medical equipment industries. Due to its unique properties, after heat treatment, the hardness can reach up to 320HBW, and the tensile strength is at least 1200 MPa. However, during processing, issues such as reinforcement crushing, pull-out, and debonding can occur, making the cutting process challenging. Therefore, studying the cutting process of Ti6Al4V is crucial for enhancing processing efficiency and quality.

 

# 02 Ti6Al4V performance analysis

The cutting difficulty of Ti6Al4V is primarily influenced by its chemical composition, metallographic structure, and mechanical properties. The chemical composition is listed in Table 1, while the mechanical properties are detailed in Table 2.

 

# 03 Introduction to thin-walled receiver parts and analysis of processing difficulties

The thin-walled receiver components are illustrated in Figure 1, while their dimensions are detailed in Figure 2. This component features a large diameter and consists mainly of a thin-walled straight tube, multiple flanges on its outer diameter, as well as bevels and grooves. It is made from Ti6Al4V titanium alloy.

The specifications are as follows: the inner diameter measures (2013.7 ± 0.5) mm, and the maximum outer diameter is (2108.7 ± 0.5) mm. The thinnest wall thickness is (6 ± 0.5) mm, and the overall height of the part is (678 ± 0.5) mm. The surface roughness is specified to be Ra ≤ 3.2 μm. Additionally, the flatness requirement for the part is ≤ 0.2 mm, and the roundness tolerance is ≤ 0.5 mm. Due to the complex shapes of the inner and outer diameters, CNC turning presents significant challenges in manufacturing this part.

# 04
Processing technology plan Through the analysis of the part structure and processing difficulties, a processing technology plan is formulated, as shown in Table 3.

 

# 05 Implementation of the process plan

5.1 Tool selection

Due to the hardness of the titanium alloy surface after heat treatment, turning operations face challenges such as a larger diameter and elliptical shape, which result in significant cutting forces. This can lead to tool chipping. For rough turning, YG8 carbide tools, known for their strong impact resistance, are utilized. For semi-finishing and finishing processes, the coated carbide inserts CNMG160612-GJ VP10RT and RPMT10T3MOE-JS VP15TF are employed.

 

5.2 CNC program for finishing parts

According to an analysis of the difficulties in part processing and the CNC manufacturing process plan, the geometric shape of the part is relatively complex. Therefore, computer-aided programming (CAM) is employed. The main steps involved are as follows:

 

Processing Parts and Process Analysis:

This includes confirming the part size, tolerance, and accuracy requirements, as well as determining the feed route, fixtures, gauges, and tools used. Additionally, the programming origin and coordinate system must be established.

 

Modeling of Processed Parts:

Utilize computer software to create a three-dimensional model of the part.

 

Inputting Processing Parameters:

This step involves selecting the machine model, blank size, tool type, and cutting amount, along with other relevant information such as the safety plane, tool trajectory, feed and retract method, and cooling method.

 

Tool Trajectory Generation and Improvement:

Based on the geometric and process information, the system automatically calculates and arranges the tool trajectory. If any issues are identified in the tool trajectory, improvements can be made through human-computer interaction.

 

Trajectory Simulation and First-Piece Trial Processing:

Import the program into the equipment and run it idly to verify the correctness of the tool trajectory. To ensure processing accuracy, a first-piece trial must be conducted to identify any loopholes or deficiencies in the program, allowing for necessary modifications and adjustments.

 

Subsequent Program Processing:

Convert the tool trajectory file into a program that can be accurately executed by the CNC lathe. Fine-tuning of the small end and the outer circle is illustrated in Figure 4.

Taking the precision turning of the outer circular groove 1 as an example, a ball groove cutter with a tool width of 6mm and a tool tip R3.0mm is selected, and the procedure is as follows.

N100
T0000
G00 X2400. Z-70.
X2111.6
S8 M03
M08
G01 X2058.2 F0.3
G03 X2054.983 Z-69.188 CR=2. F0.15
G01 X2059.809 Z-67.406 F0.5
G00 X2116.42
Z2.657
X2100.772
G01 X2110. Z-1.957 F0.3
Z-14.043
X2106.085 Z-16.
X2058.2
G02 X2054.2 Z-18. CR=2. F0.15
G01 Z-68. F0.3
G02 X2055.534 Z-69.491 CR=2. F0.15
G01 X2059.533 Z-67.254 F0.5
G00 X2400.
Z50.
M09
M05
M00

For fine turning of the inner circle of the small end, a 50° sharp tool with a tool tip R of 1.2 mm is used. The procedure is as follows.
N160
T0000
G00 X1600. Z50.
X2047.874
Z3.184
S8 M03
M08
G01 X2039.7 Z-.903 F0.3
Z-226.202
G03 X2038.553 Z-230.282 CR=14.8
G01 X2032.884 Z-240.168
G03 X2029.377 Z-244.054 CR=14.8
G01 X2029. Z-244.35
Z-271.328
X2029.542 Z-271.66
G03 X2036.222 Z-280.649 CR=14.8
G01 X2041.219 Z-377.378
G03 X2039.722 Z-382.422 CR=14.8
G01 X2039.6 Z-382.606
Z-411.1
G00 X1600.
Z50.
M09
M05
M00
M30

The finishing of the big end and the outer circle is shown in Figure 5.