Optimizing the machining parameters of bar turning aluminum parts: Improving efficiency and surface quality

In modern manufacturing, bar turning has become one of the core processes for shaft and cylindrical parts machining by virtue of its efficient material utilization and precise forming ability. Aluminum alloys are widely used in aerospace (e.g., aircraft structural components), automotive manufacturing (e.g., engine parts), electronic equipment (e.g., heat dissipation modules) and other fields due to their low density, high specific strength, excellent corrosion resistance and other characteristics.

However, the low melting point, high plasticity and other characteristics of aluminum alloys are prone to lead to chip tumors, surface roughness deterioration and other problems during the turning process, how to optimize the cutting parameters of bar turning aluminum parts in order to balance the machining efficiency and surface quality, has become a key point of concern for the industry. 

1.Comparison of Mechanical Properties of Typical Aluminum Alloys

The machinability of aluminum alloys is closely related to their alloy composition and heat treatment status. Take 6061-T6 and 7075-T6 as examples:

(1) Bar and aluminum alloy material properties

6061-T6: containing silicon and magnesium elements, tensile strength ≥ 260MPa, hardness of about 95HB, with medium strength and good plasticity, suitable for general structural turning.

7075-T6: containing zinc, magnesium, copper elements, tensile strength ≥ 505MPa, hardness of about 150HB, belongs to the high-strength alloys, but the cutting force is large when processing, tool wear is significant.

Both by T6 tempering treatment (solution quenching + artificial aging), strength and hardness significantly increased, but plasticity decreased, resulting in 7075-T6 turning more prone to cutting heat, the need for higher cooling requirements.

(2) The effect of T6 tempering state on processing

T6 treatment of aluminum alloy internal precipitation of reinforced phase (such as 6061 in the Mg ₂ Si phase), although to improve the rigidity of the material, but also exacerbated tool wear. Research shows that the cutting force of aluminum alloy in T6 state is 20%~30% higher than that of annealed state, and the increase in cutting temperature is easy to cause thermal deformation of the workpiece, especially for the bar turning aluminum parts with L/D ratio＞5, it is necessary to control the dimensional accuracy through layered cutting or low temperature cooling.

2. Overview of the process of bar turning aluminum parts

(1) Single-point tool principle

CNC turning with a single-point tool to cut the rotating surface of the bar, the main cutting forces include tangential force, axial force and radial force. The tangential force determines the power consumption, the radial force affects the vibration and runout, and the tool rigidity and workpiece clamping need to be taken into account.

The core advantages of CNC turning include:

High-precision molding: Through the CNC system to control the tool trajectory, it can achieve IT6~IT7 level dimensional accuracy and surface roughness Ra up to 0.8~1.6μm.

Flexible production: no need for complex tooling, parts can be switched by modifying the program, suitable for multi-species small batch production.

(2) Typical process flow

The standard flow of bar turning aluminum parts is as follows:

Clamping and positioning: using three-jaw chuck (for bar diameter ≤ 100mm) or hydraulic chuck, clamping length ≥ 2 times the diameter, to avoid vibration caused by overhanging too long.

Tool setting operation: Determine the coordinate system of the workpiece by laser tool setting instrument or test cutting method to ensure that the starting point of the tool is the same as the zero point of the program (error ≤ ± 0.005mm).

Rough turning: Remove 80%~90% of the residual amount, leave 0.3~0.5mm residual amount for fine turning, adopt large back draft (ap=2~4mm) and medium feed rate (f=0.15~0.3mm/r).

Precision turning: Ensure the final dimensional accuracy, back draft ≤ 0.2mm, feed rate ≤ 0.1mm/r, spindle speed is adjusted according to the tool material (e.g. carbide tool Vc=200~300m/min).

Inspection and adjustment: Use roughness meter to measure the surface roughness, adjust the parameter or rework when it exceeds the difference.

Cleaning and final inspection: Remove chips and burrs, clean the workpiece and apply antirust agent; comprehensively check the shape and position tolerance (such as roundness and coaxiality), and put it into storage after passing.

3. How to optimize the bar turning aluminum processing parameters to improve efficiency and surface quality?

(1) Cutting parameters dynamically match the material characteristics

1) cutting speed (Vc) segment optimization

Low-strength aluminum alloy (such as 6061-T6): the best speed range of 200-300 m/min, at this time the cutting heat is moderate, can reduce the formation of chip tumors, surface roughness Ra can be controlled at 0.8-1.6μm.

High-strength aluminum alloy (e.g. 7075-T6): It is recommended that Vc=150-250 m/min to avoid increasing tool wear due to excessive cutting force, and it can be increased to 280 m/min with TiAlN coated tool.

Prohibited zone: When bar turning aluminum parts, cutting speed over 350 m/min will cause vibration of the machine tool, resulting in vibration lines and deterioration of surface roughness Ra to over 3.2μm. 

2) Feed rate (f) Priority control of surface quality

Rough turning: 0.15-0.3 mm/rev, balancing efficiency and chipbreaking effect, to avoid “step” pattern too deep. 

Precision turning: down to 0.05-0.15 mm/rev, when the cutting thickness is less than the radius of the cutting edge of the tool, can form a continuous cutting, so that Ra ≤ 0.8μm.

ResearchGate test data: every 0.1mm/rev increase in feed rate, the surface roughness value increases by about 0.5μm.

3) Back-eating amount (ap) stratified control of deformation

Rough turning: ap=1.5-3mm (50%-70% of the diameter allowance), a single cut is not more than 1/3 of the tool diameter, to prevent the radial force is too large resulting in long shaft parts “let the knife”. Precision turning: ap ≤ 0.3mm, give priority to the use of “one go forming”, reduce the cumulative error of multiple feed, roundness error can be controlled within 0.003mm.

(2) Tool and clamping system optimization

1) Tool material and geometric angle adaptation

Material selection.

Ordinary aluminum alloy (such as 6063): YG6X carbide tool, low cost and good wear resistance. 

High-silicon aluminum alloy (such as A380): PCD (polycrystalline diamond) tools, hardness of 8000-9000HV, life is 10-20 times that of cemented carbide. 

Angle optimization.

Front angle γ₀=15°-20° (increasing front angle can reduce cutting force, but too large is easy to chipping) Sub-deviation angle κᵣ'=5°-8° (reducing sub-deviation angle can reduce surface roughness). 

2) Clamping rigidity enhancement strategy

Chuck selection: diameter ≤ 80mm round bar using three-jaw chuck, clamping length ≥ 1.5 times the diameter; shaped bar with a four-jaw chuck, with the percentage table to find the right. 

Long shaft support: shaft parts with L/D ratio >5 are clamped with “one clamp and one top”, and 50-100N preload is applied to the top of the tailstock to reduce the vibration of overhanging. 

(3) Cooling, lubrication and chip removal system upgrade

1) Precise coolant supply program

Roughing stage: Use 10% emulsion flood cooling (flow rate 40-60L/min) to reduce cutting temperature by 60-80℃ and reduce tool bond wear. 

Fine turning stage: switch to MQL (Minimum Quantity Lubrication), use vegetable oil-based lubricant (flow rate 80-120mL/h) with high-pressure air blow (0.8MPa), Ra value can be further reduced by 0.2μm.

Dual-nozzle arrangement: the main nozzle cools the front face of the tool, and the secondary nozzle blows away the chips, increasing the chip removal efficiency by more than 3 times. 

2) Integrated design of chipbreaking and chip removal

Tool chipbreaking groove: Arc-shaped groove is ground on the front face of the tool to force the chips to curl into C shape and avoid the banded chips from being entangled. 

High-pressure air blowing parameter: the nozzle angle with cutting area is 30°, the distance is 10-15mm, and the air pressure is 1.2MPa, which can increase the speed of aluminum chips blowing away from the tool to more than 20m/s. 

(4) Based on multi-objective parameter optimization method

1) Taguchi orthogonal test design

Bar turning aluminum test parameters, cutting speed (three levels: 180/220/260m/min), feed rate (three levels: 0.1/0.15/0.2mm/rev), depth of cut (three levels: 0.3/0.6/0.9mm) as a factor, surface roughness Ra and material removal rate (MRR) as a response index. 

The results show that the feed rate contributes 42.3% to Ra and the depth of cut contributes 51.7% to MRR, and the optimization increases the comprehensive efficiency by 28% and improves the surface quality by 35%. 

2）On-line monitoring and dynamic adjustment

Vibration triggering mechanism: when the acceleration sensor detects vibration amplitude > 8μm, the system automatically reduces the feed rate by 15% to avoid tool breakage. 

Temperature feedback control: When the thermocouple monitors that the temperature in the cutting zone is >130℃, the coolant flow rate is automatically increased to 50L/min to prevent aluminum chips from adhering and causing surface deterioration. 

4. Typical material optimization parameters for bar turning aluminum parts table

Summary: Through this paper, we can learn that the core of optimization of bar turning aluminum parts lies in the “parameter layered matching material - tool - cooling system”, through the dynamic adjustment of the three elements of cutting, strengthening the rigidity of the clamping, precise control of cooling and lubrication, combined with on-line monitoring and design of the test method, it can be realized that the efficiency can be increased by 30% -50%, surface roughness reduced by 30%, and the surface roughness reduced by 50%. Through dynamic adjustment of the three elements of cutting, strengthening of clamping rigidity, precise control of cooling and lubrication, combined with online monitoring and experimental design methods, it can realize the goal of improving efficiency by 30%-50% and reducing surface roughness by 40%-60%.