Multi-Objective Optimization in Single-Shot Drilling of CFRP/Al Stacks Using Customized Twist Drill

Area of Science:

• Materials Science and Engineering
• Manufacturing Processes
• Aerospace Engineering

Background:

• Aircraft construction increasingly utilizes composite-metal stacks, particularly carbon fiber reinforced polymer (CFRP) with aluminum alloys.
• Single-shot drilling is standard for creating aligned holes in these stacks, but conventional drills face rapid wear and poor surface quality due to material property contrasts.
• Existing drilling methods incur high costs due to frequent drill bit replacement, posing a challenge for aircraft component manufacturers.

Purpose of the Study:

• To investigate the impact of customized tungsten carbide (WC) twist drill geometries on hole quality during single-shot drilling of CFRP/Al7075-T6 stacks.
• To identify the optimal drill geometry that minimizes thrust force and improves surface roughness.
• To develop correlation models for predicting drilling performance based on tool geometry.

Main Methods:

• Fabrication of twenty WC twist drills with varied chisel edge angle (30-45°), primary clearance angle (6-8°), and point angle (130-140°).
• Drilling experiments on CFRP/Al7075-T6 stacks (3.587 mm thickness) at 2600 rev/min and 0.05 mm/rev feed rate.
• Utilized Response Surface Methodology (RSM) for experimental design and Analysis of Variance (ANOVA) to assess parameter significance on thrust force and hole quality.

Main Results:

• The primary clearance angle was identified as the most significant parameter influencing drilling thrust force and hole surface roughness, followed by the chisel edge angle.
• Correlation models were established to predict CFRP and Al7075-T6 thrust forces and hole surface roughness as functions of drill geometry.
• The optimal drill geometry determined was 45° chisel edge angle, 7° primary clearance angle, and 130° point angle, yielding prediction errors between 6.64% and 8.17%.

Conclusions:

• Customized WC twist drill geometry significantly enhances hole quality in single-shot drilling of CFRP/Al7075-T6 stacks.
• The developed correlation models provide a reliable method for predicting drilling performance indicators.
• The findings offer a practical guideline for optimizing single-shot drilling processes in aircraft manufacturing, reducing costs and improving efficiency.