Abstract
Ball-end cutters are widely used for machining the parts of Ti-6Al-4V, which have the problem of poor machined surface quality due to the low cutting speed near the tool tip. In this paper, through the experiments of inclined surface machining in different feed directions, it is found that the surface adhered damages will form on the machined surface under certain tool postures. It is determined that the formation of surface adhered damage is related to the material adhesion near the cutting edge and the cutting-into/out position within the tool per-rotation cycle. In order to analyze the cutting-into/out process more clearly under different tool postures, the projection models of the cutting edge and the cutter workpiece engagement on the contact plane are established; thus, the complex geometry problem of space is transformed into that of plane. Combined with the case of cutting-into/out, chip morphology, and surface morphology, the formation mechanism of surface adhered damage is analyzed. The analysis results show that the adhered damage can increase the height parameters Sku, Sz, Sp, and Sv of surface topographies. Sz, Sp, and Sv of the normal machined surface without damage (Sku ≈ 3) are about 4–6, 2–3, and 2–3 μm, while Sz, Sp, and Sv with adhered damage (Sku > 3) can reach about 8–20, 4–14, and 3–6 μm in down-milling and 10–25, 7–18, and 3–7 μm in up-milling. The feed direction should be selected along the upper left (Q2: β ∈ [0°, 90°]) or lower left (Q3: β ∈ [90°, 180°]) to avoid surface adhered damage in the down-milling process. For up-milling, the feed direction should be selected along the upper right (Q1: β ∈ (−90°, 0°]) or upper left (Q2: β ∈ [0°, 90°)).
Highlights
The titanium alloy Ti-6Al-4V is widely used in aerospace, chemical, and medical industries due to its advantages of high strength, low density, corrosion resistance, and good performance at high temperatures [1,2]
The subject of this paper is to study the formation mechanism of surface adhered damage in ball-end milling of Ti6Al4V, and it is considered that this damage is related to the case of cutting into/out within the tool per-rotation cycle
The cutting edge cuts into the engagement area from B in the Q2 range, compared with Q1, and there is no adhered damage on the machined surface
Summary
The titanium alloy Ti-6Al-4V is widely used in aerospace, chemical, and medical industries due to its advantages of high strength, low density, corrosion resistance, and good performance at high temperatures [1,2]. High strength and low thermal conductivity are the causes of difficulties with the machinability of Ti-6Al-4V [3,4], and it is important to find ways to increase machinability by cutting titanium alloys. Ball-end cutters are the commonly used tools in the milling process of Ti-6Al-4V, which have strong adaptability to the change of surface curvature [10]. The ball-end cutter has the problem of zero cutting speed at the tool tip, which often leads to the deterioration of surface quality and the phenomenon of ploughing [11,12]. High cutting temperature, large milling force, and serious tool wear are common problems, which have adverse effects on the surface quality of parts [13]
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