IMPACT OF PROCESS PARAMETERS ON DELAMINATION FORMATION OF FREEZE CLAMPED HIGH MODULUS CFRP

Sabbir Uddin

doi:10.7273/000006976

Given its popularity in the aerospace industry, precision machining of high-modulus thin plate Carbon Fiber Reinforced Plastics (CFRP) is paramount. To achieve high precision and low defects, selecting the right clamping methods for the CFRP plate becomes crucial to ensure the desired precision of the post-machined plate. This thesis investigates the effect of temperature, CFRP clamping strategies, tool condition, CFRP ply weaving, and machining parameters (feed rate, cut width, fiber orientation) on the damage characteristics, surface delamination length, and forces required to edge trim CFRP thin plates. Three different clamping methods were employed: freeze clamping method, cold mechanical clamping method, and ambient temperature mechanical clamping method. To analyze the impact of clamping methods, 25.4 m slots with a 1.27 mm cut width were cut under all three clamping conditions with a feed rate of 16.932 mm/sec. Experiments were conducted on four different types of coupons differentiated based on the fiber orientation of the unidirectional bottom ply (0°, 45°, 90°, and 135°). To understand more, further experiments were conducted with the freeze clamping scenario. For the second phase of experiments, the feed rate was changed between 4.233 mm/sec, 10.5825 mm/sec, and 16.932 mm/sec. Depths of cut varied between 0.254 mm, 0.762 mm, and 1.27 mm. The required force was measured for each coupon. Delamination lengths were also measured on each coupon's woven top and unidirectional bottom surface. All the experiments were conducted inside a 3-axis CNC mini mill. The spindle speed was kept at 6000 rpm. For the experiments, a high modulus CFRP (HR 40) plate with a thickness of 1.27 mm was cut into multiple 127 mm * 22.86 mm coupons. Stat-Ease was used to design the experiments, while Lab-View software recorded the required forces. A 3-axis force sensor was used to measure the forces. It was found that the freeze clamping method reduces the deamination length the most despite requiring a higher force than the other two clamping methods. The tool's quality impacted the required force, MMR, cut depth, and feed rate. With the increasing value of MMR, cut width, and feed rate as well as worn out tool increasing the required force to cut the CFRP coupons. Increasing the value of MMR, cut width, and feed rate also increases the value of delamination. Similarly, worn-out tools reduce the surface quality by expanding the delamination length. It was also observed that weaving on the surface can minimize delamination. Fiber orientation also influences the delamination, with 90° and 45° producing some of the worst cases of delamination. Delamination was lower on 135° coupons compared to these two and the weakest on 0° coupons. All the experiments indicate that the lowest delamination fresh tool should be used at a lower MRR. Cuts should be done at 0° fiber orientation, and surfaces should be weaved. To get the best surface quality freeze clamping should be employed in case of edge trimming thin plate CFRP. The findings from the thesis are particularly important for industries that require strong materials with light weight. The aerospace and automobile industries could particularly benefit from these findings.

IMPACT OF PROCESS PARAMETERS ON DELAMINATION FORMATION OF FREEZE CLAMPED HIGH MODULUS CFRP

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