Effect of Composite Material Fixing on Hole Accuracy and Defects During Drilling

Abstract

This study investigates the effect of composite material stiffness on the accuracy of drilled holes and delamination in the drilling process. Two types of composite materials were tested: glass fiber reinforced plastic (GFRP) and carbon fiber reinforced plastic (CFRP). The drilling process was performed using dedicated drill bits. Samples were clamped in a vice of the Avia-VMC 800 HS vertical machining center. Drilling parameters were maintained constant but unsupported element length was changed. The unsupported element length was defined as an unsupported distance between the drilled hole axis and the sample attachment location. The maximum feed force F f was determined in the experiments. The accuracy of drilled holes was estimated by optical microscopy. Diameters of the drilled holes were measured. Results made it possible to determine the recommended unsupported element length at which the hole dimensions were within the dimensional tolerance. The study showed a clear decrease in the drilled hole quality and a significant increase in the feed force, especially in the area of tool exit from the workpiece. In addition, the number of delaminated fibers increased with unsupported element length was determined in the study.

Study on the Machinability of Glass, Carbon and Aramid Fiber Reinforced Plastics in Drilling and Secondary Drilling Operations

“…Optical equipment was used to capture images of the holes in the tool entry and exit zone in the examined composite plates. The effect of an unsupported element length on delamination when drilling holes in polymer composites reinforced with glass and carbon fibers was investigated in [35]. The research results reported in [35] showed that the number of delamination (in the tool exit zone) increased with increasing the distance between the support and the axis of the hole being made.…”

“…The effect of an unsupported element length on delamination when drilling holes in polymer composites reinforced with glass and carbon fibers was investigated in [35]. The research results reported in [35] showed that the number of delamination (in the tool exit zone) increased with increasing the distance between the support and the axis of the hole being made. Figures 5a, 5b and 5c as well as 6a, 6b and 6c show images of the holes in the drill entry and exit zone, respectively, for GFRP, CFRP and AFRP.…”

“…This was determined by drilling using carbide drills and variable machining conditions to determine relationships between cutting forces, hole quality, tool wear, delamination during drilling, and temperature. It was established that for CFRP drilling the spindle speed ranging 500-1500 rpm and the feed rate ranging 0.02-0.08 mm/rev ensure both minimal delamination caused by drilling and low surface roughness [35]. In particular, lower feed (0.02 mm/rev) and higher spindle speed (1500 rev/ min) ensure higher feed force and cutting torque values [36][37][38].…”

Effect of Machining Settings and Tool Geometry on Surface Quality After Machining of Al/CFRP Sandwich Structures

“…Sandwich structures are usually fabricated in their near-final shapes. Two of the most commonly used machining techniques for this type of structures are milling and drilling [4][5][6]. Machining of aluminium alloy/ Carbon Fibre Reinforced Plastics (Al/CFRP) sandwich structures is troublesome as the properties of each layer can vary greatly [7].…”

Investigation of the Surface Roughness and Surface Uniformity of a Hybrid Sandwich Structure after Machining

“…During the machining of a sandwich structure composed of aluminum alloy and a carbon-fiber reinforced polymer (CFRP), it is additionally necessary to overcome difficulties related to the deformation of the upper and lower layers of the material, the interference of metal chips with the composite and the possible accumulation of aluminum shavings or carbon dust between the facings of the sandwich structure if it delaminates [ 5 ]. The heavy-duty carbon fibers used in composites are difficult to break and tend to drag, which very often causes them to develop micro-cracks and to delaminate along the operating direction of the tool [ 6 ]. Milling of CFRP composite requires frequent replacement of the milling tool, as the abrasive properties of carbon fiber cause premature wear.…”