Drilling Of Stacks Research Articles

Tool wear and hole quality when single-shot drilling of metallic-composite stacks with diamond-coated tools

This article details experimental work performed to evaluate the effects of varying feed rate (0.08 and 0.15 mm/rev) and tool coatings (diamond-like carbon and chemical vapour–deposited diamond) on tool wear modes and hole quality when drilling 30-mm-thick Ti-6Al-4V/carbon fibre–reinforced plastic/Al-7050 stacks in a single-shot operation. At a feed rate of 0.08 mm/rev, the diametrical accuracy of holes produced by both the chemical vapour–deposited diamond and diamond-like carbon–coated drills (6.38 mm diameter) was comparable within a tolerance of ±0.04 mm even after 70 holes. However, in terms of cylindricity, holes machined with chemical vapour–deposited diamond were significantly better than those produced using the diamond-like carbon–coated drills by a factor of ∼2 (65.7 vs 140.6 µm). A similar trend was also observed for hole out of roundness. Burr height at hole entry locations (Ti layer) ranged from ∼0.03 to 0.08 mm for all trials undertaken at the lower feed rate level; however, the diamond-like carbon–coated drills generated exit burrs which were ∼4 times larger than their chemical vapour–deposited diamond-coated counterparts. Subsequent wear analysis showed that diamond-like carbon–coated drills operating at 0.08 mm/rev typically exhibited progressive abrasion, workpiece adhesion and chipping leading to fracture of the tool corner, while fracture due to fatigue was prevalent in tests carried out at the high feed rate level. In contrast, poor adhesion of the chemical vapour–deposited diamond coating to the carbide substrate led to premature flaking, severe chipping and fracture of the drill cutting and chisel edge.

The Effect of Cutting Speed and Feed Rate on Hole Surface Integrity in Single-shot Drilling of Metallic-Composite Stacks

Experimental work was carried out to evaluate the influence of cutting speed (Ti/CFRP/Al: 30/120/120 and 36/144/144m/min) and feed rate (0.05, 0.08, 0.12 and 0.15mm/rev) on workpiece surface integrity following single-shot drilling of multilayer metallic-composite stacks (Ti-6Al-4V/CFRP/Al-7050) using CVD diamond coated tooling. When operating with the lower cutting speed set of 30/120/120m/min and a feed rate of 0.08mm/rev, average hole surface roughness (Ra) was ∼ 0.60, 0.87 and 0.27μm in the Ti, CFRP and Al layers respectively after 30 holes. Roughness values in the stack increased to 0.84, 1.6 and 0.43μm Ra when employing the higher cutting speed of 36/144/144m/min, with the drill lasting only 20 holes. Microhardness depth profile evaluation of the machined surfaces showed no appreciable variation in both the Ti and Al material, irrespective of cutting conditions. Matrix cracking and burn were apparent in the CFRP layer as feed rate increased due to greater wear of the drill corner.

A Comparative Study of Carbide Tools in Drilling of CFRP and CFRP-Ti Stacks

A comparative study was conducted to investigate the resulting tool wear and hole quality when drilling the stacks made of titanium (Ti) and carbon-fiber reinforced plastic (CFRP) versus CFRP only plate using micrograin tungsten carbide (WC) twist drills. The experiments were designed to first drill CFRP alone to create 20 holes. Then, CFRP mechanically stacked with Ti was drilled for the next 20 holes with the same drill bit. This process was repeated until drill bit failure. The drilling experiment was performed at two distinct speeds. Scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM) were used for tool wear analysis. Hole size, hole profile, surface roughness, and Ti burrs were analyzed using coordinate measuring system, surface profilometer and optical microscope. The experimental results indicate that the Ti drilling accelerated flank wear while CFRP drilling deteriorated the cutting edge. Entry delamination, hole diameter errors, and surface roughness of the CFRP plate became more pronounced during the drilling of CFRP-Ti stacks when compared with the results from the drilling of CFRP only. Damage to CFRP holes during CFRP-Ti stack drilling may be caused by Ti chips, Ti adhesion on the tool drill margin or the increased instability as the drill bits wear.

Axial and Orbital Drilling of Thick Stacks for New Aircraft Assembly Process

Axial and Orbital Drilling of Thick Stacks for New Aircraft Assembly Process

Local Approach of Wear in Drilling Ti6Al4V/CFRP for Stack Modelling

The drilling of stacks made of carbon fibre composite material (CFRP) and metal (aluminium or titanium alloy) is an operation more and more common in aerospace industry. However, this critical machining operation is not yet fully controlled. The knowledge of the cutting forces and the wear phenomenon is an important issue to assure a good quality of the hole.The studies on the stack drilling usually do not break down the operations on both materials (CFRP and metallic alloy), which does not allow a full understanding of the impact of each part of the stack on the behaviour of tool, especially regarding its wear. Nevertheless, a study of the drilling of a single material does not lead us to the understanding of the stack drilling, because of the influence of a piece toward another.This study, firstly, discusses the drilling of each material of the stack, titanium alloy Ti6Al4V and CFRP, individually. The impact of the local wear is assessed by investigating the variation of the cutting forces along the cutting edge (the computation is made by the decomposition of the thrust force and the torque during the progressive engagement of the drill point).Furthermore, this study explains the drilling of an alternation of titanium alloy and CFRP in order to model its effect on a stack, while allowing the analysis of the wear for each material.

Hole quality assessment following drilling of metallic-composite stacks

The use of material stacks comprising titanium, carbon fibre reinforced plastics (CFRPs) and aluminium is expanding for structural aerospace applications, especially where high mechanical loads exist such as for aircraft wing and tail-plane components. Here, the production of bolt/fixation holes is essential to the manufacturing process in order to facilitate part assembly. The paper outlines an analysis of hole quality/integrity following drilling of titanium/CFRP/aluminium stacks under flood cutting fluid and spray mist environments. Uncoated and coated (CVD diamond and hardmetal) tungsten carbide drill performance is evaluated against key response measures including hole size, out of roundness, cylindricity, burr height, hole edge quality, average surface roughness ( R a), microhardness (of the metallic elements) and swarf morphology. Burr height (up to 0.5 mm) was observed to be greater at the hole exit (aluminium) compared to hole entry (titanium) while delamination was significantly reduced when machining CFRP in the stack configuration as opposed to a standalone arrangement. Spiral shaped continuous aluminium swarf was prevalent while both short and long helical chips were found with the titanium material when cutting wet. In contrast, the CFRP layer typically produced dusty black composite particles suspended in the soluble oil of the coolant emulsion.

Drilling of composite and titanium stacks with alternating machining parameters by PCD drill

Drilling of multilayer materials with conventional machining parameters are selected in such a way that it suits the requirements of both composite and metal, which is already unsuitable for machining high holes quality due to differential mechanical and thermal properties of stacks. The present study attempts a newer research on drilling of carbon fibre reinforced plastics (CFRP) and titanium stacks with alternating machining parameters by PCD drill in order to minimise the delamination of CFRP and burrs in titanium alloy. Results show that drilled holes quality can be improved by optimising the drilling parameters for each material. It was found that PCD drill outperformed better in drilling CFRP-titanium stacks for its high hot hardness and wear resistance. From the 25th to 50th hole, the thrust force of CFRP laminates is stable of 60±5 N owing to normal wear stage. This region is ideal for the drilling performance of PCD drill.

A study on the drilling of composite and titanium stacks

An experimental study on drilling of graphite/bismaleimide (Gr/Bi) titanium (Ti) stacks was conducted by using different cutter materials with a standard geometry to understand and characterize the process. The tool materials used were high-speed steel (HSS), high-speed cobalt (HSS-Co), and carbide. It was observed that at the interface of Gr/Bi–Ti, high temperatures induced material damage near and around the hole region. Dissimilar mechanical and thermal properties affected the tool life and allowed for increased matrix degradation and burr formation in Ti, regardless of the cutting tool material. As a result, fewer holes were produced when high spindle speeds and slow feeds were used. It was also found that carbide drills outperformed all other tools in terms of tool life, minimal surface damage, and heat induced damage on both workpiece materials.