COMPOSITES I TOOLING
coated and diamond veined cemented carbide tools. These come in standard, semi-standard and engineered versions. Polycrystalline diamond (PCD) is
a very hard tool material, ideal for machining composites as well as stacked materials. A drill with cemented carbide as the core tool material with cutting edges of PCD is seen as the best option for drilling composites today, when quality levels and consistency are being tightened and higher demands are being made on productivity. Carbide offers the means to strengthen
the tool through its cutting geometry and through the drill shank, optimising cutting action and maximising clearance and material evacuation. This makes carbide-based drills especially suitable for many unstable operations involving hand tools and uneven thrust from operators, as well as variations in guide-bush/drill clearance. As such, they are also ideal for many power-fed portable operations and in machines involving single passes in stacked materials. Carbide and PCD have different limitations as tool materials: carbide is strong but wears quickly, while PCD is very wear resistant but more brittle. Combined, however, they make for excellent hole-making solutions. A range of modern standard, tailor- made and engineered drills with a PCD-
coating are available in different grades and geometries to suit material and machining conditions. These drills have also been developed to produce high quality holes in composites ranging from fibre-rich to resin-rich, as well as offering all-round alternatives and suitability for stacked materials, including titanium. Two standard drills offer a choice to optimise operations in machines and portable set-ups. Selection is according to the character of the composite at hand, with different cutting geometries and PCD grades. The CoroDrill 854 is best suited to fibre-rich materials as it features the capability to minimise hole fraying tendencies. This drill has spurs at the periphery to better cut fibres, avoiding splintering. It is also suitable for stacked material combinations involving composite and aluminium. The CoroDrill 856 has been developed
to specialise in cutting resin-rich composites. Its double-angled cutting geometry provides the ability to make softer entries and exits, thereby minimising delamination tendencies. Semi-standardisation is the route
for an all-round drill for composites and aluminium-stacked materials, such as where lightning-strike protection is added to aerospace materials. The versatility achieved with semi-standard options of this drill, for mainly fibre- rich materials, provides big potential for it to be the best practice solution for numerous applications. For integrating PCD in carbide, vein
The critical factors of tool selection: Sandvik Coromant and Precorp PCD coated and vein technology drills have been developed as dedicated solutions
technology is an advanced technique based on a patented process developed in the mid-1980s. It makes optimal use of a hard, wear resistant cutting edge in a tough drill shank. The carbide drill is equipped with a PCD edge, brazed into a slot positioned away from the drill tip, creating a high strength joint. The final tool geometry is then ground, leaving the edge shielded to an extent by the carbide part of the drill. The process allows for a variation in cutting geometries that were impractical or even impossible to achieve with
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The challenge of drilling holes: A number of machining factors have to be defined and addressed to determine the most suitable cutting tool and process
conventional PCD-bit processes. Vein technology also permits flexibility in tool design to cope with everything from less rigid set-ups, through to stable, high volume applications with precision holes. A PCD vein drill is typically engineered for a solution in an automated set-up. It provides a sharp cutting geometry that stays keen to the most abrasive of composites. Part of its unique design can include strengthening of the tool corner to allow higher cutting speeds in combination with tight entry and exit limits. Alternatively, PCD vein drills may be engineered for composite stacked metals. As such, the drill can feature micro- grinds located to cope in concentrated areas of high stress, providing it with the ability to remain sharp throughout its tool life. The tool edge cuts the composite fibres with a low thrust force, resulting in minimal fibre breakout, delamination and exit burrs on the metal in the stack. In conclusion, dedicated cutting tools
are critical to successful hole-making in composite and stacked components. The demand for quality, component consistency, long tool life, security, zero scrap and short throughput times requires tool technology based on a record of experience along with extensive
R&D resources. y
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