Seco has the edge

seco-has-the-edge
seco-has-the-edge

Composite materials such as CFRP, whilst being able to be machined on conventional CNC machines, react differently to metals during the machining process.


When metals are machined the phenomena known as plastic deformation occurs. However, when machining composites there is no chip to speak of, instead the material splinters or shatters during the removal process. The hard carbon fibres that become fractured during machining cause considerable abrasion to the cutting edge of a tool and, as a consequence, rapid wear. This hardness and characteristics of composites, when being machined, means that conventional TiCN tools suffer from short tool life. Not surprisingly diamond tools such as CVD (chemical vapour deposition) tools or PCD (polycrystalline diamond) inserts are favoured. Although the machining of metals and composites differ, they both generate heat. When machining CFRP, heat dissipation is particularly problematic because no chips are created to carry the heat away. The material itself also has low thermal conductivity and this build-up of heat can cause the material to melt or become damaged. To help mitigate this - sharp angled tools are recommended. For milling and drilling operations tools with high positive rake angles provide a cleaner cut and often incorporate clearance angles that limit the generation and build-up of heat. Cutting tool selection Carbon fibre type, its structure and composition, the manufacturing method employed to create the material etc. - are all variables that affect the ‘machinability’ of CFRP workpieces. These variables, in addition to the type of manufacturing undertaken (e.g. volume series or small batch requirements), the machine tool itself, its age, build and stability, its spindle performance, the work-holding system to be employed and the coolant being used – can all affect machining performance and results, and need to be accounted for in the selection of correct cutting tools. Seco says its engineers can be relied upon to help manufacturers identify and provide the most effective machining strategies and optimum cutting tool solutions. But the problems associated with machining composites aren’t just located at the cutting edge. The material affects the choice and selection of tool holders too because when composites are machined, abrasive particles and dust created during the process can penetrate the tool holder causing damage and wear. To overcome these problems it is advisable to use Shrinkfit tool holders as these provide: A sealed interface between the tool and the holder, thereby eliminating the risk of contamination and particle ingress; Good accessibility to the workpiece; High precision with low run out <3μm at 3xD, which enables higher speeds to be used. Seco’s new range of stocked standard products for machining composite FRP materials consists of six Jabro milling cutter types and two Feedmax drill types - all with Dura Diamond coating (thickness - 6-10μm), as well as PCD routers and drills. In addition, custom tools can be designed and manufactured for special requirements. Seco solid carbide cutters and drills all have a 6% Cobalt substrate and DURA coating. The DURA coating has a superior bonding to the substrate due to the deep cleaning of the substrate before the CVD coating process occurs. DURA has a low surface roughness and, due to the high amount of grain boundaries in relation to volume, can be applied in different thicknesses, thereby increasing tool life. Getting the diamond to bond onto the substrate is always a problem due, in part, to the relatively sharp edges of the cutter – but more because of the presence of Cobalt - used as the binder material. So, before applying the DURA coating the amount of Cobalt on the surface is reduced using a ‘deep cleaning’ process. This removes impurities and roughens the surface allowing for the deeper seeding of the diamond – resulting in a far superior bonding (adhesion) to the substrate. With an increased tool life of eight to ten times compared to that of uncoated tools, the DURA coating provides: Process security; Reliability; Increased tool life. These in turn ultimately provide the customer with reduced costs and improved performance. Seco has already mentioned that when machining composites, there are no chips created. Rather than shearing material away, the impact of the cutting edge of a tool fractures the hard carbon fibres resulting in considerable abrasion of the tool. The micro geometrical design of the tool’s cutting edge is therefore critical in order to prevent matrix material melting whilst still maintaining high removal rates and low tool wear. Seco’s JC800 series is a multi-layered CVD (DURA) diamond coated range of tools. The multi-layering makes it possible to create multi boundaries within the coating grains. This makes the coating, even when thinly applied, very strong and results in the cutting edge maintaining its sharpness – preventing delamination and splintering and reducing thermal build-up. By keeping the thermal load lower on both work piece and tool, higher cutting data can be applied. This means average cutting speeds can be increased and output improved. For example the JC840 features a left hand - right hand helix in one end mill. This makes the tool ideal to operate in non-supported areas in the work piece. Because the cutting forces generated are in opposite direction the tool stabilises the workpiece creating a more reliable process and an improved workpiece surface quality with near zero delamination. Drilling CFRP with Dura coated solid carbide drills Their sharpness and high dimensional tolerance enables superior surface finishes and excellent hole tolerances to be achieved. Seco Feedmax drills are available with C1 and C2 geometries. Seco’s PCD tools are said to be ideal for use in high volume production where they deliver a number of performance benefits: Their sharpness delivers improved surface finishes, good fibre cuts and low heat generation which reduces de-lamination, increases productivity and improves process reliability; Their hardness makes them more wear resistant and extends their life; Their accuracy allows manufacturers to achieve exceptionally tight tolerances and super fine surface finishes; Their thermal conductivity lowers process temperatures generated during cutting operations, allowing higher cutting speeds to be used. Jabro Composite PCD cutters have a special PCD blade design that improves thermal wear resistance, and enables higher feed rates to be employed. The cutters are designed and manufactured with shear angle variations (neutral, positive or negative), which extends their flexibility, and are available in a range of sizes (from 6-16mm diameter). All Jabro PCD cutters have two internal through coolant channels for efficient cooling and temperature control. The new range of Seco Feedmax PCD drills, available in 4-25mm diameter sizes, feature a special 120° drill point design and extremely sharp and durable PCD cutting edges. A particular strength of the drills is their ability to cut for long periods of time without any loss of performance or need for replacement. www.secotools.com

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