The idea of using fibres embedded in a supporting matrix hasbeen around longer initially appreciated. From the earliestbeginnings of mud bricks reinforced with straw - to the firstcomposite bows made with wood, bone and pine resin - it wasrecognised that composite materials deliver superior propertiesthan if used in isolation.

The aerospace and defence, wind energy, automotive, civilconstruction and sporting goods industries have all come toadopt composites for high performance applications – and thedemand continues to grow. A report by Credence Research in2019 estimated a CAGR of 9.3% for carbon fibre reinforcedplastics during the period 2017-2025. Duncan Thompson,Product Manager at ANCA, notes the increased sales inquiriesin this area, reflecting a growing demand by tool manufacturersto produce cutting tools to service this specialist market.

Duncan comments, “commercial applications for compositescontinues grow, and with that, the market space for specialisedcutting tools also expands. Cutting tool manufacturers need toadopt a variety of cutting tool designs and technologies,developing specialised tools for the wide and varied range ofcomposites used today. ANCA has been working with customers

to design innovative software that help address these needs,creating new tool geometries, and machines that can grind orerode market leading CFRP cutting tool solutions.”

Understanding the composite market

Today’s composites industry uses a variety of matrix materials(thermoset epoxy, phenolic, polyimide, etc.) and fibres (carbon,kevlar, glass, etc.) to suit different applications. In a polymermatrix composite material, the matrix itself is not ductile likemetal. Instead, it tends to be soft but very tough. Metal cutting

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Meeting the demands of a complex application: compositematerial cutters offer a growing opportunity for specialisedcutting tool manufacturers with 9.3% predicted growth for carbon fibre reinforced plastics by 2025*

Figure 1: Composites can have unidirectional fibre layout, or bidirectional weave

involves plastic deformation forming chips that serve to removeheat from the point of cutting. Conversely, when analysed at themicro level, machining of polymer matrix does not form chips,but rather a fine ‘dust’ that results from localised fracturing.Heat is not readily transported away from the cutting edge by the matrix due to its low thermal conductivity. The nextchallenge comes from the embedded fibres which are strong,stiff and highly abrasive when cut. Different compositemanufacturing methods call for use of unidirectional tape or bi-directional fabric weave layered in different directions to suitthe application. These will behave differently when beingmachined.

To complicate matters more, Carbon Fibre Reinforced Plastics(CFRP) can be stacked with aluminium or titanium support instructural applications. These conditions create machiningoperations that need one tool to cut materials with dramaticallydifferent properties.

Grinding with variable requirements

Duncan says: “Machining of these highly abrasive and non-homogenious materials requires careful consideration of thebest tool for the job, be it drilling, trimming or pocketing. As aresult, cutting tool manufacturers are continually creating newtool designs to meet this need.”

One of the most widely used composite materials is CFRP,principally due to its excellent strength to weight ratio andcorrosion resistance. Yet, in machining this material, correcttool selection is critical, otherwise a variety of quality issues canresult, including:

• Delamination, where the matrix separates from the fibre• Uncut fibres that remain at the cut edge• Spalling where larger fragments of matrix break away• Inconsistent cut geometry can, for example, see holeroundness fall outside acceptable tolerances

• Hole exit burring when drilling• Heat damage to the matrix• Rapid tool wear

The consequences of these types of issues are wasted time andmoney from tools that rapidly wear out, but more importantlydamaged or scrapped work pieces.

Today, ANCA machines are used by cutting tool manufacturersto create a variety of cutting tools for different compositemachining applications.

Tool Essentials for CFRP

Firstly, composite cutting tools come in one of three differentmaterial types. Carbide, coated carbide or PCD. Each has itsadvantages.

Carbide can be easily fashioned into any required geometry andwill produce a keen cutting edge but will also be expected towear quickly. For that reason, it will typically only get used inmanual and/or roughing operations where the accuracy of thefinal cut is not critical – most likely because it will be followedby a finishing cutter made of either coated carbide or PCD.

Coated carbide similarly offers flexibility in that it can be groundinto a variety of geometries, but has an additional (CVD) coatingapplied that can dramatically increase tool life. Thedisadvantage of these tools is that it is generally considereduneconomical to resharpen them.

The third class of tools is poly-crystalline diamond (PCD) tools.The cutting edge on such tools are typically produced using anelectro erosion machine, such as the ANCA EDGe, or laserablation processes.

This typically will give a keener cutting edge than CVD coatedtools and additionally can be resharpened, which extends theusable life of the tool. Within PCD tools, there are threecommon forms. Firstly, they can be a carbide base with brazedPCD inserts giving a shear cutting edge. This type of tool iscommonly used to produce complex step or profile tools and ismost easily produced by tool manufacturers looking to enter thePCD tool market.

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Machining of these highly abrasiveand non-homogenious materials requirescareful consideration of the best tool forthe job, be it drilling, trimming orpocketing. As a result, cutting toolmanufacturers are continually creatingnew tool designs to meet this need.

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Figure 2: ANCA EDGe machine used for PCD tool erosion

Figure 3: ANCA EDGe machine eroding a veined PCD drill fromSandvik Coromont

The next alternative is the veined PCD technology, initiallydeveloped in house by Sandvik-Coromont Spanish Fork (USA).This can create a helical vein of PCD, co-sintered in the carbideblank. The helical cutting edge is seen to offer a superiorcutting geometry compared to that of a shear tool, and inaddition coolant holes can be included through the carbideportion, which improves cutting conditions. For these tools, thecutting edge geometry is largely defined by the PCD vein thatwas sintered.

The answer to this challenge is typically a solid PCD tip with acarbide body. While these can be expensive up front, RobbJack,based in California, USA, produces such tools using rotaryelectro erosion process on the ANCA EDGe. This allowscomplete freedom for producing any tool (drill) geometry theyrequire.

Hole Drilling CFRP

Hole drilling is a commonly performed operation necessary toallow joining of CFRP structures. CFRP drills will have a pointgeometry distinct to that of metal cutting drills. ANCA’sToolroom software, whether applied to grinding or PCD erosionprocesses, allows creation of various special drill points suitedto CFRP, including compound point angles and brad or W-pointgeometry. Specialised drill points result in minimiseddelamination as the drill penetrates through the CFRP layer,maintaining hole geometry (roundness) and offering superiortool life.

An alternative approach for hole making is milling cutters usedwith interpolated orbital motion. While it’s a slower processrequiring a CNC machine, it has advantages with creating largerholes or holes on curved surfaces. In addition, the smallerthrust force reduces delamination at the exit point of the hole.

Milling CFRP

Another common cutting operation is trimming or cutting ofCFRP with specialised milling cutters. Again, coated carbideor PCD cutters are the order of the day.

For trimming or edge cuts, up-down cutters are most commonlyused. The opposing direction of the cutting edges ensurescutting forces are toward the middle of the CFRP layer, therebyreducing the likelihood of delamination. Shallow flute depthhelps increase tool rigidity.

Burr style routers featuremany shallow flutes that havechip breaker teeth includedon them. This form of cutterworks to produce localisedcutting forces that caneffectively shear the fibres.

ANCA grinders support themanufacture of these types of tools with dedicatedcompression router or burrcutter software packages.

For surface or pocket milling,down cut endmills again willcreate downward cuttingforces that minimise surfacedelamination. Brazed PCDrouters are also common for this application with ball or cornerradius cutting edge forms which are easily produced on theANCA EDGe.

Duncan Thompson concludes “demand for specialisedcomposite cutting tools will only continue to increase,presenting great market opportunities for tool makers with theright knowhow and manufacturing capabilities. With industryleading tool design software and tool manufacturing machines,ANCA continues to work closely with its customers at the cuttingedge of the composite cutting tool market.”

Figure 4: PCD insert brazed onto a carbide tool base. EDGe erosion process is used to generate an accurate corner radius profile

Figure 6: Compression cuttersminimise damage to the CFRP cut edge with cuttingforces toward the centre ofthe CFRP layers

Figure 7: ANCA’s ToolRoom software allows creation of uniquetool geometries for CFRP cutting applications

Figure 5: PCD vein is co-sintered with carbide allowinggeneration of a helical cutting edge

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