Figure 247. By utilising a ball-nosed cutter geometry for die-sinking sculptured surfaces, this reduces nishing stock needed to be subsequently removed. [Courtesy of Sandvik Coromant] . Machining and Monitoring Strategies .. Sculptured Surface Machining – with NURBS Prior to a discussion on the application ‘curve-t- ting’ with ‘Non-Uniform Rational Bezier-Splines’ – ‘NURBS’ for short, it is worth a brief review into the background as to why there has been a wide-ac- ceptance of them for machining operations involving sculptured surfaces. e technique of curve tting is not new, it was devised in the 1960’s, where indirect methods were found making it relatively easy to ma- nipulate these curves – without recourse to modify- ing the dierent equation parameters that dened the sculptured surface. In a typical system, a complex curve geometry would be comprised of several discrete curves – termed a ‘spline’ , equally, a surface is simply a curve with an extra dimension. us, for ‘curve-t- ting’ the cubic method is particularly suited, although a modied cubic approach that can accommodate the uneven spacing of ‘nodes’ – the start and end points – has particular benets when digitising surfaces. In France, Bezier who at that time was working for the automotive company Renault, was intrigued by car body design and found the ‘point-and-slope technique’ for curve-tting rather crude and inconvenient for accurate and precise curve design (i.e see Fig. 248a). Hence, Bezier’s philosophy was to nd a way of manip- ulating the individual parameters contained within the curve’s basic equation, but in a more easy and in-direct manner. Bezier utilised an ‘open polygon’ (i.e a plane gure of many angles and straight sides), by which a curve that approximates to passing through the start and end points of the open polygon: results in a de- signer having the ability to change the polygon and as such, achieving dierent results. By having more de- ned points in the polygon, this produces additional exible control for surface manipulation. Further, the curves generated are formed by equations comprised of parameters raised to higher powers than that of the cubic varieties, thereby having longer and more com- plex mathematical expressions. Such a curve, is a dis- crete segment in a complex curve and these segments must be joined together. In the Bezier ‘curve-tting’ technique, the transition between the curve segments, or ‘patches’ – the surface equivalent to a line segment, requires close study by the designer. A further renement, but not one developed by Bezier although incorporating his mathematical ex- pressions, was that of the ‘B-Splines’ 46 , which ensure 46 ‘B-Splines’ , were originally introduced by Cops De Bore. a smooth transition between segments/patches. While yet another and improved renement to the Bezier equations, was the development of non-uniform B- Splines – which could tolerate an uneven spacing of the nodes. Terminology which is not usually perceived, but is associated with the term ‘NURBS’ , includes the ‘rational’ and ‘non-rational’ parametric surfaces. So, a ‘rational’ parametric surface may be represented in many forms, with mathematical precision. While the cubic non-rational variety cannot express an 90° arc with mathematical precision, although it has adequate accuracy for machining requirements. e amalga- mation of the two ‘curve-tting’ approaches, namely, that of the ‘rational’ parametric surfaces together with their ‘non-rational’ counterparts, results in Non-Uni- form Rational B-Splines – ‘NURBS’. Hence, ‘NURBS’ in its simplest form, is a data compression algorithm that reduces the data necessary to dene curved sur- faces. In order to successfully utilise ‘NURBS’ impressive ‘curve-tting’ abilities, the term ‘NURBS-interpolation’ was coined by Siemens Energy and Automation – when they rst introduced its capabilities onto the market. With its ability to reduce data in dening complex curves, ‘NURBS’ oers signicant benets, such as: ties up less CNC memory producing shorter programs; al- lows higher feedrates to be exploited; produces shorter cycle-times; reduces tool vibrations – hence enhances tool wear rates; improves machined surface geometric denition and nishes; coupled to increased part pro- le accuracy and precision. Today’s CNC controllers have large memories with very high block processing speeds that can ap- ply sophisticated ‘look-ahead capabilities’ that can scan the anticipated programmed cutter path for abrupt changes. So, these ‘real-time algorithms’ can not only ‘see’ the expected turns coming, but will slow down the feedrate to keep the cutter on its conrmed path and avoid potentially inconvenient moments of ‘data-star- vation’. Moreover, even these enhanced CNC features will struggle when a dense cluster of data points gen- erated by linear interpolation possibly causing block processing problems, having the aect of signicantly reducing the feedrate as it ‘corners’ from each line seg- ment to the next. Consequently, ‘NURBS’ tool paths will undoubtedly alleviate data starvation and feedrate troubles by being more ecient, but like point-to-point toolpaths (Fig. 248b), they are not exact representa- tions of the surface. e ‘NURBS’ toolpath must be calculated which involves some approximation – simi- lar to the ‘chordal deviation parameter’ used in many CAM systems (Fig. 248c). Chapter Figure 248. CNT tool cutter path control while contouring sculptured surfaces – utilis- ing nurbs. [Courtesy of Sandvik Coromant] . Until about a decade ago, there existed only one practical way to represent free-owing curves in a cutter path. is was despite the fact that CAD/CAM systems could mathematically dene virtually any geometric shape with smooth curves. ese CAD/ CAM systems generated pristine forms which would Machining and Monitoring Strategies have to be converted into a recognisable program- ming structure that the machine tool’s servo-drives could understand and apply. is ‘translation’ took the form of representing complex curves as a series of straight lines, or linear segments, being joined end-to- end within a user-dened tolerance band (Fig. 248a). us, the length of each linear segment was governed by the curvature of the prole and the tolerance band previously set. Any tight precision radii on the work- piece, requires very small tolerance bands, creating a large number of segments needing considerable pro- grammed-blocks of toolpath data. is technique is acceptable in many respects, but its hardly very e- cient because complex 3-D surfaces need large quan- tities of data to accurately represent their geometric proles. is conict between ‘CAD shape-dening data’ to that of the machine tool’s motional kinemat- ics necessary to produce the prole, means that trans- mission rates and corresponding feedrates suer, as each line segment corresponds to a ‘bottleneck’ in the part program, this being data point expressed as an X-Y-Z co-ordinate. To minimise these problems and more specically, now that HSM capabilities are com- monplace, CNC builders are incorporating ‘complex curve interpolation’ capabilities into their controllers, enabling tool paths to be machined utilising the same mathematical terms that CAD/CAM systems use to generate them. In other words, ‘NURBS’ , which in practice largely means that for the same quantity of data, the controller can achieve faster, smoother and more accurate machining. A ‘NURBS’ is constructed from three discrete pa- rameters: Poles; Weights; and Knots 47 . As a result of ‘NURBS’ being dened by non-linear motions, the tool paths will have continuous transitions, enabling signicantly higher: acceleration; deceleration; plus enhanced interpolation speeds; than was previously 47 ‘NURBS’: e rational equation, can be expressed, as follows: P (t) = i= � n Ni, (t) GiPi i= � n Ni, (t) Gi e Non-Uniform B-Splines can be expressed, as follows: Ni, t Ki t K i Ki, Ki t Ni, k (t) = (t − Ki) Ni, k − (t) Ki + k − − Xi + (Ki + k −t ) Ni + , k − (t) Ki + k − Ki + Where: Pi = Control point; Gi = Weight; Ki = Knot vec- tor. (Source: Oakham, 1998) available by CNC controllers without the ‘complex curve interpolation’ capabilities. As ‘NURBS’ have the ability to describe any free-form curve, or surface pre- cisely and eciently, they became immensely popular with CAD Soware-developers, because it allowed Design Engineers more freedom to manipulate 3-D data, than had been available utilising simple ‘line- segments’ and ‘primitives’. e logical extension for the application of ‘NURBS’ was followed-up by CAM developers, as many systems were integrated into one by the same company that developed the CAD system. is CAD/CAM integration, enabled these companies to supply post-processors that supported all the major digital controller manufacturers oering a ‘NURBS- capability’. In order to more fully comprehend just how ‘NURBS’ works, it is worth a slight digression to briey discuss the techniques utilised to represent curved surfaces. By way of illustration, the CAD equivalent of the Draughtsman’s ‘Flexi-curve’ used to create free- from curves, is termed a ‘spline’ 48 . e alternative ‘B- Splines’ 49 dier from that of ‘Splines’ , instead, they function somewhat like a ‘gravitational pull’ acting on them, pulling and distorting the curve, but in the con- trol point’s direction. While, ‘NURBS’ are essentially a more controllable version of ‘B-Splines’. e resulting output from ‘NURBS’ is very ecient, as it describes the curve’s geometry with a fraction of the data output necessary for linear interpolation. One disadvantage is that the calculation of ‘NURBS’ are much more com- plex, necessitating considerable amounts of comput- ing power to compute them. e ‘Non-Uniform’ term in ‘NURBS’ , refers to what is called its ‘knot vector’ , which indicates the portion of a curve that is aected by an individual control point, but where it does not have to be ‘uniform’. By ‘dissecting’ the ‘NURBS’ term still further, the portion of it aected by the ‘Ratio- nal’ part of the formula, means that the weight of the control points’ pull (weighting) – which can be speci- ed. is ‘weighting’ allows conic sections to be repre- sented, without having to slice them up to determine their geometric aspect. 48 ‘Splines’ , can simply be dened as follows: As a series of equally spaced control points which the computer connects to create a smooth owing curve’. 49 ‘B-Splines’ , may be dened in a slightly diering manner to that of ‘Splines’ , such that: Utilising the end and control points that do not necessarily intersect the curve, thereby they can dis- tort the curve’. (Source: Oakham, 1998) Chapter When applying ‘NURBS’ to a complex part’s curva- ture, it is important to recognise that it denes the entire curve, not just a series of facets, enabling it to express any curve geometry, utilising less data than for other ‘curve-tting techniques’. Data transmission times are signicantly improved as a result, this is because one does not have to transfer all of the curve data, just the: control points; the order of the polynomial; the knot vector; and its weighting; as dened by the CAD sys- tem. Once this has been achieved, the machine tool’s CNC controller then decodes this information, in or- der to control its servos. While a single ‘NURBS’ ex- pression can describe a simple curve, complex curves (e.g. Fig. 248c) are described by moving ‘weighting’ on the control points, running the calculation, then mov- ing the ‘weighting’ again and re-calculating and so on, in a recursive manner. us, each point moved has an inuence on the others, but the more the control points utilised, the less their inuence becomes – in a similar manner to the so-called: ‘law of diminishing returns’. ‘NURBS’ is comparable to linear interpolation in that the greater the accuracy the more the number of points needed, although it requires less data in to- tal – with a gure of 60% data-reduction, with an as- sociated 40% improvement in time, has been claimed. Although the solution to virtually every curve-tting geometry can be undertaken by ‘NURBS’ , it cannot partake in all ‘surface-describing miracles’. If the CAD system outputs poor data, this will end up with a simi- larly pitiable ‘curve-tting routine’ , so as the old saying goes, it’s the equivalent of: ‘Garbage in, garbage out!’ In time, these ‘NURBS’ will have even more renements added to enhance the already powerful ‘curve-tting processes’. .. Sculptured Surface Machining – Cutter Simulation Once the free-owing curves for the sculptured sur- faces have been generated and the actual workpiece is about to be machined, many companies embark on a ‘cutter simulation routine’ prior to undertaking any surface machining. Many of the sophisticated surface machining soware packages, can provide several variations of complex surface machining routines. Typical of such routines, is that shown for a particular leading company’s product for the multi-axis sequen- tial machining, depicted in Fig. 249a. is specic ‘sequential surface machining’ routine (Fig. 249a), is an interactive, graphic implementation of ‘drive-part- check’ surface machining, as dened in the: Automati- cally Programmed Tool (APT) Standard. is routine is greatly enhanced when utilised in combination with two other machining soware packages, namely: ‘Se- quential machining’; and ‘Drive curve mill’. While an enhanced function incorporated into the machining package is termed ‘looping’ , which enables the user to generate multiple passes on a surface, by dening the inner and outer tool paths, allowing the system to then generate the intermediate stock-clearance tool path steps. A typical modular-package might oer: surface con- touring; parameter line machining; rough-to-depth; and zig-zag tool paths; having any design modica- tions, or changes being automatically handled through what is termed ‘associativity’ , thereby signicantly re- ducing any attendant costly, but otherwise necessary prove-outs. By utilising cutter simulation, parameters such as: feedrate; spindle speed; and part clearance; are instantly accessible and, being ‘modal’ they remain un- changed, unless the user modies these values. While at any time during the development of the simulation, a user can test a setting by generating a tool path with its accompanying high-resolution graphic display (Fig. 249a). Surface machining will automatically simulate the cutter’s tool path, being displayed on a graphics screen and generate textural output into a ‘cutter lo- cation source le’ (CLSF). Aer simulation, the user may either choose to accept the tool path simulation and then save these parameters, or reject it and modify whatever parameters are necessary to correct for any attendant problems encountered. It should be stated that if a problem had occurred when actually cutting the complex geometric component’s surface – such as ‘surface gouging’ 50 , this would have probably scrapped the otherwise expensive stock of workpiece material, that has also added signicant value to it, by the time- consuming process of machining this part’s intrinsic geometric characteristics. So the application of cutter simulation is not only economic and scally important, it oers many other signicant production benets. erefore, with such enhanced cutter simulation, a range of important fea- tures can be addressed ‘o-line’ , such as: • Supporting typical CAD ‘Surfaces and Solids’ pack- ages, • Providing both 3- and 5-axis contouring motion – including tool orientations that may be oset from 50 ‘Surface gouging’ , is if a cutter unintentionally removes mater- ial (gouges-out) a portion of surface. Machining and Monitoring Strategies Figure 249. By utilising a sophisticated cutter and part simulation technique, any potential and very costly ma- chining mistakes can be avoided . Chapter the surface ‘normals’ (i.e. cutter tilt and lead/lag angles), or being parallel to the surface (i.e. here, termed: ‘swarf-cutting’), • Gouge-checking routines and step-over control functions, during the non-cutting motions, • Allowing complete control over the quality of the machined surface texture and the attendant stock to be removed, • Control of intrinsic surface directional parameters, having input of tool paths that are projected onto a surface to be machined with its associated arbitrary curves and points ‘sets’ , • Addressing a ‘full-check’ surface capability, having specied part clearances – for xtures and clamp- ing, while stipulating both setting and gauging points in the simulation routine, • Allowing for the machining of arrays of multiple surfaces, including: trimmed and extended sur- faces; and for any multiple arbitrary holes, • Enabling the user to selective in avoiding particu- lar workpiece features, such as specic holes and islands. By utilising sophisticated cutter simulation packages, the work is undertaken ‘o-line’ by the user, thus avoiding: costly prove-outs; potential scrappage of parts; tool breakage; or under extreme circumstances, even serious damage to the machine tool. In fact, for any sculptured machining operations (i.e. typied in Figs.: 245b and c, 246b, 249b), they need to have some form of cutter path simulation undertaken and its as- sociated simulated enhancements, otherwise poten- tially costly production machining mistakes are the likely outcome. 9.9 Hard-Part Machining Introduction Since the development of ultra-hard cutting tool ma- terials, such as: cubic boron nitride (CBN); and poly- crystalline diamond (PCD) and their derivatives; to- gether with ‘sub-micron’ cemented carbides coupled with their ultra-hard multi-coatings; or diamond-like coatings (DLC) to these carbide surfaces; it has enabled the hard-part machining process to become well-es- tablished and commonplace. Prior to machining parts in the hardened state, the time-consuming and expen- sive processes were: rough-out, or nish-machine cer- tain features of the part, then heat-treat it (i.e. hard- ening and tempering – as necessary), grinding critical surfaces and dimensions. Today, by hardening the wrought stock material before it is machined, this will eliminate any potential distortions caused by thermal- inuences on the part when it was heat-treated, this enables the part to be hard-part machined: roughed and nished, normally avoiding the subsequent grind- ing processes: surface and cylindrical – as necessary. e question that could be asked concerning such a machining application is: ‘What then denes hard-part a machining process?’ Before answering this question it is worth metaphorically ‘stepping-back’ somewhat, to discuss what was considered as extremely ‘hard’ 51 around seventy, or so years ago. At that time, high- speed steel (HSS) tooling was the norm, as cemented carbide had not yet been fully-established throughout the manufacturing industries of the day. Here, HSS was the favoured tooling material, due to its superior retained edge hardness at elevated temperatures (i.e its ‘red hardness’) in combination with its improved toughness – over other tool materials at that time. Typically an M2-HSS 52 had a bulk hardness of between 58-64 HR C . Returning to the question posed above, concerning what denes a hard-part, according to one major cutting tool company it is those materials with a hardness of >42 to 68 HR C 53 – being the equivalent of machining components from M2-HSS. Previously, only through grinding operations, could the hardened component be produced to ‘toleranced-size’ , while 51 ‘Hardness’ , can be dened as: e measure of a material’s re- sistance to deformation by surface indentation, or abrasion’. (Source: Callister, Jr, et al., 2003)us, a ‘hard material’ can be considered, when large forces are necessary to cause a perma- nent indentation [machining] marks. (Source: Schaer, et al., 1999) 52 ‘High-speed steel’ (M2 – HSS), will have a typical 0.2% yield stress @ room temperature of ≈3,000 N mm –1 , while @ 600°C it is ≈1,800 N mm –1 , showing good high temperature prop- erties. Some other relevant mechanical properties, include: transverse rupture stress @ 4.8 GPa; Fracture toughness (K IC ) @ 17 MN m –3/2 ; Izod impact strength (un-notched) @ 33.4 J. (Source: Trent, 1984) 53 ‘Hard-part machining’ , today is utilised widely as both a roughing and nishing cutting process, which of late, has seen parts machined from a range of hard workpiece materi- als, having a bulk hardness of up to 68 HR C . (Source: Huddle, 2002) Machining and Monitoring Strategies having the necessary surface texture. In the case of hard-part turning – to be discussed in the next sec- tion, hard-turned surface texture of better than 2.5 Ra, is achievable, across a range of workpiece materials. According to Hanson (2005), hard materials can be classied into two distinct groups: 1. Single-component materials – might typically in- clude hardened tool steels, glasses such as Pyrex™ and borosilicate, ceramics including silicon carbide (SiC) and aluminium oxide (Al 2 O 3 ), 2. Composite materials – could be either metal/ce- ramics such as metal-matrix composites (MMC’s) and tungsten-carbide /cobalt, glass/ceramics such as Zerodur™ and Cervit™, as well as ceramic/ce- ramic composites such as silicon-carbide/silicon. NB ese groupings only list a few of the hard workpiece materials currently available today, many more exist, but they can still be classied within these groupings at present. e selection of the cutting tool composition and its associated geometry when hard-part machining, is in- uenced by the severe demands made by these hard- ened workpieces. e problems encountered can range from very rapid tool wear rates, cracks and chipping of the cutting edge(s), to an unacceptable machined sur- face condition. Some multi-coated cemented carbides and aluminium oxide ceramics (Fig. 10) can cope with some operations on hardened workpiece materials, but it is more usual to utilise ultra-hard cutting tool materials, or at the very least, specialised-coatings on cemented carbide tooling. Some technical diculties can be encountered when hard-part machining, these might range from: • Elevated temperatures in the cutting zone, • Greater and more variable cutting force magni- tudes, • Intense pressure on a relatively small cross-section of the chip – near the edge, • Rapid cutting edge wear, or catastrophic break- down, • Workpiece stresses being released during the ma- chining operation, • Poor homogeneity in part material – creating vibra- tional eects on tool’s edge, • Insucient stability and rigidity – created in the ‘machine-tool-workpiece’ loop stiness. e extreme thermal and mechanical conditions, will dictate the manufacturing circumstances, concerning: tool material and its geometry; machining methods utilised; together with the cutting data selected. So, the properties demanded from a cutting tool when one is about to embark on hard-part machining exercise, are that it has: • Superior abrasive wear resistance, • Chemical stability at the high temperatures en- countered, • Ability to retain its cutting edge at high tempera- tures – ‘hot-hardness’ , • High compression and bending strength, • Good cutting edge strength and toughness, • Cutting edge inertness and resistance to diusion wear. e hardness of a part, should not be confused with its ‘modulus’ , or the material’s toughness. As it is the combination of elastic and plastic properties that de- termine a material’s resistance to yield, namely, its permanent deformation 54 . In the following sections, particular approaches to that of hard-part machining by various production processes will be concisely re- viewed. .. Hard-Part Turning For some years now the application of hard-part turn- ing has increased in popularity, as the time needed to nish these hardened components – with their hard- nesses ranging between 45 to ≈68 HR C – has signi- cantly reduced. e major time-saving is from the vir- tual elimination of nish-grinding operations, when ‘ne-turned’ surface texture of <2.5 Ra is now possible, with matching dimensional tolerances. Complex con- touring of a component’s prole using hard-part turn- ing operations is achievable (i.e. see Fig. 154 – top), which overcomes the previously expensive and time- consuming proling operation of cylindrical grinding with custom-formed grinding wheels. However, successful hard-part turning is more than simply ‘chucking’ a hardened component (Fig. 250a), 54 ‘Yield, or permanent deformation’ , diers here, from that of either: elastic deformation; or dislocation, slip, etc.; that may result during machining. (Source: Hanson, 2005) Chapter then utilising for example, either a CBN, or ceramic cutting insert to machine them. A variety of important factors require consideration if the turning operation is to be successful, including the fact that higher cut- ting forces involved and their aect on the machine tool’s structural rigidity and stiness (Fig. 250d). ese hard-part cutting forces can be ≈200% higher than the forces generated when similar operations are under- taken on ‘soer parts’. Due to the fact that either the CBN, or ceramic tool materials tend to be relatively brittle, cutting tool com- panies will apply chamfers to the cutting edges – to strengthen them. A problem with a ‘supporting cham- fer’ on the insert’s edges is that it reduces its shearing capability, this causes the cutting forces to increase – due to the so-called ‘ploughing-eect’. e application of higher cutting forces here, makes both the insert’s edge and the part move relative to one another – re- sulting in chatter. e onset of chatter causes surface texture degradation – at best, or destroys the cutting edge/tool and even the part itself – at worst. Moreover, the size and the shape of the workpiece when hard- part turning is important, as if too long a length-to- diameter ratio – without support, this will prove to be exceedingly dicult to successfully machine. With some hard-part machining companies stating that L/D ratios of >3:1 can be a problem – with respect to chat- ter generation, resulting from the higher imposed cut- ting forces now in operation. Workholding plays a crucial role in successful hard-part turning operations, with a rm all-round grip – from say a collet positioned and rigidly held well inside machine’s headstock, is much preferred to that of a three-jaw chuck – as this latter device may not necessarily provide either the ‘clamping forces’ 55 , nor inherent rigidity. e location of the turning insert’s 55 ‘ree-jaw chucks – clamping forces’ (Fig. 250 – bottom right), due to the fact that the ‘conventional’ chuck’s self-centring mechanism is a face-scroll – this being provided by a spiral groove cut onto the face of a at disk, then having the equi- spaced jaws oset by the scroll’s pitch and numbered for re- placement as either internal, or external jaws. When the chuck key turns the ‘scroll-pins’ which then rotates the scroll plate and thus, they simultaneously radially move the jaws – in- ward/outward. So, depending upon the scroll plate’s rotation, the torque supplied by the chuck key creates only one third of the total force supplied at each individual chuck jaw. erefore, the force may not be adequate to provide sucient force to grip and rigidly hold the part as it is hard-turned. positional location, relative to the machine’s spindle bearings is signicant. e further the distance away from the front spindle bearing’s location relative to that of the cutting action, the greater any potential for the part to ex and chatter – acting like a ‘lever mecha- nism’ (i.e. its force times distance). So, machine tools that are designed so that their collets are well-seated into the headstock and close to the front bearings and, when hard-part turning, the minimum of workpiece overhangs should be utilised. Turning centres that are designed from the out- set to cope with the demands of hard-part turning, are usually of greater size and weight, plus being ex- tremely rigid structures. Even here, concerning a ma- chine’s rigidity, there are practical limits to the amount of ‘static stiness’ (i.e. the ratio of applied force to that of an associated displacement) that can be built into the turning centre. e design objective is to increase the machine tool’s ‘dynamic stiness’ 56 , which involves dampening the frequency of vibrations via specic ap- plied technologies, such as ‘composite-lling’ 57 the ma- chine bases. While a dierent approach to dampening vibration, involves the use of hydro-static linear ways, which ride on non-contact pressurised uid bearing surfaces. In a similar manner to that of ‘conventional’ linear-ball guide ways, they exhibit low friction and resist omni-directional loadings (i.e see Fig. 250d – for a performance comparison of these two linear bear- ing types). Moreover, hydro-static guide ways provide dampening as-and-when vibrations occur during hard-part machining process. Furthermore, hydro- NB In Fig. 250e on the other hand, the force exerted by this type of self-centring mechanism, should prove to be able to cope with the demands of hard-part turning , particularly as the ‘so-machinable jaws’ have been bored-out, to provide more circumferential location and support for the part. 56 ‘Dynamic stiness’ , can be dened as: e ratio of the applied force to the displacement, occurring at the frequency of the ex- citing force’. (Source: Hardinge Inc., USA) 57 ‘Composite-lling’ – machine tool bases. is dampening te- chinque is traditionally achieved by employing such materials such as Granitan™ (i.e. typically, being a crushed granite and epoxy resin), or Harcrete™ – this latter product is a polymer composite, having an 800% better damping capacity to that of the equivalent grey cast iron structure. Although these com- posite-lled structures can be expensive, in order to alleviate some of this cost, ‘traditional’ castings have strategically-rein- forced composite-lled cavities. (Source: Kennedy, 2004) Machining and Monitoring Strategies Figure 250. Hard-part turning operations are replacing some grinding operations: assuming dimensional size and machined surface texture are acceptable. [Courtesy of Sandvik Coromant] . Chapter . (gouges-out) a portion of surface. Machining and Monitoring Strategies Figure 249. By utilising a sophisticated cutter and part simulation technique, any potential and very costly ma- chining mistakes. forms which would Machining and Monitoring Strategies have to be converted into a recognisable program- ming structure that the machine tool’s servo-drives could understand and apply. is ‘translation’. stock needed to be subsequently removed. [Courtesy of Sandvik Coromant] . Machining and Monitoring Strategies .. Sculptured Surface Machining – with NURBS Prior to a discussion on the application