Figure 245. The complex machining of either a sculptured, or die and mould surfaces, will usually necessitate both multifarious and sophisticated programming techniques . Machining and Monitoring Strategies  • Dening the minimum radii requirements and the maximum depth of the cavity, needs consideration, ensuring selected tooling can cope with these part geometries, • Approximately estimate the amount of excess stock material from the die, or mould that needs to be removed by milling operations 41 , NB Establishing what is roughing-out and semi- nishing operations, will for a large die-set oen mean that roughing-out is both more ecient and productive on conventional-speed machining cen- tres, with any semi-nishing undertaken by HSM. • In preparation and prior to milling, ensure that the workpiece xturing is both accurate and precise as well as very robust and rigid, otherwise this latter factor in particular, is a classic source for any resul- tant vibrations and will signicantly inuence the tool’s life together with degradation of the die and mould surfaces 42 , NB HSM requires a totally rigid xturing, if vibra- tional tendencies are to be minimised, as it proves disastrous for any long length-to-diameter tool ratios, that are oen utilised for high-speed milling operations. • For the machining processes, they should ide- ally be divided into at least three types of milling 41 ‘Material removal rate’ for HSM milling is generally consider- ably smaller than in conventional machining (i.e except when aluminium and non-ferrous machining occurs). Formula for material removal rate Q = a p � a e � v f  ( cm  min − ) Where: a p = axial D OC (mm); a e = radial D OC (mm); v f = feed per minute (mm min –1 ). 42 ‘Die and mould milled surface texture’ , by HSM milling op- erations dramatically reduces the manual polishing require- ment – by reducing the resultant milled surface ‘cusp-heights’. Oen conventional milling operations produce relatively large ‘cusps’ (i.e see Fig. 245a – resulting from the large width of the ‘pick-feed’). For example, when a large automobile bonnet (i.e. ‘hood’ – in the USA) die-set has been produced by conven- tional milling practices, any manual polishing activities range between: 350–400 man-hours! NB is order of manual polishing will aect the geometrical accuracy of the die-set. (Source: Sandvik Coromant, 2000) operations, namely: roughing-out; semi-nishing; nishing. NB ‘Restmilling operations’ 43 are normally under- taken during any semi-nishing, or nishing op- erations. .. Die-Cavity Machining – Retained Stock Whenever a rough-milling operation is undertaken with a square-shouldered cutter, this creates the well- known ‘stair-case prole’ 44 (i.e see Figs. 246 a and b) of remaining stock that must now be removed by a semi- nishing milling operation. e die-cavity’s cross-sec- tional prole will signicantly inuence the amount of stock remaining against the cavity wall, which will create a variation in the cutting forces and have an in- uence on tool deection. e consequence of this un- even stock will be that when semi-nishing the prole, it could aect the geometrical accuracy and precision of the die, or mould. Clearly, in the schematic diagram shown in Fig. 246a – le, the large chamfered die fea - ture when being roughed-out for a given D OC , will leave signicant material here for subsequent semi-nish- ing. Likewise, in the cavity of the convex-to-concave prole illustrated in Fig. 246 – right, it has signicant stock material remaining at the lower regions of the concave feature, obviously necessitating a following machining removal operation (i.e. semi-nishing). When a square-shouldered cutter is utilised with a triangular geometry insert, it will have relatively weak corner cross-sections (i.e. by way of illustrating this eect of insert shape strength, see Fig. 155 – bottom), creating a somewhat unpredictable machining behav- iour. Triangular, or rhombic insert geometries, will also create large radial cutting forces and as a result of number of cutting edges, they are unexpectedly, less economical than some other counterparts for such op- 43 ‘Restmilling operations’ , are those milling operations where any Ball-nosed: Slot-drills; Endmills; or in some cases, toroi- dal-geometry inserted cutters; are employed. 44 ‘Stair-case prole’ , is so-called, because it resembles an actual stair-case when taken in cross-section (i.e. see Fig. 246). e height and width of the remaining stock for each step, is de- pendent upon a proportion of the actual ‘step-size’ (pick-feed) and the D OC previously selected. Obviously requiring a semi- nishing operation at the very least, to remove this unwanted material.  Chapter  erations. On the contrary, round cutting inserts that allow milling paths to be undertaken in any direction, are oen specied because they provide a smooth transition between successive tool passes, while also leaving behind the twin benets of less and more even stock, for later removal in semi-nishing. is residual Figure 246. Die-sinking sculptured proles with a 90° square-shouldered milling cutter, introduces a ‘staircase eect’ on the machined prole. [Courtesy of Sandvik Coromant] . Machining and Monitoring Strategies  eect of less additional stock produced by round in- sert’s on the workpiece prole, is shown schematically in both Figs. 247ai and aii and, should be compared to Fig. 246a – this latter eect being the result of utilising square-shouldered cutting inserts, in terms of stock to be removed later in semi-nishing operations. Amongst the notable benets of using round inserts, are that they produce a variable chip thickness, which allows for higher feedrates if compared to other insert- shaped geometries. Round cutting inserts provide a very smooth cutting action (i.e see Fig. 246 – bottom right: inset), because the entering angle changes from almost zero – in the case of very shallow D OC ’s, to that of 90° – under certain conditions with the larger D OC ’s. us, at the maximum D OC , the entering angle is 45° and when copying with the periphery, the angle is 90°. is D OC variability using round inserts, also goes some way in explaining why these inserts are so strong in comparison to other insert shapes. Namely, round in- serts with their actual ‘work-loading’ – at the cut’s ini- tial progression – is successively built-up, rather than almost immediately with inserts having greater enter- ing angles, usually provided by their less-than-robust geometry counterparts. Consequently, round inserts should always be regarded as the primary choice in cutter selection when either roughing, or for medium- roughing operations. When 5-axis machining, the use of round cutting inserts can be usefully exploited, as they have virtually no limitations when machining sculptured surfaces. erefore, with optimum CNC programming, either round inserts, or toroid-shaped milling cutters can normally be substituted for ball- nosed end mills (Fig. 79b), as they can oer: superior cutting performance; improved chip-breaking e- ciencies; as well as better chip evacuation; this latter point is important when deep cavities might otherwise retain work-hardened swarf. Typically, the increases in productivity range between 5-to-10 times better, if compared to that of previously utilising ball-nosed end mills. Round insert tooling is very rigid so as a re- sult, they only produce a small amount of run-out and, when combined with ground, positive and light cut- ting geometries, may be used for semi-nishing and occasionally some nishing operations (Fig. 246 – bot - tom right: inset). Some of the main questions to be answered re- garding the correct application of technology is con- cerned with optimising: the cutting data; likely insert grades; together with their geometries; in relation to the: specic workpiece material to be machined; actual machining operations to be undertaken; anticipated productivity requirements; and the likely workhold- ing restaint/security issues. Die and mould work in- variably involves complex sculptured male and female surfaces, with any calculations of the eective cutting speed being based upon either the ‘true’ , or eective diameter in-cut (‘D e ’ – see Fig. 247b). So, if the D OC is very shallow – as is the case when semi-nishing op- erations are being carried out, then the ‘true’ cutting speed will be much lower (Fig. 247b). If the original cutter diameter was chosen for the cutting data calcu- lations, then for a shallow cut – due to ‘D e ’ being the eective diameter, this drastic reduction in actual cut- ting speed will not have been anticipated, causing the feedrate utilised to be severely compromised, as it is dependent on the calculated cutter’s rotational speed. is will not only severely impede component produc- tivity, but will increase the tool’s potential wear-rate signicantly, this being the case for all round insert cutters, ball-nosed end mills, plus end mills having large corner radii. Due to the adverse and miscalcu- lated cutting data, there is a likelihood for premature cutting edge frittering and chipping – created by too low a cutting speed and localised heat in the cutting zone. When undertaking either nishing, or super-n- ishing of the die and mould sculptured surfaces (Fig. 246biii) on hardened tool steel, it is vitally important to choose tool materials and coatings with ‘hot hard- ness’ capabilities 45 . A major factor to consider when milling for either nishing, or super-nishing hardened steel sculptured surfaces by HSM, is to take shallow cuts. Notably, the D OC should not exceed 0.2/0.2 mm (a e /a p – Fig. 247b). is strategic machining decision should be made, so that excessive deection of the cutting tool assembly is avoided, enabling a high tolerance level and geometric accuracy to be held on the die, or mould. Accordingly, very sti tool assemblies are essential, usually utilising solid cemented carbide: due to its inherent stiness; coupled with the maximum core diameter possible; that the die, or mould part features will allow. 45 ‘Tool materials for: hardened steel milling’ , they are usually coated cemented carbide, with the micro-grain structural matrix (i.e. typical grain size being <1 µm), providing good wear resistance and transverse rupture strength (i.e. this be- ing ‘related’ to its toughness). Coatings can include: titanium aluminium nitride (TiAlN); titanium carbonitride (TiCN); having multiple coatings of between 2 to 12 µm thick, applied by Plasma Vapour deposition (PVD). Diamond-like coatings (DLC) are also utilised. (Source: Dewes and Aspinwall, 1996)  Chapter  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 dierent equation parameters that dened 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 modied cubic approach that can accommodate the uneven spacing of ‘nodes’ – the start and end points – has particular benets 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 dierent 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 renement, 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 renement 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 dene 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 dening complex curves, ‘NURBS’ oers signicant benets, 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 denition 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 conrmed 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 aect of signicantly 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 ecient, 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 dene 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-dened tolerance band (Fig. 248a). us, the length of each linear segment was governed by the curvature of the prole 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 proles. is conict between ‘CAD shape-dening data’ to that of the machine tool’s motional kinemat- ics necessary to produce the prole, means that trans- mission rates and corresponding feedrates suer, 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 specically, 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 dened by non-linear motions, the tool paths will have continuous transitions, enabling signicantly 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  Ki     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 eciently, they became immensely popular with CAD Soware-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 oering a ‘NURBS- capability’. In order to more fully comprehend just how ‘NURBS’ works, it is worth a slight digression to briey 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 dier 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 ecient, 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 aected 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 aected 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 dened 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 dened in a slightly diering 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 denes 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 signicantly 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 dened 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 inuence on the others, but the more the control points utilised, the less their inuence 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 renements 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 soware 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 specic ‘sequential surface machining’ routine (Fig. 249a), is an interactive, graphic implementation of ‘drive-part- check’ surface machining, as dened in the: Automati- cally Programmed Tool (APT) Standard. is routine is greatly enhanced when utilised in combination with two other machining soware 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 dening the inner and outer tool paths, allowing the system to then generate the intermediate stock-clearance tool path steps. A typical modular-package might oer: surface con- touring; parameter line machining; rough-to-depth; and zig-zag tool paths; having any design modica- tions, or changes being automatically handled through what is termed ‘associativity’ , thereby signicantly 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 modies 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). Aer 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 signicant 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 oers many other signicant production benets. 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 oset 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  [...].. .Machining and Monitoring Strategies • • • • • • 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... 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 specified part clearances – for fixtures and clamping, while stipulating both setting and gauging points in the simulation routine, Allowing for the machining of arrays of multiple surfaces,... sculptured machining operations (i.e typified in Figs.: 245b and c, 246b, 249b), they need to have some form of cutter path simulation undertaken and its associated simulated enhancements, otherwise potentially costly production machining mistakes are the likely outcome 9.9 Hard-Part Machining Introduction Since the development of ultra-hard cutting tool materials, such as: cubic boron nitride (CBN); and. .. (CBN); and polycrystalline diamond (PCD) and their derivatives; together 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-established and commonplace Prior to machining parts in the hardened state, the time-consuming and expen- 507 sive processes were:... hardening 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 thermalinfluences on the part when it was heat-treated, this enables the part to be hard-part machined: roughed and finished, normally avoiding the subsequent grinding processes: surface and cylindrical... gauging points in the simulation routine, Allowing for the machining of arrays of multiple surfaces, including: trimmed and extended surfaces; and for any multiple arbitrary holes, Enabling the user to selective in avoiding particular workpiece features, such as specific holes and islands By utilising sophisticated cutter simulation packages, the work is undertaken ‘off-line’ by the user, thus avoiding:... hard-part, according to one major cutting tool company it is those materials with a hardness of >42 to 68 HRC53 – 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 defined as: The measure of a material’s resistance to deformation by surface indentation, or abrasion’... include: transverse rupture stress @ 4.8 GPa; Fracture toughness (KIC) @ 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 finishing cutting process, which of late, has seen parts machined from a range of hard workpiece materials, having a bulk hardness of up to 68 HRC (Source: Huddle, 2002) ... machined: roughed and finished, normally avoiding the subsequent grinding processes: surface and cylindrical – as necessary The question that could be asked concerning such a machining application is: ‘What then defines 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,... resistance to deformation by surface indentation, or abrasion’ (Source: Callister, Jr, et al., 2003)Thus, a ‘hard material’ can be considered, when large forces are necessary to cause a permanent indentation [machining] marks (Source: Schaffer, 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 . The complex machining of either a sculptured, or die and mould surfaces, will usually necessitate both multifarious and sophisticated programming techniques . Machining and Monitoring Strategies. Sandvik Coromant] . Machining and Monitoring Strategies  eect of less additional stock produced by round in- sert’s on the workpiece prole, is shown schematically in both Figs. 247ai and. the adverse and miscalcu- lated cutting data, there is a likelihood for premature cutting edge frittering and chipping – created by too low a cutting speed and localised heat in the cutting zone.