Aignescotec - DTJ - 1.11


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Innovative technology in polymeric composites for machining applications.

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Aignescotec - DTJ - 1.11

  1. 1. Grinding T here are many modern definitions of grinding. All of them define the process as an energy transfer from a drive unit into a workpiece surface layer, while abrasive grits fixed by the bond serve as energy transfer channels. A part Adaptive of that energy dissipates into the bond and leads to wearing and structural changes. Some of it ends up as swarf and a large portion is transferred to the surface of a workpiece causing flaws abrasive and defects. High material removal rate is considered a necessary requisite for high cost efficiency of grinding. Technical effectiveness of composites grinding is defined by three interconnected parameters, namely the removal rate, the tool life and the qualitative characteristics of a machined surface. look to the A necessity in high material removal rate requires faster transfer of large quantities of energy into a workpiece surface layer. This obviously results in more mechanical strain in the contact zone future that leads to plastic deformation and chip formation along with When we talk about adaptive control in machining high heat release. High level of cutting forces and heat in the grinding zone are in opposition to high tool durability, because both operations, we usually mean electronic monitoring factors increase bond wear, fracture and fallout of abrasive grits. systems based on sensor readings that enable the On the other hand, the utilization of a more durable tool under machining parameters (feeds, cutting speeds, depth fixed material removal rate leads to the increase of temperature of cut, etc) to be automatically varied to provide and cutting forces. In turn, the minimization of the structural changes in a workpiece optimum efficiency. This article by N. Ignatov and surface under constant machining by a tool requires lower speed of N. Tikhon, however, discusses adaptive control from material removal rate. Otherwise the increase of temperature and within the tool material itself, in this particular case, grinding forces will lead to burning, unwanted structural changes, CBN and diamond grinding wheels. As a category of residual stress and poor surface micro-geometry. Under traditional approaches, improvements to the three main tool materials, adaptive composites (abrasive grit and parameters needed for an effective grinding process require three bond together), demonstrate a new comprehension separate and practically incompatible solutions. This situation of adaptability, in that the composite serves both as a is unavoidable when almost all energy that is transferred by sensor and as a work medium, changing its properties the abrasive grits along with chip formation is spent on plastic deformation with applicable heat release. Note that the thermal according to conditions in the cutting zone. As a result, factor contributes faster than the material removal rate if we the authors claim that it becomes possible to combine increase cutting depth for example. This energy dissipation in the a high rate of material removal whilst maintaining cutting zone depends on positive feedback meaning that higher the maximum surface integrity of the workpiece. temperatures and cutting forces lead to higher bond deformability ........................................................... and larger contact zone with the machined surface. An increase in immediate contact cross section in the tool/workpiece pair stimulates an increase in temperatures and forces that leads to in efficiency of machining is possible requires an alternative further bond deformability and so on. approach. Further development and utilization of adaptive If we possess positive feedback, an increase in thermomechanical abrasive composites may be considered as a solution to current strains as a result of higher material removal rate can be slowed technological demands made for modern grinding. Adaptive down at the expense of lower tool life. But this solution is often behaviour includes self-tuning of the structure and qualities of an impossible to implement fully not only because of an increase abrasive material, including the binder and abrasive grits, primarily in tool costs as they deteriorate faster, but because of lower diamond or CBN, to varying conditions in the work zone. Whereas workpiece accuracy caused by the lower dimensional durability traditional abrasive composites demonstrate positive feedback of a cutting tool profile. Another obvious solution of decreasing between deformability and thermomechanical cutting factors, the thermomechanical intensity of grinding under higher material adaptive composites demonstrate inverse feedback. This means removal rates is an increase in quantities of cooling liquids used, that in certain temperature ranges and cutting forces, the tool especially those that are highly physically/chemically active in the material responds by decreasing its deformation values instead cutting zone. This is problematic due to ecological concerns, and of increasing them. this problem will remain unsolvable even further as time passes. This type of adaptive behaviour in a tool surface layer of a certain Aside from ecology, during the process of production grinding, depth, means that if we increase the external action, we will get a cooling liquid does not penetrate into the cutting zone, and while it reversible increase in bond rigidity as well as adhesive interaction is a useful and a desired factor, it does not bring a radical qualitative of the binder with the abrasive grits. This process occurs with a effect on processes in the instant cross section of contact. certain speed and magnitude of change of physical characteristics More obvious methods of solving these contradictory problems of the composite parameters. Discussion of microscopic molecular of increasing grinding efficiency as a whole are limited to trivial aspects of structural transitions in developed resin and hybrid optimization. Study of new horizons where a significant increase organic/non organic composites is outside the scope of this article.00 DIAMOND TOOLING JOURNAL 1·11 00
  2. 2. Grinding (DOUBLE PA of the bond that are being transformed was detected according to the changes in overlap, abrasive grits on the work surface luminescence intensity. Change time for become “aware” of each other’s condition different adaptive bonds was 10-5 – 10-3 and as a result, they create a self regulated sec (Figs 2 and 3) system, working as a single unit. Distribution of points of contact by Experimental test of this system in the luminescence intensity for a traditional immediate contact area of a tool with a polymer bond containing no abrasive workpiece is hardly possible at the present grits and for an adaptive bond is shown in moment. However, model experiments Fig 4. The efficiency of energy transfer is confirm this system. Because we decided proportional to luminescence intensity. not to touch physiochemical mechanisms With an increase of contact pressure, the At Aignesco Inc we utilise modified epoxy of adaptive behaviour of bonds in this integral intensity of luminescence increased, oligomers, oligoimides, other heterocyclic article as well as the molecular processes, but the distribution becomes wider. The compounds and hetero-organic oligomers, we will concentrate on the behaviour of whole range of intensity connected with comprising ultra-dispersed powders of grits that protrude during contact with the contact zones that exist under minimal metals and non-metals with a modified machined surface, the working behaviour contact pressure fits into the area of contact surface structure. of the tools and the properties of the with increased contact pressure. The contact We have developed a two-level system machined surfaces. (Scheme 1): Direct experimental study of contact Loading Initial rigidity ⇔ Increased rigidity behaviour of abrasive grits system is possible Abrasive composite only under static conditions. A schematic of As well as a three level system for more the experiments carried out for this study is Ultrasonic vibrations degrees of freedom (Scheme 2): Saphire monocrystal shown on Fig 1. In real conditions, the role Lower rigidity ⇔ ⇔ of the shear component of contact strains Photo detector Initial rigidity ⇔ Increased rigidity is important. To imitate that, contact pairs When it comes to mesoscopic properties (the abrasive composite or tool in contact Image analysis of adaptive abrasive composites responsible with the counterbody or workpiece) were ••• Fig 1 Detection of machining parameters for the behaviour of abrasive grits, this subject to ultra sound vibrations parallel to at the contact zone between an abrasive needs to be discussed and clarified more the contact surface. composite and a counterbody (workpiece) thoroughly as it is a new type of tool Two samples were tested, and in both material. Dynamic and force aspects of the cases we used monocrystalline sapphire with 25 adaptable bond interaction of the abrasive grits fixed in a a 5 mm thickness, one side polished to a Ra 20 (arbitrary units) Luminescence binder material with the machined surfaces 2.2 nm. The contact volume between the 15 are very dependent on the strength of pairs, given the roughness of their surfaces 10 fixation and strength of retention of the grits and the protrusion of the abrasive grits, non-adaptable bond 5 by the binder. Adaptive composites are able was filled with a special gel that contained 0 to self-tune these parameters in response to a component that is able to become 2 4 6 8 10 12 14 16 18 20 22 24 26 changes in temperature, vibration intensities luminescent under pressure. Study of the (a) Ultrasonic vibrations amplitude (microns) 30 and shear strains in the cutting zone. distribution of real areas of contact of the 25 For a three-level system, the general abrasive composite and counterbody under (arbitrary units) Luminescence 20 system of adaptive behaviour of grains is different pressures, as well as identification 15 as follows. Grits that are in contact with of components of the contact area of the 10 the machined material are entrenching grits, caused by plastic or elastic interaction 5 into the material and at the same time, with the machined material, was done using 0 they deform the bond. Energy dissipation a photo detector. A signal from the photo 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 3234 (b) Ultrasonic vibrations amplitude (microns) of this deformation within the binder detector was passed into an image analysis ••• causes a structural transition of the system that was used to identify areas of real Fig 2 Reversible contact luminescence adaptive composite into a more rigid state. contact according to luminescence levels. changes as indicators of the rigidity of the abrasive composite bond for Deformation quickly slows down (within Luminescence intensity in this scenario is (a) a two-level adaptive bond and limits of a cycle of contact for a given group directly connected to the amount of energy (b) a three-level adaptive bond of grits). For grits with the most protrusion, dissipated on contact areas under pressure the stress is larger, and this forces the bond and ultra sound vibrations (the latter mimics 4.5 4.0 into a less rigid state (Scheme 2). the shear factor). In turn, this energy is 2 (arbitrary units) Luminescence 3.5 Grits that protrude will sink into the bond, directly connected with the rigidity of the 3.0 until the energy dissipated into the contact bond in the abrasive composite. 2.5 1 2.0 micro area of the composite material will not Experiments allowed us to directly 1.5 become equal to that of the other grits. The witness reversible structural changes in 1.0 0.5 main consequence for the cutting profile of adaptive abrasive composites engaged 3.0 3.5 4.0 4.5 5.0 5.5 6.0 the composite will be leveling out of all grits in contact with the counterbody surface. -lg(t) (seconds) ••• that are in contact to the same height above Changes initiated by increasing ultra sound Fig 3 Kinetics of structural changes the bond. During that process, if volumes vibrations under fixed or non fixed pressure for different adaptive bonds (1, 2)00 DIAMOND TOOLING JOURNAL 1·11 00
  3. 3. AGE SPREAD) Grinding zone of the bond with the machined material Intensity of luminescence increases much geometry and performance attributes of increases by growing and merging of initial faster than the contact zone. surfaces generated with adaptive abrasive areas according to the principle of positive In both cases, the amount of energy composites. feedback between energy dissipated in transferred by the composite into the For composites containing abrasive grits, the contact zone and deformation of the counterbody surface layer increases with an under low pressure, when the grits are in composite. During that process, the speed of increase of contact loading. However for elastic (without penetration) contact with the growth of the contact zone on a non-adaptive non-adaptive bonds, that occurs mainly by counterbody, a second level of luminescence polymer bond with the counterbody surpasses a rapid increase in a total area of contact is observed. A third level appears at growth in luminescence intensities. and little increase in the amount of energy pressures causing a plastic contact when For the adaptive polymer bond, above per area unit. grains penetrate the counterbody. Typical a certain threshold pressure, there occurs For adaptive composites on the other distribution of contact areas connected to a sharp change in shape of distribution of hand we have a slow increase in the contact the bond as well as zones of elastic and luminescence of contact areas. Such deep area but fast increase in energy per area unit plastic deformation of the counterbody by changes are possible only with a complete (Fig 5). Principle changes in morphology of abrasive grits are shown in Fig 6. rearrangement of morphology of contact contact and speed of energy transfer over The dependence of areas of elastic grit zones under inverse feedback between a single contact section create conditions contact (correlates with the deforming contact strain and composite deformability. for qualitative changes in structure, micro- action of a tool) and plastic grit contact (correlates with cutting ability of a tool) 0.6 8 on pressure is shown in Fig 7. For both, 7 1 adaptive and traditional composites, the (arbitrary units) 2 6 (mm2/cm2) 0.4 5 area of contact of abrasive grits increases dS/dL 1 4 as we increase pressure. Increase in a S 2 3 0.2 2 dynamic factor by increasing amplitude of 1 ultra sound vibrations achieves the same 0 0 0 5 10 15 20 25 30 result under constant pressure. 0 3 6 9 12 15 (a) Luminescence (arbitrary units) (a) Pressure (MPa) The proportion of contact area for grits 7 0.6 1 where we observed plastic contact with the 2 6 machined surface and when in dynamic (arbitrary units) 0.5 Luminescence (arbitrary units) 5 0.4 4 conditions chips are separately generated, dS/dL 1 2 0.3 3 was 10-25%. For the composite that is 0.2 2 unable to adapt its behaviour, the speed of 1 0.1 an increase of cutting and deformation areas 0 0 0 5 10 15 20 25 30 contact for grits decreases with an increase 0 2 4 6 8 10 12 14 16 18 (b) Pressure (MPa) (b) Luminescence (arbitrary units) ••• of pressure. For adaptive composites, the ••• Fig 5 Relationship of pressure to S, speed of an increase of grits in deformation Fig 4 Distribution of contact point area ratio of real contact area (mm2) to by efficiency of energy transfer between (elastic contact) also decreases, but cutting nominal contact area (cm2) (a) and polymeric bond and counterbody intensity of contact luminescence (b) for ability (plastic contact) increases. It appears (monocrystal sapphire sample) adaptive (1) and non adaptive (2) bonds that in both types of composites there are (a) traditional bond and (b) adaptive bond at different contact pressures reversible and irreversible changes in grit (1 - P1 = 0.3 MPa; 2 - P2 = 1.0 MPa) 1.6 2 orientation occurring. Probably this affects 1.4 those grits, whose attack angle is close to 1.2 90° (Fig 6). (mm2/cm2) 1 1.0 D76 Even though the total areas of contact of S 0.8 0.6 abrasive grit systems for non-adaptive and 0.4 adaptive composites are close, the structure of 0.2 the contact sections has principal differences. 0 5 10 15 20 25 30 (a) Pressure (MPa) For traditional and for adaptive composites, 4.5 0.25 1 grits with purely plastic contact with a 4.0 counterbody are absent. But for traditional 0.20 (arbitrary units) 3.5 3.0 0.15 composite, grits with purely elastic type of dS/dL 2.5 2 In L 2.0 0.10 1.5 D76 1.0 0.05 0.5 0 0.00 1 2 3 0 5 10 15 20 25 30 Luminescence intensity (natural logarithm): (b) Pressure (MPa) 1 in contact of bond with a counterbody ••• 2 in an elastic contact of grits with a counterbody Fig 7 Influence of contact pressure on 3 in a plastic contact of grits with a counterbody areas of elastic (a) and plastic (b) contact range of luminescence increase with increased load of abrasive grits with a counterbody ••• (monocrystal sapphire) for adaptive (1) Fig 6 Three levels of contact and non-adaptive (2) composites luminescence intensities in an [S is the ratio of real contact area (mm2) abrasive composite/counterbody pair to nominal contact area (cm2)] 00 DIAMOND TOOLING JOURNAL 1·11 00
  4. 4. Grinding (DOUBLE PA contact (deformative grits) comprise 50 - system. The dynamics of stress distribution contact with abrasive composites. For 80% of the total amount of grits, whereas in the contact zone of normal and adaptive adaptive composites, in all experiments for the adaptive composite this proportion composites with a counterbody in a single there was a distinct localization of an area was no more than 10-15% (Fig 8). Grits cycle of loading is shown in Fig 11. of maximum strain (Fig 12). Strain maximum with elastic contact protect the composite Duration of the loading cycle with a force accurately corresponded to an average depth from wear, but increase heat generation of 0.7 MPa was 10-2 sec. Kinetic curves of indentations made by grit penetration. and damage to a machined surface. for luminescence intensity in the contact We bear in mind that in real dynamic The distribution of grits in plastic contact zone of the abrasive composite with the contact in the cutting zone, maximum strain with the counterbody, in terms of contact counterbody reflect a rearrangement of corresponds to maximum temperature area and penetration depth, are also stresses and deformations, according to softening of a machined material. principally different for adaptive and structural changes in the composite and Coincidence of the depth of localization traditional composites (Figs 9 and 10). contact interactions. For the adaptive of this area with the depths of intrusion of During an abrasive tool operation, grits composite, a quick growth of luminescence abrasive grits demonstrates one of the main that are in contact with the machined levels is seen, due to increased rigidity of principles of influence of adaptivity on the workpiece material act as a system of point its surface layer as a result of a structural behaviour of an abrasive composite. sources of heat and shear deformation, transition initiated by the load. This increase When it comes to a traditional composite, leading to chip separation. Using identical in rigidity provides quick and efficient its curve of kinetics of luminescence intensity abrasive grits and with negligible differences energy transfer, connected with the load, has a low-pitched maximum and a tail that in physical mechanical properties of the through the grit system and contact areas goes over the limit of load duration. Because composites, the adaptation ability can of the bond, and into the surface layer of of that, the setting of an equilibrium in the qualitatively change the behaviour of this the counterbody. During that process, it is contact zone occurs slowly. The speed of clear that the main role of energy transfer energy transfer from an outside source over 300 1 is done by the abrasive grits. In this case, an abrasive composite and into the surface 250 3 the role of the bond is secondary. layer of the counterbody was calculated 200 The quick completion of structural changes by the tangent of a slope ratio of the N (cm-2) D76 4 150 in the composite layer as a result of the start of the curve σ(τ). The result was that 100 loading cycle corresponds to a quick setting with practically equal microhardness and 2 50 of the residual stress in the machined surface Young’s modulus, the adaptive composite 0 0 5 10 15 20 25 30 layer. Other than tensiometric measurements, transfers energy 10-100 times faster than Pressure (MPa) optical measurements were also used to the traditional one. ••• Fig 8 Relationship between pressure and ascertain the spread of stress over the depths The role of a bond in energy transfer to common amount of grits per unit of work of the monocrystalline sapphire that was in a counterbody for traditional composites area of composite (1, 3), including those with is significant. At least it is equal to that of elastic interaction with a machined surface 0.8 30 grits, but often even more significant. Strain Luminiscence (arbitrary units) (2, 4), [1 and 2 – traditional composite; 0.7 3 and 4 – adaptive composite] 1 25 maximum in that case is usually closer to the 0.6 Pressure (MPa) 0.5 2 20 surface of a counterbody than when an 3 0.4 0.4 15 adaptive composite is used. For the latter, 1 0.3 10 the maximum remains stable in wide load (arbitrary units) 0.3 0.2 5 range, and only total strain changes. During 0.1 dN/dh 0.2 0.0 0 contact with a traditional composite, the 2 0.000 0.005 0.010 0.015 0.020 0.025 0.030 Time (seconds) 0.1 ••• 0.9 Fig 11 Dynamics of stress redistribution 2 (arbitrary units) 0.0 0 2 4 6 8 10 12 14 in the contact zone between an abrasive 1 0.6 Penetration depth (microns) composite and a counterbody during a dN/dS ••• process of load increasing: (1) trajectory of Fig 9 Distribution of number of grits with load, (2) changes in contact luminescence 0.3 plastic contact (N) by penetration depths for an adaptive composite, (3) changes into a counterbody (h) for adaptive (1) in contact luminescence for a traditional and non adaptive (2) composites (non adaptive) composite 0.0 0 1 2 3 4 5 6 (a) S (mcm2·10-3) 0.7 0.7 0.30 1 0.25 0.6 0.6 (arbitrary units) 1 (arbitrary units) 0.5 0.5 h2 h1 0.20 dN/dS 0.15 Stress dN/dS (MPa) 0.4 0.4 2 1 2 0.3 0.3 0.10 2 0.2 0.2 0.05 0.1 0.1 0.00 0.0 0.0 0 1 2 3 4 5 6 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 0 1 2 3 4 5 6 7 8 (b) S (mcm2·10-3) S (mcm2·103) Penetration depth (microns) ••• ••• ••• Fig 13 Relationship between number of Fig 10 Distribution of number of grits Fig 12 Distribution of stress over depth grits (N) and area of contact points with a (with plastic contact N) by area of contact of penetration (h) of the monocrystal counterbody (S) when grinding with (a) an with a counterbody (S) for adaptive (1) sample in contact with traditional (2) adaptive composite and (b) a traditional and non adaptive (2) composites and adaptive (1) composites composite (1 - P1 = 0.3 MPa; 2 - P2 = 1.0 MPa)00 DIAMOND TOOLING JOURNAL 1·11 00
  5. 5. AGE SPREAD) Grinding location of a maximum and a shape of profile depths were very close (10-15% difference). tools. In general, we posses numerous can greatly change under load changes. The However, the surface micro-geometry of comparison results for tool resilience for principal difference to an adaptive composite the monocrystalline sapphire formed with different composites, where only the highest is the absence of correlation between test tools showed significant differences. quality commercially available samples were maximum strain in the surface layer of a With an almost equal Ra value (0.36 µm used. In many cases adaptive composites counterbody with the depth of indentations for non-adaptive and 0.38 µm for adaptive showed increased resilience. However, made by the protruding abrasive grits. composite), the maximum deviation of whereas high resilience of grinding wheels Interesting information about features the profile Rmax formed with the adaptive is always desirable and very important in of the interaction of abrasive composites composite was 3.5-4.5 times lower. The some cases, it is never the most important with a counterbody as a “static model” of surface of roughness bearing face on an factor in gauging tool effectiveness. a machined workpiece was obtained by 0.8 µm level for the sample machined The example where compared wheels measuring the influence of pressure on the with the adaptive composite was 0.60, have very close resilience at all ranges of shape of the density of distribution of abrasive whereas non-adaptive composite’s result cutting depths used, allows us to fully value grits by contact points (Fig 13). This analysis was 0.11. The significance of these results the effect of adaptability on the structure demonstrates qualitative differences in the for processing of items like substrates and micro-geometry of the surface layer of behaviour of adaptive and non-adaptive for photoelectric cells or joint implants the machined workpiece. On Figs 15b, c and materials. For traditional composites, areas components is obvious. In the first case, the d we can see the effect of grinding depth on of contact points form a wide massif. With most important consequence of using an the (Rmax) value, the bearing face area and increased load, the areas of contact for all adaptive composite will be less time spent on the mean radius of asperities. when using grits increases, as well as the width of the polishing of workpieces. In the second adaptive and non-adaptive composites. With distribution, but any correlation in values of case this advantage will be supported by a 20 m/s speed, the Aignescotec composite additional area is absent. For abrasive grits increased frictional characteristics and the has a clear advantage. The surface created in an adaptive composite, the distribution of life duration of the part. by Aignescotec demonstrates structural areas of contact with a counterbody was much In other tests, the tools made with differences that will provide greater narrower in all cases. With increased loads, Aignescotec adaptive composites were areas of additional contact definitely correlate used for grinding cemented carbides and 200 between each other and the width of hardened steel. Samples of hard alloy H10F 150 2 1 distribution practically does not change. were subject to face grinding by a 4A2 D64 Grinding 60 m/s ratio These results show that grits that stand out wheel using coolant. The main recorded 100 20 m/s 20 m/s 60 m/s of an adaptive composite during contact with parameters were grinding ratio, surface 50 a counterbody create an interconnected system finish (Rmax), bearing face area and mean 0 that reacts to changes in an environment as radius of asperities (summits) (Fig 15). All 0.00 0.02 0.04 0.06 0.08 0.10 0.12 a single unit. This is their primary difference parameters were recorded with cutting (a) Cutting depth (mm) 5 from grits in traditional composites that speeds of 20 m/s and 60 m/s. When it 2 Surface finish Rmax poorly interact and affect machined material comes to grinding ratios (Fig 15a), the tool 4 (microns) linearly and additively in character. with an adaptive composite showed more 3 20 m/s The process of grinding is always stable behaviour at 20m/s with increased 2 1 connected with oscillations of all parameters cutting depth. However an increase of speed 2 1 60 m/s 1 of contact of the abrasive grits with the to 60m/s almost nullified any differences 0 machined surface of a workpiece. If grits between the adaptive and non adaptive 0.00 0.02 0.04 0.06 0.08 0.10 0.12 (b) Cutting depth (mm) create a single interconnected system, these 70 oscillations have a tendency for coherence. 3.0 60 m/s 60 Carrying surface Surface finish Rmax This can lead to different phenomena, similar 2.5 2 20 m/s 50 1 20 m/s to non linear effects in optics. These can 2.0 (microns) (%) 60 m/s 40 1.5 2 60 m/s be seen as “self-focusing” of shear strains 30 on the protrusion depth of the grit system 1.0 20 1 20 m/s 20 m/s into the machined material. However, even 0.5 10 D91 60 m/s 0 0.00 0.02 0.04 0.06 0.08 0.10 0.12 if the individual grit particles form a cutting 0.00 0.02 0.04 0.06 0.08 0.10 0.12 (c) Cutting depth (mm) profile with minimum height differences (for (a) Cutting depth (mm) 50 edge rounding (microns) Radius of roughness 70 1 example in precision electroplated tools), 1 40 20 m/s 60 Carrying surface but grits do not “feel” each other and not 50 20 m/s 30 60 m/s form a single system, self-focusing does not 60 m/s 40 2 (%) 20 occur because of coherence absence. 30 60 m/s 20 10 Tests of grinding wheels, made with 2 60 m/s 20 m/s 10 0 adaptive composites, were made compared D91 20 m/s 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0 to commercially available traditional resin 0.00 0.02 0.04 0.06 0.08 0.10 0.12 (d) Cutting depth (mm) (b) Cutting depth (mm) ••• bonds. In all cases cooling liquid was applied ••• Fig 15 Influence of cutting depth on at 4 bar pressure. In the experiments sapphire Fig 14 Relationship between depth of grinding ratio (a) surface finish [Rmax] (b), was used as the counterbody (Fig 14). cut and surface roughness (a) and contact bearing face area (c) and mean radius of surface area (b) of monocrystalline asperities (summits) (d) for adaptive (1) Grinding ratios for adaptive and non- sapphire when ground with adaptive (1) and traditional (2) abrasive composites adaptive composites for the applied cutting and traditional (2) composites under different cutting speeds 00 DIAMOND TOOLING JOURNAL 1·11 00
  6. 6. Grinding wear resistance, better fatigue strength, stability in areas of coherent-scattering (10% higher for the Aignescotec composite) better frictional characteristics, and as for regions provides minimum lattice defects. and a cutting depth of 0.06 mm, the adaptive the sharpened edge cutters – increased Macroscopic evidence of these structural composite ensured material removal with a sharpness and absence of spalls. differences is demonstrated by the dry much lower concentration of defects in the With a 60 m/sec speed, the differences friction quotient of a ground cemented created surfaces layers of the workpieces. With in the Rmax value are nullified, but the key carbide/aluminium alloy pair (Fig 18). high homogeneity of workpiece structure and advantages of the surfaces created by Hard alloy cutters and mills sharpened using high quality of surface layer formed by non- Aignescotec remain stable . This conclusion grinding wheels with adaptive composites adaptive composite, the adaptive composite is confirmed by data on the residual stress demonstrate service lives 2-3.5 times greater introduced several positive advantages. in ground samples of cemented carbide when used on steel and cast irons, than those Fig 21 demonstrates a reduction by 10 and the structural changes in the tungsten sharpened with non adaptive counterparts times the previous amount in the number carbide crystalline lattice, caused by grinding with similar grinding ratio (Fig 19). of ground workpieces whose durability (Figs 16 and 17). Regularities of the grinding ratio, surface is less than 90% of that specified. The Compression stresses caused by the finish, bearing face area, mean radius of average service life of these workpieces will adaptive composite increase the mechanical asperities and residual stresses in a workpiece be higher compared to those machined by durability and life of a workpiece, whereas such as hardened steel when ground using non-adaptives. With large-scale production CBN tools with adaptive composites and this in itself will be a noticeable advantage. 1.2 3 non-adaptive composites are very similar Also, the chance of a sudden destruction Residual strain 10-3 0.8 to results obtained when grinding of hard during forced operation or because of 0.4 alloys with diamond wheels. This proves fatigue defects decreases, in this case by an (MPa) 0.0 2 1 that this behaviour is not connected with a order of magnitude. This may constitute a -0.4 selection on the tool/material pair, but shows prominent competitive advantage for heavy -0.8 deep differences in the physicochemical loaded components like shafts, gearwheels, -1.2 0 4 8 12 16 20 24 28 32 mechanisms of the contact behaviour of bearings and turbine blades. Depth (microns) ••• adaptive and traditional abrasive bonds. Fig 22 shows general tendencies in the Fig 16 Distribution of residual stress in The influence of adaptive behaviour morphology changes in the machined samples of hard alloy: (1) initial sample, of abrasive composites on the surface surfaces of a workpiece when grinding with (2) sample ground with a traditional abrasive composite, (3) sample ground structure of machined steel components is adaptive and non-adaptive composites. with an adaptive abrasive composite very significant. In Fig 20 we can see the We are not talking about dramatic, relationship between cutting depth and the visually obvious profile charts, but about 20 dislocation density in the surface layer of stable, qualitative tendencies leading to Size of coherent scattering 18 region (nanometers) 1 60 m/s rods made of hardened steel ground by an increase in bearing capacity and contact 16 2 20 m/s 14 an abrasive wheel with adaptive and non rigidity, decreased unsoundness and 12 adaptive composites (grit: CBN B76). With improvement of frictional parameters. Full 10 8 60 m/s negligible differences in the grinding ratio implementation of the potential abilities 6 20 m/s of adaptive composites assumes not just 4 0.00 0.02 0.04 0.06 0.08 0.10 0.12 2.0 minimal surface defects but improvement Depth of cut (mm) Flank surface wear ••• 1.5 2 of whole complex of qualities compared Fig 17 Structural changes made in a to the unchanged machined material. (mm) tungsten carbide crystalline lattice made 1.0 1 In many cases this leads to noticeable by grinding with an adaptive abrasive composite (1) a traditional abrasive 0.5 differences in operational performances. composite (2) [abrasive grit D 64] 0.0 0 30 60 90 0.40 Time (min) 0.35 1.0 2 of cemented carbide ••• 0.30 Friction coefficient 0.8 Fig 19 Wear of hard alloy cutter over 0.25 dN/dσ flank surface during steel machining 0.20 Strength less 0.6 0.15 than 0.9σmax when cutter was sharpened by an 0.4 0.10 adaptive composite wheel (1) and 0.05 1 0.2 a traditional composite wheel (2) 0.00 1800 2000 2200 2400 2600 2800 0 σ (MPa) 0 50 100 150 200 250 3.0 Density of dislocations 10-12 (a) Friction time (s) 20 m/s ••• 2.5 60 m/s Fig 21 Strength distribution of 1.0 of cemented carbide steel rods ground by adaptive (1) Friction coefficient 2.0 0.8 and traditional (2) abrasive composites (cm-2) 1.5 0.6 (N = number of rods, σ = strength of rod) 1.0 20 m/s 0.4 60 m/s 0.5 0.2 (a) (b) 0.0 0 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0 50 100 150 200 250 Depth of cut (mm) (b) Friction time (s) ••• ••• Fig 20 Relationship between cutting Fig 18 Dry friction quotient of a depth and density of dislocations ••• cemented carbide/aluminium alloy pair in a steel rod surface ground by an Fig 22 Differences in surface morphology ground by adaptive composite (a) and adaptive abrasive composite (1) and formed by traditional (a) and adaptive (b) non-adaptive composite (b) a traditional composite wheel (2) abrasive composites00 DIAMOND TOOLING JOURNAL 1·11 00