Advanced Machining Technologies

H. Shinno , in Comprehensive Materials Processing, 2014

11.02.4.1 Main Spindle System for Micro- and Nanometer Scale Processing

A spindle system is one of the most important key components in an overall machine tool structure. A typical spindle system is fundamentally constructed by a spindle, bearings for supporting the spindle, a driving system for driving the spindle rotation, a cooling system for circulating fluids, and spindle housing for supporting the spindle and the bearings, etc. The rotational speed, power, torque, dynamic stiffness, and thermal properties of the spindle system determine the machining accuracy and productivity of the machining process. An air turbine–driven aerostatic spindle system provides high speed and precision spindle rotation in a noncontact condition. The air turbine has 2D spiral grooves from the rotational center and provides the rotational torque without ripple by supplying air from the spindle center. Therefore, the spindle system is one of the most effective spindle systems for micro- and nanometer scale processing.

Figure 7 shows the structural configuration of the spindle system. In this figure, a main spindle is driven by an air turbine, which has a cooling effect proportional to the spindle rotational speed. The spindle rotation causes an increase in heat generation at bearing clearance, but the heat generation can be canceled out by the cooling effect of the air turbine, which is located near the axial bearing. The main spindle made of ceramics is supported by aerostatic bearings in both the radial and axial directions. The aerostatic bearings are made of porous materials.

Figure 7. An air turbine–driven aerostatic spindle system.

The slot restrictor used for the radial bearings makes it possible to isotropically support the main spindle system, as shown in Figure 8. Radial error motion of the spindle system can be minimized by the laminar air flow from the slot restrictor of radial bearings.

Figure 8. Slot restrictor of radial bearing.

Figure 9 shows an example of the air turbine–driven aerostatic spindle system (9). As can be seen, the spindle system has a simple and compact structure. In consequence, the heat generated at bearings can be successfully cooled by the adiabatic expansion in the air turbine. Actually, performance evaluation results of the spindle system confirm that thermal deformation of the spindle system is negligibly small at high-speed rotation.

Figure 9. An example of the air turbine–driven aerostatic spindle system.

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Linear Systems Analysis in the Time Domain

John Semmlow , in Signals and Systems for Bioengineers (Second Edition), 2012

Khoo (2000) shows that the muscle spindle system can be approximated by the transfer function:

(7.24) T F ( s ) = M ( s ) θ ( s ) = s + 60 s + 300

where M(s) is the effective counter torque produced by the spindle reflex and θ(s) is the angle of the elbow joint. In addition, there is a gain term in the spindle reflex nominally set to 100 and a time delay (i.e., e −sT ) of 20   msec. Since the spindle system is a feedback system, the overall model is represented as shown in Figure 7.35.

Figure 7.35. Model of the neuromuscular reflex system developed by Khoo (2000).

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Sensors, data storage and communication technologies

Bernd Breidenstein , ... Ludger Overmeyer , in Cyber-Physical and Gentelligent Systems in Manufacturing and Life Cycle, 2017

2.1.2.3 Piezo-electric actuator-driven milling tool

Another main focus of the research is the development of a spindle system to produce micro patterns on flat surfaces and the description of the interrelationships between the manipulated and system variables of the new process and the produced surface. Based on the knowledge gained from the development of the activated turning tool, a piezo-electrically actuated tool for the production of micro patterns in a milling process is developed. Fig. 2.1.2.5 shows the design of the milling tool [5,6].

Fig. 2.1.2.5. Left: milled, information-bearing micro patterns; right: actuated tool holder.

To produce axial deflection of the milling cutter tip, a ring actuator with a maximum force of F max  =   20   kN and a deflection of a max  =   60   μm at a maximum permissible voltage of A max  =   1.0   V was used. The system is mounted by two diaphragms made of spring steel acting as solid-state joints. The use of a ring actuator increases the performance capacity compared with cylinder actuators due to the larger surface area and the associated better thermal properties. Furthermore, the ring design allows rotationally symmetrical, central spring loading by disc springs. For use in machine tools, the milling tool has a standard HSK-A 63 shank. Due to the high power to be transmitted, a slip ring is employed. In addition to the voltage, this slip ring also transmits a temperature signal and a strain gauge signal to determine the expansion of the actuator. The use of titanium for the tool body reduces the rotating mass including a conventional screw-in milling head (D  =   20   mm) to 320   g. This enables a highly dynamic controlled excitation (natural frequency ω 0  =   4.7   kHz). A precise real-time control system based on a static and dynamic characterization of the system is constructed. By coupling the FTS control to the machine tool control, the patterns can be produced according to the main spindle's rotational angle [7,8]. Both the actuated tool and the technology described later are the subject of patent applications and have already been put into practical use in industrial applications [9].

Thus the classic flat milling process is supplemented by the two controlled variables, structuring frequency f s and structuring amplitude a s. The main variables influencing surface and micro pattern quality were determined on the basis of a static testing plan. An approach for measuring surface roughness along the tooth cutting arc is developed in order to determine the micro pattern quality and the effect of axial excitation on topography. A confocal microscope with suitable algorithms for profile distortion correction is applied. The surface roughness along the tooth path decreases with increasing cutting speed and structuring frequency. An increasing rake or clearance angle has a comparable effect. In feed direction, the influence of the structuring amplitude on the roughness is 2.5 times higher than the influence of the structuring frequency. Feed per tooth and clearance angle are significant influencing factors in this context. The results correlate with the existing findings without axial excitation [10,11].

The resulting data density is restricted by the kinematic relations. The number of patterns along the tool's engagement is determined by the relation between the structuring frequency f s and the rotational speed n. The number of patterns in feed direction is determined by the structuring amplitude a s and the feed per tooth f z. In order to generate patterns with defined depth and length, an exact control of the axial tool movement is essential [12–14].

In order to demonstrate the process kinematics and the achievable quality of the patterns, comparative tests are carried out on Al7075, C45, 42CrMo4, and TiAl6V4. For this purpose, the actuator is stimulated with a sinus oscillation every 15 rotations during finish milling in order to generate defined patterns in the surface. To change the pattern's length and depth, frequency and amplitude are varied on two levels. Cutting speed and feed rate are set according to a finish milling depending on the particular material. The process parameters are summarized in Table 2.1.2.1.

Table 2.1.2.1. Process parameters depending on the workpiece material

Material Rotational speed [min−   1] Feed per tooth [mm]
Al7075 3500 0.08
C45 3000 0.06
42CrMo4 3000 0.06
TiAl6V5 2500 0.04

Furthermore, two cutting edges are used that differ in their width between 250 and 500   μm. Fig. 2.1.2.6 shows the cutting edge's geometry.

Fig. 2.1.2.6. Cutting tool for binary structuring.

By using these cutting tools it is possible to generate defined patterns in the workpiece surface during the finishing process. As an example, generated patterns in TiAl6V4 are shown in Fig. 2.1.2.7. The figure is made with a confocal white-light microscope.

Fig. 2.1.2.7. Surface topography of milled micro patterns in TiAl6V5.

The characteristics of the generated micro patterns vary for the four different materials. These variations occur in form of geometry and the distance between the patterns. Furthermore, the surface roughness varies depending on the workpiece material and the corresponding process parameters.

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Conversion of Fibre to Yarn

R. Alagirusamy , A. Das , in Textiles and Fashion, 2015

8.6.3 Combined Systems

Combined systems were first established in order to unite the benefits of the ring and hollow-spindle systems in a single machine, as it was thought that a yarn with twist had a more stable and reliable structure than one with a fasciated structure. Later, it was recognised that two hollow spindles could also be assembled in series and that this would offer a variety of yarns and a different range of benefits. This is illustrated in Figure 8.24, which depicts two hollow spindles, arranged one above the other, which wrap the staple strand with two binders applied in opposing directions.

FIGURE 8.24. Schematic of two-spindle wrap system.

This technique is used to produce special-effect yarns that have a more stable structure, as the effect fibres are trapped by two binders instead of one.

Figure 8.25 shows the original combined system in which the hollow spindle and ring spindle are combined in a single machine. In this case, the wrapped yarn is provided with some true twist by the ring spindle placed immediately below the hollow spindle. It was thought that the speed of the hollow-spindle assembly would be enhanced by the true twist inserted by the ring spindle, and that it would therefore be able to create yarns that are less expensive than true ring-spun yarns while still retaining some of their characteristics.

FIGURE 8.25. Combination of ring and hollow spindles.

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The Structure of Motor Programs

Steven W. Keele , Jeffery J. Summers , in Motor Control, 1976

B Evidence Discriminating between the Two Theories

Both follow-up servo theory and alpha-gamma coactivation theory posit active programming of the spindle system predicting that spindle output should either increase or at least remain constant during active movement. If, on the other hand, the spindle receptor only responds passively to stretch of the main muscles, and is not itself programmed, the spindle output should decrease as the main muscles contract and reduce the stretch. One suitable preparation for studying whether spindle output increases, stays constant, or decreases during active movement is the intercostal muscles involved in breathing. The intercostal muscles are useful because a regular movement pattern is maintained even when the animal is anesthetized and immobilized. Von Euler (1965) found in cats that as the intercostal muscles contract, forcing air out of the lungs, firing rate from the muscle spindles increases, as predicted by active programming of the muscle spindles. Moreover, if during the course of breathing an unexpected load is placed on the intercostal muscles by temporarily occluding the windpipe and creating a partial vacuum to retard further muscle contraction, the spindle output is increased even further. This increased output to unexpected loads is exactly the sort of error correction expected by either theory.

A very similar phenomenon was observed by Taylor and Cody (1974) for movements of the jaw in licking and eating by cats. Whereas spindle output varied as a function of main muscle stretch during passive jaw movements, spindle output remained practically constant during self-generated licking, indicating active programming of the muscle spindle. The fact that output remained constant supports alpha-gamma coactivation.

A necessary implication of follow-up servo theory is that the gamma system must become active before the alpha system and the main muscles, since the alpha system is activated by the feedback from the gamma loop. Historically, studies indicated that the gamma system leads the alpha system but those studies involved animals under deep anesthesia. Apparently anesthesia can alter the time relationships of alpha and gamma. Phillips (1969) with his colleagues Koeze and Sheridan studied muscle responses from the hand of the baboon under light anesthesia that more closely approximates the normal state. They elicited the muscle responses by electrical pulses to the cortex and observed the onset times of the electromyographic response from the muscle and the discharge from muscle spindles recorded at the dorsal roots. Under some conditions they found spindle discharge to increase during muscle contraction. As with Euler's study of breathing movements and Taylor and Cody's study of jaw movements, this finding indicates active programming of the muscle spindles, since muscle contraction by itself would lead to a decrease in spindle output. In addition, the spindle discharge in some circumstances occurred at the same time as or followed the muscle response, indicating that the gamma system is not activated early enough for its discharge to feedback on and start the main muscles. This study therefore rules out follow-up servo theory and supports the theory of alpha-gamma coactivation.

Even more convincing evidence comes from a study by Vallbo (1971) of voluntary muscle contractions by people. He inserted an electrode into the median nerve of the arm and located responses from a single afferent fiber from a muscle spindle. Subjects in the experiment were then asked either to flex a finger for 2 or more seconds or twitch the finger. In either case a large proportion of spindle responses followed, rather than preceded, activation of the muscle underlying finger movement. Again this supports alpha-gamma coactivation theory.

The studies of the activation and timing of the spindle system are, therefore, consistent with deafferentation studies. Some movements are programmable directly through the alpha system to the main muscles without feedback from the spindle system. Some cautions are worth holding in mind, however. Neither Phillips' study of the baboon hand nor Vallbo's study of finger movement, the two studies most critical for differentiating the two theories, involved sequential movement skills. All they demonstrated is that movements can start without a follow-up servo mechanism, but they have little to say about whether terminal movement points are also programmed through the alpha system. There is some provocative evidence that the gamma system or other feedback sources are more directly involved in finely controlled movements after they have started.

Smith et al. (1972) attempted to selectively anesthetize gamma fibers by injecting Xylocaine in the radial nerve. The gamma fibers are small in diameter compared to alpha fibers. Under the right dosage, the small fibers appear blocked, since hot and cold stimulation which also involves small fibers is not perceived. At the same time, strength and tactile sensations subserved by large fibers are normal. This suggests that alpha fibers are also intact. In one task following selective blocking of small fibers, subjects were asked to rapidly touch their noses. Normally one observes a slight pause just before touching the nose, but people with gamma blocking failed to stop their fingers on the first couple of tries and instead forcefully hit their cheeks or mouths, as though the feedback was needed for stopping the movement. Although they were soon able to overcome this failure to stop, the results raise the possibility that the gamma system is normally involved in terminating movements. Other interpretations, such as some motor impairment, are possible, however.

Evidence of a similar sort comes from Bizzi's studies (1974) of eye and head movements in monkeys. Normally when a spot of light comes on in the periphery of the visual field, the eyes make a saccadic jump to fixate on the spot. Very soon after the eyes begin moving, the head also begins to turn toward the source; as the head rotates, the eyes make a compensatory back turn in the sockets. Eventually the head is pointing at the spot, and the eyes are again pointing straight ahead in their sockets. When vestibular feedback was surgically interrupted, eye and head movements were both initiated but compensatory eye movement failed to occur; apparently that final phase of compensatory movement was reflex controlled. With several weeks of training, compensatory movement did recover, perhaps then under complete central control. Like Smith et al., Bizzi appears to have uncovered a movement sequence that is initiated by program, but the termination normally is partly under feedback control, in this case vestibular feedback.

A final behavioral study is of interest in this context. Stelmach et al. (1975) required people to rapidly move a slider to a position along a track, remove their arm momentarily, and then recall the same ending location by moving from a different starting position. In one condition the first movement of the pair was determined by the subject himself. Since the movement was rapid, the subject presumably selected the stopping location prior to beginning the movement. In two other conditions, the subject's hand was either passively moved to a location matched to positions in the preselection case or the subject actively moved until hitting a stop at the location. In neither of the latter cases did the subject know in advance where he would stop. At the final stopping position, subjects in all conditions held position for 2 sec. Despite this end pause, preselection subjects were more accurate in reproducing the location. Why? There are perhaps several possibilities, but an intriguing one is that only the preselection condition allows advance programming of the movement. But programming of movement distance is not possible in this situation since the subjects reproduce location. Perhaps it is the muscle spindles that are set for a final location and are remembered during reproduction. If so, then the finding would constitute evidence that spindles are intimately involved in precise movement termination.

Although the bulk of evidence supports a motor programming theory involving alpha-gamma coactivation, these latter studies, while far from conclusive, raise the possibility that a hybrid between the coactivation and follow-up servo mechanisms might be involved. Perhaps the alpha system conveys programs for the initiation of movements and even their rough termination. Parallel with the initiation of movements through the alpha route, spindles may be coactivated. While they may not be necessary for starting the movement, they may come into play, as supposed by follow-up servo theory, in finely graded movement termination. Again, the fusimotor system may not be absolutely necessary for ending movements, but it may aid such termination and make it more precise. Coactivation theory, in contrast, gives the gamma system a role only in correcting errors and not in the normal stopping of movement. Such a hybrid system would include all the advantages of the follow-up servo theory, including partial explanation of context dependent variations in movement, but also would be consistent with rapid starting of movements, the persistence of movements following deafferentation, and coactivation of alpha and gamma. Such a hybrid model is similar to a servo-assisted model proposed by Merton (1972) but is only speculative at this time as evidence is suggestive but definitely not conclusive.

The main conclusion to draw at this point is that at least some skills appear under motor program control. Some skills are directly programmed through the alpha route, but subsidiary programming may also occur through the gamma route resulting in more precise movement termination. Yet other skills may not be under program control. Thus, we do not know whether finer skills or skills performed by distal elements such as the fingers are programmed, since they are disrupted more by loss of feedback; they could be programmed, but feedback is needed for more frequent correction, or feedback may actually be needed for initiating movements as supposed by S-R chaining or closed-loop conceptions of skill.

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Developments in fancy yarns

R. Wright , in Specialist Yarn and Fabric Structures, 2011

4.4.4 Combined systems

The combined systems were first developed in order to unite the benefits of the ring and hollow spindle systems in a single machine, since a yarn with twist has a more stable and reliable structure than a fasciated yarn.

Then it was realised that two hollow spindles could also be mounted in series, offering a different variety of resultant yarns, and a different range of benefits. This technique is used to produce special effect yarns that have a more stable structure, resulting from the fact that the effect fibres are trapped by two binders, instead of one.

Figure 4.23 shows the original combined system in which the hollow spindle and ring spindle were combined in a single machine. In this case, the wrapped yarn is being given some true twist by the ring spindle located immediately beneath the hollow spindle. Thus the speed of assembly offered by the hollow spindle, enhanced by the true twist inserted by the ring spindle, creates yarns less expensive than true ring-spun yarns, while still retaining some of their desirable characteristics.

4.23. Original combined system.

In its earliest form the combined system involved at most two spinning points, in a choice of only two configurations (hollow spindle followed by hollow spindle or hollow spindle followed by ring spindle). However, much has changed in recent years. The changes have resulted in part from advances in electronic process control, processor power, and (crucially) in the usability of the machine control interface, and in part from truly inspired engineering. In the past process control was limited to basic parameters for the yarn, with a little variability to reduce the possibility of striping effects; now the control is such that several different structures may be created within a single process.

Figure 4.24 indicates the various points at which changes in the machine set up have occurred.

4.24. Changes in the combined system.

Whereas before the feed into the hollow spindle involved only one set of four drafting rollers, now there are two separate fibre feeds, each consisting of four drafting rollers. Each roller is individually controllable, and the third of each set of four has an apron to improve fibre control. As a result of this development it is now possible, for example, to create a yarn with an 'ombré dyed' fibre effect purely by a series of programmed changes to the proportions of delivery from each feed. Indeed, such is the detailed level of control available through the programming interface that the system may even be used to create Fair Isle-effect yarns, which when knitted produce an impression of the familiar Fair Isle patterns seen in knitwear.

On some equipment the hollow spindle may be removed or bypassed, while maintaining the feed variability. This allows the production of ring spun slub yarns, or of the ombré effects on ring spun yarns. Alternatively, on certain equipment, the hollow spindle may be replaced by a chainette knitting head, to create an entirely different range of effects.

A further detail in the hollow spindle element of these machines is the introduction of a double belt system, allowing differing speeds, or even contrary motion, between the spindle itself and the false twist insertion, still further increasing the range of resulting yarns. Again, it is the excellent work that has been done on the details of the programming interface that makes these developments useable within the production environment.

In certain equipment set-ups, the core yarns are guided from the creel through tubes to ensure that the necessary separation is maintained – this is, again, a refinement of the equipment rather than a radical change, but it reduces the risk of yarns catching and tangling with one another, especially when the machine is stopped suddenly. Such additional refinements improve machine efficiency, improve yarn quality, and thus contribute to improved margins for the spinner.

Some machines offer a choice of package draw off, including precision winding to create dye-vessel-ready packages. This in turn reduces the number of processes involved in preparing the yarn for further processing. Since it is now also possible to produce loop yarns on this system straight from sliver without an intervening roving process, the new equipment will change the economics of fancy yarn production in a variety of ways that might not have been foreseen prior to its introduction.

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Staple systems and modified yarn structures

Peter R. Lord , in Handbook of Yarn Production, 2003

10.6.2 Wrap spinning by the hollow spindle process

This technology provides a means of wrapping filaments about core yarns to enhance the performance of the composite. Figure 10.9 is a diagram of a hollow spindle system in which filament is taken from a bobbin mounted coaxially with the yarn Y. A hollow spindle with a hook rotates about the same axis. The hook engages the yarn and creates false twist above the hook, but the staple strand below the hook should have little or no twist. The filament yarn, F, passes through the hollow spindle and should have sufficient twist induced above the hook for the filament and staple components to be brought into firm contact. The hook acts like an untwister similar to a false twist spindle in texturing. Most of the false twist in the staple component is removed as it passes through the hook. The twisting action causes the filament to follow the surface of the staple component and the filament becomes tightly wrapped about the very low twist staple core that emerges from the hook (yarn Y′). Because of the high tenacity of the filaments, high production speeds are possible (up 35 000  r/min, which is about twice that of ring spinning). Sometimes, sliver-to-yarn systems are used and the filament is wrapped around the drafted sliver. Occasionally, both a filament and a staple strand (roving or sliver) are passed through the drafting system to produce a bouclé or other effect. The system can handle short or long staple but it is predominantly used for long-staple wrapped yarns. Xie et al. [16] created a theoretical model and tested 64   s wool yarns to find that yarn tenacities of up to 12   g/tex were possible, with wrapper twists in the range 3 to 5 wraps/cm (≈ 1.2 to 2 tpi).

Fig. 10.9. Hollow spindle spinning

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Advanced Machining Technologies

T. Matsumura , in Comprehensive Materials Processing, 2014

11.07.3.2 Dynamic Response

In micromilling, the tool displacement induces not only the machining error but also the tool breakage because of small diameter of the end mill. Therefore, dynamic behavior of the end mill should be evaluated with dynamic response of the tool, the workpiece, and the machine tool. Generally, in dynamic analysis, the tool displacement x at the time t is given by:

[2] m ⅆ 2 x ⅆ t 2 + c ⅆ x ⅆ t + k x = F

where m, c, and k are the equivalent mass, the coefficient of viscous damping, and the stiffness, respectively. F is the cutting force at the external force, which changes with the cutting thickness and the tool displacement. Although the dynamic response of the end mill can be estimated numerically in the structure analysis such as in finite element method (FEM), the tool-spindle system, which includes the end mill, the collet, and the spindle should be evaluated from a practical point of view. Normally the modal parameters, m, c, and k, for large diameter end mill can be estimated in impulse response tests using the displacement sensor and the special hummer, on which a force sensor is mounted. If the impulse response test is applied to estimation of the modal parameters of the miniature end mill, the tool will be broken.

A method is shown to measure the dynamic response of the small diameter end mill, here (3). The dynamic response of the tool-spindle system mounting the microend mill is measured with the vibration generator, as shown in Figure 8. The vibration tests are performed to measure the exciting load with changing the frequency of the tool displacement. The end mill is mounted on the spindle with the cutter axis inclination. The edge is clamped on the excited table made of tungsten carbide, which is small enough to ignore elastic deformation of the table, as shown in Figure 8(b). The exciting load can be measured at the given displacement with a piezoelectric dynamometer mounted under the excited table. The displacement of the table is controlled by the sinusoidal wave generator. A displacement sensor measures the distance between the sensor head and the table with eddy current. The compliance can be acquired with measuring the power spectrum of the load and that of the displacement on an Fast Fourier transform (FFT) analyzer. The modal parameters in eqn [2], then, are estimated in the dynamic response.

Figure 8. Dynamic response test: (a) vibration test and (b) ball end mill on excited table.

Figure 9 shows an example of the compliances with the vibration frequencies. The frequency is changed from 0 to 1000 Hz in the test. The figure shows the dynamic response around the natural frequency. The natural frequency is estimated as 335 Hz based on the peak of the compliance. Because the vibration test is performed on the tool mounted on the spindle, the measured peak can be regarded as one of the vibration modes in the tool-spindle system, which includes the tool, the collet, the spindle, and the spindle-clamping device for mounting on the machining center. Then, the modal parameters for the radial direction of the tool are estimated, as shown in Figure 10. F ϕ and δ ϕ are the load and the displacement of the tool in the test with the inclined tool, respectively. Because the radial stiffness is much larger than the axial stiffness in the tool-spindle system, it is assumed that the tool displacement is mainly subjected in the radial direction of the tool. The load and the displacement in the vibration direction are transferred to the components of the tool radial direction as follows:

Figure 9. Compliance. Inclination angle of the cutter axis, 30°; the overhang of the end mill from the collet, 15 mm.

Figure 10. Vibration model.

[3] { F = F ϕ sin ϕ δ = δ ϕ sin ϕ

where ϕ is the inclination angle of the cutter. δ and F are the displacement and the load in the radial direction of the tool, respectively. Therefore, the compliance G in the tool radial direction can be given by:

[4] G = G ϕ sin 2 ϕ

G ϕ is the compliance in the vibration direction, which can be measured in the vibration test shown in Figure 8.

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Digital twin driven lean design for computerized numerical control machine tools

Yongli Wei , ... A.Y.C. Nee , in Digital Twin Driven Smart Design, 2020

10.4.1 Analysis of workload

Analysis of the workload of CNCMTs starts from the physical entities (e.g., CNCMTs, workpiece, and environment) that participate in the machining process. As a multilayer system, the physical CNCMTs need to be analyzed meticulously at the subsystem and component level to reveal the complex workload data. As shown in Fig. 10.2 , the CNCMTs can be divided into different functional subsystems (e.g., spindle system, tool system, and feed servo drive system), and these subsystems can be further divided into smaller unit at component level.

Figure 10.2. Detailed analysis of CNCMTs workload. CNCMTs, computerized numerical control machine tools.

After classification, data to be collected from the physical entities are determined based on the analysis of factors that influence the performance of CNCMTs during processing. This analysis provides guidance for sensor selection and installation. Taking the thermal stability of the spindle of CNCMTs as an example, the influencing factors include spindle speed and temperature distribution axially along the spindle. However, it is impossible to collect temperature values at continuous points along the spindle. In this case, only the temperature at both ends of the spindle and the spindle speed need to be collected, and then the intermediate temperature can be calculated using formulas. This example suggests that some collected data cannot directly reflect the working conditions of CNCMTs and thus implicit workload data for subsequent use need to be calculated through processing the raw data (see Section 10.5.1.2 for reference).

For LD of CNCMTs, different types of simulation (e.g., fluid mechanics analysis, structural mechanics simulation, and thermodynamic simulation) will be carried out using different workload data to make the design of CNCMTs meet target performance indicators. To collect and utilize the workload data efficiently, these data are divided into several categories (e.g., structural mechanics workload, thermodynamics workload, and fluid mechanics workload). Taking the thermodynamic workload data of spindle for example, the thermodynamic workload contains not only temperature data such as spindle temperature, environment temperature, and tool temperature, but also data related to thermodynamic simulation such as spindle speed. It might be noted that the same data can belong to different workload categories as long as it plays a role in certain types of simulation.

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Thermal Engineering of Steel Alloy Systems

V.I. Rudnev , D. Loveless , in Comprehensive Materials Processing, 2014

12.15.2.4.3 Scanning Inductors

Parts with a high degree of rotational or axial symmetry are often induction hardened using scanning techniques in which the parts are moved progressively through the coil; alternatively, the coil moves along the workpiece length/height. Thus, with scan hardening only a small portion of the workpiece is induction hardened at any given time. Scan inductors have become popular for surface hardening and through hardening of various types of shafts in high-volume production lines. As an example, Figure 21 shows a vertical dual-spindle system for induction scan hardening of the steel shafts. Scan rate and coil power are varied during scanning to allow proper accommodation of changes in shaft geometry. The trade-off is coil cost and power supply size that are typically much greater for single-shot inductors than for scan inductors.

Figure 21. Dual-spindle systems for induction scan hardening of carbon steel shafts.

 Courtesy of Inductoheat Inc.

Scan inductors are particularly attractive for hardening elongated workpieces for which a single-shot method would substantially increase the cost of power supply, coil, tooling, and auxiliary equipment. Scan inductors also provide superior flexibility compared to single-shot inductors allowing operating components of various lengths.

Scan inductors (vertical or horizontal) may be one or more turns. Figure 22(a) shows examples of two-turn coils for scan hardening of straight shafts (Figure 22(b)). Those coils require using spray quench followers. In contrast, Figure 23 shows a cross-section of the machined integrated quench scan inductor (MIQ inductor) used in the dual-spindle shaft hardening system shown on Figure 21. Both a coil-cooling chamber and a quench chamber are clearly visible.

Figure 22. Examples of two-turn coils for scan hardening of straight shafts.

 Courtesy of Inductoheat Inc.

Figure 23. Machined integral quench inductor.

 Courtesy of Inductoheat Inc.

The required number of turns is determined by the ability to load match (also called impedance match or load tune) the coils to the power supply and/or by specific process requirements. The impedance (load) matching process is particularly important if maximum power is required from the power supply. There should be a balance in power, voltage, frequency, and current to achieve the desired heat intensity and heating pattern. The term load matching or load tuning is used to describe this process and will be discussed further.

Scan coils with wider heat faces allow faster scan rates, because with the longer inductor, the part will be in the inductor for a longer period of time; this means that the scan rate can be higher.

One main restriction for using the wide heating face scan coils is related to the longer and gradual pattern run-outs and potential difficulty in meeting some hardness pattern specifications when sharp transition is required. Hardness pattern controllability sometimes suffers when wide-face inductors are used.

Single-turn inductors with narrow heating faces are used for hardening fillets with small radiuses and/or where sharp pattern run-outs (cutoffs) are required. An example is the case in which a pattern must end near a snap ring groove. Inductors with narrow heating faces are also useful for obtaining a short transition zones (both axial and radial).

Hairpin inductors are often used for scan-hardening flat surfaces. Transverse flux inductors have limited use in induction through hardening due to its high sensitivity.

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