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A production type CNC hobbing machnie (a maximum module to be cut of 4 mm and a maximum workpiece diameter of 150 mm) has been newly designed and manufactured based on the concept that a special attention is paied to a rigidity and a thermal deformation of the machine structure as well as a rotational transmission mechanism to enable high speed drive. A maximum speed of hob shaft is 1200 rpm and a table speed is possible up to 160 rpm due to a full spur gear drive. A CNC controller used is a common type for a hobbing machine which has a 32 bit CPU and five axes are numerically controlled. By paying a special attention to a torsional rigidity and a dynamic synchronous error between a hob and table, some tests are carried out. The results are compared with those of a full mechanical drive (FMD) hobbing machine. It is ascertained that by high accuracy gear cutting tests spur gears are generated with a sufficiently high accuracy although a correction of synchronous error between a hob and table is not applied at all by NC software. Also, in a production shop, it is demonstrated that a lot of helical gears for automobile can be manufactured with high-productivity and high-accuracy, that is : a machining cycle time per one gear is shortened by shortening a loading and unloading time of gear blank; a lead error is maintained within a small deviation in spite of high feed rate; and a measured value by over roll method is maintained within a permitted limit during a continuously long machining operation, for example, all day-long.

Inspection is defined as determining the conformance of a product to specifications or requirements. In general, inspection can be classified as done by attributes or by variables. Inspection by attribute is carried out with the use of gauges, resulting in a 'Yes' or 'No' (Go, No-Go) decision. With attribute inspection, decision making could become challenging in borderline cases, relying entirely on the subjective judgement of the operator. The consequences of a bad decision could be significant when the result of inspection is used to control a process. This paper presents a fuzzy rule-based in-process decision-making system for attribute inspection of a component gear ring (pinion) manufactured by a gear-hobbing process. Analysis of the performance of the proposed system in a simulated environment indicates that it improves the decision-making process in the presence of ambiguity, thus resulting in reduced manufacturing and defect costs.

In this investigation, workpiece and cutting tool dynamics in a turning operation are investigated. It is shown that dynamic information from the workpiece propagates to the cutting tool more consistently in the tangential cutting direction than in the radial cutting direction since there is a preload that seeks to keep the tool in contact with the workpiece. Finally, trajectories in the state space comprised of workpiece accelerations parallel to the radial and tangential cutting directions were investigated and it is graphically shown that stable cutting results in more organised dynamics and unstable cutting results in less organised dynamics, which agrees with previous work.

In this paper, the superplastic and isothermal hobbing process for manufacturing die cavities is described. The technical parameters, the design method of the set-up and the lubrication are also mentioned. Recently, these technologies have been applied in hobbing automobile link rod dies and other parts. By means of finite element analysis and experiments, the deformation paramaters for superplastic hobbing are obtained. They can be used in determining the process and choosing the blank sizes.

Recent studies have shown that the tooth profile errors of hobbed gears were mainly caused by geometrical error and eccentricity of the hob under good cutting conditions. Because manufacturing a highly accurate hob is very difficult and a highly accurate gear may not be obtained, even though a highly accurate hob is used, it is very important to investigate how to improve the actual meshing accuracy of the hob in the cutting process. In general, the meshing error of the edges caused by the hob eccentricity is nearly sinusoidal and the geometrical errors often contain sinusoidal components. On the basis of these facts, this report proposes a method which makes both of the sinusoidal error components cancel each other out in order to obtain an accurately hobbed gear. The test results clearly show the method's effectiveness in improving the tooth profile accuracy of gears.

A design and production system of the conical involute gear is established. First the basic rack composing of the normal tooth profile and the plane of symmetry, and basic dimensions are defined. Gear dimensions are expressed in terms of the basic dimensions. Second, a method of designing the generating rack is developed and designs of both straight and helical conical involute gears are studied. Finally two methods of taper hobbing are investigated, in which any conical involute gear can be cut by a cylindrical hob. One is the table-sliding taper hobbing, and the other the inclined-work-arbor taper hobbing. Many gears were made for trial and it was confirmed that this system has a practical utility.

Two types of TiN‐coated gear cutting hobs were compared in the hobbing of case hardening steel under production conditions. The coating reduced the wear of the hobs significantly, even though 25% and 50% increased cutting speeds as compared to the uncoated hobs were used. The performance of the two types of TiN coatings denoted by A and B differed markedly. The coating B lasted generally from 1.5 to 2 times longer than A. Mechanical testing of hardness and adhesion by a scratch test gave, however, slightly better values for coating A. Nuclear resonance broadening analysis showed coating A to be essentially stoichiometric TiN, while B showed a gradually increasing nitrogen content towards the surface. Scanning electron micrographs revealed columnar microstructure with coating A while B was almost featureless. The columnar microstructure of coating A is suggested as an explanation for the poor performance of coating A as compared to coating B.

A relative new development on the area of high-speed-steels are the powder metallurgical high-speed-steels (PM-HSS). On account of the manufacturing method a nearly homogeneous structure can be obtained. Based on practical knowledge, improved cutting properties, an increased grindability and an insensitiv behaviour during the heat treatment can be expected. In this paper, the application of some differently alloyed PM-steels at the two main methods of gear manufacturing, gear hobbing and gear shaping, is systematically examined and with regard to the economy compared among themselves and with conventionally manufactured high-speed-steels.

The machining of grinding wheel is an important research problem related to wheel finishing process. This subject is also a typical example of ceramic composite material machining. However, there is insufficient information about this type of cutting. In this study, a turning experiment was performed on white alumina grinding wheels by the use of cemented carbide, sintered CBN and sintered diamond single point cutting tools. The cutting speed ranged from 0.003 to 150 m/min, the maximum depth of cut was 1.0 mm, and the feed was 0.6 mm/rev. Thus, the tool wear and cutting force were measured for various cutting conditions, and the optimum operating condition and mechanism of chip formation were obtained. The effects of cutting speed, rake angle, and nose radius were specially investigated. The cutting mechanism was also studied from a specially low speed orthogonal cutting experiment and FFT analysis. It is evident from this study that grinding wheel can be cut easily by using a proper cutting tool, such as K01 and sintered diamond tool, and by selecting relatively low cutting speeds, great negative rake angle and large nose radius. The chip is mainly formed by compressive fracture.

Recently, smooth tooth surfaces have been obtained by hobbing with accurate finish hobs, resulting in the production of as-hobbed gears for practical use. However, further improvement of the gear accuracy in gear hobbing is needed in order to obtain high load-carrying capacity. In this study, the relation between the hob accuracy and the hobbed gear accuracy is investigated by calculating the tooth profile errors of gears caused by the various hob errors. From the analytical comparison of both hob and gear accuracy, the following are summarized. (1) The tooth profile of hobbed gears are not always highly accurate, even if they are hobbed with a highly accurate hob. (2) For the improvement of the gear accuracy, it is necessary not only to reduce the tooth profile error of hob, the lead variation of hob and the eccentricity in hob setting, but also to consider the hob error patterns.

Recent research indicates that tooth surface roughness has a significant influence on the surface durability of gears. In order to obtain smooth tooth surfaces economically, the authors have developed new finish-hobs, which have many numbers of gashes and a positive rake angle to control the occurrence of built-up edges. By applying these hobs to the finish-hobbing of medium-hardness gears(HB 340), the surface roughness is reduced to a half or a third compared with usually hobbed gears. The surface durability of finish-hobbed gears is investigated by using a power circulating-type gear testing machine. The relation between tooth surface roughness and pitting area ratio can be grasped quantitatively. And it is clear that these new finish-hobs are practical for obtaining a high load-carrying capacity of the gears.

著者の一人がすでに開発した回転駆動系のねじり動特性解析法を,過去に振動の問題が発生した最大歯切り直径1.5mの中形ホブ盤および最大歯切り直径7mmの大形ホブ盤に適用した.その結果,中形ホブ盤に発生した激しいびびり振動の原因が明確にできただけでなく,エネルギ分布および振動モード形に基づいて具体的設計改善策を明示できた.一方,大形ホブ盤については高能率・高精度ホブ切を可能とするための最適歯切り条件を明示する.

An optimization method for hobbing is presented. Hobbing is a typical manufacturing process which can be optimized. However optimization is usually applied in other machining processes. The identification of the process was quantitatively done by determining a tool life equation. The proposed method for optimization of hobbing conditions and the given equation for calculation of the hob Cost between two resharpenings are also suitable for hob comparison from different suppliers, and it can be used to compare hobbing on different hobbing systems. The method for optimization of hobbing is illustrated by an example.

To provide optimal manufacturing data with the aid of the resources of an information centre for machining gata, process-specific mathematical models are used. These models describe the influence of the respective data on important significant process parametrs, e.g. that of tool wear and cutting force. On account of the large number of influence data in gear hobbing, no mathematical models Eire yet known for thin method of gear manufacturing. In the following paper process models for the mathematical coverage of tool wear and cutting force at gear hobbinq are presented. On the basis of these process models, a concept can be shown, which permits a carefully directed optimization of the manufacturing data for any cutting cases and enables the incorporation of gear hobbing into an information centre for machining data.

The results of an investigation of the effect of hob wear on the vibration of the tool post of a hobbing machine are described. The analysis of the results was concentrated on the application of the vibration signal for the purposes of hob wear detection. Analysis of the signal components showed that the z -direction component of a third-octave bandwidth and central frequency of 125 Hz had the most suitable characteristics. Of the basic process parameters analyzed only the value of feed was shown to have significant effect on the parameters by which the signal suitability is expressed. The suitability of the signal for tool wear detection is significantly reduced with the higher values of feed.

A new method is introduced for calculating the shape of a gear hob for generating gears with an arbitrary tooth profile. This is applicable to calculate the shape of the tooth profile generated by a hob with an arbitrary shape of the cutting-edge. Because this method simulates exactly the metal removing process in gear tooth profile generation, it is possible to calculate the generated tooth profile when an interference occurs between the cutting edge and the finished tooth profile. As an example, the shape of the cutting edge of a hob was calculated for cutting cylindrical gears with a circular-arc tooth profile (Novikov gears). The profile errors produced in the calculation were less than 1 μm for gears with a module of 5 mm.

For the strength-design of hob teeth, the decision of optimum cutting conditions and the analysis of vibrations on a hobbing machine, it is necessary to determine the maximum hobbing torques in advance. This paper presents the equation fro calculating the maximum hobbing torque for practical use, and also shows the corrective coefficients by which the specific cutting forces in orthogonal turning tests are applied to those in hobbings. Form a comparison of the calculated hobbing forces with the measured ones reported in another paper, it is confirmed that this calculating equation of the maximum hobbing torque can be used practically in the case of steel gear materials such as JIS SCM435 and SCM415.

Fundamental research was made on the effect of the components of the soluble cutting fluids and on the range of application of the fluids for the purpose of developing soluble cutting fluids which have cutting ability close or superior to that of cutting oils. The follwing results were mainly obtained : there are some soluble cutting fluids which decrease the damage of cutting tools more than the cutting oil at a high speed of l59m/min ; among the testing fluids containing rape-seed oil, chlorinated paraffin and sulfurized fatty oil respectively, the fluid, 40% of which consists of sulfurized fatty oil, gave the best performance in the wear on cutting tool and in the roughness of finished surface.

The requirements for finish machining of case hardened gears are described; also the process and the range of its application. The machine tool and its specific equipment for the hard cutting process are discussed. The tools and their properties are demonstrated especially those of the cutting edges. Some considerations about the machining process, cutting conditions, chip formation and cutting forces are explained. Cutting edges of poly crystalline boron nitride are analysed by means of REM-graphs. Some practical results are shown as lead and profile charts. Machining times and DIN qualities are indicated.

Summary Due to their weight and size, it is recommendable to conduct the geometrical measurements of large gears within the manufacturing machine itself. Such measurements are done today with the aid of portable gear measuring apparatus. Another alternative for checking gears is to equip the gear-machine with suitable probe and measuring systems so that it will be possible to measure directly on the production machine. This presentation deals with the functional extensions of the gear machine from a pure cutting machine to one capable of conducting gear measurements as well.

Determination of the errors of hobs and a hobbing machine is necessary in order to improve the hobbing accuracy. This paper focuses on the configurations remaining on the tooth surfaces of hobbed gears, and clarifies analytically the tooth surface configurations affected by the errors of hobs and the hobbing machine. The errors of concern are lead variation and eccentricity, while the errors of the hobbing machine are the change of the revolutionary center and the rotational irregularity of the table. From the relationships between the surface configurations and the errors of hobs and the hobbing machine, it is possible to estimate the errors by the observation of the tooth surface configurations.

High accurate worm gears can be effectively used as an angle dividing standard. Wildhaber worm gearing is a kind of hourglass worm gearing. Due to the geometrical simplicity, its worm and worm wheel can be easily finished and accurately measured. This study describes a precision grinding method of the Wildhaber worm. Hobbing machine can cut the hourglass worms, but cannot give them higher accuracy than its master worm gears. To overcome this limitation, a special grinding device is made. The features of this grinding device are as follows : the linear motion of ball screw gives a grinding spindle very accurate circular feed, and this device has no mechanical connection between that circular feed and the rotation of the workpiece. In the first place, the working accuracy of the device was measured. The rotational accuracy of the rotary table relative to the worm was 1 second of arc. The accuracy of the ground worm using this device was 1.5 second of arc.

Estimation of the errors of a hob and a hobbing machine is necessary in order to improve the hobbing accuracy. This paper focuses on the configurations remaining on the tooth surfaces of hobbed gears, and illustrates analytically the tooth surface configurations caused by the errors of the hob and the hobbing machine. The errors of hobs concerned are the lead variation and the eccentricity, while the errors of the hobbing machine include the variation of the rotational center and the rotational irregularity of the table. The above-mentioned hobbing errors are closely related to the tooth surface configurations, and particularly, the feed marks express the characteristics of the tooth surfaces very well. As a result of the investigation on the tooth surface configurations and the formation mechanism of the feed marks, it is possible to estimate the hobbing errors by the calculated tooth surface configurations of hobbed gears.

Fabrication et performances des engrenages en fonte a graphite spheroidal. Cas des engrenages de durete moyenne

As the cutting condition of generating gears such as in hobbing is very complex, the specific cutting forces are different from those of orthogonal turning. In general, the specific cutting forces in hobbing are large, since the flowing chips interfere on the tool face. When two or three edges of a cutting tool cut simultaneo usly, the chips flow in different directions, and interfere with each other. In this paper, the specific cutting forces caused by the interference of flowing chips are investigated by cutting tests with round nose straight tools with various nose radii. As a result, the influence of the interference of flowing chips on the specific cutting forces becomes large with large undeformed chip thickness.

ホブ切用切削油に水分が混入した場合,とくに高速切除(159m/min)では少量(1〜15%)の水分混入でホブ刃先が大きく損傷し,多量の水分や水 100%の場合よりも被害が大きいことを発見した.少量の低級アルコールの添加によって,混入水分に基づくホブの損傷を完全に防止できる.ホブ摩耗と切削面粗さは水分混入前の切削油よりもかえって良い成績を示す.適量範囲の広さからn-プロピルアルコールが最適であることなどが分かった.

With the development of the carbide hobber and improvement in the manufacturing of the carbide hob, carbide hobbing has found extensive use in industry. For example, annealed gear blanks which are often used in mass production can be carbide-hobbed without trouble. In addition, it can also be adopted to hob gear blanks of heat-treated or hard materials which have thus far proven to be difficult to cut using high-speed steel hobs. However, in the case of carbide hobbing for gear blanks which have been heat-treated, damage from chipping or thermal cracks, seen as an increase of relief wear, will occur during the lifetime of carbide hob because of unsuitable cutting conditions. In this paper, the authors have investigated the cause of and countermeasures against damage by systematically classifying the shapes of damage on the cutting edge in carbide hobbing.

In order to develop CBN finishing hobs, the cutting performance of the sintered CBN tool is valued based on the intermittent turning tests. The sintered CBN cutting tool is very hard but fragile. The cutting edge of hob is liable to break, because the cutting mechanism on the hobbing is a kind of intermittent cutting. chamfering of the cutting edge is effective as a prevention against chipping. In this paper, first, the optimum form and size of chamfer is found out based on cutting tests. Secondly, the tool wear and the surface roughness are investigated under various cutting conditions. In spite of the cutting by CBN tools, a dead metal occurs on the cutting edge. It acts as built up edge and roughes the cutting surface.

The hobs are theoretically reconsidered on their peripheral taper and their rough cutting mechanism. The taper angle under a fixed length of hob varies according to the helix angle of gear and the setting angle and the cutting feed direction of hob. A method of determining the optimum taper shape is described on a calculation example. Additionally, in order to relieve the cutting load concentrated on the side edge of end tooth, a new type side taper hob, whose tooth thickness is gradually reduced in the rough cutting teeth, is proposed. Design example is given and satisfactory result is obtained in a hobbing with the trial hob., Bulletin of JSME. 1981, 24(198), p.2218-2225

Carbide hobbing is suitable for high efficiency production with excellent hobbing precision, and moreover, it can make it possible to cut hard material gears. Recently it was been adopted by factories of automobile, electric and gear production. To decrease the cost of the tools, the authors want to lengthen the life of the carbide hob. In this paper, we report on the carbide hobs made by the PVD methods. For determining the life of carbide hob, the authors examined the effect of coating on carbide hobs. The results are as follows: (1) Coating a carbide hob of PVD methods can delay the occurrence of flank wear on a carbide hob. (2) It can delay the microchipping on a cutting edge with a small entrance. (3) It can delay the large chipping on a cutting edge with a large cutting volume. (4) It can delay the thermal crack on a cutting flank edge.

The authors introduced a new method (element removal method) for calculating the profiles of the tools (hob, form grinding wheel, etc.) used for finishing gears with an arbitrary tooth profile. Because this method simulates exactly the metal removing process in the gear tooth profile generation, it is possible to calculate the generated tooth profile when interference occurs between the cutting edge and the finished tooth profile. Using this method, the authors calculated the exact wheel profile which can produce and involute tooth profile with a tip relief at a transverse section of the involute helical gears. The wheel profile was generated by a single point diamond dresser using a universal NC milling machine with an attachment made by the authors. The tooth flank and root of test gears were ground at the same time to prevent a step (notch), which is apt to be produced at the boundary of ground and unground surfaces. The accuracy of the form ground test gears was in the zero class of JIS and the surface roughness was in the range of 0.5 to 1.0 μm Rmax.

The inclining work-arbor taper hobbing is considered one of the most practical methods to cut a conical gear. But an exact hobbing theory has not been made clear, and besides an ideal hobbing machine available inpractical use has not been developed so far. In this paper, an exact kinematic analysis of this taper hobbing is presented, and an imaginary generating rack is obtained. A gear generated by this rack is defined as an ideal gear. Practical hobbing of conical involute gears is discussed. A hobbing machine having an inclining rotary table is tested, and some test gears are cut and inspected. And it is confirmed that the ideal gear can be considered representative of the gear cut by this taper hobbing, and the hobbing machine with an inclining rotary table has a practical utility. Finally, grinding of the conical involute gear based on the principle of this taper hobbing is presented.

This paper is intended to find out the best cutting condition for the purpose of improving the cutting efficiency of a spiral bevel gear and the roughness of its finished surface. But the cutting experiment by the gear generator requires too much trouble. Therefore the authors analysed conditions in which a single blade of the cutter cuts the spiral bevel gear, and clarified the cutting conditions of the single blade, with a view to simplifying the experiment by using a single blade instead of the cutter.

In order to obtain hobbed steel gears with a high accuracy, not only are accurate hob and hobbing machine necessary, but making the tooth surface smooth is also required. Recent studies have shown that a very smooth tooth surface can be hobbed by hobs with cemented carbide tips or cermet tips for hardened and tempered gears. In this report, the tooth profile errors of steel gears by finish hobbing are investigated and the possibility of obtaining a highly accurate gear by hobbing is discussed. As a result, it is clarified that the tooth profile errors of steel gears are mainly caused by geometrical errors and eccentricity of hob in any case of the hobs tested. Therefore, if using an accurate hob and hobbing machine with sufficient stiffness and selecting suitable cutting conditions, steel gears can be accurately manufactured by hobbing.

There have been different approaches to utilising the whole length of the hob in order to increase its tool life: diagonal hobbing and conventional shifting. When diagonal hobbing or shifting is used many teeth are not completely worn out but must neverthless be resharpened along with the other teeth which have reached the tool wear criterion. This paper presents a method for increasing tool life in hobbing (MITL-hobbing). A theoretical equation is proposed for determining a K value which would enable the hob to be moved gradually along its axis in such a way that the majority of the teeth which would be exposed to approximately the same wear, thus improving utilisation of all the teeth and prolonging the tool life. When this MITL-hobbing was used in industrial conditions, the tool life was increased approximately 232% in comparison with the tool life obtained by the traditional methods of diagonal hobbing and conventional shifting. Application of MITL-hobbing can be automated and applied when using advanced hobbing systems or conventional hobbing machines.

The following conclusions summarize the above results. 1. In drilling the SCr420 series as heat treated, the maximum tool life occurs around Hvl70 to 190 in the ferrite plus pearlite structure and is considerably reduced with the coexistence of spherical cementite. 2. In drilling the SCr420 series after cold forging, tool life is shortened slightly, while the torque is suppressed. Free machining additives, S and Te, improve tool life even for heavily forged materials. 3. In the gear hobbing SCM420 series, the softer and more spheroidized steel exhibits the longer tool life. The Ca addition with S and Te increases the life of the TiN coated hob tool.