Development of SelectG7 General Purpose Cylindrical Grinder

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1 TECHNICAL REPORT Development of SelectG7 General Purpose Cylindrical Grinder E. FUKUTA JTEKT has developed a new CNC general purpose cylindrical grinder with a built-in unit enabling manual swiveling of the wheelhead being capable of machining large workpieces. The wheelhead can be swiveled with ease between 0 and 20 degrees to enable optimal grinding of each of the workpiece's grinding areas. A GC50CNC device has been installed to make grinding operation easy, and a manual intervention operation function developed by JTEKT enables the high-accuracy grinding of individual workpieces. Key Words: large-sized parts, wheelhead swiveling, GC50, interventional operation 1. Introduction In recent years, global warming, the representative of environmental issues, has urged the reduction of fossil energy consumption. As a solution, European countries have led the introduction of wind power generation, followed by the U.S.A. and China, where activities are dramatically expanded to reduce fossil energy consumption. The demand for wind turbine equipment has thus been growing rapidly. Also, in China and India, construction of railway infrastructure has become quite active contributing to the increase in demand of large components, such as construction equipment. It is, consequently, expected that the demand will continue to grow for equipment suitable to large-sized components, and capable of coping with assorted-smalllot production and high value-added production. In order to meet such customer demands, we have developed a large-size general purpose cylindrical grinder (hereinafter referred to as "this grinder") as presented hereunder (Fig. 1). 2. Machine Features 2. 1 High Accuracy Manually Swiveled Wheelhead This grinder enables optimum grinding to be performed by selecting use of either a plane wheel or an angular wheel depending on the areas of the workpiece to be ground. Selection of either the plane wheel or angular wheel is made by manually swiveling the wheelhead. On an ordinary grinder, it is common practice to place the wheel on the left side of the wheelhead for plane grinding, and on the right side for angular grinding to prevent interference between the workhead or other devices and the wheelhead itself. On the other hand, not only by accommodating a large diameter wheel, which minimizes the interference problem, but also by providing a swiveling unit on the wheelhead, this grinder can serve as a dual-purpose grinder, i.e. plane grinding and angular grinding, and offers excellent cost performance. This grinder can accommodate a maximum wheel diameter of u1 065mm (plane) or u915mm (angular). As the swiveling unit is comprised of a "pneumatic mass reduction + handle screw feeding mechanism," switching between plane grinding and angular grinding on the wheelhead is easy. Fig. 1 SelectG7 Cylindrical Grinder 77

In addition, this grinder, equipped with a high rigidity wheel spindle, can use a wheel with a maximum width of 300mm.

To alleviate such an adverse effect, this grinder uses a 20 angle, instead of the commonly used 30, and also pays consideration to reducing the limitation of wheel effective layers caused by

In the case of single piece grinding, it is necessary to check the relative positions of the workpiece and the wheel in preparation for grinding.

In order to counter this thermal displacement, this grinder incorporates an isolation cover to keep the bed free of direct contact with coolant that has been heated by grinding.

2 In addition, this grinder, equipped with a high rigidity wheel spindle, can use a wheel with a maximum width of 300mm. In the case of angular grinding using a wide wheel, the significant difference in surface speeds on the wheel surface may cause uneven wear on the wheel. To alleviate such an adverse effect, this grinder uses a 20 angle, instead of the commonly used 30, and also pays consideration to reducing the limitation of wheel effective layers caused by interference with the flange during dressing of the minimum diameter side (Fig. 2). Position of linear guide Swivel center position Position of linear guide a right angle to the workpiece. In the case of single piece grinding, it is necessary to check the relative positions of the workpiece and the wheel in preparation for grinding. This layout allows the operator to do this either visually or intuitively Isolation Cover The thermal displacement of the bed is one major factor causing thermal displacement in the grinder. In order to counter this thermal displacement, this grinder incorporates an isolation cover to keep the bed free of direct contact with coolant that has been heated by grinding. This isolation cover has been successfully adopted in our multi-purpose CNC cylindrical grinders, the GXN and GPN series (Fig. 3). Gravity center for plane grinding Gravity center for angular grinding Table Screw feeding device Isolation cover Insulation of grinding heat by air gap provided between bed and cover Bed Fig. 3 Isolation cover Fig. 2 Schematic construction of the wheelhead Wheelhead Feeding Slide For the wheelhead feeding slide, this grinder uses a roller slide instead of a V-frat slide, improving the feeding rigidity through increased restraining force. The above-mentioned wheelhead swivel center is located in a position that minimizes the variation of center-of-gravity balance, as well as minimizes the wheelhead traveling distance caused by switching between the angular wheel and the plane wheel, so that the length of the ball screw may be reduced, and that the effect of yawing during the forward and backward traveling of the wheelhead may be suppressed. In this way, the straightness of the wheelhead can be assured, while minimizing the inclination of the wheel generated during reversing the travel. Furthermore, since the roller slide is subject to less frictional resistance, the capacity of the servo motor for the feeding axis can be reduced, even if the wheelhead is heavier, contributing to energy conservation. In this grinder, the slide for the wheelhead is laid out at Figure 4 compares the dimensional variations results of a test grinding of 20 workpieces continuously under indirect sizing with the use of an isolation cover and conventional bed oil pan. It was revealed that the isolation cover helps reduce dimensional variation. Dimensional variation, µm 9 Without isolation cover 5 With isolation cover Fig. 4 Dimensional dispersion 78

3 Dresser Generally, dressers on multi-purpose cylindrical grinders use point diamonds. For the dresser used on this grinder, however, service life of the diamond is liable to be affected to a great extent by chipping between the wheel and the diamonds. Therefore, rigidity of the base on which the diamonds are mounted is vital. This grinder, in which the dresser is mounted on the workhead, maintains rigidity five times as high as when it is mounted on the table. In addition, taking into account the fact that diamond wear is severe when wide wheels are used, the mounting of a rotary dresser is also possible. The dresser can also be mounted on the tailstock to reduce dressing cycle time Operability and Safety Interventional Operation Large components have a high unit cost, making defective grinding unforgivable, and trial workpieces nonexistent. Furthermore, if high accuracy is required on general purpose grinders, it is effective for the operator to grind the workpiece manually using a handle while checking the grinding state. This grinder incorporates interventional operation functions to support this, so that high accuracy grinding with a CNC grinder is made as easy as that with a hydraulic multi-purpose grinder. The interventional operation functions include the following: 1) If a portion requiring high accuracy grinding is ground in one pass, it is difficult to ensure dimensional and other accuracies. Therefore, such high accuracy grinding is often performed in two passes, with the first pass leaving some stock removal for the final pass which is to be done after checking the results of the first pass and correcting the grinding conditions and dimensions reflecting such results. In this final grinding, however, because the original stock removal has already been half completed, time is wasted performing air-cut. To counter this problem, this grinder adopts a grinding-resumption-after-in-processstop function, which allows the wheelhead to be rapidly fed down to the position where the previous grinding ended so as to reduce the cycle time. Furthermore, if "Grinding Resumption ON" is selected at grinder setup, it is also possible to set-up the target dimension for the next grinding pass after the first over-size grinding, and repeat this designated process many times until completion instruction is given (Fig. 5). 2) The software positive stop function provides protection against defects in manual grinding operation by stopping the instruction signal from the handle when cutting depth becomes excessive. 3) During automatic traverse grinding, the table direction can be manually reversed at any position within the traversing range. This function facilitates correction of convex profile generated in rough grinding. In other cases where the workpiece has uneven stock removal, this function can be used to grind the portion where stock removal is greater until it becomes even, followed by the standard traverse grinding operation to reduce grinding time (Fig. 6). Over-size dimension Grinding stock removal Finish diameter Dimensional measurement Change of over-size dimension Finish diameter Over-size dimension Fig. 5 Grinding resumption after in-process stop Fig. 6 Manual table reverse function Overall Cover Conventionally, most multi-purpose grinders have used open covers putting priority on workability and visibility. On the other hand, the requirement for improved machinery safety has been grown stronger in recent years. This grinder is therefore designed to meet both workability and safety requirements by developing an overall cover which considers workability in such work areas as the workhead, wheelhead and belt tension adjustment where routine maintenance and inspections are conducted, as well as the table swivel adjustment area where work is required during set-up operation. 79

4 3. Main Specifications The main specifications of this grinder are summarized in Table 1. Table 1 Main specifications u u u u u u uuu u uu u u u u 80

4. Machine Layout Standard layout of this grinder is shown in Fig. 7. SelectG7-100 SelectG7-250 SelectG7-320 SelectG7-400 W (mm) 6 600 9 600 11 000 12 600 D (mm) 2 840 Fig. 7 Machine layout 5.

5 4. Machine Layout Standard layout of this grinder is shown in Fig. 7. SelectG7-100 SelectG7-250 SelectG7-320 SelectG7-400 W (mm) D (mm) Fig. 7 Machine layout 5. Conclusions This grinder has been developed for the purposes of coping with assorted-small-lot production of large-sized components and the reduction of production preparation time as well as improving the safety of the generalpurpose cylindrical grinders. Concerning the machining of large components, JTEKT will continue to work towards making proposals for machining technology that centers to workpieces of various shapes and materials as well as the development of machines with better operability capable of high accuracy machining. References 1) M. Nonoyama, S. Abeta: GE4P-50 CNC General Purpose Cylindrical Grinder, JTEKT Engineering Journal, no (2006) 33. E. FUKUTA * * Development Dept., Machine Tools & Mechatronics Operations Headquarters 81

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