Takayuki Kitajima

Theoretical Study on the Effect of Form Error of Grinding Wheel Surfaces under Free Form Grinding

Free forms can be efficiently generated through the three-dimensional motion of a grinding wheel with round-off. In this method, however, form error of the grinding wheel directly affects machining accuracy. The effects of form deviation of the wheel surface on form error of the generated shape ER have been investigated through computer simulation. The wheel surface is assumed to have waviness with amplitude a and a wave length . It is found that the duplication ratio ER/2a is a function of ) /( 2 Rg a and Rg/Rw, where Rg and Rw are the curvature radii of the grinding wheel and the workpiece surface, respectively. The longer is, or the smaller a is, the larger the duplication ratio becomes. When and a are constant, the grinding wheel with large curvature radius is suitable for precision machining of convex surfaces. Form deviation of the wheel surface must be smaller than the objective machining accuracy when it is within a sub-micrometer. Introduction In order to efficiently generate non-axisymmetric aspherical lenses and their dies, the envelope-grinding method was recommended by K.Shoji [1]. In this method, a workpiece surface is generated along the envelope of the moving wheel periphery. Since machining accuracy is affected by form error of the wheel surface, some methods for precisely round-off truing the wheel surface were proposed; [1-4] however, it is difficult to generate the wheel within a sub-micrometer in form error. Since the relationship between form deviation of the trued wheel surface and that of the ground surface has never been clarified, the necessary form accuracy of the wheel surface corresponding to the objective machining accuracy could not be appropriately decided. If this relationship is clarified the tolerance design for precision form grinding and accuracy prediction for the envelope grinding will be reasonably performed. In this paper, computer simulation has been performed to clarify the effects of the characteristics of form deviation of a grinding wheel and dimensions of the wheel and a workpiece on form accuracy of the generated surface. Preceding the simulation, the effects of radius error, Rg, and radius deviation, Rg( ), of the wheel surface on machining accuracy has also been analyzed and the methods for compensating the effects have been proposed. Effects of Radius Error of Wheel Surface Scope of the Problem. Figure 1 shows the schematic drawing of the envelope grinding method, where the grinding wheel is three-dimensionally moved by a CNC system. The workpiece shape in Z-X plane is affected by Fig.1 Schematic drawing of envelope grinding method Grinding wheel

Grinding Performance of a Grain-Arranged Diamond Wheel against Industrial Pure Aluminum

A grain-arranged diamond wheel is developed and grinding performance of the wheel against industrial pure aluminum, one of the most hard-to-grinding materials, is investigated. The developed wheel efficiently ground pure aluminum without adhesion even when general-purpose grinding fluid, Type A3-1, was used. Moreover, wheel wear was not observed during the experiment, and grinding energy was extremely low. By using the developed wheel, a mirror surface can be easily obtained by one-pass surface grinding with very low table speed.

Performance of the Speed-Stroke and Creep-Feed Grinding under Constant Removal Rate

A surface-grinding machine with a linear motor driven table and a high-speed spindle has been developed. The table speed can be changed from 1mm/min to 100m/min and an achieved acceleration is 19.6m/s 2 . The maximum peripheral speed of the 200mm diameter wheel is 200m/s. This paper examines the grinding performance for chromium molybdenum steel (SCM440) under speed-stroke grinding characterized by a high table speed with a small depth of cut and creep-feed grinding characterized by a low table speed with a large depth of cut. The performance of each grinding method is compared under a constant material removal rate of 100 mm 3 /mm min. It was confirmed that the advantage of the speed-stroke grinding is a lower grinding force and less temperature rise at a grinding zone. On the other hand, the advantage of the creep-feed grinding is a higher grinding ratio and smaller surface roughness. In addition, a higher wheel peripheral speed results in lower grinding force, higher grinding ratio and smaller surface roughness.

Planing of Cobalt-Free Tungsten Carbide Using a Diamond Tool -Cutting Temperature and Tool Wear-

Diamond tools wear easily under cutting tungsten carbide. To clarify the wear mechanism, the authors composed a temperature-measurement system of a cutting point using a dual-colorinfrared pyrometer and performed planing experiments. Infrared rays, emitted from the contact point between a mono-crystal-diamond tool and a cobalt-free tungsten carbide, are transmitted though the diamond tool and an optical fiber and then they are detected by the pyrometer. Before the planing experiments, rubbing experiments were performed using a mono-crystal-diamond stick and a tungsten-carbide disk. The effects of gas environments and rubbing conditions on contact-point temperature, friction coefficient, and diamond wear were experimentally investigated. Planing experiments of the tungsten carbide using mono-crystal-diamond tool, were performed. The effects of planing conditions and gas environments on cutting-point temperature and tool wear were investigated. Through the experiments the following results were obtained. Rubbing and cutting point temperature is the highest in Argon gas followed by Nitrogen gas and is the lowest in Air. Diamond-tool wear is the greatest in Argon gas, less in Nitrogen gas, and the least in Air. The reason for this is that a chemically or physically absorbed layer of oxygen or nitrogen on tungsten carbide acts as a lubricant at the contact point. Cutting-point temperature was in proportion to cutting speed. The temperature under cutting speed at 90m/min and cutting depth at 1.0μm in Air was approximately 170degrees Celsius.

An Adaptive Control of Machine Table Reciprocation Using a Hydrophone - A Method for Improving the System Efficiency and Reliability -

In order to eliminate unnecessary table-over-travel of a surface grinding machine, the authors previously developed an adaptive table-reciprocation-control system using a hydrophone. The system eliminated the over-travel and reduced grinding time by 20-40%. However, during the stage of the grinding-wheel approach to a workpiece the system did not work. In order to improve the efficiency and reliability of the system, a fluid-flow stabilizer and a new coolant-supply nozzle have been developed and their performances were experimentally investigated. By using these devices, the reciprocation-control system showed its capability even during the stage of the grinding-wheel approach and this ability improved the system efficiency and reliability.

Adaptive Table-Motion Control of a Surface Grinding Machine Using an AE Sensor

Improvement in grinding efficiency is very important to economically produce precision parts. This paper proposes a new table-motion control system for reducing non-machining time in the surface-grinding process and describes the results of performance tests of the system. The table-motion is adaptively controlled so that the table stroke is shifted along a workpiece shape. That is, an AE signal is emitted from the contact zone between a grinding wheel and a workpiece and is diminished when the wheel leaves the workpiece. When the signal level becomes less than a preset trigger level, a command is sent to a table controller to reverse the table-motion. By using the proposed system, unnecessary table over-travel is successfully eliminated and total machining time is reduced by 22 to 38 percent.

A Study of the Machining Accuracy of the Round-Off Truing Method: Effects of the Set-Up Angle for the Brake Truer

The round-off truing method for precision form grinding was proposed by the authors. The circular motion of a CNC grinding machine is utilized together with an abrasive stick or a brake truer. In previous studies, experiments and simulations were performed to clarify the mechanism and appropriateness of this method. Accurate truing for the precision form grinding, however, could not be realized through these studies. In this study, the mechanism of the round-off truing when there is a set-up angle between the truer spindle and the grinding-wheel spindle z has been clarified through vector analysis. The appropriateness of vector analysis and effect of z on the truing accuracy has been confirmed experimentally. The form error of the trued wheel surface shows the minimum value when z is in the range 10-20 degrees. Introduction A part of information technology, IT, is supported by optical devices such as aspherical lenses and mirrors, which require the super-precession machining technology in production. In order to generate non-axisymmetric aspherical lenses and their dies, precision form grinding using a grinding wheel with round-off (toroidal shape) is necessary [1-2]. In this case, the form error of the grinding wheel directly affects the form accuracy of the generated shape. In the previous studies [3-5], the authors proposed a very simple round-off-truing method utilizing the circular motion of a CNC grinding machine. In this method, a brake truer (or an abrasive stick) is set on the machine table and a grinding wheel is moved around the truing wheel along the circular path as shown in Figure 1. Effects of the circular-motion radius, G, thickness of the truing wheel and the grinding wheel, Ts, Tg, on the generated curvature radius of the grinding-wheel surface, Rg2, and error factors introduced in the truing process were examined by computer simulations and experiments [3-7]. Through these studies following results were obtained. Regardless of size and wear ratio of a truing wheel, , Rg2 settles into the value that can be calculated by ). 1 ( 1 1 + = Tg Ts G Rg (1) A brake truer has the capability of efficient round-off truing in comparison with an abrasive stick. Truing wheel Ts Grinding wheel Tg Rs2 Brake truer Rg2 G Fig.1 Setup for the round-off truing Key Engineering Materials Online: 2003-04-15 ISSN: 1662-9795, Vols. 238-239, pp 321-326 doi:10.4028/www.scientific.net/KEM.238-239.321