Rei Hino

Influence of Material Composition on Ductile Machining of Tungsten Carbide in Elliptical Vibration Cutting

Tungsten carbide is a crucial material for glass molding in optical industry. The present study investigated a feasibility of ductile machining of sintered tungsten carbide for glass molding by applying ultrasonic elliptical vibration cutting technology with single crystal diamond tool. Grain size and binder material of sintered tungsten carbide have an influence on hardness and/or toughness of the material. Binder material also has a chemical affinity to diamond. In order to examine the influence of material composition on ductile machining of tungsten carbide, a series of grooving and planing experiments were conducted to several different tungsten carbide workpieces with the different binder phase and the different grain size. The experimental results indicated that micro grooving in a ductile mode can be attained successfully by applying ultrasonic elliptical vibration cutting, while finished surface deteriorates with brittle fractures in ordinary cutting. It was also clarified that grain size and binder material have significant influence on the deteriorations in the surface quality, the tool shape and the cutting forces.

A new method to machine sculptured surfaces by applying ultrasonic elliptical vibration cutting

A new machining method is proposed to obtain sculptured mirror surfaces by applying elliptical vibration cutting. The tool is vibrated elliptically, unlike conventional rotating end mills, and is fed along the sculptured surface while the rotational position of the tool is controlled in accordance with the sculptured surface orientation in the proposed method. In order to realize the sculptured surface machining of hardened die steel with single crystal diamond tool, special components are required, i.e. a vibration system that can generate an arbitrary ultrasonic elliptical vibration in the 3D space, a 4-axis controlled precision machine tool and a special CAM system. The elliptical vibration system, which consists of a 3 DOF ultrasonic vibration tool and a vibration controller, is developed. The vibration tool can generate the arbitrary elliptical vibration at 34.4 kHz by combining two bending vibrations and a longitudinal vibration. The vibration controller is fabricated to keep the elliptical vibration to have a desired lotus in the 3D space. The 4-axis controlled precision machine tool, which consists of an air spindle, precision linear guides, precision ball screws and so on, is developed. Commercial CAM software is utilized and a special post processor is developed to generate tool paths for the 4-axis control machining of sculptured surfaces. The developed ultrasonic elliptical vibration machining system is applied to precision diamond cutting of hardened die steel, and it is confirmed that mirror surface machining with surface roughness of less than 0.28 /spl mu/m Rz can be realized for spherical surface machining of hardened die steel.

Chatter suppression in milling with anisotropic tools

Chatter vibration in milling often results in poor surface finish and rapid tool wear, consequently limiting productivity. Thus, chatter suppression is one of the most important themes in industry. Self-excited chatter vibration in milling is generally caused by two kinds of mechanisms, i.e., regeneration and mode-coupling, and both mechanisms should be handled simultaneously to suppress the chatter vibration. Since the mode-coupling can be restricted by separating the natural frequencies of the vibration modes, it has been considered that use of an anisotropic rotating tool is effective on suppressing the chatter vibration in milling. However, the practical effects of the several parameters have not been revealed because it was difficult to predict the chatter stability accurately. On the other hand, the accurate analytical model of the milling process with the anisotropic rotating tool have been developed and verified experimentally by the authors. In order to reveal the practical chatter suppression effect of the anisotropic rotation tool, several cutting conditions, i.e., the immersion angle, the spindle speed and the number of flutes, on the chatter stability are investigated with the developed analytical model in the present study. By comparing the analytical results, it is confirmed that the mode-coupling is restricted and the stability limit in the axial depth of cut increases especially within the low spindle speed range by using the anisotropic rotating tool. The chatter suppression effect also depends on the radial depth of cut considerably. The relationships between the tool conditions, such as the difference of the natural frequencies and flutes angular position, and the chatter suppression effect are also investigated, and it is revealed that both affect the chatter stability significantly.

Study on Re-entrant Flowshop Scheduling Problem(1st report)

A new theoretical formulation for re-entrant flow shop scheduling problem is derived to plan an optimum production schedule by mixed integer programming. Flow time, which is an index of the evaluation of the planned schedule, is minimized to decrease amount of work-in-process. Cycle time, which is another important index, is determined by the total load time on a bottleneck machine to manufacture the products at the highest productivity. Both objective function and constraint conditions are described in linear expressions and a general optimization tool is adopted to solve the formulated scheduling problems. Another objective function is also introduced in order to shorten the time for the optimization. Computational scheduling results obtained by the optimization are evaluated and discussed in the present paper.

Experimental Verification of CMP Process Analysis

The present study performs an experimental verification of an analytical model of the Chemical Mechanical Polishing (CMP) process, focusing on friction force and the distribution of the material removal rate. A coupled Fluid-Structure analytical model, which can predict the friction force and the distribution of the material removal rate, is developed. Oxide CMP experiments are conducted using a fabricated CMP system, and measured friction force and distribution of the material removal rate are compared with the analytical results. As a result, it is confirmed that the wafers rotational speed affects the friction force and the distribution of the material removal rate. Additionally, the results determined by the developed analytical model agree with the measurements. The magnitude of the friction force under a condition in which the wafer does not rotate becomes smaller than when the wafer rotates at the same speed as the polishing pad. The direction of the friction force inclines against the rotational center of the polishing pad. The material removal rate when the wafer does not rotate is high around the edge of the wafer as compared with that at other areas. In particular, it becomes high around the leading edge and the area where the rotational radius of the polishing pad is large. These specific characteristics of the friction force and the distribution of the material removal rate are explained using the analytical results.

Optimization by Pre-Assignment of Processes for Re-Entrant Flowshop Scheduling Problem

A new optimization procedure for a re-entrant flowshop scheduling problem is proposed to plan a medium sized production schedule by mixed integer programming. Flow time is an index used to evaluate production work-in-process. The flow time is calculated from the total required cycle terms after a feasible schedule is planned. In the present paper, the reverse procedure is performed: the total cycle term is assumed before the scheduling, and the feasible schedule is planned under the assumed terms. The assumption of the total cycle term restricts the pre-assignment of every process into a corresponding cycle term. Therefore some pre-assignments never yield a feasible schedule and are eliminated from the evaluation. Methods for the assumption of the total cycle terms and for the examination of the pre-assignment of the processes are described here. The amount of times required to plan the optimal schedule is evaluated for different sizes of problems in order to validate the proposed procedures.Copyright

Cyclic scheduling and re-scheduling in response to change of product mix

This paper deals with a cyclic job shop scheduling problem requiring agile planning of an appropriate production schedule corresponding to a change of product mix. The product mix, which is defined as the total composite of products offered by a company, is generally changed to meet demand in a market. We propose the formulation of a cyclic scheduling problem in the form of mixed integer programming to plan optimum schedules under different product mix conditions. We also introduce a formulation of the re-scheduling problem that allows shifting to a new production schedule as soon as possible. Numerical simulations are carried out to verify the proposed formulations.

A New Method to Control Work-in-Process Inventory for High Manufacturing Productivity

A new method for controlling the WIP inventory is proposed in order to restrict the excessive production of un- finished products, while the manufacturing productivity is kept at a certain high value. Excessive WIPs decrease business profits and prevent the realization of agile manufacturing along with changes in markets, while insufficient number of WIPs reduce manufacturing productivity and flexibility to cope with malfunctions of production resources. Theoretical formulations of a scheduling problem without buffer is derived, and heuristic procedure is adopted to plan a feasible schedule. The proposed control methods are verified by computational simulations regarding job-shop type production system.

Walking Drive Enabled Ultra-precision Positioners

A driving method named “walking drive” is introduced in this chapter. The method is suitable to feed an ultra-precision table continuously over a long stroke by utilising piezoelectric actuators. The table is driven smoothly in a similar way to walking motions of animals. Ultraprecision positioners and their control algorithms have been developed, and it is confirmed that ultra-precision positioning can be realised by combining a laser-feedback system. The positioners driven by the walking drive have advantages such as high positioning resolution, smooth continuous motion, a long stroke, high stiffness, 3-axis motion, direct drive without conventional guides, high load capacity after positioning, and no need for lubricant.