Hiroyasu Iwabe

Effect of Tool Stiffness upon Tool Wear in High Spindle Speed Milling Using Small Ball End Mill

Longer tool life can be tentatively achieved at a higher feed rate using a small ball end mill in high spindle speed milling (over several tens of thousands of revolutions per minute), although the mechanism by which tool life is improved has not yet been clarified. In the present paper, the mechanism of tool wear is investigated with respect to the deviation in cutting force and the deflection of a ball end mill with two cutting edges. The vector loci of the cutting forces are shown to correlate strongly with wear on both cutting edges of ball end mills having various tool stiffnesses related to the tool length. The results clarified that tool life can be prolonged by reducing tool stiffness, because the cutting forces are balanced, resulting in even tool wear on both cutting edges as tool stiffness is lowered to almost the breakage limit of the end mill. A ball end mill with an optimal tool length showed significant improvement in tool life in the milling of forging die models.

Evaluation Method Of Resistant Torque Acting On Rotating Spindle System Including Rolling Bearing. Evaluation Under High-dm N Condition.

This paper describes that the proposed method is able to evaluate accurately the resistant torque acting on rotating spindle system which includes rolling bearing, under high-dm N condition lower than two million mm rpm. The resistant torque is calculated as the product of the angular acceleration during free-running and the equivalent moment of inertia of spindle. The acceleration is calculated from the accurate measurement of change in series of each rotation-cycle under free-running. The equivalent moment of inertia is the sum of the moment of inertia of spindle rotor, the effect of rolling elements and the effect of retainer for the elements.

Study on Cutting Mechanism of Tapered End Mills. Geometrical Analysis of Cutting Edge Shape and Cutting Process by Chip Areas.

Tapered end mills are useful cutter for machining of inclined surface, for example side surface of mold and die. But there are a number of unclarified points regarding to cutting mechanism of tapered end mills. This paper therefore tries to clarify the cutting mechanism of tapered end mills and aims at presenting basic data on tool design and effective method for using the tools. The main results are as follows. (1) The cutting edge shape and cutting process by chip areas are analyzed geometrically for tapered end mills, and calculating method of the chip areas is shown. (2) Cutting patterns are classified into two types and chip areas for various cutting conditions are calculated. (3) The basic behavior of chip areas by tapered end mills are similar to that by square end mills. But chip areas increase by almost constant ratios in the middle part of cutting process by square end mills in case of type I. (4) Incremental rates of the chip areas in the middle part become large with increase of taper angles and decrease of helix angles.

Fundamental Study on Cutting Mechanism of Different Helix Angles End Mills. Investigation of Cutting Process based on Cutting Tests by 2-Tooth End Mills.

This paper deals with the cutting mechanism based on cutting tests by 2-tooth end mills with different helix angles. The results are as follows. ( 1 ) There was a chip area decrease by a low helix angle edge and increase by a high helix angle edge, in the cutting process with no transition period in the end milling. ( 2 ) Behavior of the cutting force is coincident to that of chip area. However, in the cutting process except the transition period, the change in the cutting force is larger than that in the chip area. ( 3 ) Under the cutting conditions, the machined surface from the bottom to 5 or 7 mm is generated by a 41°helix edge due to smaller normal force, and the other part is generated by a 38°helix edge in the same manner. ( 4 ) Light and heavy chips are obtained by the 2-tooth end mill, but the chip weight is lighter for the former and heavier for the latter than each ideal value. ( 5 ) On the assumption that a high helix angle edge cuts a workpiece overmuch in the feed direction based on the results of cutting tests, calculated values of chip weight and cutting force agree with experimental values, respectively.

Study on Corner Cut by End Mill. (2nd Report). Influence of Cutting Force on Machining Accuracy and Improvement of Accuracy.

This paper deals with influence of cutting force on machining accuracy and improving method of the accuracy in corner cut by end mill. Errors by corner cut are extremely greater than that of steady state cutting. When a cutter radius is equal to a radius of curvature of the corner, maximum machining error becomes 13 to 22 times as large as that of steady state cutting. Describing the position of maximum error by rotating angle φ from start point of corner cut, the position by the angle is φ=10° in down milling and φ=0°in up milling. And also cutting forces in corner cut are measured, and machining accuracy is analysed by a simple error generating model that depends upon cutting force vector and resulting stiffness of machine-tool-workpiece system. Calculated values or shape errors are almost coincident with that of experimental values. To improve machining accuracy, plunge and twice looped path cutting are recommended. But under the experimental conditions, difference of accuracy between steady state cutting and corner cut is smaller by diameter 17 mm in down milling and 14 mm in up milling.

Influence of deflected chuck and collet on working accuracy.

This paper deals with the influence of chuck and collet on deflections in end milling. The results are as follows. (1) The deflection of spindle E0 in end milling is divided into three portions, namely, by chuck E1, by collet E2 and by end mill E3. And the distribution ratios are given by E1/E0, E2/E0 and E3/E0 for various diameters of end mill. (2) The ratio E3/E0 by end mill is from 25 to 45% for 16 mm diameter. So it is obvious that working accuracy with end milling is affected significantly by the deflections E1 of chuck and E2 of collet. (3) The ratio E3/E0 by end mill increases, but the ratios E1/E0 by chuck and E2/E0 by collet become decrease with smaller diameter of end mill. (4) The deflection curve of spindle shows a discontinuous manner by collet, however deflection curves are independent of any slit position.

Improvement of Profile Error by Dwell Function of Controller

This paper deals with the influence of the dwell function of a controller on profile error of contouring. The results are as follows.(1) Using intermittently the dwell function, the dwell time longer than 0. 04 sec is controllable in our controller.(2) For the improvement of accuracy, the dwell function is applicable in down millingwith a positive dimensional error.(3) The means of dimensional error and shape error decrease by using the dwell function.Errors present in the same manner of the transient phenomenon and reach to a steady state above one second under the experimental conditions. Longer than one-second-dwell makes the machining time increase.(4) The effect of the dwell on the accuracy of contouring is verified in machining a circular contour. Using intermittently the dwell function is applicable to improve profile error.