Helical Flutes Research Articles

Precision measurement for section of drill helical flute

A measuring system of drill geometry parameters has been proposed in the previous report. The system is based on laser displacement sensor, slide and rotary tables. Different types of errors may occur while collecting the coordinate data of the drill geometry parameters. This paper describes the calibration of the measuring system for estimating grinding parameters and geometry parameters of the drill point. The calibration procedure, calibration method and error correction method are proposed in this paper. To develop a practical apparatus of the measurement system all setup errors have been considered and measured and as the database they are preserved. Thus, the error can be corrected automatically according to the measuring position. The measured data agrees well with the designed values. It was proved theoretically that the accuracy achieved by this method is enough for the measurement of the drill.

Manufacturing models for design and NC grinding of truncated-cone ball-end cutters

This paper presents a set of mathematical models for the design and manufacture of the helical flute and cutting-edge curve of a pair of truncated-cone ball-end cutters. The section profile and relative feeding velocities of the grinding wheel in NC machining of the cutter are deduced. In addition, the deviation of the cutting-edge curve, residual material and the land lack caused by the modified radial feeding velocity are taken into consideration. In order to finish the residual material and rebuild the land of the cutter, the technique for compensation has been developed in this research. The accuracy of the theoretical models is verified by means of an experimental machining test using a WALTER CNC grinding machine. The experimental results are in good agreement with those predicted theoretically, thereby confirming the accuracy and reliability of the proposed models. This study serves as a valuable reference for researchers investigating the NC machining of cutters with special forms.

Precision measurement for normal section of drill helical flute

The normal section shape (flute curve) of the drill flute has a big influence on the shape of the main blade, the exhaust of the chip, and the supply of the coolant etc. To measure the flute curve of drill is essential to its design and the evaluation of cutting performance of drill. In this paper the measurement system of drill geometry by laser displacement sensor is developed and the measuring method of flute curve is described. As the measuring method, the curve of flute was divided into several parts and was measured one by one. Then the measured data are analyzed with digital filtering, smoothing etc., thus the flute curve data is gained. The measured data agree well with the known values. The proposed measuring method may be applied not only to the measurement of flute curve of the drill but also to the measurement of the other helical flute curves.

Geometric modeling and grinder design for toroid-cone shaped cutters

This paper presents a set of mathematical models for the design and manufacture of the helical flute and cutting-edge curve of a toroid-cone shaped revolving cutter. The study not only considers the section profile and relative feeding velocities of the grinding wheel used in the NC machining of the cutter, but also addresses the deviation of the cutting-edge curve, the residual material which exists between adjacent flutes, and the lack of cutter land. Through a process of numerical simulation, a compensation technique is developed which reduces the residual material and rebuilds the missing land. The accuracy of the theoretical models is verified by means of an experimental machining test using a WALTER CNC grinding machine. The experimental results are in good agreement with those predicted theoretically, thereby confirming the accuracy and reliability of the proposed models. This study serves as a valuable reference for researchers investigating the NC machining of cutters with special forms.

Mechanics and Dynamics of Serrated Cylindrical and Tapered End Mills

Serrated end mills are effectively used in suppressing chatter vibrations in roughing operations. Mechanics and dynamics of serrated cylindrical and tapered helical end mills are presented in the article. The serrated flute design knots are fitted to a cubic spline, which is then projected on helical flutes. Cutting edge geometry at any point along the serrated flute is represented by its immersion angle and tangent vectors in radial, tangential and helical directions. The chip thickness removed by each cutting edge point is determined by using exact kinematics of dynamic milling. The cutting forces are evaluated by orthogonal to oblique cutting mechanics transformation. The experimentally proven model is able to predict the cutting forces and chatter stability lobes in time domain. It is shown that the proposed model can be used in evaluating the performance of serrated end mills during their stage.

Processing Design in Machining Ball-End Cutter with a Parallel Grinding Machine

Processing Design in Machining Ball-End Cutter with a Parallel Grinding Machine

Cutting Force Prediction in End Milling with Small Depth of Cut in Consideration of Cutting Situation Change

The study deals with an accurate cutting error prediction of end milling in the finishing operation. As it was indicated that the consideration of cutting edge roundness improves the accuracy of cutting force simulation, a new estimation method of cutting force has been proposed for end milling with the straight flute tools, based on the calculation of the actual depth of cut. The influence of cutting edge roundness was not considered in the conventional cutting error prediction. Then, the study proposes an extended estimation method of cutting error for the helical flute end mill. It is necessary to calculate the actual depth of cut with an accurate description method of workpiece surface since the amount of cutting error on workpiece surface usually changes with the height of a cutting flute. As a change in workpiece surface in machining is correctly estimated by the calculation of the actual depth of cut, the estimation of cutting error is attained by referring to the form of machined workpiece surface, which is left behind after the end mill passed. A prototype of simulation system is developed, based on the proposed method. The effectiveness of the proposed estimation method is demonstrated by making cutting experiments with helical flute end mill under the cutting condition of finishing operation. The predicted cutting error shows a good qualitative agreement with the measured one, thus the more accurate prediction of cutting error is realized by the proposed method.

On-Machine Cutting Edge Profile Measurement for Micro Milling Tool (1st Report, Laser Diffraction Gauge Method and its Verifications)

A new optical measuring method of cutting edge profiles with a few nanometerresolutions for micro milling tool is proposed. The edge profile is scaled by the width between the first order maxima in a diffraction pattern, which relates to the spacing of a slit-type aperture formed between a reference knife-edge and a tool cutting-edge. The technique is applicable for on-machine measurement due to simplicity and long working distance of the optical system. In this paper, first, the theoretical analysis reveals the measurement resolution, and then the proposal of laser diffraction gauge method is mentioned. Next, the calibratability and the practicability of our technique are affirmed with fundamental experiments. Furthermore, experimental verifications are carried out for commercial tools such as straight-flute and helical flute of micro endmills. Subsequently, excellent agreement of the profiles, which are measured with our developed experimental systems, with an image from scanning ion microscope verifies that the proposed method is efficient to accurately measure cutting-edge profiles.

Cutting behavior of a TiN-coated carbide drill with curved cutting edges during the high-speed machining of stainless steel

Stainless steel plates were drilled in high-speed machining to investigate the effect of tool life, surface roughness, tool wear and burr formation. Drilling was done using a TiN-coated carbide tool with curved cutting edges. The cutting speed V=75 m/min is optimum for minimum surface roughness and burr height. The surface roughness produced was less than 1 μm. Four distinct kinds of burr were observed, namely, burr without any attachment, burr with a drill cap, flange burr and burr with a sharp remnant. The chipping of the helical flutes and the outer corner wear were the main causes of drill failure.

A Precision Tool Model for Concave Cone-End Milling Cutters

The paper presents a comprehensive manufacturing model that can be used to produce a concave cone-end milling (CCEM) cutter on a two-axis NC machine. A CCEM cutter possesses many distinct features that are superior in many cases to the traditional flat-end milling cutter for producing parts with multiple sculptured surfaces. Based upon the given design parameters and criteria, the equation of the helical flute groove and the curve of the cutting edge at the end of the helical flute are derived and presented. By using an inverse problemsolving technique, the sectional profile of the grinding wheel, the tool compensation for machining, and the feedrate of both NC axes are consequently obtained. The design results are compared with the measured data obtained from the NC produced CCEM cutter. The satisfactory comparative verification indicates that the tool design and manufacturing model presented in this paper is theoretically sound and it can be automated easily. The proposed method is widely applicable for the mass production of various high-efficiency milling cutters.

Manufacturing models for the design and NC grinding of a revolving tool with a circular arc generatrix

This paper presents a systematic method for the design and manufacturing of a revolving tool with a circular arc generatrix. The mathematical models of a helical flute and cutting-edge curve for this special shaped revolving tool are presented. The geometry of the flute grinding wheel can be obtained from the solution of the inverse envelope problem for a given flute profile on the waist part (maximum sectional radius) of this tool. The equations for axial, radial and rotary feeding velocity of the workpiece in the flute NC grinding process are also derived. In addition, the deviation of cutting-edge curve, residual material and the land lack caused by the modified radial feeding velocity, are taken into consideration. In order to finish the residual material and to rebuild the land of the cutter, a technique for compensation has been developed in this research.

Mechanics and dynamics of general milling cutters.: Part I: helical end mills

A variety of helical end mill geometry is used in the industry. Helical cylindrical, helical ball, taper helical ball, bull nosed and special purpose end mills are widely used in aerospace, automotive and die machining industry. While the geometry of each cutter may be different, the mechanics and dynamics of the milling process at each cutting edge point are common. This paper presents a generalized mathematical model of most helical end mills used in the industry. The end mill geometry is modeled by helical flutes wrapped around a parametric envelope. The coordinates of a cutting edge point along the parametric helical flute are mathematically expressed. The chip thickness at each cutting point is evaluated by using the true kinematics of milling including the structural vibrations of both cutter and workpiece. By integrating the process along each cutting edge, which is in contact with the workpiece, the cutting forces, vibrations, dimensional surface finish and chatter stability lobes for an arbitrary end mill can be predicted. The predicted and measured cutting forces, surface roughness and stability lobes for ball, helical tapered ball, and bull nosed end mills are provided to illustrate the viability of the proposed generalized end mill analysis.

Nonlinear dynamics of milling processes

In this article, dynamics and stability of milling operations with cylindrical end mills are investigated. A unified–mechanics–based model, which allows for both regenerative effects and loss–of–contact effects, is presented for study of partial–immersion, high–immersion and slotting operations. Reduced–order models that can be used for certain milling operations such as full–immersion operations and finishing cuts are also presented. On the basis of these models, the loss of stability of periodic motions of the workpiece–tool system is assessed by using Poincare sections and the numerical predictions of stable and unstable motions are found to correlate well with the corresponding experimental observations. Bifurcations experienced by periodic motions of the workpiece–tool system with respect to quasi–static variation of parameters such as axial depth of cut are examined and discussed. For partial–immersion operations, consideration of both time–delay effects and loss–of–contact effects is shown to have a significant influence on the structure of the stability boundaries in the space of spindle speed and axial depth of cut. The sensitivity of system dynamics to multiple–regenerative effects, mode–coupling effects and feed rate is also discussed.

Basic study of ball end milling on hardened steel

This study deals with ball end milling with a (Al,Ti)N-coated tool on hardened steel. The cutting forces in ball end milling with a helical flute were obtained theoretically and experimentally not only for a flat surface, but also for an inclined work surface. They are agreed with each other. The influence of the cutting conditions on tool life is discussed: it changed from 200 to 1100 m, depending on the cutting conditions. For the cutting conditions of a large inclined angle of the work-piece surface and a large feed rate, a long tool life was obtained. The causes of reduced tool life changed, depending on the cutting conditions.

Generalized Modeling of Mechanics and Dynamics of Milling Cutters

This paper presents a generalized mathematical model of most helical end mills and inserted cutters used in industry. The end mill geometry is modeled by wrapping the helical flutes around a parametric envelope of a cutter body. The edge geometry for inserted cutter is defined in the local coordinate system of each insert, and placed and oriented on the cutter body using cutter's global coordinate system. The coordinates of a cutting edge are mathematically expressed for both cases. The chip thickness at each cutting point is evaluated by using the true kinematics of milling including the structural vibrations of both cutter and workpiece. By integrating the process along each cutting edge or tooth, which are in contact with the workpiece, the cutting forces, vibrations, dimensional surface finish, and chatter stability lobes for arbitrary end mills and inserted cutters are predicted. The predicted and measured cutting forces, surface roughness and stability lobes for helical tapered ball, bull nosed end mills and inserted cutters are provided to illustrate the viability of the proposed generalized end mill analysis. The algorithms are integrated to an advanced cutting process simulation program which is used for process planning of milling operations to avoid chatter vibrations, torque and power limit constraints, and dimensional form errors.

Sharpening of Hob Cutting Edges with Helical Flutes.

Sharpening of a hob with helical flutes is a difficult problem in the gear production field because interference between a grinding wheel and hob rake face is apt to occur. In this paper, mechanism of interference in hob sharpening is analyzed and the condition without interference that causes a trouble is shown by means of the figure. Then, the profile of grinding wheel for sharpening the hob with helical flutes is calculated using the element removal method in the same way as form grinding of the helical gear with a profile of straight line. Also, the relation between the depth of hob flute and the tooth height of hob rake face being finished is shown by means of the figure. The sharpening test of the involute worm hob(mn=5, N=3, γ=23.917°)was conducted using the CNC gear form grinding machine. The radial alignment of hob rake face after sharpening was less than 5μm.

Prediction of ball-end milling forces from orthogonal cutting data

The mechanics of cutting with helical ball-end mills are presented. The fundamental cutting parameters, the yield shear stress, average friction coefficient on the rake face and shear angle are measured from a set of orthogonal cutting tests at various cutting speeds and feeds. The cutting forces are separated into edge or ploughing forces and shearing forces. The helical flutes are divided into small differential oblique cutting edge segments. The orthogonal cutting parameters are carried to oblique milling edge geometry using the classical oblique transformation method, where the chip flow angle is assumed to be equal to the local helix angle. The cutting force distribution on the helical ball-end mill flutes is accurately predicted by the proposed method, and the model is validated experimentally and statistically by conducting more than 60 ball-end milling experiments.

Prediction of Ball End Milling Forces

Mechanics of milling with ball ended helical cutters are modeled. The model is based on the analytic representation of ball shaped helical flute geometry, and its rake and clearance surfaces. It is assumed that friction and pressure loads on the rake face are proportional to the uncut chip thickness area. The load on the flank contact face is concentrated on the in cut portion of the cutting edge. The pressure and friction coefficients are identified from a set of slot ball end milling tests at different feeds and axial depth of cuts, and are used to predict the cutting forces for various cutting conditions. The experimentally verified model accurately predicts the cutting forces in three Cartesian directions.

A General Mechanics and Dynamics Model for Helical End Mills

The mechanics and dynamics of helical end milling processes are integrated to a general model. The chip removal geometry is evaluated by considering the true kinematics of the operation and chatter vibrations. The cutting forces are predicted by transforming shear angle, shear stress and friction angle stored in an orthogonal cutting data base to local oblique edge segments along the helical flutes. The general model allows prediction of cutting forces, vibrations, dimensional surface errors and chatter stability lobes for a class of helical end mills. The model is verified experimentally on cylindrical and ball end mills with complex helix geometry.

Estimation of Grinding Wheel Profile for Generating Helical Flute and Cutting Edges of Drill.

The generation of three dimensionally formed cutting edges such as drills and endmills, has been quite a difficult problem for tool makers, because those cutting tools have been manufactured on specially designed tool grinders, and conventionally, cutting edges have been generated with formed grinding wheels, profiles of which were obtained empirically by trial and error. Recently, with the development and widespread use of the multiaxis NC tool grinder, the theoretical analysis of the relationship between the cutting edge and the profile of a grinding wheel used is earnestly required. This paper aims to estimate the profile of a formed grinding wheel and the wheel-work relative movements in the NC programming necessary for realizing the desired flute configurations and cutting edges of drills. It was clarified that the results theoretically obtained here by computer simulation agree quite well with experimental ones.