Dynamic modeling and experimental investigation of hole making accuracy in the helical milling process

Helical milling is one of the novel hole-making methods to create a hole with high accuracy and quality. In this study, the helical milling process is dynamically modeled using a set of second-order differential equations. In this modeling, the tool is considered a cantilever beam with a degree of freedom in all three directions of x, y, and z. Experimental tests were conducted to investigate the validity of the obtained theoretical relations and the effects of different parameters such as material, diameter, and rotational speed of the cutting tool on the precision of the created hole. The error of the theoretical relations in predicting the hole diameter is 2.7%, indicating the high precision of the accomplished modeling. Theoretical relations show that the error of the chip removal path decreases by increasing each of the parameters, namely, tool stiffness, the rotational speed of the tool, tool diameter, and tangential feed per tooth. In contrast, the error of the chip removal path increases by increasing each of the parameters, namely, the speed of the tool in the helical path and axial feed per tooth. It has been shown that improving the cutting tool material in terms of strength or increasing the rotational speed of the tool and the cutting tool diameter causes a reduction in the diametrical error. It has been shown that the diametrical error rate is 0.9% with the change of the cutting tool from HSS-E to carbide, and it has reduced to 0.6% by increasing the rotational speed of the tool from 900 r/min to 2100 r/min.

Machining of titanium alloys for medical application - a review

Titanium alloys for their characteristics have acquired a prominent position in numerous industrial applications. Due to its properties, such as high resistance to corrosion, reduced density, high specific strength, and low Young’s modulus, titanium alloys became indispensable as a biomaterial with high use in medical devices, with special emphasis in the area of orthopedics. Problems associated with its manufacturing by conventional machining processes, such as milling, turning, and drilling are well known and studied. Its low thermal conductivity, high chemical reactivity, high hardness at high temperatures make it classified as difficult to machine material. Despite the already extensive knowledge about machining titanium alloys problems, and the constant technological development to overcome them, it is not yet possible to machine this material like other metals. This work is based on research and review papers from Scopus and Scholar from 2010 to 2020 and addresses the main issues related to the machining of titanium alloys used in medical devices manufacturing and current solutions adopted to solve them. From the research consulted it was possible to conclude that it is consensual that for milling, turning, and helical milling cutting speed can reach up to 100 m/min and up to 40 m/min in drilling. As for feed rate, up to 0.1 mm/tooth for milling and helical milling and up to 0.3 mm/rev for turning and 0.1 mm/rev for drilling. Also, that Minimum Quantity Lubrication is a valid and efficient solution to mitigate titanium alloys machining problems.

TOOTH LEG EXCESSIVE UNDERCUT ELIMINATION IN HELICAL CYLINDRICAL GEARS WITH PROTUBERANCE OF HOBBING CUTTER BASED ON GRAPHIC RUN-IN

In the paper there are considered procedures for designing a transition curved tooth leg of helical cylindrical gears. A significant parameter of a transition curve is a diameter of boundary points. The boundary point diameter belongs to a bottom point of the involute profile of the teeth side surface of a gear ring. The boundary point position must be lower of the design end point of the involute profile defined by the designer of gearing. A diameter value depends upon a great number of production factors: a profile and wear of a grinding disk, setting up parameters, teeth machining modes of a gear ring, but it is impossible to ensure the specified values of the diameter of boundary points without a correct design solution in the course of the form choice of milling cutter protuberance. The solution on protuberance acceptable parameters of a gear-cutting tool is made by the designer of a cutter during graphic run-in fulfillment. In the paper there are revealed conditions under which arise mistakes in the course of graphic run-in fulfillment within the limits of one teeth pitch of a milling cutter. There are shown recommendations for the fulfillment ensuring the diameter dimension of boundary points of the transition curve specified by the designer of gearing. The data on the design parameter impact of the hob protuberance upon the continuance of cutting edge interaction are shown. There are recommendations given to prevent undercut arising caused by the fulfillment of graphic two-dimensional run-ins of cylindrical helical gears. The work purpose: the elimination of tooth leg excessive undercut in helical cylindrical gears with the protuberance of a worm milling cutter at the expense of the fulfillment of graphic run-in conditions. The investigation methods: the graphical modeling of a run-in process. The investigation results and novelty: there are defined conditions of arising an excessive undercut in the tooth leg of helical cylindrical gears during the fulfillment of graphic run-ins of a tool rack. The conclusions: for mistake prevention in the calculations of the protuberance geometrical parameters of the helical milling cutter the graphic run-in must be carried out not less than on the 1.5 pitch of the milling cutter.

Study on Hole Making Process of Thick-section Carbon Fiber Reinforced Plastics

In this paper, the mechanism of helical milling was analyzed at first. Then, the orthogonal experiments on the 24mm thick carbon fiber reinforced composite material (CFRP) that affect the quality of hole making, such as spindle speed, feed per tooth, and number of tool’s blades were conducted. The influence of process parameters on the quality of hole making was analyzed. Finally, the range analysis method was used to obtain the best hole-making parameters: spindle speed is 4500rpm, feed per tooth is 0.02mm/z, the number of tool’s blades is 2. Based on the obtained optimal parameters, the step-by-step hole making of thick-section CFRP with variable parameters was studied, and two sets of parameters were designed. Through the measurement of the hole morphology, roughness, axial force and aperture deviation after the experiment, it is concluded that hole making process with variable parameters can meet the technical requirements of thick-section CFRP.