Effect of Cutting Parameters on Chips and Burrs Formation With Traditional Micromilling and Ultrasonic Vibration Assisted Micromilling

In the traditional micromilling(TMM) of Inconel718 alloy, due to the influence of material plasticity and size effect, relatively large burr will be produced. In order to solve the burr problem in micromilling, ultrasonic vibration in feed direction is applied to the workpiece to complete vibration cutting. Combined with trajectory simulation and cutting experiment, the burr formation mechanism of TMM and ultrasonic vibration assisted micromilling(UVAMM) was studied. The results show that when the ratio of amplitude(A) to feed per tooth(ƒz) is greater than 0.5, continuous cutting changes to intermittent cutting. Compared with TMM, UVAMM improves chip breaking ability, facilitates the propagation of burr crack and effectively inhibits the formation of burr. However, due to the influence of cutting edge radius, A/ƒz should be set larger. When the chip breaking condition is reached, the burr shape is usually tearing or flocculent. Under the conditions of low speed(n), large ƒz and large A, the burr suppression is more obvious.

Influence of the frequency of pulsating high-pressure cutting fluid jets on the resulting chip length and surface finish

High-pressure cutting fluid supply is a proven technology for chip breaking when turning difficult-to-cut materials, such as Inconel 718. However, the technology is usually not suitable for the finish turning of safety-critical parts in aero engines. The acting force of the cutting fluid jet on the back of the chip causes chip breaking. The broken chips are then accelerated by the cutting fluid jet towards the workpiece surfaces where they cause damage on impact. One approach to minimize surface damage is a specific increase in the chip length. The center of gravity of the chips with an adjusted length is shifted out of the focus where the cutting fluid jet hits the chips. Hence, the already finished surface is subjected to fewer impacts of the chips. In this study, the adjustment of the chip length by pulsating high-pressure cutting fluid supply to prevent surface damage was investigated. A valve unit was used to generate two alternating cutting fluid supply pressure levels in certain time intervals. During the low-pressure stage, the force of the cutting fluid jet does not lead to chip breakage and the chip length increases until the valves switch and the high-pressure stage is released. The focus of this work was the analysis of the relationship between the duration of the low-pressure and high-pressure time intervals and the chip length. Additionally, the influence of the depth of cut, the feed, and the cutting speed on the chip length during pulsating high-pressure cutting fluid supply was investigated. Finally, a case study was carried out to evaluate the effectiveness of the pulsating high-pressure cutting fluid supply technology. Therefore, the shoulder surface of a demonstrator part was finished by face turning. Following, the cylindrical surface was finished with a continuous and pulsating high-pressure cutting fluid supply with varied supply parameters. Microscopic analyses of the surface prove that the pulsating high-pressure cutting fluid supply prevents the surface from being damaged by the impacts of chips.

Modelling and controlling the process of cutting with complex-geometry tools to improve efficiency of mining machines and plants

Constant quality improvement through automation of production processes is an important prerequisite for increased viability of mining machines and plants. Factors that limit the automation of the cutting machining operations include the problem of controlling the chip formation and chip crushing. Solution of this problem necessitates theoretical description of the material cutting conditions for tools with curvilinear surfaces. The paper describes basic principles of modeling the cutting process using complex-geometry tools with curvilinear rake. The theory is based on the concept of chip formation as a process of inhomogeneous strain in the plastic zone where the chip originates. Based on the analysis of the stress-strain state in the cutting zone, criterial relationships were derived that correlate the geometric parameters of the chip shape and machining conditions of the curvilinear-rake tool. Prerequisites for chip breaking are stability of the chip shape during cutting, stable chip-to-obstacle contact, high chip stiffness and low flexibility. The machining conditions leading to chip fragmentation could be found by solving the strength problem. Through establishing the cause-and-effect relationships of the processes of chip formation, curling and breaking, new approaches to achieving favorable chip shape may be found by exerting deliberate impact on the plastic zone of the chip formation through optimizing the conditions for the chip flow off the tool. The established relationships between the output parameters of the cutting process and process conditions of cutting with a complex-geometry tool offer the way to control the chip flow parameters in various machining operations. The research is aimed at creating scientifically informed design codes and optimization of cutting parameters for tools with curvilinear chip-curling and chip-breaking rake surfaces.

Chip Breaking During Automated Processing by Cutting Hard-to-Work Steels by Integrated Use of Chip Breaking Tools and High-Temperature Embrittlement

Purpose of research is to increase productivity when cutting hard-to-work steels by integrated use of chip breaking tool geometry and cutting modes, which reduce the viscous properties of the chips and the processed material. The article discusses the problems of mechanical processing of parts of oil production equipment at enterprises in Western Siberia. It is presented the main condition for ensuring chip crushing and revealed the problem of low efficiency of existing methods in modern industry, to one degree or another guiding, curling and chip-cutting method.Methods. Simulation modeling, calculation of chip direction and crushing were performed; effective methods for solving the problem of chip crushing during the machining of parts made of materials with corrosion-resistant, heat-resistant properties were identified; laboratory, persistent tests of the complex method were carried out.Results of studying the mechanism of chip formation during processing by cutting heat-resistant and corrosionresistant alloys are given here. To solve the problem, we have formulated two tasks that were solved using information taken from the theory of material resistance, tensile diagrams when testing samples of corrosionresistant, heat-resistant materials with high operational properties. A chip breaking exchangeable insert with a variable rake angle is designed and presented. The results and analysis of laboratory test data, in which a plate with chip breaking geometry of the front surface is used, are presented, the operating conditions of effective chip breaking are shown. The conclusions on the solution of the first problem are formulated, it is shown that the determining factor in chip breaking is the physical and mechanical characteristics of the processed material, which vary with different cutting conditions.Conclusion. The work shows that chip removal from the cutting zone prevents it from entering the cutting edge area, reducing impact loads on it and improving the quality of machining. It is possible to form stress concentrators in the chips, leading to chip self-destruction even when processing viscous heat-resistant alloys. The hypothesis is used that the temperature conditions for the maximum workability of heat-resistant and corrosion-resistant steels and alloys correspond to the conditions of high-temperature embrittlement, with the help of which it is possible to create conditions for effective chip crushing and conditions for maximum workability when cutting heat-resistant steels and alloys.