Hu Gong

Review: 5-axis flank milling: A state-of-the-art review

Flank milling is of importance to machining aircraft structural parts, turbines, blades and several other mechanical parts. It decreases manufacturing time, enhances quality and reduces cost. Since flank milling developable ruled surfaces do not contain geometrical errors, research on flank milling focuses on the generation of optimal tool trajectory for non-developable ruled surfaces, even generic free-form surfaces. This includes: envelope surfaces, geometrical errors (overcut, undercut), energy optimization in tool movement, surface deviations, tool geometry adaptation, tool wear and temperature, and surface roughness. In this article we present a survey on flank milling as well as suggesting guidelines for future considerations in solving flank milling tool trajectory optimization.

Second order approximation of tool envelope surface for 5-axis machining with single point contact

For 5-axis machining with single point contact, this paper proposes a method to calculate second order approximation of the tool envelope surface by using only one tool position. As we known, the true machining errors are deviations between designed surface and tool envelope surface. But it is impossible to determine the whole shape of the tool envelope surface before all tool positions are obtained. Hence, it is difficult to position the tool individually and consider true errors at the same time. Basic Curvature Equations of Locally Tool Positioning (BCELTP) are presented to solve this problem in some degree. By using them under some special conditions, given one tool position, the local shape (second order approximation) of the tool envelope surface can be calculated precisely at the corresponding cutter contact point. These equations make it convenient to adjust the tool position individually until true errors are reduced in some degree. So, they are useful for optimizing tool positions locally. Finally, some examples are given to verify the correctness and practicability of theory.

Optimization of tool positions locally based on the BCELTP for 5-axis machining of free-form surfaces

The Basic Curvature Equations of Locally Tool Positioning (BCELTP) are an accurate description of the relationships between the second order approximations of the cutter surface, the tool envelope surface and the designed surface, which was proposed in our previous paper [Gong Hu, Cao Li-Xin, Liu Jian. Second order approximation of tool envelope surface for 5-axis machining with single point contact. Computer-Aided Design 2008;40:604-15]. Based on them, for a given tool path with single cutter contact point, a new local optimization method of tool positions is presented to maximize the machining strip width by minimizing the relative normal curvature between the tool envelope surface and the designed surface. Since the BCELTP are accurate analytical expressions, the proposed optimization method of tool positions is accurate and effective in computation. Furthermore, another new optimization method of tool positions based on a dual-parameter envelope is subsequently proposed. The most interesting point is that it will result in the same results as the method based on the BCELTP. It also proves the correctness of the method based on the BCELTP from a different angle. Finally, several examples are given to prove its effectiveness and accuracy.

5-axis flank milling free-form surfaces considering constraints

A new tool path generation method of flank milling considering constraints is proposed for ball-end cutters in this paper. It will not only reduce the machining error range but also meet the following two constraints: (a) The ball end of the milling tool is tangential to the constraint surface; (b) There is no overcut and the minimum error is zero, which is called nonnegative-error constraint. The two constraints are very useful in some situations of engineering applications, such as flank milling impeller blades. Based on the proposed method, two types of cutter will be used to generate tool paths for the same designed surface and constraint surface. The effectiveness and accuracy of the proposed method will be finally proved with some examples.

Spiral tool path generation for diamond turning optical freeform surfaces of quasi-revolution

Space Archimedean spiral is defined firstly in this paper. Thereafter, a new spiral tool path generation based on space Archimedean spiral is proposed for diamond turning optical freeform surfaces of quasi-revolution, which is defined as a surface close to some surface of revolution. By projecting the space Archimedean spiral onto the freeform surface along the normal direction of the base surface instead of a fixed direction like traditional method, a quasi-uniform spiral tool path on the freeform surface can be obtained. This method can be used on diamond turning optical freeform surfaces. Finally, two examples are presented to prove its effectiveness and adaptability. Space Archimedean spiral is defined.A new spiral tool path generation based on space Archimedean spiral is proposed to machining freeform surfaces with big slope.The proposed method can be used for 3-axis and 4-axis ultraprecision diamond turning optical freeform surfaces of quasi-revolution.

Effects of surface modifications on steel's machinability in single-point diamond turning

Surface modifications are employed in single-point diamond turning of steels to reduce the chemical-reactive wear of diamond tool to an acceptable degree. Different thermochemical modifications, i.e., plasma nitriding, boronising, siliconising, boronitriding and compound boronising-aluminising, are designed to bond the atoms of transition metal elements in steels with the chosen elements. The effects of various surface modifications on steels machinability are investigated mainly in terms of tool wear and workpiece surface quality. It is found that nitrogen (N) is beneficial to improve the tool life; N, silicon (Si) and aluminium (Al) may help to obtain a mirrorlike surface; B plays the negative role in steels machinability in single-point diamond turning. Developing suitable-for-diamond-cutting materials on which nanometric surface finish can be achieved is proposed according to the role of the permeated elements.

Ultrasonically Assisted Single Point Diamond Turning of Optical Mold of Tungsten Carbide

To realize high efficiency, low/no damage and high precision machining of tungsten carbide used for lens mold, a high frequency ultrasonic vibration cutting system was developed at first. Then, tungsten carbide was precisely machined with a polycrystalline diamond (PCD) tool assisted by the self-developed high frequency ultrasonic vibration cutting system. Tool wear mechanism was investigated in ductile regime machining of tungsten carbide. The cutter back-off phenomenon in the process was analyzed. The subsequent experimental results of ultra-precision machining with a single crystal diamond tool showed that: under the condition of high frequency ultrasonic vibration cutting, nano-scale surface roughness can be obtained by the diamond tool with smaller tip radius and no defects like those of ground surface were found on the machined surface. Tool wear mechanisms of the single crystal diamond tool are mainly abrasive wear and micro-chipping. To solve the problem, a method of inclined ultrasonic vibration cutting with negative rake angle was put forward according to force analysis, which can further reduce tool wear and roughness of the machined surface. The investigation was important to high efficiency and quality ultra-precision machining of tungsten carbide.

Generation of spherical non-uniform rational basis spline curves and its application in five-axis machining

A method of generating spherical non-uniform rational basis spline curves based on De Boor’s algorithm is presented in this article. The spherical curve preserves many good properties from non-uniform rational basis spline curves in Euclidean space, such as local modification property, convex hull property, rotation invariant property, knot insertion property, and so on. Construction of closed spherical non-uniform rational basis spline curve will be discussed too. Furthermore, a progressive iterative approximation scheme is proposed to approximate the given points on unit sphere using spherical non-uniform rational basis spline curves. The convergence and curve continuity will be discussed. Since the analytical expression of the spherical non-uniform rational basis spline curve is messy, numerical differentiation is used to test its continuity at interior knots. Finally, several examples are presented to verify the effectiveness of the proposed method. The proposed method is applied on tool path generation of five-axis machining to avoid interference by adjusting fewer directions and obtain smooth tool path simultaneously.