Pocket Machining Research Articles

Geometric modeling of offset curves in contour-parallel pocket machining of engineering products

In the present paper analytical solutions to suggested geometric models of equidistant curve formation for flat contours represented by second-order curves and areas bounded by them are considered. Geometric models are spatial and based on cyclographic representation. They differ from the known algebraic models and their solutions to the formation task under consideration in that they present capability to acquire a more complete and vivid spatial representation of interconnection and interrelation of all the geometric objects of the model on the stage of computer spatial visualization. Examples confirming the validity of the suggested geometric models of the considered formation task are provided. The models can be applied in automated cutting tool trajectory design for pocket machining on NC units.

Geometric model of generation of family of contour-parallel trajectories (equidistant family) of a machine tool

In the present paper the analytic solution to the geometric model of formation of equidistant curves (contour-parallel curves) is considered for the case of flat boundary contour and an island within it. The geometric model is spatial and based cyclographic representation. It differs from the known models of the considered formation task and their respective solutions in that on the stages of computer visualization it allows us to achieve a more complete and vivid spatial representation of interconnection and interrelation of all the geometric objects of the model. An example proving the validity of the proposed geometric model of the considered formation problem is provided. The model can be applied in computer-aided machine tool trajectory design in pocket machining on NC units

Pocket milling strategies using combined-mode and feed-direction-dependent stability criteria

Pocket milling remains a key operation in the machining of aerospace structural components. This paper motivates a new combined-mode and feed-direction-dependent stability criteria to minimize pocket machining times, thereby improving productivity. Combined-mode milling models that include the influence of pre-existing slots in the workpiece to determine the optimal combination of engagements for up/down milling conditions are discussed in conjunction with feed-direction dependent stability models that exploit the role of dynamics projected in different feed directions to determine maximum machining stability limits. Model predictions supported by limited experimental validation demonstrate potential productivity gains of up to 60% using this new approach.

Spiral tool paths for high-speed machining of 2D pockets with or without islands

Abstract We describe new methods for the construction of spiral tool paths for high-speed machining. In the simplest case, our method takes a polygon as input and a number δ>0 and returns a spiral starting at a central point in the polygon, going around towards the boundary while morphing to the shape of the polygon. The spiral consists of linear segments and circular arcs, it is G1 continuous, it has no self-intersections, and the distance from each point on the spiral to each of the neighboring revolutions is at most δ. Our method has the advantage over previously described methods that it is easily adjustable to the case where there is an island in the polygon to be avoided by the spiral. In that case, the spiral starts at the island and morphs the island to the outer boundary of the polygon. It is shown how to apply that method to make significantly shorter spirals in some polygons with no islands than what is obtained by conventional spiral tool paths. Finally, we show how to make a spiral in a polygon with multiple islands by connecting the islands into one island. Highlights It is described how to construct a spiral to be used for pocket machining. The spiral respects a user-defined maximum stepover distance between neighbouring revolutions. The algorithm can create a spiral that morphs an island to the boundary of the pocket. The obtained spirals are in some cases much shorter than previously described spiral toolpaths. The algorithm is fast and a popular industrial strength implementation has been created.

Removal of critical regions by radius-varying trochoidal milling with constant cutting forces

This work presents a novel milling strategy for complex pocket machining by integrating radius-varying trochoidal (RVTR) toolpath with contour parallel (CP) toolpath. Based on a quantitative analysis on the fluctuation of material removal rates (MRR), the proposed strategy is able to precisely identify critical regions from complex pocket geometries, and then by integrating flexible trochoidal radius with adaptive trochoidal step, the proposed approach is able to integrate the RVTR toolpath into CP toolpath under a consistent transition of material removal rate. Moreover, by applying RVTR toolpath, the cutting force can be maintained constantly when machining critical regions. Comparing with the trochoidal milling function available with current mainstream CAM software, experimental investigation has shown that the proposed RVTR-CP toolpath integration strategy offers a better machining condition with minimized fluctuation of cutting forces. Moreover, the total length of toolpath is decreased considerably and hence the machining efficiency is greatly improved.

SELECTION OF THE FASTER POCKETING STRATEGIES FOR REDUCTION OF MACHINING TIME IN MANUFACTURING OF CAR WHEELS-RIMS

Pocketing is one of the milling operations most used in the aeronautical and automotive sector. They are employed in the roughing during the manufacture of complex geometries, for dies cavities and moulds, as well as for the machining of pockets of simple geometry. In literature, there are many works focused on the generation of new strategies that allow machining complex geometries by reducing the cutting forces generated or obtaining a best surface quality. However, there are hardly any work focused on the study of the milling of pockets with simple, but with great industrial interest geometries. In this case, by its presence in many components of products manufactured in mass causes, the most important parameter to control is the machining time. In the present work, we studied what strategy is the most efficient in the pocketing of an aluminum car wheel. The strategies employed have been: direction-parallel (one-way, zig-zag), parallel to the contour (contour-parallel, cleaning the corners, constant) and the spirals (real spiral, morph spiral). It has been used a simple design of a wheel, formed by four simple geometries: large circular, small circular, triangular and rectangular. The results show that the family of parallel strategies to the contour are the fastest, even in the machining of circular pockets, where apparently the spiral strategies could have some advantage. In three of the geometries studied (large circular, small circular and triangular) the winning strategy has been the contour-parallel. However, the global faster strategy is the constant. Besides, in non-passant pockets (small circular ones, in this case), it is interesting to choose this strategy since it guarantees the removal of excess material in the corners and changes of direction of the tool. Keywords: tool path; pocketing strategy; optimizing; machining time; automobile parts

Investigating the effect of shape, orientation and position of an island on spiral tool path

Pocket machining is widely used in aerospace, shipyard, automobile, die and mould industries. In high speed pocket machining, the preferred tool path is one that has least number of sharp turn. The conventional tool path, e.g. directional parallel or contour parallel, has various drawbacks such as rise in the cutting load, stop and go motion of cutter, shorter tool life. However, the spiral tool path overcomes the above mentioned drawbacks. The presence of island inside a pocket greatly affects the generation of spiral tool path. Therefore, in the present work the effect of shape, orientation and position of an island inside a pocket is studied. The spiral tool path is generated in MASTERCAMTM X6. The resultant tool paths are observed and comparative study of tool paths is carried out.

An optimal approach to manufacturing planning for complex prismatic parts with interacting feature

While interacting feature recognition has received a significant amount of attention, there has been relatively less study of manufacturing planning on interacting feature. At present, most features are machined independently without considering the feature interactions, which more or less induce the reduction of machining efficiency of pockets with interacting features. To address this problem, based on the classification of interacting features, this work proposes an optimal approach to manufacturing planning for aggressive machining of the complex pocket. Firstly, based on the classification of interacting features, the features are grouped and stored in a tree data structure. Secondly, the machining volumes (MVs) are optimized by maximum cutting depth from the root node to the leaf node of the tree model. Finally, the MVs that are composed of complex machining faces are split into several machining cells (MCs), and genetic algorithm (GA) is employed to get optimal MVs. To demonstrate the advantages of the innovative approach, two case studies are rendered, and the results are compared to those obtained by the traditional methods. The proposed approach can be directly implemented into current CAD/CAM software to promote aggressive rough and finish machining of complex pockets in industry.

A new cutting depth model with rapid calibration in abrasive water jet machining of titanium alloy

Titanium alloys are widely used in the aeronautical and engineering fields as they show an excellent trade-off between the mass and mechanical properties, but as hard materials, they are difficult to machine using cutting tools. The abrasive water jet affords a good solution to produce titanium parts, especially slim ones. To do so, there is a need to adopt a modelling approach for the depth milled. However, a general methodology that takes into account all the parameters leads to complex models based on a large number of experiments. The present article proposes a depth of cut model combined with a rapid calibration method. The case addressed is that of open rectangular pockets on a Ti-6AL-4V titanium alloy. The approach introduces the machine configuration notion considering that a given machine, pressure level and abrasive impose the abrasive flow rate needed in order to obtain an optimal material removal rate. For a chosen configuration, calibration of the model is performed from a series of elementary passes and just three pocket machining passes. The method is rapid and effective as the accuracy of the models obtained over a number of configurations was to within the order of 5%.

A Study on the Cutting Forces and Tool Deformation when Flat-ended Pocket Machining

A Study on the Cutting Forces and Tool Deformation when Flat-ended Pocket Machining

Engagement Angle Modeling for Multiple-circle Continuous Machining and Its Application in the Pocket Machining

The progressive cutting based on auxiliary paths is an effective machining method for the material accumulating region inside the mould pocket. But the method is commonly based on the radial depth of cut as the control parameter, further more there is no more appropriate adjustment and control approach. The end-users often fail to set the parameter correctly, which leads to excessive tool load in the process of actual machining. In order to make more reasonable control of the machining load and tool-path, an engagement angle modeling method for multiple-circle continuous machining is presented. The distribution mode of multiple circles, dynamic changing process of engagement angle, extreme and average value of engagement angle are carefully considered. Based on the engagement angle model, numerous application techniques for mould pocket machining are presented, involving the calculation of the milling force in multiple-circle continuous machining, and rough and finish machining path planning and load control for the material accumulating region inside the pocket, and other aspects. Simulation and actual machining experiments show that the engagement angle modeling method for multiple-circle continuous machining is correct and reliable, and the related numerous application techniques for pocket machining are feasible and effective. The proposed research contributes to the analysis and control tool load effectively and tool-path planning reasonably for the material accumulating region inside the mould pocket.

Aggressive Spiral Toolpaths for Pocket Machining Based on Medial Axis Transformation

High-speed machine tools typically provide high spindle speeds and feedrates to achieve an effective material removal rate (MRR). However, it is not possible to realize the full extent of their high-speed capabilities due to the sharp corners of toolpaths which are introduced by conventional machining strategies, such as contour- and direction-parallel toolpaths. To address this limitation, spiral toolpaths that can reduce the magnitude of sudden direction changes have been developed in previous researches. Nevertheless, for some pockets, the average radial cutting width is significantly decreased while the total length of the toolpath is significantly increased as compared to contour- and direction-parallel toolpath. In this situation, spiral toolpath may take more machining time. To overcome these drawbacks, an aggressive spiral toolpath generation method based on the medial axis (MA) transformation is proposed in machining pocket without islands inside, which refers to no additional material inside the counter. The salient feature of this work is that it integrates the advantages of both conventional contour-parallel machining strategy and the existing spiral toolpath machining strategy. The cutting width at each MA point is determined based on the diameter of the locally inscribed circle (LIC) of the MA point and the topological structure of MA. A distance-constrained contour determination algorithm is utilized to calculate the toolpath for each pass. Finally, a circular arc transition strategy is used to transform all the isolated passes into a spiral toolpath. Experiments are conducted to show the effectiveness of the proposed method.

Quantitative Comparison of Pocket Geometry and Pocket Decomposition to Obtain Improved Spiral Tool Path: A Novel Approach

In the 2.5D pocket machining, the pocket geometry (shape of the pocket) significantly affects the efficiency of spiral tool path in terms of tool path length, cutting time, surface roughness, cutting forces, etc. Hence, the pocket geometry is an important factor that needs to be considered. However, quantitative methods to compare different pocket geometries are scarcely available. In this paper, we have introduced a novel approach for quantitative comparison of different pocket geometries using a dimensionless number, “DN.” The concept and formula of DN are developed, and DN is calculated for various pocket geometries. A concept of percentage utilization of tool (PUT) is also introduced and is considered as a measure and an indicator for a good tool path. The guidelines for comparing pocket geometries based on DN and PUT are reported. The results show that DN can be used to predict the quality of tool path prior to tool path generation. Further, an algorithm to decompose pocket geometry into subgeometries is developed that improves the efficiency of spiral tool path for bottleneck pockets (or multiple-connected pocket). This algorithm uses another dimensionless number “HARIN” (HARI is the acronym of “helps in appropriate rive-lines identification” and suffix “N” stands for number) to compare parent pocket geometry with subgeometries. The results indicate that decomposing pocket geometry with the new algorithm improves HARIN and removes the effect of bottlenecks. Furthermore, the algorithm for decomposition is extended for pockets that are bounded by free-form curves.

Cutting time in pocket machining for different tool-path approximation segments

Despite of the importance of cutting time in pocket machining for manufacturing cost prediction and process planning, its estimation is usually neglected and conducted dividing the total tool path length by the programmed feed rate. Nevertheless, driving the tool with a constant feed rate is, in general, not possible. We study the cutting time dependency with the tool-path curvature, type of interpolation (linear G01 or circular G02) and the distance between interpolation points (segment length). The study, conducted in two different milling machines, shows how shorter segments increase the actual cutting time, which is lower for G01 than for G02. According to the experimental results, we define a piecewise equation that estimates the real cutting time respect to the segment length and type (G1 or G2).

Double spiral tool-path generation and linking method for complex pocket machining

ABSTRACTComplex pockets with one or more islands have been widely used in industrial and manufacturing production. In this paper, a new double spiral tool-path generation and linking method are proposed for complex pockets with islands which can be used for high-speed machining (HSM) is used. Taking into account the path interval, step length and other processing parameters, precise milling can be achieved without cutter lifting and retraction motions to guarantee machining accuracy and reduce processing time. The method has been implemented in several simulations and validated successfully through the actual machining of a complicated pocket. The results indicate that this method is superior to other existing machining methods, and it can achieve HSM of complicated shaped pockets based on parametric surface.

A smooth double spiral tool path generation and linking method for high-speed machining of multiply-connected pockets

Complex pockets have been widely used in industry for the production. At present, the basic forms of tool-path which most commercial CAM software systems used are still limited to direction-parallel and contour-parallel offset. If the pocket contains multiple islands, the tool-path will include many cutter lifting and retraction motions. In this paper, we propose a new double spiral tool-path generation and linking method for complex pockets with multiple islands which can be used for high speed machining. We also provide segmentation rules to divide surface for further improving machining accuracy and efficiency. Taking into account the path interval, step length and other processing parameters, precise milling can be achieved without cutter lifting and retraction operations to ensure optimal processing performance and reduce processing time. The proposed algorithm has been implemented and tested bounded by 2D straight lines and circular arcs of various shapes, and validated successfully through the actual machining of a complicated pocket. The results indicate that this method is superior to other existing machining methods, and it can realize high speed machining of complicate-shaped pocket based on parametric surface with multiple islands.

Adaptive trochoidal toolpath for complex pockets machining

This work proposes a novel adaptive trochoidal (TR) toolpath model for complex pocket machining. The proposed model is able to adjust its TR radius, while simultaneously offers an adaptive trochoidal step for generation of each toolpath cycle. With the varying radius, complex regions can be machined by a single strip of TR toolpath. Moreover, the step of each TR cycle can be adjusted with reference to the varied radius so as to maintain a constant radial depth of cut, and hence more stable material removal rate among all TR cycles can be achieved. For the pocket machining cases with complex inner and outer boundaries, experimental study has shown that the proposed TR toolpath can effectively minimise the fluctuation of cutting forces, and achieve better toolpath efficiency.

Optimization of toolpath with circular cycle transition for sharp corners in pocket milling

The toolpath for a sharp corner is important in pocket machining during high-speed machining with numerical control. When milling a sharp corner, a longer tool engagement length generates larger engagement angle and milling force, which reduces the machining precision. To reduce the milling force at a sharp corner and clear up uncut materials, the toolpath at corners must be optimized. In this paper, a new method of generating the toolpath with circular cycle transition at a sharp corner is put forward to provide a new numerically controlled toolpath pattern for pocket milling. On the basis of a common contour-parallel toolpath, minimum radius arcs and circular cycles are added in sequence at a sharp corner. When the cutter comes to the sharp corner, the corner material is removed step by step with a sequence of circular cycles. The validity of the proposed method is confirmed through simulation and tests. The proposed toolpath method is realized by employing the Institute of Manufacturing Technology (IMT) computer-aided manufacturing (CAM) system. The toolpaths at sharp corners generated through commercial software and IMT-CAM software are tested by comparing the corresponding milling forces. It is illustrated in the results that the proposed method reduces the milling force effectively and is of great significance when it is applied in high-speed machining.

Experimental investigation of CNC machining of elliptical pockets on AISI 304 stainless steel

The shape of a pocket geometry, a tool path strategy and various machining parameters (speed, feed rate, and depth of cut) affect pocket machining process in terms of machining time, surface finish, material removal rate, tool life, etc. Most of the literature related to pocket machining deals with the tool path generation and the effect of various machining parameters. But, the effect of the shape of a pocket geometry and the tool path strategy on the overall performance of pocket machining is scarcely reported. In the present work, an attempt has been made to investigate the effect of aspect ratio (i.e. changing the shape of pocket), feed rate and tool path strategies (zig-zag, spiral and contour parallel) on tool path length, cutting time, percentage utilisation of tool and average surface roughness in machining of elliptical pocket using design of experiments. A novel concept of percentage utilisation of a tool is developed to compare the different tool path strategies and different aspect ratios. The results show that tool path strategy and aspect ratio are significant factors that affect the tool path length and percentage utilisation of tool, whereas aspect ratio, feed rate and tool path strategy are important factors that affect cutting time and surface roughness.

Experimental investigation of CNC machining of elliptical pockets on AISI 304 stainless steel

Experimental investigation of CNC machining of elliptical pockets on AISI 304 stainless steel