A 2.5D pocket milling is extensively used in aerospace, shipyard, automobile, dies and molds industries. In machining of 2.5D pockets, directional parallel tool-path and contour parallel tool-path are widely used. However, these tool paths significantly limit the machining efficiency. In the present work, an attempt has been made to generate a spiral tool path for machining of 2.5D star-shaped pocket for improving machining efficiency. The spiral tool path is developed using second order elliptic partial differential equation (PDE) and it is free from sharp corners inside the pocket region. Further, the implementation of proposed method is presented on complex non-star-shaped polygon, pocket bounded by free-form curve and pocket with island.
The shape of pocket geometry, tool path strategy and various machining parameters (speed, feed rate and depth of cut) affect machining performance. However, the effect of the shape of a pocket geometry and tool path strategy on the performance of pocket machining is scarcely reported. Hence, an attempt has been made to investigate the effect of aspect ratio, feed rate and tool path strategies (zig-zag, spiral and contour parallel) on tool path length, cutting time, percentage utilization of a tool and average surface roughness in machining of AISI 304 stainless steel using design of experiments (DOE).
From the findings of above experimental investigation, it was anticipated that there is a need to develop a method (or technique) for comparing different pocket geometry quantitatively and predict the effect of pocket geometry on pocket machining. A novel approach is reported for quantitative comparison of different pocket geometries using a dimensionless number, Divyang Number (DN). The concept and formula of DN are developed and DN is calculated for various pocket geometries. The guidelines for comparing pocket geometries based on DN and PUT (percentage utilization of tool) 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 (parent geometry) into sub-geometries is developed that improves the efficiency of spiral tool path for bottle-neck pockets using HARI Number. The results indicate that decomposing pocket geometry with the new algorithm improves HARIN and removes the effect of bottle-necks. Furthermore, the algorithm for decomposition is extended for pockets that are bounded by free-form curves.
Inhaltsverzeichnis (Table of Contents)
- Introduction
- Background and Motivation
- Organization of Thesis
- Literature Review
- Introduction
- Basic Terminologies Associated with Pocket Machining
- Tool Path Requirements for High Speed Pocket Machining
- Organization of the Literature Review
- Noteworthy Literature Reviews
- Various Types of Pockets and Pocket Machining
- Conventional Tool Path Strategies
- Directional Parallel
- Contour Parallel (Boundary Parallel or Offset) Tool Path
- Space Filling Curves
- Corner Machining Tactics
- Advance Tool Path Strategies for HSM
- Mapping Based Approaches for Tool Path Generation
- Medial Axis Transform Based Method for Tool Path Generation
- Clothoidal Spiral Tool Paths
- Spiral Tool Paths Based on the Solution of PDE
- Trochoidal Tool Paths
- Interpolating Tool Paths Based on Bezier, B-spline and NURBS
- Miscellaneous Tool Path Planning Strategies
- Current Status of Development in Tool Path Strategies
- Summary Table
- Observations
- Objective of Present Research
- Spiral Tool Path Based on PDE and NURBS
- Introduction
- Methodology
- The Algorithm for Generating Spiral Tool Path for Star-Shaped Polygon Using PDE
- Extending the Method for Non-star-shaped Polygon and Free-form Curves
- Results and Discussion
- Effect of Mesh Size on Tool Path.
- Effect of Permissible Error and Number of Degree Steps
- Conclusions
- Study of Elliptical-pocket Machining
- Introduction
- Experimental Details
- Tool Path Strategy and Pocket Geometry
- Tooling Details and Machining Conditions
- Experimental Plan Procedure
- Results and Discussion
- Tool Path Length
- Cutting Time
- Percentage Utilization of a Tool (PUT)
- Average Surface Roughness (Ra)
- Conclusions
- Quantitative Comparison of Pocket Geometries and Pocket Decomposition
- Introduction
- Dimensionless Number (DN) for Comparing Pocket Geometries
- Analogy of Reynolds Number
- Percentage Utilization of a Tool (PUT) as a Measure of Effectiveness of Spiral Tool Path
- The Concept of Dimensionless Number (DN)
- Various Ratios and Their Effects
- Dimensionless Number, DN
- Modified DN for Spiral Tool Path (DNspiral)
- Results and Discussion
- Pocket Decomposition
- Decomposition of a Polygon Geometry
- Free-form Pocket Decomposition
- Decomposition of a pocket with an island
- Conclusions
- Study of speed, feed and step-over in pocket milling
- Introduction
- Experimental Investigation
- Selection of Process Variables, Responses, Workpiece/Tool Material and Tool Path Strategy
- Experimental Setup
- Fixture Design
- Designing the Experiments
- Selection of Sampling Frequency
- Results and Discussion
- Cutting Time
- Surface Roughness
- A Method of Analysing Cutting Forces
- A Crucial Test Before linear Cutting Forces Experiments
- Conclusions
- Overall Results and Discussion
- Overall Results and Discussion
- Conclusions
- Conclusions
- Scopes of Future Research
- References
Zielsetzung und Themenschwerpunkte (Objectives and Key Themes)
The main objective of this thesis is to improve the efficiency of 2.5D pocket machining, specifically focusing on the use of spiral tool paths generated through partial differential equations (PDE) and NURBS curves. The work aims to address several critical issues associated with traditional pocket machining methods and spiral tool path generation.
- Development of a robust spiral tool path algorithm: This involves overcoming the challenges associated with ensuring a bounded distance between consecutive iso-contours in PDE-based spiral tool path generation.
- Analysis of pocket geometry influence: The research investigates the impact of pocket shape, particularly aspect ratio, on the performance of different tool path strategies, including zig-zag, spiral, and contour parallel.
- Quantitative comparison of pocket geometries: A novel technique, using a dimensionless number (DN), is introduced to provide a quantitative comparison between different pocket geometries, aiding in tool path strategy selection.
- Pocket decomposition algorithm: This algorithm focuses on improving the efficiency of spiral tool paths by decomposing complex pocket geometries into simpler sub-geometries, particularly for pockets with bottle-necks.
- Study of cutting parameters: The research examines the effect of speed, feed, and step-over on key machining outcomes like cutting time, surface roughness, and cutting forces.
Zusammenfassung der Kapitel (Chapter Summaries)
- Chapter 3: Spiral Tool Path Based on PDE and NURBS: This chapter focuses on developing a spiral tool path algorithm using PDE and NURBS for star-shaped polygons. It addresses the challenge of maintaining bounded distance between iso-contours and extends the method to handle non-star-shaped pockets and free-form curves.
- Chapter 4: Study of Elliptical-pocket Machining: This chapter presents an experimental investigation using DOE to study the effect of aspect ratio, feed rate, and tool path strategies on tool path length, cutting time, percentage utilization of the tool, and surface roughness.
- Chapter 5: Quantitative Comparison of Pocket Geometries and Pocket Decomposition: This chapter introduces a new dimensionless number (DN) for quantitatively comparing different pocket geometries, demonstrating its use in predicting tool path effectiveness. An algorithm for decomposing pocket geometries with bottle-necks into sub-geometries is presented.
- Chapter 6: Study of speed, feed and step-over in pocket milling: This chapter investigates the effect of speed, feed, and step-over on cutting time, surface roughness, and cutting forces through experimental analysis. A new method for selecting the appropriate sampling frequency for dynamometer analysis of spiral tool path machining is also developed.
Schlüsselwörter (Keywords)
The primary keywords and focus topics of this thesis include: CNC pocket machining, spiral tool path, partial differential equation (PDE), NURBS curves, pocket geometry, aspect ratio, dimensionless number (DN), HARI number, pocket decomposition, cutting time, surface roughness, cutting forces, design of experiments (DOE), high-speed machining (HSM).
- Quote paper
- Divyangkumar Patel (Author), Dr. Devdas I. Lalwani (Author), 2016, Pocket Decomposition using DN and HARI Number. A Novel Approach, Munich, GRIN Verlag, https://www.grin.com/document/388579
