Three-axis Milling Research Articles

An Operation Planning System for Multi-Axis Milling of Sculptured Surfaces

Multi-axis milling of sculptured surfaces with cylindrical or toroidal cutters has many advantages compared to the use of three-axis milling with ball nose cutters. Surfaces to be machined are often of complex shape and characterised by convex, concave and saddle areas. Today, CAM-systems do not support the user in the selection of the different operations in order to finish the workpiece. This paper describes an operation planning system, which facilitates process planning for the multi-axis machining of sculptured surfaces. The core of the system is surface analysis, which divides the surfaces into regions, each characterised by a preferred milling direction and tool diameter. Further, for each region or set of regions, a drive surface is constructed that is used as the basis for the tool-path calculation. The drive surface approximates to the original workpiece as closely as possible, and the isoparametric lines which will be the tool-path feed direction lie in the preferred milling direction.

A CAD-CAM methodology to produce bone-remodelled composite femurs for preclinical investigations

Femoral bone remodelling, following total hip arthroplasty, is a clinically observed phenomenon attributed to the changed stress environment of the postoperative implanted hip. While this process cannot be avoided, there is concern as to its consequences on the long-term survival of hip joint replacements. Previous methods of studying remodelling, such as clinical or animal-based studies, or finite element analyses, have their limitations. The aim of this study is to develop experimental specimens incorporating bone resorption features typical of clinically successful implants. This work describes the use of computer aided design/manufacturing methods (CAD-CAM) to produce these specimens, based on modifying commercially available composite femurs. The procedures are investigated and verified for two different designs of cemented prostheses (Lubinus SPII and Muller Curved). Quantitative clinical data is used to define the remodelled geometry of a CAD model of the femur for each stem design. Composite femur specimens are machined using a three-axis milling machine, where each specimen can be accurately positioned using a custom-designed jig and a digitizer system. The accuracy of the process is assessed by analysing the deviation of the digitized premachined and postmachined surfaces of each specimen in relation to the CAD model. The results demonstrate that the procedure can be used for developing in vitro specimens with bone resorption features. These specimens are proposed as a useful tool for performing preclinical trials, such as load transfer or longevity/stability testing, with the advantage of modelling a long-term clinical situation, rather than solely analysing implanted femurs in an immediate postoperative state.

Geometric Criteria for Gouge-Free Three-Axis Milling of Sculptured Surfaces

The paper presents a geometric investigation of collision-free 3-axis milling of surfaces. We consider surfaces with a global shape condition: they shall be interpretable as the graphs of bivariate functions or shall be star-shaped with respect to a point. If those surfaces satisfy a local millability criterion involving curvature information, it is proved that this implies globally gouge-free milling. The proofs are based on general offset surfaces. The results can be applied to tool-motion planning and the computation of optimal cutter shapes.

Computer aided design and fabrication of models for in vitro studies of vascular fluid dynamics.

An integrated computer aided design/computer aided manufacture system has been used to model the complex geometry of blood vessel anastomoses. Computer models are first constructed with key dimensions derived from radiological images of bypass grafts, and from casts of actual blood vessel anastomoses. Physical models are then fabricated in one of two ways: the surface geometry data can be used to control the movement of a three-axis milling machine; alternatively, the same data can be exported in a form that can be interpreted by a stereolithography apparatus. Both methods produce geometrically defined solid investments that can be used in a multistep casting process that yields high-quality physical models for vascular fluid dynamic studies. This technique is useful for parametric studies.

Generation of collision-free cutter location data in five-axis milling using the potential energy method

In five-axis milling, optimal cutter location data (CL-data) should be generated to have advantages over three-axis milling in terms of accuracy and efficiency. This paper presents an algorithm for generating collision-free CL-data for five-axis milling using the potential energy method. By virtually charging the cutter and part surfaces with static electricity, global collision as well as local interference is eliminated. Moreover, machining efficiency is simultaneously improved by minimising the curvature difference between the part surface and tool swept surface at a cutter contact point (CC-point).

Finding Feasible Tool-Approach Directions for Sculptured Surface Manufacture

Determining tool-approach directions is an important issue when an effort is made to transfer CAD data into manufacturing automatically. An algorithm is developed to determine whether a given part can be machined on a three-axis milling machine. In the algorithm, a sculptured surface is first approximated with smaller subpatches by an adaptive subdivision method. For the unit normal vector to each subpatch, a hemisphere is then defined. Any point on the hemisphere defines a feasible tool-approach direction for the corresponding subpatch. The intersection of the hemispheres for the sculptured surface is a polyhedron. A set of points on the polyhedron is the set of feasible tool-approach directions for the sculptured surface. If a set of feasible tool-approach directions exists for a sculptured surface, the NC tool paths and G-codes for machining the surface on a three-axis milling machine can be generated automatically by an NC tool-path generation algorithm. The algorithm can be used for orientation and fixturing of the workpiece for interference free machining. The algorithm for finding feasible tool-approach directions is implemented in C running on a Sun engineering workstation as a module in an integrated sculptured surface design and manufacturing (ISSDM) system.

Computational Geometry for Optimal Workpiece Orientation

Workpiece orientation is formulated as an optimal design problem based on a discrete approximation of design surface geometry, the kinematic capabilities of the process machine tool, and processing cost. The primary process application addressed is three-and four-axis numerically controlled (NC) milling, although the techniques presented may be applied to machines with more general articulation. Recent developments in applied spherical geometry are employed to formulate a constrained problem, and furthermore, a nonlinear optimization problem. For three-axis milling applications, a weight is assigned to each surface normal of the discrete model corresponding to the actual area it represents. Workpiece/machine orientation is optimized such that the angle between the weighted normals and the milling tool axis is minimized. This formulation is augmented, for four-axis milling, to incorporate limitations of the rotational degree of freedom, into the optimization formulation. The influence of tool geometry is also discussed and incorporated within constrained orientation algorithm.

Modeling and control of cnc machines using a PC-based open architecture controller

A PC-based open architecture computer numerical controller (CNC) is introduced to control milling machines. The controller is implemented on two systems: (1) a single-axis high speed milling machine using analog control signals where the PC-based controller assumes all CNC functions and (2) a three-axis milling machine controlled by digital signals where the existing CNC continues to monitor peripheral functions but the PC-based system generates the reference commands for the axes and spindle. System models are developed using sinusoidal inputs to build the frequency response functions of each axis drive. An experimental controller is implemented with the open architecture controller to maintain constant peak cutting force in the presence of uncertain machining conditions in end milling. An adaptive cross-coupling controller is also introduced to reduce tracking and contour error for a two-dimensional contour via the open architecture controller.

RTX: A Real-Time Operating System Environment for CNC Machine Tool Control

A low cost (IBM/PC microcomputer based) computer numerical controller has been developed and successfully adapted for use in a three-axis milling machine application. The heart of this system is a simple, yet powerful real-time multitasking operating system environment (termed RTX) that was developed as a real-time extension to the standard disk operating system (DOS). Basically, RTX acts as an interrupt driven priority based round-robin scheduler running in the background under DOS. The scheduler is extremely efficient since it is not called at a pre-determined frequency but is called upon demand by the hardware timer of the priority level requesting service. Since the processes running on a given priority level can dynamically set the interrupt rate of the hardware timers, the frequency of execution of the scheduler is infinitely variable. The implementation of RTX for the CNC controller uses three priority levels; however the design philosophy is generic and can be extended to accommodate most system requirements.

Automated machinability checking for CAD/CAM

The authors present a method to determine whether or not a part is machinable on a three-axis milling machine by consideration of tool motion. The method focuses on determining sets of candidate machining directions, called the basis set, and testing if the process plan generated from any particular set of machining directions succeeds in machining all of the part features. This constitutes a machinability test that can be used at design. The range of parts that are successfully handled include all simple polyhedrons and simple three-dimensional curved faces such as cylinders, cones, and spheres.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A new method for generating ceramic restorations: a CAD-CAM system

The CAD-CAM CEREC system is a small, complex unit developed for electronically designing and milling ceramic restorations. The system makes it possible to generate a restoration without taking impressions, developing temporary prostheses, and without laboratory assistance. The entire restorative procedure is performed in one appointment. Basic features include the following: the cavity preparation is scanned stereo-photogrammetrically, using a three-dimensional miniature video camera; the small microprocessor unit stores the three-dimensional pattern depicted on the screen; the video display serves as a format for the necessary manual construction via an electrical signal; the microprocessor develops the final three-dimensional restoration from the two-dimensional construction; the processing unit automatically deletes data beyond the margins of the preparation; the electronic information is transferred numerically to the miniature three-axis milling device; driven by a water turbine unit, the milling device generates a precision-fitting restoration from a standard ceramic block; the entire process of electronic designing and subsequent milling of a ceramic restoration requires approximately 10 to 15 minutes.

An Approach to the Low-Cost Computer Aided Manufacture of Components Embodying Free-Form Surfaces

The numerical control (NC) machining of free-form surfaces is usually accomplished utilizing minicomputer or mainframe computer aided design and manufacturing (C ADC AM) systems. The resulting NC data are suitable for either three-axis or five-axis machining dependent upon machine tool type/capability and CAM package complexity. However, the cost of such packages and systems precludes the use of these in smaller companies with an occasional requirement for components embodying free-form surfaces. The increasing availability of powerful yet reasonably priced personal computers (PC) coupled with improving software provides such companies with a far cheaper alternative approach. However, a common feature of PC-based CADCAM systems is that they are limited to 2 1/2-axis machining for all but special applications such as three-axis canted Z-plane milling of four-axis wire electro discharge machining (EDM). This paper presents a method for manufacturing true three-dimensional free-form surfaces using PC-based 2 1/2-axis CADCAM systems. All the main functions performed on mainframe systems can be performed on personal computers, such as toolpath generation for free-form surfaces, cusp height determination and change in shape and volume which may be used for the compensation of shrinkage or to suit market requirements. This is significant for manufacturers who make use of moulds, such as are found in the plastic processing industries. The manufacture of a blown plastic bottle mould is presented as a typical example. The inclusion into the PC environment of features to be found in mainframe systems is also discussed, such as machining the surface patch by patch in any direction or machining a number of patches at one time, shape and volume change in any direction, cusp height determination, etc.

Fixed-axis tool positioning with built-in global interference checking for NC path generation

An algorithm for generating tool positions for three-axis mill cutter paths on parametric surfaces is presented. The novelty of this algorithm is in its use of a surface subdivision technique as an alternative to the traditional APT-style iterative approaches based on local tangent-plane extensions. The algorithm presented provides global interference checking and does not exhibit the convergence problems of the traditional approaches.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>