This paper presents a new spiral smoothing method to generate smooth curved tool paths directly on mesh surfaces. Spiral tool paths are preferable for computer numerical control (CNC) milling, especially for high-speed machining. At present, most spiral tool path generation methods aim mainly for pocketing, and a few methods for machining complex surface also suffer from some inherent problems, such as selection of projecting direction, preprocessing of complex offset contours, easily affected by the mesh or mesh deformation. To address the limitations, a new spiral tool path method is proposed, in which the radial curves play a key role as the guiding curves for spiral tool path generation. The radial curve is defined as one on the mesh surface that connects smoothly one point on the mesh surface and its boundary. To reduce the complexity of constructing the radial curves directly on the mesh surface, the mesh surface is first mapped onto a circular region. In this region, the radial lines, starting from the center, are planned and then mapped inversely onto the mesh surface, thereby forming the desired radial curves. By traversing these radial curves using the proposed linear interpolation method, a polyline spiral is generated, and then, the unfavorable overcuts and undercuts are identified and eliminated by supplementing additional spiral points. Spline-based technique of rounding the corners is also discussed to smooth the polyline spiral, thereby obtaining a smooth continuous spiral tool path. This method is able to not only greatly simplify the construction of radial curves and spiral tool path but also to have the ability of processing and smoothing complex surfaces. Experimental results are presented to validate the proposed method.

Feedrate optimization for computer numerically controlled (CNC) machine tools is a challenging task that is growing in importance as manufacturing industry demands faster machine tools. The majority of research in this area focusses on optimizing feedrate using modeled process constraints. Some researchers have suggested using measured process parameters instead. The former approach suffers from uncertainties in the modeled process data that is the starting point of the optimization. The latter approach has difficulties achieving high levels of optimality. This study proposes the combination of both modeled and measured process data. To this end, a control architecture is described that allows combining measured and modeled process constraints. Within this architecture, a new algorithm to determine time optimum feedrates using modeled velocity and acceleration constraints is proposed. The new control structure including the novel feedrate optimization algorithm is verified experimentally on a high speed biaxial table.

This paper presents a novel trajectory generation technique, which has the capability to avoid excitation of inertial vibrations in precision manufacturing equipment. A major source of vibrations in fast moving precision manufacturing equipment is the inertial vibrations that are excited due to frequency content of reference motion commands (trajectory). In general practice, those inertial vibrations are avoided within the controller architecture through notch filtering. Or, input-shaping methods are utilized to attenuate critical frequency components of the reference trajectory so that lightly damped vibration modes of the structure are not excited. Instead of employing those postfiltering techniques that add unwanted delay to the coordinated motion, this paper introduces a direct trajectory generation technique with a shaped frequency content to suppress inertial vibrations. The time-stamped acceleration profile of the feed profile is defined as a ninth-order polynomial. Polynomial coefficients are solved through an optimization procedure where the objective function penalizes total frequency energy in a desired frequency band. As a result, generated reference acceleration commands do not contain any excitation near the vibration modes of the system and hence excitation of inertial vibrations is avoided. The proposed frequency optimal feed profiling (FOFP) system can be utilized to generate high-speed accurate point-to-point (P2P) trajectories as well as to interpolate continuous multi-axis coordinated motion. Effectiveness of the proposed FOFP scheme is evaluated through rigorous comparison against the well-known minimum jerk feed profiles (MJFP) technique through simulations and experiments. Experimental validation is performed on an in-house controlled machine tool with flexible structure.

Visual appearance of an object significantly influences a consumer's choice and largely controls the market economy. The perceived quality of products is governed by surface's optical properties (reflection, refraction, etc.), geometrical properties (roughness, waviness, etc.), and chemical properties (oxide layer formation, thermal variation, etc.). Surface shininess attracts researchers from many different disciplines, in particular manufacturing, metrology, psychology, physiology, and computer science. Unfortunately, there are still huge knowledge gaps on characterizing and appraising shiny surfaces in a reproducible way. This paper introduces the main definitions and physics of shininess and gloss, methods of gloss sensing, and relates these definitions and methods to surface generation by grinding. Automated gloss measurement is difficult in particular for free-form surfaces, and optical quality is still often evaluated by human workers. Gloss models are often based on the bidirectional reflection distribution function (BRDF) of the surface, but the models are commonly not connected with the manufacturing process. This study proposes to consider the geometrical features (defects, waviness, lay, and roughness) of metal surfaces as well as the physical and chemical features (grain structure and microlayers) to understand surface appearance and manufacturing in a holistic way. Preliminary tests show that 2D roughness measurements are not connected well with measured gloss units (GUs) and subjective, perceived quality. More fundamental research on the generation and measurement of surface appearance is needed and would benefit many industries.

Plunge milling is an effective roughing operation, especially in pockets roughing, because it can efficiently remove a large amount of stock material without high manufacturing costs. However, plunge milling of complex pockets with islands, whose boundaries could be designed with free-form curves, is quite challenging for multiple plungers have to be used including small plungers to cut necks between islands and their plungers paths are expected to have fewer times of plunging and shorter travel to achieve efficient machining. Unfortunately, little research on this topic was carried out in the past, and the challenge has not been addressed yet. In this research, a new approach is proposed to generate plunger paths for efficient plunge milling of the complex pockets. Its main features include (1) packing plunger circles at a minimum number of locations inside the pocket for fewer times of plunging, (2) placing plunger circles to cover the areas enclosed by the afore-packed circles to clear out the interior pocket material, and (3) planning the shortest paths to connect plunger locations for less traveling time. The advantages of this new approach over the overlapped circles filling (OCfill) and the Catia methods are demonstrated with two examples, and it can be directly used for pocket plunge milling in industry.

A new computer numerically controlled (CNC) lathe with a pipe frame bed has been developed. This structure is expected to have enough space between the truss bars to solve the space problem and have enough rigidity for machine tools. Therefore, a CNC lathe whose frame consists of pipes, joints, and diagonal braces has been developed with enough rigidity and space utility for chip evacuation. From the viewpoint of machine tool usage, real-time vibration control theory is applied to control the relative displacement between the tool post and the spindle to suppress specific relative vibration modes.

In machining process, machining accuracy of part mainly depends on the position and orientation of the cutting tool with respect to the workpiece which is influenced by errors of machine tools and cutter-workpiece-fixture system. A systematic modeling method is presented to integrate the two types of error sources into the deviation of the cutting tool relative to the workpiece which determines the accuracy of the machining system. For the purpose of minimizing the machining error, an adjustment strategy of tool path is proposed on the basis of the generation principle of the cutter location source file (CLSF) in modern computer aided manufacturing (CAM) system by means of the prediction deviation, namely, the deviation of the cutting tool relative to the workpiece in computer numerical control (CNC) machining operation. The resulting errors are introduced as adjustment values to adjust the nominal tool path points from cutter location source file from commercial CAM system prior to machining. Finally, this paper demonstrates the effectiveness of the prediction model and the adjustment technique by two study cases.

The need to simultaneously measure sheet metal geometry and strain arises during research, die tryout, statistical process control production part approval, or in response to manufacturing exceptions. Several optical systems have been developed for strain and geometry measurement of small specimens. Large scale geometric measurement is possible using coordinate measuring machines equipped with touch probes. This Technical Brief summarizes the extension of these methods using three dimensional gray level point clouds obtained from either laser digitizers or an in-house developed stereo vision system.

A procedure for manufacturing cardiovascular system models using patient-specific data, rapid prototyping, and a multistep dip-spin coating process is presented here. Improvements to a previously developed process permitted the fabrication of flexible complex vascular replicas. The primary improvement included the development of a two-axis rotation mechanism that enabled a pseudorandom rotation of the coated mold in space, providing uniform coats. Other improvements included the use of a low viscosity ( 1500 – 2000 cP ) silicone solution that allowed for complete coverage of the mold, and developing a procedure for fixing defects. The dip-spin coating procedure was shown to be effective for the manufacture of compliant cardiovascular membranes, such as an arterial bypass graft with an internal flow passage and an abdominal aorta with nonuniform radial geometry, tapered diameters, bifurcations, and small branches. Results from a design of experiments comparing two dipping setups demonstrated that horizontally dipping the model produced coatings with more uniform thicknesses along the length of the model when compared to vertical dipping. For a 250 - mm -long model, the difference in thickness between the top and bottom of the membrane was 0.42 ± 0.069 mm and 0.09 ± 0.077 mm for vertical and horizontal dippings, respectively. Mold diameter also affected the thickness of the membrane, with membrane thickness increasing as mold diameter decreased. Thickness data comparing locations at approximately the same height of the mold but with different diameters showed thicknesses of 2.54 ± 0.198 mm and 1.95 ± 0.140 mm for 7.85 mm and 15.20 mm diameters, respectively. Moreover, the differences in thickness between these locations were 0.60 ± 0.128 mm and 0.58 ± 0.231 mm for vertical and horizontal dippings, respectively; thus, membrane thickness variations occurred with mold diameter irrespective of the dipping setup. Depending on the prescribed tolerance for membrane thickness, the vertical dipping setup may be recommended for use because (1) it was easier to use since only the mold was immersed in the coating solution and no special protection of the dipping mechanism was required and (2) it produced fewer defects in the coatings since the solution always dripped from downfacing surfaces of the mold. Using this dip-spin coating procedure, patient-specific cardiovascular membranes can be manufactured and used in the development of medical devices, research requiring accurate anatomical models, and education and training.

This paper presents an enhanced marching cubes algorithm to construct an iso-boundary for in-process geometric modeling for material removal processes. The author first analyzes the tool motion and the geometric properties in material removal processes. The result shows that the in-process geometry is the complement of the tool swept volume from the raw material. The in-process geometry can be determined by continuously updating itself from the swept volume of the tool. This study uses a three-dimensional G-buffer to update the intersection information between the tool swept volume and the in-process geometry. Rather than traditionally searching for all intersection points ranging in a cube, the developed algorithm uses certain specific intersection points that are selected based on the removal geometry properties to construct the iso-boundary. It avoids the unfavorable ambiguities and holes on constructed boundaries. In addition, the developed algorithm is able to handle multiple intersection points in a cubical edge. This study also discusses material removal volume and tool collision issues. The computer implementation shows that the developed method is superior to the traditional ones in material removal applications.

A method for rapid computer numerically controlled (CNC) machining is being developed in an effort to automatically create functional prototypes and parts in a wide array of materials. The method uses a plurality of simple two-and-a-half-dimensional ( 2 1 2 -D) toolpaths from various orientations about an axis of rotation in order to machine the entire surface of a part without refixturing. It is our goal to automatically create these toolpaths for machining and eliminate the complex planning traditionally associated with CNC machining. In this paper, we consider a problem that arises in automating this process— visibility to the surface of a model that is rotated about a fourth axis. Our approach involves slicing the computer-aided design (CAD) model orthogonal to the axis of rotation. The slice geometry is used to calculate two-dimensional visibility maps for the set of polygons on each slice plane. The visibility data provides critical information for determining the minimum number and orientation of 2 1 2 -D toolpaths required to machine the entire surface of a part.

Commercially-available reconfigurable fixtures, used for holding compliant sheet metal, composite and plastic parts during secondary machining operations, are extremely expensive and overly-complicated devices. A computer-controlled, reconfigurable fixturing device (RFD) concept for compliant parts, based on a matrix of individually-stoppable pins lowered by a single rigid platen, has been developed as a simple and low-cost design alternative to commercially-available devices. Two different approaches to stopping and clamping individual pins have been investigated: a combination electromagnet assist and gas springs compressed with a toggle mechanism, and a pneumatic clamp. Simple mechanical models have been developed for predicting the stopping and clamping performance of both designs including pin positioning accuracy, vertical load-carrying capacity of a pin, and deflection of a pin subjected to lateral loads. An RFD prototype, consisting of a single pin actuated by a servoed platen, has been designed, built and tested. It has demonstrated the feasibility of this new RFD design. [S1087-1357(00)02204-8]

A considerable amount of research has recently been performed on automated die and mold finishing systems. The research has tended to focus on the development of the finishing tool, the means of positioning and controlling the tool or efficient algorithms for moving the tool to achieve desired degrees of surface roughness. However, there has been relatively less effort to develop sensors suitable for providing the critical surface finish data necessary for any closed loop system. This paper presents two algorithms that, when coupled with machine vision hardware, are capable of providing surface texture information. The algorithms are developed and the results calibrated against a stylus profilometer. Tests have been conducted on mold cavity surfaces and the results evaluated against standard tactile means. The hardware has been incorporated with a computer controlled coordinate machine.

In this paper, a dynamic model for removal of edge burrs with a compliant brushing tool is reported. Description of the burr geometry is assumed to be known through on-line measurement methods such as a computer vision system in the flexible manufacturing cell. Dynamic response of the brush/workpiece system is evaluated on the basis of experimentally obtained data. Master Curves are introduced as machining descriptors which characterize the incremental burr removal performance of the brush/workpiece system, leading to the development of an analytical dynamic model for orthogonal burr removal using a finite-width brushing tool. Based upon the dynamic model for material removal, a control strategy for automatic deburring is presented for burr configurations having constant height as well as variable height. A closed-form solution for transverse brush feed rate is obtained which is applicable for removal of burrs having variable height, as described by suitable geometry functions. For illustrative purposes, simulations are carried out for a straight-edge burr profile and sinusoidal burr geometry. Results are reported which identify important relationships among brush feed rate, brush penetration depth, and brush rotational speed. In order to help assess the validity of the proposed analytical model and control strategy, experimental results are reported for a combination ramp/straight-edge burr configuration. The results demonstrate generally good correlation between the predicted and actual profile for the edge burr that has been machined. In addition, some important observations include; (1) burr removal is most rapidly carried out by using the highest brush speed and deepest brush/workpiece penetration depth, subject to the condition that the brush fiber is not damaged, (2) Currently available polymer abrasive brushing tools exhibit very slow machining characteristics and must be improved in order to be used in a production environment where burr size is appreciable, (3) Material removal characteristics of the leading and trailing edge of brushes may be a source of error which merits further investigation.

A general thermal modeling and control methodology for thermal processing of layered materials for rapid prototyping technologies is established in this article. An analytical multivariable model of lumped temperature outputs generated by heat inputs on a surface grid is developed, based on Green’s function and state-space descriptions. The few independent parameters needed in such a linearized formulation are experimentally identified, and their time-variability reflects the heat transfer nonlinearities and process disturbances. A robust controller with thermal feedback is designed by pole placement methods, to obtain a specified dynamic temperature field yielding the desired material structure and properties. The regulated thermal processing is optimized in real time by proper heat source power modulation and torch guidance through a simulated annealing strategy. Its performance is tested on both the computer model and a laboratory station, using robotically guided plasma-arc cutting and infrared thermal sensing, in regulating the sensitized zone during blanking of an elementary contour pattern on stainless steel.

An automatically reconfigurable discrete tool (matrix of pins) has been developed and demonstrated for sheet metal part forming and composite part molding in the aerospace industry. A GUI-based control system positions each of the hydraulically-actuated pins according to a computer model of the intended tool surface. Open-loop position control of individual pins (timing the upward movement of each pin) is possible but accuracy and repeatability are inadequate for most sheet metal forming and composite molding applications. However, closed-loop position control is shown to provide sufficient accuracy and repeatability for these same applications. Once the pin matrix shape is set, it can be made into a rigid forming or molding tool by side clamping with a hydraulic ram. Since the pin ends are spherical in shape, the resulting dimpled tool surface is covered with an interpolating layer of material. The pins can be reset to their lowest position by either withdrawing hydraulic fluid or pushing them down with the setting platen. [S1087-1357(00)01403-9]

Path optimization is desirable in many problem instances occurring in discrete manufacturing and pick and place technology. The problem may refer to applications ranging from two-dimensional movements such as in milling processes to three-dimensional movements required in many robotic operations. The optimal path can be found using tour construction techniques, sub tour elimination techniques and tour to tour improvement techniques. The limits to which these solution methodologies can be applied are restricted to a certain number of nodes. The optimal path for two- and three-dimensional TSP is determined using a stochastic search procedure based on a tour improvement technique. An optimal solution is presented for 500 node TSP in two dimensions. A procedure for finding optimal path for an even larger number of nodes is outlined. The optimal path in three dimensions is also presented using nodes distributed along the periphery of three-dimensional primitives. [S1087-1357(00)71601-7]

Residual stress distributions due to plating and polishing were determined for nickel-phosphorus plated aluminum alloy disks. Knowledge of these stresses provides insight into the material deformation and removal processes, information as to the effects of processing conditions on residual stress magnitude and can also serve as a basis for development of models of material deformation and removal in polishing. Measured disk shape data was fitted to an analytical solution for plate displacement due to bending moments, and residual stresses were calculated. Plating and polishing residual stresses were separated. Polishing residual stress is compressive indicating differential plastic deformation between the surface and interior regions of the workpiece. Residual stresses produced in polishing operations in which process motions were constrained so that polishing was unidirectional were measured. The results show large differences between amounts of deformation in the polishing direction and the direction perpendicular to it.