Showing papers on "Machining published in 1994"

Constant Scallop-height Machining of Free-form Surfaces

Abstract: A novel approach for the NC tool-path generation of free-form surfaces is presented. Traditionally, the distance between adjacent tool-paths in either the Euclidean space or in the parametric space is kept constant. Instead, in this work, the scallop-height is kept constant. This leads to a significant reduction in the size of the CL (cutter location) data accompanied by a reduction in the machining time. This work focuses on the zig-zag (meander) finishing using a ball-end milling cutter.

Parametric interpolator versus linear interpolator for precision CNC machining

Abstract: The paper presents a comparative study of linear and parametric interpolators used for command generation during CNC machining. For many decades, linear interpolators have been used in NC machines for command generation. Recently, a parametric interpolator has been developed that is designed for command generation for parametric curves (or surfaces). Two algorithms for the online implementation of this parametric interpolator are introduced. The comparison is mainly based on memory size, feedrate fluctuation and CPU time. Other considerations include tracking errors and jerk magnitude. Results show that the parametric interpolator is favourable in the machining of free-form geometry in terms of high speed and tight tolerancing.

5-axis machining of sculptured surfaces with a flat-end cutter

Abstract: In theory, the 5-axis machining of sculptured surfaces offers many advantages over 3-axis machining, including faster material-removal rates, improved surface finish, and the elimination of hand finishing. In practice, 5-axis machining suffers from a number of drawbacks, which are mostly related to gouge avoidance. The paper describes research on algorithms for the generation of gouge-free, nonisoparametric 5-axis tool paths across composite surface patches. The approach includes (a) the tesselation of the parametric surfaces into triangles, (b) algorithms for the placement of a cylindrically shaped cutting tool onto the triangulated surface, and (c) interference detection and tool-position correction.

Intelligent machining and manufacturing

Abstract: A method and apparatus is disclosed for 'intelligent' control (410) of production processes such as machining, casting, heat treating and welding. The key enabler of such control is of an electro-optical (25, 95, 305, 405) or other suitable sensor type. The sensor is generally of non contact type, capable of rapidly and accurately acquiring data from parts and the tools used to produce the parts in a production 'in-process' environment. Systems are disclosed to control not only the instant operation, but those processes connected therewith, both upstream and downstream. Data bases are generated and knowledge bases are used. Application of the invention can improve quality and productivity, and allow the production of parts which have unusual or individual material characteristics (1000-1008).

Laser machined replication tooling

Abstract: The invention relates to a method of manufacturing a replication master tooling article suitable for manufacturing replicated articles by machining a substrate surface with laser energy to produce a plurality of geometric structures in the substrate, the geometric structures having side surfaces extending from the surface of the substrate into the substrate.

Simple technique for observing subsurface damage in machining of ceramics

Abstract: A simple technique is proposed for directly observing subsurface damage in the machining of ceramics. The technique requires two polished specimens and an optical microscope with Nomarski illumination for examination. The subsurface damage created by the grinding of an alumina ceramic is investigated using this technique. The mode of damage is identified as intragrain twinning/slip, and intergranular and transgranular cracking. Chipping along the twinned planes and along the transgranular crack planes, and dislodgement of the intergranularly debonded grains are suggested to be the mechanisms of material removal in the machining of this alumina ceramic.

Modelling Machining Dynamics Including Damping in the Tool-Workpiece Interface

Abstract: Machining instability, namely chatter, occurs due to the interaction between the structural dynamics and the cutting process. The process damping generated at the tool-workpiece interface is an important parameter of that interaction. A significant enhancement to the chatter simulation model in milling is presented. It includes tracking of the interference between the tool flank and the generated wavy surface, which is the source of process damping. Results of simulation runs performed to determine the limits of stability are presented for sharp tools as well as for tools with various amount of flank wear. The phase relationship between the ploughing force and tool vibrations is explained using these simulations. It is also shown that the improved model accurately predicts the increase in the limit of stability due to tool wear, as well as the effect of the wave length of the machined surface undulations on process damping. Cutting tests of aluminum confirmed the simulation results.

Feed rate optimization based on cutting force calculations in 3-axis milling of dies and molds with sculptured surfaces

Abstract: The use of CAD/CAM systems and NC machine tools for die and mold manufacturing offers considerable advantages over conventional methods, such as reduction in machining time and costs, and improvements in accuracy and reproducibility. However, the selection of cutting tools and machining strategy and parameters, which have a significant impact on overall machining efficiency and process reliability, still depends on the experience of the machinist or the NC programmer. Based on these considerations, this study had two major objectives: (a) develop a method for estimating the cutting forces in 3-axis milling so that the NC programmer can “optimize” the machining parameters; and (b) establish the “best” rough milling strategy to reduce machining time and cost. This paper concentrates on the first objective, namely on optimizing the feed rate to improve machining efficiency in end milling. By simulating the end milling process and predicting the cutting force in 3-axis milling of sculptured surfaces, an approach and the associated computer program have been developed to optimize the feed rate, already at the NC programming stage. The calculated cutting force, which includes the overall net effect of all process variables, is used as a feedback variable to adjust the feed rate. The method also allows the NC programmer to visualize cutting forces in a CATIA CAD/CAM environment.

Direct adaptive control of end milling process

Abstract: A direct adaptive control algorithm, which is spindle speed and drive dynamics independent, has been developed for machining operations. The combined dynamics of feed motion and cutting process are modelled as a third order system whose parameters may vary with spindle speed and part geometry changes during machining. The algorithm does not use any specific time interval, thus sampling time dependent discrete transfer functions and pole assignments are avoided. The adaptive controller is designed to have a closed loop characteristic function which behaves like an open loop regular and stable machining operation. The proposed direct adaptive controller is practical, can be used in any multi-axes machining, and can be combined with chatter suppression techniques which require spindle speed regulation. The algorithm is applied to the adaptive control of milling. Satisfactory results are obtained in constraining the maximum cutting forces and dimensional surface errors in milling experiments.

Application of minimum quantity cooling lubrication technology in cutting processes

Abstract: In spite of the manifold efforts to reach a total renouncement of the use of cooling lubn'cants in metal cuttingfor en­ vironmentally reasons, cooling lubrication is an essential condition to achieve an economical tool life and the re­ quired surface quality in many cases. Against this background, the minimum quantity cooling lubrication is an interesting possibility for an economical and environmentally compatible production which combines the functional­ ity of the cooling lubrication with an extremely low consumption of cooling lubricants. With help of various results achieved in turning, milling and broaching experiments, this report describes the possibilities of application of mini­ mum quantity cooling lubricating systems in machining with geometrically defined cutting edges.

Space-filling curves in tool-path applications

Abstract: Several methods have been developed for the computerized generation of space-filling curves, but these curves have never been used for NC tool-path generation. The paper discusses the application of space-filling curves as tool paths for sculptured-surface machining. Tool paths that are space-filling curves, single-direction conventional paths, and 2-direction conventional paths are compared. The efficiency ratings of the paths require further testing, but the preliminary conclusions are favourable for space-filling curves.

Fundamental studies of driven and self-propelled rotary tool cutting processes—I. Theoretical investigation

Abstract: The various types of rotary tool cutting operations and their performance advantage over conventional machining operations are reviewed together with the simplified or fundamental operations used to study the cutting mechanics of these novel material removal operations. The fundamental driven and self-propelled rotary tool cutting operations have been simulated as wedge tool cutting processes and their relationships to the kinematically and perfectly equivalent “classical” orthogonal and oblique cutting processes explored. Based on the modified thin shear zone cutting models the simulated driven orthogonal and oblique rotary tool cutting processes have been analysed and represented as perfectly equivalent classical oblique cutting processes accounting for all the cutting forces and energy, together with a chip transportation process, owing to the tool lateral motion along its cutting edge, which involves no additional energy. By contrast, the self-propelled oblique rotary tool cutting process has been modelled as a perfectly equivalent classical orthogonal cutting process together with chip transportation. The proposed models will be experimentally verified in the next part of this investigation.

Predicting total machining performance in finish turning using integrated fuzzy-set models of the machinability parameters

Abstract: Due to the numerous interacting machining variables involved in finish turning, it is extremely difficult to assess the total machining performance (TMP) encompassing surface finish, tool-wear rate, dimensional accuracy, cutting power and chip breakability. This paper presents the development of a new methodology for assessing each aspect of the TMP in finish turning of steels as follows. First, a machining reference database is established from the representative machining experiments to provide a primary quantitative standard. Second, a knowledge poo) is developed based on the extended experiments and the present knowledge of the major influencing factors on the TMP. Then, a fuzzy-set method is introduced to quantify the effects of these factors. Finally, a series of fuzzy-set models are developed to give quantitative assessments of the TMP for any given set of input conditions, including work material properties, tool geometries, chip-breaker types and cutting conditions.

The Effects of a High-Pressure Coolant Jet on Machining

Abstract: A high-pressure coolant system was used to machine Ti6Al4V and Inconel 901. A 14.5 MPajet of cutting fluid was applied against the chip flow at the rake face of the tool and this works as an efficient chip-breaker. Conventional overhead flood cooling was also used to establish a base for comparison. Chip control, cutting force, cutting temperature, chip-tool contact length, surface integrity, tool lives and wear mechanisms were studied. The high-pressure coolant system used improved tool lives significantly when machining the titanium alloy but it proved to be detrimental to tool lives when machining the nickel alloy.

Determination Of Machining Volumes From Extensible Sets Of Design Features

Abstract: In a design by feature system, the database may contain features that are not known to a process planning system. Also, additional features arise from the shape and size of the workpiece from which the part is to be machined. Production rules are inadequate for dealing with these undocumented features. In order to get machining features, one must enhance and transform the design database. A volume decomposition method called minimum convex decomposition by halfspace partitioning has been developed to recognize machining features. First, the total volume to be removed by machining is obtained by subtracting the part from the stock. This volume is decomposed into minimum convex cells by halfspace partitioning at every concave edge. A method called maximum convex cell composition is developed to generate all alternative volume decompositions. The composing subvolumes are classified based on degree of freedom analysis. Manufacturing knowledge is characterized in fundamental terms, based on tool and workpiece motion (deep knowledge), by means of algebraic expressions. Inverse mapping of decomposed volumes into these expressions determines feasibility of various machining operations. The method deals effectively with feature interactions and results in alternative machining sequences.

Stress distributions on the rake face during orthogonal machining

Abstract: The authors describe the design, calibration and testing of a split tool dynamometer that has been developed to allow the estimation of rake face stress in a true orthogonal machining process. The device is unique, in that force measurements can be made on the front and rear portions of the cutting tool simultaneously. The normal and shear stress distributions over the rake face of the tool have been calculated based upon cutting tests using AISI C1045 steel, SAE CA360 free cutting brass and AISI 304 stainless steel discs as the work material at a cutting speed of 130 m/min. The experiments also gave insight into the chip sticking length and comparison with scanning electron microscope (SEM) images of the rake face revealed that the dynamometer indeed provides an accurate assessment of the overall chip contact length along the rake face.