Non-constant parameter NC tool path generation on sculptured surfaces

An algorithm for three-axis NC tool path generation on sculptured surfaces is presented. Non-constant parameter tool contact curves are defined on the part by intersecting parallel planes with the part model surface. Four essential elements of this algorithm are introduced: initial chordal approximation, true machining error calculation, direct gouge elimination, and non-constant parameter tool pass interval adjustment. A software implementation of this algorithm produces graphical output depicting the tool path superimposed over the part surface, and it outputs cutter location (CL) data for further post-processing. Several applications examples are presented to demonstrate the capabilities of the algorithm. The results of this technique are compared to those generated from a commercially available computer-aided manufacturing program, and indicate that equivalent accuracy is obtained with many fewer CL points.Notation C cutting curve - C ¹ cutting curve tangent - CC ₀,CC ₁, ... cutter contact points - d chordal deviation - /_ABC triangle - w incremental step in parameterw - ABC angle - a small quantity - l chord length - n _s ,n _p , ... normal vectors - P, P _r ,P _c ,P ₁ ,P ₂ , ... space point - Q parametric equation of a surface - R radius of a ball-end milling tool - TC ₀,TC ₁, ... tool center points - u, v, u _s ,u _c ,w, t parameters - angle - curvature - h cusp height - T machining tolerance     

An Intelligent Tool for Process Redesign: Manufacturing Supply-Chain Applications

Manufacturing enterprises face intensive competitive pressures, and many firms are forced to redesign processes just to stay even with the competition. But process redesign is an expensive, time-consuming, and labor-intensive activity, and first-generation computer-based tools are inadequate for redesign today. Alternatively, knowledge-based systems and intelligent tools have the ability to address the key intellectual activities required for effective process redesign. The research described in this article addresses an intelligent redesign tool called KOPeR. The article describes the KOPeR design and implementation and highlights its use and mechanics in the context of a manufacturing supply-chain example. It then turns to application of KOPeR as a redesign tool in the field, through an industrial-strength reengineering engagement, to redesign major supply-chain processes. The field results reveal insights into the use, utility, and potential of this tool in procurement, manufacturing, and beyond. The article closes with a number of promising future directions for related research.     

Hybrid FMS control architectures based on holonic principles

The escalation in processor technologies and the corresponding reduction in costs have enabled alternative FMS control architectures to be developed without the restrictions of fixed machine controller boundaries. These new architectures can be based upon the use of intelligent servo axes, which are desccribed in this article, as flexible numerical control (FNC). In current parlance, the FNC is a part movement holon within a manufacturing cell. The control architectures that can be derived from the FNC concept are referred to as hybrid architectures and share the emerging attributes of holonics. This article details the problems that arise in the scheduling and control of FMSs in the light of hybrid control architectures. A number of traditional scheduling approaches have been devised to cope with the scheduling of parts to discrete machines, but the problem here is to ascribe the processing (machining) of part features to axis groups. This article documents how two research programs, undertaken at the CIM Centre at Swinburne University of Technology in Hawthorn, Victoria, Australia, have endeavored to address the problem of hybrid architectures and their associated scheduling.     

An activity-based predicate/transition net model of operational control planning for a flexible manufacturing system

An effective flexible manufacturing system (FMS) relies on a hierarchy of decisions, including the control of the FMS operation. The FMS operation usually is dynamically constrained by the limited resources such as pallets, machines, tools, carts, etc. Most analytical models make many assumptions and oversimplify the complicated decision problems. This study proposes the predicate/transition (Pr/Tr) net, a high level petri net, as a model for operational control planning. Firstly, the activities (modes) and their resources usage in FMS were analysed and aggregated into activity sets. Then, the flow of parts among activities was traced to obtain the mode transition diagram, and then the Pr/Tr net model was introduced. We incrementally defined the predicates and transitions into this model. Finally, a comprehensive FMS Pr/Tr net model was derived. By implementing it into a rule-based simulation model, it is well suited for FMS operational control planning because of its inclusiveness and high flexibility.     

Time partitioning based on the job-flow schedule — A new approach to optimum allocation of jobs on machine tools

A time-partitioning scheme with constant job-mix divisions (stages) is presented. The scheme is the basis for using a combination of linear programming and heuristic to solve the dynamic optimisation problem of job allocation through an algorithm which also incorporates the set-up times. The algorithm uses a pull logistic towards the due dates. The results of a case study of a single operation job-shop, indicate increased utilisation of machine tools, reduced work-in-process inventory and additional free capacity owing to reduced makespan of jobs. Application of the algorithm can be extended to multiple-operation job shops, which are common in industrial practice.     

Plastic snapfit fastener design

This paper presents a systematic procedure for selecting and designing snapfits integrated into plastic parts. A classification is proposed based on the geometry of the parts to be assembled and the ease of dismantling. The part geometry influences the type and shape of the snapfit. Depending on the space available, recommendations are made for choosing from a classical straight beam shape, a tapered shape, an L shape and a U shape. The snapfit fastener may be separable if so designed. A distinction should be made between: dismantling with or without a tool (screwdriver or specialised tool); access to the insertion face only; access to insertion face and opposite or lateral faces.     

Toroidal versus ball nose and flat bottom end mills

This paper compares the surface roughness along and across the feed directions produced by toroidal, ball nose, and flat bottom end mills. The study is conducted numerically and by cutting tests of aluminium. The results show that the toroidal cutter inherits the merits of the other two cutters; it produces small scallops across the feed direction, and low roughness along the feed direction.Nomenclature h scallop height - R _s radius of curvature of surface - inclination angle - 2a _c cross-feed - 2 subtended angle between the point of contact on the tool profile and the surface - R _a surface roughness - e offset distance of insert from tool axes for toroidal cutter - r _c cutter radius - r _i radius of insert for toroidal cutter - f _t feed per tooth - h _u undercut height - y, , intermediate variables     

A novel representation of tandem systems with inter-stage storage applied to on-line system monitoring

One of the goals of operating a tandem manufacturing system with finite inter-stage storage and asynchronous operations is to meet the demand without over-producing, under-producing or carrying large quantities of material in storage. We believe that analysing the operation of such a system on a real-time basis helps achieve this goal. The first step in this real-time analysis would be to quantitatively associate the causes and effects of over-production or under-production as they occur. This requires determining the cumulative effect that the performance that any stage has on the system, based on its history, the current system state and the interrelationships between the stages. This paper proposes a method which first represents uniquely and completely each stage and surrounding storage as an element. While this system, which consists only of this simple type of element functions in exactly the same way as the original one, each element is put into an ideal world for decoupled measurement. Though an element behaves in exactly the same way whether it is in the ideal world or in the real world, the elapsed times in the two worlds since the beginning of production can be different, since the responses (occurrences and durations of the blockings and starvations) of the two worlds can be different. A phase parameter is introduced for each element to represent this difference. Once the formation of the phase parameter of the output element is formulated, quantitative relationships between causes and effects of over-producing or under-producing can be explained as they occur.     

Computer-aided selection of optimum machining parameters in multipass turning

In this paper a model and the interactive program system MECCANO2 for multiple criteria selection of optimal machining conditions in multipass turning is presented. Optimisation is done for the most important machining conditions: cutting speed, feed and depth of cut, with respect to combinations of the criteria, minimum unit production cost, minimum unit production time and minimum number of passes. The user can specify values of model parameters, criterion weights and desired tool life. MECCANO2 provides graphical presentation of results which makes it very suitable for application in an educational environment.Nomenclature a _min,a _max minimum and maximum depth of cut for chipbreaking [mm] - a _w maximum stock to be machined [mm] - C _a, _a, _a coefficient and exponents in the axial cutting force equation - C _r, _r, _r coefficient and exponents in the radial cutting force equation - C _T, , , coefficient and exponents in the tool life equation - C _v, _v, _v coefficient and exponents in the tangential cutting force equation - D _w maximum permissible radial deflection of workpiece [mm] - F _a axial cutting force [N] - F _b design load on bearings [N] - F _c clamping force [N] - F _k ^/* minimum value of criterionk, k=1, ...,n, when considered separately - f _m rotational flexibility of the workpiece at the point where the cutting force is applied [mm Nm^–1] - f _r radial flexibility of the workpiece at the point where the cutting force is applied [mm N^–1] - F _r radial cutting force [N] - F _tmax maximum allowed tangential force to prevent tool breakage [N] - F _v tangential cutting force [N] - k slope angle of the line defining the minimum feed as a function of depth of cut [mm] - l length of workpiece in the chuck [mm] - L length of workpiece from the chuck [mm] - L _c insert cutting edge length [mm] - M _g cost of jigs, fixtures, etc. [$] - M _o cost of labour and overheads [$/min] - M _u tool cost per cutting edge [$] - n number of criteria considered simultaneously - N _q, N_p minimum and maximum spindle speed [rev/min] - N _s batch size - N _z spindle speed for maximum power [rev/min] - P _a maximum power at the point where the power-speed characteristic curve changes (constant power range) [kW] - R tool nose radius [mm] - r workpiece radius at the cutting point [mm] - r _c workpiece radius in the chuck [mm] - s _min,s _max minimum and maximum feed for chipbreaking [mm] - T tool life [min] - T _a process adjusting time [min] - T _b loading and unloading time [min] - T _d tool change time [min] - T _des desired tool life [min] - T _h total set-up time [min] - T _t machining time [min] - V _rt speed of rapid traverse [m/min] - W volume of material to be removed [mm³] - W _k weight of criterionk, k=1, ...,n - x=[x ₁,x ₂,x ₃ ] ^T vector of decision variables - x ₁ cutting speed [m/min] - x ₂ feed [mm/rev] - x ₃ depth of cut [mm] - approach angle [rad] - _a coefficient of friction in axial direction between workpiece and chuck - _c coefficient of friction in circumferential direction between workpiece and chuck     

A heuristic for a batch processing machine scheduled to minimise total completion time with non-identical job sizes

This paper studies the problem of scheduling semiconductor burn-in operations, where each job has non-identical lot sizes and an oven (a batch processing machine) that processes several jobs within its capacity limit simultaneously. We present some properties of the problem and an efficient heuristic algorithm. In a computational experiment, pairs of burning operations (,) were presented with the arrival time r_i and processing time p_i for different (,) pairs to examine the effect of arrival time and the processing time on minimising the total completion time. The result shows that a ratio of to greater than 1 was superior to other ratios, which can be a guide for schedule planners of burn-in operations. The heuristic obtains a satisfactory average performance rapidly. This revised version was published online in October 2004 with a correction to the issue number.     

铣削加工中心对刀方案及刀具长度补偿措施

数控程序控制机床用刀具对工件加工之前,不仅要定义刀具参考基准相对工件的位置,还必须定义刀具刀位点相对工件的位置。文章分析了不同对刀方案的对刀原理及操作方法、刀具长度补偿措施及应用特点。     

Part family formation by memory association

Most of the part family formation methods are concerned with how to form the families as opposed to how to identify the families. However, a more appropriate approach would be to identify naturally occurring families since these methods are based on the production flow analysis, which uses already implemented routing data. This paper presents a new approach using the memory association of neural networks to identify naturally existing families. The developed system, Feature-Based Memory Association Network (FBMAN), operates by the exhaustive association approach which deals with the difficult problem of exceptional parts. Comparison with the results generated by other methods proves the effectiveness of FBMAN.     

Real-time control and scheduling of flexible manufacturing systems: An ordinal optimisation based approach

A unique real-time control and scheduling framework for flexible manufacturing systems (FMS) is presented in this paper. The framework enables the adoption of different scheduling policies for short-term intervals when responding to the dynamic changes of the FMS shop floor status. Each time when rescheduling is called for, standard clock (SC) simulation is first employed to evaluate the performance of a set of scheduling policies for a short planning horizon. The ordinal optimisation concept is then used to choose quickly the most desirable scheduling policy. Owing to the use of the standard clock technique and the ordinal optimisation concept, this framework accomplishes a dramatic reduction in the time needed for decision making, the essential requirement for real-time control. It is also found that as the scale of the problem increases, the decision-making time increases linearly rather than exponentially. These two important features indicate that this framework has the potential for being successfully implemented in real FMS settings. Although the framework cannot always guarantee the global best performance, the case study indicates that satisfactory performance results are always achieved by using this framework.     

Calculation of tool paths for a torus mill on free-form surfaces on five-axis machines with detection and elimination of interference

Within the framework of a study carried out in cooperation with the Sapex Company, we sought to develop an overall machining program for free-form surfaces on a 5-axis NC machine tool. This program comprises a certain number of general cases that will then have to be adapted to specific situations. In this paper, we present the algorithms allowing the following cases to be dealt with:Positioning a torus mill at a given point on the surface with automatic search for interference between the end of the tool and the surface.Angular correction or the raising of the tool to avoid interference.Calculation of trajectories for a rolling torus mill on a ruled surface resting on a free-form surface of the NURBS (Non Uniform Rational B-Splines) type.The latter can be broken down into two parts:Seeking the axis position on the adjusted surface.Determination of the tool's point of contact on the freeform surface.     

Optical Transmission of Silica Fibers Exposed to γ Rays

The results of a study of the dynamics of an induced attenuation of light in optical fibers exposed to radiation are presented. The doses were as high as 10 and 100 Mrad at dose rates of 10 and 100 rad/s. Two types (silica–silica and polymer–silica) of fibers produced by INFOS (Russia), Polymicro (USA), and Hestibel (Turkey) were investigated.     

Improved Tools for the Turning of Complex Surfaces

The low cutter productivity in the turning of complex discontinuous surfaces is analyzed. New tools with composite cutters are proposed. Thanks to the cutter configuration with respect to the machined surface, the consequences of tool impact on insertion in the workpiece may be minimized.     

并联机床数控加工碰撞干涉检验算法研究

由于并联机床与通用数控机床在结构上差别较大 ,因此在开发与其配套的CAD/CAM系统时 ,考虑到并联机床的结构特点 ,针对哈尔滨工业大学研制的并联机床BJ -30的结构形式 ,提出了并联机床的数控加工碰撞干涉检验算法。该算法较好地解决了刀具过切、少切 ,以及动平台与工件、刀具夹具与工件的碰撞等数控加工中较难解决的问题。仿真结果证明了该算法具有运算速度快、检验效率高等优点     

Optimal number and allocation of controls among serial production stages

A production system comprised of multiple stages in tandem is considered. Each stage may be in either of two states: desirable or undesirable. Each stage may be placed under control so that it remains in the desirable state and produces the maximum fraction of conforming production units. Stages remaining uncontrolled may change randomly from the desired state to the undesired state. The controls may be mechanical or manual but involves costs which may or may not be dependent on the stage being controlled. It is desirable to find the optimal number of controls and their allocation among the stages which will maximise the net profit of production. The problem is formulated as a nonlinear mathematical program with binary variables. For the identical control cost case (independent of the stage to which control is applied), an 0(n) linear runtime algorithm is provided, wheren is the number of stages. It is shown that a k or nothing (wherek is the total number of controls applied) control policy is optimal and depends on a critical cost computed from the given parameters of the problem. In addition, conditions are provided under which all or nothing control policies are optimal. This is based on the computation of a critical cost and is independent of the number of stages in the system. It is shown that when these conditions are met the profit function is pointwise convex ink. Optimal solution techniques are provided and analysed for special cases in terms of the relationships between control cost and production parameters. Sensitivity analysis is provided for each of the parameters of the problem. The solutions are in general robust, with respect to these parameter variations. Numerical examples are provided throughout the paper to illustrate the relevant theorems. The paper ends with a discussion on the general control cost case and some feasible bounds on the optimal solution are offered.     

Performance of Uncoated and Coated Carbide Tools in the Ultra-Precision Machining of Stainless Steel

Ultra-precision machines are widely used to turn aspherical or spherical profiles on mould inserts for the injection moulding of optical lenses. During the turning of a profile on a stainless steel mould insert, the cutting speed reduces significantly to 0 as the cutting tool is fed towards the centre of the machined profile. This paper reports experiments carried out to study the wear of uncoated and PVD-coated carbide tools (carbide tool coated with 2000 alternate layers of AlN and TiN, each layer 1.5 nm and carbide tool coated with 0.5 m TiN, 5.5 m TiCN and 0.5 m TiN) in the ultra-precision machining of STAVAX (modified AISI 420 stainless steel) at low speeds with and without lubricant. A sprayed mixture of compressed air, liquid paraffin oil and cyclomethicone was used as lubricant. Examination of the wear at the rake face of the tool suggests that during machining of the alloy with a hardness of 55 HRC without lubricant, the cutting edge is subjected to high compressive stress, resulting in fracture. Reducing the hardness of the alloy would therefore result in a lower stress acting on the cutting edge, thus rendering the tool less susceptible to fracture. Both the rake and the flank faces of the coated tools exhibited lower wear than the uncoated tools. This was due to the former tools possessing higher fracture resistance owing to the presence of the coating. The lubricant was effective in improving surface finish, preventing surface fracture and reducing flank wear.     

Fast evaluation of cutting forces in milling, applying no approximate models

A new method for fast evaluation of cutting forces in milling is introduced and tested experimentally. Unlike all existing procedures, which include the use of cutting models and approximate assumptions, in this method, the elementary functions of the cutting force are obtained from measured values only.The basic force functions for the whole feed range are acquired from one experiment using a single-tooth full-diameter (slot) milling, applying a specially developed procedure. The milling experiment is conducted under low-impact conditions, enabling accurate measurement and convenient signal processing. The basic force functions are then integrated and superimposed, using known procedures, to combine the total force in any multitooth milling combination. In this work the method is explained and tested experimentally.The suggested method enables a reliable evaluation of the cutting forces, while demanding minimal experimental work, the method applies to cutters having complicated edge geometry, and to high speed milling.Nomenclature a radial depth of cut 0<a<D - feed per tooth ratio 0<1 - d axial depth of cut - D cutter diameter - a/D radial depth ratio - cutter rotation angle - cutter rotation angle [6] - F _x,y,z() instantaneous edge cutting forces in fixture coordinates - F _t,r,z() instantaneous edge cutting forces in tool coordinates - F _x,y,z ^* F_t,r,z tool cutting force components on a multitooth cutter - h instantaneous chip thickness [6] - h* equivalent edge coefficient [6] - r ₁,r ₂ tangential radial ratio coefficient [6] - K _T tangential specific cutting force [4] - K _R radial specific cutting force [4] - N number of teeth - R _r resolution reduction factor - t instantaneous chip thickness - S ₁,S feed per tooth