Dimensional Workpiece Research Articles

Numerical prediction of machining induced residual stresses when hard cutting AISI 4140

In today’s manufacturing industry, there is a clear focus not only on the accurate manufacturing of geometrically dimensional workpieces but also on maintaining strict tolerances on workpiece rim zone properties. These workpiece rim zone properties, such as grain sizes, deformation zones or, in particular, residual stresses, are generally summarized under the term Surface Integrity. While changes in the Surface Integrity properties of the machined surface can have positive effects, such as compressive stresses induced by hammering, there is at the same time a risk of lasting damage to the rim zone due to a negative change in these properties. As a consequence, a weakening of the workpiece rim zone may later on lead to component failure. For this reason, the design of manufacturing processes for safety-critical components according to the current state of the art is complex, time-consuming and cost-intensive, as it is largely empirical and based on experience. Knowledge-based prediction of process-induced changes in Surface Integrity changes, on the other hand, enables process design times to be shortened and process quality to be increased at the same time. The basis of such a knowledge-based process design is, on the one hand, the knowledge of the physical interactions and, on the other hand, an adequate description of these interactions within the framework of either analytical or numerical models. With the aim of predicting the occurring residual stresses after hard machining of hardened AISI 4140, a numerical chip formation and residual stress model is presented in the following paper and subsequently validated with the aid of experimental test data.

DEVELOPMENT AND RESEARCH OF PROMISING SCHEMES FOR DIVIDING PIPES INTO DIMENSIONAL BILLETS

The purpose of this work is to study the known method of division of pipes by introducing a figure knife and the development of promising designs of equipment for division of pipes into measured workpieces. Based on the analysis of the actuating crank-slider mechanisms used in the equipment for division of pipes into measured workpieces, promising schemes of short-connecting rod mechanisms have been discovered that provide a local pipe section along the perimeter. The developed design of the device for dividing pipes into dimensional workpieces by the eccentric twisting method, which contains a wedge-joint mechanism in combination with a compact circular actuator, also allows to reduce energy and power costs for separation, reduce the consequences of instantaneous unloading of equipment and ensure high quality workpieces. A mathematical model of the proposed equipment was developed and the modeling of the cutting process was carried out using the DEFORM-3D software package. The analysis of the results obtained showed that in the extreme positions of the knives, jamming of the knives is possible. To eliminate jamming, it is necessary that the knives do not reach the extreme position. The adequacy of the mathematical model is confirmed by experimental studies. The error of the calculated and measured values of the torque on the cutting knife does not exceed 10%. This is due to the need for a more correct accounting of friction on the contact surfaces of the equipment. Cut tubular blanks have high geometric accuracy and high quality of the cut surface.

Relationship of the method of obtaining the original billet with the accuracy of manufacturing of the extended axisymmetric bodies

A comparative description of the technology for producing blanks for the artillery shell cases or the rocket shell bodies using flat rolled stock or rolled tubular products is given. It is noted that the lower cost of flat rolled stock leads to its wider application for stamping blanks of cartridge caps or bodies, including cutting a circle from flat rolled stock, convolution and several transitions of drawing, alternating with heat treatment. It is noted that the disadvantage of this technology are the errors in the shape of the blanks, amounting to 0.75÷1.5 of the tolerance for diametrical dimensions. When machining, these errors decrease according to the laws of copying the errors, however, the anisotropy of the material of the part blank leads to the appearance of errors in the shape-ovality and curvature of the pipe, which lead to the formation of a large radial runout of the prefabricated rocket body. It has been found that the scattering fields of all output quality parameters exceed the existing tolerances: radial runout of the assembled body by 1.3 times; ovality of the middle centering bulge by 2.15 times. It is shown that the technological process of manufacturing prefabricated housings using initial blanks from flat rolled stock does not provide the required precision technology reliability. For the manufacture of monolithic extended axisymmetric bodies, hot-rolled thickwalled pipes are used as an initial billet. The operations are performed in the following sequence: cutting pipes into dimensional workpieces; machining (turning, boring); heat treatment (quenching, tempering); machining (fine turning, boring); rotary drawing (first and second transitions); crimping the thickening; low temperature annealing. Statistical studies have found a regression equation showing at a confidence level β = 0.95, dependence of the diameter of the base hole of the workpiece after drawing in from the current value of the diameter before drawing.

Investigation of dimensional accuracy in incremental sheet metal hammering process: a parametric study

With the increasing demand for low-volume production, the incremental forming process is developed as a rapid prototyping method. Incremental sheet metal hammering method has been used in recent years. In this process, a sequence hammer moving over a clamped Aluminum sheet and a three dimensional workpiece can be produced by using a simple die. In this paper, the influence of the punch diameter on the dimensional accuracy was studied. This component was divided to four sections: thickness, overall geometry, surface quality and spring-back. By using the image processing and roughness tester, the values of results were obtained and analyzed. The results had revealed that the surface roughness and spring-back were decreased by decreasing the punch diameter. Overall geometry was deviated from the ideal shape by increasing the punch diameter.

Optimization of machining fixture layout for tolerance requirements under the influence of locating errors

Dimensional accuracy of workpart under machining is strongly influenced by the layout of the fixturing elements like locators and clamps. Setup or geometrical errors in locators result in overall machining error of the feature under consideration. Therefore it is necessary to ensure that the layout is optimized for the desired machining tolerance for a given deviation in the set up or geometry of the locator. Also, the locator layout should be capable of holding the workpart in a unique position during machining thus providing deterministic location. This paper proposes a Genetic Algorithm (GA) based optimization method to arrive at a layout of error containing locators for minimum machining error satisfying the tolerance requirements and providing deterministic location. A three dimensional workpiece under the 3-2-1 locating scheme is studied. Results indicate that by optimally placing the error containing locators the geometric error component of the machining error can be substantially reduced thus enabling compliance to overall dimensional requirements. Keywords: Machining error, optimal layout, locator error, genetic algorithm

Joint allocation of measurement points and controllable tooling machines in multistage manufacturing processes

Stream of variations (SoV) modeling of multistage manufacturing process has been studied for the past 15 years and has been used for identification of root causes of manufacturing errors, characterization and optimal allocation of measurements, process-oriented tolerance allocation, fixture design, and operation sequence optimization. Most recently, it was used for optimal in-process adjustments of programmable, controllable tooling (controllable fixtures, CNC machines) in order to enable autonomous minimization of errors in dimensional product quality. However, due to the time and resources needed to take the measurements and the high cost of controllable tooling, it is plausible to strategically position such measurements and controllable devices across a manufacturing system in a way that the ability to mitigate quality problems is maximized. In this article, a distributed stochastic feed-forward control method is devised to optimally (in the least square sense) reduce the variations in dimensional workpiece quality with a limited number of controllable tooling components and measurements distributed across a multistage manufacturing process. Based on this, a reactive tabu search algorithm is proposed to enable joint optimal allocation of measurement points a controllable tooling devices. Theoretical results are evaluated and demonstrate using the SoV model of an actual industrial process for automotive cylinder head machining.

超硬金型の自動ラッピングシステムにおけるラップ剤の最適化とその評価(機械要素,潤滑,工作,生産管理など)

Recently the dies with cemented carbide are used for many products using its high stiffness and high wear resistance. The hand lapping is even now used as finishing process of them because of difficulty of its mechanization. The new lapping system was developed in our previous study from these reasons. And the lapping system could machine to flat surface of cemented carbide (V10) with mirror-like surface. In that case, mixture of diluted starch syrup and diamond grain was used as lapping slurry. However, this slurry can machine only flat bottom surface because of dropping the grain for lapping. So, it has to improve for the lapping to three dimensional work pieces including vertical surface, concave-convex surface. In this study, the mixture of polymer material and diamond grain was used as new lapping slurry for suspending the diamond grain using special properties of polymer. The distribution density of grain in the slurry medium was researched by experiment. Relationship between the lapping condition and the grain retention propaties on tool head was researched. Finally improving the surface roughness of large work piece was confirmed. It is concluded from the results that; (1) New lapping slurry with polymer can keep the diamond grain while enough time for machining. (2) The best lapping condition was confirmed from TAGUCHI methods and experiment. (3) New lapping slurry can be used for lapping the mirror-like surface of large or complex dies.

플라스마 이온증착 기술을 이용한 스테인리스강의 질화처리에 관한 연구

Plasma immersion ion beam (PIIB) nitriding process is an environmentally benign and cost-effective process, and offers the potential of producing high dose of nitrogen ions in a way of simple, fast and economic technique for the high plasma flux treatment of large surface area with nitrogen ion source gas. In this report PIIB nitriding technique was used for nitriding on austenite stainless steel of AISI304 with plasma treatment at 250~500℃ for 4 hours, and with the working gas pressure of 2.67 × 10SUP-1/SUP Pa in vacuum condition. This PIIB process might prove the advantage of the low energy high flux of ion bombardment and enhance the tribological or mechanical properties of austenite stainless steel by nitriding. Furthermore, PIIB showed a useful surface modification technique for the nitriding an irregularly shaped three dimensional workpiece of austenite stainless steel and for the improvement of surface properties of AISI 304, such as hardness and strength

Recent Advances in Mechanical Micromachining

This paper reviews some of the main drivers, developments and future requirements in the field of micromanufacturing as related to the machining process from the perspective of the recent research and development literature. For the purposes of this paper micromachining includes creation of precise two and three dimensional workpieces with dimensions in the range of a few tens of nanometers to some few millimeters by cutting using defined geometry cutting tools. The review includes topics of process physics, including materials and microstructural effects, machine tools, tooling and sensing, workpiece and design issues, software and simulation tools, and other issues, e.g. surface and edge finish, and outlook for future developments.

A cutting force induced error elimination method for turning operations

The aim of this study is to compensate the cutting force induced dimensional workpiece errors in CNC turning operations. In realising this, a strain gauge based cutting force dynamometer is designed and constructed. Cutting forces are measured and recorded by a computer for standard specimens under various machining conditions. Empirical equations between the diameter errors and cutting forces are established experimentally. A compensation method based on computer-aided generation of an alternative tool path, which is symmetrically inversed to error characteristics, is developed. The model was developed initially for unidiameter case and then adapted to other workpiece geometries. The validity and reliability of the compensation method is examined by the Chi Square test method. The developed approach reduced the cutting force induced workpiece diameter error by 90% approximately.

Motion Planning for a Cutting Task Based on Criteria of Skilled Operators.

This paper proposes a motion planning method for cutting a three dimensional workpiece by a redundant robot arm. The method applies a genetic algorithm to optimize rotational angles of the end-effector on a path which is a redundant parameter. For a fitness function, an evaluation function is defined based on references from skilled operators. The proposed method reduces the operator's efforts, so that he only has to determine a path without considering redundant parameters. Through simulations and experiments the effectiveness of the proposed method is demonstrated.

New system of electrochemical form machining using universal rotating tools

A new system of electrochemical machining (ECM) of three dimensional workpieces using universal tools has been developed. This paper explains the new system and reports on its development and experimental results. The system has been patented.