RESEARCH CONCERNING THE WORKABILITY OF METALLIC SHELLS THROUGH FINE BLANKING

Transcription

1 TECHNICAL UNIVERSITY OF CLUJ-NAPOCA FACULTY OF MACHINE BUILDING Eng.Nicuşor Mircea MIHAI Summary of Ph.D. Thesis RESEARCH CONCERNING THE WORKABILITY OF METALLIC SHELLS THROUGH FINE BLANKING Ph.D. Supervisor Prof.Dr.Eng. Gheorghe ACHIMAŞ 2008

2 TECHNICAL UNIVERSITY OF CLUJ-NAPOCA FACULTY OF MACHINE BUILDING Eng.Nicuşor Mircea MIHAI Summary of Ph.D. Thesis RESEARCH CONCERNING THE WORKABILITY OF METALLIC SHELLS THROUGH FINE BLANKING Ph.D. Supervisor Prof.Dr.Eng. Gheorghe ACHIMAŞ COMMITTEE FOR PUBLIC UPHOLDING President: Members: Prof.Dr.Eng. Petru BERCE Dean, Faculty of Machine Building Technical University Of Cluj-Napoca Prof.Dr.Eng. Gheorghe ACHIMAŞ - Ph.D. Supervisor Technical University Of Cluj-Napoca Prof.Dr.Eng. Tudor ICLĂNZAN - Reviewer Politehnica University of Timisoara Prof.Dr.Eng. Octavian C. BOLOGA - Reviewer Lucian Blaga University of Sibiu Prof.Dr.Eng. Dorel BANABIC - Reviewer Technical University Of Cluj-Napoca Dr.Eng. Mihai SUDRIJAN - Reviewer S.C. Uzina Mecanica Cugir S.A. 2008

3 Contents Introduction: 1. CURRENT STAGE OF THE RESEARCH CONCERNING THE SHEET METAL PROCESSING THROUGH FINE BLANKING 1.1 Short history 1.2 Technological elements of the fine blanking process 1.3 Materials used in fine blanking 1.4 The construction of tools for fine blanking 1.5 Presses and fine blanking technological lines 1.6 Conclusions 2. RESEARCH OBJECTIVES AND METHODOLOGY 3. METHODS USED FOR ASSESSING THE WORKABILITY OF SHEET METALS THROUGH FINE BLANKING 3.1 The properties of the raw materials 3.2 Conditions of part separation through fine blanking 3.3 Conditions of limiting the workability of sheet metals through fine blanking 3.4 Conclusions 4. PRELIMINARY STUDY CONCERNING THE FINE BLANKING 4.1 General considerations 4.2 Determining the separation resistance of presses through blanking Separation resistance as a maximum tangent stress Separation resistance according to the mechanical characteristics of the separated material Separation resistance according to other characteristics of the material 4.3 The calculation of forces needed for cutting through fine blanking 4.4 Materials recommended for fine blanking 4.5 Operational stages of the fine blanking System of tools with mobile punches System of tools with fixed punches 4.6 The constructive particularities of the tools used in fine blanking 4.7 The life time of the active elements used in fine blanking 4.8 The quality and accuracy of the parts obtained through fine blanking 4.9 Modeling and simulation of the fine blanking process 4.10 Conclusions 5. SIMULATION OF THE MATERIALS BEHAVIOR IN FINE BLANKING BY USING THE FINITE ELEMENT METHOD 5.1 Generalities 5.2 Fracture analysis in the case of elasto-plastic materials The stages of the fracture Theoretical fracture resistance Griffith theory Griffith, Orowan and Irwin theory 5.3 The implementation of a constitutive elastoplastic model with ductile fracture in the LS-DYNA finite element program Presentation of the LS-DYNA program Equations of the ductile fracture constitutive model Temporal integration of the constitutive equations 5.4 Simulation of the material separation mechanism through fine blanking by using the combination of deformation - pressure and the finite element method

4 5.4.1 Generalities Modeling the ductile damage and fracture Numeric simulation Analysis of the shear band development Analysis of the ductile damage and fracture 5.5 Conclusions 6. LABORATORY EXPERIMENTS FOR CONFIRMING THE PARAMETERS OF THE SHEET METAL WORKABILITY THROUGH FINE BLANKING 6.1 Generalities 6.2 Determining the mechanical parameters of the aluminum based alloys 1050 and 1050A Anisotropy coefficient Hardening coefficient Statistical analysis of the mechanical parameters Determining the number of mechanical tests according to the trust interval Verifying the normality of the distribution Determining the average value when having a known dispersion Average quadratic deviation 6.3 Experimental results regarding the mechanical parameters for aluminum 6.4 Determining the parameters of the hardening law 6.5 Determining the hardness of the parts made through fine blanking using the Vickers method 6.6 Structural characteristics of the parts made through fine blanking 6.7 Macroscopic study on polished and chemically attacked sections of the separation area through fine blanking 6.8 Wearing of the tools used in fine blanking Calculating the wearing of the left slider of the tool Calculating the wearing of the right slider of the tool Calculating the wearing of the die and ejector of the tool Calculating the wearing of the guiding plate and punch 6.9 Conclusions 7. CONCLUSIONS AND PERSPECTIVES FOR CONTINUING THE RESEARCH APENDIX 1 APENDIX 2 APENDIX 3 APENDIX 4 APENDIX 5 APENDIX 6 APENDIX 7 APENDIX 8 APENDIX 9 APENDIX 10 BIBLIOGRAPHY The constructive particularities of punches used in fine blanking Fine blanking- technological aspects

5 INTRODUCTION The PhD theses presents theoretical and experimental studies on the fine blanking process in order to identify a methodology of assessing the sheet metal workability through fine blanking. Present studies certify the need of research in this particular area, in order to identify the complex mechanisms taking birth in the raw material, during the part separation through fine blanking. The analysis of the elasto-plastic fracture of metals is also presented, including the fracture stages, the theoretical fracture resistance and the Griffith, Orowan and Irwin theories. A specific importance is assigned to the implementation of an elastoplastic constitutive model with ductile fracture in the LS-DYNA finite element program. Further on, the LS-DYNA program is presented with the equations of the ductile fracture constitutive model, and also the temporal integration of the constitutive equations. In this way, the simulation of the separation process was possible by using the combination deformation - pressure and finite element analysis. Several investigations were thus possible: the modeling of the ductile damage and fracture, the numerical simulation, the analysis of the shear band occurence, the analysis of ductile damage and fracture. Chapter 1 CURRENT STAGE OF THE RESEARCH CONCERNING THE SHEET METAL PROCESSING THROUGH FINE BLANKING Fine blanking is considered to be the procedure in which, during one operation, planar parts, with smooth cutting surfaces and very small shape and dimensional deviations can be obtained. The processing technologies in the field of fine blanking first appeared in 1923 and were invented by Schiess in Germany. This technology was held a secret for many years, and had some application in the watch industry. In 1950, the first papers mentioning the fine blanking were published, and by the year 1960, the applications in the watch industry were also extended to other industrial domains. Starting with 1970, the applications reached the industry of automobiles, aeronautics, electrical devices, etc. By 1980, over 2800 special presses for fine blanking were used worldwide. Various sheet metal parts, with the thickness of s=1...20mm, can be obtained through this procedure. Finished parts can also be processed; they can have small and medium sizes, simple and complex shapes which would require great expenses if obtained through other procedures (wheels, cams with watch elements, parts of the automobiles, phones, electrical and photo devices, etc.) Chapter 2 RESEARCH OBJECTIVES AND METHODOLOGY The research objective consists in the theoretic and experimental study of the fine blanking process in order to identify a methodology of assessing the sheet metal workability through fine blanking. The strategy of the experimented research includes the following steps: preliminary theoretical study of the process of part separation trough fine blanking experimental laboratory stage industrial scaled experimental stage, with real tools simulating the part separation through fine blanking, with the help of finite element programs. The proposed investigation and study methodology is based on the conclusions revealed by the research of the current stage of the research on fine blanking.

6 Chapter 3 METHODS USED FOR ASSESSING THE WORKABILITY OF SHEET METALS THROUGH FINE BLANKING Workability means the ability of a material to be processed through fine blanking, but also its behavior during the process. Choosing the appropriate material, both from a technological and an economical point of view, must be made according to the constructive - functional requirements for each particular product. The correct choice of the material for fine blanking will be made according to: the conditions imposed to the finished product from a constructive and functional point of view; the conditions imposed by the workability of the sheet metal through fine blanking In this chapter the methods of assessing the workability through fine blanking were defined. Chapter 4 PRELIMINARY STUDY CONCERNING THE FINE BLANKING The process of part separation through blanking operations is influenced by a variety of factors which can be gathered into the following categories: factors that characterize the processed material, such as: physical - mechanical properties, thickness, shape and dimensions of the processed contour; factors depending on the tool construction, the gap between the active elements, the shape of the active contour of the die; factors which depend of the way in which the blanking is executed: speed of separation, condition of the active element edges and the lubrication of the separation area. The accuracy of the parts depends on several factors, representing error sources which appear in the fine blanking process and which are mainly the following: the configuration and dimensions of the part, the characteristics of the punched material, the execution precision of the tool active elements, the condition of the active element edges and amplitude of their wearing, the gap between the die and punch, and also the evenness of its distribution, the type of the tool and its particularities, the flatness of the raw material, the type and condition of the press. The quality of the separation surfaces is evaluated according to their roughness, condition and depth of the superficial hardening layer and edge condition (with burrs or bulges). The main factors affecting the quality of the separation surfaces are: the physical - mechanical characteristics, the condition of the active element edges, the roughness of the punch and die, the size and evenness of the gap between the active elements, the construction and condition of the punch, the material speed of separation. Chapter 5 SIMULATION OF THE MATERIALS BEHAVIOR IN FINE BLANKING BY USING THE FINITE ELEMENT METHOD Both the equations of the finite elements, and those resulting from the application of other calculation methods in the mechanics of deformable bodies, form global systems with a large number of unknown parameters which define the number of equations to be solved. The quick and effective solving of such equation systems becomes highly dependent on the computational technique.

7 The finite method has become a general method for solving different types of complex problems regarding both stationary and unstationary phenomena, in all the areas of engineering sciences. In this chapter we present the finite element method which is applied in the mechanics of deformable bodies. Chapter 6 LABORATORY EXPERIMENTS FOR CONFIRMING THE PARAMETERS OF THE SHEET METAL WORKABILITY THROUGH FINE BLANKING The value of theoretical research increases when it has a practical application in industry, thus becoming a work instrument for the researchers and specialists involved in the field of part processing through fine blanking. The programs and the tests presented in this chapter, with the appropriate adaptations, will hopefully receive the adequate application in the industrial practice to help specialists in solving problems related to the production, the high variety of executed products, which can only ensure the corresponding rentability by using the fine blanking technology. All programs and tests were developed for parts encountered within S.C. Uzina Mecanică Cugir S.A. They have been tested on this parts and their viability has been confirmed by the industrial practice. The field of producing parts trough fine blanking is in a constant development, spectacular changes and modernizations of the equipment are reached in this field of activity, this being proved by the literature published in the past few years. The preparation of production, the planning of the equipment and the technical documentation to be used, all these must be solved in a short time, because of the increasing requirements of the clients concerning the execution time, accuracy and quality of the products. The production of parts using a fine blanking technology is a field where, in the future further results and performances are expected. Chapter 7 CONCLUSIONS AND PERSPECTIVES FOR CONTINUING THE RESEARCH The theoretical research consists in: defining a model of assessing the sheet metal workability through fine blanking; bibliographical study on the current development stage of the fine blanking technologies; evaluating the material theoretical fracture resistance in fine blanking; implementing a constitutive elastoplastic model with ductile fracture in the LS-DYNA finite element program; simulation of the separation process through fine blanking using Schiffmann s model The experimental research consists in: determining the mechanical parameters of the aluminum based alloys, 1050 and 1050A; determining the experimental hardening curves of the two alloys determining the micro-hardness of the materials through Vickers method; determining the structural characteristics of the parts executed trough fine blanking microscopic study in sections of the parts; evaluating the wearing of the active elements and other components of a tool used in fine blanking; determining the punch force vs. stroke variation in fine blanking.

8 The comparison between the experimental results and the numerical predictions of the LS-DYNA program leads to the following conclusions: A valid simulation model of the fine blanking process was established, based on the combined deformation - pressure with finite elements. By comparing the results of the simulation, with the experimental ones it was proved that Schiffmann model is an effective one and that it can be used with good results; The hydrostatic pressure plays an important role in fine blanking. The higher is this pressure, the better is the quality of the parts. When the gap between the active elements is small, the density of the separation work slowly increases in a stable manner. This evolution has favourable effects on the quality of the parts, because the vibrations accompanying the separation process are not so intense. The hardness of the material in the separation area can double its value as compared to the undeformed area, due to the material hardening. No significant structural modifications of the material occur in the separation area. The elongation of the grains in the separation area is small which leads to a good roughness of the separated surface. By applying the simulation of fine blanking, important data is obtained regarding the influence of certain parameters on the separation force and the effects of those parameters on the whole blanking process. The perspectives of continuing the researches: Use of other damage models for simulating the process of fine blanking; Including these models in finite elements programs for the simulation of the fine blanking processes; Implementing more complex hardening laws; Extending the models so that they include the effect of springback; Implementing the simulation model in the industry, in order to optimize the fine blanking processes; Creating a more friendly interface with the finite elements program. The approach presented in the thesis is very general. It can be applied to any type of part with the purpose of its global optimization. Despite the importance and utility of fine blanking, there is still a lack of research in this field both in our country and abroad. Hopefully, the results of the research presented in the thesis will be useful to specialists involved in this field, and that they will be applied successfully.

9 TECHNICAL UNIVERSITY OF CLUJ-NAPOCA FACULTY OF MACHINE BUILDING Personal data Name: Mihai Surname: Nicuşor - Mircea Birth date: Address: RO Cugir 92, Ion Creanga St., Bloc C9 Ap. 7 Phone/Fax: & nicusormh@yahoo.com Nationality: Romanian Current position January present AVAS Bucharest General Manager Experience October June 1997 June June June June Uzina Mecanica Cugir Mechanical Engineer Production coordination and product tracking Uzina Mecanica Cugir General Manager Uzina Mecanica Cugir Production Manager Star Transmission Cugir Technical and Administrative Manager Romtehnica National Company General Manager