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Technical Paper

Towards Further Understanding of the Mechanics of Tube Hydroforming

1998-09-29
982276
The objective of this work is to shed some further understanding into the mechanics of tube hydroforming. Initially this process was developed with the philosophy of forming the tube around the pure shear line, such that the deformation can be obtained with the least changes in thickness. To design a process to achieve this intent is very challenging, considering the complex shapes that are designed. The work starts by examining some simple geometries to provide an understanding and a methodology for the process design. It is shown that by changing the amount of material feed in, the part can be made to split, wrinkle or form around the pure shear line, and hence with the least thinning at the areas of interest. The work also confirmed that the material r value has a major impact on the ability of the material to maintain its thickness in this process; the higher the r value, the better the formability and the less changes in thickness.
Technical Paper

On the Role of Binder Shape for Metal Stampings

1994-03-01
940940
The effect of binder shape on the formability of metal stampings is addressed in this work. The paper starts with a discussion of a binder development approach for developable or near developable binders. An FEM based test for closeness to developable surfaces is also presented. In this case, the binder surface is meshed using standard FEM discretization techniques. The test is used as an evaluator for the proneness of wrinkle formation at the binder closing stage under the binder surface. The formability of a door outer panel is evaluated and the forming severity related to binder shape. It is shown that addendum and binder designs are key process variables that have to be designed up front and related to product characteristics.
Technical Paper

Blank Development and Metal Flow Analysis for Multi-Stage Drawing of Box Shaped Stampings

1991-02-01
910516
Blank development is the basis for calculating the material cost and hence the product cost, at the quoting stage. Understanding the metal flow under the binder is a critical activity during the tooling design stages, as well as during phototyping. The paper describes a computer aided blank development and metal flow analysis system, that will assist in performing the functions described above, before the tools are built, for box shaped parts drawn in multi-stage forming operations with a flat punch face, and a flat binder. Development of the minimum blank shape, using the SLF technique for shrink flanged components is not new. The paper addresses the extension of the approach to: i. multi-stage forming operations and, ii. the incorporation of the effect of thickness changes on the blank shape. Applications are given in the paper using the computer program BLANKDEV.
Technical Paper

From Stamping Engineering to an Alternative Computer-Assisted Environment

1991-02-01
910770
The time and cost to introduce new quality products are emerging as major competitive factors in the world automotive market. The industry will need to achieve substantial improvement, if metal stampings are to be introduced within the time frames being established by major international companies. There will need to be significant advancement in the technology of designing and tooling metal stampings. A present limitation is the lack of predictability in the actual forming operations of metal stampings. To achieve predictable results, without extensive development and trial and error, requires that the present “ART” of tooling development be transformed to an experience-enhanced science based technology. This suggests that an alternative system is required. The alternative system would utilize Computer Aided Analysis Tools. While much work has been done to develop such systems, to date there has been little acceptance by the industry.
Technical Paper

On a Geometric Based Mechanistic Program for Tooling Contact Analysis of Stampings

1991-02-01
910777
It is a well known industry fact, that the geometry of material in contact with tooling, is a major factor which affects its formability. A collary to this is that many problems can be identified and solved using geometry based mechanics approaches. Because of the simplicity in modelling, and hence speed of processing, the geometric based tooling contact techniques are gaining more and more acceptance as tools for product, process and tooling design of automotive stampings. The paper describes the implementation of a stretch/draw formulation of tooling contact, in two dimensions. The formulation is based on a belt friction assumption, with special elements developed to deal with thickness distribution around the contact area. The program tracks the change in the location of the neutral point at every forming step. The program is designed to handle multi-tooling as well as multi-stage forming operations.
Technical Paper

A Methodology for Computer Aided Stamping Engineering

1989-02-01
890502
The stamping engineering process is reviewed in this work, to provide a needs analysis and requirements for computer aided methodologies and methodology based tools for the practitioners in the industry. Although many computer aided tools are identified and are applicable to this “market” driven stamping industry, the demands placed on the background of the practioners, the economics of design and analysis, as well as the lead time constraints, impose further limitations to the use of some computer tools. The work provides an overview of some recent developments of computer aids within the stamping engineering perspective. It is shown that no one computer tool is sufficient to address the stamping engineering tasks, and that emphasis should be geared towards a set of design, analysis, and production maintenance tools that complement each other.
Technical Paper

A Simultaneous Engineering Approach for Automotive Structural Cross Members

1993-03-01
930524
A simultaneous Design/Process/Material engineering approach for the analysis of automotive structural cross member designs is presented. It is shown that it is possible at the product design stages to evaluate i. forming severity, ii. blank shape and nestability, iii. spotting requirements, and iv. structural analysis based on yield stress and thickness distributions after forming. The approach allows the reduction of material content in the part (by nesting and possible weight reduction), a better estimate of part performance during stamping, the evaluation of the effect of the material properties, the construction of the blanking die at the same time as production form tooling, and the reduction of a significant portion of the product design/manufacturing cycle. A production cross member is used to validate the approach. The production cross member information also served as a basis for a new prototype cross member.
Technical Paper

A Die Load Prediction and Die Plate Balancing Technique for the Selection of Presses for Sheet Metal Stampings

1993-03-01
930281
The paper describes a methodology, developed for process engineering at the quoting stage, for matching the press requirements with the tooling requirements in the quest for achieving a quality pressing, with low tooling and press maintenance costs. The starting point is the process plan of the part. The approach is based on subdividing the deformation of the part within a station into elemental deformation regions. The load-displacement diagram for each elemental region is calculated individually, and then totalled to estimate the total load-displacement curve for each forming station. The total energy requirements, as well as the change of the load centre during the stroke for each forming station, is then calculated. The procedure also incorporates the effect of change of timing (e.g. staggering of actions). The approach is then extended for the case of multiple dies acting on the same press (e.g. transfer press and progressive tooling).
Technical Paper

Using Axisymmetric Solutions to Estimate the Forming Severity of Three Dimensional Metal Stampings

1992-02-01
920636
This paper presents several guidelines useful when applying axisymmetric solution techniques to the problem of estimating the forming severity of complex three dimensional stampings. Although the axisymmetric solutions are seemingly restricted in their number of applications, these two dimensional techniques can be used to analyze a wide variety of stamping configurations. However, great care must be taken to ensure that the underlying requirements of Axisymmetry are not “seriously” violated. Presented in this paper are several guidelines, including a discussion of the rationale behind them, suggesting how to apply AS solutions to stretch and shrink flanging stamping operations.
Technical Paper

A Novel Approach for Trouble-Shooting Stamping Problems Based on The Concept of Process Signatures

1990-02-01
900277
The paper introduces the concept of process signatures, the main intention being to change the grid analysis from a merely data processing activity to a knowledge based methodology. The process signature is the shape of the strain envelope, which depicts the strain state of contiguous elements on the surface of a stamping. The signature is strongly influenced by the tooling geometry, process induced modes of deformation, and to a lesser extent by the lubricating conditions, material characteristics, etc. Essentially the deformation of the whole part can be analysed by subdividing it into the fundamental modes. It is shown that the total response of a stamping depends on certain combination of these basic fundamental signatures. Distinct areas on the signature correspond to the punch and die actions. The work demonstrates that the process signatures respond in a predictable fashion to changes in tooling, material and set up.
Technical Paper

Understanding Blank Holder Effect on Formability of Sheet Metal Stampings

1989-02-01
890347
Blank holder design, set-up and maintenance are crucial for successful stamping of sheet metal parts. Educated spotting as well as adjustment of the appropriate levels of blank holder forces at the different contact areas is a complex process involving the interaction of die design, die making, prototyping and set-up. The response of the part to a blank holder set-up depends on the type of press and the source of blank holder action. A finite difference based microcomputer program CUPDRW will be used to illustrate the effect of the type of blank holder and its set-up on the formability of circular drawn shells. A methodology is also presented in this work for the design of blankholders and its set-up for complex parts formed under drawing conditions. It has been recognized by the industry that control of process and material windows is a prerequisite to the production of quality parts.
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