https://orbit.dtu.dk/files/5556704/2010_Keynote_FR21.pdf

Environmentally benign tribo-systems for metal forming

Evaluation of tool materials, coatings and lubricants in forming galvanized advanced high strength steels (AHSS)

Analytical model for planar tube hydroforming: Prediction of formed shape, corner fill, wall thinning, and forming pressure

An experimental investigation has been carried out to determine the effect of extent of deformation (ironing) over the cup wall at elevated temperatures. Clearance between punch and die is varied to decrease the amount of deformation over the cup wall. The thickness distribution of the drawn cups at different temperatures and clearance is studied and it is found that even at elevated temperatures there will be a certain limit unto which clearance between punch and die can be decreased. For EDD steel sheet of 2 mm thickness this temperature appears after blue brittle regime in which material exhibits unusual strength. In this region punch load requirements increases which leads to necking at the punch corner and finally fracture in the initial stages of drawing operation. Upon increasing the clearance the quality of cups are similar to that in case of deep drawing operation.

A study on the extent of ironing of EDD steel at elevated temperature

Galling is a known failure mechanism in automotive stamping. It results in increased cost of die maintenance and scrap rate of products. In this study, rectangular pan and U-channel stamping experiments are used to (1) investigate the effect of stress states on galling performance in sheet metal forming, (2) select proper tool materials and surface treatments for improved galling properties, and (3) differentiate galling performances of bare and coated steel sheets. The results indicate that problems with galling are of major interest at the regions where sheet materials deform under the action of compressive stress. For the four investigated tool materials, Mo–Cr alloy cast iron shows the best galling performance. A combination of hardening, surface polishing, and Cr coating is suggested as the optimum tool treatment in the forming of bare high-strength steel. Hot-dip galvanized steel shows better galling behaviors than galvannealed and bare steel sheets. Galling performances of hot-dip galvanized and bare steels are improved with increased hardness of the forming tool. However, galvannealed steel results in severe galling when the hardness of the forming tool is very high.

Selection of tool materials and surface treatments for improved galling performance in sheet metal forming.

Lubricants are employed in stamping operations in order to (a) improve the material flow into the die cavity, (b) reduce wear and galling in the die and (c) obtain good surface finish of the part. Process conditions such as high temperatures and pressures could cause the lubricant to fail, thus resulting in galling or tearing of the part, damage to the tooling, and lost production. Therefore, selection of an appropriate lubricant based on the process conditions is important in the stamping industry. Several benchmark tests emulating stamping operations have been developed and are used to evaluate the performance of candidate lubricants. The major drawback of most of these tests is their inability to emulate high contact pressures and sliding velocities, which are crucial parameters for lubricity, especially in the case of high-speed progressive or transfer die operations involving ironing. Moreover, most of these tests are conducted at room temperature, while in reality; the process temperature can reach as high as 200 °C. The ironing tribotest developed at the Engineering Research Center for Net Shape Manufacturing (ERC/NSM) induces high contact pressures and temperatures, thus emulating the conditions in a production environment. Application of the test to screen candidate lubricants for stamping operations involving the ironing process is discussed in this paper.

Evaluation of stamping lubricants at various temperature levels using the ironing test

A methodology for progressive die sequence design for forming round cups using finite element method (FEM) based simulations is discussed. The process sequence design developed was applied to forming of an automotive part and was compared with the design obtained from past experience. The methodology proposed in this paper has shown that the integration of design experience and FEM simulations can enhance the robustness of the procedure for die design sequence and reduces the die development cost considerably.

Nitin Jain

Papers

Evaluation of stamping lubricants at various temperature levels using the ironing test

Progressive Die Sequence Design for Deep Drawing Round Cups Using Finite Element Analysis

Progressive die sequence design and blank shape determination in stamping