Cup Wall Thickness Research Articles

Stretch-drawing of titanium sheets

Stretch-drawing is a type of the popular deep-drawing process, which utilizes a sharp die shoulder of less than three times the sheet thickness, whereas the conventional process adopts about eight times. When the sheet slides over the die shoulder it is subjected to a strong bending under tension and thus the sheet becomes thinner to yield a deeper cup. Titanium is paid much attention to for its lightness and property of anti-rust. Here, its ability and behavior in the stretch-drawing process is investigated in detail. Two kinds of pure titanium and one of its alloys are tested, of which the thickness is commonly 0.5 mm. It is evidenced that the merit of stretch-drawing or bending under tension is remarkable for titanium sheets as much as for other metals. The variation of the cup wall thickness with the die profile radius, and the relationship between the blank diameter and the depth of formed cups are clarified. The shape quality of the formed cups is also inspected, especially regarding the roundness and the three-dimensional radius distribution of the cup wall cross-section. The former indicates the level of deviation of any cup cross-section from an exact circle, and the latter the global distortion pattern of the cup. The shape quality of a stretch-drawn cup is confirmed to be better than that of a deep-drawn cup. Furthermore, the measurement of the shape implies that its feature depends on the planar anisotropy of the sheets tested.

Development of a combination punch speed and blank-holder fuzzy control system for the deep-drawing process

To improve the productivity and formability of sheet metal having strain rate sensitivity, a new control system using a combination punch speed and blank-holder fuzzy control for the deep-drawing process is proposed. The control algorithm is based on an alternate switch mode system of both blank-holding force (BHF) and punch speed (SPD) control. A newly developed deep-drawing apparatus with the novel control system achieved on-line simultaneous fuzzy control on both BHF and SPD during the process. The experimental results for a steel sheet show that higher speed deep drawing can be successful at the SPD over 150 mm/min, at which fracture occurred under constant SPD condition. In addition, it was confirmed that the new combination of SPD and BHF fuzzy control system increased high performance productivity with 25% forming time reduction. Cup wall thickness distribution was also improved and deep drawability, beyond that for a constant SPD.

Hydrodynamic lubrication of the ironing process

AbstractA theoretical model is presented to calculate the lubricant film thickness in an unsteady hydrodynamic lubrication of cup‐shaped products to be formed by the ironing process. The model covers the development of hydrodynamic lubrication in various phases of the ironing process. The model provides equations for estimating the lubricant film thickness for each phase.Experiments were conducted to study the effect of lubricant viscosity on die expansion and punch force in making cup‐shaped products by the ironing process. It was found that the die expansion varied between unlubricated and lubricated cups and depended on the lubricant viscosity. The film thickness was estimated from the difference between the increased die/punch clearance, which was calculated from the expansion, and the lubricated cup wall thickness. The theoretical film thickness was compared with the estimated film thickness based on the die expansion measurement.

Optimum Blank Shapes for Prismatic Cup Drawing—Consideration of Friction and Material Anisotropy

A theory employing the concept of potential flow and an easily implemented numerical method are developed. It can offer a preliminary prediction of the optimum blank shape with a little computational effort. The effects of the material anisotropy and the interfacial friction between the workpiece and blank holder on the material flow can be modeled by superimposing a “sink” or “source” term in the potential field. Variations in the cup wall thickness are considered. Both convex and non-convex punch profiles are studied. Generally speaking, the contours of the present theory are smoother than the solutions from the slip-line method. The discrepancy of the optimum blank contours between the plane strain and anisotropic cases is more significant for polygon and irregular cup drawing. The influence of friction on the optimum blank contour is not negligible.

Product thickness analysis in pure cup-drawing

An analytical model is developed to estimate the variation of wall thickness of a drawn cup in a pure bending-drawing process, the model including both non-linear strain-hardening and frictional force between blank and die. The theoretical prediction of cup wall thickness is in agreement with the results of experimental measurement. The reduction of the friction coefficient between the blank and the tooling surfaces reduces the stretching effect and the thinning of the wall of the cup, conversely a high value of the friction coefficient and high strain-hardening enhancing the stretching effect and thickness reduction, particularly at the outside edge. The validity of the theoretical analysis has been investigated by experiment, the theoretical prediction of the variation in the wall thickness of the cup being in agreement with the results of experimental measurement.

Experimental and theoretical investigation of the flexible-mandrel ironing process

Ironing is a cold-forming process used for reducing the wall thickness of a cup without changing its internal diameter. Whilst ironing with a rigid mandrel is well established in practice, ironing with a flexible mandrel may give several advantages. The aim of the present study is to investigate the feasibility of using a flexible mandrel, and to study the effects of various process parameters such as the die semi-cone angle, the mandrel hardness, the ironing ratio, the cup wall thickness, etc., on the flexible-mandrel ironing of thick-walled non-ferrous cups. Both experimental and theoretical investigations have been carried out to study the process. Flexible-mandrel ironing is similar to the conventional ironing process except for the construction of the mandrel. In flexible-mandrel ironing the metallic mandrel is replaced by a rubber mandrel, which helps in reducing the cup wall tension, permitting higher ironing ratios. The other advantages include minimization of galling, elimination of the stripping problem, less set-up cost, etc. The mandrel hardness plays a significant role in controlling the amount of redrawing, whilst lubrication on the mandrel side has less effect. A theoretical model using the upper-bound method is developed to calculate the energy required for the process. The optimum die-angle obtained with the theoretical analysis is found to tolly weith that obtained experimentally.

4872921 Sheets of aluminium alloy containing magnesium, suitable for producing bodies of cans by drawing and ironing, and method of obtaining said sheets : Didie Teirlinck, St Egreve, France assigned to Cegedur Societe de Transformation de l'Aluminium Pechiney

Ironing is a cold-forming process used for reducing the wall thickness of a cup without changing its internal diameter. Whilst ironing with a rigid mandrel is well established in practice, ironing with a flexible mandrel may give several advantages. The aim of the present study is to investigate the feasibility of using a flexible mandrel, and to study the effects of various process parameters such as the die semi-cone angle, the mandrel hardness, the ironing ratio, the cup wall thickness, etc., on the flexible-mandrel ironing of thick-walled non-ferrous cups. Both experimental and theoretical investigations have been carried out to study the process. Flexible-mandrel ironing is similar to the conventional ironing process except for the construction of the mandrel. In flexible-mandrel ironing the metallic mandrel is replaced by a rubber mandrel, which helps in reducing the cup wall tension, permitting higher ironing ratios. The other advantages include minimization of galling, elimination of the stripping problem, less set-up cost, etc. The mandrel hardness plays a significant role in controlling the amount of redrawing, whilst lubrication on the mandrel side has less effect. A theoretical model using the upper-bound method is developed to calculate the energy required for the process. The optimum die-angle obtained with the theoretical analysis is found to tolly weith that obtained experimentally.

Research on extrusion process with effective stick friction. (2nd report, Experimental investigation of forming of cylindrical thin-wall cup)

Using three kinds of round bar work metals 5 mm in diameter, cylindrical cup-forming was examined in the tribo-extrusion proposed in the first report and the backward extrusion. The punch pressure pm in the tribo-extrusion of the aluminium and the copper was about 30% lower than that in the backward extrusion. The pm in the tribo-extrusion of low carbon steel was about 2.1∼2.35 GPa within the range of reduction of area of 70∼97%, while it was impossible to finish the cup owing to the danger of punch failure by the backward extrusion. The relative punch pressure pm/Y in the tribo-extrusion of copper and low carbon steel ranged from 2.5 to 4, and these values were approximately consistent with those predicted theoretically. The cup surface was finished without galling, and the surface roughness Rmax was about 0.5∼1.8 μm, regardless of the dry frictional condition. The cup wall thickness also was produced with a relatively high accuracy.