Press-tool design

The tools used in presses are punches and dies. The punch is attached to the press slide and is moved into the die, which is fixed to the press bedplate. In blanking and piercing, the punch and die are the shape of the required blank and hole and the metal is sheared by passing the punch through the die. In bending, the punch and die are shaped to the required form of the bend and no cutting takes place. In each case, the punch and die must be in perfect alignment. The complete assembly of punch and die is known as a press tool. 

In blanking and piercing operations the work material, placed in the press tool, is cut by a shearing action between the adjacent sharp edges of the punch and the die. As the punch descends on to the material, there is an initial deformation of the surface of the material followed by the start of fracture on both sides. Fig. 16.5. As the tensile strength of the material is reached, fracture progresses and complete failure occurs. 

Work material Clearance per side (% of work-material thickness) 

It is required to produce 50 mm diameter blanks from 2 mm thick low-carbon steel. If a clearance of 6% is chosen, then diameter of die = diameter of blank = 50 mm clearance per side = 6% of 2 m m = 0.12 mm clearance on diameter is therefore 2 x 0.12 mm = 0,24 mm Thus the diameter of the punch is smaller than the die by this amount therefore 

It is required to punch 20 mm diameter holes in 1,5 mm thick copper. If a clearance of 4% is chosen, then 

The shape of the side wall produced by this operation is not straight as in machining operations and is shown greatly exaggerated in Fig. 17.6. The exact shape depends on the amount of clearance between the punch and the die. Too 

In blanking and piercing operations, the punch establishes the size of the hole and the die establishes the size of the blank. Therefore in piercing, where an accurate size of hole is required, the punch is made to the required hole size and the clearance is made on the die. 

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Ismail, H.S. and Hon, K.K.B., 1992. New approaches for the nesting of two-dimensional shapes for press tool design. International Journal of Production Research, 30, 825-837. 

Table 16.1 Typical values of clearance for press-tool design...

In single-punch tablet presses (reciprocating tablet presses), the punches are fixed to the punch holders which travel up and down, and in many cases fixation screws are used. Each make has its own holder design for punches and dies, and consequently for the tooling sets as well. Therefore little can be said in general terms, but it would appear that on the whole the remarks on the rotary press tooling apply correspondingly. 

Fig. 6.7-32 Tooling section of a horizontal isostatic press for the manufacture of tableware preforms a) open section in a free fall horizontal isostatic press, b) the two parts of the die system, c) parts of a raw ceramic bowl and the corresponding tooling design (courtesy Sama, Weissenstadt, Germany)...

Alvarez W (2006) Roll form tool design. Industrial Press, New York... 

When parts are to be blanked from strip material, it is essential that the blank is arranged within the strip to gain the greatest economical use of the material by minimising the amount of scrap produced. The final layout will determine the width of strip, which in turn determines the general design and dimensions of the press tool. 

Walker TJ, Shaw MC. Advances in machine tool design and research. Oxford, England Pergamon Press 1969. pp. 241-252. 

For the realization of complex geometries it may be necessary to use a CCM press which is equipped with pressing units in vertical and in horizontal direction. Alternatively, the pressure application can be realized with a complex tool design. However, there will always be an inhomogeneous pressure distribution inside the tool. This is affected by the profile angles which are mostly different to the direction of the applied pressure. 

Ghabrail, S. R. et (198M) Electrochemical Wirecutting. Proc, 2Mth Int. Machine Tool Design and Research Conf. , Department of Mechanical Engineering, University of Manchester in association with Macmillan Press, pp. 323-8. 

To avoid process problems and damage to adjacent components, there shonld be sufficient clearance in the PCA design to permit room for the pressing tool, board snpports, and use of any associated rework tools. 

The best support will be localized directly under the connector to be pressed. Ensure that the support includes clearance for backside pin protrusion otherwise, pins will stub and bend on the supporting anvil. Support tooling design should carry appropriate rehef features for bottomside components. 

Machine tool builders have traditionally utilized a number of press-fit designs for incorporating studs, bushings, and bearings. Designs of this type require very close tolerances and expensive machining. 

Compacting tools must be propedy designed, constmcted, and fitted to the press. These maybe made of heat-treated steel or cemented carbide, depending on the economics and number of parts to be produced. Carbide tools are more expensive however, they can be used much longer than steel tools. 

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