Designing of Die Block in Press Form

Points Covered

  • Introduction.
  • Designing of Die Block.
  • Process of making 1800 Press Form Points to be Covered.


  • Rubber parts are used in aircraft.
  • Rubber parts are moulded under heat and pressure in a die.
  • The dies or moulds are commonly called as Press Forms.
  • Moulds are made from mild steel by machining, milling and finishing by hand.

Designing of Die Block

  • Design of die block depends upon work piece size and thickness.
  • Overall dimensions of the die block will be determined by the minimum wall thickness of the die required for strength.
  • Sharp corners may lead to crack during heat treatment, therefore it requires greater
  • Two dowels should be provided in each block, for accurate and permanent positioning.
  • Thickness of the die block depends upon the size of the seals to be manufactured.
  • The minimum thickness of the die should not be less than 12.5mm.
  • In the process of rubber moulding, the accuracy of the product depends upon the construction of the dies.

Process of making 180 degree Press Form

  • The two pieces or a split die is most common.
  • Two-piece dies are turned on lathe first.
  • It is always not necessary that all dies are in circular form.
  • It may be in rectangular form also. Special care must be taken for the alignment of the dies every time.
  • Alignment of dies can be achieved by guide pins and dowels.
  • Guide pins are preferably larger in size, to avoid confusion in assembly.
  • Die plates are ground on the faces to keep the thickness uniform for proper profiling and grooving.

Manufacturing of 180 degree Dies

  • Drawing is studied and dimensions such as pitch circle diameter (PCD) and tool thickness are calculated.
  • Raw material for female part is held in lathe chuck, faced and turned. Parallelism of the block is maintained by measuring at three to four places using micrometer of required range.
  • Blank is prepared by taking finishing cut on face of female part and removing from the chuck.
  • The male part of the press form is held in lathe chuck, faced and turned and blank is manufactured.
  • Remove the male blank from the machine. Compound slide is set at an angle of 15 degree and taper bore upto 8 to 10 mm length is made.
  • Female blank is held in chuck.
  • Its concentricity and perpendicularity are adjusted within 0.01 mm using dial test indicator. Undercut of 7 to 8 mm depth and upto 8 mm width is made for facilitating separation of die blocks.
  • Compound slide is set parallel to the jobs axis.
  • Required tool of specific thickness is set to centre height using height gauge, and parallelism of tool is set with dial test indicator.
  • Under cut dia is measured and tool advancement is calculated as per formulae.
  • Tool advancement = (1/2 OD) – (1/2 PCD) + R
  • Where, OD = Step dia of block (under cut dia) PCD = Pitch circle dia R = Half of cross sectional thickness of seal Manufacturing of 1800 Dies

Observe The Following Points

  • Take reference of step down diameter.
  • Tool is advanced as per calculated amount using cross slide and cross slide is locked in position.
  • By advancing saddle of machine, tool is brought in contact with face of block and saddle is locked.
  • Groove is cut to half of ‘O’ ring thickness by using compound slide. Measurement is taken by DTI.
  • Groove is polished using lapping compound.
  • Without disturbing the saddle and cross slide, the female part is removed. Pre-made male part is held and trued by using DTI.
  • With same set up, the groove is cut using compound slide and DTI. Extra groove on either sides of main groove is given to accommodate extra rubber.
  • Compound slide is set at an angle of 150 and taper fitment is given to suit the female part. Further, press form number is punched.
  • Thermometer hole is drilled by holding press form on drilling machine. Dispatched to rubber seal for further process.

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