Pressing green bodies

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Pressing green bodies is an essential step of ceramic processing. There are many ways of pressing green bodies. This article focusses on axial pressing.

As powder is being handled, make sure to wear PPE and use a hood whereever possible.

Powder properties for good pressing

Pressing green bodies does not work equally well for all ceramic powders. Very coarse powders tend not to give a mechanically stable green body, and very fine powders are difficult to handle due to their low tapping density. Powders with a particle size of 0.5-3µm are generally easiest to press into green bodies. It might be required to add a binder to assure a good mechanical stability of the green body. In this case, remember to remove the binder before sintering by a thermal treatment at 600-800°C in oxidizing atmosphere.

Round Pellets

Quantity of powder

To obtain a given size of the green body after pressing, the amount of powder needs to be approximated. This requires knowledge of the green density and the density of the material itself.

Calculate the Volume of the required green body. Multiply with the green density and the density of the ceramic material itself. the result is the amount of powder required for pressing the green body.

Filling the die

First, the die should be cleaned carefully to prevent contaminations and to assure that no powder particles are squeezed between the die and punches.

Typical pressing die.

The lower punch is put into the die. The desired amount of powder is weighted on paper and filled into the die. Make sure to evenly distribute the powder within the die, e.g. by shaking. Insert upper punch. Put the die into the press. Remember to hold the lower punch.

Weighting the powder
Powder evenly distributed within the die
Die with upper punch.

Square bars

Quantity of powder

To obtain a square face of the green body after pressing, the height of the die must be adjusted using spacers. This requires knowledge of the Shrinkage during pressing.

Filling the Die

First, the die should be cleaned carefully to prevent contaminations and to assure that no powder particles are squeezed between the die and punches.


Place two spacers on top of the long punch and then put the two conical walls, with the smaller side up, on top to form the die. Hold the walls in place with the union ring, the inside of which is also conical. Fill the powder a little bit over the top of the pressing die and secure that the die is filled even. The excess powder is carefully removed with a spatula. Close the die with the short punch and put it in the press. When the press is closed hand tight, remove the spacers.

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An important parameter of pressing green bodies is the pressure. Its selection depents on many aspects:

1.) No Cold Isostatic Pressing (CIP) will be used after axial pressing. In this case, the final green density is only governed by the axial pressing step. Here, high pressures should be selected to assure a good green density.

2.) Cold Isostatic Pressing (CIP) will be used after axial pressing. Then, the axial pressing is only needed for shaping and the final green density will be reached during CIP. In this case, the lowest possible pressure should be chosen.

3.) The powder particle size: fine powders (e.g. D50 < 500nm) require higher pressures than coarse powders. The coarser the powder, the lower the pressure.

If, after pressing, the green body falls apart, this is usually more a sign of too high pressure than of too low pressure. A clear sign of too high presure is a lens-like fracture of the top or bottom surface of the the green body.

The pressing time is not very important, but should be selected such that the maximum pressure stops to drop while the press is not operated. Slowly remove the pressure and take the die out of the press.

Now the green body needs to be removed from the die. This works best in the press. Turn the die upside down and remove the lower punch. Some dies require to put a spacer on top of the die so that the die can be pushed down in a controlled way. Now slowly press the die down while holding it with one hand. Carefully remove the green body e.g. with polymer tweezers.

Removing the green body from the die

Measuring the green density

Measuring the green density is easily done geometrically by calculating the volume from the dimensions. Remember that after Cold isostatic Pressing, the shape of the green body can become irregular so that measuring the diameter and height can be difficult. In this case, measurign the green density is difficult.

Do I need Cold Isostatic pressing?

Cold isostatic pressing (CIP) assures a homogeneously high green density, which is always good for sintering. If there are issues with remaining proosity, inhomogeneous shrinkage or distortion after sintering, is is worth to add a CIP treatment after axial pressing.