Die Shut Height—Not Always a Single Setting
March 31, 2022Comments
Setting the press shut height correctly during the die-change process proves critical for part quality and prevention of damage to the die and the press. Set blocks usually mount inside of the die assembly to assist with fine shut-height adjustments. Most dies feature two to four set blocks, but small dies may house a single block due to limited space inside of the die.
When dies require parallels, set blocks must be positioned directly over parallels to support any excess force applied to the set blocks by the upper die. This often is referred to as ‘over-hitting the die.’ Parallels under the set blocks reduce the likelihood of a permanently bent or distorted die shoe.
Set blocks may be round, square or rectangular. The overall height may be incorporated into a single block or divided between an upper and lower block, with the setting surface completely flat or containing a machined groove.
Set blocks sometimes are referred to as stop blocks. I discourage use of the term ‘stop blocks’ as it creates a false sense of security on the shop floor—implying that accurate shut-height adjustments are not critical because the ‘stop blocks’ will maintain proper shut height.
A Single Shut Height May Not Suffice
The inside shut height of the die shown in Fig. 1 is established by adding together the form-punch height, the draw-pad height in the home position and the minimum thickness of the part being formed. When part thickness is greater than minimum, the upper will not reach the set block when the lower pad reaches its home position, creating a difference in shut height.
Unfortunately, many die setters have been trained to set the die shut height by bring the ram down (with the die stations fully loaded) until the upper die just touches or ‘kisses’ the set blocks. This usually is accomplished by placing a thin film of grease on the top of the set block and looking for it to transfer to the upper die half.
When running thin metals with a total thickness variance of 0.002 in., the shut-height difference may not be much of an issue. However, when running 0.100-in.-thick hot-rolled steel (per ASTM A1011), expect a thickness variance of as much as 0.016 in. In this case, bringing the ram down onto the set blocks results in significant tonnage increases, which may greatly exceed the calculated tonnage for that die. A press without a tonnage monitor provides no way to know if press capacity is being exceeded. Even for material procured to half-standard tolerance (0.008-in. variance), this still represents a considerable amount of overhitting on the die, especially when forming stainless steels and higher-strength steel grades.
Unfortunately, no industry standard describes how to establish the set-block height, the depth of the solder-check groove or procedural steps for making final shut-height adjustments. Fig. 2 provides one option that allows a die setter to set the die shut height relative to material thickness. 
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