Forged blocks are some of the most common forgings made. With just three dimensions to protect, the block is also one of the easiest forgings to make.
Block forging consists of starting with billet or bar. The easiest way to estimate material needed for the block is to add the finishing allowances, which helps to guarantee the part can be machined from the block. In most situations, these allowances are 0.250" to 0.500" per side. For instance, if the block needed is 4" x 4" x 6" Long, then the forging size would be 4.5" x 4.5" x 6.5".
Once the forging dimensions have been developed, a billet needs to be selected.
For optimum properties (to receive greatest benefit of forging process), you want a forging that has at least 20% work in it. Some companies will also indicate a MHWR or "Minimum Hot Working Ratio", which helps a forger to understand the total amount of work the piece has received since it was cast.
Calculate the hypotenuse of the width and thickness. For our example the hypotenuse is the square root of thickness squared plus the width squared. SQRT(T^2 + H^2) for ours is 6.36", we use this measurement as a minimum Diameter to match up billet or bar to use.
If you wish to calculate the amount of work the piece would see, it is fairly easy to calculate also - using the original area and the final area of the piece. The effective reduction for this piece would be original area minus the final area, all divided by the original area. Using our example it would be ( PI*r^2 - T*W ) / PI*r^2 = ( 31.769 - 20.25) / 31.769 = 36.2% Reduction.
Superalloy blocks usually have demanding applications in nuclear, aerospace, defense environments. This means that once the forging is made, we usually need to test it for properties. Non-critical applications may only need a hardness verification that the material exhibits similar properties to known samples. Critical applications require a full mechanical test (destructive) that may also entail a stress rupture test to qualify the lot. If mechanical testing is required, a sample piece will be needed to submit for testing. Usually the specification that requires the testing indicates where the sample should be from, and the size of the samples needed. I mention this, as the material for a sample usually requires additional material, which can add to the overall length of the part being made - or in some cases another piece long enough to obtain the sample from. Typical samples can be 6" long, while in some cases a sub-sample of 3" is all that is required. ASME samples require at least 8" of material.