Hammer support systems using oak timbers may serve as a benchmark to compare other isolation systems. Because the anvil is much more massive than the ram and the blow force is of short duration, the force reduction is very small, usually less than 0.02%. The use of soft isolation systems will slightly decrease the peak force of the blow, an effect of great concern to hammer users. Figure 2 shows the theoretical hammer force relative to an extremely massive anvil that is 100 times as large as the ram. Hammer builders understand that to develop maximum force on the part, the anvil must be much more massive than the ram. Hot open-die blows will generally impart lower magnitude and longer force duration between the ram/part/anvil than a finishing blow. In practice, the magnitude of the blow and its duration can vary significantly. The short time in which the ram contacts and deforms the workpiece is the most important of the hammer’s operation. Relationship of hammer blow force to part deformation Knowing the impact velocity and the falling weight is critical to designing a proper isolation system.įigure 3. If the falling weight is accelerated quickly by the piston, the recoil may unload the isolation system, possibly leading to instability. If the system is traveling downward when the next blow arrives, the blow will increase the amplitude of the downward motion more than the prior hit, possibly overstressing the isolation system. In such systems, sufficient damping must be applied so that there is little or no movement when the next blow occurs. Hammers that accelerate the falling weight by using a piston powered by steam, hydraulic or pneumatic pressure hit with higher blow rates. Their energy capacity may be determined by multiplying the falling weight by the height of the drop, h, as follows: Hammers that operate by picking up the falling mass and releasing it with gravity providing all the acceleration are called drop hammers. The units of energy capacity, E, are Joules for metric and foot-pound force for imperial measure. The impact velocity, Vi, should be in units of m/s or ft/s. The falling mass is calculated by taking the falling weight, w, and dividing by one gravity, g (9.8 m/s 2 or 32.2 ft/s 2 ). The energy capacity is found by the following equation: Most hammers are designed such that the falling weight impacts the workpiece at 6-7 meters/second (18-23 feet/second). Hammer capacity is rated by the energy that can be delivered by the falling mass, which includes the ram and upper die.
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