Selecting Die Springs A general rule to observe in spring selection is to always use as many springs as the die will accommodate which will produce the required load with the least amount of deflection. This will increase the useful life of the spring, reduce the chances of spring failure and resulting downtime, loss of production and increased maintenance costs. Die springs costs are a very small percentages of the total cost of the die. An effort to save a few cents on die springs is a misguided act that can cost many dollars in lost time and labor. The more rapidly a spring works, the more attention must be paid to its fatique limits. In slow moving dies or fixtures, it is possible to get good performance with springs operating near maximum deflection. As the working speed increases, the life expectancy of the spring at that deflection decreases. When selecting a die spring it is necessary to determine the type of performance required of the springs: short, normal or long run. Another approach when selecting a spring is to work back from the amount of operating travel the springs will be subjected to as indicated by the die layout. Select springs in the appropriate pressure range which will operate efficiently at the required travel. Calculate the number of springs needed by dividing the load supplied by one spring into the total load required. Round the total number of springs to the next higher even number for balance performance. Correct Die Spring Usage Some spring mounting do's and don'ts are below. For optimum performance, die springs should be mounted in flat bottomed holes. These holes should be at least two coils deep. When mounting springs over a rod, the rod should be long enough to fully support the spring's I.D., thus minimizing bending. Bending results in early breakage. Do perform preventative maintenance on dies on a regularly scheduled basis. Records should be kept on the number of cycles performed by the die. Die springs should be replaced at predetermined intervals to prevent expensive downtime. Do provide proper guidance to reduce buckling. All Producto springs are designed to work within hole sizes and over standard rod sizes. Care should be exercised in mounting springs. Do preload each spring in the assembled tool to prevent the possibility of shock loading which causes a stress surge in the vibration frequency resulting in spring failure. Do provide spring safeguards from adverse external elements such as heat, corrosive atmosphere, metal chips and other obstructions. Do deepen the spring pockets proportionately when the die is sharpened in order to maintain the same spring travel and load level. Don't wait until the die is built to determine which springs and how many are needed. Make spring selection a part of the design function and work within the spring's physical limits. Don't expect maximum performance life from a spring that is producing a maximum load. Don't replace only one spring in a die. Replace all of the springs to distribute the loads evenly over each spring instead of an unbalanced assembly of new and old springs. The small extra investment will pay dividends. Don't mix springs of assorted lengths or springs with different deflection ranges on the same die section. Don't alter a die spring by cutting off coils or grinding the inside or outside diameters. This causes early spring failure and potential die damage.