Spring Making Design Considerations

 

• Design a part that meets or exceeds the stated requirements
• Be able to purchase this part from a reliable spring manufacturer at the lowest cost possible

How can he do this? By getting to know his vendors, asking questions, and acquiring an understanding of custom metal parts manufacturing.

After a spring design is reasonably established, review it by using the following check list. Some of the items may seem obvious, but it's wise to have them listed so they are not overlooked.

Designer “Don’ts”

• Don’t specify tolerances that are tighter than is essential to part function.
• Don’t specify tolerances on every dimension. Non-critical dimensions should be reference only.
• Don’t specify material that far exceeds requirements for service (adding unnecessarily to the cost).
• Don’t specify material that is available only on special purchase of a minimum quantity unless there is no other alternative. (If in doubt, consult with the spring manufacturer on this.)
• Don’t specify an AQL more restrictive than necessary for the application.
• Don’t specify load near free height, solid, or at a deflection from the free position.

• Do leave adequate space in the mechanism the spring will work it to adequately house it.
• Do design the spring to proper stress. An unnecessarily low design stress is expensive.
• Do leave the spring maker some leeway in selecting wire size. He may be able to use material on hand, speed delivery, and save special purchase charges.
• Do consider manufacturing economics. Helical compression springs may not need ground ends if the wire size is under 0.020 in., the index is large, or if they work over a rod or in a hole. Use ends on extension or torsion springs that can be made without an extra operation. It is best to consult the spring maker on this for advice.
• Do consider ordering economical quantities. Setups are costly.
• Do consider the special packaging of parts to avoid tangling and distortion, to facilitate handling, or to simplify inventory control.
• Do consider utilizing stock items when only small quantities are needed. Savings in design time, procurement cost, and delivery time could be appreciable.
• Do realize that for small quantities of springs, the cost of raw material per pound is not important. What is important are material availability and minimum quantity restrictions.
• Do realize that for large quantities the precise specification of raw material is of great importance.
• Do realize that the total cost of the part is the installed cost, not just the purchased cost.
• Do consider in your product reliability the relation between part cost, part reliability, and cost of replacement of a broken part.

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