Flat Strip Springs – Types of Tooling

There are a number of ways flat strip components can be produced, generally depending on the volume required. When a small number of components are required e.g. prototype samples, it is possible to produce most parts without tooling. Wire-eroding can produce development blanks where required, and standard tools can be used to form the parts to the required dimensions. This process is time consuming but allows the customers to have parts without investing in production tooling.

If the volume is larger, components can be blanked out on tooling, and formed in subsequent operations on separate equipment. The tooling cost is relatively small and increases the production speed considerably over the previous process. For medium to high volume production, the flat strip component is manufactured complete on one piece of equipment. The two main ways on achieving this is by using progression tooling or multislide form tools.

When producing parts on progression and multi-slide tooling, the developed components are not completely blanked out. A small section of material is left to carry the part forwards to the subsequent forming stages.

In progression tools the material is indexed forward to each forming stage. As the part progresses through the tool the component undergoes a sequence of forming operations, until the part is fully formed. The last stage cuts out the section of material that has carried the component forward. The tool has to be designed carefully to form the component in the correct sequence (see Fig.1).

This tool forms the finished part in smaller stages. A sequence of features is pressed into the material individually until the finished part is formed. The blank that can be seen in this image shows the gradual development of the part

flat-strip-spring-toolingFig.1: Progression tool for a flat strip spring

In multi-slide tools there is an initial blanking stage, but then the material is indexed forward to where a number of forming slides operate. These slides are able to move forward and backwards along their axis, controlled by either cams or servomotors. On the ends of the slides there are forming tools designed specifically for the component. During the forming operation the slides move inwards in a predetermined pattern, bending the material as desired, and parting the component from the strip. The number of slides employed in this procedure is determined by the complexity of the finished component (see Fig.2).

This type of tooling rapidly creates flat strip springs with complex forms including undercuts

multi-slide-toolFig.2: Multi-slide tool

These tools are complex to design but are able to produce finished parts at very high speed allowing very low unit prices.

Using new CAD technology it is possible to design tooling for strip components precisely and very quickly, allowing us to design the tooling as efficiently as possible.

Article written by David Banks-Fear and published on MDF by kind permission of Southern Springs & Pressings Limited.

David Banks-Fear is a Mechanical Design Forum Group member. He is a technical author and consultant design engineer with nearly 40 years of experience. He and his design team are available to assist with any technical design issues with springs, pressings and precision engineered parts. Email: david@southernsprings.co.uk

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