Tecnical information
Technical information about springs
Production
Coil springs have been made by Lesjöfors since 1852. These days, the group has 14 manufacturing facilities, each one of which is specialised for its market and its product range. We make all types of springs, except for air, plastic and rubber springs. Flat thickness range from about 0.05 mm up to about 3 mm and wire diameters from 0.03 to 65 mm.
Material
The spring material is selected to suit the application and the demands made on the spring. Cold drawn wire is generally used for uncomplicated springs and normal temperatures. Copper alloys are often used for contact springs with demands for resistivity. Stainless is often used for more difficult environments. Tungsten alloys are used for certain medical components. Quench and tempering steels is used for heavy springs. And so on.
Spring forming
The material is formed to the correct geometry by special machinery. In most cases, the material is formed to the correct shape by plastic deformation when cold. But stampings and hot forming are also commonly used. Lesjöfors uses the most modern machinery and processes available. Numerical control and automation were brought into common use a long time ago at Lesjöfors.
Heat treatment
Heat treatment in spring production is mainly used either to remove negative residual stress from plastic forming or to give the material its optimum strength properties. In the first case, this treatment is called stress relieving, where the temperature and time depend on the type of material. The second case is either precipitation hardening or quenching and tempering, where the methods used are in accordance with the material manufacturer's recommendations and our konwledge.
Grinding
Grinding is used to make one or two flat ends on helical compression springs. Grinding to make the ends flat reduces the risk that the spring could buckle. This type of grinding is done dry, with air cooling for smaller springs and with water spray for large springs. Different deburring and shamfering methods are used on various types of products.
Shot peening
Some types of springs are shot peened, i.e. subjected to a stream of small steel shots. The result is compression stress in the surface layer and a surface that is suitable for painting. Special machinery is needed for shot peening. The steel shots are accelerated to high speed by a turbine wheel and are guided towards the springs. The intensity is carefully controlled and all surfaces on the springs receive the same treatment.
Presetting and load testing
In order to increase the performance of springs are for some types controlled residual stresses introduced in the material. This is made by a controlled plastic deformation. In the spring trade, this is called pre-setting. The operation requires special machinery that subjects the spring to plastic deformation in the intended manner.
In cases with spring load requirement and verification demands is the load checked and documented in a final check. In cases where the load tolerances are tighter that the process capability a 100 % checks and sorting may be used. Sorting into force classes is also used. These days, test machinery containing load cells, electronic length measurement and computers for digital registration is used.
Surface treatment
There is a large number of different surface treatments. The surface treatments used in the group are vibration deburring, washing/degreasing, dipping in oil, spraying with oil, zinc phosphating and powder coating. Other surface treatments are provided by subcontractors, please refer to the surface treatment section.
Product identification and packing
Product identification is made according to customer request, commonly by putting a label on the packaging. Trade and industry standard barcodes can be provided. If each individual spring is marked, a text or number is usually applied with an ink-jet printer. Labels and engraving are also used.
Products are packed to suit customer requirements. The most common packaging is a cardboard box and Europe pallet, but tape and reel, vacuum-formed trays, ordinary plastic bags and sterile bags are also commonly used. Bags, paper or plastic, with vapour phase inhibitor are commonly used to prevent rust during transport.
Manufacturer's responsibility
Since we control the entire process from design to manufacture, we can assume full responsibility for the product. This means that we also indemnify our customers if any such claims might be made.
Environmental and quality work has high priority, and we are certified under ISO 9001-2000 and ISO 14001. Lesjöfors has a programme for monitoring and improving the environmental aspects of our processes.
Quality assurance
All manufacturing units at Lesjöfors have quality systems complying with ISO 9001-2000 that are certified by a third party. Companies that produce products for use in the motor industry are TF approved by a third party. All companies can manage project work in accordance with the APQP and PPAP requirements.
Quality - Environment
Environmental work has high priority, and we are certified under ISO 9001-2000 and ISO 14001. Lesjöfors has a programme for monitoring and improving the environmental aspects of our processes.