Prestressing is one of the main factors affecting life of a forging tool. By using a single, double or in rare cases triple ring systems are used to generate compressive stresses on steel or tungsten carbide (WC) die inserts to eliminate or minimize tensile stresses under loading. Due to the low hardness of conventional compression rings of steel achievable prestressing is limited and it is not possible to eliminate tensile stresses completely which results in low die life.
STRECON Stripwound Containers are made of high strength steel strip which makes it twice as strong as a tool system with a conventional steel compression ring.
The stripwinding process is performed by a special machine, which fully controls the winding tension of each strip layer during the stripwinding process. The strip material is wound around an inner core of high-alloyed tool steel or tungsten carbide. The strip material has a thickness of 0.1 mm and is fully elastic up to more than 2000 MPa while yield stress of a standard compression ring is around 1200MPa.
A prestressing tool made by stripwinding consists of several hundreds or even thousands of strip layers. Each layer of strip material will be adding to the overall strength of the stripwound tool system, and thus explaining the superior strength compared to a normal compression ring.
Types of STRECON Stripwound Containers are:
- STRECON 200/400
- STRECON 200/400+
- STRECON Axi-Fit
- STRECON Vari-Fit
STRECON 200 and STRECON 400 is a standard stripwound container made of fully steel components. The STRECON 200 container is designed for applications up to 200°C, and up to 400°C for the STRECON 400 container. These temperatures stand for the limiting temperature values on the inner surface of the container and workpiece temperature can be much higher depending on the cooling system of the tool. Interferences on this tool system can go up to 1.2% but to avoid over-prestressing the die insert it is kept between 0.6%-1.0%. Fully elastic behaviour of this prestressing system allows die insert change minimum 50 times.
The STRECON 200+ container and STRECON 400+ container is a unique high-stiffness prestressing tool system of which the winding core is made of tungsten carbide. The use of a carbide core as the inner ring of the stripwound container system ensures a tool stiffness up to 400 Gpa. In addition to the high-stiffness feature, the container itself can take a radial load which is up to twice the level of a normal compression ring. The container system is designed for achieving an optimal balance between radial prestressing and reduced die deflection under process load. The high-stiffness feature can reduce the deflection of the production die up to 30%.
The STRECON Axi-Fit Container is a 2-directional prestressing tool system that offers compressive support for the die system: Radial prestressing and axial prestressing. The radial prestressing is obtained by press fitting the forging die, whereas the axial prestressing is ensured by locking the tool system under high axial loading during tool assembly.
The STRECON Vari-Fit container is a special prestressing tool system that is designed for a safe and fully controlled fine adjustment of the inner diameter of a cold precision forging die. The die diameter is adjusted in few microns (2-5 μm) by means of an intermediate die sleeve, which is mounted between the production die and the STRECON container.