punching tool for tensile specimens from sheet metal

Special shapes / other sample shapes on request. For post-processing we recommend the sample grinding machine psm 2000

Tensile specimens from standard sheets with strengths (Rm) of 150 – 1200 MPa

Since 1970, the preparation of tensile specimens from sheet metal has been a core topic for our company. Since then, we have designed and supplied hundreds of punches and punching tools. As a rule, standard tensile specimens are produced from sheet metal with a thickness range of 0,5 - 6,0 mm. However, special tools with spring-loaded hold-down devices and particularly precise designs for soft, extremely thin sheet metal from 0.01 mm to 0,3 mm are also part of our delivery program. In recent years, we have expanded the range of sheet thicknesses to up to 10 mm at the customer's request. 

tensile specimens from hardened sheets

Press hardening / Form hardening / Hot pressing / Hot forming / Hot deforming / Hot stamping
are the keywords that cause particular problems for material testing in the automotive sheet metal industry. Currently, all manufacturers and suppliers in the vehicle construction / car body industry (and also tend to include truck construction) are urgently looking for solutions for producing tensile specimens from hardened sheet metal, where strengths of up to 1600 MPa (tendency 1700 MPa) are common. Most of the usual manufacturing methods fail with these hardened sheets. The milling cutters for machining become blunt within a short time and sometimes cause additional damage to the material (crushing / compaction due to blunt milling cutters). An additional problem arises from the fact that the samples have to be taken from a formed sheet metal part / molded piece. Since this component has a 3D contour, it is almost impossible to punch this contour using a standard punching tool in order to remove the tensile rod ("bone"). Therefore, a strip as large as possible is cut out of the component using a hand-held cutting device (angle grinder / “Flex”) so that it can then be punched.

In 2013 we were the first company in the world to deliver punching tools / punches for hard cutting of hardened sheets (Video)To ensure a high quality sample, these punched samples must be subjected to a final processing (grinding). In order to save the preparatory work of cutting out a strip, there is a growing trend to cut the tensile samples out of the hardened sheets using a laser. A laser guided by a robot arm is able to take a tensile sample (dumbbell / bone) from any point on the component. However, the hot processing causes severe damage to the edge of the tensile sample. The material at the all-important measuring length Lc is melted by the laser beam and changes the material properties extremely.

To use the words of an employee of the University of Kassel: "The only qualitatively suitable machine for the post-processing / finishing of the melting edge / punching edge is the sample grinding machine from the manufacturer SCHÜTZ+LICHT. All other grinding machines are not suitable for this. With the sample grinding machine advertised here, all contours can be ground from radius to radius. Different grinding heads and sample holders are available for this purpose or are manufactured according to customer requirements.

Notes

1. The dimensions given correspond to the nominal dimensions of the standard. To remove the punch edge damage (work hardening), a punch allowance at b(W) is required
2. In all standards, the transition radii between head and measuring length are defined as Minimum size To use the sample grinding machine PSM2000 To be able to use the grinding wheel, a radius of >15 mm is required (smallest pulleys of the grinding belt). Therefore, the radii of the samples were increased in some cases (permissible). Increased dimensions were fat and underlined characterized.
3. In all standards, the parallel measuring lengths Lc(A) are defined as Minimum size To use our sample grinding machine, a distance of 36 mm between the radii Lc(A) must be maintained to avoid contact between the deflection rollers (R15). Here too, the dimensions (permissible) have been increased. The increased dimensions are marked in blue, bold, underlined.
4. The ISO – A50 and ASTM E8 Type 12,5 tensile specimens are almost identical. To limit costs, the dimensions Lc(A) should be adjusted as far as possible to reduce the number of tools.