|
Buckling of punches The punches in a press tool are subjected to compressive stresses during the cutting operation.If these stresses are overlooked thin punches in the tool may fail by buckling.The maximum force that a punch can withstand with out buckling can be caluculated from the following formula. FB=pie square EI/Ip square Fb=Maximum force beyond which buckling occurs E=Modulus of Elasticity of punch material (in GN/mm square)I=Moment of inertia in mm 4 Ip=length of punch in mm The cutting force coming on the punch should be less than or equal to the buckling force. Worked out examples:Is it possible to punch 1mm brass sheet with a5mm square punch. Length of punch=60mm,br>T max=320N/mm square Pierce the hole=l*s*T max l=cut length in mm s= sheet thickness in mm T max=shear force in N/mm square Shear force=20*1*320=6400N=6.4kN Buckling force=pie square E I/Ip square E=210 GN/mm square I=a^4/12=5^4/12=52.08mm^4 Ip=60mm Buckling force=(3.14^2*210*52.o8*10^-12/0.06^2)=29.9835kN The punch can withstand a force of 29.9835kn.The force coming on the punch is only 6.4kN.Therefore it is possible to use the punch.
| |