guide pin 22 positioned between the vertical plate 11 and the adjusting plate 20 the plate clamping unit includes a back plate 14 fixedly mounted between the upper supporting plate and the lower supporting plate a pair of pressure plates 15 which are symmetrically disposed and a cylinder supporting frame for a cylinder 16 are respectively mounted on both sides of the back plate 14 and guidably fixed via guide bolts 18 the upper part and the lower part of the back plate 14 are respectively provided with four slidable guide bolts 18 the inner ends of the guide bolts 18 are fixed to the pressure plates 15 the outer ends of the guide bolts 18 are fixedly connected to the cylinder supporting frame the piston rod of the cylinder 16 passes through the cylinder supporting frame and can extend to the back plate 14 the two pressure plates 15 respectively correspond to the upper end and the lower end of the back plate 14 the two pressure plates 15 and the upper part and the lower part of the back plate 14 are correspondingly provided with counterbores in which springs 17 are fixedly mounted to enable the pressure plates 15 and the hack plate 14 to form a plate passage between thereof and the guide bolts 18 pass through the springs 17 when the cylinder 16 is inflated the piston rod of the cylinder acts on the back plate 14 and then the pressure plates 15 comes close to the hack plate 14 along the lower supporting plate 3 to clamp a plate referring to fig6 and fig7 the arc curving unit includes guide rollers 9 fixedly mounted between the upper supporting plate and the lower supporting plate the guide rollers 9 provide.