Investment Casting replaces machined part


By: Donald Harpold Casting Engineers


A power shear that cuts 18 gage steel sheet at speeds up to 15 feet per minute uses investment castings for its most critical operating parts, the cutting blades.


Previously machined, the cutting blades are now investment cast primarily because of the added reliability and amount of processing time saved. In addition, there was an initial cost savings of about 10 percent.


The power shear is built to pass a rigid government evalua- tion. The shears have a center blade and two side blades which make a cut 7 /32 in. wide. This balanced shearing action will not distort the metal -


it leaves a simple, un-


crimped edge. The square edges of the blades insure that no burrs are formed. In addition to sheet steel, the shear will also cut non-ferrous metals (aluminum, brass, and copper) up to 16 gage and fiberglass and laminated plastics up to 1/16 in. thick.


The center blade, which is actuated by an eccentric, moves between two stationary side blades. Originally the center blade was a stamped part made from random lengths of 114 x 2 in. hot rolled annealed 85 tool steel.


It took eight operations to process the incoming raw material into a part ready to assemble. Because the power shear is the major product, the manufacturer did not have the pro- duction volume needed to set up many of these operations within its own plant and had to use outside sources. This created a large volume of work in process and a substantial amount of paper work.


Old vs. New


When the center blades were made of hot rolled steel, the first step was to send the material outside to be pickled. Another supplier then stamped the parts. The parts were then sent to a heat treater for stress relieving, which was followed by grinding at still another plant. The parts were then returned to the manufacturer to be drilled and ma- chined. After this the .parts again had to be sent out for heat treating and then for finish grinding. The blades were then returned a second time. After the cutting edges were ground, the parts were ready for assembly.


The investment cast blades made are cast to shape as shown above. Thickness is held to .225 in. ± .005 in. The caster also performs the grinding and heat treating opera- tions as needed. Hardness is held to 57 to 59 on the Rock- well "C" scale.


When the center blade was made of hot rolled steel strips, an 85 tool steel was used. By changing to investment cast- ing it was possible to use an A2 tool steel and so obtain increased wear resistance for the blades. While the blades can easily be removed for replacement or resharpening, the A2 tool steel reduces the amount of resharpening needed.


The side blades are also cast of A2 tool steel. The investment cast side blades also require only one operation after delivery to the customer. When the side blades were formed from hot rolled 85 tool steel, seyen operations were needed to complete the parts.


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