Application - Excavator grapple
Environment - Indoor machine shop
Size - Ø 70 mm (2.76 in.), Length 130 mm (5.12 in.) x4
Method - Boring
Product - MPB60
SIFAB, operating in the construction, manufacturing, and demolition sectors on the Swedish west coast, faced the urgent task of refurbishing an excavator grapple. Over time, the grapple had worn down to the point where the connecting rods had deformed the rod seats into an oval shape, causing excessive play during operation. The customer had already replaced two rod seats on one side of the grapple and internally welded two seats on the other side. All four seats needed to be line-bored, realigned, and fitted with shrink-fitted bushings to serve as new rod seats before the grapple could be put back into use.
Solution
The customer began by measuring all four rod seats to ensure the bores would be properly aligned. Given the grapple’s application in demolition, the boring process required a tight fit but did not demand extremely high accuracy tolerances.
The MPB60 traversing boring bar machine was chosen for the task, equipped with three single-arm mounting plates and three support bearings for maximum stability. U-shaped spacers were welded directly to the grapple body to facilitate the process.
The smaller bores were well-suited to the MPB60tbA’s high rotational speed, allowing for smooth and efficient operation. Due to the small bore dimensions, a tool post could not be used.
The operator began by boring the two newly replaced rod seats to the required specifications. However, the two welded seats posed a greater challenge. Due to the hard MIG welds and tight fit the operation chose a sharpened HSS (High-Speed Steel) inserted directly in the boring bar. As the boring progressed, the operator switched to a carbide insert, which further increased the speed and efficiency of the process. After boring, the new rod seat bushings were installed and machined to the final dimensions of Ø 70 mm (2.76 in.). The whole procedure of setup, machining and teradown was managed within one working day.
Finally, the U-shaped spacers were removed from the grapple body, and the grapple was reassembled, ready for future demolition assignments.