Figure 1 Tube Mill Cutoff - Left to Right - Single Cut
A comprehensive tooling plan that includes setting up and maintaining sufficient tools according to the original design manufacturer's (ODM) specifications is critical for efficient high-speed tube mill operation. The tube mill cutoff component (Figure 1) is an integral part of this plan.
Keep at least three master die sets on hand at all times for each tube mill cutoff—one at production, one preset for the next scheduled run, and one at repair/standby. These die sets should shift position at each tube mill size change.
Three sets of die jaws for each tube size should always be on hand—one set at production, one set at production standby, and one set at repair.
Maintain a six-week supply of blades at all times.
Setup and Maintenance
All tooling should be cleaned and stored near a toolroom, and master die set setup always should be performed in a clean toolroom. Proper setup entails the following steps:
Inspect the upper shoe, cams, blade holder, and blade. Replace with new ODM parts as needed.
Inspect the lower shoe, cam guides, jaw holders, jaw holder wear pads, jaw holder springs, and jaw holder gibs. Replace with new ODM parts as needed.
Insert the master die set upper shoe subassembly into the lower shoe subassembly, without the blade and die jaw set installed. Press the upper shoe into the lower shoe to the shut position. Measure the jaw holders' closed dimension. Use shims as needed between the jaw holder wear pads and the jaw holders to adjust to the ODM-specified closed dimension. Set the master die set aside.
Inspect the die jaws. Measure them to confirm they are at ODM- specified dimensions. Pay careful attention to all regrind areas. Replace with new ODM die jaws as needed.
Incorrectly reground die jaws are one of the major causes of poor cut quality and outrageously high tooling costs.
Clean and inspect the blade. Measure it to confirm it is at ODM specifications.
Assemble the blade and die jaw set into the master die set. Close the master die set to its shut position. Lay the master die set on its side, and measure the blade-to-die-jaw clearance from the lower shoe side of the master die set using a new, clean feeler gauge long enough to reach the working surfaces of the blade. Check each side of the blade. For low-carbon steel tubing, the default clearance is 10 percent of the tube wall thickness. Shim the die jaws out from the die jaw holders, if necessary, using high-pressure precut shims.
Clearances less than 10 percent of the tube wall thickness can cause excessive heat in the blade, die jaws, and the tube. This excessive heat will reduce tooling life dramatically and promote end-cut burrs.
Insufficient blade-to-die-jaw clearance is another major cause of poor cut quality and outrageous tooling costs.
When the production schedule calls for cutting a range of tube wall thicknesses, set the blade-to-die-jaw clearance to the largest of the first three tube wall thicknesses. For example, for 0.028-in., 0.035-in., and 0.040-in. tube wall thicknesses, set the blade-to-die-jaw clearance to 0.004 in. (10 percent of 0.040-in. tube wall thickness). Preset the standby master die set to the largest of the next three tube wall thicknesses. Then switch and preset master die sets as needed.
Figure 2 Single-cut Die Set - Blade Lubrication
At the Tube Mill
Cleanness is a must throughout a tube mill. Power-wash the production master die set before removing it from the die set carriages. Power-wash the die set carriages after the production master die set is removed. (A simple power washer is a garden hose and gate valve attached to a sizing mill coolant line).
When the die set carriages are clean and free of all debris, install the preset master die set. Adjust the shear blade lubrication nozzles to ensure blade lubricant delivery to all working surfaces of the tooling (see Figure 2). Set the blade lubricant system to deliver lubricant just before each cut.
Insufficient tooling lubricant is another major cause of poor cut quality and totally outrageous tooling costs.
High blade speeds, soft or killed steels, and other factors can contribute to high-heat conditions at the default 10 percent of tube wall thickness blade-to-die-jaw clearance. Any one (or all) of the following can solve the problem:
Reduce the blade speed whenever possible (always cut at the lowest possible blade speed).
Apply a wear coating to the blade and die-jaw working surfaces.
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