Cutoff die setup for dimple-free rounds
With the right equipment and proper setup, tube mills can produce dimple-free round tubing efficiently. A multistep process using a two shear blade makes a dimple-free cut, and an inline brush end finisher can be used to remove the ever-present clearance burrs, if needed
Tube Mill Dimple-free Flying Cutoff
Modern tube mills that operate with a dual-shear blade and a flying cutoff system can produce dimple-free round steel tubing efficiently. For example, 3-inch-OD tube mills regularly make 70 cuts per minute or more on short lengths from 1 to 10 feet. Lengths 10 ft. and longer typically are run at 400 to 650 feet per minute (FPM), with some limited-product range tube mills operating as high as 1,200 FPM.
Dimple-free Cross Cut
Dimple-free die sets like the unit in Figure 1produce clean-cut ends with very little end-size distortion. In most applications, little or no end finishing is needed, which makes it possible to ship cut-to-length finished round tubing directly from the tube mill. The clearance burr that always is present with this type of cut can be removed easily with an inline wire brush end finisher.
A dimple-free cut is accomplished with a dual-shear blade when a cross-cut blade removes a small portion of the tube wall thickness before the severing shear blade enters the tube, as shown in Figure 2.
The cross-cut can be made with many different blade paths (Figures 3, 4, and 5).
Push Across Arc
The cross-cut blade produces a slot that is slightly larger than the vertical severing blade (Figure 6).
The dual-shear-blade cut sequence is as follows:
1. The tube is clamped using tube size-specific die jaws (Figure 7).
2. The cross-cut blade passes through the tube wall (Figure 8).
3. The severing blade enters the cross-cut slot (Figure 9).
4. The severing blade completes the cut (Figure 10).
Step 1 of 4
Step 2 of 4
Step 3 of 4
For top performance, the blades must be lubricated before each and every cut (Figure 11).
Shear Blade Lubrication
Shear Blade / Die Jaw Clearances
All shear blade tube cutoffs require clearances between the blades and supporting die jaws (Figure 12).
As with all shear blade tube mill cutoffs, each tube end cut has a clearance burr with a thickness that measures about 5 percent of the tube wall. The burr projects perpendicular to the tube axis beyond the tube OD approximately 5 percent of the wall thickness (Figure 13). An inline wire brush end finisher removes the burr.
Quick-change Die Jaw Cartridge
Simplified Setup and Maintenance
Setup and maintenance can be simplified with offline fixtures, such as the quick-change die jaw cartridge shown in Figure 14. These devices save costly tube mill changeover downtime and enable offline maintenance.
With the right equipment and proper setup, tube mills can produce efficiently dimple-free round tubing that requires no end finishing.