Cutoff die setup for dimple-free rounds

Figure 1 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.

Figure 2 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.

Operation

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).

Figure 3 Push Across Arc	Figure 4 Pull Across	Figure 5 Push Across

The cross-cut blade produces a slot that is slightly larger than the vertical severing blade (Figure 6).

Figure 6 Dimple-free Cross-Cut

Sequence

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).

Figure 7 Step 1 of 4	Figure 8 Step 2 of 4
Figure 9 Step 3 of 4	Figure 10 Step 4 of 4

Lubrication

For top performance, the blades must be lubricated before each and every cut (Figure 11).

Figure 11 Shear Blade Lubrication	Figure 12 Shear Blade / Die Jaw Clearances

Clearance Burrs

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.

Figure 13 Clearance Burr	Figure 14 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.

�