Ram End Forming – A Few Basics
The Need To Connect
A significant majority of fabricated tubing needs to have one or both ends formed into a specific shape. Quite often one or both ends of a tube needs to be formed so that it can be mated to another part. The mating part might be another tube, a fuel pump, or even a bulk head inside a diesel engine. Forming a specific shape takes planning. An understanding of a few basics during the planning stage can go a long way.
Ram End Forming
One of the most common types of end forming is a ram type end former. Most often the ram type end forming process securely holds a tube static in a set of clamp dies while a ram tool forms the end of the tube. Figure 1 shows a simple setup to form a bead on the end of a tube.
As the ram tool advances towards the static tube held captive by the clamp dies, the ram tool causes the tubing to cold flow. The path of flow is the path of least resistance. The ram tool simply captivates the end of the tube and then compresses it towards the clamp dies. In this case the unsupported section of the tube between the clamps and the ram tool buckles under the compressive loading on the tube thus forming the bead shown. In this particular case, the surface finish of the ram tool’s mating features are not that critical. Likewise, lubricant in this case is not critical.
Now take the case as shown in Figure 2. This is a similar end form to that of Figure 1 with one difference. The outside diameter of the tube to the right of the bead is reduced.
In this case the ram tool is performing more work then it did in Figure 1. Moreover, the surface finish and/or type of lubricant being used to reduce the outside diameter of the tube is now critical for product quality.
Surface Finish
As the ram tool advances onto the tube, the tube must first neck down. To be successful in the long haul, the surface finish of the corner radius and inside diameter of the ram tool must be smooth. Typically a 32 RMS finish is too rough for the job. A 32 RMS finish would be considered a serrated finish in this application and would most likely produce inconsistent results.
Lubrication
If the surface finish of the ram tool is acceptable, it can quickly see an early demise thru a lack of the right lubricant during the end forming process. As the ram tool necks down the tube in Figure 2, there is an enormous amount of friction between the tube and the bore of the ram tool. In the case of Figure 2, friction must be low enough to facilitate a consistent level of quality. If the lubricant is inconsistent, the process may be difficult to control.
Coating – Surface Treatments
There are several coatings that can be applied to a tool’s external surface that will help extend the life of the tool. The coatings, typically applied to heat treated steels, can extend the life of a tool by increasing the surface hardness.
Figure 3 shows the tip of a ram type tool with a .0002” gold color coating. This surface treatment, along with the right lubricant will help expand the 3/16 copper tube to 3/8. In this specific case, the surface finish of the ram tool coupled with the right lubricant is critical to making a successful expansion.
George Winton, P.E. designs and builds CNC tube fabrication equipment for Winton Machine in Suwanee, GA. He can be reached at gwinton@wintonmachine.com or 888.321.1499.
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