Materials

The materials that can be rolled are as varied as the splines themselves. However, non-ferrous materials generally have not been successful for rolling splines. Almost all of the carbon steels have been rolled at one time or another. The ideal hardness should be around 180 to 220 Brinell. Some of these materials roll better than others. When a soft material is rolled the material does not hold a set. Generally soft materials have higher spacing errors than the same spline rolled on a harder material.

In the spline rolling process, the steel chosen must be of good homogeneous quality. The material is displaced in the process of forming the spline. Therefore, a material must be chosen that will flow around the rack teeth to form the spline. The grain structure of a rolled spline looks as though most of the grains were shoved into the root of the spline. The grains can be seen flowing up the sides of the teeth also.

One problem in materials is Manganese content. A steel that is high in Manganese will tend to work harden. Silicon has somewhat of the same effect. Another area of material trouble comes from high sulfur contents. High Sulfur contents can be the cause of excessive spacing errors. The steels that are high in sulfur tend to act as if the material was too soft. The 1100 series steels have a history of bad tool life and quality problems. This is due to high manganese content.

Uniform hardness is very important to rolling high quality splines. The harness must be consistent from part to part and throughout any given part. When the hardness is not consistent throughout a given part the displacement of the material can not be equal throughout the spline. The usual effect of this condition is runout or out of round conditions. When the hardness is not consistent from part to part, the min. actual tooth thickness has high variation.

Iron has been successfully rolled in a few cases. This has usually been nodular iron. The iron used must have the ability to flow to form the major diameters and roots. Some tool life problems can be expected when rolling iron.