Common Bearing Swaging Methods

Bearing installation using anvil staking seems like the ideal option at the surface. Both sides of the bearing are staked in one process, the pressure applied is controllable and the tools are relatively cheap; however, this comes with different costs. The excessive force require for installation can have detrimental effects.

According to NMB Minebea, the force required to bearing with a 1.500” outside diameter is around 18,000 lbs. This force can damage the PTFE, or similar, bearing lining. When combined with a stack up of housing tolerances, the breakaway or swivel torque of the bearing can be significantly altered. This could lead to increased or inconsistent bearing friction. Moreover, the hydraulic press capable of applying this much pressure is very large and cumbersome. For many MRO applications, this process will be impossible or unnecessarily dangerous.

Finally, an incomplete contact between bearing v-groove and housing chamfer is very common using the anvil staking method. This is sometimes referred to as “spring back” when the formed annular lip lifts from the housing chamfer. When this occurs, the material is not adequately formed on the housing chamfer and the bearing fails during inspection.

The two-wheel swaging tool was then the next logical step in the tool progression. This tool can be modified relatively easily for use with different bearing sizes, eliminates the requirement of excessive forces and can be used in a commonly available vertical milling machine or hand-held. However, the disadvantages can be seen very quickly as there is a significant design flaw.

The rollers do not rotate at the same speed as the tool. This is due to the geometry of the rollers combined with the assembly design of the tool. As a result, significant friction is generated on the bearing v-groove which leads to galling. Therefore, the bearing surface finish is deteriorated and the failure rate of assemblies drastically increases.

Many times this style tool comes in a kit that is compatible with a large range of bearings. This means each component is manufactured to relatively loose tolerances and the operator is responsible for the assembly and performance of the tool. If the incorrect washer is chosen this produces the wrong swage diameter. The bearing or even housing could then be irreparably damaged. It is also very easy to misplace components components which can turn a standard job into a nightmare when trying to source a misplaced nut or washer. This is where the tri-roller swaging method saves the day.

When the tri-roller swaging tool was introduced into the market, it revolutionized the bearing installation process. The design consists of three rollers set 120 degrees optimising the rolling friction and accurately forming the v-groove onto the housing chamfer. 

Advantages

• Precision engineered tool to suit each bearing ensures perfect conformity, every time
• Uniform and consistent forming around bearing circumference
• Repeatable process with minimal user proficiency required
• Mirror surface finish on bearing
• Low operating pressure required
• Available in portable style
• Acceptable method by all leading aircraft manufacturers
• Requires only one operator while portable anvil staking tools can be incredibly heavy
• Custom designs to suit challenging geometries
• Quick return of investment

Disadvantages

• Higher initial cost
• More space required for tool clearance
• Tri-roller swaging can be more time consuming than anvil staking but faster than two-wheel swaging

The bearing assemblies consistently pass inspection, the process is simple and controllable and a completely hand-held method is available. The initial cost increase is easily eradicated by elimination of rejected parts. The increased space requirements is supplemented by the Engineering advancements with Unasis Tools from Carter Manufacturing Limited. Although the tri-roller swaging process is slightly more time consuming than anvil staking, the overall time spent in production is reduced due to a massively increased pass rate.

The tri-roller swaging method provides certainty that the tool chosen for the job has been precision engineered and gives complete peace of mind. When used correctly, the job will be completed correctly, every time.

In conclusion, the tri-roller swaging process is the optimum process and Unasis Tools is the premium brand. Our Engineers are on call to take on any new challenges and our warehouse is full of tools for AOG jobs. If you do require anvil style or two-wheel style tools, we also manufacture these upon request. Please contact us if you have any technical questions about or requirements involving bearing installation, removal or testing.