What is an engineered fastener?

Here we’ll look at the fasteners needed for electric motors. With the increasing use of electric motors in electric vehicles car makers are looking for small, compact but powerful engines. So, a lot of heat is generated inside the engine – having impact on its components. The shape and variety of engineered fastener along with their performance requirements are changing. For example, the stator fastener needs to tolerate thermal expansion and cooling which causes a change in component clearances. Where dissimilar materials are used between electric motor components, the engineered fastener will be required to secure the components together at min and max clearances. Bearing mounts and rotor mounts (also fasteners) need to be compliant to overcome issues such as misalignment and shock loads whilst retaining the components position.

Off-the-shelf solutions in these situations are possible, but bespoke engineered fasteners provide reassurance of fit and performance.

The stator is the non-moving component in a rotating mechanism, used in electric motors or generators for example. The function is based on interaction of a component providing an electro-magnetic field (generated by coiled copper wires) and a permanently magnetized component. One of these fields needs to be moving and the other static, which is why a stator is needed in these systems. Because of the stator’s purpose it is typically made of steel.

With the trend to reduce weight in systems, new materials for motor housings are being introduced such as aluminium. However, this introduces the problem of dissimilar materials being used between the motor housing and the stator, caused by different thermal expansion. Using a tolerance ring as an engineered fastener for stators has the benefit of tolerating clearance changes due to temperature.

Alongside its ability to cope with changes in component clearance as a result of temperature variation, the tolerance ring overcomes assembly process issues coming along with adhesives, by using a press-fit operation creating less stress to the components compared to shrink-fit options.

“No heating, acceptable forces and no messy glue; I am always impressed by the simplicity of the solution when I use a tolerance ring to assembly a stator” Andy Broadwell, Senior Application Engineer.

The RENCOL^® Tolerance Ring fixes the stator into the housing and as a stator mount it is an effective choice.

If heat conductivity is important, the Aluclad Tolerance Ring has the additional benefit of increasing thermal transfer between stator and housing because of a specific construction.

Before we completely move away from electric motors, it’s worth noting that engineered fasteners are used to mount an electric motor bearing.

But bearings are not just limited to electric motors and wherever a bearing is used the inner and outer race needs to be securely attached to the housing and shaft of the application or system the bearing is being used in.

A bearing needs to be carefully mounted to ensure optimum performance. Too tight and it will increase the torque, too loose and the bearing may dislodge or rattle. Because RENCOL^® Tolerance Rings are custom-designed they are built to fit the bearing exactly and provide a secure fixing. As a bearing mount a tolerance ring can be used for large diameter bearings in applications such as electric motors and all the way to smaller Hard Disk Drive (HDD) bearings, and provide benefits such as secure retention across operating ranges, simplified assembly, and cost and weight reduction.

Engineered fasteners are widely used in fix bearings, pulleys or gears, but there are other sub-components that need to be hold into place. Sensors, magnets and magnetic sensors are widely used in the automotive industry for detection or positioning and all need to be held in place throughout their lifetime to perform.

There has also been an increase in domestic and industrial equipment using sensors. Mechanical systems have sensors incorporated to improve detection of potential problems and they can aid users to understand and better handle their own systems.

Magnets and sensors can be brittle or delicate which means selecting the right engineered fastener is important to prevent damage. Glue is an option but it doesn’t allow for movement so should it be hit the magnet or sensor may shatter or break. The tolerance ring can protect a sensor, magnet or magnetic sensor while holding it securely in place and allowing for movement. And, like a bearing mount, because the tolerance ring is an engineered fastener with elastic waves it secures the components and also allows dis-assembly for rework, saving precious and expensive magnets from being scrapped.

The RENCOL^® Tolerance Ring has been used in a wide number of devices as an engineered fastener. It was first commissioned for use in the self-fixing ball knob for machinery. 

When used as an engineered fastener the tolerance ring provides a number of benefits: 

• It joins mating components of dissimilar materials
• It allows components the ability to disengage 
• It can transfer torque 
• It can hold components in a pre-determined position
• Misalignment can be compensated
• Clearances can be tolerated 
• Two components are prevented from moving relative to each other

These static fixings are designed for each use case. During the design phase the engineers can help develop an engineered fastener that also focuses on the other performance benefits that need to be achieved.