Designing Rugged Enclosures for beating Shock, Vibration & Impact
Think of a satellite communications controller orbiting Earth at 17,500 miles per hour and withstanding temperature fluctuations in the range of -250°F to 250°F with completely intact signal quality.
On the other hand, in a production environment, thousands of miles below, a factory floor controller resides in a constant state of vibration from the machines, occasional shocks from drops, and constant noise from the machines in operation. Both experiences are linked through their reliance on rugged enclosures as the first and last lines of defence against mechanical destruction.
Three primary mechanical challenges working covertly but striking with extreme precision confront the electronics:
- Shock protection: Unexpected impacts can shatter or damage a circuit board.
- Vibration resistance: Sustained vibrations can damage solder joints, create micro-cracks, loosen connections, degrade mounting of components, and accelerate fatigue failure over time. The mechanical stress caused by sustained vibrations negatively affects solder, connectors, and other critical components, thereby decreasing the overall reliability of an electronic assembly in an industrial application.
- Impact durability: Whether a piece of equipment survives boils down to accidental drops, collisions, or intentional misuse.
The consequences go beyond component replacement costs:
- When an industrial controller fails, the consequences are severe and not limited to the cost of parts. It can disrupt production lines, causing companies to lose millions of dollars every hour.
- A failed industrial controller could stop production lines from generating millions of dollars an hour.
Creating rugged enclosures that can endure shock, vibration, and impact is essential for mission-critical systems, guaranteeing dependable performance even in the toughest conditions.
To understand why rugged enclosures matter, we need to first understand the forces they are designed to withstand.
Understanding the Mechanical Stress Environment
Electronic systems continually experience mechanical forces (shock, vibration, impact, compression, etc.) that can potentially convert components that were originally designed with accuracy into an unreliable failure state. While there are a variety of mechanical forces that can occur in a specific configuration or series of events, each one represents a unique challenge for the enclosure designer.
The Three Mechanical Forces: Shock, Vibration, and Vandalism
1. Shock
The most significant risk arises when strong forces strike suddenly and without any warning. Imagine a factory worker who suddenly experiences a jolt when heavy machinery crashes or when a tool slips and falls during maintenance. These sudden impacts can result in serious harm due to their rapid and unforeseen nature.
These forces can strike with high speed, occurring in just a fraction of a millisecond. Once the impact increases beyond 100G, it creates immense stress on the material. As a result, the material can bend or permanently change shape due to the intensity and rapidity of the force.
The level of stress described here exceeds what is known as the “yield stress point,” which is the highest stress it can withstand without permanently altering its shape. If this limit is exceeded, the material will deform in a way that it cannot go back to its original shape, even after the force is taken away. This kind of sudden and intense force can inflict lasting damage almost instantly.
2. Vibration
Vibration creates several issues for industrial electrical systems. Vibration differs from shock in that it is a continuous oscillating force over time, generally between the frequencies of 10 Hz and 200 Hz. For instance, factory controllers placed near heavy equipment are continually subjected to steady vibrations. Over time, these vibrations will wear the materials and components through hundreds of small oscillations.
After a long time, the small stress will accumulate and lead to fatigue failures, like the bending of a paperclip repeatedly until it fails. The greater the oscillation period, the more damaging it is likely to be because it can begin to affect the natural frequencies of various electronic components, causing additional strain.
Regular vibration in industrial settings can weaken solder joints, generate micro-cracks, loosen connections, hasten fatigue, and cause a failure in function or total production stoppage. These effects, taken together, adversely affect the reliability and precision of sensitive equipment like sensors, disrupting operational capabilities and potentially expensive downtime.
To prevent the potential for equipment failure due to degradation of materials and components, sound design practices and vibration-resistant materials are necessary to lessen fatigue-related deterioration of components and maintain system performance and longevity.
3. Vandalism
Unlike unknown effects or vibrations, barbarity is deliberate; repeated damage means disabling or destroying the property. Broken or damaged enclosures destroy the internal components or seals that are worn out, and one of the problems caused by this condition is dust and moisture. The devices will be attached to incredibly strong and impact-resistant materials with reinforced locks and patterns to prevent molestation to guard the devices.
In addition, implementing advanced security features on the factory floor, such as alarm systems, motion detectors, and monitoring cameras, is important in preventing and ensuring that operators get an immediate alert about any event. In summary, vandalism presents an issue of major concern that requires adequate physical safety to protect equipment, safety, and availability, and continuous observation.
They are designed not only to protect against those potential concerns but also to alert operators to an attack in real time. Ultimately, vandalism requires appropriate physical security and monitoring for equipment safety and operations.
How Mechanical Stresses Affect Electronic Components
Mechanical stresses cause systematic damage to a PCB from flexible or bending stress, leading to trace fractures and delamination. Solder joints form micro-cracks under cyclic loads, which result in intermittent connections that appear as glitches in systems. Connectors experience displacement of pins and degradation of contacts, and sensors not only drift their calibration but ultimately fail altogether due to the mechanical stress-induced degradation of their fragile components.
Principles of Rugged Enclosure Design
1. Material Selection: The Foundation of Protection
Aluminium and magnesium alloys are often employed for typical industrial enclosure situations due to their excellent strength-to-weight ratio, along with resistance to impact and mechanical stress. Vibration-damping materials such as specialty rubbers, polyurethanes, and elastomers provide a strong ‘cushion’ around enclosures, absorbing and dissipating vibration energy from heavy machinery.
The materials protect sensitive electronics by reducing the transmission of damaging vibration, thereby preserving equipment longevity and operational reliability in a harsh factory setting.
In industrial applications, vibration-damping materials, such as specialized rubbers, polyurethanes, and elastomers, can be made into a durable cushion around enclosures to protect sensitive electronics. Vibration-damping materials absorb and dissipate vibration energy to reduce harmful vibrations propagated to wires or circuit boards from heavy machinery or equipment.
A bumper, spacer, or mount properly designed in these materials will help keep the components intact and reduce fatigue and failures that can lead to production downtime, which can be very expensive. The capability to select materials that provide appropriate strength, resiliency, and energy absorption is essential to providing dependable and long-lasting performance in a heavy-duty factor application.
2. Structural Reinforcement: Geometry as Defence
Flat panels are positioned exactly to allow load-bearing elements, helping to even spread stress over larger areas. Honeycomb patterns on enclosure walls produce designs that are light but remarkably strong, capable of resisting both twisting and compression stresses.
Shock-absorbing mounts play a crucial role in separating the internal electronics from the enclosure. The specially crafted suspension systems are meticulously fine-tuned to safeguard sensitive components against vibrations, all while keeping electrical connections secure.
Principles of Rugged Enclosure Design
3. Sealing & Isolation: Creating Barriers Within Barriers
Gaskets and O-rings are essential for creating airtight seals, which help prevent moisture from entering and provide some vibration isolation. Damping foams are employed to close any gaps, ensuring that internal components do not generate noise during transport and effectively absorb high-frequency vibrations.
4. Thermal & Mechanical Balance
To ensure ruggedness without suffering from thermal issues, it’s essential to thoughtfully design the heat dissipation process. By considering the placement of components and incorporating thermal interfaces and ventilation into the enclosures and electronic systems, we can ensure that the protective features will effectively safeguard the electronics they are meant to protect.
Testing & Standards for Ruggedization
The enclosures and electronics systems in commercial or factory environments have often been subjected to tests that visually depict the amount of durability required for a safe operation in severe environments.
IEC 60068 is one of many standards that were developed to provide for environmental testing of commercial and industrial electronics, to simulate the stresses required by the realities of the production environment, including temperature cycling, continuous vibration, and random mechanical shock. The testing conditions, such as high humidity, dust, and varying temperature levels experienced on the production floor.
The National Electrical Manufacturers Association (NEMA) establishes specific industry standards that outline environmental ratings for electrical enclosures. These ratings help ensure protection against dust and liquid ingress, which is determined by their IP classification levels.
Together with the testing procedures, these standards create a robust framework to ensure that industrial electronics can withstand continuous mechanical, thermal, and environmental pressures, which helps to minimize equipment downtime and maintain ongoing operations.
1. The Physical Testing Tools
The physical test equipment is the testing capability of any rough designs:
- Drop tests: Drop tests are intended to imitate the conditions of cause of sudden drop from various heights and angles, allowing assess the extent to which enclosers protect components from the trauma of impact.
- Vibration tables: These tables create controlled oscillations over a set of frequencies that approximate the vibration effects from engines, road conditions, and the loading effects of machinery.
- Shock pulse tests: The tests apply controlled impact forces to determine the performance of the structural enclosure resisting rapid loading from dynamic effects.
2. Modern Engineering Techniques
Modern engineering makes use of FEA tools to examine how stress is distributed, enabling the development of virtual prototypes that can identify potential failure points before any physical tests are conducted. The simulation environments create a pathway to establish where stresses are concentrated, areas where the structure is weak, and material placement optimization, with precision according to the material properties.
Engineers can see how shock waves propagate through the walls of an enclosure, identify where the maximum deflection takes place, and understand how the mounting points will bear structural loads.
When designing enclosures to endure impact, vibration, and shock, it’s crucial to consider more than just the outer layer. Start by selecting materials that have the right thermal characteristics, weight, and tensile strength. Also, the careful positioning of supports can help manage stress effectively without compromising the functionality of the enclosure. It’s wise to review the design to ensure it meets your specific requirements.
Focusing on shock and vibration resistance early in the design phase will lead to the most effective rugged enclosures. When mechanical engineers, materials scientists, and testing experts collaborate, they can turn ideas into reliable solutions. Each gasket, mount, and structural component plays a vital role in safeguarding essential electronics, making the difference between a successful mission and a disastrous failure in challenging environments.
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