Models reveal problems in electronics enclosures

Article By : Maxim Kenedys

The enclosures around your electronics must survive impacts, high temperatures, and general abuse. Models can uncover hidden defects not visible inside your molded parts.

Most electronic devices need enclosures that must withstand impacts and keep on working. Will your enclosure survive a blow in three planes? Will it deform at extreme temperatures? Is the internal cooling system of electronics well thought out?

There are two ways to answer these questions. First: test the finished device (prototype) in real life and based on the results, send it for revision. Second: simulate physical processes and correcting problems during development. This is much faster and more efficient, so you can have working prototypes already by the first iteration. Mechanical design engineers at Promwad had to try both options.

Check the enclosure’s security
Let’s start with the device built into a car’s interior that sends an emergency signal (Figure 1). According to the terms of reference, it must be secured with snap locks. The use of screws is forbidden.

Figure 1. Emergency signal-device in the car’s interior (front side) must be held in place with plastic snaps only.

We decided to simulate the collision of a vehicle with a barrier. The goal was to keep the device working after an accident and to protect passengers (they do not want to get injured because the device fell out of the mount). Figure 2 shows how the device looks on the inside of the car’s dashboard.

Figure 2. A simulated enclosure of an emergency transmission device uses clips to hold it to the dashboard.

What will happen in a collision? We knew that we needed a fairly strong mount. Simulation helped us calculate that strength and let us test the design. We calculated two conditions for the clamping forces on the latches: Inserting the device into the panel in the car’s interior and collision.

Figures 3 and 4 use animation to show the snapping process in various angles. In reality, the snapping process will be a little different, but in modeling it is desirable to simplify the task as much as possible within reasonable limits. The main thing is to account for the latch pre-load.

Figure 3. Simulation of the snapping process to get the enclosure into place.

From the animation in Fig. 3, you can see that the latch first passes through the part. This trick can and should be done when simplifying the task. In our calculation, contact parts were included later. Figure 4 shows a simulated side view of the clamp.

Figure 4. This simulation of the snapping process shows the clip bending as seen from the side.

What happens to the transmitter in an accident? The next step is the simulation of the process of a car’s collision with an obstacle, accounting for the pre-load of the latches, i.e. our first calculation is transferred to the second calculation. The Figure 5 animation lets you see the device in a simulated collision.

Figure 5. A simulated collision shows the departure of the device from the dashboard.

Simulations such as these can make you look at a product in a completely different way. Take note of how the lever is formed in the structure.

On this project, everything was ready for the production of prototypes. Deadlines were tightened. No one expected such results. Based on the results of the simulation, we suspended production of prototypes on time. It was one iteration less, which saved the customer money.

We made changes in the design, which reduced the departure of the device resulting from the selection of new components on the dashboard. We also adjusted the mounting of the lower part of the device.

Another example of modeling on this project is calculations for defects in plastic casting (injection molding). Such calculations led us to select the best materials and make the details more technologically advanced. As a result, we received a report on possible sink-ins at the start of the product in batch production. Calculations were also made for residual stresses during casting to compensate.

Such defects often arise due to uneven cooling of the casting and depend on the product’s material. Over time, they can lead to the appearance of cracks and the enclosure’s complete destruction. You could be faced with this phenomenon if you watched as a plastic product begins to crack.

Casting defects
Now let’s move on to the next project. Figure 6 shows a plastic enclosure element, produced serially.

Figure 6. In this part, simulations revealed defects occurring inside the plastic.

Figure 7 shows the results of modeling problems from the casting that are not visible from the front side of the product.

Figure 7. Simulations revealed problems that occurred inside the plastic.

Although the defects occur within the plastic, the customer must still be aware of these defects. You’ve probably noticed that famous brands do not allow such problems in their products.

As you can see, the simulation results do not coincide 100 percent with reality, but the overall picture is still similar. In a series production, one casting can differ from the other, this is a normal phenomenon.

Some products may be defective through the fault of the manufacturer. With the help of the computer-aided engineering (CAE) systems, you can convey give advice to the manufacturer and reduce the number of iterations on a part. This is exactly what we did in this project. As a result, the problem was solved in a short time. Then, the product began to be produced serially without visible defects, not only from the outside but from the inside as well.

The animation in Figure 8 shows the fill of another product. The calculation accounted for the sprue system, the cooling system of the mold, and the mold itself.

Figure 8. An animation shows the flow of plastic in a molded part.

The red in Figure 9 highlights casting defects.

Figure 9. Red areas in a simulation indicate defects in a mold.

This defect is clearly visible in Figure 10.

Figure 10. You can see the defect in this photo.

Crash tests
Strength tests are a popular topic in the reviews of tablets and smartphones. Often, forum participants discuss whether the device will operate after an accidental fall.

At Promwad, we also conduct such tests in the development of consumer electronics. Take a Bluetooth smart gateway as an example (Figure 11).

Figure 11. The housing of a Bluetooth smart gateway has openings for USB and LAN.

When falling from a height of 1.2 m, the device must remain in its original state, this was one of the customer requirements. In the technical task, possible problem points were noted in which the device could break. We conducted seven calculations and received positive results. Figure 12 shows one of the calculation results:

Figure 12. This animation shows how the enclosure responds to a 1.2-m fall.

After prototyping, we tested the fall of the device in real life. The results were again positive.

Keep in mind that milled prototypes by physical characteristics differ slightly from the standard cases that are produced by the casting method. When milling, residual stress remains in the product. In this case, however, it is better to conduct a test before committing to a cast.

After analyzing the obtained prototypes, we decided to slightly strengthen the enclosure by adding ribs to the design (Figure 13). After modeling the effect of pressing a finger on the enclosure, the rigidity of the device should have increased by about 30 percent.

Figure 13. Adding ribs to the enclosure’s design strengthened it.

We then ordered new prototypes. After testing for resistance to falling, the device nevertheless began to break down, which no one expected (Figure 14).

Figure 14. Unexpected cracks in the prototypes occurred during testing.

We decided to re-simulate and compare the results with practice. Indeed, the program showed this new problem (Figure 15).

Figure 15. A model shows the weak point in a mold.

We removed individual ribs. After the next simulation, we obtained positive results.

With any change in the design, you must perform repeated calculations and computer modeling of physical processes, which will save time and money in the development of enclosures for electronic products. It is better to check the enclosure for strength in the systems of engineering analysis, and not in real life.

Maxim Kendys is a mechanical design engineer at Promwad Electronic Design Company.

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