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We continue to delve into the car development, previous weeks we have seen aspects such as safety, crash tests and aerodynamics. In this part of the automotive course we will see the rest of the tests, except the vehicle dynamics and another final test.
With these two posts we will finalize the car development and we will launch it into production. This key point is called SOP (Start of Production). It's a critical point because we go from the development of a vehicle behind closed doors to the production stage, where there will be thousands of operators working in the factory and hundreds of suppliers producing the different components.
So, we're in the final stretch to get a car on the streets, we have gone from the imagination on paper to the prototypes. Once we enter the SOP (Start Of Production), we cannot turn back, this is why we test a vehicle so much. The real problem is time, as well as the financial resources available. As engineers, we would spend years testing the car and thinking about everything that could go wrong, but this phase takes less than a year, so it's a race against time.
Remember that this isn't a workshop, it's useless to bring the car back and check it. It's a car brand, and calling thousands of cars for review is a lack of credibility and a huge financial expense.
So we will follow these two posts by looking at the tests that are carried out during the car development. This part of the car design course is important because it contains the most inaccessible information to the public. This is because the technical know-how of the brand is located here and they tend to be very secretive with all this information.
Now we will see three tests: Tightness, Comfort and material testing. For next week: Vehicle dynamics, and the final test.
The main function is to check that no water enters the interior when it rains, for example, through the seals of the windshield. It's necessary to differentiate the test of the car prototype from the quality control carried out at the end of the production chain.
In car prototype testing, the solution to the problem applies to the entire model, including the production means such as molds. In manufacturing, all units go through a quality control, in this case, if there is a unit failure, just this unit is repaired or rejected without affecting the rest of the cars. That is why it's important to bear in mind that one change will affect thousands of cars.
The main tightness test consists of putting the car in a shower and keeping it for long periods of time to be 100% sure that the tightness is adequate. After this point, we can add multiple variables, such as tilting the vehicle to simulate that it's parked on a sloping street or introducing humidity and temperature variables.
Engineers also check the locks on the doors, trunks, hood, etc. Likewise, they also check that all electrical components work properly under adverse weather conditions.
In this department the engineers check that the car is comfortable for the driver. They check a wide variety of aspects, for example: they check that the interior lights don't dazzle the driver in different situations. This also applies to all displays and gauges in the car, it is strongly linked to the automotive ergonomics that we studied in the previous post. The sound insulation of the vehicle is also tested by testing the sound insulation of the car.
It's essential to make sure that there is no noise in the vehicle, the department that is in charge of this is called with the acronym NVH (Noise, vibration and Harshness). It wouldn't be pleasant for anyone to travel in a vehicle where components are constantly vibrating and rattling due to poor assembly, or sizing errors.
Engineers check that vehicle component settings are perfect. In the initial trial phase the engineers already checked that the pieces fit before starting any test, but this was done statically. Now, they must check that these fittings don't make strange noises when the car is in motion. So this department makes sure to reduce all possible noise that may arise in a vehicle, such as aerodynamic noise or the noise of the wheels and brakes.
Therefore, the engineers check that there is no squeak or rattle, this is known as: Buzz, Squeak & Rattle test. It's easy to design a piece for the dashboard, but then the pieces have to fit together. If this doesn't happen, when the car goes at 120km / h on the highway, these parts show slight displacement causing annoying squeaks for the driver. The removal of squeaks, and even the vehicle's own soundproofing, are directly linked to the quality of the car's construction materials. In addition to the practical test, there is a very high mathematical component in this type of test. Rolls Royce is an expert in this area, building one-piece dashboards, so there are no possible vibrations.
Noises can come in two different ways: Periodically due to, for example, the engine assembly or it can come randomly due mainly to irregularities in the road.
Engineers also conduct seat comfort tests. There are several multi-axis vibratory platforms called multi-axial simulation tables or Shaker Table, known with the acronym MAST. These tests are used to simulate vehicle vibrations and the inertial forces suffered by passengers in the vehicle seats. Vibration can be simulated in a specific terrain, simulating the layout of roads in different parts of the world from the same laboratory.
The tests of a vehicle are carried out to test certain parameters in a multitude of vehicle components, so that the same type of machine can be used for different uses, with its due adaptations. That is, the same materials test will be used when studying both the suspensions and the car engine. In the case of the MAST, it can be used for the entire vehicle or for certain components.
But we don't stop there, there are many more tests dedicated solely to the car seat, which recreate the wear and tear of it over years, but in a few hours. Everything can reach the level of detail that the imagination allows us, for example, Ford is not satisfied with heating the cushion to mimic body temperature, but also adds sweat glands to mimic the sweat of a person when sitting down.
Automotive materials testing
This is one of the most extensive areas, every engineer knows what type of material tests exist. From checking the rigidity of the chassis, to corrosion in the paint and exposure to light of the plastics on the dashboard.
Mechanical vibration, impact and shock tests are carried out, even in combination with temperature cycles and vibrations. For the temperature cycles there are special climatic chambers that simulate all kinds of environmental conditions, varying humidity and temperature. In this type of chamber, also called a climate tunnel, weather conditions are simulated in an accelerated manner, in such a way that it's possible to recreate the deterioration suffered by a vehicle for years in a matter of days.
They have different types of thermal lamps, turbines that generate wind currents of up to 300km / h, complex sprinkler systems and humidifiers. Engineers can simulate environments with temperatures of minus 55 degrees, rain and even snowfall. It's like a car wash, but a lot more fun.
These climatic chambers also act as small wind tunnels. In one of them, the engineers put the cooling of the engine, the brakes and the passenger compartment to the test by raising the temperature to around 60ºC. The vehicle is placed in front of turbines that move the air at speeds of over 250km / h.
There are also benches to produce vibrations and fatigue laboratories to study the behavior of the different elements under continuous cyclic loads. Materials testing is interdepartmental.
The area of automotive materials is relatively extensive, especially the part of materials technology that delves into the types of steels and their composition. By extension of the course, we cannot address it in depth.
Before this, we will ask a question:
Which is more expensive: a bag of chips or a car?
Taking the prices of Spain as a reference, as an example: A bag of potato chips (for example: Lay’s) costs around € 1.5 and the bag weighs 160 grams. A Renault Clio in its most basic version costs only € 9,690 and weighs 1,042 kilograms. In reality, a Renault Clio will have a higher cost once the extras are added, we enter the real financing conditions or higher versions are chosen. But let's take the base price as a reference.
The chips that we have taken as an example have a cost per ton of € 9,375. The Renault Clio has a cost of almost € 9,300 per tonne.
So a simple potato chip has almost the same price / kg as a car with all the technology and development you need. That will give us a handle on why the engineers need to cut costs and take special care with the selection of materials. As a general rule, 70% -80% of the weight of a car comes from the different metals used in the car, with steel being the main protagonist. However, we can also find other materials such as plastics, aluminum and glass.
Steels provide good strength, malleability, toughness and rigidity at an affordable cost. They are used mostly in the self-supporting structure of the car, although not all steels are the same. As we saw in the crash tests post, we are interested in a great resistance in the cabin, and having deformable areas in the front and rear of the vehicle. Therefore, engineers will select higher strength steels in the cabin.
As we are aware, steel is an alloy made up of iron with typically a few tenths of a percent of carbon. Other elements are also added that will influence its final properties. Due to this great diversity of steels used to manufacture vehicle bodies, we must divide them into groups, taking into account the elastic limit of each steel.
Mild steel is a carbon steel with a low amount of carbon that is cold rolled. Mild steel is not an alloy steel and therefore doesn't have large amounts of other elements besides iron such as chromium or molybdenum.
It's easily deformable in presses and can take different forms with relative ease. However, due to its low elastic limit, to withstand the stresses to which the pieces are subjected, it would need much greater thicknesses, which would also imply a great increase in weight. It's used at non-critical points on the self-supporting chassis or on the outer sheet of the vehicle itself.
High strength steels: This group includes steels with a high elastic limit (HEL) or High-strength low-alloy steel (HSLA), among others. Then we have a third group called very high-strength steels, but we can still go one step further and use those of the fourth group, called Ultra-high strength steels (UHSS). Last ones are outstanding steels capable of absorbing large amounts of energy without deforming. These steels are used at key points, for example, in the B-pillar of the car.
In the next post we will see the last tests, including the vehicle dynamics. Thanks for sharing, don't forget to follow us on our social media.