汽车的多材料加工工程学dissertation

关于多材料加工的工程学文章

 

在汽车设计中所使用的材料种类正在稳定增长，有一个明显的趋势出现了：为特定的目的而使用特定的材料，这种使用不同的材料的方式就被称为多材料加工。预计混合材料生产的外部部件和可生物降解材料生产的内部部件的使用率将会上升。

 

虽然多材料设计的总体趋势正在增加，但主要运用哪种材料还未明晰。轻量型的结构将是重点关注的领域，因为它会减少车辆的重量，从而提高燃油的使用率。这引导了来自世界各地材料供应商的合作。每一种材料都有特定的制造工艺，在未来的设计制造过程中选择正确的工艺和材料将是一个更大的问题。现在人们对于加工方面有更大的需求，它们想要处理不同材料的加工，可以通过配置而执行不同流程的机器。

 

同时，也会加入不同材料的新方法。粘合剂被看好，人们认为它在汽车制造中会变得越来越重要。除了多材质的设计外，这些胶粘剂减少了车辆的总重量。光粘合是粘合剂的一种，它能够在光照下变硬，是这一领域的最新发展成果。

 

虽然多材料设计有很多优点，但有一些缺点。回收这些材料是一个大问题。在一个产品中使用的材料越多，回收过程就越困难和昂贵。一些胶粘剂在加热时会松动，这易于回收利用。因此，我们必须在设计制造工艺的同时设计回收过程，使这些缺点可以最小化。

 

汽车中使用的材料

 

汽车的总重量将在1500 - 1700磅左右。重量的减少是通过使用碳纤维增强塑料（CFRP）作为外体材料完成的。（van der Wiel等）碳纤维是超强材料，同时又非常的轻。

 

The Multi Material Processing Engineering Essay

 

The variety of materials used in automotive design is steadily increasing and there is a clear trend to use specific materials for specific purposes, this type of using different materials is called as Multi- material processing. There is an estimated increase in the use of hybrid materials for the exterior parts and biodegradable materials interior parts.

 

Though the trend to multi-material design is increasing, it is not clear which materials will be the predominantly used. Light weight construction would be the key focused area as it will reduce the weight of the vehicle and thereby increasing the fuel efficiency. This has led to the collaboration of material providers from around of the world. Each type of material has specific manufacturing processes, choosing the correct process or the material would be a bigger issue in the future while designing the manufacturing process. There is a strong need for processes that can be adapted to process different materials and for machines that can be configured to perform different processes.#p#分页标题#e#

 

There will also be new ways of joining different materials. Adhesives are expected to gain in importance in car manufacturing. In addition to multi-material design, these adhesives reduce the total weight of the vehicle. Photo-bonding is a type of adhesive that hardens under light is a latest development in this regard.

 

Though there are many advantages with multi-material design, there are some disadvantages. Recycling of these materials is a major issue. The more different materials are being used in a product, the more difficult and expensive is the recycling processes. Some adhesives are loosening when heated and this enables easy recycling. Therefore we have to design the recycling processes while designing the manufacturing process so these disadvantages can be minimized.

 

汽车使用的材料-Material used in the car

 

The total weight of the car would be around 1500 - 1700 lbs. The weight reduction is brought by using Carbon Fiber Reinforced Plastic (CFRP) as the outer body material. (Van Der Wiel et all) Carbon fibers are super strong material and at the same time are lightweight. It is five times stronger than steel but weighs two thirds lesser. Though they cost more, the invention of sheet molding compound with chopped carbon fiber has led to lower material cost. It is also resistant to corrosion, acid and organic solvents hence will have longer useful life than metal. In addition, CFRP remains stable under all climatic conditions, showing very little change in shape even when exposed to large temperature fluctuations.

 

The high rigidity of this material is accompanied by excellent damping qualities and high impact strength. They have good energy-absorbing capabilities, making it damage tolerant. As a result, body components of the car would have great crash performance. The passengers would be safer in here than a car made from conventional metal.

 

Nanotechnologies are considered to be important factor in changing the manufacturing processes. Nano-powders help to improve powder metallurgy methods. This would certainly have an effect on the industry since powder metallurgy is widely increasing used in car manufacturing.

 

装配厂中使用的新型制造概念-New manufacturing concepts used in assembly plants

 

Earlier, Lean production was the portfolio for organizing manufacturing processes. But today many elements of the lean production concept have become standard means of organization. It seems that today the efforts for organizational modernization of the production in the automotive industry are slowing down and steps back are even taken in some companies.

 

While the lean production concept focused predominantly on productivity and cost issues, today flexibility and the ability to customize products are gaining importance. One of the major problems in this respect is how to handle increasing complexity and how to ensure integration while maintaining economies of scale and keeping capital lockup in manufacturing equipment under control.#p#分页标题#e#

 

The most important and also common strategy in this respect is the use of platforms and modularization. This is done on different levels of the supply chain and with respect to the product as well as with respect to the manufacturing equipment. Most important challenge is to balance the reduction of complexity on the one hand and the integration of the different modules and systems into one working car on the other hand.

 

The drive train and motor accounts for around one third of the value of a car. Demand will tend to shift away from mechanical parts such as crankshafts, cylinders and pistons, towards electro-technical components such as electrical motors or gas generating equipment. There will thus be completely new manufacturing processes for car engines. The changes in components will have an effect on the production methods used. Those production methods required in the combustion engine will only be used to a smaller extent in fuel cell drive systems.

 

In the case of vehicle electric parts suppliers and their outfitters, although the starter and dynamo will be omitted, electric motors for driving the compressor, cooling and metering pumps as well as the reluctance motor will be required. Technologically considered, these are similar components. For the outfitter, this means that he will not have to provide any new manufacturing technology to the supplier in order to remain part of the innovation process. Outfitters for suppliers who produce conventional components which are to be adapted do not have to fear any technological innovation leap. However, quantitative adaptations may take place, for example, the larger cooling system, or simpler construction of the transmission.

 

In order to achieve the cost targets and to minimize application barriers, the innovation process to the fuel cell requires parallel break-through in fields like: manufacturing (technological as well as organizational); research and development (particularly materials and system integration) and infrastructure (not only fuel cell but also maintenance skills and innovative sales and car concepts). It will continue to be difficult for quite some time to reach satisfactory manufacturing batches. Full environmental benefits will occur only if the whole fuel chain up to the final provision of hydrogen is strongly based on renewable and clean sources.

 

An important question is how the traditional innovation partnerships between automotive companies and machine tool manufacturers will react to that challenge.

 

Insert Molded Lead

 

(Tan et all ) Insert Molded Lead frame (IML) technology enables the flexibility and integration of the power module in the car. The power module consists of IML lead frames cut from the conductive metal strip, molded in a polymer casing offering a satisfactory temperature resistance such as polyphenylene sulfide (PPS). On the upper surface of the lead frame power and control, electronic components are assembled. The lower surface is in contact with the base plate in order to maximize heat dissipation. The power electronic is characterized by its maximum junction temperature at which the car can operate (175°C). An excessive temperature can cause the failure. Thus power losses generated by semiconductors must be efficiently dissipated through the packaging to the cooling system.#p#分页标题#e#

 

There are three factors to improve the power module:

 

- increase the junction temperature rating of semiconductor

 

- reduce the loss of semiconductor

 

- reduce the thermal resistance of the power module

 

A new substrate material that has a high thermal conductivity and a low coefficient of thermal expansion is designed for this car.

 

Substrate with copper graphite composite

 

Graphite has excellent electrical and thermal conductivity. But the bond strength between copper and graphite is extremely low.(Tientrakool et all) There are two methods to overcome this; first is to coat the graphite with molybdenum before the infiltration of molten copper; second is use of high pressures during the infiltration of molten copper within a graphite preform. The graphite fibers have excellent thermal conductivity along the fiber length but thermal conductivity perpendicular to the fiber is significantly low. As the conductivity of the copper matrix is high, the conductivity perpendicular to the fiber composite material is acceptable.

 

The power module is based on the IML design. The module has 3 power connections. For command wires, there are 3 command wires per semiconductor plus one wire for testing the bonding contact quality. Compared to the standard packaging, IML technology reduces component count and inevitably the number of assembly operations. The IML packaging once assembled with semi-conductors and the connection terminals is placed and fixed on the base plate using four screws. A thermal interface is interspersed between these two components to ensure the dielectric function and also compensate for the lack of surface contact between the substrate and the base plate.

 

PC Glazing

 

Polycarbonates (PC) have better insulation and hence it reduces the fuel consumption by reducing the air conditioning load. The windshields would be thinner and stronger when compared with conventional glass. The other advantages of choosing PC glazing over other materials is that it weighs 45% lesser than glass, can be molded into a variety of complex shapes, can be produced in different color and textures, it is very tough, increasing passengers safety. It does not shatter easily, like bullet proof glass but at a lower price point.

 

The car has a roof module with glazing and integrated solar. The roof is made from lightweight panoramic panel that consists of transparent polycarbonate. This ides was designed by Bayer material science for automotive glazing.

 

The tail and brake lights, indicators and the license plate lights are located behind the transparent outer shell and hence there is no need for individual sealing of all these lights. Transparent tinted colors have been developed specially for PC glazing that filter out a larger proportion of Sun's Infrared rays. So the car's interior does not heat up even when exposed under sun for a very long time. Properly treated glazing enables Infrared rays and energy transmission suitable for dark colors. Thus ventilation and air conditioning systems do not need to work so intensively during hot summer days. Thermal insulation using PC glazing is five times higher than normal glass and this increases the temperature of the internal surfaces during winter and therefore the energy required by the heater is also reduced significantly. These methods of heating and cooling improve the travel range of the car. The climatic benefits from polycarbonates are more environment friendly as there is greater percentage of reduction in CO2 emissions.#p#分页标题#e#

 

The roof of the car is darkened with a special Infrared absorbing gray tone. The driver and the passenger would have an unobstructed panoramic view but would not have the glaring from sun rays. This completely eliminates the need for a shading system and thereby more headroom in the car.

 

Manufacturing Polycarbonates

 

Production of PC auto-glazing requires special manufacturing techniques. The auto glazing parts are large and they must to be molded under low-stress conditions for optical quality and for retention of a hard coat. (Mikell Knights) Residual stresses in the part decreases the optical quality and coating quality, But high stress in the part could lead to haze or delamination of the coating. Injection-compression molding is the ideal process for making large parts with low stress.

 

The pressures for PC glazing are low even by the standards of normal injection-compression. These parts are molded with injection pressures from 2600 to 2900 psi versus approximately 3050 to 3500 psi for typical injection-compression molding. As these glazing panels are thin wall parts, they must have parallel surfaces for good optical qualities. New PC materials had to be developed for good flow and adhesion to a hard coat.

 

Post-mold coating technology had to advance in order to deliver high resistance to abrasion, scratching, and uv exposure as well as good light transmission and anti-reflective properties. Multi-component molding is emerging as another requirement for auto glazing. A second material is used as the frame and serves to hide gate marks and any functional elements molded into the part while keeping the exterior part shape clean. Both these materials must be molded at low pressure to minimize stresses. Most of the commercial glazing applications have a transparent center over-molded with a darker opaque frame.

 

着色-Painting

 

Self-Healing coating

 

The paint coating is made from a material that consists of 99.99% standard polyurethane, and remaining 0.01% is either a four-molecule oxetane with a ring four elements, three carbon atoms and one oxygen atom or a long rod of chitosan. When the polyurethane is damaged, a ring of oxetane is also broke open. Breaking the surface of the polyurethane allows ultraviolet light to enter the scratch, tears apart a rod of chitosan. The broken chitosan rods and oxetane rings bond with each other across the damaged area to eliminate the scratch. If the polyurethane coating is left in the sun, a scratch heals itself. Since it is made from a derivative of chitin, it is also environmentally friendly. The highly water-resistant coating maintains its self-cleaning property longer.

 

The time required to remove the scratched depends upon the depth of the scratch. It varies from few hours to several days.#p#分页标题#e#

 

Color changing paint

 

The car uses a color-morphing technology inspired from BMW, a special treatment called FeintPaint by Spanish company Payola Forlids. (Kınlı, Zeynep) The color of the car brightens up when the sun in down and lightens up when there is sun, so to reflect the sun-rays and keep the car cool. FeintPaint is comprised of tiny magnetic iron oxide particles which can interact with a low grade magnetic field to change the spacing of the particles, and hence its ability to reflect light and change color. The color changes take effect in seconds.

 

On rainy days the paint brightens, increasing the car's visibility to others on the road, while on particularly hot, sunny days the finish lightens dramatically to cool both the engine and the car's interior. Because the paint is so sensitive to changes in both the environment around it and conditions within the car itself a darkening hood can signal that the engine is beginning to overheat.

 

Auto Paint

 

Another method of painting would be the form of auto paint that changes color with the touch of a button. This phenomenon is termed as Paramagnetic paint and the idea is derived from Nissan. It uses special light reflecting coatings. (ABO, Toshimi ) The process starts out with a standard galvanized piece of automotive sheet metal steel. A special polymer is applied to the steel with super paramagnetic iron oxide particles embedded within it. The nanoscale crystalline particles of magnetite (iron oxide) are controlled using a low grade magnetic field which is used to effect the spacing of the colloidal crystals and thereby controlling their ability to reflect light and change color.

 

The coatings would be neat on the car as a continuous small magnetic charge is needed to keep the desired color active and the driver also has the ability to turn off the system at which time the vehicle turns back to its default color of white. The coating has the ability to reproduce the full spectrum of colors and can change to a specific color in about a second. The actual materials used in the process are not expensive and are non-toxic. A special hard clear coat is used to seal and protect the surface and testing has shown that the color consistency of the finish is uniform even with the sharp creases and severe bends utilized in the exterior of automotive panels.

 

传感器的使用-Sensors used:

 

The automotive systems application for sensors can be divided in three areas: powertrain, chassis, and body. (D'Orazio et all) In each of them, the usage of sensing elements is driven by different factors, like legislation, safety, weight reduction, comfort, and convenience. In general, their wide utilization is due to the following features: miniaturization, cost reduction, increased functionality, and improved quality. Accelerometers are mainly used in two application areas: impact detection, and motion measurements.#p#分页标题#e#

 

The Pressure sensors are used for air intake control. The car uses mass-flow sensors in order to have a better accuracy to meet the requirements of fuel consumption and emissions. All the other usages are aimed at measuring the pressure in turbocharger, oil, external atmosphere, fuel-tank, brake circuit, etc. According to the specific situation, the functioning range can vary from few kPa to several hundreds of MPa.

 

The temperature sensors are used for powertrain performance control, diagnostic, emission control systems, and comfort equipment. Its applications include monitoring and control of engine parameters, coolant return temperature measurement for fan-speed control, gearbox temperature monitoring, fuel temperature measurement, intake-air temperature measurement, outside-air temperature measurement, passenger-compartment temperature measurement, climate control unit parameter measurement, exhaust-gas temperature measurement before and after catalyst, and measurement of compressed-air temperature after turbo charger or compressor.

 

Together with temperature and pressure, the other predominantly used sensors are rotational-speed and phase sensors. Their applications are aimed at measuring wheel speed (for ABS and vehicle dynamics control), engine speed, camshaft and crankshaft phase (for motor control), and gear shaft speed (for transmission control).

 

Angular-rate is measured and used in vehicle dynamics control systems, automatic distance control systems, navigation, and rollover systems. Angular and linear position sensors are used to measure throttle valve angle, pedal angle or position, seat position, gear lever position, steering angle, mirror adjustment, and light adjustment to name a few.

 

Radar and video sensors are installed here in-spite of the high price of these components to increase the safety, and they are able to sense the surroundings of a vehicle. In particular, RF-radar and laser radar can be used to detect the presence and the relative speeds of objects and people, both near the car or far away from it. Video sensing can be used for the same purposes (with a low accuracy at a low cost), but its use is usually considered in more advanced systems, where scene viewing (e.g., blind spot and backup vehicle monitoring, night-vision improvement) and scene understanding machine vision (e.g., lane departure warning, lane keeping assistant, traffic sign recognition) are required.

 

A Fly-Eye Inspired Speed Sensor

 

(Sally Adee) Vehicle speed sensors that give system feedback for antilock braking systems are located between the axle and the wheel. As the wheel rotates, the sensor measures the position of 48 to 60 evenly spaced spokes.

 

The speed displayed on the speedometer is inexact. The error comes from the need to multiply the rotational speed of the spokes by the radius of the wheel, because radius varies with the make and model of the car and the type and wear of the tire treads. For higher speeds, 'a third eye' concept was inspired form the fruit flies. The sensor is composed of a fish-eye lens, a high-quality 60-hertz CMOS camera, and an ARM-based microprocessor running a special sauce algorithm that selectively filters incoming data. Both the lens and microprocessor are modeled on different aspects of a fruit fly's ability to navigate. The lens gives the camera a field of view of 180 degrees, approximating the vision of a fruit fly. (A standard lens can image perhaps 40 or 50 degrees.) The lens funnels light to the CMOS camera. After the visual data is filtered the image data is substantially reduced, and manageable for the microprocessor, which in turn processes this data and provides accurate results of speed.#p#分页标题#e#

 

As technology improves, it will bring an improvement in the automotive industry as well. Potential future car technologies include varied energy sources and materials, which are being developed in order to make automobiles more energy efficient with reduced emissions.

 

The huge amount of information coming from several sensors is reduced by using sensor fusion and virtual sensors techniques. More information about the sensors used in the car is explained below.

 

科技进步-Technological Advancements

 

Vehicle-to-vehicle communication systems, commonly called V2V are designed to prevent crashes in a number of scenarios. (Yang et all) In this car, a prominent red warning light flashes on the dash and an alarm blares, giving you time to hit the brakes before entering the danger zone. The system allows cars to communicate with roadside infrastructure, such as traffic lights, and work and school zones. The system allows the car in the same area to instantly communicate with one another over a wireless network, exchanging data about each vehicle's speed, location, and direction of travel. With that information, the system can determine whether a crash is likely and warn the drivers to brake.

 

Today's roads truly are danger zones. Each year, more than 10 million motor-vehicle crashes occur in the U.S. To reduce the number of fatalities V2V would be the way to go. It would address a wide range of crash and collisions than any other available safety feature.

 

Each car transmits its data 10 times per second. That allows a car equipped with this technology to create a real-time virtual map of all vehicles in the area, monitoring their position, speed, and location, and calculating whether another vehicle could cause a collision with that car. If the system determines a crash is possible, it will alert the driver through real-time audible, visual, and even tactile alerts; a vibration in the steering wheel. V2V would also alert distracted drivers to potential hazards when they're not attentive and looking away from the road.

 

There is a bright band of lights on the dash that reflect in the windshield, coupled with a warning sound. A yellow light signals a potential hazard, and a red light warns that action, such as braking, needs to occur immediately. This is similar to the type of alert used in many of today's forward-collision warning systems. The location of the lights could be viewed through the windshield.

 

The intersection's traffic signal would transmit data to the car including a detailed map of the intersection, the status of the light (red, yellow, or green), and a correction factor for the vehicle's GPS. This reduces the GPS's margin of error, allowing the system to know what lane the car is in. That is important for intersections with turn arrows or other lane-specific signals. With the data, a car can warn a driver who is about to run a red light. The car would announce "Red light!" And a bright strip of lights on the dash flashed, prompting the driver to screech to a stop.#p#分页标题#e#

 

Some of the other features of V2V are:

 

Intersection assist, When you approach an intersection, it alerts you if another vehicle is traveling at such a speed on a cross street that it could run a red light or stop sign and hit your car in the side. This helps prevent common and often fatal T-bone accidents.

 

Left-turn assist, When in an intersection, it alerts you if there's not enough time to make a left-hand turn because of oncoming vehicles. This can keep you from turning even when you can't see the oncoming car.

 

Do-not-pass warning, When driving on a two-lane road, the system warns you when a vehicle coming in the opposite direction makes it unsafe to pass a slower-moving vehicle.

 

Advance warning of a vehicle braking ahead. The system emits an alert when a vehicle that's two or more cars ahead in the same lane and possibly out of sight hits the brakes unexpectedly. This can help prevent a rear-end collision even when the driver is unaware of the proceedings occurring before him.

 

Forward-collision warning. A warning will sound if the system detects that you're traveling at a speed that could cause you to hit a slower-moving vehicle in the rear. It will also give you advance warning of a stopped vehicle in your lane that you may not see because of a vehicle in front of you or because it's around a bend in the road.

 

Blind-spot warning. When traveling on a multilane road, this illuminates a warning light when a car is positioned in your blind spot. It also emits a loud beep if you activate your turn signal when it's unsafe to change lanes. V2V is more accurate than current blind-spot monitoring systems that use cameras or radar and can even warn you of a car that's accelerating into your blind zone.

 

Currently these systems would work in some of the states and after 10 years down the line every state would have the kind of infrastructure to support this system. Highways in Dallas, Minneapolis, San Diego, and Seattle are using traffic management programs that provide real-time data on travel time or lane closures on electronic signs placed over the roadways. Minnesota has used the system to reduce traffic volume by helping drivers reroute around slowdowns. Seattle uses a traffic-signal-priority system that changes lights to allow emergency vehicles to pass through intersections, gives signal priority to buses, and synchronizes lights for better traffic flow.

 

Even with V2V systems in place, drivers still need to drive responsibly and stay focused on the road.

 

Black Box Technology

 

The car has a black box, similar to the one used in aircrafts. Here the black collects information about the driving details of every driver that drives the car. This data can be used for a variety of purposes and accident enquiry is the primary use. The data collected would be used to solve the crash investigation and would help manufacturers to improve the existing safety features and also to avoid these accidents from occurring again.#p#分页标题#e#

 

(Abraham, Mary-Rose)They are also called as Event Data Recorder (EDR) and it gathers much information like speed of the car, whether the driver pressed the brake pedal or if the seat belt was secured. This information would be very useful for insurance company in the event of an accident.

 

It constantly records last minute information and overwrites the existing old data due to limited storage capacity. The information stored won't be more than last 1 minute, but still during an accident even few milliseconds is very important and adds very high value in the processing of a claim and to make impartial decisions. To protect the privacy of the users, the device would not record any sound and the vehicle could not be tracked. The information stored should be used only in the event of an accident and not at any other time.

 

There is an array of sensors spread across the vehicle. These sensors transmit the data to chip that stores the information. The information could be opened only by using special software and can also be stored in a hard drive. Each manufacturer would use their own software and while processing a claim, the insurance company should send the device to the manufacturer to get it processed.

 

Technology for the differently abled

 

"Brain Machine Interface" is a research that gives disabled drivers the ability to maneuver their wheelchairs by thought transference alone. (Carlo Menon)The next stage is to adapt the BMI processes to the car. This uses brain technology which is a combination of brain activity measurement and eye movement patterns and scanning the environment around the car in conjunction with the car's own sensors. The technology will be able to predict what the driver plans to do while driving. The technology should be able to pick this up and help the disabled perform the maneuver in a completely safe way.

 

At this time, Nissan is undertaking this ground-breaking work by working in collaboration with the École Polytechnique Fédérale de Lausanne in Switzerland (EPFL). The Nissan and EPFL partnership is developing systems that go to the next stage of the mind reading technology by using statistical analysis to predict a diver's intentions. They are also working to evaluate a driver's cognitive state relevant to the environment in which they are driving. Often times, city driving is very different than country driving in terms of terrain and the cognitive mental state of the driver. City driving can be stressful with the need to make quick, sharp decisions, while country or rural driving might be more relaxing.

 

The car will know what the driver thinks, if he want to make a left hand turn, and without driver saying or touching anything, the car itself will prepare for the turn by changing the speed the car is moving and by changing your road position.#p#分页标题#e#