As it is seen from the equation auto mass can be reduced by taking the stuff with lower denseness or by cut downing the volume of auto parts. In footings of the first solution steel remains to be the most suited stuff because of it 's mechanical belongingss. Steel has satisfied formability, articulation ability and output strength. Customers are happy with steel. Almost all autos are made from steels and the industry has all agencies and conditions for it. However, unstained steel is rather expensive and coating must be used. There are besides some alternate stuffs with lower denseness - Ti ( I?=4.52 ) , aluminum ( I?=2.71 ) , glass ( I?=2.55-3.55 ) , Mg ( 1.71 ) , composite ( 1.55-1.93 ) , polymer ( 0.9-1.7 ) , cloths ( 0.8-0.9 ) , white pine ( 0.51 ) . ( Istochnic ) . But they can non be used by several grounds:
Cost - auto doors made of Ti, Mg, aluminum can be really expensive, so that clients will non accept these autos.
Lower mechanical belongingss. Cars may non go through clang trials
Joining troubles -it can be hard to fall in such auto outer door panel with the body-in-white. Extremist alterations of the whole fabrication procedure may be required
The alteration of the stuff may ensue in the alteration of assembly fixtures, organizing dies, etc.
Further probes are necessary
Some of these stuffs are already used in luxury autos, such as Lotus. ( Istochnik ) . But for household autos it seems to be impropriate. Hence, steel is chosen for the auto door outer panel.
To cut down auto mass another parametric quantity can be changed - V ( volume of the constituent - in our instance the volume of door ) . We can non extinguish this constituent due to safety demands. We can non change the surface of the door, because it can do the alterations of the whole building. That is why the merely possible thing we can make is to understate the thickness of the door which seems to be the best option. However, we should utilize another type of steel to follow with all safety and design standards.
to cut down the auto outer door panel mass at least by 25 %
take the thickness of the door
carry out trials on formability, articulation ability, corrosion opposition, dent and oil-canning trials
take the steel and coating method
Calculate weight and cost nest eggs
When planing auto door the most important belongingss should be considered are:
Joinability - the ability of steel to fall in, depend on the chemical science and strength ( Istochnik I change )
Formability - ability to accept the desirable signifier deue to fictile distortion. With the addition of strength formability decreases ( Change and Istochnik )
Corrosion opposition - bar of the destructive onslaught by the environment ( alteration and Istochnik )
Dent opposition - the ability of the stuff to defy local distortions. Small defects can be caused by rocks ( Change and Istochnik )
Furthermore trials are needed to be carried out in order to look into the belongingss of chosen stuff.
Dent and Oil-canning trials
Dent trial and Oil-canning trials are required to find the thickness and the output strength of auto door panel. The minimal values of this parametric quantities following with this demands should be found. Difference between as-received output and the concluding output strength. Istochnik
As-formed output strength, Mpa
Panel curvature, millimeter
Panel mass, kg
Table 1. Date from the dent and oil-canning trials for each thickness
Figure 1. Yield Strength against curvature for each thickness
What parameters does the dent trial depend on?
What parameters does the warp trial depend on?
Which strength is needed for each thickness?
The life-time warrant for auto door panel is 12 old ages. Several factors contribute to the corrosion opposition, including the stuff chosen. Stainless steel has first-class opposition to corrosion, but it will be really expensive to bring forth auto from this stuff. Uncoated steel will non last for 12 old ages harmonizing to rust procedure. So, the coated steel is the most cost effectual manner of bettering corrosion opposition of an uncoated merchandise.
There are several types of coatings, viz. : pigment coating, Sn coating, Zn coating, Cr coating and polymer coating. Paint, Sn, polymer, Cr can give aesthetic consequence but one time scratched it will non protect steel from the corrosion because they act merely like a barrier. Serious environmental concerns and high cost can be deal with in the instance of polymers and Cr. Furthermore, extra coating may be needed to give the appropriate coating and surface required by clients and marketing co-workers. That is why Zn seems to be the best coating stuff. Even if scratched it will give the steel. It gives an first-class protection due to sacrificial mechanism. However, extra bed is needed to obtained coloring material that consumers need.
Industry criterion corrosion trial is carried out in order to find the thickness of Zn coating and technique for using Zn coating. First Zn coated sheet 150x100 nanometer is treated with Zn phosphate, premier with catodic electrocoat, spray with white based coat and finish with clear coat. Scribe the painted steel - one diagonal abrasion through the coatings to the steel. The sheets are subjected to the 80 rhythms. - one per twenty-four hours. This corresponds to 3.4 old ages of exposure to existent conditions. Measurement showed how many millimeter of pigment next to the Scribe was removed.
Due to the experiments day of the month the most effectual type of surfacing are HD galvanised and HD galvannealed. Cold rolled steels showed the worst corrosion opposition.
Coating weight, g*m2
Average scribe weirdo, millimeter
Electrogalvanized steel+Zn rich primer
Hot dip galvanized steel
Hot dip galvanized steel
Hot dip galvanized steel
The size of the auto door is 700x1000 millimeter. So, the country of the door is:
S= 700*1000=700 000 mm2
It is known that the average loss of pigment is 0.01 % after 12 old ages. The country of paint loss can be calculated as:
Spain loss=700 000*0.01/100=70 mm2
If this happen due to one abrasion, it may be possible to cipher the mean scribe weirdo after these 12 old ages. However, it is assumed that horizontal Scribe is non governed by the length of the abrasion.
Scribe creep12 years=70/10=7 millimeter
Scribe creep1 year= 7 / 12 = 0.583 millimeter
Scribe creep3.4 twelvemonth = 0.583 * 3.4 = 1.9822 a‰? 2 millimeter
Using the above secret plan it is possible to happen the thinnest coating matching to 2mm scribe weirdo. The thinnest coating is 60 g. per mm2 or 8.4 Aµm.
The surface coating and the cost depend on the type of surfacing. The average cost for 60 g/mm2 coating is the undermentioned: 1.27 for galvanneal steel ; 1.3 for dip galvanized and 1.33 for electrogalvanized. Similarly the surface finish index is 1, 0.95 and 0.9, severally. Hot dip galvanized coating was chosen for this instance, because this coating showed itself better during corrosion trial and it has the mean values of the cost and surface finish index.
During formability trial a steel foliage is analyzing at particular imperativeness. This trial demonstrates the location of major strains in auto door panel. The angle parts of the panel a most likely to tear during forming.
To prove these corners Forming Limit Diagram is applied. It is seen from the trial that the location of the secret plan on the Diagram depends on several factors, such as strength, type of the coat and oil for lubrication. To put the points to the safe country the undermentioned parametric quantities were chosen:
Thickness t = 0.6 millimeter
As-received yield-strength 290 Mpa
Coating - hot dip galvinised
Lubricant - Oil 2
The as-received strength alters the work indurating advocate which affects stretching of the steel sheet. In our instance the minimal work indurating advocate was found to be 0.2.
We besides do n't take into history the R value since deep drawing is non utilize for auto door panel.
There several types of fall ining techniques, such as adhesive bonding, concentrating and welding. Adhesive bonding is non normally used for auto door because it is technically complicated and economically unbeneficial. Riveting is used for some parts of autos but this method is impracticable for doors, since it would impact the visual aspect of the vehicle. In this instance welding seems to be the most appropriative. Steels are easy welded together, what is widely used in industry.
Among the great sum of welding techniques ( electron beam welding, optical maser welding, seam welding, metal inert gas welding, opposition topographic point welding, discharge welding, clash welding ) opposition topographic point welding is the best pick for auto door outer panel. This technique is accessible and easy.
the thickness of the steel sheet and the type of surfacing can impact fall ining procedure. That is why joinability trials should be carried out to look into if steel sheets with chosen coatings can be welded together. During the trial the following values were determined:
Thickness, T millimeter
As-formed output strength, MPa
Welding current, kA
Welding clip, rhythms
Hold clip, rhythms
2000 dyer's rockets
1 rhythm = 0.02 s
What is the minimal and maximal current that produces acceptable dyer's rockets?
Which is the minimal and maximal electrode force?
What is the minimal and maximal dyer's rocket rate?
Determine this inquiries when there is no coating
Now we have to take the steel class. Harmonizing to our consequences, we were proposed 6 types of steel:
The BH220 Bake Hard steel was chosen.
The comparative tabular array of current and chosen steels:
Comparative parametric quantity
Steel thickness, millimeter
Steel curvature, millimeter
Min burden, N
Min welding current, kA
Min welding clip, rhythms
Hold clip, rhythms