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CARTECEXTERIORS Team Report: Spring 2008  José Carlos Clemente Gutiérrez ID # 339751 – Exteriors Team Member

Ángel Antonio Fernández Pariente ID # 339765 – Exteriors Team Member

Pablo Andrés Hernández Mijares ID # 788102 – Exteriors Team Member

Jorge Alberto González Medina ID # 790316 – Exteriors Team Member Copyright © 2008 SAE International

ABSTRACT

OBJECTIVES

Cartec's Exteriors Team is responsible of the manufacturing all of the body parts of the vehicle. The current team's two principal tasks are to manufacture the headlight plaster molds and the doors. During this tenure the team also helped to finish the front bumper into its final fiberglass form and in the machining of the rearview mirror molds. The Exteriors team also helped in the machining of the rearview mirror molds. They treated techniques such as glass-reinforced plastic manufacturing, computer aided manufacturing and numerical control machining. The team applied the manufacturing procedures mentioned above in order to achieve their goals.

On a broader scale, the main objective of the Exteriors team is to make all the molds for all the parts in the car, followed by the actual manufacturing on these parts. Some parts are thermoformed, while others are made of glass-reinforced plastic. More specifically, the current Exteriors team’s goals were the following:

INTRODUCTION During the past few months, students from the ITESM have been working on the Cartec. This project was divided into certain groups. This section of the report will concentrate on the progress made by the Exteriors team. The Exteriors team is responsible for everything related to the actual exterior car body. In summary, the process consists of getting the surfaces from the industrial designers and from that design the molds for these. Once the molds are design in NX, they are opened with WorkNC to make the numerical control code. The purpose of this report is to go in-depth into all of the tasks made by this team this semester. It will mainly concentrate on the headlight molds, the doors and all of the procedures, techniques, machinery and components related to these parts.

LEARNING GOALS • Learn how to use Solid Edge. • Learn about making parts of glass-reinforced plastic (fiberglass). • Learn how to use the Huron KX 10 Machining Center. • Learn to translate the NX parts into a WorkNC program to create the machining code (the Computer Aided Manufacturing aspect of the project). DELIVERABLE GOALS • Investigate which Lexan polycarbonate would be appropriate for the manufacturing of the headlights and the purchase of this thermoplastic. • Gather the surfaces from the Industrial Designers and from these create the necessary molds using the NX5 software. • Create a well made manual that explains how to use the Machining Center and the Work NC software for future Exteriors teams. • Finish the molds and manufacture the headlight clay molds and both fiberglass doors. Necessary Elements to Create Each Part Properly: The manufacturing of each vehicle part is a long and complex process. To tackle this task adequately, the


team members need to have the following characteristics: • Be well trained in the fiberglass creation process. • Being familiar with the NX CAD software, since this is the software used in the design process. • Being familiar with the WorkNC software, since this is the software used to create the numerical control manufacturing program. • Be well trained when it comes to using the Huron Machining Center. • Being familiar with the thermoforming process.

finishing of the mold. It used a spherical flat one inch tool and its operation consisted of optimizing the flat parts. The third program was also for finishing details. It used a spherical half-inch tool and its operation consisted of parallel finishing.

VEHICLE PARTS (GLOBAL) The Cartec’s body will consist of several parts. Some of these parts are already done, like the front bumper, the hood, and the front fenders. The following diagram shows the main parts of the car.

The parts labeled on the image above are the following: A. Hood – finished part B. Front Bumper – finished part C. Front Fender – finished part D. Door – current Exteriors team part E. Mirror Base – future Exteriors team part F. Lateral Panel – future Exteriors team part G. Rear Bumper – future Exteriors team part H. Roof Frame – future Exteriors team part I. Headlight – current Exteriors team part J. Lower Part – future Exteriors team part The molds for which the current Exteriors team is responsible are the headlight and the door. The team can also be credited in the process of manufacturing the rearview mirrors and the front bumper. REARVIEW MIRROR - Although the molds for this part were not designed by the Exteriors team, they are included in this report because the Exteriors team machined them. Both the left and right rearview mirror molds were machined with the same features and parameters. They were machined using 20 x 13.4 x 3.5 (inches) blocks of MDF. These molds required three numerical control programs for their machining. The first program was the roughing process and it used a flat one inch tool. Its operation was to make an outline of the desired mold. This first program had a fixed step in the z-axis of 2.54 millimeters. The second program was the first part of the

FRONT BUMPER - The front bumper of the Cartec was designed and machined by a previous Exteriors team, but it also falls into the current team’s responsibilities since this year’s team helped some of the previous team’s members into making the fiberglass part. The Exteriors team worked for roughly around a month with this part.

HEADLIGHTS The headlight was the first exclusive assignment for the Exteriors team. The first part of the process of creating such part was to gather its respective surface from the Industrial Designers. INITIAL MOLD CREATION - Once this surface was obtained, the mold design process began. This was a complex task since it was the first time the team designed a mold with its respective constraints. After a long learning curve, the design got finished. After that the design got imported into WorkNC, with the purpose of creating the numerical control programs. Once again this part of the process had a long learning curve since no member of the team had previous experience using Work NC.


The first machining attempt seemed accurate at first, but then some flaws blossomed. One of those was caused by inaccuracies when it came to fixing the axes correctly at the Work NC. The result of this was an unsymmetrical appearance. After checking the flaws with the software, the numerical control programs were edited and corrected.

required four numerical control programs for its machining. Just as the lower mold, the first program was the roughing process and it used a flat one inch tool. Its operation was to make an outline of the desired mold. This first program had a fixed step in the z-axis of 3.5 millimeters. The second program was the first part of the finishing of the mold. It used a spherical half-inch tool and its operation was to do the finishing following a three dimensional curve. Both the third and fourth programs were also used for finishing purposes. They used a flat half-inch tool and its operation consisted of planar remachining. The difference between the third and fourth programs was their specifications. The third program used a minimum x-axis zone of 0 and a maximum x-axis zone of 63.5. Its y-axis zone specifications were a minimum of 298.45 and a maximum of 360. The fourth program had much higher specifications on the x-axis but lower on the y-axis. It used a minimum x-axis zone of 527.05 and a maximum x-axis zone of 580. Finally, its y-axis zone specifications were a minimum of 0 and a maximum of 57.15.

The lower mold of the headlight was machined using a 22.75 x 14.25 x 6.5 (inches) block of MDF. This mold required three numerical control programs for its machining. The first program was the roughing process and it used a flat one inch tool. Its operation was to make an outline of the desired mold. This first program had a fixed step in the z-axis of three millimeters. The second program was the first part of the finishing of the mold. It used a spherical half-inch tool and its operation was to do the finishing following a three dimensional curve. The third and final program was also for finishing details. It used a flat one inch tool and its operation consisted of planar re-machining.

Once both molds were finished, the sanding process began. The team members used waterproof sandpaper with 120, 240, 320 and 400 grit designations (this designations cause the sandpaper to change its characteristics since the higher the designation, the lower the particle diameters). The 120 sandpapers were the most commonly used since they do a great job when it comes to leveling the surfaces, but at the same time leave a smooth surface in the mold.

The upper mold of the headlight was machined using a 22.75 x 14.25 x 6.5 (inches) block of MDF. This mold

After investigating alternatives to machining the molds again, the team concluded that the best way to correct such problem was to apply automotive body filler on top

MDF MOLD CORRECTION - A couple of days later, the team members found out that the molds were not correct after all. This was because they were designed without considering they were going to be negatives, but designed as if they were going to be the final molds. This meant that the lower MDF mold would eventually be the upper plaster mold, and obviously the upper MDF mold would eventually be the lower plaster mold. To correct this mistake, the lower MDF mold would have to be smaller and the upper MDF mold would have to be bigger for them to be congruent once they were made in plaster. In other words, the molds had to be corrected so they would acquire the present shape once they were thermoformed.


of the molds. This would help by shaping the mold differently and after that it opened up the possibility of being able to machine on top of the previous mold. This way, time and MDF would be saved. This body filler is made out of polyester resin, talc, styrene, calcium carbonate, inert filler, magnesite and quart. It is very toxic and it can cause serious damages to the brain and nervous system if it is not used correctly. This filler has to be combined with a catalyst to create a strong bond (both materials on their own don’t serve any function). Once the filler and the catalyst are mixed, the mixtures solidifies in approximately five minutes, depending on the amount of catalyst applied (normally it is 2-5%) and the room temperature.



Once the filler was applied into the molds, they got machined again on the Huron KX 10. This part was the one that clearly showed how the learning curve in this type of manufacturing process is extremely steep, since they are many factors surround into getting the molds done correctly. All of these flaws caused a time constraint, which resulted into pronounced delays when it came to the suggested deadlines given a few weeks ago by the Exteriors team.

PLASTER MOLDS - Before making the headlight plaster molds, the Exteriors team decided to make an experiment using a simple T-shaped mold to see how the plaster expanded and also to experiment with the behavior of the polycarbonate after it got heated. This would be the step before actually making the final headlight molds.

Finally the new, revised MDF/body filler molds were ready to be plastered. The first attempt was a negative one, since the plaster broke when the Exteriors team tried to separate it from its wooden box. This was because the height between the upper most section of the surface and the top of the box was too small, so the solution to this was to redo the box, making it taller. Another key element when it came to making the plaster mold was to fill the wooden mold and its box with separating wax and it Vaseline before filling it up with the liquid plaster. Another important detail in this process was to put some handles inside the plastered area. This was made in an attempt to make the release of the plaster mold easier.


The picture below shows the Lexan sheet sitting on top of the T-shaped plaster mold that was created for the Lexan tests (described earlier in the report). This sheet would be eventually pressured with the other mold to try and force some deformation.

After correcting the mistakes of the first attempt, the plaster headlight molds finally came up properly. The only thing left to do after that was to sand them using a wet kitchen sponge cloth. This method is better than using sandpaper because of the material and also because these cloths when wet work great over plaster. These molds are now ready to enter the thermoforming phase of the manufacturing process. THERMOFORMING (BRAINSTORMING) – Once the plaster molds got completely dried, it would be time to start thinking of how to perform the thermoforming tasks. The Exteriors team met with an expert at the University’s ceramics laboratory and did several tests to observe the behavior of the Lexan polycarbonate. This laboratory has several ovens like the one shown in the picture below.

The first test the Exteriors team did was with a Lexan sheet of 12mm x 12mm. At first it was heated at 50°C. This part of is the preheating, which consists of getting rid of all the moisture inside the Lexan. After approximately ten minutes, the temperature got gradually increase to 155°C. The temperature stayed constant for about 20 minutes and the deformation of the sheet was minimum. After seeing that, the team members came to the conclusion that the only solutions where to either increase the temperature or to put pressure on top of the sheet. To test this, the team did both alternatives, using one sheet under pressure, and another one at a high temperature.

After doing such tests, none of them worked adequately. The sheet that suffered the temperature rise (at around 190°C and at a point at 207°C for five minutes) toasted and crumbled, creating many bubbles (as shown in one of the pictures below). The sheet that was pressured by the other mold did deform, but not in a way wished by the Exteriors team.


After those initial Lexan behavior tests, the Exteriors team came to the conclusion that the most convenient way of making the headlights would be thermoforming. The main disadvantage of this procedure was one major constraint it had. This problem was that during thermoforming the temperatures raise extremely quickly, in other words, they cannot be controlled adequately. This would cause too many bubbles to form, so it had to be done in a very delicate manner. Talking to an expert in thermoforming, he suggested that an alternative to using Lexan could be using a material called polyethylene terephthalate (PET). This is a thermoplastic polymer resin that is commonly used in thermoforming applications. The disadvantage of using PET is that it is not an appropriate material for a car headlight, but it serves well for mock up applications. CUSTOM MADE OVEN – After discussing the results of the initial tests with their instructor, the Exteriors team decided that a good alternative to pressure form their plaster molds would be by making an oven that had the dimensions needed by their molds.

The oven made by the Exteriors team consisted of eight resistances, six of those had a power of 900 W and the other two had a power of 850 W. It was designed to fit a mold with at most the dimensions of 71.12 cm x 43.18 cm. The oven at first seemed to work great, and best of all, very efficiently. It reached a maximum temperature of around 160°C. As seen in the pictures, inside it was surrounded by bricks which worked as insulators. The next layer consisted of MDF sheets and the outer most layer of Styrofoam. This oven can be seen in the picture below.

After doing this oven, the Exteriors team came to the conclusion that this oven would be convenient when it came to drying the plaster molds and removing the extra moisture inside of them. For a bigger application, such as actually forming the Lexan headlight inside of them, it would be a much tougher task. This was because the resistances did not distribute the heat uniformly, so the results would not be very accurate. Another problem caused by this custom made oven was it broke one of the plaster molds. This could eventually be fixed with an application of a body filler. OPTIMAL THERMOFORMING OPTIONS - Once the thermoforming and the oven were tested and studied with several types of tests, the Exteriors team came to the conclusion that the most optimal option for creating the headlights would be to thermoform with Lexan 9034 by vacuum forming. Vacuum forming consists of fixing the sheet in its adequate place, followed by a sudden raise in temperature until the sheet gets elastic. Once the heat is removed, the mold table is then raises. After this, the air in the space between the sheet and the mold is removed and the sheet is drawn towards the mold and takes its form. Then the sheet gets cooled, the mold table moves down, and now the product can be taken away from the machine. The picture below shows how the headlight manufactures using this technique. It is clear to see that this technique is the most appropriate for the scenario of the Exteriors team.

To do the thermoforming with the thermoforming machine, the team had to do some re-machining. They based their most recent mold on the very first mold they machined (which was incorrect). The team first


positioned the automotive body filler around the whole mold in order for it to be given a new shape. Once the filler dried, the tool paths for the CNC machining got edited to fulfill the necessity of having a smaller mold that would have the identical dimensions of its respective plaster mold. This new MDF/body filler mold would be the one that would give the team their thermoformed headlights with the correct specifications. The other alternative would be to fill the broken plaster mold with the automotive body filler and to keep trying to pressure form with the oven. The Lexan 9034, which has been mentioned several times in this report already, is an uncoated polycarbonate sheet. It is a highly durable polycarbonate resin thermoplastic used in many applications to emulate glass. This material will be described with more detailed later in the report. Since the thickness of the Lexan sheet in our cases is 3 millimeters, the ideal method of cutting the sheet is using either bandsaws or jig saws. This should have a clearance angle between 20°-30°. The rake angle should be around 0°-5°. The rotation speed of the saw must be between 600-1000 m/min. The space between the teeth in the band-saw should be between 1.5-4 millimeters.

dimensions. Six 15-mm thick MDF sheets were placed on each block to prepare them for molding. Each quarter of the door was machined using two numerical control programs. The first program was the roughing process, which used a flat one-inch tool. This process consists of removing the excessive MDF from the mold and just leaving a general form of the desired shape. It had a fixed step in the z-axis of two millimeters, so it took on average around 2-3 hours to complete this first phase. The second program was the finishing process. It used a spherical half-inch tool and it consisted of doing the finishing following a three dimensional curve. The tool paths were different for both doors. This was because even though they are based on the same drafts and partition lines, they are horizontally different. On Figure 18 we can see the four parts of the driver side door. The top left mold is the one that gives the door its most significant shape, and thanks to this we can quickly distinguish this as the driver’s door since the door on the passenger’s side has this curvature on its top right side.

DOORS The second exclusive assignment for the Exteriors team was the making the door. This part can be considered the most important of the parts assigned to the team this semester because of its time consumption. Its huge dimensions force the Exteriors team to machine several pieces in order to achieve a final mold. This section will describe thoroughly the entire door manufacturing process. The first part of the process, the molding, was very parallel to the headlight. The first task for the door was making the mold's design on the CAD software. To do this, the surfaces given by the Industrial Designers were gathered. After a few minor flaws, the mold design began. The door will consist of four molds, which will be joined together at the end to form a big mold for the fiberglass production. The image below shows the door in its CAD model.

The doors as a whole required eight different machining procedures. As one can see in the figure above, the door is divided in four parts. This was done in such way because of constraints in the CNC machine’s

Each part took roughly around 7 hours to machine, so the team managed to machine half a door per day. Following this rate, both doors were machined in their entirety in 4 days. The next challenge was to find a way to join the four molds efficiently, without leaving pronounced gaps between them. After brainstorming a couple of ideas, including screwing them together, joining them with glue and joining them with other adhesives, the team came to the conclusion that the


most convenient way of tackling this task was to put the extra MDF boards under the four molds. These boards, after being nailed, would serve as base for the entire door.

The process continued by taking the entire MDF door to the Corrosion Laboratory. This task was done with the aid of a cargo car. Once this was done, it was time to fix the gaps between the molds. To do such thing, the same automotive body filler used for the headlights was used again. The picture below clearly shows the pink areas left by the body filler. This chemical tool was not only helpful for filling the gaps, but it was also used to level the surfaces as they were designed. This part of the process required large amounts of sanding, especially with 80 grit sandpapers. The body filler was applied three times in each door, to make sure it was done correctly. Once the door got fixed and improved, it was ready to enter the entire fiberglass process (this process will be described more in depth in the next section of the report). First it received a layer of Nitrocellulose varnish, a chemical that is useful to improve the surface of the mold. Then it got waxed and polished several times, after that it received four layers of separating film and four layer of gel-coat. Some people consider these amounts too much, but the Exteriors team decided to do this in an attempt of doing the process in a more conservative way, reducing their changes of failure. Another strategy that this team used was to apply a larger than usual amount of catalyst when they applied the fiberglass rugs. This helps because it accelerates the drying process, but it can also be harmful because it can cause the chemicals to gel before they are completely applied on top of the fiberglass. Both doors followed this process and as a result of that both doors came out successfully. The next step into finishing the doors was to cut the excessive fiberglass from the doors edges. This was done with special equipment since it can be extremely hazardous to do this work without the appropriate protection. The picture below shows some of the team members cutting the edges of the door.

The only thing left to do after the entire fiberglass process was to do a final sanding of the doors. This is critical because this is the final part of the entire procedure, in other words, the piece that will actually be part of the final vehicle. The only thing left to do for a future Exteriors team would be to cut the edges of the door. This was currently undone because the instructors suggested such decision, since those remaining edges could very well serve for parts next to the door. Another element to consider for a future Exteriors team is the door’s handle. Since the Exteriors based their molds on the surfaces given by the Industrial Designers, these were not designed in the current mold. The fact that the actual shape of the fiberglass is very friendly; it could be easily modified with the proper investigation. Before of all that, the team should consult the actual interior mechanisms that go along with the door, because the handle is directly function of these interior mechanisms.


The following pictures show some of the parts of the door manufacturing process.

SUMMARY OF THE FINISHED PARTS If the work done in previous semesters is added together with the work done this semester, we can clearly see a significant advance when it comes to the overall amount of parts available nowadays. When the Exteriors team took over this current tenure, it already had the car’s hood and its side renders. The Exteriors team then concentrated on finishing the front bumper, followed by the headlights and the doors as described in previous sections. The CAD image below shows the parts of the Cartec that are currently manufactured.

The picture below now shows some of the Exteriors team members checking the dimensions and the fitting of the parts.


PROCESSES, MATERIALS AND MACHINES This section describes the processes, materials and machines that aided the Exteriors with their assigned tasks. FIBERGLASS - Glass-reinforced plastic (fiberglass) is made of plastic reinforced by fine fibers made of glass. The fiberglass consists of plastic that is reinforced by fine fibers made of glass. Just like a typical composite material, both materials (the plastic and the fibers) act together to create unique mechanical properties. Plastic resins are strong for compression loads, but have weak tensile strengths. The fibers have contrary effects, since they are excellent for tension but weak for compression. This is the reason why fiberglass has both good tensile and compressive properties, since it takes advantage of the positive attributes of each material that makes it. The first part of the fiberglass process is sand to wooden mold until it gets to the wished shape. Sometimes it is also necessary to apply body fillers in order to fill the gaps made after joining different molds. This automotive body filler has already been described in this report in a previous section. After this, the next step is to wax the entire wooden mold. It is recommended to have four series of waxing and in between each of them a series of polishing. Once this is done, it is now time to apply the separating film to the matrix. This should also be done in four series. Once this is done the gel coat is applied to the matrix over the film.

Before the mixture gets applied, the fiberglass must be placed first. After that, the mixture goes on top of the fiberglass. Once this is done, there is nothing left to do but wait until it dries. THERMOFORMING - This is a manufacturing process which consists of heating a sheet in a heater to its forming temperature. The most common mold materials when doing this technique are cast or machined aluminum molds, but in this case the Exteriors team used MDF molds. First the Lexan sheet should be clamped along all edges inside a clamping frame. Once it goes into the heater, the temperature raises until the polycarbonate is elastic. After that the heat is removed and the mold table is raised. Then pressure is applied to the positive side of the mould to reproduce detailed mold features. After that the sheet is cooled, the mold is moved down and the product is taken out of the machine. The major benefits of thermoforming are the following: • The production level can be small to large. • It gives short lead times. • Flexibility in the design. The picture below shows the first attempt of Lexan thermoforming.

The next part of this process is to create a mixture of two materials: polyester resin and a catalyst. The main purpose of the polyester resin is to create a strong bond for the fiberglass rug. The polyester resin is considered as a thermosetting plastic, which in other words is a plastic that sets at high temperature. The mixture ratio is 49:1 (in other words, 2% of the total mixture must consist of the catalyst). Having the correct ratio is extremely important since this is what determines the time it takes for the mixture to solidify.


LEXAN - Lexan is a highly durable polycarbonate resin thermoplastic used in many applications to emulate glass. The advantage of this polycarbonate over glass is that it has much higher strength, but at the same time it is more expensive. For the CARTEC, Lexan will be used to make the headlights. As previously mentioned, the Lexan used for this project was the 9034. This uncoated polycarbonate sheet can be utilized for many applications, but in this case it was used for the headlights. It is perfect for any application where there is no need to protect against ultraviolet rays, which is our case. The pre-drying process of the Lexan is extremely important because it absorbs moisture, which can cause bubbling and other surface problems, or even a reduction of mechanical properties. There are certain standards involved in the amount of time assigned to dry a polycarbonate sheet. In the case of the Exteriors team, since it is a 3.00 millimeter thick sheet, it should dry for 4 hours, preferably in a vertical position. The mold's geometry is what determines the amount of stretching that the sheet requires. That is function of the draw ration, which is the relationship between the surface area of the thermoformed mold and the available surface inside the clamping frames. The following equation helps us determine this draw ratio:

Whenever someone works with vacuum molding, just like this case, it is important to consider factors such as shrinkage and the creation of vacuum holes. To prevent problems related to shrinkage, it is important to add 0.8%-1% to all dimensions of the mold. Doing the vacuum holes correctly is important because the evacuation of air from the mold needs to happen as quickly as possible. In this case, the Exteriors team used a 1/16 inch tool to drill the vacuum holes in the mold.

One of the biggest challenges when working with Lexan is the cutting of the material. Almost of types of saws can be used when trying to tackle this task. Some of the essential guidelines that must be followed in the cutting process are the following: • • •

The sheet must always be securely clamped to avoid vibrations. All tools should have fined toothed panel blades. The protective mask must remain on the sheet to prevent damages or scratching on its surface.

The most common type of operation for cutting Lexan is using circular saws. One should not worry so much when it comes to cutting speeds and feeds, but some guidelines must be followed to do the job properly: • • •





Another important factor that the worker should consider when working with Lexan is the headlight's radii. A rule of thumb often used in these cases is to have all radii being at least equal to the wall thickness. The draft angles are also very important to consider when working with this polycarbonate because of the shrinking that occurs upon cooling. All surfaces should have sufficient draft angles to avoid struggling in the release of the part from the mould. It is recommended to have a minimum of 2-3°, but if possible, one should try and have angles around the range of 5-7°. In this case, 5° draft angles were used for the mold design.

The preferred types of blades are the ones that are tipped with tungsten carbide. The teeth of the blades should be beveled at 45°on both sides to improve cutting and to reduce side pressure. One should always start cutting with the blade at full speed.

In our case (3 millimeters thick) or any thinner cases, as previously mentioned, bandsaws or jigsaws are preferred. After browsing through several dealers, the Lexan was finally bought and delivered to the manufacturing lab. The distributor of Lexan in the city of Monterrey is a company called Mar Industrial Distribuidora S.A. de C.V. and their contact information is the following: MIDSA Rayón 750 Sur Monterrey, N.L. México 64000 Tel: 83-44-30-61, 83-43-47-74


At MIDSA they offer other kinds of Lexan as well, including Lexan XL10, Lexan MR10 and Lexan Thermoclear. The 9034 series has the following physical, mechanical and thermal properties: PROPERTY

VALUE

UNITS

Physical Properties Specific Gravity

1.2

Light Transmission

88

Rockwell Hardness

M70

%

Abrasion Resistance

MEDIUM DENSITY FIBERBOARD - The initial molds are made out of medium density fiberboard (MDF). This material is a product of wood fibers combined with wax and resin binder. It comes in panels which are made by applying high temperatures and pressure. This craftwood is very useful since it is less expensive than many natural woods and also because of the fact that it has no grain, so it will not tend to split. Another great benefit of MDF is that it shapes well, so it gives the worker flexibility when it comes to giving it a final shape. MDF can be easily found supply stores around the city. The Exteriors team purchased the material at Home Depot. This store was very convenient because it also offered the cutting and the shipping services.

Water Absorption @ Equilibrium

0.15

%

@ 73 °F

0.35

%

@ 212 °F

0.58

%

Yield Tensile Strength

9000

psi

Ultimate Tensile Strength

9500

psi

345000

psi

Yield Shear Strength

6000

psi

Ultimate Shear Strength

10000

psi

Shear Modulus

114000

psi

Compressive Strength

12500

psi

110

%

@ 73 °F

0.2

%

@ 156 °F

0.3

%

3.75E06 1.35

in/in/°F

Mechanical Properties

Tensile Modulus

Elongation Deformation @ 4000 psi

Thermal Properties Coefficient of Thermal Expansion Coefficient of Thermal Conductivity Specific Heat @ 40°C

0.3

Btu*in/ hr*ft^2* °F cal/gm/ °C

Heat Deflection Temperature @ 264 psi

270

°F

@ 66 psi

280

°F

-211

°F

Brittle Temperature

HURON KX 10 MACHINING CENTER - The KX 10 is the machine that aided us with the machining of the MDF molds. This three-axis machine has a friendly operating system, but requires professional operational skills or at least supervision. This machine has the following specifications: • Travel Dimensions: • 1000 millimeters in the X axis • 700 millimeters in the Y axis • 550 millimeters in the Z axis • Table Dimensions: 1250mm x 700m • Table Load: 1500 kilograms • Spindle: • Maximum rotation speed: 18000 rpm • Power: 35 Kw • Torque: 130 Nm


CONCLUSION

REFERENCES

The CARTEC project has been a challenge for not only the Exteriors team, but for all the students involved. As expected, the main goal of this project is to eventually have a completed assembled car ready to run the streets. In the Exteriors' point of view, it was better to focus on certain pieces than trying to aim on getting all of them done in a couple months. That would have been unrealistic since all of the manufacturing processes discussed in this report consist of many guidelines and most of them were completely unknown to all of the members.

Coackley, Ned, Fishing Boat Construction: Building A Fibreglass Fishing Boat, Food & Agriculture Organization, ISBN: 9251031169, Rome, Italy, 1991.

Working with fiberglass is very useful because that technique can be useful for manufacturing not only car parts, but any type of parts in general. The learning curve in this process is steep since it requires knowledge of many chemical processes. It can also be a hazardous procedure because if the worker does not take the needed precautions, it can cause serious health problems to him or her. Working with numerical control machines before graduating is also very useful for anyone who wants to be a Mechanical Engineer because those are the type of machines used in the industry to manufacture nowadays. This procedure also has a very steep learning curve because the team members were never taught how to use these machines prior to this course. The numerical control coding was also something that was taught in a very general way, and here it has to be dominated in order to machine the pieces properly. The same goes to thermoforming, since it is also a very useful technique out in the industry, but it takes a lot of knowledge to do it properly. This project has been fundamental in the team’s professional career since it gave them the first glimpse of how things are out there in the real world. To following image illustrates how the car will eventually look like:

"Huron KX 10", Fortron UK, Nelson, United Kingdom, 2006 "Lexan Polycarbonate Sheet Processing Guide", The Plastic Shop, United Kingdom "The Medium Density Fibreboard Homepage", Department of Forestry, Australian National University, Canberra, ACT 0200, Australia, 1996

DEFINITIONS, ACRONYMS, ABBREVIATIONS CAD: Computer Aided Design CAM: Computer Aided Manufacturing Fiberglass: (Glass-reinforced plastic) Composite material that consists of plastic that is reinforced by fine fibers made of glass. Lexan: A highly durable polycarbonate resin thermoplastic used in many applications to emulate glass. MDF: (Medium Density Fiberboard) combined with wax and resin binder.

Wood

fibers

Thermoforming: A manufacturing process which consists of heating a sheet in a heater to its forming temperature WorkNC: Software that transforms the CAD model into a numerical control program.


Cartec Exteriors Report