Objectives - MIT



2.810 Final Report

Manufacturing Processes in Systems

Instructor: Dr. Tim Gutowski

Submitted December 13, 2000

Group B: Qing Cao, David Freeman, Jeremy Levitan, Carolyn Phillips, Cagri Savran, Eric Wilhelm, Jin Yi

Website: web.mit.edu/~geneyee/www/index.htm

As we began the task, our primary objective was to design a vehicle that has a one-inch road clearance, is robust and easy to drive. Our focus is on manufacturing the vehicle and its quick-change power-control component system. We will demonstrate its ability to function repeatedly without failure under rigorous conditions.

[pic]

Figure 1. Group B: from left to right. Jin Yi , Qing Cao, Carolyn Phillips (seated), David Freeman, Jeremy Levitan (seated), Cagri Savran, Eric Wilhelm.

A quick dimensional analysis reveals that our one-inch speed bump is comparable to bump one-fifth of the height of an actual car. From this, incurred that it is reasonable to assume that a typical suspension system, under high-speed conditions, is unlikely to greatly enhance drivability and our time and effort would be better utilized on the remaining systems.

Design Issues

[pic] [pic]

Figures 2 & 3. Completed vehicles modeled after the Porsche 911.

Overall Objectives

|Functional Requirements |Design Parameters |

|Drivability |Servo responsiveness, driving practice, suspension? |

|Rapid change of power & controls |Parts in one unit, quick change mechanical coupling |

|Robustness |Material selection, protective elements, Minimize Mass Momentum, |

Table 1. Functional requirements and design parameters for overall vehicle system. Efforts were made to minimize the interdependence of parameters through design.

Our design approach was to divide the vehicle into four systems; shell, chassis, steering and the interchangeable power-control (IPC) box. Team members choose to participate in two or more of these system groups. This allowed each group to focus on its design issues with feedback from the other systems.

| |Cagri |Carolyn |David |Eric |Jeremy |Jin |Qing |

|Shell | | |X |X | | |X |

|Chassis |X |X | |X |X |X |X |

|Steering |X | | |X |X |X | |

|IPC Box | |X |X |X | | |X |

Table 2. All members participated in system groups. Systems groups each had distinct design and manufacturing phases.

[pic]

Figure 2. Interchangeable Power-Control (IPC) Box. Time estimate for change out 3.5 seconds.

IPC Box

|Interface |IPC Box to Chassis |Servo output to steering |Power to motor |

| | |mechanisms | |

|Type |Mechanical |Mechanical |Electrical |

|Approach 1 |Coupled |Coupled |Independent |

|Approach 2 |Independent |Independent |Independent |

Table 3. Three critical interfaces of the Interchangeable Power-Control (IPC) Box. A range of alternatives were considered within approach 1 and approach 2.

[pic][pic]

Figures 4. Chassis taken from water jet. Figure 5. Solid model of chassis and IPC Box. (Locking shaft not shown)

Chassis

|Functional Requirements |Design parameters |

|Minimize momentum |Cut out excess material |

|Bend ability |Design so that there is less material at desired point of bending |

| | |

| |Design so that bending can be done without damaging parts that should not be bent. |

|Easy to Manufacture & Assemble |Minimize number of parts |

Table 4. FR’s and DP’s for the sheet metal chassis.

Steering Mechanism

|Functional Requirements |Design parameters |

|Transfer servo input to wheels. |Design interface to minimize friction within the desired operating range. |

|Easy interface with servo |Design self aligning features |

|Drivability |Adjust servo sensitivity |

Table 5. FR’s and DP’s for steering mechanism.

[pic][pic]

Figures 6 & 7. Solid model of shell and final thermoformed part.

Shell

|Functional Requirements |Design parameters |

|Pleasing aesthetics |Design an attractive shell |

|Quick access to IPC Box |Hinged top, Snap able top, hole in shell |

|Protect IPC components |Design an enclosed shell |

Table 6. Designing a new mold for our shell allowed us to gain experience using the CNC milling machine. Mold was made of wood and cut with a ball-milling tool.

[pic]

[pic] [pic]

Figures 8, 9 & 10. The classic Porsche 911.

Manufacturing Processes

Manufacturing operations were typical with the exception of the IPC Box. Design for the IPC Box was completed before decisions were made regarding its manufacture. The issues that lead to the decision to use an additive process were 1.) only one part was needed, and 2.) a subtractive process would lead to a tremendous waste of material. Therefore, the FDM 2000 rapid prototyping technology was used.

[pic]

Figure 11. The chassis underwent four redesigns before the bending problems were solved and an easy to reproduce chassis was developed.

|Process |Machine |Part |

|Milling |CNC Machine |Mold for shell |

|Sheet Metal Cutting |Water jet |Chassis, steering bar |

|Turning/Winding |Lathe |Locking Shaft |

| | |Handle |

| | |Shaft |

| | |Spring |

|Rapid Prototyping Technology |FDM 2000 |IPC Box, Aligners, Electrical connector |

| | |support |

|Bending | |Chassis |

|Injection Molding | |Wheels |

|Cutting |CNC Machine, Vertical Drill/Hole saw |Shells & wheel wells |

Table 7. Primary manufacturing processes

|Manual and Secondary Processes |

|Cutting |

|Tapping |

|Fitting |

Table 8. Manual and Secondary Processes.

Assembly Processes

[pic]

Figure 12 . Assembled vehicle.

|Method |Process |Issues |

|Job Shop Assembly |Press fitting bushings into front wheels, |Fixing & drilling required before fitting |

| |adhering foam tires to wheels. |bushing & attaching foam wheels. |

| | | |

| |Assembly of locking shaft. |Fitting required. One time job. |

| | | |

| | |Simple assembly, one time job. |

| |Fitting Power/control components and wiring| |

| |IPC Box. | |

| | |Individual preference. |

| |Painting | |

|Flow line assembly |Electrical connector assembly - soldering |Soldering iron required (one available) |

| |motor connection | |

|Cellular Assembly |Parts to chassis: electrical connector |Lean process, all members familiar with |

| |supports, IPC Box aligners, front wheel & |vehicle. |

| |steering assembly, motor, rear end (axel, | |

| |wheels, gears) hinges, shells | |

Table 9. List of assembly processes and issues incurred.

Assembly Processes

[pic] [pic]

Job Shops. Figure 13. Press fitting bushing into chassis and fitting axels (note part waiting). Figure 14. Fitting at stationary machine.

[pic]

Figure 15. Flow line manufacture assembly; soldering & shell to chassis assembly.

[pic] [pic]

Figures 16 & 17. Cellular assembly of vehicles after completion of other processes.

Redesign

During the production of our vehicle, we were required to redesign several features because of manufacturing or assembly issues. The Servo receiver, for example, was produced using the rapid prototyping process, but system software interpreted our original design as two features added together. This caused a weakened plane, which intersected the loaded threaded region. The receiver was designed such that it could only be interpreted as a single feature.

[pic]

Figure 18. Rework

Redesign Issues

|Part |No. of redesigns |Issue |

|IPC Box |1 |Assembly |

|Chassis |4 |Manufacturing |

|IPC Box aligners |1 |Assembly |

|Servo receiver |1 |Manufacturing |

|Banana clip solder connection |1 |Assembly |

|Rear axel assembly |1 |Assembly |

Table 10. Features, issues and the number of redesigns.

Performance Issues

|System |Issues |Remediation |

|Battery |Inability to maintain charge |Recharge after 8 minutes |

|Speed controller |Thermal sensitivity |Employ heat sink |

Table 11. As we completed our vehicle and began testing, performance issues surfaced regarding the components we were provided.

Lessons Learned by the Team

Qing Cao

I gained a lot of knowledge about manufacturing, especially on those processes in making our cars. Being quite unfamiliar in this field (I was not a ME major before), everything seems so challenging to me. From cutting the mold, thermal forming the shell, injection molding the wheels, using the water-jet and bending the chassis, and the whole assembly process, I got not only the basic ideas on how parts are made, but also the first hand experience on the real manufacturing process itself.

Secondly, I learned the value of teamwork. This is really the first teamwork exercise for me in America, especially in this world ranked institute. I know, as a team, everybody should be not only aggressive, but also communicate and coordinate. Due to my language barrier, I have to admit I was not doing so well in communicating with other team members as I expected, but it was really a good experience for me.

David Freeman

Having a background in both, architectural and civil engineering, I am familiar with the typical issues that arise during the design phase. Not, until this class, however, did I have the opportunity to understand how the design decisions affect manufacturing and assembly. This project really helped to drive home the DFM/DFA concepts discussed in class in addition to the manufacturing methods. We learned that by developing a schedule, taking more time and care with the design phase, we were able to do the manufacturing and assembly with minimum difficulty, finishing two weeks before the contest date. The course was also valuable in teaching project management as well as an understanding of how products are manufactured and assembled.

Jeremy Levitan

I learned a few important things from this class and the car construction project. Perhaps most tangible is that acrylic shells are very fragile. When car flips over and the shell flips with it, it's time for a new shell. Fixing cracked acrylic is also very difficult. On a more personal note, I also further developed skills of working in teams, setting deadlines and goals, and project review. It felt really nice to see everything come together and the cars completed with 2 weeks of time left to get the kinks out.

Carolyn Phillips

Since this has been my first manufacturing class, suffice to say I have learned a lot about how products are built, or how an engineer’s design goes from a CAD drawing to a product on the market. More importantly, when my roommate recently approached me with an electronic object she had broken, carefully examined it, determined how the parts had been made and then assembled, and from that figured out how the piece could be taken apart and repaired, and then reasoned out a few simple changes the manufacturers could have made to make the object less likely to break in the first place. So aside from all else, I have at least learned to impress my friends and family.

Cagri Savran

The main point that I learned in this project is the fact that manufacturing is full of surprises. In the beginning of the semester, when Prof. Gutowski gave a description of the project, I thought machining of the chassis would consume most of the time. However, the utilization of the water jet device made this one of the least troublesome steps, i.e., all we needed was a CAD drawing with the appropriate format. Water jet cutting indeed eliminated many machining steps that would otherwise be needed. Also, a 3-D printer was used to manufacture the power box that contains the battery, the servo and other relevant utilities. This tool also eliminated many machining steps. Nevertheless, certain simple machining steps such as tapping and drilling were experienced. By the same token, I would have never thought that bending a sheet metal would be as difficult as it turned out for us. Aligning the sheet metal with the bender properly required several iterations on the chassis design. The first couple of bending trials became unsuccessful. Either, the rest of the chassis hit the bending tool, making it difficult to press the handle, or the bending occurred at an undesired spot. I also learned the importance of design for assembly, and the importance of having a simple design. We experienced only minor problems during the assembly. This was mainly because our design was quite simple and required minimum number of parts. This is probably why we did not have to build a prototype, and base the production of the rest of the cars on that prototype. All of our cars were produced at the same time and every single one worked! This also surprised me a lot because in the beginning of the project I had anticipated that most problems would occur during assembly and the troubleshooting of those problems. On the contrary, having a simple design and thinking through the assembly ahead of time prevented us from having a lot of problems and saved us a lot of time.

Eric Wilhelm

Designing and bending sheet metal is not trivial! One of the key manufacturing related things I learned during this project was how to design sheet metal parts so that they bend as expected. The chassis went through 4 revisions just to get the bends correct and it was not just to get the bends to bend at the correct position, but also making the chassis so that it could be bent on the bender in the LMP shop. Material had to be cut from just the right areas making the weakest point the desired bend while other material had to be cut from just the right spot so that it did not hit the bender during the operation and destroy some part of the chassis. CAD models were helpful for the first revision, but the next three were done after taking notes on the actual bending operation.

Jin Yi

All the chasses were cut using the water jet. The chassis has many complicate features for reducing weight and fitting the battery-radio box, the motor, gear, and the steering system. It brought these difficulties to the water jet. First, for the small pieces which are cut need to be picked up after the nozzle finishing cutting them, because sometime the small pieces will block the traveling path of the nozzle. Secondly, the sand feeding system should be clear, of any obstacles. A sand clog will cause the water to beam out of the machine since it cannot cut though the aluminum sheet without the sand.

-----------------------

Dimensional analysis of suspension system.

Suspension effectiveness = (([pic],…(

hsb = height of speed bump

Hc = height of vehicle

Model ([pic]) ( Full Scale ([pic]), hsb ( 9.4 inches

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download