CS - Design Steps 6 & 7: Manufacturing and Performance Testing

Think through your manufacturing and performance testing strategies. Talk to your mentor for an expert opinion of your design. Start immediately and assign sub-tasks to all of the team. Enforce deadlines for all the team! Keep the device drawings up to date. Use your materials to make the device. Use appropriate material joining methods such as glue, nails, screws, etc.

Introduction

Manufacturing begins once the detailed design has been approved and ends when the machine is completed. In between, the machine undergoes numerous modifications. Few new designs work on the first try. Manufacturing and testing tend to take much longer than expected—probably three to five times as long.

Step 6 & 7 : Manufacturing and Testing Strategies

Manufacturing

You can employ strategies during manufacturing to minimize the time it takes to get the first prototype ready for initial performance tests. The extra time freed up for testing and design refinements can prove decisive for an effective design.

The following time-saving manufacturing strategies have been observed in successful teams:

• Talk to a mentor. Professional mentors are considered partners in the design process. If they lack in knowledge of the engineering design process and analysis, they make it up for in manufacturing and practical experience. As a practicing engineer, you will be required to consult with you mentors before finalizing your detailed design.

• Don’t delay in getting started. Take the leap of faith and begin manufacturing as soon as possible. Only then does the team gain a realistic sense of the manufacturing timeline.

• Divide up responsibilities so that team members can work in parallel on different sub-assemblies. Otherwise, you may find the entire team standing around waiting for the "same glue joint to dry".

• Keep detailed drawings up to date. If they are not up to date, only one person knows what the actual design looks like. That one person ends up doing most of the manufacturing, while the other team members watch. With accurate drawings, team members can work in parallel.

• Set and enforce intermediate deadlines. Manufacturing can span several weeks. The instructor sets the big deadlines through the milestones; the teams should set the little ones in between.

Testing is as important as manufacturing in preparing your design.

For example: three design teams were assigned the task of designing machines capable of playing 18 holes of miniature golf at a local course. The first team was stocked with experienced machinists, so it built its machine out of thick steel parts. The second team had an expert welder, so it welded together its machine out of steel beams and plates. The third team chose to make its machine out of wood. Three very different manufacturing skill sets, yet all three machines failed at the final competition for the same reason,—not enough testing. The first team did not test its machine on synthetic grass before the competition. Its steel machine was heavy, which created large friction forces between its tank-line treads and the synthetic grass. When it attempted to turn, the treads broke, immobilizing the machine. The second team did not have time to test their steering mechanism due to last-minute modifications. As a result, it could not consistently maneuver into position for putts within the time constraint. The third team completed manufacture and testing of its moving platform 2 weeks before the final competition. Over the next 2 weeks, while the putting mechanism was being made, it did not test the moving platform again until about 30 min before the start of the competition. The machine never moved.

The lessons learned by these three teams apply to all design competitions. They are summarized in the following testing tips:

• Always leave a lot of time for performance testing.

• When conducting performance tests, try to simulate as closely as possible the real operational conditions of the final product. If these conditions are not known, test under a variety of conditions to insure robustness.

Materials

When possible, the designs should be made of recycled materials, and what is available at School, or at home to facilitate manufacture and keep costs down.

If you needed you might have to set up a crowd funding site to raise the necessary funds. also talk to the STEM coordinator

Manufacturing can be simplified still further by constraining the designs to be small (less than 1 ft³) and lightly loaded. Under these conditions, for example: balsa could be used as the main structural material.

EXAMPLE: Recommended materials for a small, lightly loaded electromechanical device are listed in Table 26.1, along with their relative attributes. Balsa is listed as easy to use with hand tools because it can be cut and shaped easily with a sharp knife. On the other hand, plastic tends to deform rather than shear cleanly under the action of cutting tools, and so it is listed as hard to work with.

Table 26.1

List of Recommended Materials for a Small Electromechanical Design Project

Note: The strength (resistance to breaking) and stiffness (resistance to deformation) are normalized with respect to values for balsa wood.

When selecting a material from Table 26.1, the strength and stiffness requirements of the given part also need to be considered. For example, if there are concerns about a part breaking under load, strength considerations override ease of manufacture, leading to the use of plywood instead of balsa. If a small-diameter axle requires high stiffness so that gears can remain engaged, then a steel rod may be the best choice.

Joining Methods

For small-scale balsa and wood structures, the preferred joining methods for parts are adhesives, wood screws, and machine screws with nuts. Typical joint configurations employing these methods are shown in Figure 26.1. Use of tapes, especially duct tape, is frowned upon for their non permanence and poor aesthetics. Nails are not particularly compatible with balsa because of the large impact forces involved and the possibility of wood splitting.

FIGURE 26.1 Different joining methods.

Adhesives, in particular hot glue, are the method of choice when balsa is the predominant structural material. Hot glue cures quickly, and though essentially permanent for wood-to-wood bonds, metal-to-wood bonds can be adjusted or broken by heating. It is so general purpose that it can be used to mount a motor to a plywood base. The main drawback of hot glue is its low strength, but this is usually not an issue for lightly loaded balsa structures. When it does become an issue—for example, when the surface area available for the glue joint is very small—one of the higher strength adhesives listed in Table 26.2 may be substituted.

Table 26.2

Common Adhesives

Performance Testing

By the time this milestone is reached, teams should have completed their first manufacturing iteration and begun performance testing.

For the Performance testing Lab report review the requirements for the design experiments (Design step 4)

Remember these set of tests need to be performed on the whole prototype to test its intended functionalities.

i. Optimize the performance of your machine/project in preparation for performance testing evaluation.

ii. Design performance test with the help from your mentor according to the nature of your project.

Questions to discuss/Brainstorm with your team, Hypothetical scenarios

Manufacturing and Testing Strategies

Hypothetical question 1: Now that you have built your design, it's time to conduct the final performance test. You only few weeks left in the semester, and during your first test, What if you determine that your prototype does not function properly. How would you salvage your design before the semester ends? Think about your options.

Hypothetical question 2: When you begin testing the prototype of your design, you find that an important component you made from balsa wood breaks under load. You need to fabricate a new version of the component and replace it quickly. What material do you choose for its replacement? Your team’s final design calls for gluing two pieces of metal together. During testing, the glue doesn’t hold and the prototype fails to function properly. How do you fix this problem quickly and securely?

Hypothetical question 3: One of your team members wants to assemble the main components of the design with bolts. It turns out that the bolts add a lot of weight to the prototype and are difficult to keep from coming loose during testing. What would you recommend using instead of bolts at this late date and why?