User:Medelen8/ENES100/MakerBot PLA Design

Problem Statement
Our group aims to discover the material properties of the PLA product used with the makerbot. We intend to construct several test to quantify these properties.

Requirements for each element or component derived from system level goals and requirements
The tests that pass to the implement phase must:

1. Be feasible.  2. Be economically viable.  3. Have reproducible results.  4. Be general enough to test multiple variables.  5. Not have over 10% error.  6. be able to hold weights for long periods of time up to five minutes

Alternatives in design
Many tests were initially conceived, but many rejected due to their inability to meet all requirements. 

1. The Tension Test - A cylindrical test specimen with a smaller central diameter was clamped to a surface. Weight was slowly added and the amount of deformation was measured at each data point. These values were then plotted on a stress/strain diagram and the elastic modulus was found using a graphical method. This test failed the first requirement, because it was not feasible. The amount of force needed to produce a very small amount of deformation was far too high.

2. The Heating and Cooling Test - A rectangular test specimen was first measured using vernier calipers. The specimen was then subjected to hot temperatures in order to thermally expand it. The expanded dimensions were measured, recorded and the coefficient of thermal expansion was calculated. The test was performed a second time in cold temperatures in order to obtain multiple values to average. This test did not pass to the implement phase The group found CTE unimportant. Most printed parts operated slightly above or below room temperature which made the CTE an unnecessary factor in determining PLA's limitations.

3. The Sound Test - A small cylindrical test specimen was first used to calculate the density of PLA using the water displacement method. Then a very thin and long cylindrical specimen was laid out with two people at both sides. One person sent waves through the PLA and the other recorded how long the disturbance took to reach them, calculating the wave's velocity. The bulk modulus, also known as the elastic modulus, was then calculated using these experimental values. This test was thrown out due to technical limitations, feasibility, and accuracy. The wave traveled too fast to be accurately recorded and no technology was available to measure the propagating wave's wavelength or frequency to then calculate velocity.

The initial design
The first test that met all requirements was the 3 point bending test and later the 2 point bending test. A prototype of the 3 pt test was design and tested, picture is below.

Experimental prototypes and testing conducted during design
The first prototype you can see on your right has is mostly the same as the final prototype we made the only difference is in the first one we didn't have two sets of the prototype so on the end of the filament we had a person holding it rather than them hold a block of wood. and we had previously done different measurements then quickly realized it would not work so we could evenly distribute the weight of the blocks. so we went back and made little changes

Appropriate optimization in the presence of constraints
The constraint during the design phase was finances. The incredibly high cost of tension test machines caused the group to think more creatively and to design very simple, yet practical tests. However, the simplistic design of our 3 point prototype incorporated a significant amount of error. Some sources of error from the prototype design that could be approved upon included different weight hanging and weight measuring systems, different deflection measuring system, and a shorter string to prevent swaying.

Iteration until convergence
Not applicable.

The final design
The final design, seen to the right, is very different from the initial prototype. The process was maintained and improved upon significantly reducing sources of error. To begin with, we cut a piece of wood 6 inches by 1 inch and then another two pieces of wood 3" by 2" one stacked one of the 3" by 2" wood on top of the 6 by 1 inch wood in the center of the block. we made two holes on the piece of wood one inch from the top and and drilled two nails to hold the wood together securely, Then we took our other wood piece that was previously cut 3" by 2" and stacked it on top of the other 3" by 2 inch wood. we then drilled four nails all on the edges of each side of the block so the block was securely tightened to the other block that was on top. to make it easy to weigh the blocks with minimal error. we unscrewed the four nails enough to add the filament with the little space between the blocks we added the filament vertically then made sure there was extra filament on one side so we can hold the blocks up vertically while weighing the items. we then screwed the nails back in tightly and used the two sides of the block to evenly distribute the weight.

Technical and scientific knowledge
Being that our goal was to design a scientific method in order to calculated the material properties of PLA, formulas were an essential part of our research. One more goal to add was to test the actual filament vertical for the strength by designing a product that is able to hold weights of about 25 to 30 lbs of weights. 

Equations used in the 3 point bending test:

E = (FL^3)/(4wh^3d)

E = Elastic Modulus<br \> F = Applied Load<br \> L = Distance between the outer supports<br \> w = Width of beam<br \> h = Height of beam<br \> d = Deflection of beam<br \><br \>

The applied load, F, was calculated using hanging masses. F = mass(kg)*acceleration due to gravity (9.81 m/s^2)<br \><br \>

Equations used in 2 point bending test:<br \><br \>

σult = (FLc)/(12wh^3)<br \><br \>

σult = Ultimate Stress<br \> F = Applies load, calculated as above<br \> L = Distance between the hanging mass and the clamp<br \> c = .5h<br \> w = width of the beam<br \> h = height of the beam

Creativity, problem solving, and group decision-making
As referenced before, most of our initial ideas required extremely expensive equipment. This forced the group to look outside the box, away from the most common source of a material's elastic modulus, the durability test. The durability test requires you to put the filament in between two blocks of wood and screw the wood down. for the test we were required to test the durability vertically we decided to use human efforts to hold the weight our project required no money to make (supplies already in engineering lab)

Prior work in the field, standardization and reuse of designs (including reverse engineering and redesign)
Our test was to just test the durability of the filament since it is made from natural substances and how much weight it can withstand while using a small amount of filament for testing. the testing process required us to test out different colors and to see if the color of the filament made a difference on the strength.

Modeling and/or Simulation
Our basic design was drawn in our notebook then made into the prototype stage with little adjustments in order to effectively weigh the weights with a minimal of 10% error.

Multi-Objective Design (DFX)
As long as a test meets all requirements it may be passed to the implement phase.

Performance, life cycle cost and value
Our final design meets all initial requirements. It has a relatively low percent error and is incredibly affordable, we required minimal to no amount of money due to all the supplies already being available for us but a person who does not have these requirements only needs 4 nails and 1 block of wood cut into three little wood blocks. this prototype requires no maintenance and is more than likely to last for a reasonable amount of time.

Aesthetics and human factors
Not applicable. Our goal was to design a simplistic and accurate test for the calculations of material properties, not to appeal to consumers. Not applicable. Our goal was to design a simplistic product that is able to test the strengths of different kind and different color filaments. It wasn't meant to be for the consumers.

Implementation, verification, test and environmental sustainability
Below is the finalized experimental procedure we are passing on the implement phase. It is our hope they will be able to accurately measure the elastic modulus of PLA and determine any factors that affect it, such as color, fill direction, and temperature.<br \> 3 Point Experimental Procedure<br \><br \> We as an implement group had very different task. Usage of the above Documents wasn't required but the test was almost similar to that of previous group. It included the testing of filaments using different weights. When testing this procedure, the data and calculations recorded can be seen in the example below. This will hopefully give the implement group a place to start and a base to compare their values.<br \> 3 pt Example <br \>

Experimental Procedure 2 Point Bending Test that we have design to pass on to the next group to the implement phase. 2 Point Bending Test

Maintainability, reliability, and safety
Our very simple design incorporates no moving parts. This greatly reduces maintenance to practically zero and makes our test very reliable. Even though the design still has some sources of error, results are reproducible and very similar. Our design was simple and small to carry around anywhere. while our test does require human strength in order to be able to hold the wood and be able to hold the weight being measured for a short period of time. our test is very easy to use and reliable.

Robustness, evolution, product improvement and retirement
Even though our test met all our initial requirement and goals, there is always room for improvement. Look forward to the implement stage, any ideas that would continue to reduce error in the test would be welcome. While conducting the dry run test some notes for the implement group, the PLA beam tends to shift during loads finding a way to secure the beam while maintaining concentrated supports would improve accuracy. Also, while measuring accuracy has greatly improved it is still one of the main sources of error due to the dependence of human accuracy.