morehead state university

ITCD 615 – Advanced CADD

Homework 10

Travis Fisher

12/21/2012

Rapid Prototyping Comparison Chart

Figure 1: (Inkjet Methods, 2012)

2. Look at the part below (top). What process is the best suited for making this part? Then explain that process.

Figure 2: (Martello, 2012)

This part appears to be very large, complex, and it looks like a toy which probably be sent into heavy production eventually.

Based on the assumed information the best process for the development of this product would be Stereolithography (SLA).

Process Description:

In Figure 2 above you can see that the process begins with the movable table being lowered below the surface of the vat,

which is filled with liquid photopolymer. The system is air tight to avoid fumes from the resin from being released into the air. The

laser beam produces the part geometry by drawing over the surface of the liquid photopolymer. As the laser contacts the liquid

photopolymer, the material hardens creating the part geometry. Most photopolymer materials require ultraviolet light, although

some resins are able to produce the same results with visible light.

The laser beam moves in the X-Y directions and is controlled by the scanner system located on the top of the system. The

scanner system runs based on CAD data that simulates a fast and highly controllable motor and mirrors. Once the laser draws a

complete layer and the part is hardened, the movable table will move lower into the vat. After each layer is created, the movable

table will continue to lower into the vat at the same increments. This will allow the layers to stack up and the part to be created.

Once the part has been completed, the movable table is elevated above the surface of the liquid photopolymer and the

excess resin is able to drain. An additional curing process is performed by exposing the part to intense light. This box is similar to a

Post-Curing Apparatus (PCA). Not all resins require this additional curing step. Following the curing step, supports are removed and

additional surface finishing steps are conducted if necessary (Inkjet Methods, 2012).

Advantages: Good accuracy (approximately + 0.005 inches) Superior surface finish Able to use a wide range of materials Compatible with several color changing materials Widely available

Disadvantages: Liquid materials tend to be messy Parts produced may require a post-curing operation in a separate oven Few materials compatible Warpage and shrinkage issues Require supports

Given the overall size of this part, its rather complex design, and the fact that it could go into production I think that SLA is

the best process for development. If you refer to Figure 1 in the Comparision Chart you can see that the SLA machines have the

largest work envelope, and rated a “very good” in speed, accuracy, and surface finish. These four criteria are very important factors

to include when choosing a process for a product such as this but since it may go into production another major concern would be

the cost of the machine. The SLA machines are rated the highest in Figure 1 at $219K-$800K. A possible alternative to the SLA

process could be the 3DP or LOM since they are rated at a significantly lower price and still offer rather large work envelopes and

speedy process.

3. The following picture shows a plastic part that has been made by a rapid prototyping process. What do you think is that process which is the best in terms of time and cost? Then, explain that process with a schematic.

Figure 3: (Inkjet Methods,2012)

I think that this plastic part

was created using the

Inkjet method as seen in the schematic above because of the amount of intricacy that would be involved in creating that part.

Process Description:

As you can see in Figure 3 above in the Inkjet method the machine holds the build and support materials at elevated

temperatures in a reservoir until the fabrication of the part beings. The material is kept somewhat under melting point in all of the

RP processes to ensure that it is quickly and easily transformed into liquid form at exactly the right time. Also by keeping the

material at higher temperatures there is a lesser likelihood in the machine getting clogged up. Once the process has begun, the

liquid material moves through thermally insulated tubing to individual jetting heads. The jetting heads then disperses the material in

the form of tiny droplets to create part geometry. As the jetting heads continue to lay the material droplets, layers are formed. The

droplets begin to cool and harden immediately after leaving the jetting head.

When one layer is complete, a milling head passes over the previously created layer to produce a uniform thickness. The

material particles created from this step must be removed by a vacuum as the milling process is taking place. Before the next layer is

created, the nozzles are checked to assure that the flow path is clear. If the nozzles do not need to be cleaned, the table will move

down a set distance for the next layer to begin. Once the part is complete, the support structures are melted or dissolved away in a

chemical bath (Inkjet Methods, 2012).

Advantages: Capable of producing fine finishes Fast production of parts when using multiple jet heads

Disadvantages: Long production times for parts with fine finishes Less accuracy when using multiple jet heads Supports must be removed in secondary operations

Additional operation needed to provide uniform layer thickness

Although one of the disadvantages is the additional operation needed to remove the support material, I think that other

than the unparalleled intricacy that using a Single Inkjet Rapid Prototyper can provide, the fact that the support material can be

dissolved away will play an essential role in creating such a sophisticated prototype as the one seen above. The support material can

often be very reluctant to be removed from the part, especially from within small crevices. The additional step is a necessity for this

part because if the support material used was a solidified form that was to be broken away, the part would likely get damaged.

Even though production would be extended I would recommend developing this part using only one jet head to increase

accuracy. As you can see in Figure 1 the Comparison Chart above, the Single Inkjet is unrivaled in its ability to provide accuracy and

surface finish, as it rated an excellent on both. Although it rated poorly in the speed category this does not look like a mass

production part anyways, and even though time is important I don’t believe that in this situation it is the major concern. I think that

it will be worth the time to slow the process down and ensure a fine outcome.

As far as cost goes the single inkjet machine is in the lower middle section of the average costs for these machines. RP is a

growing field and there are new machines being developed all the time. There might always be another process that could good for

developing a part, and sometimes for the good of the company they might want to buy a machine that might not be the best for the

parts they are developing at the time but that will do the job now and be better for their future part development. For this part I feel

like the specs are spot on for what the development requires and the price is not too high.

4. The following picture shows a rapid prototyping process known as selective laser sintering. Explain the process in detail.

Process Description:

The process of selective laser sintering is similar to the process of stereolithography. In the case of selective laser sintering,

the laser beam contacts a surface of compacted powder. The powder covering the surface of the build cylinder is spread by a roller

and consists of a thermoplastic material. The amount of powder moved by the roller onto the building cylinder is controlled by the

powder delivery piston. As the powder delivery piston position increases, the fabrication piston is lowered to compensate for the

movement of powder.

During the fabrication process, the system temperature is kept slightly lower than the melting point of the thermoplastic

powder by sealing the system. When the compacted thermoplastic powder is traced by the laser it melts due to the heat generated

by the laser. The heat generated from the laser raises the temperature slightly to induce sintering and increase the speed of the

process. The laser is controlled by the scanner system, and produces a concentrated infrared heating beam.

Once the part is produced, the fabrication piston is fully raised to lift the part out from the surrounding powder. The excess

powder is then brushed away from the final part and additional cooling time is permitted before the part is moved from the build

cylinder. (Inkjet Methods, 2012)

Advantages: No Supports Required No final curing process required Can Fabricate metal and ceramic parts

o Prototype molds are low in cost and capable of producing large quantities partsDisadvantages:

Rough Surface Finishing Need to infiltrate parts with another material to improve mechanical characteristics Is unable to replicate molded parts Material changeovers are difficult

One of the greatest benefits, related to the application of stereolithography, is the reduction of costs. This method is based

on the construction of a prototype, making the production of the actual final product, much easier and more controllable. Design

and other faults of the prototype can be detected at this early phase, and all the necessary adjustments, measures and actions may

be taken, so that those faults are eliminated well ahead of the actual production of the finished product, resulting in a more cost-

sensitive technique (Helium, 2012). Otherwise, if the traditional method of trial and error had been applied, costs would certainly

have been higher.

BibliographyHelium. (2012). Retrieved from http://www.helium.com/items/1899156-benefits-of-stereolithography-advantages-of-stereolithography-why-

stereolithography

Inkjet Methods. (2012). Retrieved from http://www.ferris.edu/cot/accounts/plastics/htdocs/student/Westerdale/MJM.htm

Martello. (2012). Retrieved from http://www.martello.co.uk/rapid_prototyping.htm