Table of Contents
Items to be AddressedThe machine was not finished in it's entirety, and will require some further efforts in the future if the machine is to eventually be operational. This is a short list of some (not all) build tasks that will need to be completed before the machine can be delivered.
- The trap door/height adjustment system is still
- A dimple or divot will need to be machine into the pivot shaft at a 45 degree angle to the trap door itself. This indexing feature will allow a pointed set screw to allocate the trap door and prevent it from wandering off level. This set screw will also need to be sourced (1/4-20 thread). The set screw shown in the picture below (Item A) is just for reference.
- The lever arm will need to be re-machined with a tighter tolerance (holes closer together). With the holes too far apart, the door doesn't completely open, causing some of the straws to potentially get jammed. This is shown in the picture as Item B, and in better detail in the lever arm drawing
- The small cylinder currently has straight fittings (Item D) that were just used for testing. The final machine will require 90 degree fittings in order to better manage the pneumatic hoses.
- The height adjustment plate (trap door assembly mount) is currently only partially constrained. A bracket will need to be implemented on the back side of the plate (reference Item C), with a 1/4-20 bolt short enough to not interfere with the front face of the plate. This will allow the longest straw length to still be accounted for, and will provide full constraint of the part.
- Shorter M8 bolts will be required to properly mount the machine to the worktable (Item E).
- The front of the machine will need a plexiglass, lexan, or other cover in order to prevent scrap from exiting the containment area. This cover will allow the vacuum attachment to work properly, as well as serving to protect the operator. The area (currently open) is shown as Item F below. The corners on the current lexan top piece should be rounded off a shortened as well.
- Implementation of the pneumatic system activation switch made the existing spring return system design impossible to implement. This resulted in the quick fix shown as Item G. A better return system would be preferred on the final machine.
- Item H - The screws attaching the pneumatic system activation switch are too long. Shorter, more purposeful screw should be sourced.
- The vacuum attachment will need to be properly secured. This will require two holes to be drilled and tapped into the left side plate at the locations shown below (Item J).
Tests to be Completed
- Experimenting by changing certain variables associated with cutting the straws.
- A more extensive 5 Why's analysis could be completed to determine root cause of poor straw cut quality.
- Experiment with thinner blades
- The quality of the cut will be evaluated to see if the thickness of the current blade is truly the cause of our problem. Current blades could be ground down in the machine shop to see if thinner blades produce a better quality cut. Thinner blades could also be purchased online if available.
- Experiment with different impact angles
- Currently the 45 degree angle of the blade within the carriage spins the straws before the actual through cut is produced. This may cause scoring on the backside of the straws. A flat angle where the blade impact perpendicular to the straws could be tested through modification of the blade mount/carriage system.
- Determine difference between single and double beveled blades
- Is there a difference in the quality of the cut produced?
- Supports on the bottom and possibly top of the straws once they are loaded
- It was noticed that if a piece of rubber (mouse pad) was added to the trap door (where the bottom of the straws sit) an improved quality cut was seen. More extensive testing could be completed to determine if this addition of material will improve quality. Some method of supporting the top of the straw could also be examined.
- Slower Cutting Speed
- More extensive testing should be completed to determine the optimal cutting speed through adjustment with exhaust output valves. In order for this speed to be adjusted the Two Hand Anti-Tie Down will have to be bypassed.
- Continued high speed video analysis should be completed on some of the more promising techniques.
- Dr. Day is a great resource for help with the high speed camera and preliminary images can be seen within our Presentation sideshow.
- Adjustments with the carriage could also be completed.
- In preliminary fabrication and build it was seen that there was play when it was attached to the bearings. The bearing and carriage need to be aligned correctly to produce the optimal cut.Adjustment of this alignment could be performed to enhance quality.
Recommendations for Future Work
- Continued work on height adjustment system
Due to the lack of time at the end of the quarter the height adjustment system was not tested thoroughly. Further testing and possibly a new system could be constructed to be implemented into the design once more work has been completed.
- Blade testing
Determine ideal blade for operation. Possibly a thinner blade would produce a more acceptable cut with less deformation and burring. The thicker blade may produce a tearing which will not be eliminated without a reduction in thickness.
- Reduce speed of cylinder without sacrificing force generated
The pressure was varied to see if acceptable quality of cut at lower psi was possible. Results were negative, future testing should aim to reduce speed but not pressure as previously stated. If the two Hand Anti-Tie Down is bypassed then speed can be adjusted improving the quality of the cut slightly.
- Manual Loading Device Implementation
RESULTS AND DISCUSSIONPreliminary cutting tests were completed which showed a significant amount of deformation on the cut edge of the straw. The process and setup of the machine was analyzed and it was determined that the carriage was setup in a way which was not completely square. Once this was fixed, more acceptable straight straw cuts were seen, but it seemed as though improvements still needed to be made. Burring was also still an issue and at this point ArcWorks was contacted to get their opinion on whether or not the cut quality was acceptable. The burring which was seen along with the cut which was not fully straight in some instances did not allow Arc Works to accept the cuts which were produced. In trying to troubleshoot the issue, a theory was developed regarding the blade thickness and design as a potential cause of failure. The theory went as follows: After initiating the cut, the thickness of the blade was causing the portions of the straw above and below the blade to separate not as a result of being severed by the cutting edge, but by being pulled apart by the beveled surfaces. In other words- once the blade cut deep enough that the straw could no longer elastically deform around the bevel of the blade, the straw would fracture, resulting in an unacceptable finish. A cutting test was performed using the aid of a high speed camera in order to verify this theory. The videos and pictures which were gained from this procedure did indeed show that the straw material was prematurely tearing ahead of the cutting edge. This is the major reason why the quality of the cuts was not acceptable. This test proved that the thickness of the blade which is currently being used on the device is too thick. The video also showed definitively that the straws were deflecting in the holes. The high speed camera showed that the straws would spin prior to the cut being completed. This rotational motion was produced from the blade hitting the one side of the straw wall before the other. Another consideration is that the blade is currently not sitting completely flush within the mounting plate Another issue we were seeing was in regard to the length tolerance. We noticed that the straws at the beginning of the cutting cycle were considerably shorter than the last straws cut- somewhere in the neighborhood of a 0.1 inch difference. We deduced that the blade thickness and double bevel on the blade were the cause of this. Once the blade started to travel through the straw, the bottom bevel would cause the blade to push its way vertically since the straws were constrained on the bottom. This meant that each straw it reached would see a cut starting slightly higher than the previous straw’s cut, resulting in a gradual step up in straw length. In order to address this issue, we placed a mouse pad on the surface the straws were resting on in order to absorb the deflection and eliminate the variance. This virtually eliminated the issue.
CONCLUSIONS AND RECOMMENDATIONSThe device is able to cut all of the 12 straws. However the quality of the cuts which are produced are not to an acceptable quality level. It is a credit to the team which had no experience with designing cutting machines in past to come up with a design which is functional. There is room for improvement and possibly an opportunity for future senior design team to take a look at the work which is already complete to determine how the quality of the cut could be increased. One area of the machine which was not fully functional due to the time constraint and setbacks seen within the group was the height adjustment and trap door system. Due to the size constraint within our machine and the size requirements of the design, difficulty was encountered. Significant amounts of re- designs were required and the time constraint within MSD did not allow for enough time to trouble shoot these designs. In the future more time in the beginning stages of the design should have been allocated to the height adjustment and trap door system. Another resource on the team would have helped in this respect.
The Straw Cutting Device project at ArcWorks provides another opportunity for an MSD team to take on a challenge and potentially redesign some components within the system. Ideally a height adjustment and trap door which is fully automated should be utilized. A significant amount of design work was needed for several of the crucial systems within our design and, resources within the team were stretched thin. Future work at Arc Works could pick up from where this project had left off to make adjustments to the system infrastructure which is already in place. To enhance the productivity and efficiency of the process a cartridge loading device could also be used. This will reduce the amount of time within the process to load the straws into the machine. This idea was originally going to be implemented into our design but due to time constraints and other crucial systems within the system requiring more time to develop, the adequate amount of time to design and build a cartridge loading system was not possible.
- Designed and manufactured a functional device capable of cutting multiple desired straws.
- Theoretical production rate increased
- Number of actuations required by operator reduced
- Device will not actuate without safety systems engaged
- Robust/ durable cost effective blade identified
- Blade changing time minimized/ reduced downtime
- Ease of use for operator
- Pneumatic system functional
- Length of cut straws are within tolerance
- Debris removal system performs as expected
- Quality of through cuts unacceptable
- Height Adjustment/ Trap Door System not implemented
- Manual loading still required