Test Product Concept(s)
Define the Purpose of the Concept Test
P11008 Test Plans for Specified systems Subsystems Requiring Test 1. Cutting System a. Blade Choices i. Once our machine is able to be mocked up in a semi- complete fashion a cutting test will need to be performed to determine which Blade choice will be most adequate. Different mounting plates will be manufactured for the razor blade and knife blade options. A number of cuts will be performed using each option under different pressure values. The resulting cut will be observed and the ease in which the machine cuts through the straws will determine which option is chosen. The way the scrap material is extracted will also be monitored. Ideally we do not want the scrap shooting in random directions once the straws are cut. The resulting quality of the cut edge will also be inspected for any forms of deformation. b. Mounting Plate i. The ease in which the blades can be loaded into the plate will be observed. Ideally our spec will be less than 5 minutes. c. Production Rate i. The production rate will be determined by running the machine for a 10 minute period and extrapolating this figure out to determine the hourly rate. Currently the automated machine in use can produce 700 straws/ hr.
2. Pneumatic System a. The pneumatic system will be tested out for functionality before it is ever hooked up to actuate the components of our machine. These components will include the two handed switch, the cylinder driving the cutting force and the cylinder operating the trap door. Once all of the valves and cylinders are able to be assembled outside of our mechanical system we can determine if the logic is correct before actually hooking up the pneumatics into the machine. Of course once the machine is assembled the pneumatics will be tested to verify that they can work within our system.
3. Length Adjustment System a. The length adjustment system will be manufactured and the length from the floor of the system to the blade cutting path will be measured to verify that all of the lengths equal the lengths of the straw specifications. Once the machine is assembled sample cuts of straws can be obtained and the resulting lengths can be measured to determine if the length is within the desired specification. The following process capability test will be followed.
i. Process Capability Test-Similarly to how the Process Capability of the current machine was determined we will perform a capability analysis on our machine once it is operational. This will include cutting 200 straws at the 4.33’’ length and verifying that we have the capability to stay within the specifications of +/- .02’’. Even though this tight of a tolerance is not necessary for the function of the final assembly it is important that our machine does not decrease the capability of the system at Arc Works. Currently the Process has a Cpk of around .5. Considering how tight the tolerances are this is not unacceptable, but are machine should allow for an improvement in this area. Smaller amounts of samples can be collected from different length adjustments to confirm that our capability does not depend on the straw length which is cut. If it is determined that length adjustment is affecting the capability a more extensive test will be utilized to confirm before any alterations are made.
4. Safety System a. The major safety concern associated with our project is the hazard associated with the blade which we are utilizing to cut the straws. To eliminate this risk the pneumatics will not be activated until the safety interlocks which are installed on the Plexiglas door hatch are in contact with each other. Another backup system to this will be the utilization of a two handed switch which will only actuate the system if both buttons are pushed at the same time. This will guarantee that the operator’s hands are not within the travel of the blade. b. To satisfy the Minimal Physical Exertion Engineering specification a small number of buttons/switches are required to activate our device. 5. Material Removal System a. A preliminary test will be conducted to determine if the scrap straw material can be eliminated from our current design using a vacuum attachment. If the scrap is not able to be removed effectively an additional air curtain will be needed to push the scrap toward the vacuum system. This air curtain will be included into the BOM but may not be necessary depending on the result of the preliminary test.6. Cartridge Interface a. This subsystem relates to customers need to reduce the load time in the operation. To test this, our cartridge design will be loaded and then the interface with the cutting machine will be judged. In order for the cartridge to truly aid in efficiency the straw insertion will need to be seamless. This test can be completed as soon as the cartridge is manufactured and the plate which is holding the straws is adequate to mate with the cartridge. A test will also be performed when the machine is assembled, and fully functional. Our ideal time to load 1 straw would be 1 second, so if we can load the 12straws in under 12 seconds our specification will be met.
Feasibility• Length Adjustment Our proposed machine will need to have the ability to cut 11 different raw material straw lengths into 9 required finished cut lengths. This length adjustment will need to be accomplished easily so that the supervisor or even some highly functioning operators have the ability to change the height reliably. Discussions about the use of a dial on a roller system within the extruded aluminum were held but the risk of the dial becoming altered or not affixed in the appropriate location were a huge concern. Deciding to proceed with an option where slots within the frame are machined will be a more reliable option. The risk of having a straw cut to a non-appropriate length is huge and will not be acceptable. The mechanism which releases the cut straws from the bottom of our machine will utilize a block design where a plate is actuated to reveal holes in the same pattern of the cutting plate above. This void will allow the straws to be dropped into a finished goods location under the table.
• The blade that will be used in the final design must be both robust and relatively inexpensive in order to be a viable option for ArcWorks use. Because of this the blade will need to be either an extra-long razor blade that can be easily replaced when the blade becomes dull, or a custom made industrial knife blade that can be re-ground once it becomes dull. Listed below are the cost comparisons for each of these options as well as the cost of the blades that are currently being used in the machine. The particular type of blade that will be used however has not yet been chosen because of the uncertainty of performance and reliability of each blade and will be decided during senior design two in the testing phase.
• Blade Options
- Razor Blades
Positives - A known cutting finish since the current machine uses razor blades to accomplish the task of cutting the straws. This ability to cut the straws is low risk because we know the finished cut on the straws will be acceptable. This option is relatively cheap and would allow the customer to maintain the machine easily. If custom made razor blades are used they will be made from a high strength stainless steel which would reduce wear and increase overall blade life and will be long enough so that only one is needed at a time. Negatives- Razor blades are currently replaced every 2-3 weeks due to wear. They are relatively cheap to purchase and the only actual real cost is associated with the fabrication of a double blade by an outside fabricator. This cheap razor blade option paired with the travel of our blade and the impact associated on the straws may be an area of concern due to increase ware and need for replacement. The razor blades will need to be fastened to the plate and this would require drilling holes into the purchased blades. Purchased blades are available in quantities of 100’s. Purchasing this quantity at around $2 a blade for stock razor blades, and around $3.50 for custom made razor blades is relatively expensive if they are not used.
- Fabricated Knife Blades
Positives- These blades will be far more durable than the razor blade option. One knife blade may be able to be used in production for months depending on hours of use. This option would allow our team to manufacture blades in the machine shop which would be suitable for use. This gives our team the flexibility to test and observe the cut which will be made. Negatives- Our team does not have any experience with blade fabrication and producing an acceptable blade will be a challenge. If we would choose to go with this option enough replacement blades will also need to be manufactured for ArcWorks. In the future ArcWorks would need to have the ability to send out for blades to be manufactured once their stock eventually runs out. A work instruction will also need to be developed for them to give to a fabricator for future blades. Possible Solution- To avoid the risk of relying on a Knife blade our team has decided to design the Blade mount to be compatible with all of the possible options. This will give our design flexibility and avoid the most risk, with a very low increased cost.
• Pneumatic Systems Feasibility
- System #1
Positives - This system is the cheapest method of accomplishing the task required of it. Negatives – This method requires a rework in the mechanical design of the overall device. The switch for the scrap door is mechanically actuated; this may create difficulties in accurate actuation. This system will require the operator to engage the switch for the entire operation.
- System #2
Positives - This system is in the middle of the cost range. It is easy enough to create and can be integrated with the current mechanical device without changing the design. Negatives – This method is not the cheapest.
- System #3
Positives - This system is easy to assemble and integrate into the current device. Negatives – This method is the most expensive out of the three systems. It contains parts that could be switched out for cheaper models, as in the previous system.
• Pneumatic Actuation
- Our cylinder choice is based on the force required to cut the plastic straws. About 60 lbs. of force was determined, through experimentation, to complete a cut through a single plastic straw. In our proposed design, 12 straws can be held at a time. The pattern of the straws and the angle of the blade allows for only one and half straw to be cut at a time. Once the blade is more than halfway through, another straw will start to be cut. The pneumatic cylinder which we choose can generate 300lbs of pressure from the 100 PSI source to cut through the straws. If the actual force generated is found to be too great, the cylinder will be regulated down appropriately. This way, the risk of having a cylinder which is too small is mitigated.
• Cartridge Loading Device o This device will allow for multiple straws to be loaded into the machine at once. This will reduce the time required to load all of the straws into the machine. This was a concern because this is where much of the efficiency of the machine has been loss. Even though the process of loading will just be transferred to another operator before the process this is acceptable because another function (opportunity) will be given to the workers at ArcWorks.
- A microcontroller will be programed to give our system the logic required to run the magnetic interlock system and potentially the pneumatic system. We have some microcontroller knowledge within the team so this option is feasible. The main actuation of our system will be with the use of a two handed control switch. The only way the cutting system can be actuated is with both hands of the operator pressing down on both buttons of the switch. This along with the safety interlock door will provide robustness to our safety system.
• Scrap Removal
- The end of cutting plate will need to have an attachment which is hooked into the hose of a vacuum which will collect the scrap debris materials.
• Safety Guarding
- Our design will utilize a Plexiglas door hatch with safety interlocks located above the cutting blade. In order for the blade to be actuated the interlocks must be connected symbolizing the door is shut and there is no way an operators finger will be exposed to the blade’s sharp edge.
• Base and Frame
- Extruded Aluminum will provide us with a sturdy base and frame which will be able to withstand the force generated by or machine. The extruded aluminum will come in pre-fabricate pieces which will allow for ease in assembly along with proven reliability. Fabricating a base and frame from scratch would prove to be costly and risky when compared to the chosen option.