Effect of Blocking Cavities Experiment Jared Matola Section 002 Team Members: Sam Liptak Matt Sudak Conducted: 2/10/99 Due: 2/17/99 Turned in: 2/17/99 at 8:00 Summary of Results: The purpose of this experiment was to demonstrate the effect that blocking cavities has in an injection mold on the process window and part quality. First we had to get a 95% full part. These parts were weighed before the hold pressure was added. The hold pressure was added and parts were weighed with the high, low, and optimum hold pressure. We also recorded the peak cavity pressure max, min, average, and standard deviation for the optimum parts.
This procedure was repeated for the same mold with one blocked cavity. After calculating the cost per 1,000 part for each set up we determined that it costs $134.67 when all cavities are open, and $168.87 when one of the cavities are blocked. This is a 20% increase in the cost of 1,000 part when one cavity is blocked. When we blocked cavity #3 the average cavity pressure increased by11.47 psi. The parts had a slightly higher average weight when we blocked cavity #3. This difference was roughly .01g.
When a balance of fill was calculated for the unblocked cavity setup. The order of fill was as follows: cavity 2 was first then cavities 4, 1, and 3. When cavity #3 was blocked, cavity 2 was first to fill followed by cavities 4 and 1. Apparatus: Battenfeld injection molding machine Flashlight mold Nylon cylinder (for blocking cavity) Process monitoring equipment Super glue Digital scale ABS material Method: See attached write up titled Effect of Blocking Cavities Experiment in appendix. The alterations made to this procedure were the fact that we eliminated blocking a second and third cavity due to time limitations.
Results: 5.1 Cavities unblocked 250 parts * 54.45g/cycle * 1 lb/454g * $1.00/lb = $29.98 $50/hr * 30.15 sec/4 parts * 1hr/3600 sec * 1,000 parts = $104.69 Total Cost = $29.98 + $104.69 = $134.67 1-Cavity Blocked (Cavity # 3) 333.33 parts * 42.41g/cycle * 1 lb/454g * $1.00/lb = $31.14 $50/hr * 29.75 sec/3 parts * 1 hr/3600 sec * 1,000 parts = $137.73 Total Cost = $31.14 + $137.73 = $168.87 5.2 The average weight of each cavity is calculated on the data sheets 1 and 2 in the appendix of this report. 5.2 The balance of fill is located on the data sheet 3 in the appendix. 7.1 Our predictions were not returned to us and I do not remember what my predictions were. Therefore I cannot answer this question. 7.2 We were not told to calculate the cost per 1,000 parts with a 16-cavity mold in questions 5.1 to 5.3 therefore we do not have an exact number for this mold.
We can speculate that the cost would obviously go down due to the production of 4 times as many parts per hour. 7.3 The cost of parts from a 4-cavity mold would be higher than those from a 16-cavity due to the fact that the 4-cavity mold would have a lower pressure drop and more plastic would be packed into the parts thus increasing the cost per part. The 4-cavity mold also produces less parts per hour and this will also increase cost when compared to a 16-cavity mold. The cost might also increase if there is a possibility for the parts to go out of specifications when a cavity is blocked. Appendix.