Injection Molding Lab
Objective:
To determine the effects of various nozzle and barrel temperatures and pressures on the finished part.
To determine the tensile stress of various good specimens.
Procedure:
The machine had to be warmed to an operating pressure and the pressure on the dies had to be set to the desired value. Raw beads were inserted into the hopper and the operation was commenced. After the part was inspected the operation was retried to verify the results if deemed necessary. Then the machine was set to a new nozzle, barrel, or pressure while the other two variable were held constant.
Results:
Summary:
Many uncompleted parts or parts with flashing were generated. This was due to the temperatures and pressure set for the operation. The variables were not right for the plastic that was being injected. The machine did however produce good and bad parts at the same settings. This may have been a result of the cycle times used. The plastic in the screw may have been under the influence of the last operation. The cycle times were not consistent. Another proposed problem was that the die did not have proper ventilation. A new vent was scribed into the surface of one die and it seemed to produce better results.
The tensile stress test generated fairly consistent results for all of the specimens. The ultimate load varied proportionally to the initial width of the specimen, as it should. The elongation of the specimen at the ultimate load was quite consistently proportional to the parts thickness. However, the overall elongation varied over a large range randomly. This inconsistency may have been attributed to the density at the cross section that began the elongation. In one part it was obvious to the eye that the consistency of the plastic over the cross sectional are was poor. This specimen (7) showed considerable less overall elongation even though the initial width was greater than other specimens.