Page 374 - Injection Molding Advanced Troubleshooting Guide

39.3 Scuffs and Scratches Troubleshooting 371

Another factor that can impact the robot and cause damage to the part is if grip-
pers or nippers are misadjusted. A misadjusted nipper could be cutting off a sec-
tion of the part at worst case. Sometimes with grippers there is a need to add some
padding to prevent the metal of the gripper from scratching the part.
Watch the robot through its full cycle to determine if the part is contacting any-
thing in the molding cell. There have been cases where the part hangs slightly too
low and brushes against a guard resulting in scratches. Inspect the part on the
EOAT to determine if anything is misadjusted and causing damage. Watch the ro-
bot to verify that the parts are not being dropped from excessive heights as damage
may occur upon impact or the part may flip onto the class “A” surface. Also, parts
dropped onto a conveyor can cause tabs and part detail to bend or break (see Fig-
ure 39.2).

Figure 39.2 Bent tab from dropping on conveyor

Dirty or damaged vacuum cups can scratch a part surface. Examine the cups on
the EOAT to determine if the cups are in good enough shape. One technique that
can help identify if defects are coming from EOAT issues is to mark a part while it
is on the EOAT with a magic marker by circling the vacuum cups. Any subsequent
defects can be compared for location versus the marked part.
If the robot is picking parts that are very hot and the sprue is still molten, caution
must be exercised to avoid allowing the sprue to touch the part and create a melted
spot on the part. Watch carefully as the robot maneuvers the part and places the
part and runner on the conveyor. If possible look for opportunities to drop the run-
ner separately from the part to minimize risk of damage.