Page 271 - Injection Molding Advanced Troubleshooting Guide
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27.3 Excessive Cycle Time Troubleshooting 263
Clamp lockup to start of injection
Cool time completion to start of mold open
Mold open to start of ejection
All of these signals and movements can be instrumented and collected with a data
acquisition unit. By taking cycle time analysis to this level it is possible to start
shaving non-value-added time from the process.
27.3.3.3 Machine: Slow Automation
Watch for slow robot movements because clamp open time costs money. If robot
velocities are not being optimized this may be an opportunity for cycle time reduc-
tion. Look for opportunities to use a “pounce” position where the robot is preposi-
tioned closer to the mold. Another useful technique is using sweeping motions
rather than XYZ point-to-point movements.
Also watch for delays in the amount of time for the robot to build vacuum. Shorter
vacuum lines and larger diameter lines may allow vacuum to build quicker. Look at
potentially adding a larger vacuum pump or additional vacuum pumps. There are
even systems to locate a vacuum pump at every vacuum cup to minimize the dis-
tance the vacuum has to draw.
Does the product even need a robot? If the part can be ejected onto a conveyor with-
out damage the time required for robot movement is eliminated. Do not assume
because the machine has a robot that it always has to run for every mold.
27.3.3.4 Machine: Ejection Speed and Strokes
If a mold is being run with multiple ejector strokes ask why? Each extra ejector
stroke costs cycle time. Also, if the machine stroke is longer than required for the
mold, use adequate stroke for part removal but not extra.
Just like with the clamp of a machine the ejector cylinders can wear and leak
resulting in reduced ejection velocities.
Using short knock-out bars and returning the ejector plate all the way will create
wasted time as the ejector strokes the distance that is not engaging the mold.
27.3.4 Excessive Cycle Time Troubleshooting Material Issues
In general, some materials will provide faster cycle times than others. If running
into variation in effective cycle time due to material issues some of the possible
causes may be:
Regrind
Additive package