Page 270 - Injection Molding Advanced Troubleshooting Guide
P. 270
262 27 Excessive Cycle Time
where the hot tip contacts the cavity because there can be a large buildup of heat
in this area that can lead to increased cycle times to control stringing from the
heat.
27.3.3 Excessive Cycle Time Troubleshooting Machine Issues
Machine-related causes include:
Slow clamp speeds
Slow reaction times
Slow automation
Ejection speed and strokes
27.3.3.1 Machine: Slow Clamp Speeds
Over time injection molding machines will wear. Valve seals wear on hydraulic
presses causing leakage in cylinders. The mechanical components on a machine
can wear and become sloppy or loose over time. Both of these wear situations can
lead to reduced clamp velocities.
If cycles are slowing over time and the time increase is coming from clamp open-
ing and closing times it is time to calculate the amount of lost press time and
money. Rebuilding the clamp of a machine can bring the clamp movement speeds
back to a more normal rate.
Some machines have the ability to allow the clamp to decompress after completion
of the second stage. This decompression of the clamp can allow a quicker response
when the machine is ready to initiate clamp movement. Take a look at the machine
controller to see if this option is available and utilize it where possible.
Also evaluate the amount of breakaway distance and clamp slowdown distances.
Often there is time to be gained by optimizing where the clamp slows down and
accelerates. The clamp should be running in a smooth fashion without banging,
but the speeds should be optimized to limit the amount of time the machine spends
moving the clamp. Long travel distances at slow speeds will add to the overall cycle
time.
27.3.3.2 Machine: Slow Reaction Times
When looking for small gains in cycle time one area to examine is the amount of
delay or hesitation at various stages of the process. Using a stopwatch it is possible
to evaluate various time delays such as:
Start of cycle to start of mold close
Mold close to clamp lockup
