Page 271 - Injection Molding Advanced Troubleshooting Guide
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27.3 Excessive Cycle Time Troubleshooting  263



             ƒ Clamp lockup to start of injection
             ƒ Cool time completion to start of mold open
             ƒ 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:
             ƒ Regrind
             ƒ Additive package
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