Top 15 Reasons Molders Fail at Scientific Molding: Revisited

Initially I covered 10 scenarios that occur which cause “scientific molding” based companies to fail in their utilization of the principles they attempt to practice. There were many more I could outline, but to prevent readers from sleeping through my soap box episode, I only gave 10 reasons. In revisiting this article, I will increase the information provided in the first ten and also add another five failures, bringing the total to 15.

Too many “medicine men” and not enough processors claim they practice the scientific molding ideology that Bozzelli created, and others at the top of the industry have capitalized upon on the use of the term. I personally remember sitting in a classroom the summer of 1993 as John taught his program. It changed my entire view on molding, and developed my approach towards true standardization. It gave me a true sense of what validation truly means when as molders we establish process and develop controls. Beyond that, it defined the next 25 years of my career. I learned the importance of process development and recording. John’s insight has always steered me away from false readings, as well as defined my analysis of what a true process really is.

It is important to understand what scientific molding is. Scientific molding is not bells and whistles, with fancy terminology, beautiful pictures and fancy equipment that most plastics controllers are outfitted with now anyways. Outlining all the steps behind establishing true process would be its own article. But at the end of the day, scientific molding is a series of steps that first establish a solid repeatable process, which is then validated.

The general rule I use in validation is that if a process is true, a press meets or exceeds production requirements for a period of 24 hours with minimal (1.5%) to no scrap. This process must be repeatable, and include a fully standardized set up. True processes are generally easy to start over and over with a minimal amount of start-up scrap. In cases where the start-up procedure is more complex, there are strict start up procedures that are clearly documented and enforced to assure that the procedures are sound, and deviation is minimal. This means that the new job is easily changed over without variation and start up is achieved without a major scrap and/ or process adjustment phase.

The next step is process control. Process control limits are established to assure that process consistency is maintained. Process changes that stray outside of those limits are viewed as “red flags” requiring a deeper assessment of what changes have occurred. If a process requires multiple changes during start-up, or if a process requires frequent change during production. SOMETHING is wrong!

There is a reason scientific molding approach has been defined as a repetitive, or standardized process. It is important to remember that it IS possible to have more than one working process. Our goal as processors always remains the same. Easy start up, 0-1.5% scrap, 100%+ efficiency based on quoted cycle. This defines true process. If the process we have deemed as valid does not provide high efficiencies, low to zero scrap and adequate start up results, we must reevaluate and look for ways to achieve maximum yields.

Any and all historical data needs to be recorded for future analysis. It is important to note that when processes go “bad”, it isn’t the process that fails. Data gives us direction and insight into changes have occurred. In most cases, recordable data provides a troubleshooting blueprint which is used to correct whatever change has occurred. The first thing to remember when documenting a process is strong data is key! A great comparison would be the differences between a black and white picture vs. the same picture having been colorized. The more information that is recorded, the better we distinguish changes in molding conditions. Poor approach towards process monitoring will ALWAYS result in vague interpretations of available data, because the data sets are limited. Limited data leads to poor interpretation of data sets and slow evaluation due to the lack of information available.

With this, let’s address the meat of the topic, which is why molders fail:

  1.  Button-pushing Cowboys– Many times over the years, I have seen this situation. Rather than try to identify what has changed, a molder instead just starts pushing buttons, attempting to make corrections. Proper approach requires us to first ask, “what has changed”? Process control is set aside, and process limits are totally ignored. Think of the potential outcomes in this approach… bad parts reach the customer, hours of scrap due to poor evaluation, and consistency in the molding approach is non-existent.
  2. Material– It is important to understand the effect that material can have on process consistency. Molders need the ability to trust that the materials they are receiving are consistently produced and handled. For instance, we know for fact that one Nylon is not the same as another. They may perform in a similar fashion, but one material response can be totally different despite the base similarities. A process is established based on each specific manufacturer blend. Every time a material change occurs (regardless if the material manufacturer insists they are the same) it is a brand-new material, and a brand-new processing approach. Every time material changes, it requires a totally new process, regardless of whether the material supplier says, “Yes, it is the same compound, but better cost”.
  3. Changing Auxiliary equipment– One thermolator, dryer, hot runner controller, etc. is not the same when it pertains to process consistency. It is highly recommended that molders “marry” equipment, molds, etc. to the same press. What this means is each component is physically bound to the same production press every time so that there is not deviation in press and auxiliaries. Remember, every variation that is introduced into a process is a new process.

 

It is also important to note that there are changes that occur to auxiliary equipment itself, which requires historical data to be collected. Thermolator valves stick causing overheating or poor heat dispersion, gallons per minute readings change, valve gates stop functioning. Monitor every condition available to you for verification of true process.

  1. Mold modification– Mold modification is generally implemented during the engineering stage, not on the production floor. If a mold is modified in any way, the process is new and should be viewed as such until the modification has been re-validated. Never assume that a change to a mold will not affect the process in any way. Instead, consider the mold to be suspect, and review all historical data you have available to assure that no real change has occurred.
  2. Watering & Heating– Molds should be evaluated during the process engineering stage, allowing base historical data can be established. Set up, Flow to and from process and steel temp measurements are critical components of measuring process changes over time. It is important to note that mold steel temps can vary in different areas of the mold due to heat exposure and flow differentials. Take measurements of temperature in multiple mold locations for historical reference.
  3. Process Monitoring– Once process is validated, process monitoring is key to measuring for change. Fill time, Screw rotate time, cushion, peak pressure, etc. quickly identify change within the process and are reliable identifiers to rely on when troubleshooting system changes. Verify all key monitoring measurables, and if you identify there is a significant variance, use that change to identify what changes might have taken place, such as the 5 M’s (Man, Mold, Machine, Material, Maintenance)
  4. Barrel Temperature: Barrel temperature is not limited to set points. Temperature actuals should also be monitored. Controller measurements, as well as steel temperature between zones should be recorded and used to identify changes. In addition, watch for signs of worn heater bands such as poorly heating zones at start up. Keep historical data that includes measurement of steel temperature data between bands throughout all zones.
  5. Labor– Never rule out the machine operator as the cause for process failures. Defects can sometimes appear to be process-related, but eventually part handling/ operator procedure becomes the true cause of process change. Step back, and take the time to evaluate precisely where the defect occurs. Don’t be afraid to run a press in semi-automatic, and to inspect the part as it is removed from the mold, even prior to removal in a post-ejection state.
  6. Quality System– Make sure that quality failures are not misdiagnosed. Check part dimensions and aesthetics to print and customer requirements. Make comparisons between the last shot previous run and first shot from the new run. Utilize fit-to-function principle, when applicable. Remember, unnecessary process changes can be just as detrimental as taking the “Good Samaritan approach”, trying to adjust for false defects.
  7. Set Up– Standardized set up is fundamental to strong start up and production runs. Poorly executed and/ or inconsistent mold and process set ups quickly lead to large scrap rates and unplanned down time. Develop the changeover during the process engineering stage to assure that change overs are precise and easily repeatable. Make sure that all personnel involved in change overs are consistently performing set up duties, not multiple approaches to accomplish the same task. Establish clear change over guidelines, and enforce their implementation.
  8. Robotics- Never rule out a robot as a potential cause for part defects. Programming, and even end-of-arm tooling can cause defects such as drag, pull, scratches, etc. Inspect parts prior to robot extraction to verify that the scrap event isn’t robot-based.
  9. Automation– Similar to robotics, never assume that automation can’t be the root cause of a defect event. Inspect the parts prior to and post-assembly to verify that scrap issues aren’t being caused by poorly- performing or mal-adjusted automation equipment.
  10. Material Handling- Inspect all aspects of the material handling operation. Make sure filters are being cleaned, loaders are functioning properly, products are not being moved improperly causing damage. Inspect product just packed by operators and prior to removal from press for proper handling procedures.
  11. Mold Cleaning & Function: Many processors fail to understand that one of the first things that require analysis prior to process change is making sure the mold has been cleaned and mold components are functioning properly. No process change should ever occur without a full cleaning of the mold and an inspection of mold components for damage and/ or improper function. In some cases, inspect the parts just prior to and during ejection in an attempt to identify problems. Inspect vents that are at or near areas of shorting and/ or burns.
  12. Maintenance: Review press and auxiliaries for changing conditions and poor performance. Machine valves wear, dryers malfunction, carriages get out of alignment, screws wear and check rings crack or break. Learn to identify equipment failure using monitoring data, and work with your maintenance team to analyze potential faults and get their input into the best approach to fix them. Remember, planned maintenance events are always much more cost effective than an unplanned repair. Develop a strong preventative maintenance approach to reduce scrap and troubleshooting events.
  13. Material Handling- Inspect all aspects of the material handling operation. Make sure filters are being cleaned, loaders are functioning properly, products are not being moved improperly causing damage. Inspect product just packed by operators and prior to removal from press for proper handling procedures.
  14. Mold Cleaning & Function: Many processors fail to understand that one of the first things that require analysis prior to process change is making sure the mold has been cleaned and mold components are functioning properly. No process change should ever occur without a full cleaning of the mold and an inspection of mold components for damage and/ or improper function. In some cases, inspect the parts just prior to and during ejection in an attempt to identify problems. Inspect vents that are at or near areas of shorting and/ or burns.
  15. Maintenance: Review press and auxiliaries for changing conditions and poor performance. Machine valves wear, dryers malfunction, carriages get out of alignment, screws wear and check rings crack or break. Learn to identify equipment failure using monitoring data, and work with your maintenance team to analyze potential faults and get their input into the best approach to fix them. Remember, planned maintenance events are always much more cost effective than an unplanned repair. Develop a strong preventative maintenance approach to reduce scrap and troubleshooting events.

These are some of the biggest failures that occur while trying to practice a systematic approach towards scientific molding. The foundation of scientific molding theory is standardization and monitoring of your operation. These remove chaos from each molding system by simplifying procedures and establishing a concrete molding approach. Lean molding requires consistent replication and thorough documentation of successful runs to assure each production event is successful. Standardization, monitoring and maintaining process consistency are the keys to a strong molding foundation and solid profits.

 

Garrett MacKenzie is the owner and editor of  www.plastic411.com. and also a technical writer for both Plastics Today and Plastics Technology magazines. He currently offers 2 day processor training programs and training-based webinars.
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