Rare is the occasion that you will find me writing an article in first person. I have always just felt that the best way to include my molding peers in the depth of the topics I cover is to put them in the driver’s seat. However this article is best presented with analogies and 30 years past experience. As such, I will be covering 10 scenarios that occur which cause “scientific molding” based companies to fail in their utilization of the principles they attempt to practice. Trust me.. there are many more I could outline, but to prevent readers from sleeping through my soap box episode, I will limit my scope to 10.
Too many “medicine men” and not enough processors practice the scientific molding ideology that Bozzelli created. I personally remember sitting in a classroom in the summer of 1993 as John taught his program. It changed my entire view on molding. Beyond that.. it molded the next 30 years of my career. I learned the importance of process development and recording.. and it has always steered me away from false readings and defined my analysis of what a true process really is.
It is important to understand what scientific molding is. Outlining all the steps would be an article in itself. 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.
Another key rule of scientific molding is that set-up (both changeover and process input) is standardized. 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. A true process starts up quickly with at most minimal adjustments needed.
The next step is process control. Process change 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.
Lastly, any and all historical data is recorded for future analysis. It is important to note that when processes go “bad”, it isn’t the process that fails. Data gives direction as to what changes have occurred, and in most cases provides a troubleshooting blueprint which is used to correct whatever change has developed.
With this, let’s address the meat of the topic.. why molders fail:
- 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 in an attempt to correct. Rather than ask, ” what changed”? Process control is set aside, and process limits are totally ignored.
- 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. In addition, one Nylon is not the same as another. A process is established based on a specific manufacturer blend. Every time a material change occurs.. regardless if the material manufacturer insists “they are exactly the same”.. it is a brand new material, and a brand new processing approach
- Changing Auxiliary equipment- One thermolator, dryer, hot runner controller, etc is not the same when it pertains to process consistency. Marry equipment, molds, etc to the same press. Every variation that is introduced into a process is a new process.
- 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.
- Watering & Heating- Molds should be evaluated during the process engineering stage so that 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.
- 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.
- 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
- 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.
- 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.
- 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.
These are some of the strongest fails that occur while trying to practice a systematic approach towards scientific molding. The foundation of this molding theory is to standardize your operation, and remove chaos from each molding system by simplifying procedures and establishing a concrete molding system. Lean molding requires consistent replication and thorough documentation of successful runs to assure each production event is successful.