Definition: develop1) expand in detail 2) to generate Plan: a method of action or procedure
Once the issue and or result has been defined than a plan of action is drawn up, now in the real world or one that is based on the authors years of experience this is typically not done, as those things are just changed. It is hard and difficult to visualize and lay out a plan of attack, as in most cases the results must be immediate. Unfortunately one needs to understand the problem or issue at hand, and too often it is not done complete enough (sorry to step back to previous topic). The result as stated is that now many attempts are made at coming to a solution for the issue.
The following may both be used to plan the course of action and also determining the root cause.
Option 1
Develop a check list.
What this does is takes the processor step by step through the process at hand (this may even be used in defining the issue). This could be a list of question with fill in areas provided, which are broken out in sections, meaning that section 1 covers aspects about the material, Section 2 the machine section 3 the mold..
Thus by running through said checklist one than is formulating a plan based on answers to the questions, which to make matters simple might be yes and no type.
Option 2
Develop a flow chart per issue
What this means is that each issue, not enough material, too much material, black specs etc. each have their own chart at to what to check or actual plan. These would be formulated on questions such as yes or no but than by use of arrows would direct one to the next step or process to try. In a nut shell they than lend it to being the plan as long as all was defined properly as far as what the issue is.
Figure 1
The above is an example of a partial flow chart showing that if one answers no they move down to next question while if stated yes would move across to possible solutions.
In developing a plan, one should try and start with obvious or simplest solutions to an issue, and then work through and up to the more complex. In any plan the temperature of the material and the mold should be the last on the list to change as these take a long time to take effect. While knowledge of the mold, material and process are critical to processing correctly, this knowledge is more critical in trouble shooting an issue because of the following statement" when changing conditions to see if correct direction larger steps should confirm quicker if going in right direction". It is up to the processor how big the step should be from a safety concern as to not cause damage to the mold, machine, process, which than comes back to knowing what is allowable for material, mold and process.
If we take the issue of short shots, not enough material in the cavity and have defined it than a plan of attack is fairly straight forward dependent on what was found. An example follows:
Example:
A single cavity tool has the results of a short shot and is not consistent, meaning that some shots are full some are short and some are under filled. In reviewing the process sheets all appears good, and to specifications to the data on the sheet, though in observing the process it appears that the cushion on the screw varies widely. The back pressure is observed to be low, and screw recovery time varies at times.
Step one: Was to confirm that all the process settings were being achieved, this included checking for melt temperature, if all check out than to proceed to step 2.
Step two: to determine cushion issue, and also variation,
This is determined to be the use of back pressure by raising it and monitoring both screw recovery time, cushion. It is observed that screw recovery time does increase, but becomes a bit more consistent and cushion becomes a bit more consistent but the results are still on occasion short parts.
Step three: is to increase cushion size and see what happens. This results in a bit more consistency but on occasion results in a bottomed out screw and or short shots.
While the above did not solve completely the issue, it was determined that something was wrong with the check ring device, as it was not repeating. Thus in disassembly of the end cap/nozzle assembly and checking the check ring, it was found that the ring was good, but that retention onto the screw was not and the front of the check ring assembly did not retain at all times the check ring to the assembly thus the screw /ring did not at all time perform the way it should as a piston as the ring was left in front of the barrel or other, thus material could back feed up the flights of the screw and or not create all the pressure necessary on the plastic material.
The Plan, in the above was ordered and step by step, in checking the basics, melt temperature process settings as compared to original etc. further it was to examine the variations within the process that were initially observed in trying to define the issue as to why.
In conclusion a plan should be developed, this can be a checklist/ or flow chart type, but it must be followed and no short cuts. One does not have to look further than the airline industry to see all the checklist that must be gone through prior to takeoff, and recently this has been moving into the medical field with early results being rather promising.
While many lists and troubleshooting guides exist, when one looks to the processing floor they typically are nowhere to be found. Further when one has to develop a plan it takes a small amount of time, and hopefully this gives more clarity to the issue at hand. As one old-timer stated "I don't do nothing, I grab a cup of coffee and observe what is going on and usually it just goes away"
SLSILVEY
16082013.01
