Structured or Formal Problem Solving


There are times when informal or experienced-based problem solving alone may prove inadequate, a “band-aid” approach to a more complicated issue. Informal solutions that ignore the root cause of the problem are not likely to prevent it from rearing its ugly head again later.

Structured or formal problem solving methods and tools allow us to get to the root cause of the problem and solve it permanently. The myriad of analytical tools and structured methods available can befuddle even a trained statistician. A structured problem solving method can enable a molder to choose which problem solving tools best apply to a particular project. Many structured problem solving tools are also process improving tools. (I have always considered process improvement to be problem solving on a grander scale, but I will examine process improvement tools more specifically in a future blog entry.)

Almost all structured problem solving methods hark back to Drs. Deming’s and Shewhart’s PDCA (Plan – Do – Check – Act) Cycle, which can be traced back further to early 1600’s England and Francis Bacon’s Scientific Method. Today’s DMAIC (Define, Measure, Analyze, Improve, Control) from Six Sigma, and the various numbered (5-, 6- 7-) step methods of problem solving, all stem from Deming’s and Shewhart’s methods.

Before a problem can be solved, we must define and get to the root cause of the problem. A technique called The 5 Whys can be used. This technique was gleaned from the 1970’s Toyota Production System (TPS), and can be useful for quickly getting to the root of a problem.

For example, assume that a late delivery on a project has resulted in an unhappy customer.

Apply the 5 Why method:

1. Why is the customer unhappy? = Because the project didn’t get delivered as promised.

2. Why didn’t project get delivered as promised? = Because the job took longer than anticipated.

3. Why did it take longer than anticipated? = Because the complexity of project was underestimated.

4. Why was the complexity of the project underestimated? = Because we made a rough estimate, ignoring the complexity of separate stages of the project.

5. Why did we do this? = Because we were running late on other projects.

It is now apparent that we need to revise our time estimation methods.

We can also apply The 5 Whys to a more typical molding problem; say a reject from a good customer:

1. Why did the customer reject the shipment? = Because of short shots and small dimensions.

2. Why did we get small parts and shorts? = Because not enough plastic got packed into the mold cavities.

3. Why didn’t enough plastic get packed into the cavities? = Because the molding machine wasn’t capable of doing this.

4. Why wasn’t the machine capable of doing this? = Because the melt index of the resin lot in question was too low and the machine became pressure limited.

5. Why didn’t we know this? = Because we didn’t do incoming resin inspection and/or set process alarms on the molding machine.

Conclusion: We clearly need to revamp our incoming resin inspection procedures and assure that our process/machine is robust enough to avoid this mistake in the future.

(To be continued next month)

 

Brent Borgerson
Senior Process Engineer (Older Molder)
Matrix Tooling Inc. /Matrix Plastic Products

 

Injection molding frequently involves problem solving.  Many of the problems regularly faced by a molder are quality related problems including: short shots, flash, dimensional issues, warp, and cosmetic concerns.  The molder is also frequently confronted with the need to reduce cycle times and/or increase yields.

 

Most problem solving in injection molding falls into two broad categories: structured (formal) and unstructured (informal).  In a series of blog entries, we will discuss various problem solving tools used in injection molding.

 

First, let’s examine unstructured/informal problem solving.

 

Experience

The majority of everyday problem solving in molding relies heavily on experience as the problem solving tool. A good portion of this is the experience of the individual molder. There is an old molding tale that tells of “The World’s Greatest Molder” being interviewed for a trade journal.  He was asked what the key to his success as a molder was.   Being a man of few words, he replied, “Not making mistakes.” He was then asked how he avoided making mistakes.  He answered, “Experience.”  He was further interrogated as to how he obtained experience.  “Making mistakes,” he replied.

 

Yes, one of the most often used problem solving tools in injection molding is based upon making mistakes… but learning from those mistakes!

 

The cumulative experience of a truly cross-functional team is powerful as both an informal and formal problem solving tool.  When tackling a complex molding problem, it is a good practice to involve personnel from molding, tooling, design, and quality.  This can be done in an informal shop floor setting or in a conference room.  A group of technical people getting together to share their experiences in solving a problem is a technique called “brainstorming” which leads into our next blog discussion of structured or formal problem solving tools.

Written by:

 

Brent Borgerson
Senior Process Engineer (Older Molder)
Matrix Tooling Inc. /Matrix Plastic Products

As an ISO 13485 certified manufacturer, managing risk is always a priority. And the most basic concept of that management process is first understanding what those risks are.

Recently, the question was raised: "Can any trace mold corrosion be transferred to the final molded product?" This opened a spirited discussion because, while we've been building injection molds for over thirty years, nobody here had a definitive answer.

After consulting with others in the industry, as well as a metallurgist at our steel supplier, we came to the conclusion that while it's theoretically possible to transfer any contaminant from one surface to another, having a problem with bio-burden testing or introducing a contaminant into a product during plastic injection molding production is highly unlikely.

We are involved in a program that overmolds stainless steel with plastic. A stamped steel piece and a metal injected piece are both loaded into a tool steel mold, then overmolded with a high temperature nylon. The stamped piece is passivated; the MIM piece is as-molded and sintered. In speaking with our metallurgist, we learned that the main sources of corrosion on the mold cavities would be degraded resin coupled with high mold temperatures. Fortunately, as we are the molder on this program, we have control over both of these issues. Our processing and mold temperatures are both within manufacturers' specifications, so that helps control a major source of any corrosion. The metallurgist also explained that any corrosion sufficient enough to create a transfer problem would be visible to the naked eye.

The material we chose for this program was a high hardness, general purpose tool steel. We did this due to the fact that two metal inserts are being inserted into the mold cavity for overmolding. There are other grades with similar hardness and stainless properties available, but based on what we learned we do not feel it is necessary to change steel grades at this time. However, we have decided to add a visual check to our regular preventive maintenance plan for this job, a solution we now feel is sufficient to catch a problem before it occurs.