Improve Phase Blog

Improve Phase Blog

The goal of the Improve Phase of Six Sigma is to identify and trial/test the potential solutions to the problems that has arisen thus far in the project. Depending on the trial/test results the solutions can then be implemented. Contained below are the solutions that have been implemented or will be introduced in the near future. Changes that were tested and ruled out are also contained. In the Six Sigma report, there is a list of changes that are recommended which where however beyond the scope of this project due to time constraints.

Process 1

During the Brainstorming session of the Define Phase, it was discovered that 3 parts where rejected at the beginning of each shift and 3 after each break. On investigation it became clear that this practice began when an older model of the machine was used for manufacturing, when the newest model was purchased and introduced this practice was needlessly continued. This resulted in 4,500 parts being rejected last year. A rational was formed and approved, an internal validation was then performed. As part of this validation a number of samples where gathered and subjected to rigorous testing. The validation was approved and the number of rejects due to this practice was reduced to 156 per year.

Process 2

A number of changes where made to this process, these are outlined in the below bullet points;

• Horn cleaning product changed from IPA to Klericide
• Inspection lamps installed at workstation, this will enable the operator to insert the Septum the correct orientation.
• Piercing Pin manufacturers will supply two pins per month, this will eliminate downtime in the event that two pins break in quick succession. The average pin lasts 6 weeks, however may vary from 1 day to 10 weeks.
• A sensor which detects a falling drop of silicon has been changed to a more reliable sensor which gives a signal for the the falling drop at a high level of repeatability, without being affected by external factors such as light or vibrations. The older sensor required adjustment / re-tuning at least once per shift. This resulted in 10 - 20 minutes of downtime per shift., since the new sensor was installed it has required no adjusting or re-tuning.
• The opening product jaws, which on occasion catches the product as the nest closes where modified. If a part was caught in the jaws it would be rejected and the machine would error, needing reset. The nest was modified to leave only a lip in place to hold the part - below this lip the diameter of the closed nest was increased to a diameter larger than the part itself.
• The gripper moves slightly overtime, resulting in the robot placing the part in the wrong place.These grippers keyed into place to make movement impossible.
• A new welding nest was manufactured with the aim of reducing or bringing to a minimum the movement of the part as it is being welded. This movement is one of the causes of residual stresses in the finished product. The ideal position was found for the nest and was marked out.
• The response of the septum to temperature / environmental changes was investigated;by drying the septum out at 65 degrees for 3 hours, by cooling the septum at 4 degrees for 3 hours and by checking the moisture content of the septum the processing these septum's and testing the final product - No significant changes where noticed.

Process 3

The Inspection bench was modified to a bench with a lip around the edges in order to prevent parts falling off the inspection bench.

Changes for the combined processes

• A vision system which  will inspect the product after welding but before being the silicon is applied; this camera system has been approved and is due be installed within 6-8 weeks. After installation the time spent inspecting will be eliminated / reduced.
• A visual aid was assembled, printed and laminated for all processes. This defines clearly what is / is not acceptable.
• Operators have been made aware of Tappi cards - one has been supplied to the line for reference purposes.

These changes have been implemented or will be implemented as a result of the three previous Six Sigma phases, with the final decisions being made at the beginning of the Improve Phase. These changes will be monitored continuously and any improvements will be evident quickly as a result of the data collection method defined in the Measure Phase and the construction and continuation of the control charts.

Analyse Phase Blog - March 2016

Analyse Phase Blog

The Analyse Phase is the statistical review of the process, for the Analyse Phase of this project each of the three assembly processes were analysed individually and as a combined process. The following tools were used to analyse each process; Process 1 - A detailed process map, A P-Control Chart (both Excel and Minitab), An Ishikawa diagram and a brainstorming session. Process 2 - A detailed process map, A P-Control Chart, An Ishikawa diagram and a brainstorming session. Process 3 - Brainstorming session. Combined Processes - A P-Control Chart. 

Process 1 - The P-Chart shown on the left was of Process 1 from Jan - Dec 2015. There was special cause variation in both Jan & Dec 2015 as the defective parts exceeded the UCL. In Oct 2015 a point falls on the LCL, which indicates that the process was running at its lowest proportion of defects. Overall process 1 is statistically out of control. On the 2 occasions where the UCL is exceeded, this special cause variation could be attributed to the fact that 2 new personnel where being trained on that process. After reviewing the data, it was found that the night shift did not run in Oct, this could explain why the number of rejects declined in Oct 2015. I found the P-Charts useful throughout the Analyse phase as they clearly illustrate how a process is performing, and it is easy to see when a process is veering out of control. When there is special cause variation or unusual trends it is important to investigate thoroughly and pinpoint anything that was done differently. From the P-Chart for process 1 - we checked our training records and they coincided with the hike in rejects in Jan & Dec 15. As for Oct 15 when the defective parts where at the lowest it became apparent that the night shift did not run that month, it is understandable to have a higher reject rate at night due to no Quality / SPC / Engineer present.

Process 2 - An Ishikawa diagram was constructed in Minitab in order to determine the root causes for the high rate of defective parts produced. When the diagram was complete, all the causes where listed as well as a comment to explain the cause and a potential solution. A detailed process map and a P-Chart where also constructed for process 2. The Ishikawa diagram was found to extremely useful throughout the Analyse phase. The result was a clear and categorical root cause analysis of each process, which was extremely beneficial for the team.

Process 3 - It was decided for process 3 to concentrate on the brainstorming session that took place in the Define Phase. All the points suggested in the brainstorm warrant being investigated further in the Improve phase, however for the Analyse phase these point were elaborated on.