D. Nandakumar

Before we go into an explanation of Z.overall, Z.within and Z.bench, We need to first understand what is meant by the letter Z.  “Z” is the number of standard deviations between the mean and the specification limit. In process capability calculation it is the mean distance from USL and LSL measured in Standard deviation.
The formula for calculation Z. score is

The graph below indicates the probabilities associated with the normal distribution and Z values.

For example: our customer lead time is 240 minutes. Historically, lead time average is 150 minutes and a standard deviation of 55 minutes.
Assuming a normal distribution, Z score is,

 
      = (240 – 150) / 55
       = 1.63
i.e., 1.63 Standard deviations above the mean.
The Z score is very useful because it can convert any continuous measurement into a generic value, allowing comparisons between different process is easier.
Z.bench can be used as measure of process of capability. Various Z.bench calculation are Zwithin or ZST and Zoverall or ZLT
Minitab has a selection to calculate Benchmark Z’s or Sigma levels along with the Cp and Pp statistics. By selecting the option in minitab, these graph as shown below will be displayed.


Difference between ZOverall and Zwithin:
Sl. No
Zoverall or ZLT
Zwithin or ZST
1
It is an indices used as an alternate to Pp
 
It is an indices used as an alternate to Cp
 
2
Zoverall indicate the actual long-term capability of the process
Zwithin indicate the potential short-term capability of the process
3
Z is calculated using the overall standard deviation
Z is calculated using the within standard deviation
4
Represents long term variation of the process
 
Represents the potential variation of the process
4
Also known as Short term Z.Bench
 
Also known as Long term Z.Bench
 
 
Benefits of Z bench
Ø  Z bench converts continuous data into a number of standard deviations, which can be used as Generic value of measurement between the process.
Ø  It serves as a tool for comparison between different process. If the Process “X” has a higher Z bench than process “Y”, Process “X” is better in meeting specs than process “Y”. It doesn’t matter what the process type, the comparison is relative measure of capability. 
Ø  Process “X”  is Better when compared to Process “Y”

Zwithin is important in DMAIC project for determining the baseline performance because it is essentially a prediction of the ability of a process to meet a specification. However, Zoverall also important because it indicates how the actual process performed over a period of time.
 

TPM stands for Total Productive Maintenance founded in Japan a systematic and holistic approach to equipment maintenance and strives to achieve overall equipment effectiveness, Zero Breakdowns, Zero defects and Zero Accidents.
TPM gives importance to maintenance in detail on both proactive and preventative aspect of maintenance to improve the operational efficiency of equipment. It removes the difference between production and maintenance roles and strongly emphasis the machine operators to maintain their equipment.
Implementing TPM creates a shared responsibility among the departments (between Maintenance, Production, Quality, Purchase, etc.,) and increases involvement of the operators from shop floor on maintaining their machines thus it improves their morale and very effective in improving productivity, reducing cycle times, and eliminating defects, etc.,
Before Implementing TPM, Basic condition’s needs to set right thru 5S. 5S is the systematic methodology used to organize the for workplace. Hence, 5S is Basic foundation for TPM.
·      Sort out waste (Seiri)
·      Systematic arrangement (Seiton)
·      Shine the workplace (Seiso)
·      Standardize (Seikietsu)
·        Sustain thru self-discipline (Shitsuke)
 
The main objective of TPM is to improve the Overall Equipment Effectiveness (OEE) of plant equipment. TPM focuses on the deterioration and production losses by creating the right environment between operators and equipment to create ownership.
Most of the companies appoints consultants from JIPM (Japan Institute of Planned maintenance) to Impart, Educate and Implement TPM culture

 
Implementation of TPM:
1.      Establish and Implement the basic conditions right through 5S Methodology.
2.      In 2023, JIPM Created a check list which can be used as Self-assessment and to check their eligibility level before applying for TPM
3.      Initial Evaluation of TPM level by JIPM consultants
4.      Initial introductory training
5.      TPM steering Committee formation
6.      Master plan for TPM Implementation
7.      Training Phase by Phase for all key personals for all eight pillars
8.      TPM policy and goals finalization
9.      Road map for TPM Implementation pillar wise
10.   Period assessment by Plant executives and JIPM
 
TPM Awards
JIPM provides 5 level of Awards in TPM and sub-category also available in each award.
Level 1 - TPM Excellence Award
Level 2 - TPM Consistency Award
Level 3 - TPM Special Award
Level 4 - TPM Advanced Special Award
Level 5 - TPM World class achievement

 
8 Pillars of TPM
TPM has 8 Pillars and each pillar will be having their own steering committee to monitor the implementation and its progress. Steering committee should comprises key personals from all functions similar to CFT.

Comparison against TQM

 
However, both TQM and TPM share a lot of similarities,
Ø  TPM and TQM are considered as two different approaches in maintaining and following the world class systems.
Ø  TQM is based on five cornerstones, i.e., The Product, The Process, The Organization, The Leadership and Commitment. Whereas, TPM is based on 8 Pillars.
Ø  TQM and TPM are used to increase the quality with effective utilization of resources and to delight customer. However, the road map for reaching the objectives is different.

 

In General, When Something is mentioned as Best of the Best means “that it is of the Highest Quality, excellent or Highly desirable type.”
In Process excellence the BOB can be explained in such a way that,
In a Controlled Process, if the value of specific dimension plotted continuously in a control chart the plotted distribution goes up and down from the nominal. While this degree of variation will naturally occur in a process which is called common-cause or Natural variation.  But still Process owners can make use of this opportunity to study why the reading is not very near to Nominal always. 
From this we can understood that the Values which is very near to the Nominal are BOB (Best of the Best) and values which are extreme from the Nominal are WOW (Worst of the Worst)
Example:
In Bi-lateral tolerance, if we take a nominal value this is called Best of the Best value (BOB).
Consider the specified value 85.50+/-0.3 
Here the USL (Upper Specification Limit) is 85.80
And LSL (Lower Specification Limit) is 85.20
And the Nominal value is 85.50. 
Hence BoB (Best of the Best) value is 85.50 
In Unilateral tolerance,
Consider the Value 20.00+0.000/-0.004      
Here the USL (Upper Specification Limit) is 20.000
Here the Nominal value is the Highest limit of the dimension i.e., 20.000 
Hence the BoB value is 20,000

 
All the Process owners desire to achieve BOB in their process and WOW (worst of the Worst) being the opportunity to evaluate the process. The process must be studied thoroughly why the BOB and WOW occurs.
In Continuous Improvement, if we capture these values in exact process conditions it gives us thorough understanding of the process. also, it provides insights on variable and constant parameters to be maintained, in order to achieve the best BOB value in the process.
Based on this data, we can understand which parameters can be tuned to achieve the BOB value. Tools like DOE can be used to screen and optimize these variable parameters.
Note: Other factors like Process cost, Pricing and End user product criticality, etc., also needs to be considered while optimizing the BOB value.

The Critical elements to focus for Successful Six Sigma implementation journey is,
1.  It needs to have a Top management support and an effective organizational structure.
2. As a next step, Six Sigma needs to become a business process management system that Understands and addresses process components and boundaries
3. Identifies and collectively utilizes process owners, Internal customers and External customers, and other stakeholders.
4. Creates an environment for effective project management where the business achieves maximum benefits.
5. Establishes project measures that include key performance metrics with appropriate documentation.
6. Tools like Force field analysis can be conducted to identify the driving and restraining forces.
7. Action plans need to be created to solve the restraining forces.
6. Projects needs to be focused on areas that can yield a high ROI and address the needs of customers.
Master black belt need to Function as change agents and Conduct and oversee training like,
•       Training plan to Coach black belts/green belts.
•       Leverage projects and resources.
•       Formulate project-selection strategies with steering team.
•       Communicate the S4 /IEE vision.
•       Motivate others toward a common vision.
•       and to approve completed projects
 
7. Project black belt implementers are typically expected to deliver annual benefits of between $500,000 and $1,000,000, on average, through four to six projects per year.
8. The value of maintaining and improving customer satisfaction must not be overlooked by organizations.
9. To achieve success, organizations must wisely address Six Sigma metrics and its infrastructure.
10. The success of Six Sigma is linked to a set of cross functional metrics that lead to significant improvements in customer satisfaction and bottom-line benefits.
11. Companies experiencing success with Six Sigma have created an infrastructure to support the strategy.
Tools like Affinity diagram can be used for grouping of issues that a team believed was important to address when creating a six-sigma business strategy.
 
 
The interrelationship diagram also can be used to further subdivision of issues and to show the interrelationship of these issues,
Ø  Executive leadership and involvement
Ø  Delivered results
Ø  Customer focus
Ø  Strategic goals
Ø  Project selection
Ø  Training and execution
Ø  Resources
Ø  Black belt selection
Ø  Communications
Ø  Culture
Ø  Metrics
12. Roles and responsibilities need to be addressed for Executives, Steering committee, champion, Black and Green Belts. Etc.,