Process Capability

Concepts of precision and accuracy Precise process is one with narrow spread/std deviation. Accurate process is one which has process average close to design values ,but variability may be high

• Process A is centred at 15 cm with spread +/-1.2 cm . • Process B is centred at 15.3 cm with spread of +/- .004 • Which is better and why? Pictorially represent.

• Process A is accurate but not precise • Process B is precise but not accurate. By shifting the process average to the design value it can be accurate. In the former case, reducing variation is difficult

Process capability • It indicates the spread of the process about the mean. The purpose of process capability improvement initiatives is to minimise the process spread. • According to Genichi Taguchi, any deviation or spread is a loss to the society ,amounting to squared values of the deviation form target values.

Cp & Cpk • Cp = (USL –LSL)/UCL – LCL = (USL –LSL)/6 sigma • Cpk= Lower of the two values .i.e 1) (mean-LSL) / 6sigma 2) (USL-mean) / 6sigma Higher values above 1 for both Cp & Cpk indicate better process capability

• Problem • Ball bearings of X brand has the following spec; 245 +/-0.85mm • Two Processes are available • see matrix in next slide

centre

LCL

UCL

Process A

244.90

244.15

245.65

Process B

244.98

244.16

245.80

• Which process will you recommend and why?

• • • • •

Cp process A =1.133 Cp process B=1.037 Cpk process A =1.000 Cpk process B =1.012 A is precise due to high Cp while B is accurate having close average • Precise process is to be prefered • Both process have low Cp & Cpk values. Process variability needs further reduction

Concepts of six sigma

Fundamentally, it is a customer-focused methodology that drives out waste, raises levels of quality, and improves the financial anytime performance of organizations to breakthrough levels.

• Six Sigma’s target for perfection is to achieve no more than 3.4 defects, errors or mistakes per million opportunities whether it involves the design and production of a product or a customer-oriented service process. • It is from this target that the “Six Sigma” name originated. sigma is the symbol used to denote the standard deviation or measure of variation

Table values of different sigma levels ppm (ONE TAIL) Off centre 3 sigma

4 sigma

5 sigma

6 sigma

0 sigma

1350

32

0.29

0.001

1 sigma

22832

1350

32

0.39

1.5 sigma 66803

6200

233

3.4

Mechanics of Six Sigma The process begins with a breakthrough in attitude. The leadership of a company or organization must realize that continuous improvement is no longer sufficient to achieve strategic, financial and operational goals quickly. Breakthrough improvement is chronic to the workings of the company

It would be foolish, however, to try to achieve Six Sigma levels of performance for every process in the organization. This is because not all processes are equally important. For example, the process for requesting time-off or vacation is not as critical as the order fulfillment process. What really counts is significant improvement in the mission critical areas – critical as defined by the customer, “critical-toquality” requirements or CTQs

Define, measure Define – identify, evaluate and select projects; prepare the mission; and select and launch the team. Measure – the size of theproblem, document the process, identify key Customer requirements, determine key product characteristics and process parameters, document potential failure modes and effects; theorise on the causes or determinants of performance.

Analyze – plan for data the data, and establish and confirm the “vital few” determinants of performance. Improve – design and carry out to determine the mathematical cause-effect relationships, and optimize the

control Control – design controls, make improvements, implement, and monitor.

There is another methodology for designing and developing a new product, service or process. Design for Six Sigma follows the DMADV cycle. DMADV is quality in the eyes of the customer. DMAIC typically focuses on one CTQ, which is related to the problem at hand. Analyze – identifies alternative design concepts and develops one or more into a high-level design control mechanisms in place.

Project approach in implementation • Cross functional team formed for specific improvement projects

champion Six Sigma Project Teams are supported by the leadership of each business unit through the Champions. As influential members of management, they are expected to promote the application, acceptance and evolution of the process within their business units. They select projects, teams objectives, allocate resources & mentor teams.They are normally the owners of the process being improved

• Master Black Belt • Fully trained experts in six sigma tools& methodsThe work across organisation to develop teams,conduct training,lead change .Role of facilitator and trouble shooters • Black belts Having been trained for 160 hours they do the technical analysis on full time basis for the projectsThey help select members,assist in training, lead teams for timely completion After project they work with functional managers to implement and monitor solutions they develop and mentor green belts Highly motivated and respected ,they are future business leaders

• Green belts • Functional employees trained in introductory tools. They work on projects part time ,assisting black belts.Conduct base analysis and give ideas for improvement,To become green belt must complete one six sigma project.

• Team members • Individuals from functional as who support the project The gather data conduct experiments, due to their functional domain knowledge of process details Typically green belts are team leaders. Black belt is staff expert

tools • • • • •

Process mapping (value stream mapping) Pareto Ishikawa diagram SPC Statistical tools like anova