Pareto analysis: The cause-and-effect diagram Other Quality Tools
Pareto Analysis • a simple method for separating the major causes (the 'vital few) of a problem, from the minor ones ('trivial many') • Pareto Analysis can help prioritize and focus resources where they are most needed. It can also help you measure the impact of an improvement • 80-20 rule - a large proportion of problems resulting from a small proportion of the causes • Data is collected, analyzed and a pareto diagram constructed • TQM will focus on the small proportion of causes that have very large no. problems (I.e to the left of the diagram)
Cause-and-effect diagrams • There are three basic types of cause-and-effect diagrams used in industry: 1. Dispersion analysis: Most frequently used, allows problem solvers to focus on why variations occur. Consists of four branches: workers, materials, inspection, and tools. 2. Cause enumeration: List of all of the causes of variation that can affect a process. Helps identify the sets of common causes that inhibit a process from meeting specification. 3. Production process classification: Used to study an entire process – shows all machines used in a sequential process and the possible cause at each machine that could result in a defective product.
Quality of Design Versus Quality of Conformance • A process in Japan offers a quantitative approach to analyzing the quality aspects of design in products. The Process known as TQM address the quality problems that are built into the product and process during their design. • Quality of design area: A. The market research activity is where customer needs and expectations are defined B. The product and process development activity is where standards and specifications for the product and process are developed. * 80% of the quality problems occur from bad design and poor process
Quality of Design Versus Quality of Conformance • Quality of conformance: A. Manufacturing: Develop a product with nearly zero defects B. Delivery: Provide safe and effective delivery of the product to retailers/customers C. Customer Service: Provide full 100% customer service and support
Defect-Free Design Philosophy • In 1798, the US government needed a large amount of muskets, quickly. • This was hard to come by then due to product variability. • Eli Whitney worked to reduce the variability in the parts. • The process today is call “the six-sigma design process”
Process Capability Index - Cp • A measure of the inherent capability of the process to produce parts that meet the design requirement. • The larger the Cp, the more likely the parts will satisfy the production requirement. • This is calculated by dividing the total tolerance by six times the standard deviation.
Defects-per-unit Benchmark • Used to judge a superior manufacturer • Number of defects per unit in complex products • Superior manufacturer has a defects per unit that approaches zero • Typical manufacturer has a defect level of 5 or higher • The key to achieving level of quality lies in the capability index for the critical design tolerances on each of the parts used in the complex assembly.
Seven Steps to Six Sigma Capability • Zero Defects • 1. Identify the product / characteristic • 2. Identify the critical dimensional and functional characteristics. • 3. Identify process sequence. • 4. Determine the nominal design/ tolerances that allow for easy assembly.
Seven Steps to Six Sigma Capability 5. Determine the process capability 6. Check the capability index, Cp 7. If Cp is not equal to or greater than 2, change the design until it does.