Process Capability Analysis Materi Process Capability Analysis 1

Process Capability Analysis Materi

Process Capability Analysis 1. 2. 3. 4. 5. 6. 7. 8. 9. Introduction Specification limits and control limits Process capability analysis Natural tolerance limit Relationship between specifications and process capability Process capability indices Process capability analysis procedure Setting tolerances on assemblies and component Estimating natural tolerance limits of a process 9/25/2020 eko@uns. ac. id , ie department uns

1. Introduction Whether a product or service met the specifications required by customer p Measures indicate the ability of process to meet specification ( measures of process performance ) p Determining tolerances on assemblies p Remember : process is in state of statistical control p 9/25/2020 eko@uns. ac. id , ie department uns

2. Specification limits and control limits ANSI/ASQC standard A 1 (1987) Specification limits and tolerance limits : conformances boundaries for an individual unit of a manufacturing or service p Example Steel cable diameter = 4 ± 0. 2 cm p Control limits : identify the variation that exists between subgroup p 9/25/2020 eko@uns. ac. id , ie department uns

Distinction between specification limits and control limits 3 3 LCL 9/25/2020 X eko@uns. ac. id , ie department uns UCL

Distinction between specification limits and control limits specification limits 6 LSL 9/25/2020 eko@uns. ac. id , ie department uns USL

3. Process capability analysis p p p Process capability : performance of a process which is in a state of statistical control Process capability analysis : procedure to estimate the process capability Benefit of process capability analysis 1. 2. 3. 4. 5. 9/25/2020 It create of uniformity of output The level of quality is maintained or improved It facilities product and process design It assists in vendor selection and control It reduce theeko@uns. ac. id total cost , ie department uns

4. Natural tolerance limits p p p Natural tolerance limits are also known as process capability limits and are influenced by the process it self They are estimated based on the population or from large number representative sample They are classified : 1. 2. 9/25/2020 UNTL LNTL eko@uns. ac. id , ie department uns

4. Natural tolerance limits 3 3 LNTL 9/25/2020 µ eko@uns. ac. id , ie department uns UNTL

4. Natural tolerance limits Example 8 -1 : Spec diameter : 5 ± 0. 015 cm , X = 4. 99 cm , s = 0. 004 cm. Find the NTL ? Solution : UNTL = 4. 99 + 3(0. 004) = 5. 002 UNTL = 4. 99 - 3(0. 004) = 4. 978 9/25/2020 eko@uns. ac. id , ie department uns

4. Natural tolerance limits USL = 5. 015 LSL = 4. 985 0. 1056 3 LNTL = 4. 978 9/25/2020 3 X =4. 99 eko@uns. ac. id , ie department uns UNTL = 5. 002

5. Relationship between specifications and process capability 1. 2. 3. Case-1 : Process spread < { LSL, USL } See figure 8 -4 Case-1 : Process spread = { LSL, USL } See figure 8 -5 Case-1 : Process spread > { LSL, USL } See figure 8 -6 9/25/2020 eko@uns. ac. id , ie department uns

6. Process capability indices p p p It is sensible to estimate the ability of a process to meet specification limits Provides an easily understood aggregate measure of a goodness oh the process performance Process capability ratio ( Cp index ) 9/25/2020 eko@uns. ac. id , ie department uns

7. Process capability analysis procedure p Estimating process mean and standard deviation 1. 2. Using individual observations ( at least 50 ) Using control chart information See example 8 -4 to 8 -6 9/25/2020 eko@uns. ac. id , ie department uns

Quiz 2. Explain the difference between SL and CL ? Is there a desire relationship between the two ? What are the advantages of having a process that is less than the difference between the specification limits ? What should the value of Cp be in institution ? 3. Do problem 8 -20 1. 9/25/2020 eko@uns. ac. id , ie department uns