Process Capabilities. A successfully completed suitability study of the measuring equipment is a prerequisite for conducting process capability studies. TYPE OF EVIDENCE REQUIREMENT COMMENTS Machine capability index, short term study Cm ≥ 2,00 Cmk ≥ 2,00 sample size n ≥ 50 (n ≥ 100 recommended) (sequential parts) Preliminary process capability (= short term = ST) Xxxxxxx process Cp-ST ≥ 1.67 Cpk-ST ≥1.67 Sample size n ≥ 125 (25 samples with 5 parts each) In contrast to the long-term study, the parts that are to be examined can be taken from the production process directly one after another, unless a sufficient amount of parts is available. Preliminary process performance (= short term = ST), instable process (characteristics with varying mean values) Pp-ST ≥ 2.00 Ppk-ST ≥ 2.00 Sample size n ≥ 125 (25 samples with 5 parts each) In contrast to the long-term study, the parts that are to be examined can be taken from the production process directly one after another, unless a sufficient amount of parts is available. Process capability index Cp ≥ 1,67 Cpk ≥ 1,67 Long term study, stable process Process performance index Pp ≥ 1,67 Ppk ≥ 1,67 Long term study, instable process Cpk / Ppk ≥ 1.67 for S / C and P / C characteristics Cpk / Ppk ≥ 2.0 for C / C characteristics The supplier is obliged to adhere to the above values or higher values. The statistical process control must be carried out for all special characteristics. The supplier has to carry out a capability study based on the PPAP procedure. The capability study must be carried out separately for each cavity. If fewer than the required minimum number of parts are available, this is to be documented and the reduced number is to be taken into account by raising the standard values. The standard values are to be increased by the following amounts: NUMBER OF PARTS: CM / CMK CP-ST / CPK-ST / PP-ST / PPK-ST CP / CPK / PP / PPK 124 TO 100 - - 0,33 99 TO 50 - 0,33 0,67 49 TO 25 0,33 0,67 1,00 A copy of the detailed results of the capability test must be attached with the sampling documentation.
Process Capabilities. Wherever required by WABCO in the course of the part approval procedure, statistical evidence of process capability must be made available by Supplier. This applies to characteristics requested by WABCO during part approval process and to Safety and Significant Characteristics. In case of Safety <1> and Significant <2> Product Characteristic or additional agreed characteristics, evidence must be provided by Supplier that these characteristics are over entire manufacturing process life time in conformance with specifications. For dimensional Safety <1> Characteristics supplier must provide capability studies or install 100% inspection. In case of capability studies the process need to reach a short-term process capability ≥ (superior or equal to) 2 for at least 50 consecutively produced parts. In series production, Supplier shall give evidence for a long term process capability ≥ (superior or equal to) 1,67. Until the required capabilities are proven, Supplier shall proceed to a 100% Inspection with collection of data to be allocated at least to the production batch (traceability). On request of WABCO during the entire product manufacturing life time, supplier needs to provide long term process capability results. For non dimensional Safety <1> characteristics (e.g. material composition or material properties) an alternative way to process capability studies shall be agreed between WABCO and Supplier (e.g. evidence of capability of used process technology, special process control plan, evidence about process capability through control of process parameter, sample lot definition and related control plan connected to SPC, etc.) In case of capability studies on Significant <2> Characteristics and other characteristics requested by WABCO during part approval procedure the process capability need to reach short-term process capability ≥ (superior or equal to) 1,67 for at least 50 consecutively produced parts. In series production, Supplier shall give evidence for a long term process capability ≥ (superior or equal to) 1,33. Until the required capabilities are proven, Supplier shall proceed to a 100% Inspection with collection of data to be allocated at least to the production batch (traceability). On request of WABCO during the entire product manufacturing life time, supplier needs to provide long term process capability results. Measurement processes used for above mentioned characteristics shall be analysed by Supplier using a Measurement System Analysis (MSA)...
