# SAP QM SPC: control charts, Cpk and stability studies > Source: https://netray.co/erp-help/sap-qm-spc-control-charts-cpk-stability-study > Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems. > Section: ERP Help ## Short answer SAP QM supports statistical process control through quality control charts, created in QGC1 and evaluated with QGC2, fed by quantitative results recorded in inspection lots. Cpk and process capability indices are calculated from those results. Stability studies are a separate, time-based sampling function used mainly in regulated industries. ## Kind how-to ## System sap ## Erp SAP ECC / S/4HANA ## Module QM / Statistical Process Control ## Query sap qm spc ## Alternate Queries - sap qm stability study - sap qm control chart QGC1 QGC2 - sap qm cpk process capability ## Applies To SAP ECC 6.0 and S/4HANA on-premise; stability study availability depends on release and industry solution ## Steps ### Set up SPC for a characteristic **Items:** Make sure the characteristic is quantitative and recorded with results in the inspection plan (QP01) with a target and both tolerance limits. Qualitative characteristics cannot feed a control chart. Set the sample size so each inspection lot gives a subgroup, for example 5 samples recorded per lot, so range and standard deviation charts are meaningful. Record results in QE01 or QE51N on released lots so values exist in QAMR. Without results there is nothing to plot. Open QGC1 to create a control chart. Select the characteristic, plant and material, the chart type (for example mean and standard deviation, or mean and range) and the evaluation period. Set or calculate the control limits. You can derive them from the data or enter fixed limits from a capability study. Evaluate with QGC2. Review points outside control limits and the run rules you have configured, and open the underlying lots from the chart to see what happened. Read the Cpk and Cp values from the capability evaluation and compare them with the customer requirement, commonly Cpk of 1.33 or higher for stable processes, but follow your customer specification. ## Sections ### Data you need before SPC works **Body:** SPC in SAP is only as good as the recorded data. The results must be numeric, recorded per sample or as a mean per lot, and attributed to the correct characteristic and lot. If operators record only pass or fail, you will see no meaningful chart. For continuous production, collect results at the operation by production inspection type 03 or by in-process inspection points. For goods receipt, remember that each lot is a different delivery, so a chart across vendors mixes populations; chart by vendor to get meaningful limits. ### Control charts and capability **Body:** A control chart plots the subgroup statistic against upper and lower control limits calculated at three standard deviations around the mean. Tolerance limits come from the specification, control limits from the process. The two are different, and a process can be in control yet out of specification, which is exactly what Cp and Cpk expose. Cp compares tolerance width to process spread. Cpk also accounts for how well centred the process is. Report both, and record the sample basis: Cpk from 30 values is much less reliable than from 300. When customers ask for PPAP or an initial process study, document the sample plan and the period alongside the figure. ### Stability studies **Body:** A stability study answers a different question: how does a product behave over time under defined storage conditions. It plans samples to be drawn and tested at scheduled intervals and compares results to specification limits across time points. It is typical in pharmaceuticals and food, and is delivered as part of the QM functionality for those uses, with its own master data for study design and time points. Menu paths and transaction codes for stability studies vary by release and by whether the industry extension is active. Check Quality Management in your SAP menu for the stability study functions rather than relying on a single code, and confirm with your QM consultant whether it is licensed and activated in your system. ### When SAP SPC is not enough **Body:** SAP's standard SPC covers the common charts but not advanced capability analysis, multivariate charts or real-time machine data. Many plants pass inspection results to a dedicated SPC tool or a quality management system. If so, define what moves where: the lot and characteristic keys from QALS and QAMV are the join keys. Do not duplicate recording in two systems. ## Pitfalls - Charting qualitative data or mixed units on one chart. - Using tolerance limits as control limits, which hides drift until parts fail. - Charting across vendors or tools without stratifying, which inflates the spread. - Calculating Cpk on too few values and reporting it as a precise figure. - Assuming the stability study menu is active in every system; it may not be. ## Ai Angle For SPC questions a grounded assistant can pull the quantitative results for a characteristic from QAMR, compute mean, standard deviation and a Cpk estimate, and flag points that break a chosen rule, showing the lots behind each point. On-prem deployment keeps quality data inside your network. It supports analysis; your quality engineer remains responsible for the capability claim. ## Faq ### What transactions are used for SPC in SAP QM? **Answer:** QGC1 creates a quality control chart and QGC2 evaluates it. Both draw on quantitative results recorded in inspection lots. Capability indices such as Cp and Cpk are available in the evaluation of those results. ### Can SAP QM calculate Cpk? **Answer:** Yes, process capability indices can be evaluated from recorded quantitative results, subject to enough data and correct target and tolerance values. For advanced capability analysis many companies export the data to a specialised statistical tool. ### What is an SAP QM stability study? **Answer:** It is a time-based study that schedules sampling and testing of a product at defined intervals under storage conditions, mainly in regulated industries. It is separate from SPC control charts, which monitor process variation lot by lot. ### Why is my control chart empty? **Answer:** Usually the characteristic is qualitative, results were not saved on released lots, or the selection does not match the material, plant and period. Check QAMR for the characteristic, then widen the selection. ## Search terms sap qm spc, sap qm control chart, qgc1 qgc2, sap qm cpk, sap qm stability study, statistical process control sap, sap quality control chart, sap qm process capability --- Talk to an engineer: https://netray.co/contact?intent=erp_ai | Machine catalog: https://netray.co/agent/catalog.json