X Bar R charts are the widely used control chart for variable data to examine the process stability in many industries (like Hospital patients’ blood pressure over time, customer
call handle time, length of the part in production process etc.,). Selection of appropriate control chart is very important in control charts mapping, otherwise ended up with inaccurate control limits for the data. X bar R chart is used to monitor the process performance of a continuous data and the data to be collected in subgroups at a set time periods. It is actually a two plots to monitor the process mean and the process variation over the time and is an example of statistical process control. These combination charts helps to understand the stability of processes and
also detects the presence of special cause variation. The cumulative sum (CUSUM) and the exponentially weighted moving average (EWMA) charts are also monitors the mean of the process, but the basic
difference is unlike X bar chart they consider the previous value means at each point. X-bar chart: The mean or average change in process over time from subgroup values. The control limits on the X-Bar brings the sample’s mean and center into consideration. R-chart: The range of the process over the time from subgroups values. This monitors the spread of the process
over the time. Use X Bar R Control Charts When:
How to Interpret the X Bar R Control Charts
Steps to follow for X bar R chartObjective of the chart and subgroup size
Example: In a manufacturing industry the plate thickness is one of the important CTQ factor, during Measure phase, project team performed the process capability study and identified that the process is not capable(less than 2 sigma). In Analyze phase collected 20 sets of plate thickness samples with a subgroup size of 4. Compute X bar and R values
Determine the Control Limits
The below control chart constants are approximate values to measure the control limits for X bar R chart and other control charts based on subgroup size Control Chart ConstantsRefer common factors for various control charts Example cont: In the above example n=4 Interpret X bar and R chart
Example Cont: Use the above values and plot the X bar and Range chart From the both X bar and R charts it is clearly evident that most of the values are out of control, hence the process is not stable Monitor the process after improvement
Example cont: Control Phase- Once the process is improved and matured, team identified the X bar R chart is one the control method in Control plan to monitor the process performance over the time period Following are the measurement values in Control phase of the project Compute X bar and Range From the both X bar and R charts it is clearly evident that the process is almost stable. During initial phase one value is out of control, team has to perform the root cause analysis for the special cause and also the process is smoothing out from the data set number 16. If that continued, the chart would need new control limits from that point.
Important notes
X Bar R Control Chart Videos
Apa yang anda ketahui tentang control chart XBAR R?- R adalah jenis diagram kontrol yang digunakan di dunia industri atau bisnis untuk memonitor data variabel di mana sample didapat dari sebuah proses industri atau bisnis dengan interval yang pasti dengan menggunakan sistem rasionalisasi subgroup.
Apa yang dimaksud dengan control chart?Peta kendali atau Control Chart merupakan suatu teknik yang dikenal sebagai metode grafik yang di gunakan untuk mengevaluasi apakah suatu proses berada dalam pengendalian kualitas secara statistik atau tidak sehingga dapat memecahkan masalah dan menghasilkan perbaikan kualitas .
Apa yang anda ketahui tentang p chart dan NP chart?2. p-Chart
np-Chart adalah salah Jenis Control Chart (Peta Kendali) yang berfungsi untuk mengukur proporsi defective (kegagalan/cacat) pada produksi.
Apa yang dimaksud dengan peta kendali variabel?Peta kendali variabel adalah diagram yang digunakan untuk mengendalikan suatu karakteristik kualitas yang dapat digunakan untuk mengukur mean dan variabilitas prosesnya. Sebagai contoh suatu karakteristik kualitas yang dapat diukur seperti dimensi, berat atau volume.
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