Statistical Process Control and Engineering Process Control (2023)

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CHAPTER ONE - INTRODUCTION

1.1 Research Background

Chemical industry has employ multiple method of process control. Process control is important to maintain a specific result and to ensure the obtained product is within the set point. This will determine the value of the product and can either increase or decrease it. This make the process control as an important aspect to be considered during any chemical process and can influence the success or the failure of the process. Generally, two of the main process control widely used in industries are the Statistical Process Control (SPC) and the Engineering Process Control (EPC). SPC is standard methodology for measuring and controlling quality during the manufacturing process. It is a fairly simple process thus will not need a high cost to install.

Basically, SPC will measure the result obtained with the set point and present it as data, usually in the form of graph. By the graph, operator can determine whether the process is following the set point. In case of any deviation from the desired set point, the operator need to adjust it manually the manipulated variable and correct the deviation back to the desired set point. In general, SPC act as a visual aid to help the operator in maintaining the process control. On the other hand, Engineering Process Control (EPC) is a collection of techniques to manipulate the adjustable variables of the process to keep the output quality such as Feedback control process. EPC can collect data from the instrument, compare it to the set point and send signal for correction action. This mean that, EPC can automatically control the process to maintain it at the desired set point.

1.2 Objective

  1. To integrate both Statistical Process Control and Engineering Process Control for batch process control to detect possible variation as early as possible.
  2. To develop a methodology that integrate both Statistical Process Control and Engineering Process Control for batch process.

1.3 Problem Statement

For batch process, the variation or faults usually different from batch-to-batch that causes by several process variables. If the variation is not detected earlier, it is hard to maintain the quality of the end product between batches. This can cause the whole batch to fall below the requirement set point and would be a loss to the company. A better control process is needed that can predict the outcome of each batch process based on the disturbance and can automatically act accordingly to reduce the discrepancy.

1.4 Scope of Research

This research main focuses is on the implementation of both EPC and SPC for a batch process. The tuning methods used are Ziegler-Nichols (Z-N), Direct Synthesis (DS), and Internal Model Control (IMC). For the mathematical model used for the batch process will be obtained from past literature and re-constructed using SIMULINK MATLAB. For the statistical analyzation, MINITAB will be used to analyse the process capability and stability. At the end of this study, it is expected that integrating both process control can increase the efficiency and the capability of the batch process.

1.5 Significance of Study

Batch process is one of the process used in the industry to produces many type of chemical. Among the chemical that rely on batch process to be produces are pharmaceutical product, paints and adhesives. There is always desire to increase the efficiency and capability of the batch process. This will reduce the cost and loses for the affected industry. SPC and EPC has been research regularly as a method for process improvement and quality control. Recent publications have also reported that integration of SPC and EPC would produce an increase in performance compared when only used one process control only. This has increase interest and many have publish a study on integration of SPC and EPC. However, most of the study focus on continuous system. The integration of SPC and EPC for a batch process is not yet fully explored. This study hope to explore on this and come up with useful information and finding. Through the information and finding, it is hope to bring benefit to the chemical manufacturing industries and to provide needed exposure for future research in this field.

CHAPTER TWO - LITERATURE REVIEW

2.1 STATISTICAL PROCESS CONTROL

Statistical process control (SPC) was first developed by Dr. Walter A. Shewhart in 1920s as a tool to monitor the quality and the variability of process. SPC is useful as it display the process in a binary view of whether the process is in control or out of control. Using SPC, ones can figure out easily when the process is not conforming to the required process standard and corrective action can be taken. SPC do this by the help of statistical tools, control charts (Škulj et al., 2013). Control chart consist of three important part, the mean value or the centreline, the Upper Control Limit (UCL) and the Lower Control Limit (LCL) as shown in figure below:

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Figure 2.1 Basis of a control charts.

From figure 2.1, the UCL and LCL act as the boundary of the process line which as long as it does not go beyond the UCL and LCL, the process is considered successful. Whenever the process is detected to deviate above the UCL or below LCL, it signifies that the process is out of control and needed a correction action immediately. Subgroups can be defined as a collection of homogeneous data. Homogenous data means that the data is made up of things that are similar to each other.

For every sample, several reading is needed to ensure accurate data collection and this group of readings is considered as subgroup. For example, a subgroup sample size of 5 means that there are 5 reading for every point at a time. Different subgroups will determine the type of control charts suitable to be used. Throughout the year, many type of control charts are developed. Each with their own formulae for the mean, UCL and LCL. Different type of control chart have their own purpose or specialty and can sometimes use together with another control chart. This is important to provide both qualitative and quantitative analysis of the process (Azizi, 2015). Among the control chart commonly used are the X-bar (X̅) chart, Range (R) chart, Individual (I) chart, Moving Range (MR) chart, Cumulative Sum (CUSUM) chart, and Exponentially Weighted Moving Average (EWMA) chart.

2.1.1 X̅ Chart

X̅ chart is also known as the average chart. This is because it utilised the average or the mean value of each sample to produce the chart. It is commonly used for monitoring the quality of a product within a subgroup. X̅ chart is useful because it can be used to measure many type of qualitative parameters such as temperature, height, weight, flowrate and many more. However, in order for it to get enough information, it should be used when there are more than 10 samples available. Usually, this control chart is used together with the other types of control charts such as the R chart (Montgomery, 2009). To calculate the mean value, the following formula is used:

X̅=∑i=1nXinX̅=X1+X2+X3……Xnn (2.2.1)

Where: X̅=mean valueXi=observationtemperature,height,etc.i=1,2,…,nn=number of observation The centreline and control limit are obtained using the equation:

Centreline,X̅̅=∑i=1kX̅ik(2.2)
UCL forX̅chart=X̅̅+A2R̅(2.3)
LCL forX̅chart=X̅̅-A2R̅(2.4)

Where: X̅̅=centreline of the chartR̅=average of rangei=1,2,…,kk=number of subgroupA2=control chart constant from Table2.1 Table 2.1 Constant values for X̅ and R charts.

(Video) Quality (Part 1: Statistical Process Control)

Subgroup SizeA2d2D3D4
21.8801.12803.268
31.0231.69302.574
40.7292.05902.282
50.5772.32602.114
60.4832.53402.004
70.4192.7040.0761.924
80.3732.8470.1361.864
90.3372.970.1841.816
100.3083.0780.2231.777

Source: (Hossain et al., 1996) From the formula, the X̅ Chart can be plotted. Figure 2.2 below shows an example of X̅ Chart with one point outside of the upper limit:

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Figure 2.2 Example of an X-bar Chart

2.1.2 R Chart

R chart or also known as range chart is used to measure the variation of a sample within a subgroup. To get the variance, the highest value of the subgroup is subtracted with the lowest values. This is what it mean by range. The range is then inserted into the equation to calculate the centreline, UCL and LCL to plot the R chart.

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Figure 2.3 Example of R Chart To plot the R Chart, the following equation are used:

R=Xmax-Xmin(2.5)
Centreline,R̅=∑i=1kRik(2.6)
UCL for R Chart=D4R̅(2.7)
LCL for R Chart=D3R̅(2.8)

Where: R̅=average of rangei=1,2,…,kk=number of subgroupD3D4=control chart constant from Table2.1

2.1.3 I Chart

The I chart or individual chart is basically the same as X̅ chart. However, I chart is used when it is impractical to collect a multiple sample (Montgomery, 2009). That mean I chart is more suitable to be used when there are a small subgroup size. Larger sample size is good for sensitive chart, but smaller subgroup size may be necessary for a very slow processes or it is very expensive to obtain measurement.

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Figure 2.4 Example of I Chart The control limit for the I chart is calculated using the following equation:

Moving Range,MR=|Xi-Xi-1|(2.9)
MR̅=X1-X2+X2-X3……|Xn-Xn-1|n-1(2.10)
Centreline,X̅=∑i=1kX̅ik(2.11)
UCL for I Chart=X̅+3MR̅d2(2.12)
LCL for I Chart=X̅-3MR̅d2(2.13)

Where: MR̅=average of moving rangei=1,2,…,kk=number of subgroupn=subgroup sized2=control chart constant from Table2.1

2.1.4 MR Chart

MR chart, or also known as moving range chart is used to monitor variation within the sample by calculating the difference between two consecutive data. In practice, it is usually combined with I chart to become an I-MR chart where the I chart helps assess the process centre and the MR chart plots the process variation.

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Figure 2.5 Example of a Moving Range Chart

Centreline,MR̅=X1-X2+X2-X3……|Xn-Xn-1|n-1(2.14)
UCL for MR Chart=D4MR̅(2.15)
LCL for MR Chart=D3MR̅(2.16)

Where: MR̅=average of moving rangen=subgroup sizeD3D4=control chart constant from Table2.1

2.1.5 EWMA Chart

The EWMA control chart is typically used for an individual observation. This mean that it is used when there is only individual sample of subgroups. EWMA have the performance approximately equivalent to CUSUM control chart although it is easier to set up and operate compared to CUSUM chart (Aljebory et al., 2014). To calculate the EWMA, it is important to decide on a weighting factor, λ. This is used to determine the weight given to previous data.

(Video) What is SPC (Statistical Process Control)?

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Figure 2.6 Example of EWMA Chart The equation needed for EWMA Chart are as follow:

Zt=λXt+(1+λ)Zt-1(2.17)

Where: Zt=EWMA at the timetZt-1=EWMA at the time(t-1)Xt=sample result at timetλ=the weighting factor(0<λ≤1) To determine the control limit for EWMA chart, the following equation is used:

Centreline=μo(2.18)
UCLtfor EWMA Chart=μo+3σλ(2-λ)[1-(1-λ)2t](2.19)
LCLtfor EWMA Chart=μo-3σλ(2-λ)[1-(1-λ)2t](2.20)

Where: μo=the control targetσ=the standard deviationλ=the weighting factor(0<λ≤1) Notice that the control limit for EWMA chart include time as part of the equation. That what make the upper and lower control limit to appear curves at the start of the graph. As the time become larger, the UCL and LCL value will become constant.

2.1.6 Process Capability Analysis

Process capability analysis is used to determine the quality and efficiency of a process. Capability studies are usually used to assist during the stages of product design, such as to deciding the acceptable norms, selecting process and operators (Mahesh et al., 2010). Process capability analysis use the six- sigma (6σ) spread as a way to measure the process capability. It is done by comparing between the difference of Upper Specification Limit (USL) and the Lower Specification Limit (LSL). Not to be confused with control chart limits, because control chart limits is based on estimate of variation from the given process itself while specification limits are typically derived by user (engineer, manufacturer, etc) itself. The difference is used to compare with the 6σ and several possibility may occur. The possible scenarios and the respective meaning are tabulated below for clearer understanding: Table 2.2 Comparison of Process Capability with its explanation.

ScenariosExplanation
6σ > (USL – LSL)The process is not capable of achieving the specifications.
6σ = (USL – LSL)The process is said to be able to meet the exact specifications.
6σ < (USL – LSL)The process is capable of meeting the specifications.

A convenient way of expressing the capability of the process is by using process capability indices (PCI) denoted as Cp, and Cpk. Cp is known as the capability index. It is used to express how well the data fits between the USL and LSL. Cpk is the centering capability index. Cpk compares both the spread of the process and the location of the mean relative to the specifications (Pearn et al., 1998). The formula used to determine the Cp and Cpk are listed below:

Cp=USL-LSL6σ(2.21)
Cpk=minUSL-X̅3σ,X̅-LSL3σ(2.22)

Where: X̅=meanσ=standard deviation From the value of Capability index Cp and Cpk calculated, the estimation of the process can be estimated as shown in the table 2.3: Table 2.3 Estimations of Process based on C­p and Cpk (Johnson et al., 2001)

Capability indexEstimation of the Process
Cp < 1The process is not capable of achieving the specifications.
Cp ≥ 1.33The process is satisfactory enough
Cpk = CpThe process is placed exactly at the centre of the specification limits
Cpk < 1The Process is not capable of achieving the specification
Cpk > 1.33The process is capable

When using process capability index, several factors should be considered. This is because it usually depend on the sample size as it can affect the value of Cpk. Larger sample size is recommended for a better result. Furthermore, it is only applicable when the process is normally distributed. According to (Mahesh et al., 2010), using it on a process that is not normally distributed may often lead to inaccurate results. The process capability is expressed using the process capability chart. From the capability chart, the process can be observed whether I falls within or exceed the specification limits. Depending on several criteria, the process ability could be determined. The criteria are the process data is stable and in control, the data are normally distributed and the specification limits fall on either side of the centreline (Montgomery, 2009). Figure 2.7 show an example of process capability chart where the graph distribution is within the USL and LSL.

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Figure 2.7 Example of Process Capability Chart.

2.2 ENGINEERING PROCESS CONTROL

Engineering Process Control (EPC) or also known as automatic process control is a popular technique used for process optimization and improvement. It describes the manufacturing process as an input-output system where the input variables can be manipulated to counteract disturbances (Aljebory et al., 2014). This is achieved through controller actions which carry out continuous adjustments to the manipulated variable. The output process is used as the final product measurements. There are various types of controller for EPC, such as PID, fuzzy logic, ANN, etc. Among them, PID controller are the most popular and usually used in industry. This is because PIC controller has a simples design, cost effective and provide satisfactory performance.

The notations P, I and D for a PID controller are representative of its variables which are the process gain (Kc), time integral (τI) and derivative time (τD). Each variable is responsible in governing the stability and response of the process. There are many methods the PID controller can be configured. For example, feedback system, feedforward system and internal model control system. Among them, feedback is the simplest control strategy and widely used. Each of these methods possess their own advantages and disadvantages.

2.2.1 Feedback Control System

Feedback system operate in a closed loop manner where a controller is actively making adjustments to the process variable. The term “feedback” was derived from the condition whereby the controlled variable is measured and fed back to the controller and thus will adjust the output accordingly. According to (Smith et al., 1987), the output value is compared against the input whereby any error between the two will be compensated by adjusting the manipulated variable. The advantages of feedback control is it has a simple design thus it is easy to tune, especially for fast and short dead time processes. Due to this, feedback controller is commonly used in oil refining, chemical processing and many more. However, feedback controller also have its disadvantages, such as it can only take any corrective action once the process deviate from the set point. This is sometimes unwanted because it effect the product quantity as material defect and long recovery time. Another disadvantages of EPC is it does not remove the root cause but just simply adjusting to it continuously.

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Figure 2.8 Block Diagram of Feedback Control System

2.2.2 Internal Model Control System

Internal Model Control (IMC) system are example of PID controller that been gaining popularity recently. IMC method is to achieve a fast and accurate set point tracking by removing the effect of disturbance as effectively as possible (Korsane et al., 2014). An advantage of IMC method is that it allows uncertainty and trade-offs between performance and robustness to be considered in a systematic approach (Smith et al., 1987).

(Video) Honda Statistical Process Control

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Figure 2.9 Block Diagram of Internal Model Controller.

2.3 BATCH PROCESS

Batch process in chemical industries is a process that depend the amount of time that produced products by bulk and not in continuous (Vinson, 2008). The batch process involves charging the feed into the reactors or vessel, processing them under controlled conditions, before discharging them as final product. The process is considered a success if only the values of the process variables remain within the acceptable limits and resulting with a high-quality product while following the recipe prescribed for the respective processes (Mears et al., 2017).

Example of chemical process that utilised batch process are the production of polymers, pharmaceutical and food manufactures, semi-conductor industries, biochemical reactors and many more. Batch processes may seem simple at first, however, managing the product quality monitoring and production scheduling and organization make it quite a complicated process (Wu et al., 2017). Moreover, batch process is usually not entirely automated and require intervention by the process operator in order to ensure the quality of the end product and to avoid of an out of spec product. Hachicha (2012) stated that most batch processes run in an open-loop fashion, because of the lack of on-line information and need to be obtained off-line from laboratory assays of few product samples.

In the process control field, there is a need for innovative monitoring and control techniques of the batch process operations. This is because batch and semi-batch processes play a significant role in the production of high value added materials and product (Hachicha, 2012). Furthermore, consumer pressure has resulted in a greater emphasis on product quality (Lennox et al., 2000). According to Wang et al. (2017), a primary challenge for batch process monitoring techniques is to define which is the “normal” operation from which operating cycles that are evaluated and can be identified as successful or failed. A quality control strategy for a batch process often reduces to the on-line control of the trajectories of the key process variables. This is because it may be difficult to detect quality shifts and to counteract it if there are no on-line or real time information.

With the real time information, it is possible to perform the intervention midcourse of the batch process to compensate for the change detected. In recent years, there are high focus on this area, namely Multivariate statistical process control (MSPC). MSPC is different to traditional SPC where it identifies all of the critical variables and underlying patterns in a data set while SPC relies on data such as mean, median, standard deviation, etc., (Duran-Villalobos et al., 2016). MSPC show all process variables, including relationships which cannot be detected with traditional SPC.

This removes the need for control charts for every individual variable because traditional SPC approaches involve plotting trends of important quality parameters and ensuring that these trends do not violate the pre-set control limits. Example of MSPC technique widely applied are, multi-way principal component analysis, multi-way partial least squares, and model predictive controllers (Hachicha, 2012).

2.4 INTEGRATED SPC/EPC

SPC and EPC originate from different industries and have been developed independently in the past. Nowadays, SPC and EPC are widely practiced in manufacturing industry to control a process. Both while act as a control process, have a very different approach, where SPC monitors the process and identify the assignable causes while EPC optimizes the process by manipulation the process variable to compensate the effect of disturbance (Montgomery, 2009). According to (Hachicha, 2012), SPC should not be used to adjust dynamic process and EPC cannot be used to detect assignable causes.

Although both methods are satisfactory process control, it is evidence that both can be considered as two complementary strategies for process control. This is because SPC is able to monitor the process but cannot adjust it automatically while EPC could continuously and automatically adjust the process but cannot determine the root cause or removing it (Montgomery, 2009). It makes sense that by integrating both EPC and SPC would result with a better control system where the SPC would monitor the process and determine the assignable causes, and EPC will automatically corrected it. According to (Hachicha, 2012), integration of EPC/SPC can be done by three method, algorithmic SPC, Active SPC and Run-to-Run. Based on this three method, Run-to-Run is seemed as the most suitable to be used in batch process.

2.4.1 RUN-TO-RUN

Run-to-Run, or also known as Run-By-Run process control techniques have been developed and applied mostly to semiconductor manufacturing processes. Semiconductor product is usually a wafer and each run could consist of a batch of wafer undergoing the same process conditions. Run-to-Run control system operate such as that a control action or change in process parameter can only be implemented between runs instead of during a run (Hachicha, 2012). In this process control, SPC act as a monitoring tools using the suitable control charts detecting the need for Run-to-Run control action. Meanwhile, EPC will perform the adjustment needed to the inputs or initial conditions between run.

CHAPTER THREE - METHODOLOGY

3.1 Overview

This study was carried out in two phases, namely the off-line monitoring phase and the on-line measuring and detecting phase. The offline detecting phase is consist mainly of collecting data. A collection for the past successful batch process is done in this part and the process key monitoring variables will be selected. From the data collected, the control limits for each selected key variables (SPC) and the control adjustments of the process (EPC) is determined using Minitab. The on-line measuring and detecting phase is where the model of the integrated SPC and EPC is run using SIMULINK MATLAB R2015a. Here, fault detection and diagnosis of the SPC/EPC integration will be done. After that, the process will be evaluated again using Minitab whether the key variables is within the SPC limits. The process will be modify based on the SPC/EPC integration if the process is not within the SPC limits. Figure 3.1 will show the process flow of the SPC and EPC integration proposed.

3.2 Process Flow

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Figure 3.1 Flowchart for the proposed SPC/EPC integration approach Source: (Aljebory et al., 2014).

REFERENCES

Aljebory, K. M., & Alshebeb, M. (2014). Quality Improvement ( A Case Study : Chemical Industry - National Chlorine Industries ). Jordan Journal of Mechanical and Industrial Engineering, 8(4), 243–256. Azizi, A. (2015).

Evaluation Improvement of Production Productivity Performance using Statistical Process Control, Overall Equipment Efficiency, and Autonomous Maintenance. Procedia Manufacturing, 2(February), 186–190.

Duran-Villalobos, C. A., Lennox, B., & Lauri, D. (2016). Multivariate batch to batch optimisation of fermentation processes incorporating validity constraints. Journal of Process Control, 46, 34–42.

(Video) Statistical Process Control Overview and Basic Concepts - What You Need to Know for the CQE Exam

Hachicha, W. (2012). Batch processes monitoring based on statistical and engineering process control integration: case of alkyd polymerisation reactor. International Journal of Automation and Control, 6(3/4), 291.

Hossain, a., Choudhury, Z. a., & Suyut, S. (1996). Statistical process control of an industrial process in real time. IEEE Transactions on Industry Applications, 32(2), 243–249.

Johnson, D. W., Jeffries, A., Minsek, D. W., & Hurditch, R. J. (2001). Improving the process capability of SU-8, part II. Journal of Photopolymer Science and Technology, 14(5), 689–694.

Korsane, D. T., Yadav, V., & Raut, K. H. (2014). PID Tuning Rules for First Order plus Time Delay System. International Journal Of Innovative Research In Electrical, Electronics, Instrumentation And Control Engineering, 2(1), 582–586.

Lennox, B., Hiden, H. G., Montague, G. A., Kornfeld, G., & Goulding, P. R. (2000). Application of multivariate statistical process control to batch operations. Computers & Chemical Engineering, 24(2–7), 291–296.

Mahesh, B. P., & Prabhuswamy, M. S. (2010). PROCESS VARIABILITY REDUCTION THROUGH STATISTICAL PROCESS CONTROL FOR QUALITY 1 . 4 Process Capability Indices. International Journal for Quality Research, 4(3), 193–203.

Mears, L., Stocks, S. M., Sin, G., & Gernaey, K. V. (2017). A review of control strategies for manipulating the feed rate in fed-batch fermentation processes. Journal of Biotechnology, 245, 34–46.

Montgomery, D. (2009). Introduction to statistical quality control. John Wiley & Sons Inc. Pearn, W. L., & Chen, K. S. (1998).

New generalization of process capability index Cpk. Journal of Applied Statistics, 25(6), 801–810.

Škulj, G., Vrabič, R., Butala, P., & Sluga, A. (2013). Statistical process control as a service: An industrial case study. Procedia CIRP, 7, 401–406.

Smith, C. A., & Corripio, A. B. (1987). Principles and practice of automatic process control. Automatica, 23(3), 414.

Vinson, J. (2008). The Value of Batch Process Design in a Chemical Engineering Education, 1–8.

Wang, R., Edgar, T. F., Baldea, M., Nixon, M., Wojsznis, W., & Dunia, R. (2017). A geometric method for batch data visualization, process monitoring and fault detection. Journal of Process Control.

Wu, S., Jin, Q., Zhang, R., Zhang, J., & Gao, F. (2017). Improved design of constrained model predictive tracking control for batch processes against unknown uncertainties. ISA Transactions, 69, 273–280.

FAQs

What is statistical process control engineering? ›

Statistical process control (SPC) is defined as the use of statistical techniques to control a process or production method. SPC tools and procedures can help you monitor process behavior, discover issues in internal systems, and find solutions for production issues.

What is the difference between statistical process control and process capability? ›

Discussion -- Statistical Process Control (SPC) Defined:

Control charts provide a means of determining the type of variation (common cause or assignable cause) that is present in a process. Process capability study determines the ability of the "in control" process to produce product which meets specifications.

What is difference between SPC and SQC? ›

Activities which monitor a process in real-time to prevent defects while a lot is being manufactured are known as Statistical Process Controls (SPC). In contrast, activities which occur after manufacture to keep defects from reaching a patient by additional inspection are Statistical Quality Control (SQC).

Is statistical process control part of Six Sigma? ›

The Six Sigma method is often used to remove defects and optimize processes by monitoring operations and then analyzing the data and statistics collected. Statistical Process Control (SPC) is a subset of Six Sigma and is used to monitor operations in order to identify any abnormalities and suggest possible solutions.

What is the difference between SPC and MSA? ›

MSA validates the gage systems used for measurements of special characteristics, which are critical for proper identification of product quality failures. SPC demonstrates process stability and capability for special characteristics originally derived from DFMEA and PFMEA.

Why do we need SPC? ›

SPC helps reduce scrap, waste, defects, and rework, improve product quality, eliminate variation in processes, and maintain compliance with regulatory and customer requirements.

What is the difference between SPC and Cpk? ›

SPC Cpk Index

There are two Cpk values calculated, one that considers the upper specification limit and another that considers the lower specification limit. The reported Cpk, however, represents the lowest value of the capability against the upper or lower specification.

What is acceptable CP and Cpk? ›

In general, the higher the Cpk, the better. A Cpk value less than 1.0 is considered poor and the process is not capable. A value between 1.0 and 1.33 is considered barely capable, and a value greater than 1.33 is considered capable. But, you should aim for a Cpk value of 2.00 or higher where possible.

Do you use the same tools for both SPC and SQC? ›

Like SPC, Statistical Quality Control (SQC) is a data-based approach to quality control. In fact, more often than not, these two terms are used interchangeably. They make use of the same analytical tools to control the manufacturing process.

What is SQC quality? ›

Statistical quality control (SQC) is the use of statistical tools and techniques to monitor and maintain product quality in industries such as food, pharmaceuticals and many manufacturing environments.

Why is SQC important? ›

Statistical quality control provides off-line tools to support analysis- and decision-making to help determine if a process is stable and predictable. When SPC and SQC tools work together, users see the current and long-term picture about processing performance (refer Figure 9.9).

Is SPC good quality? ›

SPC flooring is easily one of the top alternatives to solid hardwood floors because it's so versatile. Since it's durable and waterproof, it's a perfect choice for mudroom flooring, kitchen flooring, and even laundry room flooring.

Is Six Sigma the same as SPC? ›

Statistical Process Control (SPC) is a process improvement methodology to monitor, control, and continuously optimize a process. SPC is really a subset of Six Sigma. SPC is usually associated with control charts and Design of Experiments. Use: SPC separates common-cause from assignable-cause variation.

What level of SPC is preferred? ›

Ideally, control limits should fall within spec limits. Selection of the right control chart depends on the type of data: variable (continuous) or attribute (discrete). Variable data is preferred when available.

How many types of SPC are there? ›

SPC Charts: Three Types Of Statistical Process Control Chart | InfinityQS.

Why MSA is mandatory before carrying out SPC? ›

Measurement systems/equipment being used for SPC

If the variation from the measurement system is high, then control charts will show changes in the measurement equipment, not changes in the process. So it is essential to assess measurement systems statistically prior to implementing SPC.

What is MSA and SPC in quality? ›

(SPC) Statistical Process Control. (MSA) Measurement System Analysis.

How does SPC improve performance? ›

Fundamentally, SPC enables manufacturers to inspect a random output sample from any measurable process and understand what is causing deterministic variations in product, process and quality levels that can be modeled versus completely random factors.

When should SPC be used? ›

When a process needs to be controlled and 100% inspection is not desired or feasible, then SPC is reasonable. Statistical process control costs are considered failure prevention activities. It cost less than internal and external failure costs.

What are the limitations of SPC? ›

Disadvantages of statistical process are :
  • Time Requirements. SPC emphasizes early detection and prevention of problems, which can be a benefit to the production of quality products. ...
  • Cost Considerations. Implementation of SPC is a costly endeavor. ...
  • Quality Measurements. ...
  • Possible Lack of Co-operation.
20 Sept 2020

What is the major component of SPC? ›

Statistical process control (SPC) is a technique for applying statistical analysis to measure, monitor and control processes. The major component of SPC is the use of control charting methods. The basic assumption made in SPC is that all processes are subject to variation.

Can Cpk be greater than CP? ›

When the average of the specification is equal to the target value, then Cpk is equal to Cp. Cpk can never exceed Cp. Both Cp and Cpk can be calculated with the generation of descriptive statistic views and histograms.

What is the maximum Cpk value? ›

The minimum value of "k" is 0 and the maximum is 1.0. A perfectly centered process will have Cp = Cpk. Both Cpk and Ppk relate the standard deviation and centering of the process about the midpoint to the allowable tolerance specifications. An estimate for Cpk = Cp(1-k).

What is Cp and Cpk value in SPC? ›

Cp indicates the spread of variation present in a process. Process Capability Index – Cpk: This is the capability index that accounts for the centering of the process and is defined as the minimum of Cpk upper and Cpk lower. Cpk is a measure of process performance capability.

What if CP is less than 1? ›

A Cp of less than one indicates that the process spread is greater than the specification. This means that some of the data lies outside the specification. A Cp of greater than one indicates that the process spread is less than the width of the specification.

What if Cpk is less than CP? ›

If Cpk is less than Cp and Cp is greater than one, center the process in the specification. This should make Cpk comparable to Cp.

What does a Cpk of 1.67 mean in terms of capability? ›

CPK <1.00 (Poor, incapable) 1.00< CPK <1.67 (Fair) CPK >1.67 (Excellent, Capable)

Which software is used for SPC? ›

For 50 years, Minitab has been the leading software for data analysis and quality improvement. Real-Time SPC Powered by Minitab has the real-time capabilities and trusted analysis you need to take your process monitoring to the next level all in one convenient and comprehensive solution.

Why is statistical process control SPC preferred to 100% inspection? ›

100% inspection drives a static/stagnant culture with an emphasis on COMPLIANCE – Is the part OK/NOK. However, if we want to continually improve and better understand our processes then an SPC approach (with its preventative focus) helps create a dynamic culture of process improvement, evolution and innovation.

How do I know which SPC chart to use? ›

How do I choose the appropriate type of control chart?
  1. The type of data being charted (continuous or attribute)
  2. The required sensitivity (size of the change to be detected) of the chart.
  3. Whether the chart includes data from multiple locations or not.
  4. The ease and cost of sampling.
  5. Production volumes.
26 Apr 2019

How is SQC used to control the process? ›

Relying itself on the probability theory, SQC evaluates batch quality and controls the quality of the processes and the products. SQC uses three scientific techniques, namely (i) sampling inspection, (ii) analysis of the data, and (iii) control charting.

What are the 3 quality types? ›

Quality control professionals typically classify quality defects into three main categories: minor, major and critical. The nature and severity of a defect determines in which of the three categories it belongs.

What are the 3 categories of SQC? ›

The three categories of SQC are traditional statistical tools, acceptance sampling and statistical process control (SPC). Traditional statistical tools are descriptive statistics, such as the mean and range, used to describe quality characteristics.

What is pure SPC? ›

What is Pure SPC Max Flooring? Republic's flagship flooring product is made from super-strong Stone Plastic Composite (SPC) and is 100% waterproof. It is highly durable and resistant to scratches and dents.

Is Spc better than PVC? ›

The main difference between SPC and vinyl is the construction of each plank. A vinyl floor has a PVC core that makes it soft and flexible. On the other hand, SPC flooring has a core that is made of stone plastic composite, which makes it rigid and less springy.

Is Spc water proof? ›

SPC flooring, which stands for Stone Plastic Composite, is the latest innovative material in the flooring world. It is a premium type of LVT that is 100% waterproof and a much more stable material than traditional LVT.

Is SPC outdated? ›

Statistical Process Control (SPC) appears to still hold an important position at Original Electronics Manufacturers (OEM). It is found in continuous manufacturing processes, calculating control limits, and detecting out-of-order process parameters.

Is SPC part of TQM? ›

Production personnel and quality control management recognized SPC as the part of the philosophy of TQM that empowered employees to improve their processes[10, 12].

What has replaced Six Sigma? ›

Agile. Agile has been compared to both lean and Six Sigma, but it is important to understand that agile is not a methodology, per se. Instead, agile is a set of principles that began in the software development world and quickly spread to other business disciplines.

What is stability in SPC? ›

The upper and lower limits within which a process's output must fall in order for that output to be acceptable. Spread. The amount of variability in a sample or population. Stability. A process is considered stable if it is free from the influences of special causes.

What is SPC output capability? ›

Having an "SPC Output" means you are able to press a button and send that data to a PC or data collector for statistical analysis or data recording.

Can statistically controlled process produce significant rejection? ›

To monitor the performance of the production process, SPC uses Statistical tools and predicts significant deviations that may later result in rejection.

What are the two types of data in SPC? ›

There are two types of data you can have: attributes data and variables data. Both these types of data are introduced in this module.

What is basic SPC? ›

Basic SPC is a comprehensive online SPC training course for engineers, operators, and technicians that makes understanding and applying statistical process control (SPC) concepts easy.

What is the main purpose of statistical process control? ›

Statistical process control (SPC) is commonly used in manufacturing or production process to measure how consistently a product performs according to its design specifications. By achieving consistent quality and performance, some of the benefits manufacturers can realize are: Reduced scrap, rework, and warranty claims.

What are the 3 basics of statistical process control? ›

The three main components of an SPC chart are - a central line (CL) for the average, a lower control line (LCL) for the lower control unit, and an upper control line (UCL) for the upper control unit. SPC charts were initially developed by Dr. Walter A. Shewhart of Bell Laboratories in the 1920s.

What is the meaning of statistical control? ›

If a process produces a set of data under what are essentially the same conditions and the internal variations are found to be random, then the process is said to be statistically under control.

What are the 4 components of the statistical process? ›

Consider statistics as a problem-solving process and examine its four components: asking questions, collecting appropriate data, analyzing the data, and interpreting the results. This session investigates the nature of data and its potential sources of variation.

How does statistical process control improve quality? ›

Statistical Process Control is an analytical decision making tool paramount for any manufacturing or engineering company to improve product quality by reducing process variation.

What is quality SQC? ›

Statistical quality control (SQC) is the use of statistical tools and techniques to monitor and maintain product quality in industries such as food, pharmaceuticals and many manufacturing environments.

How do you collect data from SPC? ›

SPC data is collected in the form of measurements of a product dimension / feature or process instrumentation readings. The data is then recorded and tracked on various types of control charts, based on the type of data being collected.

What is statistical control example? ›

statistical control Statistical techniques for excluding the influence of specified variables in an analysis. For example, if the data from a sample survey showed a strong association between unemployment and clinical depression, one might want to control for the effect of social class.

What is statistical process control example? ›

SPC can be applied to any process where the "conforming product" (product meeting specifications) output can be measured. Key tools used in SPC include run charts, control charts, a focus on continuous improvement, and the design of experiments. An example of a process where SPC is applied is manufacturing lines.

What are the 5 steps of the statistical process? ›

  • Step 1: Write your hypotheses and plan your research design. ...
  • Step 2: Collect data from a sample. ...
  • Step 3: Summarize your data with descriptive statistics. ...
  • Step 4: Test hypotheses or make estimates with inferential statistics. ...
  • Step 5: Interpret your results.

What are the 3 types of statistics? ›

Types of Statistics in Maths
  • Descriptive Statistics. In this type of statistics, the data is summarised through the given observations. ...
  • Inferential Statistics. This type of statistics is used to interpret the meaning of Descriptive statistics. ...
  • Statistics Example.

What are the 5 statistical process? ›

The Statistical Process has five steps: Design the study, Collect the data, Describe the data, Make inferences, Take action.

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