Enterprise AI Analysis

Integration of quality control tools applied to the management of continuous industrial processes: a case study

Authors: Lorena Marcele de Faria Leite, Euclides Antônio Pereira de Lima, Leonardo Campos de Assis

With the increasing complexity of industrial processes, there is a growing demand for integrated quality control solutions. Quality control in industrial processes is continually sought after, and the tools applied for this purpose have long been known and adopted by managers. This study arose from the need to overcome the limitations of individual quality control tools, such as Statistical Process Control, the PDCA cycle, the Ishikawa Diagram, and the 5W2H method, which, although effective in their specific functions, do not provide a comprehensive approach to effectively managing continuous industrial processes. The objective of this study was to integrate these tools into a methodology that systematically monitors, diagnoses, and corrects failures efficiently. The methodology was applied to a case study in the sugar manufacturing industry, specifically in the liming process, demonstrating its effectiveness in stabilizing the process and improving the final product quality. Control charts showed that the process was out of control, with a capability of 1.02, below the acceptable limit of 1.33. After implementing the proposed corrective actions, the process stabilized, and the capability increased to 1.45, with a significant reduction in process variability. The integration of these tools enhanced each one's problem-solving potential, demonstrating effectiveness in continuous improvement and the management of continuous industrial processes. This methodology not only proved effective in the presented case study but also shows potential for adaptation in other industrial sectors such as pharmaceuticals, food, and manufacturing, especially in the context of Industry 4.0, where integration with real-time monitoring technologies and artificial intelligence could further optimize quality control and process efficiency.

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Unlocking Process Excellence: Integrated Quality Control for Continuous Improvement

This study demonstrates a powerful integrated methodology combining Statistical Process Control (SPC), PDCA cycle, Ishikawa Diagram, and 5W2H to optimize continuous industrial processes. Applied in a sugar manufacturing plant's critical liming process, the methodology significantly improved process stability, product quality, and delivered substantial financial gains, highlighting its adaptability for Industry 4.0 environments.

1.02 Process Capability Index (Initial)

1.45 Process Capability Index (Improved)

28% Variability Reduction

$356,500 Estimated Financial Benefits

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Deep Analysis & Enterprise Applications

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PDCA Cycle

SPC

Ishikawa Diagram

5W2H Method

PDCA Cycle: Plan, Do, Check, Act

The PDCA cycle is a continuous process improvement method consisting of four stages: Plan, Do, Check, and Act. Its main strength lies in its systematic approach to continuous improvement and change implementation. In the sugar industry case study, the PDCA was essential for organizing and guiding the analysis and actions provided by the other quality tools, ensuring a structured and effective approach to stabilize the liming process.

Integrated Quality Control Methodology Workflow

SPC Monitoring

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Trend/Out of Control Detection

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PDCA Cycle Initiation

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Problem Diagnosis (Ishikawa)

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Action Planning (5W2H)

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Implementation

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Process Re-evaluation (SPC)

PDCA Cycle in Sugar Liming Process Management

Context: The PDCA cycle was essential for organizing and guiding the analysis and actions provided by the other quality tools, ensuring a structured and effective approach to stabilize the liming process.

Findings: When the SPC identifies an abnormal behaviour on a monitored variable, the PDCA starts, which offers the means to manage the strategies adopted. This structured approach was crucial for managing the entire improvement process.

Statistical Process Control (SPC): Monitoring for Stability

Statistical Process Control (SPC) tools are gaining prominence in industrial management, acting as facilitators in the ongoing pursuit of higher quality. SPC is an effective tool for monitoring process variation and identifying when a process is out of control, allowing managers to intervene before the issue affects product quality. Its strength lies in providing continuous monitoring based on quantitative data, enhancing the objectivity of decision-making. SPC's main weakness is its inability to identify the root cause of a problem, merely alerting that the process is out of specification.

Initial Process Capability

1.02 Initial Process Capability Index (Cp)

Control charts showed that the process was out of control, with a capability of 1.02, below the acceptable limit of 1.33, confirming the process was not capable of consistently meeting requirements.

Improved Process Capability

1.45 Improved Process Capability Index (Cp)

After implementing the proposed corrective actions, the process stabilized, and the capability increased to 1.45, with a significant reduction in process variability, confirming the successful stabilization of the process.

SPC Monitoring and PDCA Integration Stages

Start SPC Monitoring

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Stable and Under Control Process

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Trend Detection or Out of Control Process

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PHASE 1: PLAN (5W2H)

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PHASE 2: DO (5W2H)

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PHASE 3: CHECK (SPC, Ishikawa, 5W2H)

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PHASE 4: ACT (5W2H)

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Return to SPC Monitoring

SPC Application in Sugar Liming Process

Context: In the case study, SPC was used to detect pH variations in the sugarcane juice, indicating the process was out of control, prompting the application of other tools for problem identification and correction.

Findings: The initial control chart immediately confirmed that the process was operating out of statistical control, as indicated by numerous points exceeding the upper and lower control limits. The calculated process capability index was 1.02, significantly below the acceptable threshold of 1.33.

Ishikawa Diagram: Cause and Effect Analysis

The Ishikawa Diagram, also known as the “Cause and Effect Analysis" or "Fishbone Diagram,” is a graphical tool used to systematically analyze factors influencing the quality characteristics of production processes. Its main strength lies in its ability to identify and categorize multiple causes contributing to a problem, assisting in diagnosing and preventing failures. However, its limitation is that the Ishikawa Diagram alone does not provide a direct solution or specific corrective actions, requiring integration with other tools, such as PDCA and 5W2H.

Ishikawa Diagram for Liming Process Instability

Context: In the case study of the sugarcane industry, the Ishikawa Diagram was used to identify the causes leading to the instability of the liming process, facilitating detailed analysis of the factors influencing process quality and enabling a more targeted application of corrective actions.

Findings: Once the process achieved a controlled state (post-initial 5W2H actions), the team conducted a brainstorming session and developed an Ishikawa (Fishbone) Diagram to identify the root causes of the problem, leading to a second, more targeted 5W2H action plan.

Ishikawa Diagram: Causes of Process Error/Lack of Control in Liming

PEOPLE/WORKFORCE

Knowledge of operational procedures

ENVIRONMENT

Area lighting
Lavatory for hygiene

METHODS

Improvement of the procedure with a detailed operation flowchart
Milk of lime solubility
Baumé control forms
Baumé control in preparation

MEASUREMENTS

Electrode measurement

MACHINE/EQUIPMENT

Pump identification
Level alarm

MATERIALS

Lime quality

5W2H Method: Structured Action Planning

The 5W2H is a tool used to structure and guide the actions that make up a plan, gathering the most important information about a problem, often presented in table format. Its strength lies in the simplicity and effectiveness with which it facilitates the execution of corrective action plans. However, its main limitation is that 5W2H relies on the prior and precise identification of the problems that need to be corrected, being most useful after the clear definition of the causes of failures.

5W2H Action Plan: Initial (Plan Stage)

Action	What	Why	Who	When	Where	How
Action 1	Baumé Check of the preparation tank	Allow time for the operator to correct the Baumé of the milk of lime during its filling	Operation	Upon starting the harvest of the year 2020	Milk of lime preparation station	Ensure, via spreadsheet or area check, that the operator verifies the Baumé of the milk of lime during filling
Action 2	Ensure the necessary time of 3 h for solubility of the milk of lime	Improve the quality of prepared milk of lime	Area/Operation Manager	Upon starting the harvest of the year 2020	Milk of lime preparation station	Create a routine for the milk of lime preparation operator so that the preparation is carried out right after the tank is emptied
Action 3	Ensure that regular calibrations are carried out on the area's pH meter	Ensure the reliability of the area's pH meter reading	Maintenance, Planning and Control (MPC)/ Instrumentation	March/2020	MPC/pH meter's area	Develop a monitoring spreadsheet as well as define an electrode check routine with control via MPC
Action 4	Ensure the use of quality lime in the manufacturing process	To reduce lime consumption and costs, and to improve the quality of milk of lime preparation and the liming process	Area Manager/Quality Control/Purchasing	Upon starting the harvest of the year 2020	Quality Control/Purchasing	Increase the frequency of insoluble residue analyses by industrial quality control, and return lime loads that are out of specification

5W2H Action Plan: Post-Ishikawa (Check Stage)

Action	What	Why	Who	When	Where	How
Action 5	Insertion of low level alarm in 80m³ tanks	Avoid cases of lack of milk of lime for level zero in the tank Allow the use of operator labor in various activities when emptying the tank	Electric Maintenance/ Instrumentation	March/2020	Milk of lime preparation station	Insert automatic level alarm in the area via visual or audible signal via Industrial Operation Center (IOC)
Action 6	Insertion of a 80 m³ tank for milk of lime preparation	Provide greater volume area for better milk of lime preparation	Area manager	March/2020	Milk of lime preparation station	Option 1: Manufacture a tank; Option 2: buy tank; Perform the installation via the internal boilermaking team

5W2H for Corrective Action Implementation

Context: In the case study, 5W2H was used to organize the corrective actions defined after the Ishikawa Diagram analysis and the data provided by the SPC, enabling efficient execution of the corrections and a swift stabilization of the liming process in the sugar industry.

Findings: The team implemented the actions defined in the initial 5W2H plan. These actions were completed according to the established deadlines and priorities to ensure efficient problem resolution and significantly improved process control.

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Integrated Quality Control: 5-Phase Implementation Roadmap

Our integrated methodology provides a systematic path to continuous process improvement. Follow these key phases for successful implementation and sustained quality management in your enterprise.

Phase 1: Defining Control Variables & Baselines

Initially, the critical control points or variables are defined, which will be monitored and controlled. This involves selecting processes crucial to operations where non-conformities lead to high production and financial impact. Establish baseline performance metrics and select a dedicated implementation team.

Phase 2: Initial Process Evaluation with SPC

Implement Statistical Process Control (SPC) charts for the chosen variables. Analyze and interpret the control charts to detect process deviations and calculate initial process capability. If the process is stable and capable, routine monitoring continues. If unstable or incapable, proceed to the PDCA cycle.

Phase 3: Root Cause Analysis & Action Planning

Initiate the 'Plan' stage of the PDCA cycle. Conduct brainstorming sessions supported by the Ishikawa Diagram to thoroughly investigate the root causes of identified problems. Utilize the 5W2H method to develop detailed action plans, specifying 'What, Why, Who, When, Where, How, and How Much' for each corrective action.

Phase 4: Action Implementation & Initial Verification

Execute the actions defined in the 5W2H plan ('Do' stage). Ensure responsible teams implement changes within established deadlines. After implementation, immediately re-evaluate the process using new SPC control charts ('Check' stage) to verify the effectiveness of the actions and recalculate process capability. If the process stabilizes, proceed to act; otherwise, re-analyze.

Phase 5: Sustained Improvement & Monitoring

Implement permanent changes and standardized procedures based on successful corrective actions ('Act' stage). Communicate new protocols and provide training. Return to continuous SPC monitoring, ensuring the process remains stable and capable. This creates a cycle of continuous improvement, embedding quality control as an integral part of operations.

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Detailed Case Study: Sugar Manufacturing Liming Process

Explore the real-world application of the integrated quality control methodology and its transformative impact.

Case Study Context

The methodology was applied in the liming process of a sugar manufacturing industry in São Paulo, Brazil. Liming is a critical step to correct hydrogen potential, minimize sucrose losses, and remove impurities, directly impacting final sugar quality. pH variations were identified as the key variable for quality control.

Before Improvement

Initially, SPC charts revealed the liming process was out of statistical control, with a process capability index (Cp) of 1.02, significantly below the acceptable threshold of 1.33. This led to critical pH fluctuations, deficiencies in decantation, increased sucrose losses, and lower final product quality (402,110 sacks of lower-quality sugar).

Actions Taken

An integrated team (operations, process engineer, lab personnel) used the PDCA cycle as a framework. SPC detected the out-of-control state. Initial corrective actions were planned with 5W2H (e.g., Baumé checks, solubility time, pH meter calibration). After initial improvements, an Ishikawa Diagram identified deeper root causes, leading to a second, more comprehensive 5W2H action plan (e.g., low level alarms, tank capacity increase, quality lime sourcing).

After Improvement

Post-implementation, the process stabilized, with the capability index increasing to 1.45. There was a significant reduction in process variability (28%) and improved pH control, directly enhancing final sugar quality. This resulted in a beneficial reduction in Insoluble Residue percentage and estimated financial gains of US$ 120,633 from quality premium and US$ 155,646.45 from reduced lime consumption, totaling US$ 356,500.35.

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