Lean Six Sigma Implementation in Strainer Manufacturing Industry

Abstract— Lean Six Sigma is a methodology in a collaborative team effort to improve the performance by systematically removing waste and reducing variation. It combines lean manufacturing and Six Sigma to eliminate the waste. In manufacturing company, it is essential to improve the process. In this study, Lean Six Sigma tools are used in Strainer component manufacturing industry to analyze and improve the manufacturing process. It is observed that strainer component manufacturing are out of specification limit and production was unstable. The root cause of failure is identified, analyzed and by using Lean six sigma tools improvement are made.

Index Terms— DMAIC, Lean Six Sigma, Process Control, Strainer

Six- Sigma allows only 3.4 defects per million. Six-Sigma is a management philosophy to eliminate mistakes, rework and waste. It is a problem-solving method to increase customer satisfaction, profit and reduce cost. Six Sigma is an improvement strategy for an organization. It is a quality improvement process by reducing the defects, minimize the variation and improve capability in the manufacturing process. The objective of Six Sigma is to increase the profit.
Lean Six Sigma (LSS) combines principles of Lean with Six Sigma to improve process effectiveness. Lean focus on to reduce lead-time by removing waste and non-value added activities. Process capability analysis is a method of combining the statistical tools developed from the normal curve and control charts to analyze the data representing a process. The process capability study is to determine the process variation. The use of the process capability study should be an integral part of the quality engineering. Quantify the variability and reducing it in the manufacturing process is the main activity of the process management.

Process Capability means an evaluation of how well a process meets specifications or the ability of the process to produce and that conform to engineering specifications. Process Control means an evaluation of process stability over time or the ability of the process to maintain a state of good statistical control. The process capability is the range over which the process natural variation occurs. There are two primary capability indices

• Cp is the capability index. It measures how well the data fit into and between the upper and lower specification limits. The higher the value, the better the process.

• Cpk is the centering capability index. It measures how well the data is centered and within the specification limits. The higher is the value then data is centered.

Lean Six Sigma training provides a strong leadership and supports the initiative. LSS drive the quality improvement approach and reduce the effect in implementation process Achievement towards a continual improvement, customers satisfaction, increase sales at a minimized cost to attain targeted market share and profit level [1].

The study and understanding of quality and process at different levels will help to continuous process measurement and improvement system. A systematic and conscious effort influence and control the flow of information which leads to efficient process and improve the effectiveness of organization [2].

Process capability is a performance level of thethe process after it has been checked under statistical control. It is used to measure the variability of the output of a process and to compare that variability with a proposed specification or product tolerance [8].

The indices for process capability are based on the assumption that the underlying process distribution is approximately normal [9]. The process capability study encompasses all natural variables and the number of the sample has a significant influence on the accuracy of the Cpk estimates, smaller samples will result in even larger variations of the Cpk statistics [10].

The purpose of this study is the six sigma methodology of DMAIC process. The tools used for each phase is discussed in further topics. Project charter and SIPOC diagram are used in Define Phase. Process capability analysis is to eliminate quality problems during machining. Cause and effect diagram to identify the root cause of failure. A control chart is to check whether the process is within control limit or not.

METHODOLOGY

Six Sigma uses a standardized step-by-step process with specific tools for conducting projects. This is called DMAIC, which stands for Define, Measure, Analyze, Improve, and Control.
DMAIC process involves the following steps:
Step 1: Define Phase
Step 2: Measure Phase
Step 3: Analyze Phase
Step 4: Improve Phase
Step 5: Control Phase

DATA COLLECTION

Define Phase
In the Define phase of the project, the aim is to define the problem statement, which specifies what the team wants to improve. The need for project implementation and their benefits are to be defined in this phase. In this phase, the Project Charter, SIPOC – Suppliers, Inputs, Process, Outputs, and Customers are used.

The key elements of a Six Sigma Project charter are listed below

1. Business case
2. Problem Statement
3. Goal statement
4. Roles and responsibilities
5. Scope of the project,
6. Preliminary project plan
7. Communication plan

TABLE I

PROJECT CHARTER

Project Charter
Project Name Defect Rate Reduction
Business Unit Calmet
Department Production
Start Date 01-10-17
Project Budget 30000
Project Stakeholder Name
Project Champion Ram
Process Owner Praveen
Black/ Green Belt Guru
Team Members Anand, Murugan
Business Case

The number of orders for strainer is more but there is a problem of high rejection due to variation in size and irregularity shape. If this continues the cost of production will increase and cost of rework also increases

Problem Statement

Strainer Defect Rate is high due to manufacturing shape as per design of the final product. Rework of component is more.

Goal Statement

The goal of the project is to reduce the number of defective items.

Project Scope

The scope of the Project is to examine all processes, identify the cause for defective items and suggest the alternative method to reduce defects.

Benefits
Satisfy Customer
Produce Quality Products
Reduce Defects
Avoid Rework
To create a SIPOC diagram:
Identify Supplier.
Identify various input required.
Identify activities involved.
Identify Outputs of the process.
Identify Customers.

The SIPOC diagram which lists all the activities which convert the raw material into a final product of strainer is shown in Table III.

TABLE II

SIPOC

Supplier Input Process Output Customer
Sheet Metal
Machines
Welding Gas Cylinder
Protective Devices Manpower
Machine Tool
Equipment Sheet metal Shearing
Forming
Rolling
Spot
Welding
Drilling
Rivet Welding
Net Inserting
Packing Strainer Pump Manufacturer
Retailer

Measure Phase

The Measure Phase is the second step of the Six Sigma methodology. The goal of Measure phase is to establish a clear understanding of the current state of the process you want to improve. The Outer diameter of the Strainer is measured in subgroup size of three for each component. The measured values are presented in the Table III shown below

TABLE III

THE MEASURED VALUES OF OUTER DIAMETER

Subgroup Sample size Mean Range

1 2 3 1 102.6 102.3 102.4 102.43 0.3
2 102.4 102.7 102.5 102.53 0.3
3 102.4 102.6 102.4 102.47 0.2
4 102.3 102.6 102.5 102.47 0.3
5 102.3 102.1 102.2 102.20 0.2
6 102.6 102.7 102.4 102.57 0.3
7 102.8 102.4 102.3 102.50 0.5
8 102.5 102.6 102.2 102.43 0.4
9 102.7 102.6 102.7 102.67 0.1
10 102.5 102.4 102.6 102.50 0.2
11 102.3 102.4 102.5 102.40 0.2
12 102.4 102.6 102.2 102.40 0.4
13 102.3 102.5 102.2 102.33 0.3
14 102.4 102.6 102.4 102.47 0.2
15 102.5 102.9 102.2 102.53 0.7

Analyze Phase

In Analyze phase, identify several possible causes of variation that are affecting the outputs of the process. Commonly used tools in the analyze phase is the Cause and Effect Diagram. The Cause and Effect Diagram is a technique to identify the possible causes of a problem.

Fig. 1. Cause and effect diagram

Improve Phase

The purpose of the Improve phase is to identify improvement recommendation. The activities performed during the Improve phase are

Identify improvement
Cost/benefit analysis
Design future state
Establish performance targets and project scorecard
Implementation

The objective of affinity diagram is to develop understandable and meaningful ideas from a list of many ideas. It is helpful when ideas need to be clarified by making into smaller categories.

Machinery Operator Training Raw Material

Inspect Machine before operation Provide Training Material Standards
Regular Maintenance Assess Operator Performance Raw Material Inspection

Fig. 2. Affinity diagram

Control Phase

Control phase is to verify that the implementation is successful and ensure that the improvement will sustain over time.In the Control phase, the team should verify that training and implementation were carried out correctly. It is required to collect and analyze data to ensure that the process performance and improvements are made. The teams provide a recommendation for improvement.

A control chart consists of three lines
Central line (CL)
Upper Control Limit (UCL).
Lower Control Limit (LCL).
x̅ Chart
UCL = x̿ + A2R̅
LCL = x̿ – A2R̅
R Chart
UCL = R̅D4
LCL = R̅D3
R̅D3 is the mean of the ranges in the sample process. A2, D4 and D3 are variables in the appropriate statistical (SQC) table.

RESULTS AND DISCUSSION

Fig. 3. Process-capability analysis of outer diameter
In Fig. 3 The process-capability analysis represents that there is no component under the LCL limit. The component fails due to only higher dimension than the specification limit. From this, it is concluded that the process is not capable.

Fig. 4. Histogram of outer diameter
In Fig. 4 Histogram of Outer Diameter is shown in that component variation is higher in dimension on right side of the mean value and more than the specification limit. The distribution of value is not in specified limit this makes a poor quality product.

Fig. 5. Hypothesis test result
From Fig. 5 the hypothesis testing result determined p value greater than 1 which means insignificant finding and little or no evidence to reject the null hypothesis.

Fig. 6. X bar Chart of Outer diameter
It has been observed from the Fig. 6 that Sample 1,6,7,9 are above the UCL represents out of control limits and not meeting the specification limit. It is concluded that the process is not under statistical control.

Fig. 7. R Chart of Outer diameter
In Fig. 7 Sample 15 range is above the Upper Boundary limit represents that range is maximum and is not acceptable of huge variation.

Fig. 8. Pareto Chart for Strainer
From Fig. 8 Irregularity in the shape of the strainer is the major contribution of the failure. This can be reduced by the proper forming die and rolling process is taken care to improve the process.

Conclusion

A case study is presented of manufacturing of Strainer was systematically improved by the applying of the Lean Six Sigma methodology. Waste is eliminated by measuring and analyzing the root cause of variation and implement the change. The LSS steps are the systematic approach assessing of the current state of the process. Preparation of the SIPOC to list all process involved. In this, the process-capability analysis was carried out in Measure phase to conclude that Cpk of less than 1.0 means that the process is not capable of meeting its requirements. The process is not capable of consistently bringing out Strainer with an outer diameter as per specification required. The process average is off-centered. From Analyze phase root cause is identified. In improve, phase affinity diagram is used to list the ideas in categories. Control chart and Pareto chart are used in control to check whether the process is in control or not. The control chart represents out of control limits and not meeting the specification limit.

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