Root Cause Analysis in Improvement of Product Quality and Productivity

•   Background

Root Cause Analysis (RCA) is the process of identifying causal factors using a structured approach with techniques designed to provide a focus for identifying and resolving problems. Tools that assist groups or individuals in identifying the root causes of problems are known as root cause analysis tools. Every equipment failure happens for a number of reasons. To meet up the high changing market demands along with high quality at comparable prices, one shall have to identify quickly the root causes of quality related problems by reviewing an event, with the goals of determining what has happened, why it has happened and what can be done to reduce the likelihood of recurrence. The X Company is one of the leading companies that professionally managed and has got ISO 9002 and ISO 14001-system certification. It has also implemented Total Quality Management. The departments have been computerized and linked through Local Area Networking (LAN) to enhance accessibility. Maintenance management systems are in practice. It is also backed up by an advanced computer aided condition monitoring system. The plant processes may be roughly categorized into the following blocks (as per the material flow): 

1. Raw Material Processes 
2. Intermediate Processes
3. Final Processes 

The products manufactured by the plant comprise of different components, used in construction equipments and in conveying systems. To improve the product quality and productivity Oxy Flame cutting machine was chosen. This machine is composed of electrical and mechanical systems. The machine moves along X axis through L.T. Mechanism (Long Travel Mechanism) and through cross travel i.e. along Y axis travel is done in cross travel Beam by the three cutting torches which are fitted with sensors for which command comes from the CPU fitted with the machine. This machine has three cutting torches by which the materials are being cut by oxy flame. It uses multi channel data format for storage of time data, spectra, etc., including: function identifier, sampling frequency, input/output point and direction, input/output units, free text lines, X-, Y-, Z-axis labels, auxiliary custom fields. Extensive commands to extract information from headers including a search function. It uses dissolved Acetylene and Oxygen to generate flame to cut the material in a straight line or in curves. When a single torch is used, it can cut straight beveling. The torches have proximity sensors so that there should be an accurate distance between the Raw material to be cut and Torch tip. The tool holder is a part of the system where the sensor of the cutting edge is placed. When the machine begins cutting, the cutting torches move according to DNC (Direct Numerical Control) program. This DNC program is converted from a CNC (Computerized Numerical Control) program. A detector is also placed to capture the problems in cutting, which enables an operator to make adjustments of speed, cutting gap or Gas flow.

The problem was encountered in the initial processing of the material. The capacity utilization of the plant was around 55% to 65% due to problems in processing of materials itself and there was always fire-fighting for want of material. But, no root causes were identified as to why there was such a problem. This reason was one of the key contributory factors for the lower level of productivity.

Company Profile

Name	X Company
No. of Employee	20,000 Employees
Annual Income	USD 870 Million
Annual Profit	USD 450 Million
Product	Automotive Body Part, Tanker, Water Bowser, Tipper, Cargo Body
Export Destination	18 Countries around the world

•  State of the Problem

Based on interview from the employee and documents in last three months, the problem can be resumed as;

Focal Point	Dimensional defects and low production speed in cutting operation in CNC Oxy Flame Cutting Plant
When
Date	27/08/2010-05/09/2012
Unique Timing	During increased production schedule, After 10 straight 12 hour night shifts
Where
Location	X Company

• Impact of the Failure

The abrupt shutdowns and breakdowns (5.19% of annual sales), frequent customer complaints (367pa), line balancing delay (27%), material scarcity or unavailability of matching material (58 days pa), rejection (3.03% of sales) and various other key success factors were not up to the mark.

Resume of loss in financial calculation:

Effect(s)	% Loss of Sales	Total Loss (USD)
Shutdowns of Plant	5,19	USD      498,240
Rejection	3.03	USD   4,540,000
Total Loss		USD   5,038,240

Another effect of the failure:

Event	Effect	Total Loss
Frequent Customer Complaint	367 complaints in Three months (Decreasing 0.5% demand)	Approximately USD 4,800
Line Balancing Delay	27% Increasing of Operational Expenditure	Approximately USD 5,400

• Team of RCFA
  
  
  Thereafter, a multi-disciplinary Cross Functional Team (CFT) of knowledge workers was formed. Managers and engineers were taken from different departments namely, Mechanical, Electrical, Instrumentation, Production, and Quality departments, since they were related to above case studies.

Fig 1. The team of RCFA in the improvement of quality and productivity

A.    Organization of the details of the causes using 3W2H

The raw material was processed mainly on CNC Oxy Flame Cutting Machine. The main operations were categorized into different operational blocks like Transmission System, Gas System, Structure and different assemblies, Lubrication, Traverse Carriage System, CNC programming and Cutting Torch Suspension system.  The root cause of these items were organized and defined and against each of these blocks the Reliability per day, assuming constant rate of failures, was worked out for several days in %. It was found that three blocks namely Transmission System, Lubrication, and Cutting Torch Suspension system, were the most unreliable blocks. It was observed that the reliability per day of the entire system was 57% and the average time between two successive failures was 3 hours 57 minutes. That is, we would expect a failure will happen every 4 hours or so. The average time of repair for the system is 1 hour 28 minutes. That is, each failure one may expect to be rectified within 1 hour 30 minutes. The cutting operation was to be performed in all the items but how far it is related to or it was influencing the production processes had never been studied earlier. Therefore, a value stream mapping was done first by selecting a job (Pivot Frame) to understand the percentile impact of gas cutting operation on the production process. The defect on cut material increases the cycle time of each activity and adds more non-value adding times. Hence, to pin point non-value adding activities contributed by gas cutting, data were captured activity wise. Now, the Value Stream Mapping was done and its detail is tabulated in Table 1. Different operations have been categorized and entered in the table in abbreviated terms.

Table 1. Tabulated data of Value Stream Mapping

Fig 2. Pivot Frame of Value Stream Mapping

In the above sample study, it was found that the non-value adding activities were higher than the value adding activities. The operations entered in serial numbers 3 to 5, 7 to 12, 18 to 20, 25 and 26 (Table 1) are non-value adding activities associated to gas cutting operation. It comes out to be 7 hours 40 minutes of non-value added activity with total throughput time of 12 Hours 50 minutes.  We have considered one more items named as Dump Lever for the analysis and value mapping was done (Fig. 2) as it was done earlier so as to know its effect on the production process. It is evident from Fig. 2 that the total throughput time of the product was 46 hours in which 16 hours were non-value adding activities.

B.     Brain Storming

The CFT group then had a brain storming session to decide as to how to eliminate the problem. Thereafter, the root cause analysis of the problem has been done in the light of recommendation of the CFT. There may be one or several root causes to a particular problem. Once the causes were listed down appropriate tasks were formulated to contain the problem or eliminate the problem or monitor the problem. 

Table 3. Types of errors in processed materials

Nature of Problem	Specific Problem	FMEA Scores	Class of Problem
Edge faults	Overhanging edges	432	Primary
Scoring	Irregular scoring depth	448	Primary
Faults in cut direction	Cut surfaces undulating in direction of cut	60	Tertiary
Incomplete Cut	End not cut through	210	Secondary
Cracks	In the cut surface	180	Secondary

C.    Verification of Logical Causes and Elimination of Illogical Causes

Now, a dedicated group has been deployed to monitor the machine on a regular basis. The technique followed is termed as “Group Observation Technique (GOT)”. This technique basically aims to observe any problem through relaxed attention in individual capacity and each member shall report his or her observations. It is quite different to that of a traditional inspection. The detail observations of GOT on the earlier specified problem (pivot frame and dump leaver) is tabulated in Table 2. The GOT observed that there was a dimensional error in the machined component as compared to the specified tolerance in the machine tool (obtained from the machine manual). The variation in the tabulated observed data is due to the variation of the reported data of the GOT.

D.    Determination of Root Cause

To identify the root causes, Root Cause Analysis tools were used with Management Oversight and Risk Tree (MORT) methodology. The analysis and their root causes are presented in Table 3.

Table 4. Dimensional Problems (result of group observation technique)

 

Table 5. Types of Errors and Their Root Causes in Processed Materials

 

During the root cause analysis, it was observed that the movement of the machine was not smooth. It was causing problem in the cut surface of the material. The maintenance schedule was studied and its records were compared with its recommended schedule of the manufacturer. It was a matter of surprise that the routine periodic preventive maintenance proposed by the machine supplier has not been adhered at all. The machine was installed nearly two years ago. The number of times lubrication was necessary and actually done was different. All the related data has been tabulated Table 6. It is evident from the Table 5 and Table 6 that there was no proper system in place and there is lack of “know how of setting machine parameters”. There is a complete drawback in management initiative. The tabulated results are self-explanatory. The recommended maintenance schedule is not adhered at all. In fact, the maintenance department has made its own maintenance schedule, which is contrary to the recommended schedule by the machine supplier.  

Table 6. Lubrication Points (Frequency and Compliance)

 

Moreover, as revealed by the observation, most of the defects were due to problem at cutting torch. The problem was either attributable to gas condition or none cleaning of nozzle. Some more facts had come to our knowledge, regarding the setting advised by the machine supplier, while cross-examining the operators and maintenance personnel. Actually, proper settings of heating parameter and cutting parameter related to gas flow, speed of the machine, selection of proper size of nozzle etc were not set as per recommended setting of the manufacturer. This was also one of the reasons that contributed to some percentage of defects. This clearly indicated that there was a need of proper training to the employees first. Similarly, too much overtime was given to the workers, as sufficient workers were not available. There were many other general causes, which have been presented in the cause and effect diagram (Figure 3).