Quality and safety management in construction, Tools and techniques for quality management

1. Unit-2 CE547
Zishan Raza Khan
Associate Professor
Department of Civil Engineering
Integral University, Lucknow
INDIA

2. Content
• Tools and techniques for quality management
• Planning and control of quality during design
of structures
• Inspection of materials and machinery

3. Tools and techniques for quality
management
1. Histogram
2. Check sheet
3. Pareto analysis
4. Cause-and-effect diagram
5. Graphs
6. Control chart
7. Scatter diagram

4. • Tally Charts and Histograms
• Tally charts are a descriptive presentation of data and help to
identify patterns in the data. They may be used as checksheets with
attribute data (pass/fail, present/absent) but are more commonly
used with measured or variable data (e.g. temperature, weight,
length) to establish the pattern of variation displayed.
• Tally charts are regarded as simple or crude frequency distribution
curves and provide a quick way of recording and displaying data.
• A histogram is a graphical representation of individual measured
values in a data set according to the frequency or relative frequency
of occurrence. It takes measured data from the tally sheet and
displays its distribution.

5. Fig:1 Fig:2

6. For the treatment of continuous data of sufficient quantity, grouping is
required.
• Subtract the smallest individual value from the largest.
• Divide this range by 8 or 9 to give that many classes or groups.
• The resultant value indicates the width or interval of the group. This should
be rounded for convenience, e.g. 4.3 could be regarded as either 4 or 5
depending upon the data collected.
• These minor calculations are undertaken to give approximately eight or
nine group class intervals of a rational width.
• Each individual measurement now goes into its respective group or class.
• Construct the histogram with measurements on the horizontal scale and
frequency (or number of measurements) on the vertical scale.
• The ‘blocks’ of the histogram should adjoin each other, i.e. there should be
no gaps unless there is a recorded zero frequency.
• Clearly label the histogram and state the source of the data.

7. • Checksheets
• These are a sheet or form used to record data. The checksheet is a simple and
convenient recording method for collecting and determining the occurrence of
events. The events relate to non-conformities, including the position in which they
appear on the non-conforming item.
• The following are the main steps in constructing a checksheet:
• Decide the type of data to be illustrated. The data can relate to: number of
defectives, percentage of total defectives, cost of defectives, type of defective,
process, equipment, shift, business unit, operator, etc.
• Decide which features/characteristics and items are to be checked.
• Determine the type of checksheet to use (i.e. tabular form or defect position chart).
• Design the sheet; ideally it should be flexible enough to allow the data to be
arranged in a variety of ways. Data should always be arranged in the most
meaningful way to make best use of them.
• Specify the format, instructions and sampling method for recording the data,
including the use of appropriate symbols.
• Decide the time period over which data are to be collected.

12. • Pareto Analysis
• This is a technique employed for prioritizing problems of
any type, for example quality, production, complaints, stock
control, sickness, absenteeism, accident occurrences and
resource allocation. The analysis highlights the fact that
most problems come from a few causes, and it indicates
what problems to solve and in what order (e.g. Juran’s
(1988) ‘vital few and trivial many’).
• The diagram is named after a nineteenth-century Italian
economist, Wilfredo Pareto, who observed that a large
proportion of a country’s wealth is held by a small
proportion of the population (hence the expression ‘the
80/20 rule’).

14. • Cause-and-Effect Diagrams
• This type of diagram was developed by Ishikawa (1976) to
determine and break down the main causes of a given problem.
Cause-and-effect diagrams are often called Ishikawa diagrams, and
sometimes ‘fishbone’ diagrams, because of their skeletal
appearance. They are usually employed where there is only one
problem and the possible causes are hierarchical in nature. The
effect (a specific problem or a quality characteristic/condition) is
considered to be the head, and potential causes and sub-causes of
the problem or quality characteristic/condition to be the bone
structure of the fish. The diagrams illustrate in a clear manner the
possible relationships between some identified effect and the
causes influencing it. They also assist in helping to uncover the root
causes of a problem and in generating improvement ideas.

15. A simple cause-and-effect diagram for managing materials-
related quality

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17. • Graphs
• Graphs are meant to convey data in a pictorial way or
in a way into which data may be
interpolated/extrapolated. Graphs are used to facilitate
understanding and analysis of the collected data,
investigate relationships between factors, attract
attention, indicate trends and make the data
memorable.
• “A picture is worth a thousand words”
• There is a wide choice of graphical methods available
(line graphs, bar charts, pie charts, Gantt charts, radar
charts, band charts) for different types of application.

19. • Control charts
• The control charts record the ‘voice of the process’
• When first evolved, the control chart, using data which
provided a good overall picture of the process under
review, had control limits set out from the process average,
which reflected the inherent variation of the process. A
process with more variation than another will have wider
limits (i.e. the greater the variation the wider the limits).
This variation was established from an accurate review or
study, and consequently the limits were deemed to reflect
the actual ‘capability’ of the process. The charts so
constructed were actually called ‘charts for controlling the
process within its known capability’.

21. • Scatter Diagrams and Regression Analysis
• Scatter diagrams or scatter plots are used when examining the
possible relationship or association between two variables,
characteristics or factors; they indicate the relationship as a pattern
– cause and effect. For example, one variable may be a process
parameter (e.g. temperature, pressure, screw speed), and the other
may be some measurable characteristic or feature of the product
(e.g. length, weight, thickness). As the process parameter is
changed (independent variable) it is noted, together with any
measured change in the product variable (dependent variable), and
this is repeated until sufficient data have been collected. The
results, when plotted on a graph, will give what is called a scatter
graph, scatter plot or scatter diagram.

23. Inspection of materials and machinery
Inspection is the most common method of attaining
standardization, uniformity and quality of
workmanship. It is the cost art of controlling the
product quality after comparison with the established
standards and specifications. It is the function of
quality control. If the said item does not fall within the
zone of acceptability it will be rejected and corrective
measure will be applied to see that the items in future
conform to specified standards. Inspection is an
indispensable tool of modern manufacturing process. It
helps to control quality, reduces manufacturing costs,
eliminate scrap losses and assignable causes of
defective work.

24. • Objectives of Inspection
(1) To collect information regarding the performance of
the product with established standards for the use of
engineering production, purchasing and quality control
etc.
(2) To sort out poor quality of manufactured product and
thus to maintain standards.
(3) To establish and increase the reputation by protecting
customers from receiving poor quality products.
(4) Detect source of weakness and failure in the finished
products and thus check the work of designer.

25. • Purpose of Inspection
(1) To distinguish good lots from bad lots
(2) To distinguish good pieces from bad pieces.
(3) To determine if the process is changing.
(4) To determine if the process is approaching the pecification
limits.
(5) To rate quality of product.
(6) To rate accuracy of inspectors.
(7) To measure the precision of the measuring instrument.
(8) To secure products – design information.
(9) To measure process capability.

26. • Stages of Inspection
(1) Inspection of incoming material (Beginning)
(2) Inspection of production process (In process)
(3) Inspection of finished goods (Final)

27. • (1) Inspection of incoming materials. It is also called receiving inspection.
It consists of inspecting and checking of all the purchased raw materials
and parts that are supplied before they are taken on to stock or used in
actual manufacturing. Inspection may take place either at supplier’s end
or at manufacturer’s gate. If the incoming materials are large in quantity
and involve huge transportation cost it is economical to inspect them at
the place of vendor or supplier.
• (2) Inspection of production process. The work of inspection is done
while the production process is simultaneously going on. Inspection is
done at various work centres of men and machines and at the critical
production points. This had the advantage of preventing wastage of time
and money on defective units and preventing delays in assembly.
• (3) Inspection of finished goods. This is the last stage when finished
goods are inspected and carried out before marketing to see that poor
quality product may be either rejected or sold at reduced price.

28. • Inspection Procedures
There are three ways of doing inspection. They
are:
1. Floor inspection
2. Centralised inspection
3. Combined inspection.

29. • Floor Inspection
• It suggests the checking of materials in process at
the machine or in the production time by
patrolling inspectors. These inspectors moves
from machine to machine and from one to the
other work centres. Inspectors have to be highly
skilled. This method of inspection minimise the
material handling, does not disrupt the line
layout of machinery and quickly locate the defect
and readily offers field and correction.

30. • Advantages
• (1) Encourage co-operation of inspector and foreman.
• (2) Random checking may be more successful than batch checking.
• (3) Does not delay in production.
• (4) Saves time and expense of having to more batches of work for inspection.
• (5) Inspectors may see and be able to report on reason of faculty work.
• Disadvantages
• (1) Possibility of biased inspection because of worker.
• (2) Pressure on inspector.
• (3) High cost of inspection because of numerous sets of inspections and skilled
• inspectors.
• Suitability
• (1) Heavy products are produced.
• (2) Different work centre are integrated in continuous line layout

31. • Centralised Inspection
• Materials in process may be inspected and checked at centralised inspection centre which are
located at one or more places in the manufacturing industry.
• Advantages
(1) Better quality checkup.
(2) Closed supervision.
(3) Absence of workers pressure.
(4) Orderly production flow and low inspection cost.
• Disadvantages
(1) More material handling.
(2) Delays of inspection room causes wastage of time.
(3) Work of production control increases.
(4) Due to non-detection of machining errors in time, there may be more spoilage of work.
• Suitability
(1) Incoming materials inspection.
(2) Finished product inspection.
(3) Departmental inspection.
(4) High precision products of delicate products.
(5) Small and less expensive products.

32. • Combined Inspection
• Combination of two methods what ever may
be the method of inspection, whether floor or
central. The main objective is to locate and
prevent defect which may not repeat itself in
subsequent operation to see whether any
corrective measure is required and finally to
maintained quality economically.

33. • Methods of Inspection
• There are two methods of inspection. They are 100% inspection
and Sampling inspection.
• 100% Inspection
• This type will involve careful inspection in detail of quality at each
strategic point or stage of manufacture where the test involved is
non-destructive and every piece is separately inspected. It requires
more number of inspectors and hence it is a costly method. There is
no sampling error. This is subjected to inspection error arising out
of fatigue, negligence, difficulty of supervision etc. Hence complete
accuracy of influence is seldomly attained. It is suitable only when a
small number of pieces are there or a very high degree of quality is
required.
• Example : Jet engines, Aircraft, Medical and Scientific equipment.

34. • Sampling Inspection
• In this method randomly selected samples are inspected. Samples
taken from different batches of products are representatives. If the
sample prove defective. The entire concerned is to be rejected or
recovered. Sampling inspection is cheaper and quicker. It requires
less number of Inspectors. Its subjected to sampling errors but the
magnitude of sampling error can be estimated. In the case of
destructive test, random or sampling inspection is desirable. This
type of inspection governs wide currency due to the introduction of
automatic machines or equipments which are less susceptible to
chance variable and hence require less inspection, suitable for
inspection of products which have less precision importance and
are less costly.
• Example : Electrical bulbs, radio bulbs, washing machine etc.

35. • Drawbacks of Inspection
(1) Inspection adds to the cost of the product but not for its value.
(2) It is partially subjective, often the inspector has to judge whether a
product passes or not.
Example : Inspector discovering a slight burnish on a surface must
decide whether it is bad enough to justify rejection even with
micrometers a tight or loose fit change measurement by say 0.0006
inches. The inspectors design is important as he enforces quality
standards.
(3) Fatigue and Monotony may affect any inspection judgement.
(4) Inspection merely separates good and bad items. It is no way to
prevent the production of bad items.