Managing Quality

• According to J.M. Juran: Quality is “Fitness for use”

• According to Philip Crosby: Quality is “Conformance to specifications”

Quality

Meeting, or exceeding, customer requirements now and in the future.

Dimensions of Quality

QUALITY

Quality of Design

• Determined before the product is produced

• Determined by market research• Translates the “requirements” of

customers into specifications

Quality of Conformance

Producing a product that meets the specifications

The Quality Cycle

MARKETINGInterprets customer needsWorks with customer to

design product to fitoperations

Interpretation of needs

CUSTOMERSpecifies quality needs

Needs

OPERATIONSProduces the product or

services

QUALITY CONTROLPlans and monitors

quality

Product

ENGINEERINGDefines design conceptPrepares specifications

Define qualitycharacteristics

Specifications

Implementation of quality improvement

Define quality attributes on the basis of customer needs

Decide how to measure each attributeSet quality standardsEstablish appropriate tests for each standardsFind and correct causes of poor qualityContinue to make improvements

Quality Costs

Quality Costs are classified into four categories:

• External failure costs,• Internal failure costs,• Appraisal costs, and• Prevention costs.

Statistical Process Control

• Assignable Causes,

• Random Causes.

Process Control Chart

x

y

Time

Upper control limit (UCL)

Center line (CL)

Lower control limit (LCL)

Average + 3 standard deviations

Quality measurement

average

Average - 3 standard deviations

Mean Charts

• The Goliath Tool Company produces slip-ring bearings, which look like flat doughnuts or washers. They fit around shafts or rods, such as drive shafts in machinery or motors. In the production process for a particular slip ring bearing the employees have taken 10 samples of 5 slip ring bearings (i.e., n=5). The individual observations from each sample are shown as follows:

Sample Observations1. 5.02 5.01 4.94 4.99 4.962. 5.01 5.03 5.07 4.95 4.963. 4.99 5.00 4.93 4.92 4.99 4. 5.03 4.91 5.01 4.98 4.895. 4.95 4.92 5.03 5.05 5.016. 4.97 5.06 5.06 4.96 5.037. 5.05 5.01 5.10 4.96 4.998. 5.09 5.10 5.00 4.99 5.089. 5.14 5.10 4.99 5.08 5.0910. 5.01 4.98 5.08 5.07 4.99

The company wants to develop mean and R-chart to monitor the process variability.

Control Charts for Attributes

• An electronic company manufactures several types of cathode ray tubes on a mass production basis. During the past month, tube type A has caused considerable difficulty. The following table contains data from 21 days of this troublesome period. 100 units are inspected each day. Compute the central line and 3-sigma control limits for a p-chart for this tube process.

Day Fraction Day Fraction Rejected Rejected

1 .22 12 .462 .33 13 .313 .24 14 .244 .20 15 .225 .18 16 .226 .24 17 .297 .24 18 .318 .29 19 .219 .18 20 .2610 .27 21 .2411 .21

C-chart• The Ritz Hotel has 240 rooms. The hotel’s housekeeping department is

responsible for maintaining the quality of the rooms’ appearance and cleanliness. Each individual housekeeper is responsible for an area encompassing 20 rooms. Every room in use is thoroughly cleaned and its supplies, toiletries, and so on are restocked each day. Any defects that the housekeeping staff notice that are not part of the normal housekeeping service are supposed to be reported to the hotel maintenance. Every room is briefly inspected each day by a housekeeping supervisor. However, hotel management also conducts inspection tours at random for a detailed, thorough inspection for quality-control purposes. The management inspectors not only check for normal housekeeping service defects like an inoperative or missing TV remote, poor TV picture quality or reception, defective lamps, a malfunctioning clock, tears or stains in the bedcovers or curtains, or a malfunctioning curtain pull. An inspection sample includes 12 rooms, i.e., one room selected at random from each of the twelve 20-room room blocks serviced by a housekeeper. Following are the results from 15 inspection samples conducted at random during a 1 month period:

• Sample Number of Defects

1 12 2 8 3 16 4 14 5 10 6 11 7 9 8 14 9 13 10 15 11 12 12 10 13 14 14 17 15 15

The hotel believes that approximately 99 percent of the defects are caused by natural, random variations in the housekeeping and room maintenance service, with 1 percent caused by nonrandom variability. They want to construct c-chart to monitor the house keeping service.