W9 Quality and Maintenance Manangement Flashcards
Quality
- the transcendent approach which views quality as meaning ‘innate excellence’ (e.g. quality in
Rolex Watches and Rolls-Royce Cars); - the manufacturing-based approach which views quality as being ‘free of errors’ (e.g. quality in
a Swatch watch, or a Ford Mondeo); - the user-based approach which views quality as ‘fit for purpose’ (e.g. user centric view of what
is good in a night time flight, food or silence); - the product-based approach which views quality as a ‘measurable set of characteristics’ (e.g. a
watch that has to work for 5 years without service and keep time within 5 seconds); - and the value-based approach which views quality as a balance between ‘cost and price’ (e.g.
the quality of an EasyJet flight or a McDonalds meal).
Quality generic
Consistent conformance to customers’ expectations. An
increase in quality will ultimately cause an increase in profits through a series of causal links.
What causes perception of good and bad quality
Gaps between customers’ expectations and their perception of the products and services they
receive cause the perception of good and bad quality
How are quality problems diagnosed
Diagnosing quality problems is done
by analysing various gaps to determine the cause for the existence of a gap between customer
expectations and perceptions.
Types of gaps
The customer’s specification-operation’s specification gap (Gap 1), the conceptspecification gap (Gap 2), the quality specification-actual quality gap (Gap 3) and the actual
quality-communicated image gap (Gap 4).
Marketing, Manufacturing and Product design departments generally handle Gaps 1 & 2 in a
joint manner. Manufacturing generally handles Gap 3 and Marketing handles Gap 4.
What happens when quality goes up?
Image up
Service costs down
Inspection and test
costs down
Rework and scrap
costs down
Complaint costs
down
Inventory down
Processing time
down
Price competition
down
Sales volume UP
Sales economies
UP
Operations costs
Down
Productivity UP
Profits
UP
Capital cost down
Revenues UP
6 steps of quality planning
- Define the quality characteristics
- Decide how to measure these
- Set standards for each characteristic
- Control quality against those standards
- Find & Correct causes of poor quality
- Continue to make improvements
Define the quality characteristics
a) Functionality or how well the product or service does its job. This includes its performance
and features.
b) Appearance refers to the sensory characteristics of the product or service: its aesthetic
appeal, look, feel, sound and smell.
c) Reliability is the consistency of the product’s or service’s performance over time, or the
average time for which it performs within its tolerated band of performance.
d) Durability means the total useful life of the product or service, assuming occasional repair
or modification.
e) Recovery means the ease with which problems with the product or service can be rectified
or resolved
Decide how to measure these
Some characteristics are easily quantifiable
as continuous real numbers. These are referred to as variables. Other characteristics are
assessed by judgement and are dichotomies (i.e. have two states, for example: right or wrong,
OK or not OK). These are attributes
Set standards for each characteristic
For each characteristic, the acceptable level of quality needs to be
defined in clear terms. (e.g. 2000 hours of life for a lightbulb).
Control quality against those standards
Flashcards 14-20
Find & Correct causes of poor quality
This entails identifying operations and processes that
create the errors and trying to mend them
Continue to make improvements
Achieving better quality is a journey and not a
destination. Ongoing improvement is essential for competitiveness.
Where should the quality be controlled?
Checking at the start of the process could be
used to inspect raw material (e.g. a car manufacturer checking headlights received from tier 2
suppliers). During the process checks can take place at any stage but are more desirable in specific situations (i.e. before a costly part of the process, before a series of process that are
difficult to check, immediately after a well known fail point, before the process after which
recovery of raw material becomes impossible, etc.) Checks at the end of the process can be
used to ensure the quality of the product or service that is delivered to the customer.
How should the checks be performed? (Statistical Process Control SPC)
Statistical Process Control (SPC) is a technique that monitors processes as they
produce products or services and attempts to distinguish between normal or natural
variation in process performance and unusual or ‘assignable’ causes of variation.
SPC assumption
SPC is based on the assumption that quality variables measured on products form Normal (Gaussian) probability distributions. Assuming that the process has a natural variation,
the quality variables are modelled with normal curves. This
is useful as in a normal distribution 68% of the population
is within µ ± σ, 95% of the population is within µ ± 2σ and
99.7% of the population is within µ ± 3σ. .
How should the checks be performed? (Acceptance Sampling)
Acceptance sampling is where batches of products or services are inspected before
or after a process to decide whether the entire batch should be accepted. Acceptance
sampling uses the proportion of defectives to acceptable products in a sample to form the
basis of the judgement.
Check every product or take a sample?
dangerous or impractical, destructive tests are inappropriate, time consuming, costly, despite checking every item-relaible data might nto be obtained
Error Type 1 or false positives or producer’s risk
sample indicates a trait in the
population while the real population does not have that trait.
Error Type 2 or false negatives or consumer’s risk
sample does not indicate a
trait in the population while the population possesses that trait
Six Sigma
Six-Sigma (6σ) is a broad ‘philosophy of improvement’ that adopts
a specific approach for controlling, improving and managing quality.
It is named six-sigma because it requires the natural
variation of processes (±3σ) to be half of their required specification
range. In other words, processes should be chosen in such a manner
that the specification range of the product is ±6σ of the process.
Total Quality Management
TQM is a management approach that pursues three main objectives:
* achieving customer satisfaction;
* improving continuously; and,
* involving the entire workforce in quality management.
In TQM the aspiration is to meet customers’ requirements first time, every time. The implication
here, is that customers may be external or internal. So in a multi-stage production system, each
subsequent stage is the customer for the preceding stage of production. In order to implement this
mentality, it is necessary for everyone active in production to embed quality in their processes and
relying on the inspection department to catch errors later in the process will not be sufficient.
Inspection
Inspection is performed before, during and after Manufacturing. It involves the use of measurement
techniques to determine whether a product, its components, subassemblies, or starting materials
conform to design specifications. Product designer provide design specifications, which typically
refer to dimensions, tolerances, surface finish, and similar features.
Non-Destructive Testing
Nondestructive testing refers
to techniques that do not damage the sample.
Modern inspection technologies include:
* Coordinate Measuring Machines (CMM)
* Scanning laser systems
* Machine Vision systems
* Ultrasonic techniques
Maintenance and 3 types
- Breakdown maintenance is where equipment is serviced or repaired only when it fails.
- Preventive maintenance is where equipment is either periodically inspected, serviced,
cleaned and replaced to prevent sudden failures or where on-line monitoring of equipment is
carried out to use expensive parts to the limit of their service life (and no longer). - Corrective or predictive maintenance is where equipment and components are improved
so that reliable preventive maintenance can be carried out.
Reliability Parameters
Probability of system staying functional during given time period
Mean time between failures (MTBF) is the average time between two successive failures
of the system. The inverse of MTBF (λ = 1/MT BF) is the rate of failure.
Mean time to failure (MTTF) is used for components or items that are not repairable
such as lamps, resistors and capacitors
