Showing posts with label Operations Management. Show all posts
Showing posts with label Operations Management. Show all posts

Friday, November 19, 2010

Quality Control


Quality

Quality is the extent (sigma value of the process) to which a firm’s product or service consistently (again and again) conforms to customer’s requirement and expectations.

Textbook definition – Ability of a product / service to consistently meet or exceed customer expectation (Should be an integral part of product / service).

Quality may be defined as the extent to which a firm’s product or service consistently conforms to customer’s requirements and expectations. To manage quality, it should be specific and measurable – what can’t be measured, can’t be managed.

Voc TO CTQs (Critical to quality factors that are specific and measurable)

Product Quality parameters

Performance – Main characteristics of the product / service

Aesthetics – Appearance, feel, smell, taste

Special features – Extra characteristics

Conformance – How well a product or service corresponds to design specifications

Reliability – Consistency of performance

Durability – The useful life of the product or service

Perceived Quality – Indirect evaluation of quality (Example – Reputation)

Serviceability – Handling of complaints / repairs

Service Quality parameters

Convenience – The availability and accessibility of the service

Reliability – The ability to perform a service dependably, consistently and accurately

Responsiveness – The willingness of service providers to help customers in unusual situations and to deal with problems

Time – The speed with which service is delivered

Assurance – The knowledge exhibited by personnel who come into contact with a customer and their ability to convey trust and confidence

Courtesy – The way customers are treated by employees who come into contact with them

Tangibles – The physical appearance of facilities, equipment, personnel and communication materials

COST OF QUALITY

Cost of Quality: Any cost that would not have been expended if quality was perfect (It is not the price of creating a quality product or service). Every time a rework is done, the cost of quality increases.

The price of non-conformance (Philip Crosby) and cost of poor quality (Joseph Juran)

· Cost of Conformance

o Preventive costs (Proactive): The cost of all activities specifically designed to prevent poor quality in products or services. Example- Periodic preventive maintenance of machines, training, product/ process design effort.

§ New product review, quality planning, supplier capability survey, process capability evaluations, quality education and trainings.

o Appraisal costs (Reactive): The costs associated with measuring, evaluating or auditing products or services to assure conformance to quality standards and performance requirements. Example- Policy cost (Inspection), Inspection of raw material, external inspection / audits, debugging.

§ Incoming and source inspection / test of purchased material

§ In-process and final inspection / test

§ Calibration of measuring and test equipments.

· Cost of Non-conformance

o Internal failure cost: Failure costs occurring prior to the delivery or shipment of the product, or the furnishing of a service, to the customer. (Producing defective product, but I detect the product before it goes out of company’s premises).Example- Rework / Repair before dispatch, overtime work, scrapping defective output.

§ Scrap

§ Rework

§ Re-inspection

§ Re-testing

§ Material review

§ Downgrading

o External failure costs: Failure costs occurring after delivery of the product or during or after the furnishing of the service to the customer. (Defective product reaches the customer). Example: Toyota recall, i-phone antenna problem, products falling within warranty, litigation with customer, loss of goodwill.

§ Processing customer complaints

§ Customer returns

§ Warranty claims

§ Product recalls

Critical to Quality factors

· Factors of CTQ

· Metric

· Unit of measurement

· Target Value

· Tolerance (acceptable)

· Definition of defect

CTQ

They are derived from customer needs. Customer delight may be add-on while deriving CTQ parameters. For cost considerations, one may remain focused to customer needs at the initial stage.

They are key measurable characteristics of a product or process whose performance standards or specifications limits must be met in order to satisfy the customer. They align improvement or design efforts with customer requirements.

It represents the product / service characteristics that are defined by the customer (internal / external). They may include the upper or lower specification limits or any other factors related to the product or service.

Definition: They are the spoken needs of the customer…..what customer expects from the product. The customer may express it in plain English, but it is upto the CTQ expert to convert them to measurable terms using tools such as DFMEA (How can product design fail in real world)

Expense Details

Notes

Legal expenses to handle customer complaints / notices

External failure costs

Overtime

Internal failure costs

Inspection of incoming materials from vendors

Appraisal costs

Consultant’s fees for advising on latest quality systems

Prevention costs

Product rejections by customers

External failure costs

Product inspected out of delivery consignments by quality inspection staff

Appraisal costs

TQM and 6-sigma training

Prevention costs

Poka Yoke process design development (Mistake proofing device)

Prevention costs

In-house laboratory testing of materials, WIP, finished goods

Appraisal costs

External agency testing and certification of finished goods

Appraisal costs

Transportation of rejected products from customer’s premises

External failure costs

Transportation of reworked products back to customers (means customer already received defective product earlier)

External failure costs

Rework – materials, labor and overheads – after defects noticed in final product

Internal failure costs

Servicing of defective products within warranty period

External failure costs

Printing of quality training manuals

Prevention costs

Kano Model


Kano Model

It is a quality measurement tool used to prioritize customer needs based on how they impact customer satisfaction. It breaks down components of a product or service in categories based on impact on customer satisfaction.

Customer looks at attributes at 3 different perspectives: Basic (Threshold), Satisfier (Performance needs) and Delighters (WOW factor)

1. Basic / Must Be / Threshold: Represents basic musts or functions expected of a product or service. When it is present, it is neutral; when absent, dis-satisfies customer. Example: Punctuality, cabin comfort (Leg room, temperature), staff courtesy. Non performance leads to strong dis-satisfaction

2. Satisfier / performer / More is better: Directly linked to voiced demand of customer relative to quality and their willingness to pay. Its presence enhances satisfaction and absence reduces it. Linear relation to customer satisfaction, the better you do, the more they like it. Example: No of music channels, quality of food, ticket price

3. Surprise / Delighter / Excitement: It satisfies latent needs. Their presence increases satisfaction, but their absence does not decrease it. It acts as a source of differentiation. Example: Automatic flight status (KMs, Temperature – Shown on screen by Kingfisher for the 1st time), Latest movies, Lap-top & cell phones power point at each seat

Refining the model:

1. Indifferent attributes: Attributes of a product / service whose presence or absence doesn’t affect customer satisfaction.

2. Dis-satisfiers / Reverse quality attributes: Presence causes dis-satisfaction, absence causes satisfaction

Observation

· Each customer’s needs are usually unique.

· Basic : Entry Barrier (Value) ; Satisfier: Comparable features (Quality); Exciter needs: Competitive advantage / USP (Innovation)

· Attitude towards needs change over time. Yesterday (Exciter)……Today (Satisfier)…….Tomorrow (Basic)

· Customer never talks about basic needs, only performer / satisfier needs are expressed.

Product development uses KANO model

Benefits

1. Guides decision in quality strategies by prioritizing customer needs

2. Useful tool to analyze demand

3. It is customer focused

4. Quantifies satisfaction, making effective trade-offs.

The Kano model is a theory of product development and customer satisfaction developed in the 80's by Professor Noriaki Kano which classifies customer preferences into five categories:

  • Attractive
  • One-Dimensional
  • Must-Be
  • Indifferent
  • Reverse

These categories have been translated into English using various different names (delighters/exciters, satisfiers, dis-satisfiers, etc.), but all refer to the original articles written by Kano.

Use - The Kano model offers some insight into the product attributes which are perceived to be important to customers.

The purpose of the tool is to support product specification and discussion through better development team understanding.

Kano's model focuses on differentiating product features, as opposed to focusing initially on customer needs.

Kano also produced a methodology for mapping consumer responses to questionnaires onto his model.


Balancing of a Assembly Line

Line Balancing

Aim – It only applies to assembly lines. It aims at minimizing the idle time along the line by dividing work equally among members. Tasks are grouped in such a way that they have equal time requirement.

When is line Balancing is Done

· When the line is initially set-up

· When the changes are made in process / desired output rate

Difficulty associated with LB – Not feasible to combine certain activities

Necessity of line balancing – In absence of line balancing, it might create morale problem for workers at slower station who work continuously

(Draw Precedence Diagram)

Cycle Time = Longest time at the any of the work element OR (Operating Time / Desired Output Rate)

CT = 1 min

(In Question, it may be given as 480 units per 8-hour day, Hence CT = 8*60 min per day / 480 units per day = 1 minute per cycle)

Theoretical Minimum number of workstations, Nmin = Sum of time at all WS / CT = (0.1+1.0+0.7+0.5+0.2) / 1.0 = 2.5 = 3 Workstations

Rules in Assigning task

1. Choose new WS if

a. All preceding tasks are completed

b. Task Time is less than or equal to Time Remaining

2. Always first assign the task with greatest task time to a workstation, in case there is a choice between work elements. In case task time is same, choose the element having greatest number of followers.

3. For every new WS, always start with cycle time

WS

Time Remaining

Eligible

Assign Task

Revised Time remaining

WS Idle Time

1

1.0

A,C

C(0.7)

0.3 (1.0-0.7)

0.3

A

A(0.1)

0.2

0.2

2

1.0

B

B(1.0)

0

0

3

1.0

D

D(0.5)

0.5

0.5

E

E(0.2)

0.3

0.3

Total Idle time = 0.2 + 0.3 = 0.5 minutes

Balance Delay in % (% of idle time on assembly line) = Total idle time * 100/ (Actual No of WS * Cycle Time)

=0.5*100/(3*1) = 16.7%

Line efficiency = 100% - Balance delay% = 83.3%

Other considerations in line-balancing

1. Technical considerations –

a. Skill requirement of different tasks - If the skill requirements of tasks are quite different, it may not be feasible to place the tasks in the same workstation

b. Incompatible tasks - If the tasks themselves are incompatible (example – Use of fire and flammable liquids), it may not be feasible even to place them in stations that are near to each other

2. Variable tasks by human –

a. Reasons for variation are Fatigue, boredom and failure to concentrate on the task at hand.

b. Absenteeism can also affect the balance

Other approaches to achieve smooth flow of production

1. Make parallel workstations – They increase the workflow and provide flexibility

2. Cross-train workers / Dynamic line balancing – It helps workers perform more than 1 task. In case they are idle, they can assist other workers who are temporarily over-burdened

3. Mixed model line - Design a line to handle more than 1 product on the same line. The different products are similar in many ways and hence, the process applied on them is also same