Design for Manufature

Question 1

What causes a variation in manufacturing dimensions?

Answer 1

• Machine misalignment
• Tool wear
• Material property variations

Question 2

What is the preferred distribution around the mean target?

Answer 2

Symmetrical normal distribution

Question 3

What is the equation for tolerance range?

Answer 3

Tolerance Range = 2z(Sigma)

Question 4

What should z ideally be between?

Answer 4

4 to 7.5 (i.e. 4(Sigma to 7.5(Sigma))

Less than 4 is too many failures, more than 7.5 is too costly.

Question 5

What causes asymmetrical distribution?

Answer 5

Tool wear

Question 6

What is the equation for process capability in a symmetrical distribution?

Answer 6

Cp = t/3(Sigma)

If Cp is above 1.33 then the process is capable.

Question 7

What is the equation for process capability in an asymmetrical distribution?

Answer 7

Cpk = |Xm - Ln|/3(Sigma)

If Cpk is above 1.33 then the process is capable.

Note that if Cp - Cpk > 0.5 then Cpk must be used.

Question 8

What is the equation for standard deviation?

Answer 8

Sigma = Sqrt({Sum}((Xi - X)^(2)/(N-1)))

Question 9

Explain the house of quality design method.

Answer 9

It helps convert the customer requirements to engineering requirements.

Customer requirements are on LHS and engineering requirements are across the top. Terms are given a weighting, multiplied and then summed to determine the most important requirements.

Question 10

What are the various types of product orders?

Answer 10

Engineer to Order (ETO) - designed and built to customer specification.

Make to Order (MTO) - based on standard design but production/manufacture/assembly is linked to customer order and specification.

Assemble to order (ATO) - product is built to customer spec from stock of existing components.

Make to Stock (MTS) - product is built against a sales forecast and sold to customer from finished goods stock.

Ship to Stock (STS) - as MTS but stock is held in a retailer.

Question 11

What are the advantages of modular units?

Answer 11

• Ease of maintenance
• Ease of work split
• Quality control over assembly
• Aids testing
• Sealed-for-life
• Integration of new technologies
• Enables platform design

Question 12

What are the disadvantages of modular units?

Answer 12

• Small defects cant be easily replaced

- Requires high volume to be feasible

Question 13

Give some examples of car parts built in a modular way.

Answer 13

Bearings, lights, gearboxes, engines and window drive units.

Question 14

What are the advantages of platform design?

Answer 14

• Easier inventory management
• Lower development costs
• Increased quality
• Global standardisation
• Greater product variety

Question 15

Give a summary of product architecture.

Answer 15

To achieve lowest mass and volume it is best to have integrated products with minimal interfaces.

To minimise assembly complexity it is often best to have modular design with sub-assemblies and standard interfaces.

Question 16

What are Quality Management Systems for?

Answer 16

To ensure adequate paper trails for design reviews, material sourcing, component sourcing,product testing, and company decision making.

Question 17

Describe the BS 7000 Design Management System.

Answer 17

Part 1 -Managing innovation
Part 2 -Managing design of manufactured products
Part 3 - Managing service design
Part 4 - Managing design in construction
Part 5 -Managing inclusive design

Question 18

Describe the ISO 9000 Quality Assurance philosophy.

Answer 18

A set of international standards aimed to help companies effectively document the QS elements to be implemented to maintain an efficient QS system.

Question 19

Describe Total Quality Management (TQM).

Answer 19

Japanese philosophy that emphasises prevention rather than inspection; right first time; continuous quality improvement.

Question 20

Describe the Six-Sigma philosophy.

Answer 20

Uses statistical tools to improve manufacturing quality by elimination of defects. If the manufactured parts have a distribution such that six sigma falls within the tolerance limits then there will be very few failures.

Question 21

Describe Lean Manufacturing.

Answer 21

It is a production philosophy that aims to reduce waste.

Minimises waste (Muda) within a manufacturing system. It also takes into account waste due to uneven workload (Mura). All of this is done without sacrificing productivity.

It makes obvious what adds value by removing everything that does not add value.

A poka-yoke is any mechanism in a lean process that helps an equipment operator avoid mistakes. Its purpose is to eliminate defects by preventing, correcting, or drawing attention to human errors as they occur.

Question 22

What are the questions to ask when thinking about product architecture?

Answer 22

• What should a car’s structural architecture be? One part or distinct sections?
• Should the suspension be modular?
• What else should be modular?
• Should there be multi-functioning sub-assemblies?
• Should there be mass customisation?
• Should it be part of a platform design?