Design for manufacturing Flashcards
What may process variations be due to
- Machine misalignments
- tool wear
- material property variations
What does a symmetrical distribution around a mean target look like?
SKETCH
What is the most preferable distribution of variations in manufacturing
symmetrical about the mean
What is the ideal value of z where z = t/sigma
z should be between 4 and 7.5
4 sigma corresponds to _____ parts per million failure for two tails
63
7.5 sigma corresponds to ____ parts per million failure for two tails
0
< 4 sigma is considered ____
too many failures
> 7.5 sigma is considered to be ____
too much precision (too costly)
What is the 6 sigma philosophy
6 sigma is considered the ideal balance between precision and the number of failures
What does a asymmetrical distribution around the mean target look like
SKETCH
When can an asymmetrical distribution occur and give an example
when there is tool wear
tool wear on a lather can cause the shaft diameter to increase and therefore the distribution shifts to the right
Which value of z is used in analysis of an asymmetrical distribution
the largest value of z (z2) as it gives the worse case scenario
How can z2 be calculated
z2 = (xm - L2)/sigma
How can unsymmetrical distribution in machine variance be avoided
by regular checking of the tool for wear and regularly checking the machine settings
What is Cp and how is it calculated
In industry, Cp is used which is a capability measure of a symmetric distribution
Cp = t/(3 x sigma)
What value must Cp have if the process is capable
Cp < 1.33
What is Cpk and how is it calculated
Cpk is the capability measure used in industry for a asymmetric distribution
Cpk = (xm-Ln)/(3xsigma)
What does xm stand for
the actual mean
What does Ln stand for
the worst case tolerance limit
How do you calculate the drift from mean
Drift from mean = target mean - actual mean
When should Cpk be used over Cp
If Cp - Cpk > 0.5 then Cpk must be used
What is the equation to calculate the standard deviation
EQUATION
Describe the house of quality design method
it helps to convert customer requirements into engineering requirements.
It help to determine the most important engineering requirements
It is subjective but nevertheless can help teams to improve product quality
What is the disadvantage of the quality of house design method
It is subjective but nevertheless can help teams to improve product quality
Describe the table produced to complete the quality of house design method
column of customer requirements, then each have a customer priority rating (1-5), these are then compared to engineering requirements that form the other columns, which get given a score of 1, 3 or 9 depending on their relationship to the customer requirements
The points rating is then found through multiplying the priority rating and the score and adding these together for each engineering requirement
What are the series of questions to ask when introducing a new product and trying to work out the right manufacturing strategy for it
- what is the best product footprint?
- What is the best product family?
- Should the product be a service?
- Should a company be ‘first to market’ or a ‘fast follower’
- When should a product be retired from the market
- Which parts of the product should be bought from suppliers and which parts made by the firm
- should there be mass customisation
- what should the product architecture be
Expand on the question
‘What is the best product footprint’
The product footprint defines the brand, therefore it needs to be decided whether the product will be cheap, luxury or high performance etc.
Expand on the question ‘Should the product be a service’
whether a customer pays to use a product (hire it out) as if it were a service. This has the advantage that manufacturers have a big incentive to lower maintenance costs and increase reliability
Expand on the question ‘should a company be ‘first to market’ or a ‘fast follower’
to be first to market means producing a new product or technology and seeking the first mover advantage though premium prices etc. Whereas being a fast follower allows you to learn from the mistakes of the first to market
What does ETO stand for
Engineering to order
Where the artefact is designed and built to a customers requirements
What does MTO stand for
make to order
where the artefact is based on a standard design, but component production and manufacture/assembly is linked to the customer’s order and specifications
What does ATO stand for
Assemble to order
where the product is built to customer specification from a stock of existing components
What does MTS stand forq
Make to stock
where the product is built against a sales forecast and sold to the customer from finished goods stock
What does STS stand for
ship to stock
where the product is built against a sales forecast and the stock is held in a retailer
What are the 5 different kinds of order a product can be made for
- Engineer to order
- Make to order
- Assemble to order
- make to stock
- ship to stock
Give an example of engineer to order
F1 car
Give an example of make to order
high end car (rolls royce)
Give an example of assemble to order
high end car (ferrari)
Give an example of make to stock
low end cars
give and example of ship to stock
roller chain, gears
Expand on the question ‘which parts of the product are to be made by the firm and which bought from suppliers’
this question is very tied up with questions of globalisation and the offshoring business processes
Expand on the question ‘should there be multi functioning subassemblies’
sub assemblies can be designed for multiple functions which can then be used on different products, so they can share the same manufacturing process and reduce costs
Expand on the question ‘Should there be mass customization’
mass customisation is a marketing and manufacturing technique that combines the flexibility and personalisation of custom made products with the low unit costs associated with mass production
Expand on the question ‘what should the product architecture be’
A compromise must be made when planning product architecture and will depend on the context of the product, especially sales volumes and required performance
What is the key question around product architecture
should the product be composed of sub systems or modules that can be assembles and disassembled?
Should the interfaces be standardised to allow different manufacturers to supply parts
What is the structural architecture for a car
High volume car = made from distinct sections for cost reduction
Low volume high performance cars = made from integrated structures
What should the structural architecture be for a car suspension system
normally should be highly modular because maintenance is always required
Do cars or bikes have modular bearings
cars tend to have modular bearings where as bikes do not
What are the advantages of modular units
- ease of maintenance (lower skill required to assemble and replace)
- Quality control over assembly (assembly guaranteed)
- Sealed for life (solid state approach)
- ease of work split
- aids testing
- enables new technologies to be easily integrated
- enables platform design
What are the disadvantages of modular units
- small defects cant be easily repaired -whole modules have to be replaced
- requires high volumes to be feasible
Give examples of car parts that are made in a modular way
- lights
- gear boxes
- engines
- window drive units
What are the advantages of platform design
- easier inventory management/smaller number of parts
- lower development costs
- increased quality
- global standardisation
- greater product variety
Draw a diagram showing platform design
SKETCH
To achieve the lowest mass and volume ____
it is best to have integrated products with minimal interfaces but this is not always the best solution
To minimise assembly complexity ____
it is best to have a modular design with sub assemblies and standard interfaces
Give examples of where modular parts are used and the advantages of this
- modular parts are used in cars so that they can be assembled together - saving costs with the assembly line
- office buildings use modular windows and doors systems so that they are easy to assemble on site
What is platform design?
multi use of sub assemblies in product families
Does modular help with recycling
recycling may or may not be aided by modular design. Modules make high level disassembly easier, but make disassembly of sub assemblies harder
Modules sometimes make re-manufacture easier (the reuse of a whole sub assembly)
Why do companies need high quality management systems
to ensure quality of design and manufacture is maintained.
They ensure adequate paper trails for design reviews, materials sourcing, component sourcing, produce testing and company decision making
What are the key quality management approaches
- BS 7000 design management systems
- ISO 9000 Quality assurance
- Total Quality management (TQM)
- Six sigma
- Lean manufacturing
- poka-yoke
What does the BS 7000 design management system give guidance on
- managing innovation
- managing the design of manufactured products
- managing service design
- managing design in construction
- managing inclusive design
Expand on the ISO 9000 Quality assurance
it is a set of international standards on quality management and assurance to help companies effectively document the quality system elements to be implemented to maintain an efficient quality system
Expand on total quality management (TQM)
originally from japan emphasising prevention rather than inspection, right first time and continuous quality improvement
Expand on six sigma quality management
developed by motorola
uses statistical tools to improve manufacturing quality by elimination of defects
if manufactured parts have a normal distribution such that 6 sigma falls within the tolerance limits then there will be very few failures
Expand on the lean manufacturing quality management
a production philosophy that aims to reduce waste (anything not of value to the costumer) without sacrificing productivity
takes into account the waste that is created through unevenness in workloads
lean manufacturing makes obvious what adds value by reducing everything else.
Developed by toyota
What is a poka yoke in lean manufacturing
A poka-yoke is any mechanism in a lean manufacturing process that helps an equipment operator avoid mistakes. Its purpose is to eliminate product defects by preventing, correcting, or drawing attention to human errors as they occur
