Material Selection and costing Flashcards
What does material selection effect
Part function, cost, manufacture process, Quality test method, ability to be painted coated etc
Name 2 general material properties
Density and price
Name 2 Mechanical Properties
Elastic modulus (stiffness) Ultimate strength
What is a material index dependant on
Function, Geometry, How we want to optimise performance
Give an example of how we might want to optimise performance
Light and strong or strong and cheap
For material selection what is the function
What the part needs to do, e.g. support a tensile load or support a bending load
What are the objectives in material selection
Goals that need to be achieved when selecting the material
e.g. minimise mass or minimise cost
What are constraints on material selections
Specifications that constrain the selection when trying to meet the objectives
e.g have to have a thermal conductivity > 10
What are free variables in material selection
Parameters not fixed by the initial design specification,
e.g. Cross sectional area or Material
What is the first step of the material selection strategy
Identify the functions and objectives and constraints
The 2nd step of the selection strategy is to Screen, what does screening use
Constraints
What would you rank the material choices using for the 3rd selection step
Material Index
For an example to select a material for the lightest stiffest tie What is the Function
Safely support a tensile load without breaking
Light/ stiff tie. What are the free variables
Cross sectional area and material
Light/ stiff tie, what is the objective
Minimise mass
Light/stiff tie. What is the constraint
CSA must be strong enough to keep stress < failure stress
What material index would you use for a Light/stiff tie
(failure stress)/(density)
For a light/strong tie with a minimum value for electrical conductivity how many coupled constraints are there and what are they
2, Lightest/strongest
For a light/strong tie with minimum electrical conductivity what is the uncoupled constraint
Electrical Conductivity
For a problem with multiple constrains what constraint would you apply first
The uncoupled constraints
How many material indices would you need for the lightest/strongest/stiffest tie
2
What is the material index for a light/stiff tie
(density)/(young’s modulus)
What would be the equation for the minimum mass a tie will have using a given material if it is to meet both constraints (m’)
m’=max(m1,m2)
What is the equation for m1, the mass for the lightest strongest tie
m1>FxLx((density)/(failure stress))
What is the equation for m2, the mass of the lightest strongest tie
m2>SxL^2x((density)/(Youngs modulus))
For the cheapest strongest tie what is the objective
Minimise cost
For cheapest strongest tie what is the constrain
Area of rod must be great enough so that stress stays bellow failure stress
For cheapest strongest tie what is the Free variable
Area
What is the basic equation for cost
Cost=mass x Cost per part
What is the material index for the cheapest strongest tie
(failure strength)/((density) x (cost per part))
Name some basic shaping processes
Casting, moulding, deformation, powder formation
Name secondary shaping processes
Drilling, punching, turning
Name a property enhancing process
Heat treatment
Name some joining processes
Adhesives, welding, fastening
Name some finishing processes
Polishing, Coating, Painting, Turning
List the key process steps in order
Basic shaping secondary shaping Property enhancing Joining Finishing
What is the process selection dependant on
Material selection, size, shape, precision, quality of parts
In process selection what are the classification steps
Family
class
member
attribute
What does the family of process selection influence
Function
What does the attribute of the process selection influence
Constraints
What is the economic batch size
Size found by experience to e competitive in terms of cost
How do batch size, investment cost and rate of production relate
Higher the batch size the higher the investment cost but also the higher the rate of production
In the cost model what is Cm
Cost of material £/kg
In the cost model what is Ct
Dedicated cost £
In the cost model what is Cc
Capital cost £
In the cost model what is the Coh
Overhead cost per hour £/hour
in the material cost equation what is f
The scrap fraction
In the dedicated cost equation what do n and nt mean
n is the number of parts
nt is the number of parts before replacing
In the capital cost equation what does Two mean
Capital write off time
In the capital cost equation what does L and n’ mean
L= labour cost and n’= rate at which units are produced
What is the cost per part equal to
material cost per part + dedicated cost per part + overhead cost per part
