Post on 14-Mar-2018
transcript
ME 349
Design for Manufacturability (DFM)
"The key objective in any design for manufacturing
effort is to achieve simplicity ... There are many
things which are ... valid measures of simplicity ...
First is the number of parts. Second is assembly
time. You cannot assemble something in a very short
time if it's complex. Third is the number of
processes employed (And last) ... is the complexity
of the process ..."
Fred Schwager, DFM expert
ME 349
What is DFM?
DFM is an approach followed during the design
process that has the aim of improving
manufacturing productivity.
In a “for profit” endeavor:
productivity = profit
Objective is to reduce cost
ME 349
DFM is a tool
Estimation of part and tooling costs based upon:
Monolithic versus “built-up” geometry
Type(s) of material(s) used
Type(s) of process(es) used
Part size
Part complexity
Supplier operating cost
DFM Concurrent Costing software (CAE)
Manufacturing Cost Estimate Tool
ME 349
DFM Use
Do you, or the customer, have requirements on who
or where the product is manufactured?
Designers should keep up to date with available;
• Manufacturing processes (and assembly methods)
• Each has advantages and limitations
• Materials
• Unique properties that can be exploited in design?
• What manufacturing processes can shape a material?
• Components
ME 349
DFM
DFM is often divided into two subdivisions
DFP - Design for the Process
• Ease of fabrication
DFQ - Design for Quality
• Accuracy of features
DFM is intended to be used in conjunction with the
Design for Assembly (DFA) process.
These subdivisions overlap and sometimes
contradict
There always exists an element of trade-off in
applying DFM principles
ME 349
Common Rules of DFM
Simplify part geometry
• Minimizes the chances of a defective part
• Reduces the total cost of fabrication
Utilize common parts and materials across
product line
• Reduces component costs
• facilitates design activities
• minimizes the amount of inventory in the system
ME 349
Common Rules of DFM
Design modular products
Facilitates assembly with building block components
and subassemblies.
Design verifiability into the product and its
components
Eases testing and/or inspecting (non value added)
Increase part symmetry
Avoid unnecessary (non-functional) features
ME 349
Common Rules of DFM
Design for ease of fabrication (e.g., machining)
Avoid designs requiring sharp corners or points
• The required cutting tools break more easily
• Another process may be required: e.g., EDM, broaching, etc.
Do not to use walls and webs that are too thin
• These features can cause a part to distort during the machining
process.
Do not include pockets and holes that are too deep
• greater than 5:1 diameter to depth
Avoid tapers and contours unless required for part
functionality.
Place machined features in the same plane or same
diametric access if possible.
ME 349
Common Rules of DFM
Use the widest possible
tolerances that ensure
function and assembly
Be aware of tolerance
stack-up which will
occur in assembly
ME 349
Common Rules of DFM
Design in the middle of a processes' tolerance
range
This allows you to avoid tight tolerances beyond the
natural capability of the manufacturing processes
ME 349
Specify
surface
qualities
(roughness)
based upon
standard
practices
Design for adequate Surface Quality
ME 349
Common Rules of DFM
Consider the surfaces required for…
fixturing and clamping during fabrication,
inspection reference (datum features and targets)
Design parts for orientation and handling
Parts should be designed with surfaces so that they
can be easily grasped, positioned and fastened by
either a human or machine.
• Minimizes unnecessary manual effort
• Facilitates automation
• Avoid ambiguity in orienting and merging parts
ME 349
Common Rules of DFM
Surfaces to be machined must be accessible
when workpiece is fixtured
During machining, the tool and toolholder must not
interfere with remaining surfaces of workpiece
Avoid the requirement of part reorientation during
fabrication
Non-value added operations (time consuming)
Increase tolerances
Multi-axis and multi-function machine tools may
allow some relaxation of this restriction
ME 349
Common Rules of DFM
For example, provide relief to allow room
for thread cutting tool.
No Yes
ME 349
Common Rules of DFM
Design parts with multiple functions and uses
For example, combine mounting points into the
design of functional components.
Easier to make multiple parts of the same design
Use common parts across product lines
Make sure a dialogue is maintained between
designers, engineers, manufacturers and any
other individuals who play a part in determining
final product costs, especially during early stages
of design.
ME 349
Common Rules of DFM
Additionally…
Remember that the prototype may be
manufactured with different processes than will be
used for mass production
Shape parts and products for ease of packaging
Product/part should fit into standard packaging
cartons
Facilitates automation and shipment to customer
ME 349
DFM Examples A part where mating
surfaces need to be ground
Flatness
Positional accuracy
Surface roughness
Redesign is performed
Reduce area to be ground
Design all surfaces to be
ground in the same, or
parallel, planes
How was the net shape of
this part made?