Design For Manufacturing
Kenneth A. Crow
1. Simplify the design and reduce the number of parts because for each
part, there is an opportunity for a defective part and an assembly error. The
probability of a perfect product goes down exponentially as the number of parts
increases. As the number of parts goes up, the total cost of fabricating and
assembling the product goes up. Automation becomes more difficult and more
expensive when more parts are handled and processed. Costs related to
purchasing, stocking, and servicing also go down as the number of parts are
reduced. Inventory and work-in-process levels will go down with fewer parts. As
the product structure and required operations are simplified, fewer fabrication
and assembly steps are required, manufacturing processes can be integrated and
leadtimes further reduced. The designer should go through the assembly part by
part and evaluate whether the part can be eliminated, combined with another
part, or the function can be performed in another way. To determine the
theoretical minimum number of parts, ask the following: Does the part move
relative to all other moving parts? Must the part absolutely be of a different
material from the other parts? Must the part be different to allow possible
2. Standardize and use common parts and materials to facilitate design
activities, to minimize the amount of inventory in the system, and to
standardize handling and assembly operations. Common parts will result in lower
inventories, reduced costs and higher quality. Operator learning is simplified
and there is a greater opportunity for automation as the result of higher
production volumes and operation standardization. Limit exotic or unique
components because suppliers are less likely to compete on quality or cost for
these components. The classification and retrieval capabilities of product data
management (PDM) systems and component supplier management (CSM) systems can be
utilized by designers to facilitate retrieval of similar designs and material
catalogs or approved parts lists can serve as references for common purchased
and stocked parts.
3. Design for ease of fabrication. Select processes compatible with the
materials and production volumes. Select materials compatible with production
processes and that minimize processing time while meeting functional
requirements. Avoid unnecessary part features because they involve extra
processing effort and/or more complex tooling. Apply specific guidelines
appropriate for the fabrication process such as the following guidelines for
- For higher volume parts, consider castings or stampings to reduce
- Use near net shapes for molded and forged parts to minimize machining and
- Design for ease of fixturing by providing large solid mounting surface &
parallel clamping surfaces
- Avoid designs requiring sharp corners or points in cutting tools - they
- Avoid thin walls, thin webs, deep pockets or deep holes to withstand
clamping & machining without distortion
- Avoid tapers & contours as much as possible in favor of rectangular shapes
- Avoid undercuts which require special operations & tools
- Avoid hardened or difficult machined materials unless essential to
- Put machined surfaces on same plane or with same diameter to minimize
number of operations
- Design workpieces to use standard cutters, drill bit sizes or other tools
- Avoid small holes (drill bit breakage greater) & length to diameter ratio
> 3 (chip clearance & straightness deviation)
4. Design within process capabilities and avoid unneeded surface finish
requirements. Know the production process capabilities of equipment and
establish controlled processes. Avoid unnecessarily tight tolerances that are
beyond the natural capability of the manufacturing processes. Otherwise, this
will require that parts be inspected or screened for acceptability. Determine
when new production process capabilities are needed early to allow sufficient
time to determine optimal process parameters and establish a controlled process.
Also, avoid tight tolerances on multiple, connected parts. Tolerances on
connected parts will "stack-up" making maintenance of overall product tolerance
difficult. Design in the center of a component's parameter range to improve
reliability and limit the range of variance around the parameter objective.
Surface finish requirements likewise may be established based on standard
practices and may be applied to interior surfaces resulting in additional costs
where these requirements may not be needed.
5. Mistake-proof product design and assembly (poka-yoke) so that the
assembly process is unambiguous. Components should be designed so that they can
only be assembled in one way; they cannot be reversed. Notches, asymmetrical
holes and stops can be used to mistake-proof the assembly process. Design
verifiability into the product and its components. For mechanical products,
verifiability can be achieved with simple go/no-go tools in the form of notches
or natural stopping points. Products should be designed to avoid or simplify
adjustments. Electronic products can be designed to contain self-test and/or
diagnostic capabilities. Of course, the additional cost of building in
diagnostics must be weighed against the advantages.
6. Design for parts orientation and handling to minimize non-value-added
manual effort and ambiguity in orienting and merging parts. Basic principles to
facilitate parts handling and orienting are:
- Parts must be designed to consistently orient themselves when fed into a
- Product design must avoid parts which can become tangled, wedged or
disoriented. Avoid holes and tabs and designed "closed" parts. This type of
design will allow the use of automation in parts handling and assembly such as
vibratory bowls, tubes, magazines, etc.
- Part design should incorporate symmetry around both axes of insertion
wherever possible. Where parts cannot be symmetrical, the asymmetry should be
emphasized to assure correct insertion or easily identifiable feature should
- With hidden features that require a particular orientation, provide an
external feature or guide surface to correctly orient the part.
- Guide surfaces should be provided to facilitate insertion.
- Parts should be designed with surfaces so that they can be easily grasped,
placed and fixtured. Ideally this means flat, parallel surfaces that would
allow a part to picked-up by a person or a gripper with a pick and place robot
and then easily fixtured.
- Minimize thin, flat parts that are more difficult to pick up. Avoid very
small parts that are difficult to pick-up or require a tool such as a tweezers
to pick-up. This will increase handling and orientation time.
- Avoid parts with sharp edges, burrs or points. These parts can injure
workers or customers, they require more careful handling, they can damage
product finishes, and they may be more susceptible to damage themselves if the
sharp edge is an intended feature.
- Avoid parts that can be easily damaged or broken.
- Avoid parts that are sticky or slippery (thin oily plates, oily parts,
adhesive backed parts, small plastic parts with smooth surfaces, etc.).
- Avoid heavy parts that will increase worker fatigue, increase risk of
worker injury, and slow the assembly process.
- Design the work station area to minimize the distance to access and move a
- When purchasing components, consider acquiring materials already oriented
in magazines, bands, tape, or strips.
7. Minimize flexible parts and interconnections. Avoid flexible and
flimsy parts such as belts, gaskets, tubing, cables and wire harnesses. Their
flexibility makes material handling and assembly more difficult and these parts
are more susceptible to damage. Use plug-in boards and backplanes to minimize
wire harnesses. Where harnesses are used, consider foolproofing electrical
connectors by using unique connectors to avoid connectors being mis-connected.
Interconnections such as wire harnesses, hydraulic lines, piping, etc. are
expensive to fabricate, assemble and service. Partition the product to minimize
interconnections between modules and co-locate related modules to minimize
routing of interconnections.
8. Design for ease of assembly by utilizing simple patterns of movement
and minimizing the axes of assembly. Complex orientation and assembly movements
in various directions should be avoided. Part features should be provided such
as chamfers and tapers. The product's design should enable assembly to begin
with a base component with a large relative mass and a low center of gravity
upon which other parts are added. Assembly should proceed vertically with other
parts added on top and positioned with the aid of gravity. This will minimize
the need to re-orient the assembly and reduce the need for temporary fastening
and more complex fixturing. A product that is easy to assemble manually will be
easily assembled with automation. Assembly that is automated will be more
uniform, more reliable, and of a higher quality.
9. Design for efficient joining and fastening. Threaded fasteners
(screws, bolts, nuts and washers) are time-consuming to assemble and difficult
to automate. Where they must be used, standardize to minimize variety and use
fasteners such as self threading screws and captured washers. Consider the use
of integral attachment methods (snap-fit). Evaluate other bonding techniques
with adhesives. Match fastening techniques to materials, product functional
requirements, and disassembly/servicing requirements.
10. Design modular products to facilitate assembly with building block
components and subassemblies. This modular or building block design should
minimize the number of part or assembly variants early in the manufacturing
process while allowing for greater product variation late in the process during
final assembly. This approach minimizes the total number of items to be
manufactured, thereby reducing inventory and improving quality. Modules can be
manufactured and tested before final assembly. The short final assembly leadtime
can result in a wide variety of products being made to a customer's order in a
short period of time without having to stock a significant level of inventory.
Production of standard modules can be leveled and repetitive schedules
11. Design for automated production. Automated production involves
less flexibility than manual production. The product must be designed in a way
that can be more handled with automation. There are two automation approaches:
flexible robotic assembly and high speed automated assembly. Considerations with
flexible robotic assembly are: design parts to utilize standard gripper and
avoid gripper / tool change, use self-locating parts, use simple parts
presentation devices, and avoid the need to secure or clamp parts.
Considerations with high speed automated assembly are: use a minimum of parts or
standard parts for minimum of feeding bowls, etc., use closed parts (no
projections, holes or slots) to avoid tangling, consider the potential for
multi-axis assembly to speed the assembly cycle time, and use pre-oriented
12. Design printed circuit boards for assembly. With printed circuit
boards (PCB's), guidelines include: minimizing component variety, standardizing
component packaging, using auto-insertable or placeable components, using a
common component orientation and component placement to minimize soldering
"shadows", selecting component and trace width that is within the process
capability, using appropriate pad and trace configuration and spacing to assure
good solder joints and avoid bridging, using standard board and panel sizes,
using tooling holes, establishing minimum borders, and avoiding or minimizing
Need Help! Or do not have resources for PCB design?
Our fully qualified PCB engineers are capable design or layout your PCB
from circuit diagram or even from sample PCB.
comprehensive PCB service from PCB design to PCB fabrication and parts
procurement to prototyping assembly.
Our technical team is
ever ready to provide
advise to your PCB design problem and design improvement for manufacturing.
Send your question to our technical team at