HO2 - L8: Design for manufacture and assembly

Question 1

Define DFMA.

Answer 1

1. Design tool developed by Boothroyd and Dewhurst, mid 1960’s.
2. It is a structured method to review and simplify product designs for lower cost & higher quality manufacture.
3. There is dedicated software to support DFMA that many companies use.

Question 2

What are the benefits if there are formal and effective links between the design and production teams?

Answer 2

1. Provides a more structured procedure for product development
2. Less problems to “iron out” in the manufacturing phase
3. Products can be largely made in-house and/or suppliers have adequate facilities
4. Designers: aware of recent process developments and production methods
5. New products can be produced at a lower cost and with a lower lead time
6. Components can be design so that they can be made with the most efficient process
7. Historical quality issues can be discussed and see if small design changes could eradicate the problem
8. Check that tolerances are appropriate for the current processes.

Question 3

What are the general rules for DFMA?

Answer 3

1. Minimise total number of parts
2. Develop modular design
3. Minimise part variation
4. Design parts to be multi-functional
5. Design parts for multiple use
6. Use near net shape processes
7. Avoid separate fasteners
8. Minimise assembly directions
9. Minimise tangling of identical parts
10. Contains suitable base on which to build assembly
11. Minimise handling in assembly

Question 4

Describe minimise total number of parts.

Answer 4

1. Do the parts need to move relative to each other?
2. Do the parts have to be made of different material?
3. Do the parts have to be individual to allow for assembly?
   - If the answer is “No” then the parts can be combined
4. Less parts to make, inspect, assemble, service.

Question 5

Describe develop a modular design.

Answer 5

1. A module – self-contained component with a standard interface.
2. Different combinations of modules: create different products.
3. Assembly and maintenance are made simpler.

Question 6

Describe minimise part variation.

Answer 6

1. Specify and use “off-the-shelf” components.
2. Cheaper and easier to source.
3. Reduces risk of errors during processing and assembly because parts are familiar to staff.

Question 7

Describe design parts to be multi-functional.

Answer 7

1. Can a part have more than one purpose? This reduces the number of parts.
   E.g. the shape of a part could make it self-fixing – speeds up assembly
2. Use of chamfers or tapers to guide and position part correctly.

Question 8

Describe design parts for multiple use.

Answer 8

1. Use the same part (or even sub-assembly) in different products - reduces production and logistics overheads.

Question 9

Describe use near shape processes.

Answer 9

1. Choose the material that will give as near net shape from a primary process.
   E.g. primary process – casting, injection moulding, forging
2. Secondary processes e.g. machining, are expensive so should be minimized.

Question 10

Describe avoid separate fasteners.

Answer 10

1. Avoid nuts and bolts – expensive and time consuming to fasten – also need a tool(s) to tighten.
2. Use snap fits wherever possible.
3. If separate fasteners are needed use the same type throughout the product or if you really need two sizes choose a “large” and a “small” one - makes assembly easier and faster.

Question 11

Describe minimise assembly directions.

Answer 11

1. All parts to be added to the assembly in one direction (usually top-down)
2. The need to manipulate (usually rotate) parts during assembly is inefficient.
3. Make parts either perfectly symmetrical or exaggerate asymmetrical features.
4. Makes assembly easier and faster.

Question 12

Describe minimise tangling of identical parts.

Answer 12

1. Design individual parts to minimize tangling with identical parts when placed in feeder bins on the assembly line.
2. Projections, holes and slots cause tangling – make holes and slots smaller than projections.
3. Can consider using magazines rather than feeder bins but this is usually an expensive option.
4. Makes assembly easier and faster.

Question 13

Describe contains suitable base on which to build the assembly.

Answer 13

1. If product doesn’t have a ‘natural’ base, consider designing a fixture.
2. Product is taken off the fixture at the end of the line (or sometimes even shipped on the fixture)
3. Makes assembly easier and faster.

Question 14

Describe minimise handling in assembly.

Answer 14

1. Design parts so that they are easy and comfortable to get a hold of.
2. Can think about different sizes of product e.g. easy to get hold of with; a pair of tweezers, fingers, sack truck, crane.
3. Avoid shape corners – use chamfers/fillets
4. Makes assembly easier and faster.
5. Similar design rules also exist for more specific production processes such as metal removal operations.
6. These can be found in relevant textbooks or design manuals

Question 15

DFMA has been largely described in this lecture as a design tool, i.e. how can we
design the product to be easier to manufacture. Discuss other contexts in which it could be used.

Question 16

Research “Concurrent Engineering” and discuss how DFMA fits in with concurrent
engineering.

Question 17

What is DFE?

Question 18

Discuss rule number 5 above from an inventory management point of view. (You
may not be able to answer this question fully until you’ve done the inventory section of the course)

Question 19

An example of using rule 3 might be “Can you design the product using a single
thickness of steel for all components?”. Discuss the pros and cons to this.