Lecture 3

Question 1

What is manual assembly?

Answer 1

Manual assembly is the process of assembling products and sub-assemblies by hand, relying on human dexterity, skill, and judgment, typically for low-volume or prototype work.

Question 2

What are the two main tasks in manual assembly?

Answer 2

1. Part handling (acquiring, orienting, moving the parts)
2. Insertion and fastening (mating a part to another part or group of parts)

Question 3

What guidelines are suggested for part handling in manual assembly?

Answer 3

1. Design parts with symmetry.
2. Use obvious asymmetry if parts cannot be symmetric.
3. Prevent jamming for parts stored in bulk.
4. Avoid features that cause tangling.
5. Avoid parts that stick, are slippery, or are hazardous.

Question 4

What is the purpose of chamfers in part insertion?

Answer 4

Chamfers guide the insertion of mating parts, reducing resistance and preventing jamming.

Question 5

What are common guidelines for part insertion and fastening?

Answer 5

1. Use chamfers for easy insertion.
2. Standardize parts and processes.
3. Design for pyramid assembly along one axis.
4. Avoid holding parts for alignment; secure them quickly.
5. Locate parts before release.
6. Minimize repositioning of assemblies.

Question 6

List some fastening methods in manual assembly.

Answer 6

1. Snap fitting
2. Plastic bending
3. Riveting
4. Screw fastening

Question 7

What are some key design guidelines to improve assembly efficiency?

Answer 7

1. Minimize parts.
2. Standardize function and style.
3. Provide location features for easy insertion.
4. Design for easy handling.
5. Minimize directions of insertion.
6. Group components into sub-assemblies.

Question 8

What is the systematic design for assembly?

Answer 8

A systematic approach evaluates designs quantitatively for assembly ease, focusing on minimizing part count, handling, insertion, and fastening difficulties.

Question 9

What is the Hitachi approach in assembly design?

Answer 9

The Hitachi approach assesses design assemblability using an assemblability score (E) and assembly cost ratio (K), which help identify improvements in design and assembly operations.

Question 10

Describe the Lucas approach in design for assembly.

Answer 10

The Lucas approach starts with product design specification and analyzes part necessity, aiming to eliminate non-essential parts and standardize design.

Question 11

What are the main steps in the Boothroyd-Dewhurst DFA approach?

Answer 11

1. Identify parts
2. Determine a feasible assembly sequence
3. Estimate handling and insertion times
4. Calculate design efficiency
5. Estimate total assembly operation cost

Question 12

What is “alpha symmetry” in assembly design?

Answer 12

Alpha symmetry is the rotational symmetry of a part about an axis perpendicular to its insertion axis; 360° symmetry requires no specific orientation.

Question 13

What factors influence the manual handling time of a part?

Answer 13

Factors include weight, size, ease of alignment, access, vision restrictions, and part symmetry.

Question 14

What formula is used to estimate total assembly operation cost in manual assembly?

Answer 14

TC = Rw × TM / 3600, where Rw is the labor rate ($/hr) and TM is the total manual assembly time.

Question 15

What is “theoretical minimum number of parts” in assembly?

Answer 15

It is the minimum part count required to maintain function, isolating parts only if necessary for movement, material properties, or assembly.