Week 5: Assembly and Automation

Question 1

What is assembly?

Answer 1

Assembly is the process where the manufactured components that form products are joined together to form the final product.

Question 2

What is a workbench (cell) assembly system?

Answer 2

In workbench system a single fitter at a single bench does all the work required for a product. To increase production rate the number of benches is increased and they work in parallel.

Question 3

What are the advantages of a workbench assembly system(2)?

Answer 3

• Flexible: it is possible to add or remove cells without affecting the rest of the factory
• Good accountability: easy to determine who was responsible for any quality issues

Question 4

What are the disadvantages of a workbench assembly system(4)?

Answer 4

• Require more space (low output per m^2): the work is duplicated across workbenches, the same tools and auxiliary resources should exist at each bench. Redundant use of space
• Require more assembly stores: duplication results in the need of more additional space
• Require more equipment: the same set of equipment is required at each workstation
• Difficult to track products

Question 5

What is an assembly line?

Answer 5

In assembly lines the work for each product is split into a number of packages, each workstation carries out the work in one package.

Question 6

What is cycle time?

Answer 6

Cycle time is the time between two consecutive finished products coming off the assembly line

Question 7

What is takt time?

Answer 7

Takt time is the maximum cycle time that can meet the customer demand

Question 8

What are the advantages of a fixed fitter line(6)?

Answer 8

• Fast throughput times
• Minimise tooling
• Minimise stores
• Allow fitter specification
• High output and quality
• Very efficient when on

Question 9

What are the disadvantages of a fixed fitter line(4)?

Answer 9

• Low flexibility
• Need consistent demand
• Difficult to balance
• Typically on or off

Question 10

What are the advantages of a moving fitter line(6)?

Answer 10

• High flexibility
• High product variation
• Multi-skilled fitters
• Fast throughput times
• Minimise tooling
• Minimise stores

Question 11

What are the disadvantages of a moving fitter line(2)?

Answer 11

• Multi-skilled fitters

- Difficult to manage

Question 12

What is the advantage of hybrid lines?

Answer 12

It combines moving fitter lines with fixed fitter lines

Question 13

What are the disadvantages of hybrid lines(2)?

Answer 13

• Very difficult to balance

- Large complicated lines

Question 14

What is line balancing?

Answer 14

Ensuring an even workload and maximum throughput across workstations in an assembly line with the given resources

Question 15

Draw a precedence diagram

Answer 15

Diagram

Question 16

What is the equation for a cycle time of N workstations?

Answer 16

C=60/P

- P is number of products produced per hour

Question 17

What is the equation for the minimum number of required workstations?

Answer 17

Nmin - 1 < sum(tn)/C < Nmin

- tn is the sum of times of the activities assigned to workstation n

Question 18

Describe the RPW algorithm

Answer 18

Rank Positional Weighting Table:

Element
Weight: task time plus all subsequent task times
Time
Precedence
Work station
Time remaining

Assign larger task times first

Question 19

What are the goals of Industry 4.0/Automation (6)?

Answer 19

• Integrate various aspects of the manufacturing system to improve product quality and uniformity while minimising cycle times
• Improve productivity to reduce costs by better control of the production
• Improve quality by using repeatable processes and thus reducing variance
• Reduce human involvement, boredom and thus potential for human error
• Raise the level of safety, especially in hazardous environments, for personnel
• Economise space by arranging machines, materials handling etc. more efficiently

Question 20

What is hard automation?

Answer 20

Machines are designed to produce standard parts, these machines are not flexible only some parameters can be changed (product size, machining speed, feed, depth of cut etc.)

Question 21

What is soft automation?

Answer 21

In soft automation, or flexible or programmable automation, greater flexibility is achieved through the use of computer controlled machines. The machines can be easily reprogrammed to produce new parts that are completely different to the previous parts. This is mainly enabled by numerical control

Question 22

What is numerical control?

Answer 22

Numerical control is a method for controlling the movements of machine components by directly inserting coded instructions. This uses open loop and closed loop circuits(uses feedback sensors).

Question 23

Define two types of numerical control

Answer 23

Point-to-point systems: axes of movement are controlled independently and move with various velocities i.e. positioning operation is completed before the machining operation commences. (drilling)

Contouring systems: continuous path systems where the axes of movement are controlled simultaneously and therefore it is possible to perform machining operations at the same time. (milling)

Question 24

What are the types of interpolation used in contouring systems(3)?

Answer 24

1. Linear interpolation
2. Circular interpolation
3. Parabolic and cubic interpolation