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L#6 Assembly System Design
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- 1What are the two principal types of assembly systems? (2)1. Workbench
2. Line - 2How does a workbench assembly system work? (1) How is production rate increased? (1)1. In workbench systems a fitter at a single bench does all the work required for a product
2. To increase production rate, the number of benches is increased and they work in parallel - 3Explain the two advantages of a workbench system (2)1. FLEXIBLE:
Since the complete set of activities take place in each single cell, it is possible to add or remove cells without affecting the rest of the factory
2. GOOD ACCOUNTABILITY
A single fitter assembles each product. It is therefore, very easy to determine who would be responsible for any quality issues - 4Explain the four disadvantages of a workbench assembly system (4)1. REQUIRE MORE SPACE (LOW OUTPUT PRE METRE SQUARED)
The work is duplicated across all workbenches. Consequently, the same tools and auxiliary resources should exist at at each work-station. This results in redundant use of space.
2. REQUIRE MORE ASSEMBLY STORES:
Like above, the duplication would result in a need for additional storage space
3. REQUIRE MORE EQUIPMENT:
Again, like above, the same set of equipment is required at each work station
4. DIFFICULT TO TRACK PRODUCTS - 5Discuss manual/automated workbench assembly lines1. Cells can be automated or manual: Automated cells are built using robots or a single machine when the long-term demand is assured and the required investment is justified
2. These cells have a high output rate but are typically used to manufacture a limited variety of parts.
3. Automated cells are highly flexible with the range of products for which they have been designed
4. Manual cells allow workers to choose their own work patterns
5. In these cells, the performance level is usually negotiated so that each worker agrees to produce so many products per week (or per hour or year, depending on the product)
6. These cells are highly flexible and are suitable for products that have a high variety and low volume
7. They can be used on products of various sizes (e.g. a mobile pone or a Viking Ship)
8. Manual cells are often used for assembly of new products. If the product is successful and the volume starts to increase the assembly system evolves; it changes from manual cells to an assembly line - 6Discuss workbench assembly system storage options (2)1. Each cell requires a storage space where all parts necessary for producing a product are stored
2. Two prevalent approaches for realising this space are kitted assemblies and bench stores - 7Describe kitted assemblies (2)1. Are used in high variety, low volume production
2. In such kits, the components necessary for a single part are loaded into a kit and the kits are kept together with the products in the factory - 8When are bench stores used instead of kitted assemblies? (1)1. Bench stores are used for smaller products with cheap components (1)
- 9Draw a diagram of two benches in a workbench assembly system (1)1. See notes
- 10Describe an assembly line (3)1. The work for each product is split into a number of packages
2. Each workstation carries out the work in one package
3. A product goes through various workstations and the work packages are consecutively carried out to assemble the product - 11Draw an assembly line diagram (1)See notes (1)
- 12What are the three different assembly line type? (3)1. Fixed fitter lines:
The fitters remain stationary and the products move from one station to the next.
2. Moving fitter lines:
The fitters are either walking or riding and the products are often stationary
3. Hybrid lines:
Combine moving fitter and fixed fitter line together - 13What are the two types of fixed fitter lines? (2)1. Single fitter stations, where each workstation is manned by a single operator, useful for small products
2. Multi fitter stations, manned by multiple operators, useful for large products - 14Categorize assembly lines based on the variety of products that are assembled on the line (3)1. Single product line that assemble a single product
2. Multi product lines where several types of products are assembled using the same workstations
3. Mixed product line, where parts of the assembly line are used for multiple products and other parts are unique to a single product - 15Give the 6 advantages of a fixed fitter assembly line. (6)1. Fast throughput times
2. Minimise tooling
3. Minimise stores
4. Allow fitter specialisation
5. High output and quality
6. Very efficient when on - 16Give the four disadvantages of a fixed fitter assembly line (4)1. Low flexibility
2. Need consistent demand
3. Difficult to balance
4. Typically on or off - 17Give the 6 advantages of a moving fitter assembly line (6)1. High flexibility
2. High product variation
3. Multi-skilled fitters
4. Fast throughput times
5. Minimise tooling
6. Minimise stores - 18Give the two disadvantages of moving fitter assembly lines (2)1. Multi-skilled fitters
2. Difficult to manage - 19Give the advantages of hybrid assembly lines (1)Combines advantages of fixed fitter and moving fitter lines
- 20Give the disadvantages of hybrid assembly lines (2)1. Very difficult to balance
2. Large complicated lines - 21What is line balancing (1)Determining the task assignment for each workstation to ensure an even workload and maximum throughput with the given resources (1)
- 22What is idle time in assembly line? (1)Time when fitters have nothing to do in a production cycle (1)
- 23How does unbalanced assembly line system performance compare to workbench systems? (1)It is typically worse
- 24Give the second definition for line balancing (1)The assignment of assembly tasks to workstation in such a way that uneven workload, bottlenecks and stock hold-ups are eliminated and a smooth overall flow of components is achieved throughout the system (1)
- 25What is the first step in effectively balancing an assembly line? (1)1. Constructing a precedence diagram for the assembly process
- 26Summarize precedence diagrams (3)1. A simple diagram that identifies the various ways in which a product can be assembled
2. In many assemblies, it is possible for some tasks to take place in various sequences.
3. There are also task which can only take place in a given time order - 27Draw the assembly precedence diagram for the electrical plug shown in the notes (1)See notes (1)
- 28Give the three basic equations for assembly lines given in the notes (3)See notes (3)
- 29What are the three line balancing methods? (3)1. Intuitive balancing
2. The mathematical model
3. Heuristic methods - 30Explain the 'intuitive balancing' line balancing method (1)The engineer uses their experience to divide the work among the workstation trying to equalise the load and eliminate bottlenecks (1)
- 31Explain 'The Mathematical Model' line balancing method (2)1. Line balancing can be considered as a mathematical optimisation problem (binary programming) with the objective of minimising the number of workstations
2. As finding an exact solution is often difficult, heuristics are usually used instead - 32Explain the 'Heuristic' line balancing method (3)1. These are experience based methods used to reduce the need for calculations
2. In such approaches, the objectives of the optimisation is often replaced by a rather simpler goal which is likely to produce good results in the original problem
3. One such method used in assembly line balancing is the Rank Positional Weight method - 33Describe the Rank Positional Weight method (RPW) in six steps (6)1. Calculate each elements positional weight, which equals its elemental time plus all subsequent elemental time in the precedence chains
2. Construct a rank positional weight table of elements
3. Assign the unallocated element with the highest available rank to the first available workstation
4. Assign the next highest ranked unallocated element precedence and time permitting
5. Continue assigning the next highest ranked unallocated element until the workstation time equals the cycle time or no further elements are available for adding
6. Adopt the assigned element group as the next workstation and go to 3 or finish if there are no more unallocated items - 34In RPW, what should you do when assigning elements with equal rank? (1)Assigning the element that has the larger task time often yields better results, but not guaranteed (1)
- 35Do the two examples for RPW in the notes (2)See notes (2)
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- Manufacturing Operations and Technology Fichas sobre L#6 Assembly System Design, creado por Block el 01/05/2014.
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