unit-1-automation of assembly lines.pptx

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1. Subject Robotics & Automation

2. UNIT – I AUTOMATION Definition of automation, Automation Production and Flow Lines – Methods of Work part Transport, General Terminology and Analysis. Production Economics – Costs in Manufacturing, Break-Even Analysis.

3. Course Objectives To develop the student’s knowledge concept of the automation industry .

4. Concept of Automation Automation can be defined as the technology by which a process or procedure is accomplished without human assistance. It is implemented using a program of instructions combined with a control system that executes the instructions .

5. To automate a process, power is required, both to drive the process itself and to operate the program and control system. It was in the context of manufacturing that the term was originally coined by an engineering manager at Ford Motor Company in 1946 to describe the variety of automatic transfer devices and feed mechanisms that had been installed in Ford’s production plants

6. What is Low Cost Automation ? It is a technology that creates some degree of automation around the existing equipment, tool, methods, and people, using mostly standard components available in the market.

7. Terms automation and mechanization are often compared and sometimes confused.

8. Mechanization Mechanization refers to the use of machinery (usually powered) to assist or replace human workers in performing physical tasks, but human workers are still required to accomplish the cognitive and sensory elements of the tasks.

9. Automation Automation Refers to the use of mechanized equipment that performs the physical tasks without the need for oversight by a human worker.

10. The position of automation and control technologies in the larger production system is shown in Figure

11. Types of Automation Fixed Automation Programmable Automation Flexible Automation

12. Fixed Automation sequence of processing (or assembly) operations is fixed by the equipment configuration. The operations in the sequence are usually simple. Integration and coordination of many such operations into one piece of equipment that makes the system complex. Typical features are

13. The economic justification for fixed automation is found in products with very high demand rates and volumes. The high initial cost of the equipment can be spread over a very large number of units, thus making the unit cost attractive compared to alternative methods of production. Examples : Mechanized assembly and machining transfer lines.

14. Programmable Automation In this the production equipment is designed with the capability to change the sequence of operations to accommodate different product configurations.

15. operation sequence is controlled by a program Set of Instructions New programs can be prepared and entered into the equipment to produce new products. Some of the features that characterize programmable automation are: a. High investment in general-purpose equipment; b. Low production rates relative to fixed automation; c. Flexibility to deal with changes in product configuration; and d. Most suitable for batch production. Automated production systems that are programmable are used in low and medium volume production.

16. The parts or products are typically made in batches. To produce each new batch of a different product, the system must be reprogrammed with the set of machine instructions that correspond to the new product. The physical setup of the machine must also be changed over: Tools must be loaded, Fixtures must be attached to the machine table also be changed machine settings must be entered.

17. Flexible Automation NDT Extension of programmable automation. A flexible automated system is one that is capable of producing a variety of products (or parts) with virtually no time lost for changeovers from one product to the next. There is no production time lost while reprogramming the system and altering the physical setup (tooling, fixtures, and machine setting).

18. Features of Flexible Automation 1. High investment for a custom-engineered system. 2. Continuous production of variable mixtures of products. 3. Medium production rates. 4. Flexibility to deal with product design variations. Essential features that distinguish flexible automation from programmable automation 1. The capacity to change part programs with no lost production time; and 2. The capability to changeover the physical setup, again with no lost production time.

19. Concept of Automation in Industry Automated manufacturing systems operate in the factory of physical product. Processing, assembly, inspection and material handling Reduced level of human participation compared with the corresponding manual process. In some highly automated systems, there is virtually no human participation.

20. Examples of Automated Manufacturing System Automated machine tools that process parts Transfer lines that perform a series of machining operations Automated assembly systems Manufacturing systems that use industrial robots to perform processing or assembly operations Automatic material handling and storage systems to integrate manufacturing operations Automatic inspection systems for quality control.

21. USA Process

22. It may turn out that automation of the process is unnecessary or cannot be cost justified after it has been simplified. If automation seems a feasible solution to improving productivity, quality, or other measure of performance, then the following ten strategies provide a road map to search for these improvements.

23. Specialization of operations Combined operations Simultaneous operations Integration of operations Increased flexibility Improved material handling and storage On-line inspection Process control and optimization Plant operations control Computer-integrated manufacturing (CIM )

24. Specialization of operations use of special-purpose equipment designed to perform one operation with the greatest possible efficiency. concept of labor specialization

25. Combined operations Production occurs as a sequence of operations. The strategy of combined operations involves reducing the number of distinct production machines or workstations through which the part must be routed. Simultaneous operations simultaneously perform the operations that are combined at one workstation. In effect, two or more processing (or assembly) operations are being performed simultaneously on the same workpart , thus reducing total processing time.

26. Integration of operations Another strategy is to link several workstations together into a single integrated mechanism, using automated work handling devices to transfer parts between stations. In effect, this reduces the number of separate machines through which the product must be scheduled. Increased flexibility This strategy attempts to achieve maximum utilization of equipment for job shop and medium volume situations by using the same equipment for a variety of parts or products. Prime objectives are to reduce setup time and programming time for the production machine.

27. Improved material handling and storage A great opportunity for reducing nonproductive time exists in the use of automated material handling and storage systems. Typical benefits include reduced work-in-process and shorter manufacturing lead times. Inspection for quality of work is traditionally performed after the process is completed. Incorporating inspection into the manufacturing process permits corrections to the process as the product is being made. This reduces scrap and brings the overall quality of product closer to the nominal specifications intended by the designer.

28. Process control and optimization Intended to operate the individual processes and associated equipment more efficiently. By this strategy, the individual process times can be reduced and product quality improved. Plant operations control Whereas the previous strategy was concerned with the control of the individual manufacturing process, this strategy is concerned with control at the plant level. It attempts to manage and coordinate the aggregate operations in the plant more efficiently. Its implementation usually involves a high level of computer networking within the factory.

29. BALANCING OF ASSEMBLY LINES USING AVAILABLE ALGORITHMS Assembly Line Balancing  (ALB) is the term commonly used to refer to the decision process of assigning tasks to workstations in a serial production system. The task consists of elemental operations required to convert raw material in to finished goods.

30. Most manufactured consumer products are assembled. Each product consists of multiple components joined together by various assembly processes. These kinds of products are usually made on a manual assembly line. What is Assembly ?

31. Factors favoring the use of manual assembly lines • Demand for the product is high or medium • The products made on the line are identical or similar • The total work required to assemble the product can be divided into small work elements • It is technologically impossible or economically infeasible to automate the assembly operations.

32. Additional factors One Line Specialization of Labor -. Each worker becomes a Specialist Inter Changeable parts- Manufactured to sufficiently close tolerances Work Flow Principle- W hich involves moving the work to the worker rather than vice versa. Each work unit flows smoothly through the production line, traveling the minimum distance between stations. Line Pacing- ( Cycle Time ) Pacing is generally implemented by means of a mechanized conveyor.

33. Fundamentals of Manual Assembly Lines Sequence of workstations where assembly tasks are performed by human workers Products assembled as they move on the go. Each portion worker works on a part of the total work on the unit. Launch Base Parts on Beginning Line Base part travels through successive stations and workers add components that progressively build the product. Material transport line-move the base parts along the line as they are gradually transformed into final products. Fast working stations are ultimately limited by slowest station.

34. Assembly Workstations

35. When the workers stand, they can move about the station area to perform their assigned task. This is common for assembly of large products such as cars, trucks, and major appliances. The product is typically moved by a conveyor at constant velocity through the station. The worker begins the assembly task near the upstream side of the station and moves along with the work unit until the task is completed, then walks back to the next work unit and repeats the cycle.

36. Smaller assembled products (such as small appliances, electronic devices, and subassemblies used on larger products), the workstations are usually designed to allow the workers to sit while they perform their tasks. This is more comfortable and less fatiguing for the workers and is generally more conducive to precision and accuracy in the assembly task

37. Work Transport Systems MANUAL MECHANIZED MANUAL- Passed from station to station by the workers themselves Two problems result from this mode of operation: starving and blocking.

38. Starving is the situation in which the assembly operator has completed the assigned task on the current work unit, but the next unit has not yet arrived at the station. The worker is thus starved for work. Blocking means that the operator has completed the assigned task on the current work unit but cannot pass the unit to the downstream station because that worker is not yet ready to receive it. The operator is therefore blocked from working.

39. MECHANIZED Power conveyors and material handling equipments were utilized Classified into three categories Continuous Transport System Synchronous Transport System Asynchronous Transport System

40. Layout of Three Types

41. EXAMPLES

42. Line Pacing A manual assembly line operates at a certain cycle time that is established to achieve the required production rate of the line. On average each worker must complete the assigned task at his/her station within the cycle time, or else the required production rate will not be achieved. This pacing of the workers is one of the reasons why a manual assembly line is successful. Pacing provides a discipline for the assembly line workers that more or less guarantees a certain production rate.

43. Three alternative Levels of Pacing rigid pacing, Worker is allowed only a fixed time (2) pacng with margin , the worker is allowed to complete the task at the station within a specified time range. The maximum time of the range is longer than the cycle time, so that a worker is permitted to take more time if a problem occurs or if the task time required for a particular work unit is longer than the average (3) no pacing, meaning that no time limit exists within which the task at the station must be finished. This case can occur when manual work transport is used on the line, work units can be removed from the conveyor, allowing the worker to take as much time as desired to complete a given unit, or an asynchronous conveyor is used and the worker controls the release of each work unit from the station.

44. Types of Assembly Lines single model, batch model, and (3) mixed model.

45. Single model line Produces only one product in large quantities. Every work unit is identical, so the task performed at each station is the same for all products. This line type is intended for products with high demand.

46. Batch-model and mixed-model line BATCH MODEL Produces each product in batches. Workstations are set up to produce the required quantity of the first product, then the stations are reconfigured to produce the next product, and so on. MIXED MODEL A mixed-model line also produces more than one model; however, the models are not produced in batches; instead, they are made simultaneously on the same line. While one station is working on one model, the next station is processing a different model.

47. Analysis of Single Mode Assembly Lines Cycle Time and Workload Analysis Hourly Production Rate is given by

48. Total Cycle time Tc = cycle time of the line, min/cycle; Rp = required production rate The constant 60 converts the hourly production rate to a cycle time in minutes; and E = line efficiency. Typical values of E for a manual assembly line are in the range 0.90–0.98. The cycle time Tc establishes the ideal cycle rate for the line

49. work content time ( Twc ) The total time of all work elements that must be performed on the line to make one unit of product. It represents the total amount of work that is to be accomplished on the product by the assembly line. It is useful to compute a theoretical minimum number of workers that will be required on the assembly line to produce a product with known Twc and specified production rate Rp .

50. Fundamentals of TLMS

51. WORKPART TRANSPORT The transfer mechanism of the automated flow line must not only move the partially completed workparts or assemblies between adjacent stations, it must also orient and locate the parts in the correct position for processing at each station. The general methods of transporting workpieces on flow lines can be classified into the following three categories: Continuous transfer Intermittent or synchronous transfer Asynchronous or power-and-free

52. ALSO… The most appropriate type of transport system for a given application depends on such factors as: The types of operation to be performed The number of stations on the line The weight and size of the work parts Whether manual stations are included on the line Production rate requirements Balancing the various process times on the line

53. 1) Continuous transfer The workparts are moved continuously at Constant speed. This requires the workheads to move during processing in order to maintain continuous registration with the workpart. For some types of operations, this movement of the workheads during processing is not feasible, It would be difficult for example, to use this type of system on a machining transfer line because of inertia problems due to the size and weight of the workheads. Examples of its use are In beverage bottling operations, Packaging,

54. 2) Intermittent transfer As the name suggests, in this method the workpieces are transported with an intermittent or discontinuous motion. The workstations are fixed in position and the parts are moved between stations and then registered at the proper locations for processing. All workparts are transported at the same time and, for this reason, the term "synchronous transfer system" is also used to describe this method of workpart transport .

55. 3) Asynchronous transfer This system of transfer, also referred to as a "power-and-free system,“ It allows each workpart to move to the next station when processing at the current station has been completed. Each part moves independently of other parts. Hence, some parts are being processed on the line at the same time that others are being transported between stations. In-process storage of workparts can be incorporated into the asynchronous systems with relative ease. Parallel stations or several series stations can be used for the longer operations Single stations can be used for the shorter operations. A disadvantage of the power and-free systems is that the cycle rates are generally slower than for the other types.

56. Transfer mechanisms- There are various types of transfer mechanisms used to move parts between stations. These mechanisms can be grouped into two types: # Linear travel for in- line machines , # Rotary motion for dial indexing machines.

57. Linear transfer System  We will explain the operation of three of the typical mechanisms; The walking beam transfer bar system The powered roller conveyor system, and The chain-drive conveyor system.

58. The walking beam transfer bar system The work-parts are lifted up from their workstation locations by a transfer bar and moved one position ahead, to the next station. The transfer bar then lowers the pans into nests which position them more accurately for processing. For speed and accuracy, the motion of the beam is most often generated by a rotating camshaft powered by an electric motor or a roller movement in a profile powered by hydraulic cylinder

59. Powered roller conveyor system This type of system is used in general stock handling systems as well as in automated flow lines. The conveyor can be used to move pans or pallets possessing flat riding surfaces. The rollers can be powered by either of two mechanisms. A belt drive A chain drive Powered roller conveyors are versatile transfer systems because they can be used to divert work

60. Chain-drive conveyor system Either a chain or a flexible steel belt is used to transport the work carriers. The chain is driven by pulleys in either an “over-and- under“ config, in which the pulleys turn about a horizontal axis, or an “around-the-corner“ configuration, in which the pulleys rotate about a vertical axis.

61. Rotary transfer mechanisms  There are several methods used to index a circular table or dial at various equal angular positions corresponding to workstation locations.

62. Rack and pinion This mechanism is simple but is not considered especially suited to the high-speed operation often associated with indexing machines. It uses a piston to drive the rack, which causes the pinion gear and attached indexing table to rotate, A clutch or other device is used to provide rotation in the desired direction.

63. Buffer Storage It is not uncommon for production flow lines to include storage zones for collecting banks of workparts along the line. One example of the use of storage zones would be two intermittent transfer systems, each without any storage capacity, linked together with a workpart inventory area. It is possible to connect three, four, or even more lines in this manner. Another example of workpart storage on flow lines is the asynchronous transfer line. With this system, it is possible to provide a bank of workparts for every station on the line.

64. Analysis of Transfer Lines There are a few assumptions that we will have to make about t he operation of the Transfer line & rotary indexing machines The workstations perform operations such as machining & not assembly. Processing times at each station are constant though they may not be equal. There is synchronous transfer of parts. No internal storage of buffers.