Automation in manufacturing unit 2 slides

Automation in manufacturing unit 2

1. Automation in Manufacturing Assembly Systems and Line Balancing UNIT II By Dr. M Vishnu Vardhan Associate Professor Department of Mechanical Engineering

2. The Assembly Process Assembly involves the joining together of two or more separate parts to form a new entity (assembly or subassembly) The processes used to accomplish the assembly of the components can be divided into three major categories. 1. Mechanical Fastening –Mechanical action to hold components together. Threaded fasteners - screws, bolts, nuts etc. Rivets and other methods 2. Joining Methods –welding, brazing and soldering 3. Adhesive Bonding –thermoplastic, thermosetting (chemical reaction)

3. Assembly Systems There are various methods used in industry to accomplish the assembly processes Major methods can be classified: Manual Single-Station Assembly Manual Assembly Lines Automated Assembly System

4. Manual Single-Station Assembly Consist of a single workplace to accomplish the product or some major subassembly of the product. Generally used on a product that is complex and produced in small quantities, one or more workers depending on the size of the product and the production rate. *Such as machine tools, industrial equipment, aircraft, ships and complex consumer products (appliances, car,...)

5. Manual Single-Station Assembly

6. Manual Assembly Lines *Consist of multiple workstations in which the assembly work is accomplished as the product (subassembly) is passed from station to station along the line. At each workstation one or more human workers perform a portion of the total assembly work on the product, by adding one or more components to the existing subassembly.

7. Manual Assembly Lines

8. Automated Assembly System Use of automated methods at the workstations rather than human beings

9. Line Balancing The line balancing problem is to arrange the individual processing and assembly tasks at the workstations so that the total time required at each workstation is approximately the same If the work elements can be grouped so that all the station times are exactly equal, we have perfect balance on the line and we can expect the production to flow smoothly

10. Terminology for Line Balancing Minimum Rational Work Element Minimum rational work element is the smallest practical indivisible tasks into which the job can be divided. These work elements cannot be subdivided further *Example: drilling a hole, screw and nut etc.

11. Total Work Content *Total work, Twc , content is the aggregate of all the work elements to be done on the line. Workstation Process Time * Work is preformed either manually or by some automatic device. The work performed at station consists of one or more of the individual work elements .

12. Cycle Time Cycle time, T c , is the ideal or theoretical cycle time of the flow line, which is the time interval between parts coming off the line Precedence Constraints Technological sequencing requirements, the order in which the work elements can be accomplished is limited

13. Precedence Diagram A graphical representation of the sequence of work elements as defined by the precedence constraints Balance Delay (Balancing Loss) *Balance delay is a measure of the line inefficiency which results from idle time due to imperfect allocation of work among station

14. Line Balancing Problem – Largest Candidate Rule Problem: In an assembly line the elements is to be assembled as per the following information Construct Precedence diagram If Cycle time is 1 min, calculate the number of stations required Determine balance delay and balance efficiency of the line using Largest candidate rule.

15. Step1: Precedence Diagram

16. Work element Te Immediate predecessor 3 0.7 1 8 0.6 3,4 11 0.5 9,10 2 0.4 ---- 10 0.38 5,8 7 0.32 3 5 0.3 2 9 0.27 6,7,8 1 0.2 --- 12 0.12 11 6 0.11 3 4 0.1 1,2 Step 2: Arrange Time (Te) in descending order

17. Step 3 . To assign elements to the first workstation, start at the top of the list and work done, selecting the first feasible element for placement at the station. A feasible element is one that satisfies the precedence requirements and does not cause the sum of the Tej value at station to exceed the cycle time Tc .

18. Balance Delay (d) d= (5*1 – 4) / (5*1) = 0.2 = 20 % Line Efficiency (E or η ) η = Twc / n Tc = 4 / (5*1) = 0.80 = 80% ** We can also find Balance Delay (d) as d = 1 - η

19. Kilbridge and Wester's Method (KWM) * It is a heuristic procedure which selects work elements for assignment to stations according to their position in the precedence diagram. *This overcomes one of the difficulties with the largest candidate rule (LCR), with which elements at the end of the precedence diagram might be the first candidates to be considered, simply because their values are large. Procedure: Step 1. Construct the precedence diagram so those nodes representing work elements of identical precedence are arranged vertically in columns. Step 2. List the elements in order of their columns, column I at the top of the list. If an element can be located in more than one column, list all columns by the element to show the transferability of the element. Step 3. To assign elements to workstations, start with the column I elements. Continue the assignment procedure in order of column number until the cycle time is reached ( Tc ).

20. Kilbridge and Wester's Method (KWM) Problem: In an assembly line the elements is to be assembled as per the following information Construct Precedence diagram If Cycle time is 1 min, calculate the number of stations required Determine balance delay and balance efficiency of the line using kilbride and Wester Method (KWM)

21. Step1: Precedence Diagram

22. Step 2. Work elements arranged according to columns

23. Step 3. Work elements assigned to stations

24. Step 3. Work elements assigned to stations

25. Balance Delay (d) d= (5*1 – 4) / (5*1) = 0.2 = 20 % Line Efficiency (E or η ) η = Twc / n Tc = 4 / (5*1) = 0.80 = 80% ** We can also find Balance Delay (d) as d = 1 - η

26. Ranked Positional Weights Method

27. Balance Efficiency ( η ) = Twc / (n* Tc ) = 3.8 / 4 = 0.95 = 95% Balance Delay (d) = (1- η ) = 1-0.95 = 0.05 = 5%

28. Material Handling “ The movement, storage, protection & control of material through out the manufacturing and distribution process including their consumption and disposal ”

29. Material Handling System Handling of material should be performed S afely Efficiently At low cost In timely manner Accurately ( right material in the right quantities to the right location in right time ) Without Damage

30. Material Handling System Cost of material handling is a significant portion of total production cost Estimate average around 20-25% of total manufacturing labor cost (in USA) The proportion of total cost varies , depending on the type of production and degree of automation in the material handling function

31. Categories of Material Handling Equipment Material Transport Equipment Storage system Unitizing Equipment Identification and Tracking Systems

32. Material Transport Equipment Used to move materials inside a factory, warehouse, or other facility Five main types of equipment are: Industrial Trucks Automated Guided Vehicles Rail guided vehicles Conveyors & Hoists and cranes

33. Storage S ystem Work in process and finished products likely to spend some time in ware house or distribution center before being delivered to the final customer. Conventional storage methods ( bulk storage, rack systems, shelving, bins storage ) Automated storage systems ( AS/RS system and Carousel Systems )

34. Unitizing Equipment Containers used to hold individual items during handling and equipment used to load and package the containers . Containers include pallets, boxes, baskets, barrels, pails, and drums

35. Unit Load Containers (a) Wooden pallet, (b) pallet box, (c) tote box

36. MATERIAL TRANSPORT EQUIPMENT There are five categories of material transport equipment commonly used Industrial Trucks AGVS Monorails and other rail-guided vehicles Conveyors Cranes and hoists  

37. Summary and Features of these five categories of Material Handling Equipment

38. Industrial Trucks Divided into two categories Non-powered P owered Also referred to as hand trucks as they are pushed or pulled by human workers. Quantities moved are low and distance moved is small. They are self-propelled to relieve the worker of having to move the truck manually.

39. Non-Powered TWO WHEEL HAND TRUCK HAND OPERATED LOW LIFT PALLET TRUCKS FOUR-WHEEL DOLLY

40. Powered WALKIE TRUCK FORKLIFT TRUCK TOWING TRACTOR They are battery operated. Speed is limited to 5 km/ hr Have cab for the worker to sit in and drive. Load carrying capacity is 450 kg to 4500 kg. Are IC engines or electric motor driven. Used for moving large amount of material between major collection and distribution areas. Are IC engines or electric motor driven.  

41. Powered Trucks: Walkie Truck Wheeled forks insert into pallet openings No provision for riding; truck is steered by worker using control handle at front of vehicle

42. Powered Trucks: Forklift Truck Widely used in factories and warehouses because pallet loads are so common Capacities from 450 kg (1000 lb ) up to 4500 kg (10,000 lb ) Power sources include on-board batteries and internal combustion motors

43. Powered Trucks: Towing Tractor Designed to pull one or more trailing carts in factories and warehouses, as well as for airport baggage handling Powered by on-board batteries or IC engines

44. AGVS (AUTOMATED GUIDED VEHICLE) AGVS is a material handling system that uses independently operated, self-propelled vehicles guided along defined pathways. They are powered by on-board batteries. AGVS is appropriate where different materials are moved from various load points to various unload points. Types of AGVS : Driverless trains Pallet trucks Unit load carriers

45. Automated Guided Vehicles: Driverless Automated Guided Train First type of AGVS to be introduced around 1954 Common application is moving heavy payloads over long distances in warehouses and factories without intermediate stops along the route

46. Automated Guided Vehicles: AGV Pallet Truck Used to move palletized loads along predetermined routes Vehicle is backed into loaded pallet by worker; pallet is then elevated from floor Worker drives pallet truck to AGV guide path and programs destination

47. Automated Guided Vehicles: Unit Load Carrier Used to move unit loads from station to station Often equipped for automatic loading/unloading of pallets and tote pans using roller conveyors, moving belts, or mechanized lift platforms

48. AGVS (AUTOMATED GUIDED VEHICLE) Driverless trains Pallet trucks Unit load carriers

49. AGVS (AUTOMATED GUIDED VEHICLE) Vehicle Guidance Technology : The guidance system is the method by which AGVS pathways are defined and vehicles are controlled to follow the pathways. There are three technologies that are used : Imbedded guide wires. Paint Strips. Self-guided vehicles. (dead reckoning and beacons) Dead reckoning is used to move the vehicle between beacons and the actual position of beacons provide data to update the computer’s map . The advantage of SGV is its flexibility.

50. Vehicle Guidance Using Guide Wire

51. Monorails and other rail guided Vehicles This system consists of either one rail (called monorails) or two parallel rails. Monorails are normally suspended overhead from the ceiling. Presence of fixed rail pathways distinguishes it from AGVS. These work with electrical power unlike AGVS which were powered by their on-board batteries.

52. Overhead Monorail

53. Conveyors U sed when material must be moved in relatively large quantities between specific locations over a fixed path, which may be in the floor, above the floor or overhead . Conveyors can be either powered or non-powered. Powered conveyors are moved with a mechanism using chains, belts, rotating rolls etc. They are usually used in automated material transport system. In non-powered conveyors , materials are moved either manually by humans who push the loads along the fixed path or by gravity from one elevation to lower elevation.

54. Types of Conveyors Roller Conveyors

55. Types of Conveyors Skate-wheel conveyors

56. Types of Conveyors Belt conveyors

57. Types of Conveyors Chain conveyors

58. Types of Conveyors Overhead trolley conveyor

59. Types of Conveyors In-floor towline conveyors

60. Cart-On-Track Conveyor Carts ride on a track above floor level Carts are driven by a spinning tube Forward motion of cart is controlled by a drive wheel whose angle can be changed from zero (idle) to 45 degrees (forward)

61. Hoist Hoist with mechanical advantage of four: (a) sketch of the hoist (b) diagram to illustrate mechanical advantage (a) (b)

62. Bridge Crane

63. Gantry Crane A half-gantry crane

64. Jib Crane

65. Design Considerations in Material Handling Material handling equipment is usually assembled into a system. The system must be specified and configured to satisfy the requirement of a particular application . The following factors influence the design of the material handling system. 1. Material Characteristics : Category Measures Physical state Solid, gas, fluid Size Volume, length, width, height Weight Weight per piece, weight per volume Shape Long and flat, round, square Condition Hot, wet, dirty Risk of damage Fragile, brittle Safety risk Explosive, flammable, toxic, corrosive

66. Design Considerations in Material Handling 2. Flow Rate, Routing and Scheduling : Flow rate means the amount of material to be moved per unit time. (pcs/hr, loads/hr, tons/hr, ft 3 /day) If a large amount of material is to be handled, then a dedicated system is to be used. If a quantity is small but different types of material are to be handled, then material handling system must be designed such. Routing factors include pick up and drop off locations, move distances, routing variations and conditions along the route. Handling cost is directly related to the distance of the move. Scheduling relates to timing of each individual delivery. Prompt delivery when required Use of buffer stocks to mitigate against late deliveries

67. Design Considerations in Material Handling 3. Plant Layout Process layout   Hand trucks and fork lift trucks are commonly used. These days application of AGVS is growing in such applications.   Product layout   Conveyor systems are mostly used in this type of layout   Fixed Position Layout Cranes, hoists and trucks are commonly used.     When a new facility is being planned, the design of the handling system should be considered part of the layout

68. Design Considerations in Material Handling A unit load is simply the mass that is to be moved or handled at one time. It can be a one part, a container loaded with multiple parts or pallet loaded with multiple containers of parts 3. Unit Load Principle The reasons for using unit load principle are : Multiple items can be handled simultaneously. Required numbers of trips are reduced. Loading and unloading time is reduced. Product damage is reduced. Lower cost and higher operating efficiency.