Unit 1 manufacturing system design
- 1. 15MF110-MANUFACTURING SYSTEMS DESIGN UNIT-I INTRODUCTION TO MANUFACTURING SYSTEMS ENGINEERING Done by S. Annamalai S. Ayyandurai A. Karthik M.E. Manufacturing Engineering20-12-2018 1
- 2. Introduction to Manufacturing Systems Engineering Process Planning – Logical design of a process planning – Shortcomings of traditional process planning – Computer aided process planning – Computerization of files management – Variant (Retrieval) approach – generative approach – Semi generative approach – General remarks on CAPP developments and trends. 20-12-2018 2
- 3. Manufacturing Systems We define a manufacturing system to be a collection of integrated equipment and human resources, whose function is to perform one or more processing and/or assembly operations on a starting raw material, part, or set of parts. The integrated equipment includes production machines and tools, material handling and work positioning devices, and computer systems. Human resources are required either full time or periodically to keep the system running. The manufacturing system is where the value-added work is accomplished on the part or product. 20-12-2018 3
- 5. Components of a Manufacturing System A manufacturing system consists of several components. In a given system, these components usually include: • Production machines plus tools, fixtures, and other related hardware • Material handling system • Computer systems to coordinate and/or control the above components • Human workers 20-12-2018 5
- 6. 1.1 Process Planning The activity that translates part design specifications from an engineering drawing into the manufacturing operation instructions required to convert a part from a rough to a finished state. It represents the link between engineering design and shop-floor manufacturing. It is a major determinant of manufacturing cost and profitability. The gap between CAD and CAM can be shortened considerably by developing better systems for process planning. 20-12-2018 6
- 7. Scope of process planning • Interpretation of design drawings. The part or product design must be analysed (materials, dimensions, tolerances, surface finishes, etc.) at the start of the process planning procedure. • Processes and sequence. The process planner must select which processes are required and their sequence. A brief description of all processing steps must be prepared. • Equipment selection. In general, process planners must develop plans that utilize existing equipment in the plant. Otherwise, the component must be purchased, or an investment must be made in new equipment. 20-12-2018 7
- 8. • Tools, dies, molds, flxtures, and gages. The process planner must decide what tooling is required for each processing step. The actual design and fabrication of these tools is usually delegated to a tool design department and tool room, or an outside vendor specializing in that type of tool is contracted • Methods analysis. Workplace layout, smaf tools, hoists for lifting heavy parts, even in some cases hand and body motions must be specified for manual operations. The industrial engineering department is usually responsible for this area. • Work standards. Work measurement techniques are used to set time standards for each operation. • Cutting tools and cutting conditions. These must be specified for machining operations, often with reference to standard handbook recommendations. 20-12-2018 8
- 9. Process planning for parts For individual parts, the processing sequence is documented on a form called a Route sheet. (Not all companies use the name route sheet; another name is "operation sheet.") Just as Engineering drawings are used to specify the product design, route sheets are used to specify the process plan. 20-12-2018 9
- 13. 1.2 Logical design of a process plan 1. Preliminary analysis of a design inpyt 2. Material selection 3. Process sequence 4. Machine and tool selection 5. Fixture selection 6. Machining parameter selection 7. Cost/time estimation 20-12-2018 13
- 14. To give a global idea of the preparation of a process plan, it seems appropriate to analyse a typical mechanical part and to define the different stages of decisions to be taken. It is clear that many of the logical steps taken in machining can be transferred easily to other processes. Having correctly analysed the part drawing from a geometric point of view, it should be possible to define the process plan on the basis of information available on production facilities(machine, tooling, accuracy capabilities etc.,) Before going into detail, study the outline of the part inorder to think of ways of designing its final process plan. 20-12-2018 14
- 15. 1.3 Shortcomings of Traditional Process Planning The approach becomes rapidly inefficient and unmanageable when the number of process plans and revision to those plans increase. Consequently, inconsistent plans and large time requirements for planning often result. The plans by this approach reflect the personal experiences and preferences of the process planner. This is considered a poor use of engineering skills because of the high clerical content in most of its functions20-12-2018 15
- 16. Approaches in Process Planning Process planning Computer Aided Process Planning Variant Approach Generative Approach Semi- Generative Approach Manual Process Planning 20-12-2018 16
- 17. Manual Process Planning Traditionally, skilled planners perform process planning. Planning is based on planner’s decisions. The quality of the plan highly depends on individual skill, knowledge and experience. Planning is very time consuming, because of voluminous routine work and calculations. Only little time is left for creative work and updating planner’s knowledge. 20-12-2018 17
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- 19. Importance of Computer Aided Process Planning The aim of Computer Aided Process Planning is to eliminate or at least reduce the manual intervention in process planning. By using a computer, the tedious and repetitive aspects of process planning can be speeded up and this helps to optimise the total manufacturing function by releasing the experienced planners and enabling them to concentrate on those aspects outside the scope of a computer. At the same time, more consistent process plans can be obtained by applying a standard set of rules, which increases confidence in the system and helps in the rationalisation of production. To automate process planning, the logic, judgement and experience required for process planning must be captured and incorporated into a computer program. 20-12-2018 19
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- 21. Conventional Vs CAPP The advantage of CAPP over conventional process planning is manifold. It improves the quality and consistency of process plans. Savings in lead time: In today’s concepts of TQM and batch manufacturing lead time seriously effects the delivery time of the product which plays a major role in deciding the market share of any company. Process rationalisation: CAPP generated process plan is more likely to be consistent (because the use of same software for all plants), logical and optimal (because the company has presumably incorporated the experience and judgement of its best manufacturing people into process planning software and computer can evaluate more number of alternatives in a less time). Integration with manufacturing support functions: These functions involve NC part program generation, computerised work standards etc., If done independently these functions involve duplication of clerical work. Increases the efficiency of process planning. 20-12-2018 21
- 22. The advantage of CAPP over conventional process planning is manifold. Decreases the variety of tooling. Error reduction: Helps in overcoming the casual errors committed by human process planners. If the error goes unnoticed, it penalise heavily from the cost point of view. It can reduce the skill required by planners. It can increase productivity. It can consider all available equipment while process planning. 20-12-2018 22
- 23. Objectives of Process Planning Systems Consistency A good process planning system should provide consistently same process plan for same set of input data. Accuracy Accuracy is another important objective to maintain in any process planning system. Inaccuracies in process plans and corresponding information in them can greatly undermine the integrity of the system. 20-12-2018 23
- 24. Ease of application This is another important trait, which determines how quickly a response can be made to generate a new process plan or make revision to an existing process plan. This is of particular importance in today's short lead-time environment Completeness Information about manufacturing processes, machines, tools, cutting parameters etc., must be completely known while decisions about process planning g are made. If complete data is not provided, then the choice can easily lead to inconsistency in processing methods and corresponding inconsistencies in part quality and costs. 20-12-2018 24
- 25. Challenges in the area of CAPP Process planning systems, in order to provide integration, automation and flexibility should ■ be generative ■ be technology based ■ use features as a technological and communicational interface between design and process planning ■ be able to extract automatically all product data ■ use a supervisory control system to ensure user-friendliness and flexibility in use ■ integrally support all planning tasks, including capacity planning and scheduling ■ take decisions based on optimization techniques ■ be fit for close-loop planning20-12-2018 25
- 26. 1.4 COMPUTER AIDED PROCESS PLANNING
- 44. 1.5 Computerization of files management • This is the first step in computer aided process planning • A computer is a machine built to store and retrieve data at high speed; it performs computations at high speed and with accuracy; • The current idea is to utilize the power of computers to assist the process planner with clerical work, leaving him/her free for technical work. • The idea is to divide the work between the process planner and the computer, letting each perform the tasks they know best. • This will reduce the pre-production lead times and increase process planner productivity by 600%, allowing more time to be spent on the planner evaluating alternatives. The result will be complete and consistent processes. 20-12-2018 44
- 45. Approaches to CAPP • Variant Approach • Generative Approach 20-12-2018 45
- 46. 1.6 Variant Approach The variant approach is comparable with the traditional manual approach where a process plan for a new part is created by recalling, identifying, and retrieving an existing process plan for similar part, and making necessary modification making it suitable for the new part. 20-12-2018 46
- 47. Variant Approach In general this system has two operational stages. i. Preparatory stage: in this stage the parts are coded and families are formed based on group technology (GT) principles. Standard process plans are prepared for each family and stored in database. ii. Production stage: Process plan for a new part can be made in this stage. Whenever a new part comes for process planning, it’s code and family will be identified and the standard processing plan for that family is retrieved. Necessary modifications are made by the process planner to satisfy the component design. 20-12-2018 47
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- 49. 1.7 Generative Approach Generative CAPP systems represent an alternative approach to automated process planning. Instead of retrieving and editing an existing plan contained in a computer data base, a generative system creates the process plan based on logical procedures similar to the procedures a human planner would use. In a fully generative CAPP system, the process sequence is planned without human assistance and without a set of predefined standard plans. The problem of designing a generative CAPP system is usually considered part of the field of expert systems, a branch of artificial intelligence. 20-12-2018 49
- 50. Generative Approach Contd.., An expert system is a computer program that is capable of solving complex problems that normally require a human with years of education and experience. There are several ingredients required in a fully generative process planning system. First, the technical knowledge of manufacturing and the logic used by successful process planners must be captured and coded into a computer program. In an expert system applied to process planning, the knowledge and logic of the human process planners is incorporated into a so-called "knowledge base”. The generative CAPP system then uses that knowledge base to solve process planning problems {i.e., create route sheets). 20-12-2018 50
- 51. 1.8 Semi-generative Approach This approach is the combination of variant and generative approaches. However, compared with the variant systems, editing work is less. The advantage of using such systems is reduced time for preparation of process plans; modifications of generated process plans are necessary in order to implement in the real work. 20-12-2018 51
- 52. 1.9 RECENT TRENDS IN CAPP In the global competitive market, various areas such as design process planning, manufacturing and inspection plays a vital role in reducing cost and lead time. In the various areas, different kind of interference mechanism has been developed. A lot of difficulty arises while integrating the goal in CIM environment. The major challenges of and research areas are to make CAPP system affordable to the medium and small scale manufacturing industries. 20-12-2018 52
- 53. Recent trends in CAPP systems include : •Automated translation of the design dimensions. •Tolerances into manufacturing dimensions. • Tolerances considering process capabilities. •Dimensional chains. • And to make CAPP system affordable for small and medium scale manufacturing industries. 20-12-2018 53