Cellular Manufacturing

1. Cellular Manufacturing Adapted from:

2. Introduction to Cellular Manufacturing (CM) • Product layouts (assembly lines, mass production one a few products on the same line) is the most efficient of the basic layout options • Many products are not made in volumes that require a product layout • Cellular manufacturing (group technology) – forms families of products that have common production requirements • Locate machines, people, jigs, fixtures, drawings, measuring equipment, material handling equipment together (focused factory)

3. Introduction to Cellular Manufacturing • The cellular approach is to organize the entire manufacturing process for particular or similar products into one group of team members and machines known as a "Cell". • These "cells" are arranged in a U-shaped layout to easily facilitate a variety of operations. • Parts or assemblies move one at a time (or in small batch sizes). • The parts are handed off from operation to operation without opportunity to build up between operations.

4. Introduction to Cellular Manufacturing

5. Introduction to Cellular Manufacturing

6. Introduction to Cellular Manufacturing • Fast setup and quick changeovers are essential to Cellular Manufacturing systems since production runs are shorter. • Setup reduction principles are used to achieve one piece flow and mixed model synchronization. • All cells concentrate on eliminating waste.

7. Empowered Employees in CM • Goals and tracking charts are maintained and posted. • Problems are solved through daily cell meetings and problem solving teams. • The inventory management system is a KANBAN Demand Pull instead of a work order/kit picking system. • Cells are responsible for planning, scheduling and expediting directly with vendors. • They establish and maintain a KANBAN system with the vendors.

8. Advanced CM • The cell operates like an independent business with total responsibility for quality, manufacturing and delivery of the product to the customer. • All cells have the resources within their organization to accomplish their mission. • The requirements are known and goals are established. • Cell members are flexible and work in teams to accomplish their goals including continuous improvement.

9. Benefits of CM • Common tooling required for many products (fewer setups) • Tooling can be justified since many products require it (more volume when products are grouped) • Minimized material handling • Simple production schedule • Short cycle time • Low WIP

10. Benefits of CM • Cross-training – employees operate several machines • Minimized material handling costs – since no paperwork is required and distance is small • Employees accept more responsibility of supervision (scheduling of parts within cell, scheduling of vacation, purchasing of material, managing a budget) • Simple flow pattern and reduced paperwork • Buffers are small if batch size is small

11. Disadvantages of CM • Lower equipment utilization • Increased set-up costs • Less flexibility than functional departments

12. Family Formation • Various levels – macro and micro • Macro – entire factories (focused factories) can specialize in a particular type of part • Micro – families can be based on similarities in part geometry (group shafts, flat parts, gears, etc…), process requirements (castings, forgings, sheet metal parts, heat-treated parts, printed circuit boards) • How are these groupings determined? • Coding

13. Finding Part Families • Visual Inspection of physical parts or photographs to identify similarities. • Coding and Classification of parts by examining design and/or manufacturing attributes. • OPITZ System • MICLASS System • Here a code is assigned to specific features of the part. • Is the part cylindrical or prismatic ? • Does it have threads? • Does it have through slots? • Does it require heat treatment? • This requires a large initial time investment in coding and classifying all parts.

14. Finding Part Families • Production Flow Analysis : Since the parts in a part family have similar manufacturing processes, it is possible to identify similar parts by studying the route sheets. • Parts with similar routes can be grouped into families.

15. Group Analysis • To create part families and machine groups a part-machine matrix is created. • This is a 0-1 matrix in which a one signifies that a machine is required for a given part. • While creating this matrix the machine refers to a "type" of machine. • Thus, if there are 5 identical CNC lathes we will create one row in the matrix for these lathes. • Also, the number of times a part visits a machine is not considered at this stage

16. Group Analysis • Once a the part-machine matrix is created, it is customary to remove approximately 10% of the most heavily used machines. • Several copies of these machines are likely to be available and thus it is always possible to split these machines between different groups later. • The remaining matrix is then inspected for part families.

17. Group Analysis • To identify the part-families the rows and columns are interchanged such that a block-diagonal structure is obtained. There are several algorithms that can be used to do this. A simple algorithm for this problem can be described as follows: • Pick any row and draw a horizontal line through it. • For each 1 in the row that has been crossed once draw a vertical line through the corresponding column. • Pick each new column identified in the previous step. For each 1 in the column that has been crossed once draw a horizontal line through the row. • Repeat this process until there are no singly-crossed 1s in the matrix. • Remove the rows and columns that have been crossed to form a part family-machine group. • Continue for the rest of the matrix

18. Group Analysis

19. Coding • GT coding and classification schemes attempt to capture design and manufacturing attributes such as the main shape, size, features of the product, production quantity, and material. • A large number of GT coding schemes have been developed for discrete machined parts including MICLASS, Opitz and DCLASS

20. Coding • Code should contain information about: • Part or assembly itself • Manufacturing process (manufacturing engineering, industrial engineering, tool engineering, scheduling, line supervision, quality assurance, etc…)

21. Coding Requirements • Precise nonambiguous meaning, no double or triple definitions for the same phrase • Tightly structured and concise • Easy to use

22. Coding Options • Codes can be chain or hierarchical • Chain – each digit’s specific location is fixed for a particular meaning • Chain Example – • First digit is reserved for the product type • Second digit for material • Digits 3-6 for part geometry

23. Coding Options • Chain Advantage – easy to learn • Chain Disadvantage – requires more digits making it difficult to handle manually and with low power computers (not as big a problem today as the price of computers has dropped)

24. Coding Options • Hierarchical code – each code character depends on the preceding one – a tree type structure • Advantages – code can be sort since many branches can be eliminated • Disadvantages – difficult to learn

25. Code Generation • CM codes are typically generated manually or interactively by answering a series of questions and applying appropriate coding rules. • However, this is a slow and inconsistent procedure which inhibited the widespread use of CM.

26. Opitz Coding Scheme • Shah and Bhatnagar developed an automated CM coding system based on the Opitz coding scheme for machined parts. • The system assigns pre-defined taxonomy codes for each feature of its feature-based CAD system. • The generic information captured by the taxonomy codes is used to determine individual feature characteristics and the relationships between features and the entire parts. • The CM code generator uses the resulting feature information and Opitz coding rules to generate the CM codes.

27. Using Codes • Comparing the CM codes of two products is a quick and efficient method for estimating product similarity in selected attributes. • CM codes can be used to search a database of products and retrieve the designs and process plans of those products which are similar to a given design • To generate new process plans automatically using a knowledge-based system • To assess manufacturability of a product design

28. Cell Layout • Usually U, L or circular shaped • Minimizes transportation distance for operators (human or robotic) • Encourages multiple machines per operator • Most machines are automatic or semiautomatic, resulting in considerable idle time • In a job shop (functional layout) there is one operator for each machine

29. Supply Push • Input availability triggers production or work • Emphasis on “keeping busy” to maximize resource utilization as long as there is work to be done • Will synchronize supply with demand at each stage if: • If all information (about product recipe, processing lead times, and part inventories) is accurate • If forecasts of finished goods are correct • If there is no variability in processing

30. Demand Pull • Output need triggers production • Each station produces only on demand from its customer station • Each station signals demand by picking up a part from its input buffer • The supplier station produces a new unit as a replacement in the buffer • Toyota formalized demand pull with cards called kanbans

31. Kanbans • Kanbans are attached to output flow units in the buffer between customer and supplier processes • Each card lists the following information: • Customer process • Supplier process • Parts description • Production quantity

32. Kanbans • As the customer withdraws output flow units from the buffer, the attached kanban goes back to the supplier • It signals an authorization for the supplier to produce the listed quantity to be replaced in the buffer • Upon producing the required quantity, the supplier returns the output with an attached kanban to the buffer • Kanbans control buffer inventory and provide information and discipline to the supplier as to when and how much to produce • In the case of a process that handles multiple products, each supplier station must also know what to produce

33. Problem 2 - Test 2 Summer 2001

34. Problem 2 - Test 2 Summer 2001

35. Problem 2 - Test 2 Summer 2001

36. Problem 2 - Test 2 Summer 2001

37. Problem 2 - Test 2 Summer 2001 Thus all parts require all machines and only cell is formed