Value Stream Mapping in Custom Manufacturing and Assembly Facilities

Shahrukh A. IraniDepartment of Industrial, Welding and Systems Engineering

The Ohio State UniversityColumbus, OH43210

Introduction

Suzaki (Suzaki, 1987) defines flow as “the progressive movement of product through a facility from the receiving of raw material to the shipping of finished products without stoppages at any point in time due to backflows, an inefficient layout, machine breakdowns, scrap, or other production delays”. In their drive to become “lean”, vertically integrated factories (army munitions, shipbuilding, jet engine), Make-To-Order and Engineer-To-Order manufacturers of complex fabricated assemblies (furniture, security cabinets, cranes, tractors), repair and maintenance facilities, jobshops (machining, welding fabrication, stamping, diecasting) that process a large variety of products, must design their facilities for flow by implementing Value Stream Mapping (VSM). However, their efforts to implement VSM face a major obstacle – the need to manually map and analyze the flow paths of anywhere between 100 to 5,000+ routings being produced in the typical custom parts manufacturing facility.

To address this difficulty faced by custom manufacturing and Make-To-Order assembly facilities, Jim Womack, President of the Lean Enterprise Institute, recommends that “a way to simplify reality (is) by grouping many products into product families ….. by understanding which of the products can be grouped by the common process steps they follow ….. (Although) the process steps need not be absolutely identical, because later on we may create flow in such a way that several products can pass through each step with some slight detours (in a cell) if required, the key is to think in terms of shared processes”. According to Mr. Womack, the best tool for drawing and analyzing the Value Stream Map for hundreds or thousands of products is the Product Family Matrix.

Product Family Matrix Analysis (PFMA) for Custom Manufacturers

Product Family Matrix Analysis (PFMA) is an effective step to identify product families as a basis for design of a “lean” layout to achieve flow in a custom manufacturing facility (Irani, 1999). To do this analysis, we first create a 0-1 product-workcenter1 incidence matrix using the route sheets of a large representative sample of products obtained from the manufacturing facility. In this matrix, we list the products across the top of the matrix, one product per column, and list each workcenter down the matrix, one row per unique piece of workcenter. Then, referring to the routing of each product, we enter all the workcenters that it must visit into the matrix. We place a “1” at the intersection of the product’s column with every row that

1 A “Product” could be a “Part”, “Component” or “Sub-Assembly”; a “Workcenter” could be a “Machine”, “Process”, “Department” or “Equipment”.

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represents a workcenter associated with an operation in the product routing. For example, in Figure 1(a), Product #1 uses Workcenter #s 1, 2, 4 and 8 and Workcenter #1 processes Product #s 1, 3, 6 and 8.

Having created the initial product-workcenter matrix, the identification of product families using PFMA is done as follows: The rows and columns in the initial matrix are rearranged automatically by computer so as to pack the 1's in the matrix into approximate blocks along its diagonal, as shown in Figure 1(b). The new arrangement of 1's in the final matrix shown in Figure 1(b) is called a Block Diagonal Form (BDF). Each block in the BDF matches a product family with a group of workcenters that could be co-located into a manufacturing cell (or Focused Factory) dedicated to the manufacture and/or assembly of the product family. For example, in Figure 1(a), the products and workcenters were initially listed in the sequence 18 and 110, respectively. However, after the application of the PFMA technique, in Figure 1(b), the same products and workcenters are sequenced differently – the products are now listed in the sequence {16385274} and the workcenters are now listed in the sequence {28417631059}. In the final product-version matrix, three blocks of 1’s appear along the diagonal of the matrix: Block #1 = (Product Family: [1, 6, 3] and Workcenter Group: [2, 8, 4, 1]); Block #2 = (Product Family: [8, 5, 2] and Workcenter Group: [7, 6, 3]) and Block #3 = ((Product Family: [7, 4] and Workcenter Group: [10, 5, 9]). The blocks become the basis for design of a “lean” facility layout by (a) collocating each group of workcenters into a manufacturing cell and (b) creating a single composite Value Stream Map for the process flows of the products in each family.

Products Workcenter

1 2 3 4 5 6 7 8

1 1 1 1 12 1 13 1 14 1 1 15 1 16 1 1 17 1 18 1 1 19 1 1

10 1 1

Figure 1(a) Initial product-process matrix representation of flows in the jobshop

Products Workcenter

1 6 3 8 5 2 7 4

2 1 1 Cell #1

8 1 1 14 1 1 11 1 1 1 17 1 1 Cell

#2

6 1 1 13 1 1 1

10 1 1 Cell #3

5 1 19 1 1

Figure 1(b) Final product-process matrix representation of flows in the jobshop

Industrial Applications of PFMA

PFMA can yield extremely useful information for guiding a comprehensive study to achieve flow in any custom parts manufacturing or Make-To-Order assembly facility. For example, Tables 1 and 2 present routing data for an unsolved industry case study that deals with designing a flowline layout for a machining cell (Sekine and Arai, 1992). The initial Product-Workcenter matrix generated from the routing data in Table 2 is shown in Figure 2(a). This matrix was solved by computer to obtain the Block Diagonal Form shown in Figure 2(b). Analysis of the final matrix in Figure 2(b) yields the following insights about the product flows in the cell : There appear to be two smaller product families contained in the data: Part Family #1

consists of Parts {3,4,6,7,8,9,10} and Part Family #2 consists of Parts {1,2,5,11,12,13}. The cells associated with these part families are as follows: Cell #1 consists of Machines {3,4,6,7,9,10,11,12} and Cell #2 consists of Machines {1,2,3,4,5,7,8,9,10}.

The overall flow in the cell will be disrupted because the two part families have Machine #s 4, 7, 9 and 10 in common. However, since Machine #10 involves manual operations, and an extra Machine #9 (Drilling Machine) could be purchased at low cost, only the Machine #4 (Upright Mill) needs to be centrally located in the cell to allow sharing by the two part families. Or, if an extra Machine #4 is purchased for the cell, the only disruptive flow in the cell would correspond to the “exception operation” where Part #5 in Part Family #1 must visit Machine #7 (these visits to Machine #7 will disrupt the setups to produce the parts in Part Family #2).

In addition to the above insights on the layout of the cell, PFMA will automatically guide the implementation of various Lean Manufacturing strategies – setup reduction, optimization of process parameters, outsourcing, revision of existing process plans and product designs, introduction of automation – to eliminate all obstacles to flow in the cell. Figures 3(a)-3(b) show the initial and final matrices from a PFMA study to organize a pump parts manufacturing facility into cells. Figures 4(a)-(c) show the results from a PFMA study to design a modular layout for a complex fabrication facility that manufactures industrial scales.

Table 1 Operation Sequences for the Part Family to be produced in a Machining Cell

Part # Part Name Operation Sequence Batch Qty.1 Slider (a) 69101112 12 Slider (b) 469101112 13 Press Brace 58910 14 Bracket #1 47910 15 Table 371012 16 Damper 17910 2

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7 Bracket #2 18910 18 Support 479 29 Housing 279 110 Flange 29 111 Shaft 391012 112 Base 3641012 113 Spacer 4641012 1

Table 2 Description of Machines in the Machining Cell

M/C # Machine Name No. available1 NC Lathe (LB15) 12 NC Lathe (LB20) 13 Horizontal Mill (M) 14 Upright Mill (VM) 15 Compact Mill (BM) 16 Upright MC (6VA) 17 NC for Screw Holes (TNC) 18 Marker (MRK) 19 Drilling Machine (B) 110 Manual Operations (MAN) 111 Honing (H) 112 Grinder (G) 1

Figure 2(a) Initial Machine-Part Matrix generated from Table 1

P/M m1 m2 m3 m4 m5 m6 m7 m8 m9 m10 m11 m12p1 1 1 1 1 1p2 1 1 1 1 1 1p3 1 1 1 1p4 1 1 1 1p5 1 1 1 1p6 1 1 1 1p7 1 1 1 1p8 1 1 1p9 1 1 1p10 1 1p11 1 1 1 1p12 1 1 1 1 1p13 1 1 1 1

Figure 2(b) Final Machine-Part Matrix generated from Figure 2(a)

P/M m5 m8 m1 m2 m7 m3 m9 m10 m4 m6 m12 m11p5

Part

Fam

ily #

1

1 1 1 1 p11 1 1 1 1 p1 1 1 1 1 1p2 1 1 1 1 1 1p12 1 1 1 1 1 p13 1 1 1 1 p6 1 1 1 1

Part

p7 1 1 1 1 p3 1 1 1 1

Fam

ily #

2

p4 1 1 1 1 p8 1 1 1 p9 1 1 1 p10 1 1

Computer Methods for PFMA

All of the results presented in this paper were obtained using PFAST (Production Flow Analysis and Simplification Toolkit), a prototype software package for material flow analysis and design of flexible facility layouts for custom products manufacturing and Make-To-Order fabrication-type assembly companies. The analysis programs in this package include those recommended by Suzaki to do process analysis for multiple varieties of items – Product-Quantity Analysis, Process Route Analysis and Product Item Grouping (Suzaki, 1987, pp.72-74). The package requires a simple EXCEL input file that contains the following information required to generate the Product-Workcenter Matrix: List of products, the Annual Production Quantity for each product and the routing for each product (inclusive of vendor operations). Further information on PFAST can be obtained by visiting http://www-iwse.eng.ohio-state.edu/~fmpf/irani.html . Click on the link “Future Manufacturing and Production Facilities” and then click on the link “Software for Material Flow Analysis – PFAST” to access the documents.

Conclusion

Custom manufacturing and Make–To –Order assembly facilities that wish to conduct a Value Stream Mapping exercise will often grapple with the difficult task of manually doing a Product Family Matrix Analysis of a large Product-Workcenter Matrix that could contain anywhere between 100 to 5000+ product routings. This difficult task has now been partially computerized using a prototype software called PFAST that has been used to assist several manufacturers to implement flow in their facilities.

Bibliography

Chen, C. Y. & Irani, S. A. (1993). Cluster first-sequence last heuristics for generating block diagonal forms for a machine-part matrix. International Journal of Production Research, 31 (11): 2623-2647.

Daita, S.T.S., Irani, S.A. & Kotamraju, S. (1999). Algorithms for production flow analysis. International Journal of Production Research, 37 (11): 2609-2638.

Irani, S.A. (1999). Modern concepts in facility layout. Lecture Notes for a two-day course, October 7-8, 1999, Dearborn (Detroit), MI: Society of Manufacturing Engineers.

Irani, S.A., Zhang, H., Zhou, J., Huang, H., Udai, T.K. & Subramanian, S. Production flow analysis and simplification toolkit (PFAST). To appear in International Journal of Production Research.

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Sekine, K., Arai, K. & Talbot, B. (1992). Kaizen for quick changeover: Going beyond SMED. Portland, OR: Productivity Press.

Shargal, M., Shekhar, S. & Irani, S.A. (1995). Evaluation of search algorithms and clustering efficiency measures for workcenter-product matrix clustering. IIE Transactions, 27: 43-59.

Suzaki, K. (1987). The new manufacturing challenge: Techniques for continuous improvement. New York, NY: The Free Press.

Womack, J. (February, 2000). The product family matrix: Homework before value stream mapping (VSM). http://www.lean.org/community/thinkers_start.cfm.

Figure 3(a) Portion of the Initial Product-Workcenter Matrix for a Machine Shop that produces Pump Parts

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Figure 3(b) Portion of the Final Product-Workcenter Matrix for the Machine Shop that produces Pump Parts

Figure 4(a) Operations Process Chart for a Fabricated AssemblyProduct

Figure 4(b) Common_Substrings of Operations in the Operations Process Chart for the Product

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Figure 4(c) Modular Layout developed for the Assembly Facility