Unformatted text preview: PERFORMANCE EXCELLENCE
IN THE WOOD PRODUCTS INDUSTRY EM 8772 • January 2002
$2.50 Part 4: Flowcharts
S. Leavengood and J. Reeb Part 1 in this series introduced the reader to Statistical Process Control, and Part 2
provided an overview of how and why SPC works. Part 3 began the step-by-step
process of building the practical skills necessary for hands-on implementation of
SPC. It discussed Pareto analysis, a tool to help decide where to focus initial efforts.
Part 4 discusses flowcharts. Part 5 in the series will continue building implementation skills by discussing cause-and-effect diagrams. Future publications in the
series will discuss case histories of wood products firms using SPC, providing realworld evidence of the benefits of SPC and examining pitfalls and successful
approaches. What’s the next step in implementing SPC?
After achieving top management’s commitment to using SPC, the next step in
beginning an SPC program is to determine where to focus initial efforts to get the
“biggest bang for the buck.” In Part 3, we presented Pareto analysis as a tool to
locate the primary causes of nonconformities and therefore where to focus initial
efforts. Now we need to know which specific activities in the process cause the
nonconformity and which quality characteristic(s) to monitor.
An example will help to clarify the above discussion and the objective of this
report. The Pareto analysis conducted in Part 3 of this series revealed “size out-ofspecification” as the major nonconformity, from the standpoint of both frequency
and relative cost to scrap or rework. We now need to know:
• The specific step or steps in the process (e.g., dry kilns, rip and chop, moulding)
responsible for causing size out-of-specification
• The quality characteristic (e.g., moisture content, width, thickness, motor amps,
or proportion of nonconforming parts) to measure
Cause-and-effect diagrams are commonly used to identify specific activities
responsible for causing nonconformities. However, we have chosen to discuss
flowcharts first, postponing a discussion of cause-and effect diagrams until Part 5 in Scott Leavengood, Extension wood products,
Washington County; and James E. Reeb,
Extension forest products manufacturing
specialist; Oregon State University. STATISTICAL PROCESS CONTROL Flowcharts can
activities such as
redundant steps, and
bottlenecks. this series. Our choice is based on the fact that flowcharts have
been found to be valuable tools for initiating discussion during
cause-and-effect analysis and for ensuring that everyone understands and agrees on what really happens—rather than what’s
supposed to happen—in the manufacturing process. Flowcharts
Flowcharts graphically represent the steps in creating a product
or service. The process of creating a chart is often beneficial
because personnel may be unaware of all the “nitty-gritty” details
involved in producing the product. Also, people often are surprised
to learn of the differences between the ideal process flow and what
actually occurs in the mill. This is particularly true when the team
developing the chart includes representatives of all departments of
the plant, not just production personnel.
In addition to understanding processing steps, flowcharts provide other benefits. If detail is sufficient, flowcharts can help to
reveal non-value-added activities such as inspection, rework,
redundant steps, movement, unnecessary processing loops, and
bottlenecks. From the standpoint of SPC, flowcharts also help to
reveal the stages in the process where data may be collected.
Flowcharts are also excellent tools for training new hires.
Brassard and Ritter (1994) list six steps to flowchart development.
1. Determine the start and stop points the chart will cover.
2. List the major steps (inputs, decisions made, activities, inspection, delays, and outputs) in the process.
3. Put the steps in the proper order.
4. Draw the flowchart.
5. Test the flowchart for accuracy and completeness.
6. Look for opportunities to improve the process (i.e., reduce nonvalue-added activities). Developing a flowchart: An example
We will demonstrate flowchart development using a secondary
wood products manufacturer as an example. Background
XYZ Forest Products Inc. produces wooden handles for push
brooms. Their customers produce finished brooms by adding a
rubber grip to the top of the handle, inserting a threaded metal
ferrule to the bottom of the handle, and attaching the broom head.
2 FLOWCHARTS Last year, business began to fall off for XYZ; orders dropped
40 percent in just 6 months. Several customers stated that the
competition’s quality was better. A few customers had begun
asking XYZ to provide documentation of process performance—
namely histograms, control charts, and process capability indices
(see Part 2 in this series for an overview of these subjects). Therefore, XYZ was inspired to use SPC.
Because customers reported several different quality problems
(fuzzy grain, size out-of-spec., warp, etc.), XYZ personnel did not
know precisely how and where to start their quality improvement
program. They conducted the Pareto analysis, as presented in Part
3 in this series, to help them decide where to focus initially. Size
out-of-specification was found to be the primary quality problem.
Following the Pareto analysis, the general manager of XYZ convened a team of personnel from engineering, sales, production,
quality control, and management to develop a flowchart for their
process. We will summarize their activities using the six steps
described above. Creating the flowchart
Step 1. Determine the start and stop points that the chart
Because XYZ had never developed a flowchart for the process,
the team decided to chart the process from start to finish. The start
point was green lumber receiving, and the stop point was finished
product storage. The team agreed to create a macro-flowchart; that
is, a chart showing only the general flow of the process with
minimal detail. The team decided that once they’d created a causeand-effect diagram for the problem, and had determined the specific steps in the process most likely responsible for the problem,
they would then create a flowchart with a narrower focus and more
detail. Steps 2 and 3. List the major steps in the process, and put
the steps in the proper order.
The team brainstormed (see Brassard and Ritter for a discussion
of brainstorming) to develop the steps involved in the process.
Then, they put the steps in the proper sequence. (Brassard and
Ritter list steps 2 and 3 separately because, in a group setting,
people usually name the activities most familiar to them, which 3 STATISTICAL PROCESS CONTROL It is imperative…
to list what actually
production versus the
ideal for the process. generally leads to a list of steps that is out of sequence). In our
example, the team identified these steps.
• Receive rough green lumber; tally.
• Sticker lumber.
• Move stickered lumber to green storage.
• Move lumber to dry kilns.
• Kiln dry lumber.
• Unsticker, tally, and stack dry lumber.
• Move lumber to dry storage.
• Move lumber to planer.
• Unload and plane lumber.
• Crosscut surfaced lumber.
• Rip lumber to handle blank widths.
• Tally handle blanks.
• Shape broom handles from blanks.
• Inspect handles with go/no-go gauge; tally and scrap no-go.
• Load and move good handles from shaper to taperer.
• Taper ferrule end.
• Round grip end of handles.
• Inspect handles for appearance; tally and send nonconforming to
scrap and rework.
• Load and move handles to sander.
• Sand handles.
• Load and move handles to packaging.
• Move packaged handles to finished product storage.
Note: It is imperative to list what actually happens during
production versus the ideal for the process. For example, if lumber
leaving the planer goes to storage, as opposed to going directly to
the crosscut saws as listed above, this should be specified. Step 4. Draw the flowchart.
Symbols are used in flowcharting to identify different categories
of activity. For example, ovals may be used to indicate inputs/
outputs, and boxes indicate a processing step (Figure 1).
It is important to maintain a consistent level of detail in the
flowchart. Brassard and Ritter suggest the amount of detail to
include in a flowchart. Macro-level flowcharts show key action
steps but no decision boxes. Intermediate-level flowcharts show
action and decision points, and micro-level flowcharts show
4 FLOWCHARTS Each step in the process should be labeled. Arrows should be
used to indicate the flow of steps. To make the chart easier to read,
it is helpful when using yes/no decision boxes to have the “yes”
boxes branch down and the “no” boxes branch to the left. This
will, of course, depend on the amount of space available. For
future reference, names of team members, the date, and the purpose for creating the chart should be included (Figure 2, page 6). Inputs
Processing Step 5. Test the flowchart for accuracy and completeness.
The team should make certain that symbols are used correctly,
process steps are identified clearly, and that process loops are
closed (that is, every path flows to a logical end). Also, if the chart
contains any process boxes with more than one output arrow, the
team may wish to consider adding a decision diamond. As a final
check, someone outside the team should be asked to verify the
chart’s accuracy and completeness. Step 6. Look for opportunities to improve the process
(reduce non-value-added activities).
This is where the team seeks opportunities to optimize the
process. An ideal process flowchart should be made and compared
to the actual process flowchart. The team should then examine the
non-value-added activities, which might include the following.
• Unnecessary redundancy. (Two machines performing the same
operation might be necessary redundancy if they increase
throughput without creating bottlenecks; multiple inspection
points for the same quality characteristic are often unnecessary
• Many movements (for example, movement to a staging area,
then to storage, then to another holding area, and then to
production). Decision Storage Delay Data entry Movement Inspection
Figure 1.—Flowchart symbols. Montgomery suggests several ways to eliminate non-valueadded activities.
• Rearrange the sequence of worksteps.
• Rearrange the physical location of the operator in the system.
• Change work methods.
• Change the type of equipment used in the process.
• Redesign forms and documents for more efficient use.
• Improve operator training.
5 STATISTICAL PROCESS CONTROL • Improve supervision.
• Identify more clearly the function of the process to all employees (flowcharts are good visual aids for explaining the process to
• Eliminate unnecessary steps.
• Consolidate process steps.
A macro-level flowchart (Figure 2) lacks the necessary detail to
identify non-value-added activities. Once XYZ team members
have constructed a cause-and-effect diagram for the defect category, they will know the step(s) in the process for which they need
a more detailed flowchart. Consider, for example, that the team
determines shaping through sanding as the processing steps that
deserve a closer look for size out-of-specification troubles. Their
flowchart for this part of the process may look like the charts in
Figures 3 and 4. Macro-flowchart
lumber Storage Sticker Kiln dry Team members
W. Harold Finished
handles Package Figure 2.—Sample macro-flowchart. Sand Storage Unsticker
and stack Handle
blanks Rip Crosscut Purpose
concerns re: size
out-of-spec. 6 Storage Plane Dried
lumber Shape Round Taper FLOWCHARTS Micro-flowchart From
ripsaws XYZ, Inc.
01/4/02 Team members
W. Harold Purpose
concerns re: size
Focus on shaping
through sanding Handle
blanks Load blanks
on pallet Move
into shaper 1 Move
into shaper 2 Shape Load handles
on pallet Delay Move
into shaper 3 Shape Shape Load handles
on pallet Load handles
on pallet Load handles
into taperer Delay Check
Shape OK? Inspect. No?
on page 8
Figure 3.—Sample micro-flowchart, part 1. 7 STATISTICAL PROCESS CONTROL From
page 7 Round Load handles
to sander dept.
Free from nonconformities? No? Yes? Inspect.
Sand Tally Tally
handles Scrap Rework
patchline Figure 4.—Sample micro-flow chart,
part 2. 8 Load handles
to packaging Potential areas for improvement are revealed in Figure 3.
Notice the delay at the taper
machine. Three shapers feed
one taper machine which
appears to lead to a bottleneck. More detailed data
(downtime, throughput, costs,
etc.) would need to be collected to determine a solution.
Another area to examine is
the two inspection points, one
before the taper machine and
the other before the sander.
Handles are inspected for
conformance to size specifications at the infeed to the taper
machine and are checked for
appearance at the infeed of the
sander. The team might
address numerous questions,
1. Are both inspection points
necessary? Could the
product be inspected for
both size and appearance
before the taper machine?
2. Could appearance be
checked earlier in the
process? It probably isn’t
cost effective to check for
conformance to appearance
specifications after significant value has been added
to the product.
3. If there is a problem with
conformance to size specifications before the taper
machine, can it be determined which of the shapers
is the likely source of the
problem? Are size data fed
back to the operators? FLOWCHARTS 4. Can the handles be checked with calipers instead of go/no-go
gauges? Much more information is obtained using measurement
data than go/no-go information. For example, a go/no-gauge
might reveal that handles are “small” after they go out of specification. Charting data obtained with calipers, on the other hand,
would enable the operator to detect trends and make corrections
before the product went out-of-spec.
Let’s examine one more potential area for improvement. Notice
all the movements in Figure 3. This company probably has a fleet
of forklifts. Product is loaded on pallets, moved, and unloaded
many times. How might throughput increase if the process flow
were improved by, for example, using just in time (JIT) or lean
manufacturing techniques such as work cells, which are groups of
machines dedicated to producing a particular product or part.
That question can be addressed by creating another type of
flowchart known as a value stream map. These maps track the flow
of value and information from customer order all the way back to
first-tier suppliers. Value stream maps add a dimension—time—
that flowcharts don’t cover. By tracking process cycle times,
equipment uptimes, and inventories, companies can estimate the
amount of time they spend doing things the customer would not be
willing to pay for (movement, queues, delays due to large batches,
problems related to the scheduling system, rework, etc.) versus
time spent altering the product in ways the customer will pay for
(generally, those are process cycle times). The current value stream
map is used to redesign the process to reduce non-value-added
time (thus eliminating waste) and reduce customer lead time.
A detailed discussion of value stream mapping is beyond the
scope of this report. For more information, see Rother and Shook. Conclusion
We now have graphical representations of the steps involved in
creating the product. In the process of creating the chart, we have
had the opportunity to increase company personnel’s understanding of “how we do things around here” and perhaps also to streamline the process and reduce non-value-added steps. We now also
have a valuable tool for initiating discussion during cause-andeffect analysis, the next step in beginning an SPC program. 9 STATISTICAL PROCESS CONTROL For further information
Brassard, M. and D. Ritter. 1994. The Memory Jogger II: A Pocket
Guide of Tools for Continuous Improvement & Effective Planning (Methuen, MA: Goal/QPC). 164 pp. http://www.goalqpc.
Grant, E.L. and R.S. Leavenworth. 1988. Statistical Quality Control, 6th ed. (New York: McGraw Hill). 714 pp.
Ishikawa, K. 1982. Guide to Quality Control (Tokyo, Japan: Asian
Productivity Organization). 225 pp.
Montgomery, D.C. 1996. Introduction to Statistical Quality Control, 3rd ed. (New York: John Wiley & Sons). 677 pp.
Rother, M. and J. Shook. 1999. Learning to See: Value Stream
Mapping to Add Value and Eliminate Muda, v. 1.2 (Brookline,
MA: The Lean Enterprise Institute). 102 pp. http://www.lean.org
Walton, M. 1986. The Deming Management Method (New York:
Putnam Publishing Group). 262 pp. 10 FLOWCHARTS PERFORMANCE EXCELLENCE
IN THE WOOD PRODUCTS INDUSTRY ABOUT THIS SERIES
This publication is part of a series, Performance
Excellence in the Wood Products Industry. The various
publications address topics under the headings of wood
technology, marketing and business management,
production management, quality and process control,
and operations research.
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