Roll Forming Handbook / Edited by George T. Halmos
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References
[384] U.S. Department of Labor,OSHA 3067, 1992 (Revised) Concepts and Te chniques of Machine
Safe Guarding.
[385] Occupational Safetyand Health Administration (OSHA) 1988. Standard CFR 1910.217.
Occupational Safetyand Health Standards —Subject O—Machineryand Machine Guarding.
[386] General IndustrySafetyand Health Standards, (OSHA) 29 CFR 1910.
[387] 20 CFR 1910.147. The control of Hazardous Energy(Lockout/Tag Out) Inspection Procedures
and Interpretive Guidance.
[388] B11-TR3 ANSI Te chnical Reportfor Machine To ols —Risk Assessment and Reduction —
aGuideline to Estimate Evaluate and ReduceRisks Associated with Machine Tools.
[389] ANSI B11.12-1996. Roll-Forming and Roll-Bending Machines—SafetyRequirements for
Construction Care,and Use.
[390] ANSI B15.1-1992. SafetyStandard for Mechanical Power Transmission Apparatus.
[391] ANSI B11.19-1990. Machine To ols Performance Criteria for the Design, Construction, Care and
Operation of Safeguarding when Referred by Other B11 Machine To ol SafetyStandards.
[392] ANSI-NFPA-79-1994. Electrical Standardfor Industrial Machinery.
[393] ANSI Z535.4-1991. Product Safety Signs and Labels.National Electrical Manufacturers
Associations.
[394] EN292 Standard, ISO 12100-1 and 2. SafetyofMachinery—Basic Concepts, General Principles
for Design —Part1:Basic Te rminology, Methodology, Part 2: Te chnical Principles and
Specifications.
[395] EN1050, SafetyofMachinery—Principles of Risk Assessment, November,1996.
[396] Liberty Mutual, StandardDrawing2110 June, 1990 “In-Running Rolls”.
[397] Liberty Mutual, StandardDrawing1063-2 January, 1997 “Power Press”.
Roll Forming Handbook13-16
14
Increasing Efficiency of
Roll Forming Lines and
Case Studies
GeorgeT.Halmos
Delta Engineering Inc.
14.1 Output, Productivity, and Efficiency ............................. 14-1
14.2 Line Utilization ................................................................ 14-2
14.3 Improving Productivity................................................... 14-3
Low Cost Improvements
†
Medium and High Cost
Improvements
14.4 Case Studies ..................................................................... 14-4
General Information about Case Studies
†
Case Study
“A” —Hat Section
†
Case Study “B” —Shelving
†
Case Study “C” —Studs
†
Case Study “D” —Guard Rail
†
Case Study “E” —Siding and Roofing
†
Case Study
“F” —Special Products
14.5 PreliminaryTool and Equipment Cost Analysis ........... 14-10
14.6 PreliminaryCost Analysis ............................................... 14-10
Base Prices
14.1 Output, Productivity,and Efficiency
The output of aplant or aproduction line can be measured by the number of units produced in agiven
time period. The output can be increased by working overtime, using additional shift(s), or adding more
equipment and operators, but these actions will not change significantly the unit cost of the product.
Frequently,the unit cost will slightly increase, for example, when paying premium for working overtime,
other times it can modestly decrease.
Productivityonthe other hand is measured by the number of units produced per operator in a
given time. The most common unit to measureproductivityisthe output per person-hour.The
output can be measured in number of pieces, weight, length, covered area, value, or other units. In
the roll forming industry, the most practical wayistomeasurethe output of aline in length units
(feet, meters), or occasionally by the number of pieces produced per production line or per person
per shift.
The traditional but not necessarily the best waytomeasure productivityistoestablish production
standards by time studies or other methods. These standards reflect the average output that can be
achievedbythe operators without extra effortand are usually considered as the “norm”or100%. The
standards are based on past experience,and in the case of rollforming, they include the accepted
14-1
“nonproductive”times, such as coil change, removal of finished products, checking quality, completing
administrative, and other tasks.
Comparing the actual output with the “standard” can lead to contentment. Plants regularly achieving
100, 105, or 110% of the standardconsider themselves efficient. This attitude can lead to complacency
and does not provide incentive to look for further improvements.
Measuring the utilization of aline is amuch better waytojudge efficiency and it leads the wayto
productivityimprovements. Continuous increases in productivityare essential to remain competitive
and are akey element to the success, profitability, and growthofeverycompany.
14.2 Line Utilization
Aline is theoretically fully (100%) utilized if it rollforms products nonstop,full time, at the maximum
possible speed. Of course, in real life, it is not expected that aline will run nonstop all the time, but the
closer the actual running time is to 100%, the better.Eventhe “continuously running lines,”like tube
mills —roll forming mills with extrusions or foam filling operation —stop once in awhile for product
change, maintenance, or other reasons.Most rollforming mills are also idle for additional reasons,for
example, for coil change and other activities.
An actual case described herehighlights the difference between working to standardsand line
utilization. An older,roof deck roll forming line was regularly running at 100 to 110% of the standard
established by time studies. The management was satisfied and not much effortwas put into further
improvements until they werechallenged by their first “computer exper t” who pointed out the
following:
*
The line produced 57,000 ft (17,375 m) of roof decks in 2shifts (16 hr)
*
The line was running at its maximum speed of 180 ft/min (55 m/min)
*
The maximum capabilityofthe line was 180 (ft/min) £ 60 (min/hr) £ 16 (hr) ¼ 172,800 ft
(52,670 m).
The actual line utilization during above described production run was
Actual Production
Max Mill Capacity
£ 100 ¼
57; 000
172; 800
£ 100 ¼ 33%
Furthermore, the line was running one profile for 16 hr,followed by an 8-hr tool change to another
profile. The line was idle during the tool change. Therefore, the real line utilization during this 16 þ 8hr
period was
57; 000 £ 100
180 £ 60ð 16 þ 8 Þ
¼ 22%
The management was taken aback at first, but soon realized that when the running time of the
20,000-lb coil is about 15 min and the coil change takes 15 min (approvedstandardatthat time) then
this nonproductive coil change alone reduces the line utilization to 50%. Action was taken
immediately to find out what happened during the unproductive times, at the time when the line was
not running.
Time studies revealed that this and the other lines were stopped for the following reasons:
*
Feeding in coil ends or attaching the leading end of the coil to the tail end of the processed coil
*
Changing coilsorpositioning new loads of sheets or strips
*
Setting and changing of lengths
*
Inspecting dimensions and other checking quality
*
Adjusting equipment
*
Removing or piling of finished products
*
Packaging or moving piles or bundles
Roll Forming Handbook14-2
*
Waiting for material handling equipment
*
Waiting for instructions and clarification
*
Counting and marking of products and administration
*
Equipment or tooling problems
*
Labor problems, lack of power,orcompressed air
*
Others
Rather than being satisfied with the 100 to 110% productivitybased on the old method, the management
took immediate action to minimize coil changeover,length changing and measuring methods, and other
“nonproductive”times indicated as the highest nonproductive activities by the time studies. The
improvements significantly increased the line utilization and productivity.
The nonproductive or “downtime” list shown in the above old study can be replaced withnew studies
using actual times for existing lines. Because the roll forming line generates income only when it is
running,itisimperativetoreduce the downtimes.
14.3 Improving Productivity
The steps to improveproductivity(line utilization) are endless and their cost ranges between practically
zerotoveryhigh.
14.3.1 Low Cost Improvements
Among the low cost improvements are:
*
Improved production scheduling —for example, placing one type of material on the line only
once aday.
*
Better inventorycontrol —running out of material too frequently reduces efficiency but “never
running out”requires so much extra inventory, that acompanycannot affordtocarryit.
*
Improveproduct design —for example, changing from “nonnesting”profiletonesting one, the
rollforming speed can be increased by 40 to 75%.
*
Eliminate the waiting time for coils —always storeafew extra coils in the areaaround the
uncoiler.
*
Minimize the time spent on administrativeassignments.
To meet with the accountingrequirements, it is not unusual that the operator (and coworkers) spend 1/2
an hour or more with administrativefunctions (filling out work orders, time cards, counting and
marking products, and other functions etc.). If, in an 8-hr shift, the operator works 7.17 hr (assuming
30 min lunch and 2 £ 10-min coffee breaks), then 1/2 an hour represents 7% of the working time or the
cause of an additional 7% when the line is not working.Certain amount of administration is required,
but reducing the time takenfor this task will improve line efficiency.
*
Order good tooling instead of mediocre ones; all tooling should be operator-friendly.Itisstrongly
advisable to rather havetwo morepasses over the minimum requirement than to haveone less.
*
Have good and updated setup charts available.
*
Provide the necessarysetup,equipment adjusting and packaging tooling for the work. All the
required tooling,likewrenches, Allen keys, screwdrivers, strapping tools, measuring gages, and so
on should be located at the line.
*
Educate employees —all operators, supervisors, maintenance, and management personnel should
have regular roll forming and safetyeducation.
Given the importanceofthe above items, details on the abovesubjects are provided in separate chapters.
Increasing Efficiency of Roll Forming Lines and Case Studies 14-3
14.3.2 Medium and High Cost Improvements
Oncethe no cost/low cost improvements havebeen exhausted, it is time to consider the moderate/high
cost efficiency improvements. They may include:
*
Installing better coil handling equipment to minimize coil change times (such as double uncoiler
and individual coil lifter). In sheet fed lines, it is important to reduce the sheet feeding/bundle
replacement times and to consider using automatic sheet feeders.
*
Improving finished product handling.Often, the line speed has to be reduced to match slower
finished product handling/packaging.Mechanizing or automating material handling can speed up
rollforming and even moresignificantly reduce the number of people working in the line. It is not
unusual to havetwo,three, or four material handlers/packagers for one operator.The elimination
of two, three, or four material handlers/packagers can reduce the labor content of the productby
40, 60, or 80%.
*
Improving line adjustabilitytominimize wasted downtime and to improvequality.
*
Considering replacing the press(es) if the maximum line speed is restrictedbythe slow punching
or cutting press(es).
*
Increasing the line speed (one of the last medium cost resources).
*
Purchasing new and moreefficient line.
There are countless other ways to contribute to productivityimprovement and thus reducing product
cost. Each individual case has to be separately assessed but thereare hardlyany production lines, which
efficiency (utilization) cannot be increased by 10, 20, 30, or sometimes over 50%.
14.4 Case Studies
14.4.1 General Information about Case Studies
*
All case studies are based on real life examples but using fictitious data.
*
In the “case studies,”imperial units (inch, feet, pound, etc.) and dollar ($) values are used. They
can be easily substituted with metric units and other currencies.
*
Labor rates, material costs, equipment, and tooling costs are fictional and are used as examples
only.Actual costs should be substituted in the equations.
*
In the case studies the available production time (hours, minutes) per shift or per year are based
on the following figures:
or 237 £ 430 ¼ 101,910 working minutes per year per shift, or rounded up 102,000 min per year
per shift.
Naturally,working overtime, weekends, and holidays as well as working in two or twoshifts will increase
the available working minutes per year.
*
The 30 to 40% line utilization used in the examples is based on the average of the actual results in
manyrollforming plants. The figures can be substituted with actual figures based on local
365 Days in the year
2 104 Days of Saturdays and Sundays
2 10 Days of statutoryholidays
2 14 Days of maintenance or other reasons the line is not operating
Total 237 Days in the year are available for production
8.000 Hour shift
2 0.833 Hour breaks (30 min lunch, 2 £ 10 min coffee breaks)
7.166 Hour shift £ 60 min ¼ 430 working minutes per 8-hr shift
Roll Forming Handbook14-4
observations and calculations, but it is suggested not to apply overly optimistic highutilization
figures.
*
If, in the example, the line utilization factor is, say, 0.33, then the line is running only at
102,000 £ 0.33 ¼ 33,660 min/year.
*
Continuing the above example, the total length produced in ayearbyamill running at 120 ft/min
willbe120 £ 33,660 ¼ 4,039,200 ft/year (over 4million ft).
The production per shift for amill running at 120 ft/min and at 33% line utilization will be
430 min/shift £ 120 ft/min £ 0.33 ¼ 17,028 ft/shift.
*
If the product is 3-ft long (36 min), then the shift output will be 17,028 4 3 ¼ 5676 pc and the
yearly output will be 4,039,200 4 3 ¼ 1,346,400 pc.
Warning: To calculate the line utilization, the maximum feasible process speed should be used. If an in-
line process, such as welding or packaging,significantly reduces the actual speed the utilization
percentage will be misleadingly highbecause of the few coil changes in ashift (see also Section 14.4.7). In
such cases, for example, installing an additional welding or packaging unit and running the mill twice as
fast, the output can be doubled.
14.4.2 Case Study “A” —Hat Section
Company“A” plans to purchase asingle-purpose roll forming line to produce “hat” sections (1-in. high,
1-in. center width, 1-in. wings).
The required lengths are 18, 36, and 54 in. in about equal quantities.
Based on the previously calculation, 102,000 min per year per shift per equipment production time is
available. Past experienceindicate that this type of single purpose line utilization can be 38%. Therefore,
the actual production time will be:
102,000 £ 0.38 ¼ 38,760 min/year
The production quantities will depend on the line speed and product lengths. Forthe first approach,
consider three different line speeds (50, 100, or 200 ft/min). To cut the threedifferent length of parts (1.5,
3, and 4.5 ft), the following number of cuts per minute are required:
RequiredNumber of Cuts (Strokes per Minute)
At Line Speed (ft/min) 1.5 ft (18 min) 3ft(36 min) 4.5 ft (54 min)
50
33 16.7 11.1
100 66.7
33.3 22.2
200 133.3 66.7 44.4
If amechanical press with 40 strokes per minute is purchased, then the maximum forming speed is
limited to 40 times the product length or,inother words:
the 18-in. (1.5-ft) pieces can be rollformed at amaximum 60 ft/min speed
36-in. (3-ft) pieces can be rollformed at amaximum 120 ft/min speed
and 54-in. (4.5-ft) pieces can be rollformed at amaximum 180 ft/min speed
The production quantities havetoberecalculated with these speeds:
60
1 : 5
¼
120
3
¼
180
4 : 5
¼ 40 pc= min ð for any of these three lengthsÞ
Available time per year is 38,760 min.
The yearly total output will be 38,760 £ 40 ¼ 1,550,400 pc/year:
or 516,800 pc of 1.5-ft long part
516,800 pc of 3.0-ft long part, and
516,800 pc of 4.5-ft long partifequal quantities are required.
Increasing Efficiency of Roll Forming Lines and Case Studies 14-5
If moreparts are required, then apress with ahigher stroke per minute is required. Forexample, utilizing
a60strokeper minute press, the output can be 50% higher assuming that the line can run faster.
However,the maximum line speed may be restricted by the length tolerance. This means not only a
different press, but different die accelerator and possibly different length measuring system willbe
required. The maximum number of pieces per minute can be also constrained by the handling/bundling/
packaging capacity at the end of the line.
Alternative solutions to produce moreparts can be for example operating the same line in morethan
one shift or running twoproducts side by side at the same time. Forthe latter and moreeconomical
solution, adouble capacityuncoiler,adifferent and atwice as wide mill and adouble capacitypress
would be required.
If the hat section has prepunched hole(s), then the technological aspects of this case study must be
extended.
One hole close to the end may be punched with the punch incorporated into the single shear cutoffdie.
If there is one hole at each end of the product, then the punches might be incorporated into adouble shear
cutoffdie, but this press must haveacapacitytwice as highasthat of the single shear press. One, two,ora
larger number of holes can be prepunched in aseparate press, or in certain cases they can be rotary punched.
14.4.3 Case Study “B” —Shelving
Company“B” decides to roll form metal shelving and has to choose one of the tworecommended
production technologies (Line B1 or Line B2). The shelf lengths are 24 in. (2 ft), 36 in. (3 ft), and 48 in.
(4 ft).
Line B1 is acontinuous line producing shelves with single end bends (Figure 4.51). Shelvesare
separated in the last operation. If amechanical press is used, then the maximum speed of the line is
restrictedbythe 40 strokeper minute press.
Maximum line speed 2ft £ 40 ¼ 80 ft/min
3ft £ 40 ¼ 120 ft/min
4ft £ 40 ¼ 160 ft/min
With this method, theoretically,40shelvescan be manufactured per minute while the mill is running.
Using a35% line utilization factor,the output would be
40 £ 60 £ 7.166 £ 0.35 ¼ 6,019 shelves per 8-hr shift.
However,40shelves per minute means that one shelf is produced every1.5 sec. Removing the shelf from
the line, possibly flipping (turning over) everysecond one, nesting and bundling the finished products
will be amajor challenge and most probably alowerline speed must be used. Amorereasonable output
figure is 8to10shelves per minute.
Line B2 is also acontinuous line but the shelf blanks are separated in the second operation, after corner
notching.
The line speed is restrictedbythe end (wing) bender.The maximum speed can be 8sec/cycle. After the
blank with the roll formed longitudinal edge enters the wing bender,ithas to be located and stopped, two
ends clamped, shortends bent, clamps and benders released, and shelf has to be driven out from the
winger bender.
8sec/shelf ¼ 7.5 pc/min speed
Line B1 Line B2
Starts from coil Startsfromcoil
Blanks four corners Blanks four corners and cuts to length
Roll forms twolongitudinal edges Roll forms longitudinal edges
Cuts to length and bends shortends Bends short ends
Roll Forming Handbook14-6
The estimated shift output, using 40% line utilization (slowerspeed, less coil changes) is
7.5 £ 430 £ 0.40 ¼ 1290 shelvesper shift.
The line speed will be 7.5 £ 2 ¼ 15 ft/min for the 2-ft long shelves, 22.5 ft/min for the 3-ft long shelves,
and 30 ft/min for the 4-ft long shelves.
Additional considerations to reducechangeover time (increase utilization) can be
*
Forvariable widths, use duplex line
*
Forwidths and length changes, use PLC/computer control and servo motors
*
Usecomputer control for the completeline, including packaging.
If the shortend requires adouble bend, then the line speed for both Line B1 and Line B2 will be 7.5
shelvesper minute.
It is feasible to double the line output to 15 shelves per minute by splitting the line after roll forming
and having two end-bending lines attached to it.
The corner notching operation can be combined with punching holes into the shelves at the entryside
of the line.
There are several morealternative ways to produce shelves. This case study emphasizes the
importanceofselecting the most suitable roll forming line. The chosen technology, method, equipment,
and tooling predetermine the cost and qualityofthe products, as well as the profitabilityofthe
operation.
14.4.4 Case Study “C” —Studs
What are the estimated yearly outputs of an older,traditional stud mill and aspecial, shortchangeover
stud mill?
Forthe sake of simplicity, this case study is based on roll forming 8-ft. long studs with punched holes at
every2ft, with the first hole always at afixeddistancefrom one end of the stud.
14.4.4.1 Traditional Line C1
Line speed is 160 ft/min, the required cutoffpress cycle is 20 strokes per minute.
Holes at every2ft, the prepunch press cycle must be at aminimum of 80 strokes per minute.
Shift output: 160 ft/min £ 430 min/shift £ 0.36 ¼ 24,768 ft/shift or approximately 3096 pc/shift.
Yearly production: 160 £ 102,000 £ 0.36 ¼ 5,875,200 ft/y or 734,400 pc/y.
14.4.4.2 Specialized Stud Line C2
Line speed 350 ft/min, the cutoffpress cycle is close to 44 strokesper minute.
Holes punched at every2ft, the prepunch press cycle must be over 175 strokes per minute if sing le
holes are punched. Line utilization is assumed as 30% (more coil changes).
Shift output: 350 £ 430 £ 0.3 ¼ 45,150 ft/shift or 5644 pc/shift.
Yearly production: 350 £ 102,000 £ 0.3 ¼ 10,710,000 ft/year or 1,338,750 pc/year (8-ft long).
The output of Line C1 is 20 pc/min or one stud in every3sec. One person can turn over everysecond
stud and bundle them in packages of 10 pieces. Another person prepares the “shipping bundles”from
these 10 packs.
The output of Line C2 is 44 pc/min or one stud in every1.36 sec. Automated highspeed packaging for
both the “10 packs”and “shipping bundles”isrecommended.
The output of the specialized line is 2.2 times higher than that of the traditional line and it requires one
operator only instead of three. This means that the labor content of the traditional line is 6.6 times higher
than that of the specialized line. Because the material content is already reduced to the minimum, saving
Increasing Efficiency of Roll Forming Lines and Case Studies 14-7
in the labor cost is an important consideration. On the other hand, the specialized lines are considerably
moreexpensive.
Additional important concern is the changeover time from one profiletothe next one.
Typical ChangeoverTimes in Minutes
WebLeg
Traditional (old) mill Standardspacers 180 240
Split spacers 30 240
Duplex mill 3200
Specialized mill 33
14.4.5 Case Study “D” —Guard Rail
Company“D” is considering the installation of anew special-purpose roll forming line to produce“W”
guard rails. The required quantityisabout 390,000 pc/year in one shift operation.
Let’sassume that all guard rails are 12 to 6-in. long and havethe standard hole pattern at both ends and
at the center.
Company“D” requested quotations for aguard rail line from different suppliers. Suppliers suggested
four different technologies to fabricate the same product, all starting from coil.
(a) Cut-to-length —transfer (longitudinally or across)
Punch holes —transfer (longitudinally or across)
Roll form
Punching can be completed
*
All in one hit in along press
*
One larger press to punch the end holes in one group and asmaller press punching the
center holes at the same time
*
One press punching the two groups of end holes and after 5-ft feed, the center holes
(using gagged punches).
(b) Punch the holes (in one of the three different ways as described above)
Cut-to-length
Roll Form
(c) Punching holes and cut-to-length in one die (or 2separate dies operated at the same time)
Roll Form
(d) Punch the holes (in one of the different ways as described above)
Roll Form
Cuttolength after rollforming
After alengthyevaluation process, the companydecided to adopt the following technology:
*
Starting coil size will be 20 tons
*
Pull the coil from the uncoiler by aflattener into aloop
*
Arotary feeder will feed the coil into the twopresses located one after the other.The first press
punches the center holes, the second one punches the twoadjacent group of end holes
*
From the presses, the prepunched strip enters into aloop
*
From the loop,the strip enters the roll former
*
The guard rails, gaged from the end holes, will be cut to length at the end of the mill and willbe
automatically stacked.
The technologyofcutting to length after roll forming was selected because it was anticipated that the
continuously roll formed product will haveless end flare than the guard rails rollformed from precut
blanks.
Roll Forming Handbook14-8
Punching all holes at the same time offers the best hole location tolerances. If the complete punching
and coil feed cycle is 6sec, then the output is 10 pieces per minute (125 ft/min production speed).
At that speed and 0.100-in. material thickness, it will take about 12 min to run one 10-t coil (or 18 min
for 15-t coil and 24 min for 24-t coil). The coil change and the strapping and removal of the stacked
bundles take time. If the stackedbundles can be removedefficiently,then using larger coils can increase
the line utilization. Assuming a38% line utilization, the shift output would be
125 £ 60 £ 7.166 £ 0.38 ¼ 20,425 ft or approximately 1633 pc/shift or
1633 pc/shift £ 237 shifts/year ¼ 387,021 guardrails/year in one shift operation.
This output can greatly vary, depending on the coil weight, efficiency of coil loading,method of finished
product removal, qualityofthe equipment and tooling,know-how and attitude of the operators, time
spent on qualitycontrol,administration, and others.
The technologytobeselected depends on the suppliers’ know-how and experience,price, and the
expertise of company“D”.Depending on several factors, possibly flying prepunching dies will be used in
lieu of the coil feeding.Using flying dies, the speed of rollforming maybeincreased but the permissible
rail length tolerancemust be checked. Tight hole-to-hole tolerancecan be kept if the threegroups of
punches hit the guard rail at the same time. However,regardless which approach is selected, sufficient
number of rollforming passes and good tooling will always be an important factor.
14.4.6 Case Study “E” —Siding and Roofing
Company“E” initiated acost reduction study.They concentrated on the labor content of the product
(output), based on the assumption that thereisnoroom for saving material because the profile (blank
width) and thickness is predetermined. However,they found out that the old length-measuring system
provides inaccurate length for the first piececut after each stopping; therefore, the operators always start
with ashortpiecethat is thrown into the scrap bin. In addition to this waste, when they almost run out of
the coil, the operator had to estimate wheretocut the coil at the uncoiler so as to leaveenoughmaterial
to roll the last piece. After forming the last piece, the leftover ended up in the scrap bin too.
Changing to an updated length measuring system, the first shortpieceand the last “leftover” piece
scrap can almost entirely be eliminated.
The mill producing the sidings was subplated (rafted) and run at 190 ft/min speed.
To provide ashortdelivery cycle, the operator changed profiles in an average three times per shift. The
profilechange took 40 min (0.66 hr). Because of the highspeed and frequent color and thickness (coil)
change, the line utilization was at the best 30% for each profile.
Production time: 7.17 2 (3 £ 0.66) ¼ 5.20 hr ¼ 311 min/shift
Production output: 310 £ 190 £ 0.3 ¼ 17,727 ft/shift.
If the profile would havebeen changed only once per shift, then the output had been
(7.17 2 0.66) £ 60 £ 0.30 £ 190 ¼ 22,264 ft/shift
or 26% higher than with threeprofilechanges.
Fewer profile change would yield higher productivityand lower cost, but, in this case, providing
customer satisfaction requires morefrequent changes. The management of the companymust establish
the priorities and keep aprecarious balancebetween production cost and “supplying on demand.”
It is possible that abetter productivitycan be achievedwith better scheduling and reducing the
nonproductive times (increasing line utilization), while customers are still kept satisfied, but most
probably causing an increase in the in-plant material handling cost.
14.4.7 Case Study “F” —Special Products
This companyisroll forming prepainted, nonnestable products that wereseparated by paper
(interleafed) during in-line packaging.Owing to the slow manual packaging,the line was running only at
Increasing Efficiency of Roll Forming Lines and Case Studies 14-9