Post on 02-Jun-2018
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The little book of
Big Bolts
This guide is intended as an introduction to the world of
high torques. It gives an overview of the general trends
in production, points to the key areas of process improve-
ment, presents the different types of tooling and fixtures,
as well as what to think of when choosing tools.
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CONTENT
General trends in assembly..............................................................1
How to improve the assembly process............................................4
Quality..................................................................................................4
Ergonomics.......................................................................................8
Productivity......................................................................................10
Choosing assembly tools...............................................................12
Fixturing.........................................................................................14
What to consider when selecting tools..........................................18
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General trends in assembly
When looking at manufacturing operations in their most general sense,
there exist several trends for how the industry is building products and
taking them to the market. Some of these stand out in importance, and
will influence the look of the assembly operations of tomorrow.
We need to produce faster, better and cheaper!
The number of models per product has increased significantly dur-
ing the last years and product life cycles have become shorter, as
a result of that more and more companies are now consolidating
their operations into specialized plants. In these plants, production
flexibility and cycle rates are key, which in turn has several implica-
tions on production methods:
Use of platform concepts means faster time to marketand lower production costs
Higher line speeds is one of the answers to the demand
for increased production levels
Better production flexibility is needed to respond to short-
er product life cycles and low extra capacity in production
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We need to ensure an appropriate quality!
Manufacturers have understood that good quality will affect not only
their costs but also their revenues. On top of that, badwill stemming
from quality concerns is any companys nightmare. Therefore, there
is a strong drive towards eliminating assembly related problems by
reducing the possibilities for assembly errors, so called Error proof-
ing. Included in this comes a need to ensure an appropriate clamp
force in the joints that are tightened. For example, the pump & valve
industry have products with critical seals on many different models.
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Quick check:Are you subjected to demands for higher line speeds or
better quality output, and will this have effect in how your
assembly operations will look like in the future?Do you see a drive towards common processes in your as-
sembly environment?
Is operator wellbeing and health & safety issues more of a
concern for you today than it was 5 years ago?
We want to use the same
manufacturing methods in all
our plants!
Manufacturers have understood
that there are significant sav-
ings to be made by using the
same assembly processes in
plants manufacturing the same
products. This has led to the cre-
ation of master-member manufacturing setups, where one factory
is responsible for the process and similar factories then copy meth-
ods and equipment at another location. Although not going as far as
relieveing their factories of the process ownership, these companies
are exchanging best practices and benchmarking manufacturingmethods to a larger extent than before.
We want to ensure the wellbeing of our operators!
The need to address health &
safety related issues has in-
creased as companies have un-
derstood the profound benefits
of having a sound working en-
vironment for their employees.
Manufacturing companies are
continuing to strive to reduce
potential and existing problems
in operations.
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QualityDo it right the first time!
The later an error is detected on the assembly line, the more it costs
to adjust. Fact!
A manufacturer should always strive to correct any assembly errors
in the fastest possible way, when they occur on the assembly line.
How to improve the assembly process
Improvement areas for any assembly process is of course heavily
dependent on the unique assembly situation. However, there are
a number of aspects that can be done on a process security andtooling level that can contribute significantly to improvements in as-
sembly operation.
There are three different cornerstones which all contribute to the
total cost reductions that can be experienced by the end user.
Quality
Ergonomics Productivity
Station 1
If an assembly error is committed and detected here, the operator
can fix it by simply by retightening the bolt. No damage is done and
the additional cost is the extra time to tighten and perhaps the cost
of a new bolt.
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Customer detects error
The worst possible scenario is that the error that was committed in
Station 1 goes undetected all the way to the customer and that the
product breaks down during operations. Not only will the manufac-
turer have large warranty costs because of this problem, but good-
will might be damaged.
Station 2
If the error from Station 1 is passed on to Station 2, the additional
cost becomes higher. Now the operator perhaps needs to dismantle
the product to retighten the bolt or must walk over to Station 1 to
get components. Specially designated rework areas are also com-
monally used.
End station
If the error is not corrected in Station 2, it is hopefully detected in
the End station, where the quality check is being made. If the error
has reached this far, the cost of fixing it has gone up dramatically. The
product needs to be taken aside for dismantling and rebuild and if the
product is made to order, there is an angry customer somewhere out
there who will not get his product on time.
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How to eliminate assembly problems
There are a few assembly problems that occur frequently on produc-
tion lines globally. The problems on the line or on an application is
one important factor to consider when determining what tool type(s)to choose for assembly operations.
Lost
quality Missing screwsStripped screws
Wrong
torqe
Too early
shut-of
Wrong
forgotten
Bad
repeatability
Missed
rework
Delivered
quality
Problem Solution
Missing screws
Stripped screws
Wrong torque
Screw counting to ensure all screws
are accounted for
Slower shut-off speed to prevent
strip out
Defined parameter sets with jointspecific characteristics
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Wrong / forgotten parts
Bad repeatability
Missed rework
Too early shut-off
Quick check:
Who monitors the costs associated to warranty claims and scrap
frequency today?
What quality checks have you built into your assembly process?
Do these checks detect the most common assembly problems?
Do they ensure that a faulty product is not passed on down theline?
Do you have a rework area today that takes care of products not
built to specification?
Are all operators trained on how the various tools should be
operated?
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Measuring rundown angles and
counting screws ensures correct
type and number of components
Defined parameter sets with joint
specific characteristics
Line control incorporates quality
check points to ensure no faulty prod-
uct is passed down the lins
Operator guidance to notify of any
rundown problems
Problem Solution
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ErgonomicsSound ergonomics increase productivity
Ergonomics is playing a more important role than ever in assembly
operations. Many companies have ergonomic departments or special-
ists who work closely together with their production departments.The importance of ergonomics is also strengthened by the increased
media coverage on the issue and trade practices adhered to on a
global basis.
It is clear that sound ergonomics increase productivity. Happy and
safe employees are more productive. Furthermore, downtime as well
as labor absence related costs will go down when improving ergo-
nomics. For High Torque tools, this becomes even more of an issue,
as tools are often big and heavy and generate high reaction force.
Bad ergonomicsGood ergonomics
When working to improve the ergonomic situation in the high torque
assembly environment, you always have to take a work station per-
spective. The workstation itself though, is quite complicated and the
selection of power tool is one important parameter for workstation
design. Ironically, the best power tool on the market will not trans-
form a badly designed workstation into a safe, comfortable work
area for the operator
Noise
The lowest possible noise level should be aimed for. This consists ofreducing process noise, noise transmitted by vibration and potential
aerodynamic noise.
Example:Avoid using an impact wrench in a hollow compart-
ment without ear protection.
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Regardless of tool type, it is
only as good as the
reaction device or fixture
which it is used with
Vibration
All machines vibrate to some extent. By re-
ducing vibration levels and process times,
operator health problems can be prevented.
Example: Make sure to take frequentbreaks when running a highly vibrating
tool during long periods of time.
Quick check:What ergonomic guidelines governing workplace design do
you have today?
Do these guidelines take the entire workplace into account; i.e.
power tools, work organization, workplace, and operator?
Do you have any health and safety issues in work areas today?
Are there any hand wrench operations above 100 Nm?
Are all applications with heavy tools and or high torques
fixtured and supported?
What costs does your factory associate to injury and work
related health issues?
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Working posture
Avoiding bad working postures is of high
importance. This can be done by reducing
the load on the static muscles and short-
ening the duration of each operation, as
well as providing the operator with theright working technique.
Example:Never use a tool during long
periods above shoulder level.
Operator strain
High torque tools are often heavy and
can cause unnatural strains for the opera-
tor. With the use of balancers and torque
arms, operator strains can be minimized.
Example:A big tool amounts to many
kilos of weight when carried around
continuously during a day. Always use
a balancer.
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ProductivityProductivity is about finding a balance.
Productivity should not be confused with tool speed, since tool
speed and process speed are two completely different things. Fur-
thermore, productivity can only be maximized when considered
alongside quality. It is easy to build a lot of poor quality product. But
it is equally easy to build low volumes of high quality products!
There are two key areas to focus on when trying to increase the
productivity of assembly operations:
Decrease the number of operations, and/or
Increase the speed of process.
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Decrease the number of operationsBy reducing the number of operations, cycle times can be cut dra-
matically. This in many instances have a higher impact on total cycle
time than choosing the tool with higher speed.
Example:
Conventional method
Station 1
Tighten with hydraulic toolStation 2
Click Wrench to secure the
joint has been fastened
Station 3
Paint marker to prove the
joint has been tightened
Preferred method
Station 1 Safety / quality critical
application
Tighten with electric tool
Station 1 Other application
Tighten with shut-off pneumatic tool
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Increase the speed of process
The cycle rate in a factory depends partly on the speed of the assembly
operations. Other factors that contribute are for example: overall product
demand, feeder line speeds, speed of paint, machining or other non-as-
sembly operations, airline installation pressure for pneumatic tools etc.When looking solely at assembly operation speed, the fastest tool that
does not compromise error proofing level or ergonomics should always
be selected. To maximize assembly operation speed, the following basic
rule can be applied:
Step 1: Determine the level of Error Proofing
Here you choose your error proofing require-
ments as well as the desired accuracy of the
tool for the job. The 5 steps to error proof-
ingshould be used as reference.
Step 2: Determine the ergonomic de-mands of your installation
Good ergonomics has a strong impact on
overall productivity.
A tool should always comply with regulations
and standards regarding noise and vibrations.
Usually companies have specific ergonomic
guidelines governing the tool choice.
Good ergonomics is good economics!
Step 3: Choose the fastest possible tool
or rundown for the application
With Step 1 & 2 taken into consideration, the
goal should be to maximize the rundown speed
of the tool. Here numerous aspects must be
considered: component materials, fastener con-
straints, tool propulsion system etc.
Quick check:Have you taken ergonomics and error proofing level into ac-
count when trying to maximize productivity?
Which bottle neck operations do you have today that are depen-dant on assembly tools?
Are multiple assembly operations performed in some stations
and if yes, is there a possibility to reduce the number of these
operations? Do you use click wrenches or paint markers?
Are there needs for quality checks and for what reasons are there
needs?
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Choosing assembly tools
Today, there is scarcely any discussion on technical issues relating
to tightening that does not also include process quality. However,
everyone understands process control and process quality slightlydifferently. Atlas Copco has divided our products into different cat-
egories depending on error proofing functionality. This definition pro-
vides a common ground for discussion and helps provide some long
overdue clarity on the subject.
The 5 steps to error proofing
Step 1
Precise &
pre-de-
termined
torque
Operator
Dependant
Torque OK !
Step 2
Screw counting
No re-hits
Batch OK !
Step 3
Angle monitor-
ing => joint
control
Calculated
torque values
Joint OK !
Step 4
Traceability
Tightening data
collection
Transducerized
tool
Safety critical
tightening OK !
Step 5
Controllers are
networked with
factory production
system
Reject manage-
ment
Zero fault fasten-
ing!
Tool
examples
EP LTP RE - controller Tensor DS Tensor S
Integration of
the tightening
process into the
production
management
network
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Selection guide
Every application and indeed customer have their own specific re-
quirements when it comes to tool selection. Depending on how
critical the application is, or the demands on access or line speed
all play a part in choosing the correct tools. Below is a simplifiedselection process, according to process functionality levels, which
highlights the key factors that differentiate the tools.
Pulse Tool
EP PT / PTS
Pneumatic
Nutrunner
LMP / LTP
DC Electric
Nutrunner
Tensor DS
Technology:
Torque control Shut-off Stall type / Shut-off DigiTork* TransducerDocumentation -- -- Only OK/NOK Yes
Angle monitoring -- -- Yes (360Steps) Yes
Parameter sets -- --- 10 / 64 Up to 250
Networking -- --
-- Yes
Applications:
Safety Critical No No No Yes
Quality Critical No No Yes Yes
Standard Yes Yes Yes Yes
Accuracy: +/- 15% +/- 10%** +/- 7,5%* +/-5%**
Price level: 100% 200-400% 400600% 600-1000%
*Algorithm of motor current, frequency, voltage and temperature.** Tested
according to ISO 5393. These values should be seen as a guideline.
DC Electric
(transducerised)Nutrunner
Tensor S
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Tool fixturing
When dealing with high torque applications, it is extremely impor-
tant to consider the issue of torque reaction and fixturing of the tools
to be used. In all cases where adirect drive
nutrunning system,such as pneumatic shut-off, stall type or DC nutrunner are to be
utilised on such an application, particular consideration must be paid
to both how the tool will be supported and how the torque reaction
will be dealt with.
Reaction Device:
Reaction taken through an additional reaction device fitted onto
the tool.
Support Fixture:
Reaction taken through a device or fixture onto which the tool is
supported
Holding System:
Where a bolt or nut is held in position whilst the other part isfastened by the tool
1.
2.
3.
Below you find an overview of the
different types of fixturing solu-
tions for common applications
in the High Torque sector.There are different categories
of tool fixturing devices that all
have their advantages and disad-
vantages. The three that we will look at
further are as follows:
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1. Reaction device
This method consists of mounting
a reaction bar onto the front part of
the tool. This will then rest against,
or locate onto an associated com-ponent or fixture in the work area.
The result is that when the bolt is
tightened, the tool cannot rotate or
move in any way.
The most important thing to con-
sider in this case is to ensure that
the area which the reaction bar is
to react against is both stable and
cannot move in any way, especially
bearing in mind that the reaction force will be equal to the torquebeing applied to the fastener.
A simple reaction bar with a dummy
socket which can locate over another
bolt head to take the torque reaction,
for example in wheel assembly.
2. Support Fixture
This method of solving the issue of torque reaction is different from the
above, in that rather than mount a device on the tool, we instead can
mount the tool onto an additional support device. This mounting device or
fixturecan take many different forms, commonly referred to by names
such as support arms, torque tubes,
or articulated arms. Although all are
different in terms of how they are used,the principal in which they solve the
issue is the same.
Bench or Floor Mounted
Torque Arms
These can be simple bench mount-
ed type whereby the tool is fixed
in an arm, and the tool carries out
the tightening operation in a similar
manner time after time. Alternativelyif the arm has a knuckle or is floor
mounted, this may give the flexibility
for the tool to rotate about a point to
reach a variety of positions near the
working area.
A typical installation showing
an articulated arm with an angle
nutrunner mounted
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Torque Reaction Tubes
Where a tool needs to be
suspended in such a way
that it must move along a
production line, or acrossa work cell area, it is often
difficult to use an arm of
any description. In the
case of an excavator for
example, the work area
may be very large but you
still want both to take up
torque reaction and pro-
vide the necessary flexibility in production. An alternative method of
installing a tool is then to put it on a Torque Tube. This is in effect ametal tube which can move in both the horizontal and vertical planes
to give flexibility whilst at the same time absorbing the torque reac-
tion through the tube itself.
A typical installation showing an articulated arm with
an angle nutrunner mounted
Articulated armsArticulated torque
arms have many ad-
vantages, in that not
only can they take the
torque reaction that isgenerated but, they
can also take the en-
tire weight of the tool.
Furthermore, when
mounted on an over-
head carrier or track,
this gives the flexibility
to manoeuvre the tool
parallel to a moving line such as in a tractor manufacturing plant, or
to several positions in a static build cell, such as in excavator assem-bly. As the tool is held by the armthe torque reaction generated is
taken through the arm itself, whether it be mounted overhead, or
fixed to the floor.
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3. Holding System
Trombone devices
Below we can see three typicalexamples of what is known as
trombonereaction devices. You
can see how a reaction bar is
mounted to the front part of the
tool, which in turn has a dummy
socket or opening on the other
end, holding it in place while the
nutrunner drives the bolt head (or
vice versa). The reaction is taken
up by the reaction bar, as dur-ing the tightening process. The
forces generated on each side,
work in the opposite direction
to each other, and hence cancel
each other out.
Examples of trombone devices
Straight nutrunner with Trom-bonereaction device
Separate Trombone
device and angle toolPistol Pneumatic Nutrunner withTrombonereaction device
Angle nutrunner withTrombonereaction device
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What to consider when selecting tools
The selection of the appropriate tool for a given application is seldom
straightforward and in most cases there is no right tool, but sev-
eral tools can do the job. Many different factors must be consideredwhen choosing a tool, all of which have an influence on the final
decision. Below we have listed the most crucial aspects that should
be discussed before a tool investment decision is taken. These are
grouped according to the cornerstones Quality, Ergonomics & Pro-
ductivity described in the chapter previously.
Who monitors the costs associated to warranty claims and
scrap frequency today?
What quality checks have you built into your assembly pro-
cess? Do these checks detect the most common assembly
problems? Do they ensure that a faulty product is not passed on
down the line?
Do you have a rework area today that takes care of products
not built to specification?
Are all operators trained on how the various tools should be
operated?
What ergonomic guidelines governing workplace design do
you have today?
Do these guidelines take the entire workplace into account; i.e.
power tools, work organization, workplace, and operator?
Do you have any health and safety issues in work areas today?
Are there any hand wrench operations above 100 Nm?
Are all applications with heavy tools and or high torques fix-
tured and supported?What costs does your factory associate to injury and work
related health issues?
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Ergonomics
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Quality benefits
Productivity benefits
Ergonomics benefits
Have you taken ergonomics and error proofing level into ac-
count when trying to maximize productivity?
Which bottle neck operations do you have today that are de-pendant on assembly tools?
Are multiple assembly operations performed in some stations
and if yes, is there a possibility to reduce the number of these
operations? Do you use click wrenches of paint markers?
Are there needs for quality checks and for what reasons are
there needs?
Low noise
Low vibration levels
Superior tool control
No heavy straining
or lifting
Cost savings
with correct
tools
Quality
Ergonomics Productivity
Consistent accuracy
Traceable result
Elimination of
assembly problems
Process control
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Fewer operations
High process speed
Less maintenance process
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Productivity
By selecting the correct tool for the application,
numerous cost savings will be realized:
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More information
Atlas Copco has extensive experience and know-how of assembly
solutions in the High Torque segment. We provide literature, cours-
es, seminars and audit services for our partners. If you want to knowmore, either order the following information, or contact with your
nearest Atlas Copco responsible who can provide specific informa-
tion in the areas of your interest, e.g. Industry best practices for as-
sembly or High torques assembly culture, among many others.
Pocket guides Ordering number
Error proofed productionStatistical analysis technique
The art of ergonomics
Tightening technique
9833
1498
01
2004:2
9833 1437 019833 8637 01
9833 8587 01
9833 8648 01