The Little Book of Big Bolts UK

8/10/2019 The Little Book of Big Bolts UK

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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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2

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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4

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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8

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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10

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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Process speed


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12

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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13

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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Quality

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

The Little Book of Big Bolts UK

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