Production Optimization

Joint analysis and friction coefficient analysis

Tightening Services – the Atlas Copco tightening laboratory

What does “Tightening Services” mean?

The Tightening Services department of Atlas Copco is concerned with the development, optimization and verification of joints. We identify optimization potential in the field of industrial tightening technique and help you to improve the quality and efficiency of your production process.

What happens in the tightening laboratory?

Atlas Copco Tools has a specially equipped tightening laboratory where we can investigate the behavior of tightening operations under real conditions using a variety of measurement procedures. You then receive results and recommendations for the optimization of your tightening operations.

What are the benefits?

Industrial tightening technique is a complex topic. Our team of tightening specialists helps in selecting the optimum type of joint in the design phase, identifying any tightening errors and highlighting issues such as stripped threads, material problems or operator errors.

Should you just go ahead and tighten that screw? Things are often not quite so simple in industrial production. Even if a joint is not safety-critical, loose components almost always result in higher recall, guarantee and reworking costs. This applies irrespective of whether a screw becomes loose or breaks off during tightening – tightening errors can significantly impair the quality of a product. In the worst possible case, a tightening problem may result in the risk of personal injury or even death.

So what does effective tightening mean? In order to understand how a joint works, we need to consider a number of different physical factors:

Torque:

Torque:

In order to insert a screw or bolt into a thread, force must be applied in the form of torque. The torque required depends on the clamp load, the shearing force and the tensile force. The preload corresponds to the load on the screw or bolt.

In order to insert a screw or bolt into a thread, force must be applied in the form of torque. The torque required depends on the clamp load, the shearing force and the tensile force. The preload corresponds to the load on the screw or bolt.

Klemmkraft, Zugkraft, Vorspannkraft und Scherkraft

Friction:

Friction:

The force applied in the form of torque must be sufficient to overcome the friction under the bolt head and between the threads of the bolt and the nut. Friction depends on a number of factors including the material and the surface texture. Depending on the friction factors, the preload may be undesirably high or low. In order to set the optimum torque for tightening, it is therefore essential to have full information on the friction factors of your fasteners.

The force applied in the form of torque must be sufficient to overcome the friction under the bolt head and between the threads of the bolt and the nut. Friction depends on a number of factors including the material and the surface texture. Depending on the friction factors, the preload may be undesirably high or low. In order to set the optimum torque for tightening, it is therefore essential to have full information on the friction factors of your fasteners.

Relaxation behavior:

Relaxation behavior:

Every threaded joint is subject to relaxation following tightening. Relaxation normally occurs very fast. In less than 30 ms, the clamping force in the joint will be lower than immediately after tightening. In the case of joints with elastic components (“soft” joints), this relaxation phenomenon may be very pronounced. Relaxation will normally be less significant in the case of “hard” joints. In both cases, special tightening sequences or subsequent tightening may be needed.

Every threaded joint is subject to relaxation following tightening. Relaxation normally occurs very fast. In less than 30 ms, the clamping force in the joint will be lower than immediately after tightening. In the case of joints with elastic components (“soft” joints), this relaxation phenomenon may be very pronounced. Relaxation will normally be less significant in the case of “hard” joints. In both cases, special tightening sequences or subsequent tightening may be needed.

Effizient verschrauben

Rotational angle:

Rotational angle:

In more complex assembly processes, the rotational angle may be used for tightening up to or beyond the yield point of the joint. The yield point represents the transition point of a threaded fastener to plastic deformation. Beyond the yield point, the deformation of the fastener can no longer be reversed.

In more complex assembly processes, the rotational angle may be used for tightening up to or beyond the yield point of the joint. The yield point represents the transition point of a threaded fastener to plastic deformation. Beyond the yield point, the deformation of the fastener can no longer be reversed.

What we offer

Our services can be subdivided into two main areas:

Joint analysis and joint design

The design of a joint provides information on the optimum tightening parameters for the joint. Measurements identify the behavior of the assembly in a joint taking into consideration the relevant measured parameters.

Our laboratory analyses include the following services:

Failure measurements
Measurements for setting optimum parameters
Verification measurements
Evaluation and assessment of torque and angle diagrams
Preparation of an analysis report including tightening diagrams, measured values, torque and angle at the seating point and yield point as well as a proposal concerning appropriate tightening parameters and general notes as well as proposed solutions to any problems identified.

Friction coefficient analysis

These services provide information on the friction factors of your threaded fasteners and allow you to optimize the quality of your joints.

The friction factors connected with a threaded joint are determined under standardized conditions or using materials taken from the customer’s production process.

Our laboratory analyses include the following services:

Measurement of prestressing force at analysis torque
Determination of overall friction factor, friction factor at the bolt head or nut seating point and thread friction factor in accordance with DIN EN ISO 16047 at standardized conditions
Upon the completion of the analysis, we prepare documentation of the results obtained. This includes a presentation of all relevant input factors and measured values together with graphs of prestressing force as a function of torque

Did you know that we also carry out tightening analyses in accordance with OEM specifications? This way, we provide car manufacturer with support for meeting special quality management requirements.

You will find further information on our services for production optimization in the following documents:

Flyer friction coefficient determination 1.5 MB, PDF
Flyer joint analysis with seating point detection in the laboratory 745 kB, PDF
Flyer tightening analysis accordin to OEM guideline 986.5 kB, PDF

Learn more in our series of articles on bolting case analysis with head contact detection:

Tightening curve

Interview: Joint design with seating control (part 1)

In part 1 of our interview series with our tightening technology expert Michael Laue, find out what seating control is and in which cases Atlas Copco Tools uses it.

Interview: Joint design with seating control (Part 2)

In part 2 of our interview series with our tightening technology expert Michael Laue, find out exactly what happens in a screw joint after seating control and what errors can occur.

Do not miss this video! Take a look behind the scenes at our tightening laboratory and learn more about our production optimization services.

Seminars & training sessions

Seminars and training sessions

Seminars & training sessions

It is important not to underestimate human factors. It is crucial for people to know not only what makes a safe joint but also how it is be tightened properly. With our practically oriented seminars and training sessions concerning tightening technique, we can help your employees develop sustained competence. Learn more here.

It is important not to underestimate human factors. It is crucial for people to know not only what makes a safe joint but also how it is be tightened properly. With our practically oriented seminars and training sessions concerning tightening technique, we can help your employees develop sustained competence. Learn more here.

It is important not to underestimate human factors. It is crucial for people to know not only what makes a safe joint but also how it is be tightened properly. With our practically oriented seminars and training sessions concerning tightening technique, we can help your employees develop sustained competence. Learn more here.

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Joint analysis and friction coefficient analysis