Bolt terminologies and working


Bolts are the temporary fastening elements used for assembling of parts. There are 4 models of engines are producing. In these 4 models there are different application, about 40.
Maximum torque of 120 Kg-m is required for torquing Main bearing cap bolts of 170 engine model and Connecting rod bolts, Cylinder head bolts, Damper and crank pulley, fly wheel etc. Conventional method of torquing the engine component bolts using manual torque wrench is more operator fatigue and precise control of applied torque is not possible. The difficulties involved in torquing for tightening engine component bolts are listed below.

No fool-proofing arrangement
Measurement of applied torque is not possible
Consuming more Torquing cycle time

Electric Nut Runner is newly emerged torque control fastener tightening tool that is usually powered by Electric power. Electric nut runner mainly consists of 3 components.

They are

Spindle is equipped with brushless motor and it will tighten the bolt and the spindle is connected to the controller through a cable. Controller receives the feed back signal from the spindle and based on that signal it gives the controlling signal to the spindle. Cable is used to connect both the spindle and controller.


In the existing method, impact wrench and manual torque wrenches are using for torquing the Main Bearing cap bolts, Cylinder head bolts, Damper and crank pulley, Fly wheel and Fly wheel housing bolts in engine assembly line. In this existing method of bolts torquing cycle time is more and also precise control of torque is not possible.

The objective of proposed work is to study the process requirements and Torquing sequence, mounting height details for Main Bearing cap bolts, Cylinder head bolts, Damper and crank pulley, Fly wheel and Fly wheel housing bolts and propose the Electric Nut Runners spindle and Controller Specifications based on the studied process requirements and torquing sequence, mounting height details to the Manufacturer of Electric Nut Runners.

The Proposed work also includes Installation of 5 Electric Nut Runner in Main Bearing cap bolts, Cylinder head bolts, Damper and crank pulley, Fly wheel and Fly wheel housing stations and 10 pneumatic Nut runners at Selected points in Engine assembly line.

The proposed work also involves calculation of bolts torquing cycle time by Existing Manual Air guns and Pre-calibrated Torque wrench method and by using Proposed Electric and Pneumatic Nut runners Method and to determine how proposed methods are more economical compared to existing process.
Finally we discuss here about the working of all the electrical nut runners, there procedure of operation, schematic diagram, and other supportive to nut runners lke PLC programming, Bosch programming.

Scope of the Work:

In six Engine assembly stages namely Main bearing cap bolts, Connecting rod bolts, Cylinder head bolts, Flywheel housing bolts, Flywheel bolts requires high torque with precise control (± 2%). In case of connecting rod bolts in addition to the above, the bolts are to be tightened i.e. “yield to torque”. In these cases number of bolts per engine assembly is ranging from 6 to 36 bolts.
With the targeted increase in production levels to 1500 (during 2007-08) the present production practices need to be more reliable and free from operator dependencies. With enhanced levels of production it is increasingly difficult and practically not possible to achieve a consistent torquing accuracy since the click-type torque wrenches used at present have an accuracy of +/-15%.
In this industry, Present practice of pre-torquing using Pneumatic impact wrenches which is followed by manual torquing with pre-calibrated torque wrenches to ensure the final torque consumes lot of time, leave scope for improper torque application apart from need for extra operator to assist while tightening.

The objective of the company is to increase the capacity of the Assembly shop. Thus the primary option is to reduce the Torquing cycle time.
Application of Electric and Pneumatic Nut Runners results in reduction in torquing cycle time required for the Assembling of Engine, thus solving the problem of the company.

Scope of project extends to the installation of the electrical nut runners, suitable for all the models, conducting trials to test the feasibility of the nut runners with all the models, check all the sequences, calibration of the nut runners, educating the supervisors, workers so the t they can easily use it.

Bolt Terminology

Helix: The curve formed on any cylinder by a straight line in a plane that is wrapped around the cylinder with a forward progression.

External thread: A thread on the outside of a member. An example is the thread of a bolt

Internal thread: A thread on the inside of a member. An example is the thread inside a nut.

Major diameter: The largest diameter of external or internal threads

Axis: The center line running lengthwise through a screw.

Crest: The surface of the thread corresponding to the major diameter of an external thread and the minor diameter of an internal thread.



This is standardized storage system which is used in many of the companies. The schematic sketch of the two bin system is shown above. There are 18 such racks which are placed at the 18 stages of the line. This bins contain hard ware items like like nuts, bolts, washers, O rings etc.

Working Procedure:

The racks contain two storage levels and one level. The bins on the top and middle of the rack contain all the parts of an engine which are coming on the respective stage. Items from bins are drawn for engine assembly, after drawing of parts these bins are put in to return line i.e. bottom level.

There are 4 models of engine which are produced and colour code is used to identify bins containing parts for a particular operation.