In this article we will discuss about roll forging, it’s processes, methods, applications and certain MCQs related to forging.
What is Roll Forging ?
Roll forging is a process of production of discrete pieces of lengths of varying cross-section by rollers and simultaneously changing the shape of heated bars, billets, or plates.
But, plane rolling is done on the work of uniform cross section.
Roll forging is considered one of the most modern forging processes.
Roll Forging Process Working
Roll forging process performs an impression-, but in this system there are two roll segments on parallel shafts as depicted in Fig. 8.21 have one or more set of grooves. A piece of stock is placed between the rolls which then turn and squeeze the stock in one set of grooves. The stock is passed to a second set of grooves, the rolls turn again, and so on until the workpiece is finished. Each set of grooved segments is made to do a specific job.
Roll forging may be used to make reductions in the cross-section and distribution of the metal of a billet, thus saving considerable work in the forging hammer or press. Because it is rapid, roll forging is of advantage in preparing some shapes for forging machines and hammers and also for completely foreign parts like levers, leaf springs, cutlery and scissors, and axles. The most important use of this process is in the preparation of preformed blanks for forging.
In a roll forging machine, circular bars, flats and squares can be formed to tolerances grade IT- 15. The straightness obtainable in such cases in 1 mm per meters length. Similarly, on ring rolling mills the tolerances of plus, minus 0.5 mm can be obtained.
Skew Rolling is the process that uses two specially designed opposing rolls, that rotate continuously. Round stock is fed into the rolls, the material is forged by each of the grooves in the rolls and emerges from the end as manufactured product. This is shown in Fig. 8.21. Each roll has as outside helical pattern that carries the stock along and progressively shapes it as the rolls turn. Such diverse products as steel balls and railway car axles are forged by skew rolling.
A typical skew rolling machine set up’ includes the feeder, the medium frequency induction furnace, skew rolling mill, quenching machine and so on.
Skew rolling mill is the special equipment which applies the spiral groove skew rolling forming process to manufacture milling steel ball, bearing ball blanks and other metal ball. This skew rolling mill applies the semi closing frame so it is easy to change the roller. The skew rolling mill have the complete adjusting function; The rigidity of machine base is good. The manufactured products have the high accuracy. The whole machine includes major motor, speed reducer, universal-joint spindle and the working main machine.
The skew rolling forming process is a new technology to produce the rotary parts or blanks. It can be used to manufacture the milling steel ball, bearing ball, auto part and other products.
Advantages of Skew Rolling
The advantages of skew rolling process are :
1. Greatly improve the productivity;
2. Highly reduce the cost;
3. Improve quality and the working condition .
Ring Rolling starts with a small ring blank and deforms it between once or two work rolls and an idler. The ring is increased in diameter and decrease and shaped in cross section. The blank may be prepared by forging or punching. Pieces finished by this method range from small roller-bearing races to rings 5 m and more in diameter.
Advantages of Ring Rolling
Ring rolling produces seamless rings with forged properties, which results in optimum mechanical properties, and predictable and efficient machinability. Tooling cost is low, set-up time is fast, rolled sections require little or no machining. The process is also highly material efficient. Even though basic shapes with rectangular cross-sections are the norm, rings featuring complex, functional cross-sections can be forged to meet virtually any design requirements.
Aptly named, these contoured rolled rings can be produced in thousands of different shapes with contours on the inside and/or outside diameters. A key advantage to contoured rings is a significant reduction in machining operations. The process typically utilizes up to 95% of the starting billet.
This is illustrated in Fig. 8.21.
Roll Forging MCQs
1. Roll forging…….
A. Causes a steadily applied pressure instead of impact force
B. Is used to force the end of a heated bar into a desired shape
C. Is a forging operation in which two halves of rotating die open and close rapidly while impacting the end of the heated tube or shell
D. Is a forging method for reducing the diameter of a bar and in the process making it longer
E. None of the above
Right answer is D. Is a forging method for reducing the diameter of a bar and in the process making it longer
2. Roll forging is done with the help of______
a) cylindrical rolls
b) semi-cylindrical roll
c) both cylindrical and semi cylindrical rolls
d) None of the above
Right answer is C. both cylindrical and semi cylindrical rolls
Conclusion :- Roll forging is done with the help of both cylindrical and semi cylindrical rolls. These both rolls contains one or more shaped grooves.
Suggested : Impression Die Forging – Complete Process
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