What Is a Rolling Machine?
A rolling machine is a machine tool for plastic forming by applying a strong force to a material.
Metal has a property called “plasticity” that prevents it from returning to its original shape when a certain amount of force is applied. Plastic forming is a processing method that takes advantage of this property. In rolling machines, a tool called a die is pressed strongly against a rotating workpiece to transfer the shape of the workpiece, which is then plastically deformed into the required shape.
They are often used in forming processes such as screws. Cutting, in which the workpiece is cut, is a comparable process. Unlike cutting, form rolling does not produce chips and waste material.
It also has the advantage of shorter machining time and longer tool life, making it a more productive and efficient machining method compared to cutting. Furthermore, the strength of the material can be increased because the fibers of the material are connected without cutting.
Uses of Rolling Machines
Rolling machines are used to form screws, gears, and involute splines and serrations. Initial investment is required because dies must be prepared according to the specifications and shape of the product.
In addition, the setup time to switch between different types of products tends to be long. Therefore, they are not suitable for small-quantity, high-mix production.
Once setup is done, the tool life is long and product accuracy is stable, making it superior for small-lot, high-volume production. Also, machining time can be reduced compared to that of cutting.
Principle of Rolling Machines
Rolling machine processing can be broadly classified into round die rolling, flat die rolling, and planetary rolling.
1. Round Die Form Rolling
Circular die form rolling is a forming process in which the workpiece is sandwiched between two or three round dies rotating at the same speed. The principle remains the same: the dies are pressed against the workpiece by hydraulic or other force.
By changing the distance between the dies, the dimensions of the workpiece can be adjusted as desired. Because of its excellent machining applicability, it is also widely used for processes other than thread rolling. On the other hand, productivity is inferior to other thread rolling methods because the material to be processed is supplied and discharged at the same location.
Round die form rolling can be divided into three types according to its processing method. The other is the “push-in” form rolling, in which the workpiece is pushed in by hydraulic pressure or other means while the space between the dies is closed, and the “through” form rolling, in which the workpiece passes through the closed dies.
Through-feed form rolling is used for workpieces with leads, such as screws and worm gears. It is important to select the most suitable forming method considering the shape of the product.
2. Flat Die Form Rolling
Flat die form rolling is a forming process in which the workpiece is sandwiched between a pair of flat dies and the dies are moved in parallel as the workpiece rotates.
This is a highly productive method and suitable for mass production of general-purpose screws.
3. Planetary Form Rolling
Planetary form rolling is a method of processing by feeding the workpiece between the inside of a fixed die and a rotating round die.
Since the distance between the dies cannot be changed, the applicability of the process is limited. However, productivity is high, and this method is often used in the mass production of general-purpose screws.
Other Information on Rolling Machines
1. Automation of Rolling Machines
Rolling machines can be applied to a wide variety of parts processing, other than screws. In addition, there are numerically controlled, automated “form rolling machines” that can be used for advanced form rolling. This is due to the industry’s desire to shift parts processing from cutting, which tends to waste material, to plastic forming, which offers higher yields.
Computer-controlled rolling machines can achieve higher product precision than conventional rolling machines because the left and right spindle stands allow machining to proceed while absorbing load fluctuations while maintaining the center-to-center distance between the two dies mounted on the ram.
Another notable feature is the ability to accommodate an increase in the number of tool axis control axes. For example, in the case of a 7-axis computer-controlled form rolling machine, the spindle rotation, tilt angle, and distance between spindles can each be independently controlled, allowing more complex and precise movements than those used in a conventional round die form rolling, such as yose form rolling and through form rolling.
2. Advanced Control of Rolling Machine Dies
Automation of rolling machines has led to the development of new processing methods that have evolved from conventional round die rolling, such as reciprocating and multiple rolling.
Reciprocating form rolling is a form rolling process in which the dies rotating in the same direction are synchronized, alternating between forward and reverse rotation. The advantage of this method is that it suppresses the amount of movement of the workpiece as it moves and avoids contact with non-machined parts, thus facilitating the manufacture of high-machined parts that require repetitive machining.
Multiple-form rolling is a processing method that allows different patterns to be rolled in multiple locations in a single operation. This is achieved by feeding the workpiece into the exact position by means of a servo-controlled slide table. With a conventional rolling machine, two or more machines are required to process multiple parts, but with multiple rolling, only one machine is needed.