CNC Centerless Grinder Guide
There are several types of grinding machines available on the market, such as cylindrical grinders, centerless grinders, surface grinders, just to name a few. Each of them is designed for particular grinding tasks. In the following sections, we will talk about CNC centerless grinders and centerless grinding techniques.
Fig. 1 STC-18_20, Supertec Taiwan
CNC centerless grinders are one of the machine tools that provide workpieces with a high-quality surface finish. The grinding methods a CNC centerless grinder applies make it ideal for processing bar stocks in particular. So what is centerless grinding and what does it do? Let's take a look.
Centered and Centerless: What's the Difference?
Centerless grinding is defined as a type of OD (outer diameter) grinding. The difference between centerless grinding and traditional centered grinding lies in how the workpiece is positioned. A centerless grinder does not hold the bar stock in place with the headstock or chuck. Instead, the bar stock is set on a work (rest) blade between two rotating wheels.
Grinding Wheel and Regulating Wheel
The two rotating wheels are the grinding wheel and the regulating wheel. The grinding wheel has a larger diameter and spins faster compared with the regulating wheel. It is the component that performs the grinding action. The regulating wheel applies pressure against the workpiece to hold it in place. The grinding wheel is stationary whereas the regulating wheel is movable.
How does Centerless Grinding Work?
The two wheels turn at different speeds. It is the different speeds that enable the grinding action. The speeds relative to each other also determine the removal rate. The regulating wheel is movable so that bar stocks with a range of diameters can fit the machine. Since the workpiece is aligned between the wheels rather than held by a fixture, feeding and exiting the workpiece become efficient. Below is a video simulating a centerless grinding process:
Centerless Grinding, Koyo Machine Industries
Why Centerless Grinding?
As aforementioned, the feeding and exiting of workpieces are efficient without any traditional work-holding system. As a result, when there is a need to process a large volume of parts within a short cycle, centerless grinding is the best option. Besides the efficiency, the three-point (grinding wheel, regulating wheel, and work blade) contact allows for better roundness of the workpiece.
Where is Centerless Grinding Applied?
Good surface finish and roundness of the bar stocks are required in a number of sectors in the metalworking industry. It is often the last procedure following other machining processes such as milling, drilling, or turning, etc. It can also serve as the pre-processing stage to prepare the workpieces for other operations.
What are the Grinding Wheels Made of?
Grinding wheels are not made of general materials; they are usually a composite of different substances. The material is composed of coarse-grained aggregate, which is pressed and bonded together by a cemented matrix. Further, the wheels come with various profiles and cross-sections, which are used for achieving different tasks.
Except for composite grinding wheels, there are metallic wheels as well, such as the solid steel wheels and aluminum wheels that are coated with abrasives. In the past, stones were the most common material for grinding wheels. In modern days, it is usual to make these wheels with artificial aggregates.
Types of Centerless Grinding
Based on the three-point contact mechanism, centerless grinding has evolved into three types, and they are thru-feed grinding, in-feed grinding, and end-feed grinding. Here is a video that explains these three methods in detail. We concluded the keynotes down below for you too!
Types of Centerless Grinding, Soumen Sir
Thru-feed Grinding
through-feed grinding is the process where the workpiece goes through the two wheels from one end to the other completely. Such a process is suitable for grinding long and slender bar stocks without shoulders or other even profiles. One thing to note here is that the regulating wheel inclines (canted) at an angle (around two to ten degrees vertical to the rotary axis).
In-feed Grinding
In-feed grinding is used to process bar stocks that have portions with different diameters or profile designs. It is similar to plunge grinding. Because of the diameter difference in different parts of a single workpiece, the workpiece does not go through the two wheels. There is an end stop on one end of the wheels.
End-feed Grinding
Just like in-feed grinding, end-feed grinding uses an end stop to prevent the bar stock from exiting the wheels. The only difference between end-feed and in-feed grinding is that the former is used primarily for processing spherical workpieces or short tapered bar stocks.
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