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centreless grinding is a special technique used to grind or cut away excess material from the outer diameter (OD) of a workpiece, to create a product adhering to required specifications and dimensions. Widely used to mass-produce mechanical parts for automotive and bearing industries, tools and implements for healthcare and custom manufacturing of tubes, rotors, bars etc., this technique differs from methods usually employed to cut metals.
Centreless Grinding - The Concept
It is the unique concept or principle of grinding employed in this technique that sets it apart it from other grinding methodologies.
In this process, the workpiece or metal piece is not mechanically constrained or rather not held in place with the help of any fixtures, such as spindles or chucks and, hence, does not require any drivers, workhead fittings or central holes for support.
The grinder used for machining comprises three main components - a larger grinding wheel that operates at high speed, a relatively smaller regulating wheel running at slower speeds, and an angled workblade positioned between the two wheels. The workblade is usually sloped towards the regulating wheel to ensure the workpiece is rightly placed and supported.
The workpiece is set in place by snugly fitting it on the workblade and supported by its outer diameter, with its centre (mandatorily) higher than those of the adjacent wheels, to achieve uniform grinding.
In fact, this OD machining process is famed for its effectiveness to create uniformly rounded finished goods from irregular work pieces. The results in terms of impeccable precision, enhanced efficiency and higher rates of processing, or removal of excess material are also characteristic of centreless grinding, provided the key parameters for machining are addressed.
This process is most suited for mass processing of thin or long work pieces - especially made of pliable, soft or brittle materials that most often cannot be processed using other types of grinding.
Different Types of Centreless Grinding
There are, in fact, different ways in which this process can be carried out, primarily based on how the workpiece is fed into the grinder.
i) In-Feed Grinding - Specific parts of the workpiece is processed at a time. This is similar to plunge grinding in centred OD machines.
ii) Thru-Feed Grinding - Work pieces generally longer than the grinding wheel are fed through the grinder and processed along their entire length to uniform shape. This is ideal for continuous processing of multiple smaller pieces at the same time.
Advantages of Centreless Grinding
There are several advantages in using this process, including but not limited to
1. No pre-requisite preparation needed to load the workpiece on the grinder (clamping, transmission of movement, etc.)
2. Continuous loading can be suitably automated, cutting downtime to change work pieces
3. Grinding wheel can be operated at high speeds
4. Machine setup is both less daunting and fast
5. Out-of-shape errors (roundnesscylindricity) greatly minimised
As mentioned earlier, pliable materials can be processed without any deformations, and so can the extremely long work pieces.
To sum up, this OD machining process varies from other techniques of grinding metals, right from the basic principle and complex key process parameters to the multitude of advantages it can offer, when executed with care.