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Lefaillet: between centres grinding solutions

Between centres and CNC clamp

Between centres grinding is a process whereby material is removed by abrasion with the aim of calibrating to very precise dimensional tolerances (a few microns), of improving the surface state (up to Ra: 0.1-0.2) and of correcting the geometric defects of mechanical parts (coaxiality, perpendicularity, run-out, straightness, etc. 5µ to 10µ) caused by precision turning or thermal treatment. Grinding is applicable on several materials (treated and non-treated steels, stainless steel, aluminium, etc.).

There are several ways to hold the workpiece during grinding. A grinding process will be chosen according to the shape of the workpiece (presence of centre points, flange, boring, etc.), the shape of the grinding (diameter, cone, face, etc.) and geometric characteristics to be obtained.

The two most commonly used workpiece holding techniques are:

CNC between centres

Positioning between centres for grinding: performed in two carbide tips and driven with a brass dog.

Advantages:

Correction of buckling of the workpieces

Correction of major geometric defects (up to 5/10ths of a mm)

Disadvantages:

The workpiece must have two centre points

CNC clamp grinding

Clamp grinding: the workpiece is held on a diameter and held by a clamp in mid-air.

Advantages:

Correction of major geometric defects (up to 1/10ths of a mm)

No need for centre points

Disadvantages:

Limited on long workpieces
Not suitable for workpieces with major geometric defects (>1/10th mm)

Between centres and CNC clamp grinding

In between centres and CNC clamp grinding, the machine alternates between milling and diamond dressing cycles. There are different types of milling. They are chosen according to the work to be done, the dimensional characteristics of the workpiece, material, etc.

A few grinding cycle examples:

Straight plunge: Diameter, cone or form grinding…

Scanning: Grinding of diameters or cone when the length of the workpiece is higher than the width of the mill

Multiple plunging and scanning: ditto scanning but for workpieces with a larger extra thickness or hard material to grind.

Oblique plunge: grinding of face(s) or of face(s) and diameter(s).

Form plunge: profile grinding with a profile grinder (several diameters, cones, spheres, radii, etc.).

Linear or circular interpolation: profile, sphere or cone grinding with high angular value or complex profile.

Diamond dressing: An operation that consists in regenerating the shape of the grinder.

Different types of grinders:

corundum (the most used)

cubic boron nitride

diamond

For each application, it is also necessary to define:

the size of the grain

the binder

the diameter

the width

The advantages of between centres and CNC clamp grinding:

Improvement in the surface state (Ra: 0.1-0.2)

Diameter precision (+/-2µ)

Correction of geometric defects (coaxiality, perpendicularity, run-out, straightness… 5µ to 10µ)

Correction of form defects (circularity, cylindricity, cone shape, etc.)

We have appropriate verification tools to check the dimensional characteristics of workpieces. We own a large quantity of passameters with comparators offering resolution of 0.2, 0.5 and 1µ, between centres benches, digital columns, etc.

On request, we can protect your parts with a rust inhibitor to ensure long-lasting protection. We can also pack them in specific packaging (to avoid impacts during transport).

The company’s strengths in between centres and CNC clamp grinding:

Know-how going back 30 years

8 CNC machines (more precision, complex parts, repeatability of operations, etc…)

Grinding with automatic feed stops (the machine compensates for the wear of the grinder)

Grinding with positioners (the machine handles different workpiece lengths)

Production capacity:

Up to 100,000 workpieces per year

Dimensional capacities:

Ø3 to 350mm, maximum length: 1000mm

Examples of applications:

For any requests for informations or queries…

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