Impregnated Cluster Tools
Introduction
Randomly impregnated diamond cluster tools have proven their cost effectiveness in the truing and dressing of abrasive wheels for many years. However, although far from a new concept, the continued development of diamond and bond combinations has meant that the impregnated tool still has an important role to play in modern grinding. It is particularly effective for the more severe and dimensionally less demanding applications. Hamilton Lichfield manufacture a range of these tools which have been designed to cope with a variety of common dressing operations where they supersede the traditional single point dressing tools.
Dressing Concept
Unlike the conventional single point tool, impregnated dressers have many small points of diamond in contact with the wheel at any one time. In this way the heat generated during the dressing operation, which is the principal cause of wear, is shared and absorbed by the numerous small particles. To effect maximum performance from the tool it is necessary for the full dressing face to be in contact with the wheel. Therefore, any drag angle employed on a machine utilising single point dressing, must be compensated for in the impregnated tool shank design.
Once properly 'bedded in' with the full face of the tool exposed by the wheel, the tools may be used to open up or close down the wheel, to achieve different grinding requirements, by varying the traverse rates and infeeds, in much the same way as normal dressing.
Tool Shanks
Impregnated dressers may be supplied in any form of holder including taper shanks, usually at no extra cost. It is, however, important to specify any drag (approach) angle that may be built into the machine in order that the appropriate allowance can be made on the shank. If the exact angle is not known it may be easily determined by grinding a piece of mild steel inserted in place of the normal single point tool. This sample and shank dimensions are all that we require to manufacture the dresser.
Tool Composition
The tools described below are all produced using closely graded natural or synthetic diamond grits bonded with a specified bond, developed to give the optimum combination of wear resistance and friability. Although in these tools the diamonds are randomly mixed, as opposed to hand set, several techniques are employed to ensure an even distribution of the diamond throughout the impregnated layer.
Tool Types
Table 1 illustrates the basic range of impregnated dressing tools and the following offer full descriptions of the tool types. Bespoke impregnated tools can be designed and produced on request.
Impregnated Diamond Tools:
Table 1
Top Dress Tools
Despite their conventional appearance Topdress dressers are sophisticated tools which have been specially developed for dressing large and medium size wheels found on centreless and some cylindrical grinding machines. The tools employ selected drilling diamond set in a reinforced tungsten carbide matrix which gives exceptionally long tool life and the capability of producing surface finishes down to 2-3 micro inches CLA.
In order to achieve the best results it is necessary to select the correct diamond particle size for the wheel being dressed from the following table:
Table 2
The dimension of the tool face is also important in relation to the
dimensions of the abrasive wheel being dressed and although there is
no exact rule for this, a guide can be obtained from Table 3. In
practice using a larger tool than is necessary is not detrimental and
will adequately repay the extra cost, whereas, specifying a smaller
tool may lead to premature tool failure and consequently poor cost
effectiveness.
Impregnated Dress Tools
Imp-dress tools are a cheaper alternative to the Topdress range being based on natural diamond grit rather than the selected drilling material. These tools are intended for general purpose grinding applications, off-hand grinding, preforming wheels etc. Being inexpensive and extremely durable they are ideally suited for use with semi or unskilled labour and are often specified as the 'work-horse' of the shop floor.
The rules for selection and application of these tools are similar to the Topdress range.
Indress Tools
A high concentration of very strong synthetic, cubo-octahedral diamond grit is used in these tools and is held in a toughened copper bond. This combination enables the Indress tool to provide a very clean, precise dress on small internal grinding wheels where they will quickly bed in without glazing. The tools may also be used on larger, soft or fine grit wheels usually employed on finish grinding, they are not suitable for coarse, silicon carbide wheels.
Formdress tools
Formdress tools utilise the same diamond and bond formulations as the Impdress range, however, the nib shape has been altered to allow them to perform a variety of profiling operations. The tools may therefore by applied in the generation of open profiles, initial form generation on new wheels and other areas where the use of expensive chisel tools or other forming devices may be avoided.
Notes on the use of Impregnated Tools
To obtain the best results from impregnated dressers please observe the following:
- Select a tool of sufficient diamond area for the job in hand.
- Select a grit size commensurate with the wheel grit and finish required.
- Apply the tools so that the full diamond face is in contact with the wheel.
- Once 'bedded in' do not turn the tool as you would a single point.
- If during its life the tool becomes dull or glazed, open the dressing surface up by applying one or two heavy cuts, i.e., increase the infeed to 0.010" (0.25mm).
