in Vol. 9 - September Issue - Year 2008
Mass Finishing Applications
Example of deburring
Example of radiussking
Example of cutting down or blending
Example of burnishing
Example of deflashing
Example of cleaning
The processes which can be carried out in vibratory or disc finishing machines need to be carefully defined in terms of what can or cannot be done.
In all mass finishing processes there are 5 basic ingredients to be considered. These are:
A. The component to be processed and the work to be done on it.
B. The type and size of the machine in which the work will be done.
C. The media to be used in the process.
D. The compound to be used in the process.
E. The time taken for the process to be carried out.
By varying these ingredients it is possible to carry out a range of engineering operations which will replace expensive hand de-burring and other finishing methods. The operations which can be performed are:
1. The removal of burrs from machined or pressed components.
2. The generation of radii on component edges.
3. The production of fine surfaces and micro-inch finishes on machined components.
4. The elimination of cutting tool and/or grinding marks.
5. The cutting down or blending of castings and forgings including the blending of die lines.
6. The removal of rust or heat treatment scale.
7. The removal of discolouration due to welding or brazing operations.
8. The preparation of surfaces for painting or subsequent plating operations.
9. The colouring or burnishing of components to give a bright lustrous finish and to bring out the natural colour of the metal.
10. The de-flashing of die-cast components.
11. The de-flashing of plastic or rubber components.
12. The fine finishing of die-castings.
13. Cleaning of components.
When these processes can be carried out in vibratory or disc machines they are usually accompanied by the advantages of cost reduction, quality improvement, controlled processes and consistency of results. Advantages can also be seen in the fact that, if required, a variety of operations can be achieved in the machine without removing the components. This is sometimes achieved be simply changing the compound so that, for example, parts may be cleaned, de-burred, de-scaled and burnished in sequence.
It must be stated however that these processes are not a panacea for all metal surface finishing problems. There are some restrictions as to what can be done and these should be recognised if the processes are effective and offer economic justification.
Having listed the possible applications for the process it is necessary to define some of the processes and parameters which apply.
Is the removal of burrs and sharp edges from machined or pressed components. This can be carried out without critical changes in important dimensions, especially on close tolerance diameters and faces. The process follows the contours of the component so that the edges are the first to be treated and burrs removed before critical dimensions are affected.
This can be said to be an extension of the deburring process in that it goes beyond the removal of sharp edges and is able to produce a definite radius on a component.
This is a useful application since the work cannot be properly done or controlled when hand methods are used. A component "radiussed" by hand usually, on close inspection, displays not a true radius but a number of flats. It is also evident that by hand methods the degree of radius will vary from one component to another.
The radius produced by mass finishing methods is true on all edges and the amount of radius can be controlled by process time and condition of the edge to be treated.
The process is not selective and will treat all the component edges in the same way unless masking techniques are used.
Cutting Down or Blending
This refers to the treatment of components’ surfaces rather than edges. The value of this operation lies in the surface improvement of castings and forgings. It is used on a variety of components such as automotive parts, turbine blades, cutlery, sports equipment, surgical instruments and many others.
A point to note when carrying out these down processes is that whilst work is done on the surfaces there will be heavy radiussing of any sharp corners. If sharp edges are required then the cut down operation should be carried out before the creation, by machining, of such edges.
Colouring or Burnishing
This process can be used on most metals to give a bright, lustrous finish and to bring out the natural colour of the metal. The finish achieved is bright and reflective but not necessarily smooth since it is not a cutting process and it follows the imperfections of the surface.
High lustre finishes can be achieved on brass and aluminium components in particular and parts treated in this way tend to retain their colour longer than those ‘polished’ by more traditional methods. The media used is usually of steel, porcelain or glass in conjunction with special polishing pastes. The ultimate in this type of finish is achieved by using the Keramo® Finish Process.
This involves the removal of the flash and die lines from aluminium or zinc alloy die castings. It is a process widely used in the die-castings industry. As with de-burring, the thickness and position of the flash to be removed must be carefully controlled.
This refers to the cleaning of components as a finishing operation rather than a pre-treatment process. There are many applications for this type of operation which is part chemical and part mechanical as imparted by the vibrating or centrifugally motivated media. Applications include the cleaning of automotive components prior to re-work or re-conditioning where it is often necessary to remove baked-in carbon and oil deposits, general degreasing, light surface or edge treatment combined with cleaning and surface conditioning prior to painting. Often this type of process can replace more expensive alkaline or solvent degreasing systems and phosphating plants.
by Paul Rawlinson,
Contributing Editor MFN and
General Manager Rösler UK
Tel: +44.151.482 0444
Fax: +44.151.482 4400