GB2137121A - Cutting Tools with Galvanic Cathodic Protection - Google Patents

Abstract

A metallic cutting tool is coated with an auxiliary anode made of a baser metal (such as magnesium, aluminium, zinc or their alloys) than the tool material or its anodic components. The anode comprises either a complete or partial coating applied onto the tool surface by means of any suitable coating process, or a separate piece mechanically attached to it. In the presence of an aqueous cutting fluid or other electrolytic solubles, the anode, by being sacrificed, will prevent the electro-chemical corrosive wear of the tool, reducing thus the total rate of tool wear, the overall result being an improved general performance of the aqueous cutting fluids as well as wear characteristics of wood cutting tools. <IMAGE>

Description

SPECIFICATION Cutting Tools with Galvanic-Cathodic Protection This invention relates to cutting tools and its object is to provide a simple form of protecting metallic cutting tools from electro-chemical corrosive wear associated with aqueous or electrolytic cutting fluids as well as soluble components in woods.

In most metal cutting operations a cutting fluid is used the primary function of which is to reduce the rate of cutting tool wear or to increase the tool life by its lubricating as well as cooling action.

There are three main types of cutting fluids, namely neat cutting oils with or without various additives, soluble oils which, mixed with water, form the so-called oil-in-water emulsions, and synthetic fluids or chemical solutions consisting of inorganic and/or other materials dissolved in waterand normally containing no mineral oil.

As compared to the neat cutting oils, the latter two aqueous fluids have several advantages; their main constituent being water, they are better coolants, cheaper, easier to handle and cleaner.

The aqueous cutting fluids, however, are electro-conductive or electrolytic, and due to this characteristic, they tend to induce an electrochemical corrosive wear of cutting tools. In fact, in many cases, they have been observed to increase the total rate of tool wear part of which is attributable to the electro-chemical corrosive wear mechanism.

The increase in the rate of wear by aqueous fluids has been reported to be particularly notable at certain part of the tool wear region, namely at the trailing or secondary cutting edge, wherein flank wear develops in the form of a groove or a series of grooves (1) (2). Besides being the controlling factor of the surface finish of a machined workpiece, the said trailing edge wear may, in some instances, become predominant governing the complete tool failure.

If such a detrimental effect of the aqueous cutting fluid is suppressed, their general performance will be largely improved, providing them a better ability to improve tool life as well as surface finish. This will encourage an increased use of the aqueous fluids enhancing their inherent advantages over the neat oils, such as an economy in petroleum consumption and a reduced pollution.

Similarly in green or wet wood cutting operations, the predominant tool wear mechanism is believed to be an electro-chemical corrosive wear, arising from the galvanic action of the electrolytic liquid components in woods (3) (4), and therefore by preventing such a wear mechanism to occur, an overall increase in tool life can be expected.

The electro-chemical corrosive tool wear in metal cutting in association with aqueous cutting fluids, as well as in green wood cutting operations, can be prevented or reduced by applying the so-called "galvanic-cathodic protection" onto the cutting tool so as to depress the potential of the tool material, or of its local anodic components, into the cathodic or noble range. This can be achieved by placing an auxiliary electrode, made of a baser metal than the tool material or its anodic components, onto the cutting tool. It then forms a sacrificial anode in the galvanic cell the cathode of which is the cutting tool, protecting thus the latter from electro-chemical corrosion and subsequent wear.

The obvious choices for the sacrificial anode against the usual cutting tool materials, such as tool steels, high-speed-steels and various carbides, are Magnesium, Zinc and Aluminium or their alloys.

The protective method as described above may be put into practice in various ways depending upon the type, shape and size of a particular cutting tool. The practical requirements for the sacrificial anode are that it should be located as close to the actual cutting edge as convenient, and that its interference with regrinding of the tool should be avoided as far as possible. Several alternative arrangements are possible to meet these requirements within the scope of the invention. These are; (a) complete and (b) partial coating of the cutting tool with one of such anodic metals as mentioned before by means of any suitable coating process, and (c) a separate anode mechanically attached to the cutting tool.

Each of these arrangements will be described together with a few embodiments by way of example.

(a) Complete coating; this comprises a full coating all over the surface of a cutting tool. It will be the simplest arrangement and enables the anode to be located at the closest possible position to the actual cutting edge. The complete coating, however, is not convenient with large size tools for economical reasons, nor is it always practicable with such tools whose areas subject to subsequent regrinding are large, as the coating will be ground away when the tool is reground, It can best be applied onto small size tools, tool bits, and particularly throw-away carbide inserts since these are usually of small size and not subject to regrinding, and also to such tools regrinding area of which is not extensive as is the case with hacksaw blades and band saws.

(b) Partial coating; this consists of confining the coating within a limited area of the tool surfaces as close to the actual cutting edge as is convenient. Such surfaces as are subject to severe rubbing actions during machining as well as regrinding operation may also be left uncoated.

It may be conveniently applied onto large size cutting tools.

As an example Fig. 1 shows a large diameter circular saw wherein a partial coating can be applied on the narrow bands near the teeth on both sides as indicated by 1.

Another example illustrated in Fig. 2 is a brazed carbide tip tool in which part 2 of the tool holder 3 is coated leaving the tip 1 bare.

Partial coating can also be achieved by applying initially a complete coating on a cutting tool. Part of the coating subject to rubbing actions during machining as well as regrinding operation will then be worn away resulting in a partially coated tool. Such will be the case with the twist drill, as illustrated in Fig. 3 wherein the coating will remain on the flutes 1 as well as the body clearance surfaces 2 whilst the end clearance surfaces 3 and the lands 4 will become bare.

Similar result can be obtained with small size milling cutters.

(c) Separate anode; this comprises a piece of one of such anodic metals or alloys as mentioned before, of suitable shape and size, which can be either mechanically attached onto the tool holder or mounted on the tool holding device of a machine tool together with a cutting tool, so as to be located as close to the actual cutting edge as possible without interfering with its cutting action. Fig. 4 illustrates such as separate anode 1 mounted on the lathe tool post 3 together with a cutting tool 2.

Reference (1) Kurimoto, T. and Barrow, G., The wear of High-Speed Cutting Tools under the Action of Several Different Cutting Fluids, Proc.

22nd Conf. Machine Tool Design and Research, Manchester, Sept. 1981 pp.237-245.

(2) Kurimoto, T. and Barrow, G., The Influence of Aqueous Fluids on the Wear Characteristics and Life of Carbide Cutting Tools, Annals of the CIRP. Vol. 31/1/1982, pp. 19-23.

(3) Mohan, C. D. and Klamecki, B.E., The Susceptibility of Wood Cutting Tools to Corrosive Wear, Wear 74, 1981-82, pp.

85-92.

(4) Tsai, G.S.C. and Kiamecki, B.E., Separation of Abrasive and Electro-chemical Tool Wear Mechanisms in Wood Cutting, Wood Science, Vol. 12, No. 4April1980, pp.

236-242.

Claims (4)

1. A cutting tool for metal and other material cutting, whereupon an aqueous cutting fluid is used or electrolytic solubles are present within the material being cut, having the auxiliary anode made of a baser metal, such as magnesium, aluminium, zinc and their alloys, than the tool material or its anodic components.

2. A cutting tool according to Claim 1, wherein said anode comprises either complete or partial coating applied onto it by means of any suitable coating process.

3. A cutting tool according to Claim 1, to which or to the holder of which a separate anode is mechanically attached so as to be located as close to the actual cutting edge as possible.

4. A cutting tool according to Claims 1 and 3, wherein a separate anode is attached by means of the tool holding device of a machine tool.