US2252893A - Cutting tool - Google Patents

Description

Allg 19, 1941- K. R. MAcKLlN 2,252,893

CUTTING TOOL Filed Jan. 5, 1940 INYENTR KRMAKLIN I gij/#M2511 TTOB/NE S Patented Aug. 19, 1941 UNITED j STATES PTENTgGFFlCE CUTTING TooL Kenneth R. Maupin, Toronto, ontario, caneda Application January 5, 1940,.-A`Serial:No.`3l2,565

4c1aims. (eicel-lett l This invention relates to cast tools made of stellite and other hard cutting alloys. In producing such tools the molten alloy is simply poured into the casting mold and permitted to cool. Cooling and solidication of the mass starts at the outer surface and proceeds inwardly at a progressively slower rate. This produces a tool consisting of a solid mass of hard alloy having a grain structure which is relatively fine at the outer surface of the tool but becomes progressively coarser toward the centre. The cutting eiiciency of such tools diminishes as the cutting edge is shifted toward the centre by removal of the surface metal. This, of course, is due to the fact that the fine grained metal at the surface of the tool naturally cuts better than the coarser grained metal nearer the centre. The inherent brittleness of such tools is also such that they break easily when subjected to hard usage, such as intermittent cutting, chattering and sudden shocks.

The purpose of the present invention is to provide finer grained tools that will cut faster and last longer than the tools produced in accordance with conventional methods of manufacture. This object is achieved by casting the hard alloy around a soft metal core centered in the tool casting mold prior to the introduction of the molten alloy. The temperature at which the alloy is poured is preferablyV such that the alloy becomes firmly welded to: the soft metal core throughout its area of contact therewith. In any event the shrinkage of the cooling alloy causes it to hold the soft metal core securely in place so that the latter becomes practically an integral part of the nished tool. The casting of the alloy around the soft metal more enhances the quality of the finished tool or tool bar in several important respects. During cool-- ing of the molten mass the core serves as a centre chill so that cooling and solidication of the mass starts at the centre as Well as at the outer surface of the mass. This ensures a more rapid and uniform cooling of the mass and produces a tool in which the alloy is of a more homogeneous nature and is characterized by a grain structure which is exceptionally ne and uniform throughout. Cored alloy tools made in this way will cut faster and stand up longer in service than the solid alloy tools made in accordance with the conventional method. The cored tools may be ground down to a much greater extent than ordinary solid cast tools and without diminishing the cutting efficiency thereof.

The soft metal core also serves to conduct heat away from the nose of the tool when the latter is in use and thus prevents failure of the tool due to overheating of the nose portion. The thermal conductivity of the hard alloys used in the manufacture of cast tools is so low that when the nose of a conventional solid cast tool is operating at a red heat the body of the tool will be only slightly warm an inch or so from the nose portion. It thus frequently happens that the nose of a solid cast tool becomes so hot that tool failure results. In the case of the cored tool provided in accordance with my invention the core serves as a heat conducting element extending the full length of the tool. In the operation of these cored tools it has been found that the rear end of the soft metal core will almost reach a red heattthus clearly indicating that the core is taking a substantial amount of heat away from the nose of the tool. The toughness and reinforcing effect of the soft metal core also enables the cored tools to stand up longer when subjected to rough usage, such as intermittent cutting, chattering and shocks. The cored alloy tools are also cheaper than solid alloy tools since they require from 20 to 25% less alloy in the manufacture thereof.

Proceeding now to a more detailed description of the invention reference will be had to the accompanying drawing in which- Fig. l is a side elevation of a cored tool or tool bar produced in accordance with my invention.

Fig. 2 is an end View of the tool or bar appearing in Fig. 1.

In the drawing the tool or tool bar is generally indicated at 5. It comprises an outer portion 6 and a central core 1. 'I'he portion 6 may be composed of Stellite or any other hard cutting alloy usually employed in the manufacture of cast tools for lathe and similar Work. The core 'l comprises a rod of soft steel or other suitable soft metal. As previously stated this cored tool is produced by casting the alloy i5 around the core l so that chilling action of the core during the cooling down of the molten alloy ensures an exceptionally ne and uniform grain structure throughout the mass of the alloy.

In the present instance the core T is shown as a round bar extending the full length of the tool but it will be understood that the cross sectional shape of the core is not an essential feature and may vary as desired. It is, however, important that the core l be made of a metal which is softer, tougher and more heat conductive than the surrounding alloy.

Having thus described my invention, what I claim is:

1. A cast cutting tool or tool bar comprising an outer portion composed of a hard cutting alloy. cast around a central core portion coinposed of a softer and tougher metal of relatively high thermal conductivity compared with the thermal conductivity of the surrounding alloy, 10

said tool or tool bar being characterized in that the grain structure of the outer portion or alloy is exceptionally ne and uniform from the outer surface of the tool to the central core as compared with solid cast tools made entirely of such 15V alloy.

2. A cast cutting tool comprising an outer portion composed of a hard brittle cutting metal characterized by relatively low thermal conductivity and an inner or core portion around which the outer portion is cast, said inner portion or core being characterized by relatively high thermal conductivity compared with said outer portion and the latter being characterized by a grain structure which is exceptionally fine and uniform from the outer surface of the tool to the central core as compared with the grain structure of solid cast tools made entirely of such alloy.

3. A cutting tool as set forth in claim 2 in which said inner portion is composed of a metal which is relatively soft and tough.

4. A cutting tool as set forth in claim 2 in which the inner portion is composed of a metal which is relatively soft and tough and in which the outer and inner portions are (zo-extensive in length.

KENNETH R. MACKLIN.

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