US2518890A - Die sinking - Google Patents

Description

Aug. 15, 1950 J. A. HERON ETAL 2,518,890

DIE SINKING Filed Aug. '7, 1947 v 3 Sheets-Sheet 3 F/G.8. F/GQ.

:QQHILHHERNE HERON on sHnw mmmz 140mm nockmq Patented Aug. 15, 1950 UNITED STATES PATENT OFFIE DIE SINKINGV v John Aherne Heron, John Shaw, and Lothar N. Hocking, Farnham Common, England Application August 7, 1947, Serial No. 767,098

In Great Britain. January 19, 1946 Section 1 P-ublic Law 690, August 8, 1946 Patent expires January 19, 1966 ing and trailing edges, all requiring to be accu-v rately reproduced to very narrow tolerances, present considerable diificulties in manufacture particularly in the production of precision dies by the customary methods of hand tooling master models or die gauges, and these difficulties entail reat expense .and delay in production and cause a high proportion of rejects.

These disadvantages are avoided by the present invention which is predicated on the photographic reproduction usually from. large scale sectional pattern drawings of the. article. .to be made, .on to a sensitised gauge plate, which plate is then out to the form of the image reproduced to provide templates for assembly in an appropriate jig and from this jig the die is formed as a print in low melting point alloy, suitably tin bismuth because of its low casting shrinkage.

Dealing specifically, for simplicity of description, with the manufacture of dies for producing wax injection models or patterns for the casting of turbine blades, the pattern drawings are conventionally twenty times the actual blade size and for the purpose of the method of die making according to the present invention only need show the sections of the blade at successive stations longitudinally spaced along the blade, with blade and station identifications clearly marked as well as the die datum line and-it may be--a division line as between the two dies of the mating pair, these latter being arbitrarily selected by the die sinker to permit, if possible, the splitting of the dies with no undercuts and usually followin the leading and trailing edges of the blade.

For each station the drawing with these datum and split lines is photographed on to a sensitised gauge plate and this provides the outline for a template. Allowances for shrinkage during casting are very simply made by arranging that the photographic reduction on to the gauge plate is say 19.6 instead of which is the scale of the drawing.

The invention will now be described with reference to the accompanying explanatory drawings which illustrate schematically the successive stages in the process.

4 Claims. (01. 76-107) For instance, Fig. 1 shows a fragment of the gauge-plate 1 upon which there has been reproduced photographically by printing the sectional outline 2 and 3 of a particular station along the length of the blade as well as the die datum line 4 and 5 and the arbitrarilyxselected split lines 6 and I,

Fig. 2 shows the contours of the mating dies at this station and the mating templates from which they are to be formed while Fig. 3 shows one of the templates cut to the outline of the print, 1. e. after the gauge plate has been filed to shape and checked by projection against the large scale drawings.

As shown in Figs. 4 and 5 the checked templates It for the selected stations. are now assembled with interveningv accurately machined spacer blocks 1 1 corresponding to the station in tervals in a steel jig [2 having walls L3 with flanges :4 which are complementary to the die datum lines A and 5 and therefore to the marginal profile of the templates 1.0., which are clamped in place with the platform 15 and through the medium of screws 16. the blade rootshapes are in the :main straightforward parts, machined models ll of these parts are used .101' assembly with the templates H1 in the jig l2.

The spaces between the upstanding contoured portions of the templates H] are then filled with a modelling material 20 such as plaster of Paris which is strickled to the contour of the templates, and result in a, pattern assembly in the jig as shown in Fig. 5.

A print is then taken of this jig assembly as shown in Fig. 6 at 2|, such print constituting one die of the pair required and to ensure accurate complementary conformation to the assembled jig 12, a special technique has been evolved which consists in mounting the assembled jig in the head 22 of a press 23 as shown in Fig. '7, the bolster 24 of which press mounts a die chamber 25 equipped with means, such as thermostatically controlled resistances (not shown) for raising the temperature of the tin-bismuth or other low melting point alloy in the chamber 25 to bring it to a molten condition. The jig I2 on the press head 22 is then lowered or plunged into the molten metal and the die chamber 25 is rapidly cooled by the circulation of coolant thereby forming the print or die 2|.

For the production of the other die of the pair, the complementary templates one of which is shown in Fig. 8 at 30 could be assembled as previously described in a separate jig similar to I2 but great difficulty would then arise with an article of this shape in matching the split lines 6 and I of the two dies of the pair and accordingly it is preferred to use the same jib l2 for forming both dies. To achieve this, the strickled impression in such jig I2 is saw slotted at the appropriate stations adjacent to the templates l0, and the complementary templates 3!] are mounted in the saw cuts and anchored in position on the steel jig l2 by means of holding bolts 3| and crosspiece 32 with spacer members 33 as shown in Figs. 10 and 11. The complementary templates 30. thus assembled share the split lines 6 and I of the first templates In in the surround of the impression and in this way the same datum and split line jig surface are used in the production of both dies of the pair.

A print is then taken of the jig with such projecting templates in position as represented in Fig. 9 by press casting as before, but in this case the complementary templates 30 are disengaged from the jig l2 and left in the cast print which is shown at 36 in Fig. 12.

The machined root I1 is now removed from the jig l2 and positioned in the print 36, plaster of Paris 34 is then strickled to the contour 3 of the templates 30 as shown in Fig. 13 and a second print 37 is taken from it by press casting as described in reference to Fig. 7, which second print 31 is the complementary die.

The complementary dies 21 and 31 making up the pair for the accurate reproduction of wax models or patterns are shown together in Fig. 14.

Although the invention has been described with more especial reference to dies for the plastic moulding of models for the precision casting of compressor and turbine blades it will be understood that it is not limited in this respect but is applicable to the making of dies in any appropriate material for the production of shaped articles to precision limits.

What we claim is:

1. A method of die making including the steps of preparing templates to the contours corresponding to the cross section at successive sta- 45 tions along the length of the article, assembling the templates in a jig, forming one component of the die by taking a casting of the assembled jig, removably applying to said jig templates conforming to the contour of the surface of the other component of the die, taking a casting of the jig and applied templates, and on removal of said jig leaving said applied templates in said lastnamed casting.

2. A method of die making according to claim 1 wherein the dies are pressure cast by plunging the assembled jig into a molten bath of low melting point alloy and thereafter rapidly cooling such alloy by circulation of coolant therearound to form a print of the assembled jig.

3. A method of die making according to claim 1 wherein the mating dies of a pair are formed as prints in low melting point alloy and wherein the split line surfaces of both dies of the pair are generated from one and the same jig surface.

4. A method of die making according to claim 1 wherein the templates conforming to the contour of the other component of the die are applied as a unit and inserted in slots intermediate the stations of the first-named templates.

JOHN AHERNE HERON. JOHN SHAW. LOTHAR N. HOCKING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Miller et al. May 1, 1934 Alexander Sept. 20, 1938 Brennan Sept. 16, 1941 Hart 1- Feb. 24, 1942 Tryon -1 Aug. 3, 1943 Gage et al. a Feb. 20, 1945 Bergstrom et al. Mar. 27, 1945 Bennett et al July 30, 1946 Singleton et al Aug. 24, 1948 OTHER REFERENCES Di-Metal for Dies and Punches, published by Federated Metals Division American smelting and Refining Co., 120 Broadway, New York 5.

Images