Metal tools and implements – making – Blank or process – Die
Patent
1993-03-31
1994-08-16
Parker, Roscoe V.
Metal tools and implements, making
Blank or process
Die
164 19, 164 46, B21K 520, C23C 408, C23C 418
Patent
active
053376315
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of producing tools and dies.
Tools and dies for use in the plastics industry are frequently made by a replication technique from a master pattern. Such techniques typically involve spraying low-melting metals such as zinc onto the pattern followed by releasing the solidified metal from the pattern and subsequent use. Such negative replicas are very succesful and are able to replicate fine detail.
Meanwhile, work on spray forming of metal has established that dense massive artefacts in high-temperature metals including die steels can be manufactured by a spray forming technique using atomised liquid metal. The advantages (as with low-temperature metals) are fine grain size, absence of macro segregation, good mechanical properties and low cost per kg of deposit. Unfortunately this technique cannot be applied directly to making tool steel dies by replication because high internal stress during deposition and subsequent cooling of high-temperature metals cause marked distortion. Such distortion invalidates this process as a possible contender for making dies that have to withstand very high pressures during the pressing and forging of metals.
A further development of spray forming is simultaneous spray peening, described in GB Patent No. 1605035, and used for making dense ductile products. The disclosure of GB 1605035 is incorporated herein by reference. Simultaneous spray peening as there described achieves controlled internal stress in the products while preserving the other benefits of spray forming. In more detail, the spray deposit is continuously densified as it builds up by the mechanical work which is imparted from the peening at high temperature to the deposit, and the tensile thermal stresses, which normally lead to distortion of spray formed deposits more especially at higher temperatures, can be neutralised by the compressive stresses induced by the peening action. By adjusting the kinetic energy of the incident peening shot, internal stresses can be controlled so as to eliminate distortion of high temperature deposits (e.g. tool steel or Stellite), in theory enabling reliable replication in even these metals.
However, tn practice, various difficulties remain in some cases. Thus, at the commencement of deposition during simultaneous spray peening, the peening balls hit the pattern surface or the first few splats of metal deposited on the pattern. If the pattern is of a soft material such as wood, plaster or a polymer, the impact of the peening balls may shatter or indent the pattern. In the case of plastics and wood, the high temperature splats of tool steel impacting the surface may also decompose or char the pattern surface, which may render it unusable for repeated use. Metal or refractory patterns are less likely to suffer from this problem but are inherently more expensive to make. A further difficulty occasionally met is that if the first few splats are solidified very rapidly, the first 50 .mu.m of the negative replica surface may be slightly porous, making the surface of the die slightly softer than the rest of the deposit. This undesirable effect is particularly evident with metal patterns, which have high thermal conductivity.
Another well-known technique of replication of a pattern is electroforming. This technique is so good at copying fine detail that it is used for making phonographic record masters. In electroforming, the pattern surface is copied by electroplating. Thus, the pattern surface, if not already electrically conductive, must be made so by (for example) spraying or painting it with a volatile suspension of colloidal graphite or sputtering it with gold. The pattern surface is made the cathode in a solution of a salt of an electroplatable metal.
An electrodeposit of the metal thereupon gradually forms on the pattern (cathode) and builds up to produce an electroformed shell or "electroform". The process is continued until the electroform has reached its desired thickness, when it is detached from the pattern, whose surface derail it will hav
REFERENCES:
patent: 2258452 (1941-10-01), Ingham et al.
patent: 2281634 (1942-05-01), Stoessel
patent: 3826301 (1974-07-01), Brooks
Patent Abstracts of Japan, vol. 13, No. 111, Nov. 1988, JP 63-286563.
Patent Abstracts of Japan, vol. 4, No. 60, Feb. 1980, JP 55-027245.
McGeough Joseph
Roche Allen D.
Singer Alfred R. E.
British Technology Group Limited
Parker Roscoe V.
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