Die coating

A metal die for use in casting pistons for internal combustion engines having over at least a part of its internal cavity forming surfaces, indentations of predetermined depth, area, distribution and cross sectional shape, formed by employing a technique selected from the group comprising photoetching and electrochemical etching, the die cavity forming surfaces also having thereon over at least the part of those surfaces with indentations, a coating of a hard, corrosion and erosion resistant material which extends into and between each indentation as a continuous coating layer, said coating layer having a substantially uniform thickness and a controlled surface roughness.

A method of making a metal die having a coating thereon for use in casting pistons for internal combustion engines, the method comprising the steps of forming in at least some internal die cavity forming surfaces of the metal die, by employing a technique selected from the group comprising photoetching and electrochemical etching, indentations of controlled depth, area and distribution, and depositing over at least those surfaces having indentations a hard, corrosion and erosion resistant material which extends into and between each indentation as a continuous coating layer, said coating layer having a substantially uniform thickness and a controlled surface roughness, and wherein variation in area of said indentations is achieved by using a sequence of masks.

A metal die including internal die cavity forming surfaces for use in casting pistons for internal combustion engines having over at least a part of said internal die cavity forming surfaces, indentations of predetermined depth, area and distribution, formed by employing a technique selected form the group comprising photoetching and electrochemical etching, the die cavity forming surfaces also having thereon over at least the part of those surfaces with indentations, a coating of a hard, corrosion and erosion resistant material which extends into and between each indentation as a continuous coating layer, said coating layer having a substantially uniform thickness and a controlled surface roughness, and wherein at least some of said internal die cavity forming surfaces are provided with both indentations and a hard coating, and other surfaces of the die which are in contact with each other in the assembled die, and which move relatively to each other during assembly and disassembly of the die, have a hard coating only.