Method of manufacturing a mould for producing a lamp lens element

摘要

A mould for producing a lamp lens element comprises a mould plate having a plurality of recesses in one face thereof. Each recess is adapted to produce a projection on one face of the lens element produced from the mould, and is shaped so as to define in the projection a lens integral with and overlying a prism. In one embodiment, each recess has a concave part-spherical surface portion whose axis is inclined to the perpendicular to the general plane of the said one face of the mould plate. Alternatively, each recess is in the form of an elongate groove having a part-cylindrical mid-region whose axis is inclined relative to the general plane of the said one face of the mould plate. In the latter case, the groove also has part-spherical end regions whose axes are each either perpendicular to the said general plane or inclined at an acute angle to the perpendicular to the general plane. In a further embodiment, each recess is in the form of an elongate groove wich is concavely curved in a longitudinal plane thereof and shaped so that the said lens and the said prism are each of part-annular form. In all of the above cases, adjacent recesses overlap and are arranged in a plurality of rows. A method of manufacturing a mould for producing a lamp lens element comprises effecting a cutting operation on a mould plate to produce in one face thereof a plurality of recesses of the type described above. The cutting operation is effected using either a spherical cutter or a Woodruff-type cutter, as the case may be. Where a spherical cutter is used, the rotation axis thereof is either oriented perpendicularly with respect to the general plane of the said one face of the mould plate, or is inclined at an acute angle to the perpendicular to the general plane of the said one face of the mould plate. Where the spherical cutter is used to produce a groove, the cutter is first brought into contact with the said one face of the mould plate, and the mould plate and cutter are then moved relative to one another at an angle to the said general plane.