The Amalgamated Society of Engineers, Machinists, Smiths, Millwrights and Pattern-makers was formed in 1851 when a number of engineering unions decided to amalgamate. These included the Journeymen Steam Engine, Machine Makers and Millwrights Friendly Society (the 'Old Mechanics') and the Smiths' Benevolent Sick and Burial Society. By July 1851, both the Society of Millwrights and the Society of Engineers and Machinists had also amalgamated with the new society. It was during this initial period of development that the name of the society began to be shortened to the Amalgamated Society of Engineers or ASE.
The objective of this new union was to abolish all cases of systematic overtime and piecework, to restrict the number of apprentices trained by each group of journeymen and to oppose employment of men who had not served time in the industry ('illegal' men). Membership of the Amalgamated Society of Engineers was also limited to men and only workmen who were free from physical defects which may affect their ability to work, e.g. glasses. These objectives were first tested in 1852 when men employed at Hibbert and Platt made demands for the abolition of overtime and the exclusion of 'illegal' men from the machines. Their employers complied and other union members began to make demands about stopping overtime and piecework. This led to the closure of every engineering firm in London and Lancashire for three months of intense negotiation. Eventually, the need for money and work meant that ASE members returned to work and were forced by their employers to sign a document resigning their union membership. The workers duly signed these agreements but did not actually leave the union.
In 1891, many of the engineering societies who had chosen not to amalgamate with the ASE, formed the Federation of Engineering and Shipbuilding Trades. The ASE refused to join until 1905 but had withdrawn from the Federation by 1918 as it wanted to pursue the idea of uniting all engineering workers in one union. By 1919, they had managed to get 17 societies to ballot their membership on this issue but only 9 of these agreed to the principle of amalgamation. On 1 July 1920, the society changed it's name to the Amalgamated Engineering Union
Source: A Marsh & V. Ryan, The Historical Directory of Trade Unions (Aldershot, 1984), Vol. 2., pp.15-6
From the guide to the Swansea Amalgamated Society of Engineers, 1917-1925, (Swansea University)