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Selection of the type of side locating is performed according to the type of strict face connection. Those types of connections are obtained by analysis of the possible positions of the toleranced inside diameters in the plane face. Two types of strict connections are pertinent to this case: deviation from perpendicularity between axes and distance between skew axes. Cases of concentricity of axes, parallelism of axes, and distance between
axes are always associated with the components on opposite faces. Two opposite faces should be machined in the same clamping, especially if they are strictly tolerance-related, which is why those cases are unimportant from the fixture standpoint.The requirement of perpendicularity of the two axes does not influence the fixture configuration but increases the necessary fixture accuracy in respect of parallelism as well as the surface quality of the workpiece plane locating surface (Fig. 8).
The tolerance of the distance between the skew axes depends on the number of axes and connection direction; therefore, typical cases of strict connections have been established with regard to the plane locating faces (Fig. 9). The most suitable types of side locating have been established for typical cases, based on the analysis of locating errors for the main clamping which depends on the machining accuracy in the first (additional)clamping. Strictly tolerance-related inside diameters in the plane locating face are selected for side locating surfaces.
Clamping types s1.1 and s1.2 are used in this strategy.
With this strategy, the main clamping always comes second in the sequence.
4.2 Reduction of technological process into clampings
After solving the main clamping fixture, it is possible to reduce technological process to main and additional clamping. The following strategy is used in the reduction:
• If the plane locating type is pos1, four workpiece faces are machined in the main clamping, while in the additional clamping,the plane locating face and its opposite face are machined.
• If the plane locating type is pos2, then three workpiece faces are machined in the main clamping. In the additional clamping, the plane locating face from the main clamping should be machined together with the face, which is facing the machine table and the face opposite to it.
• If the plane locating type is pos3, then reduction of the technological operation to main and additional clamping presents a more complex task because the main clamping plane locating face has to be partially machined in both the main and additional clamping.
Fig. 10. A test example for the fixture solution system
Table 1. The output presentation from the expert system for set-up and fixture planning
Partial output based on the facts Meaning
Fixture for main clamping
fixture_solution(m_clamp, seque, second) The main clamping is the second clamping
fixture_solution(m_clamp, plane_loc_type, pos1) The plane locating type is horizontal (pos1)
fixture_solution(m_clamp, plane_loc_face, bottom) The plane locating face is the bottom face
fixture_solution(m_clamp, plane_loc_surf, 27) The plane locating surface is the feature denoted with number 27
fixture_solution(m_clamp, side_loc_type, p22) The side locating type is p22 (see Fig. 5.)
fixture_solution(m_clamp, guid_loc_surf, 28) The guiding surface is the feature number 28
fixture_solution(m_clamp, endw_loc_surf, 29) The endwise locating surface is the feature number 29
fixture_solution(m_clamp, clamp_type, s12_4) The clamping type is s12_4 (see Fig. 6)
fixture_solution(m_clamp, clamp_surf1, 24) The clamping surfaces are the features with number 24, 23, 25 and 26
fixture_solution(m_clamp, clamp_surf2, 23)