Tricone bit jaw CAPP system (2)

The reference orientation represents only a certain orientation, and it does not necessarily represent the actual machining surface. The determination of the reference orientation will make the spatial relationship of each machining feature easy to handle, and also greatly simplify the design of the clamping scheme in the process design.

2.2 Based on describing part features

In the actual process design, the feature of the part is always considered as the most basic processing unit considered in the machining process, so the feature of the part can be used to represent the geometrical characteristics of the part. Based on the analysis and finishing of the claw parts, the system takes into account the similarity of the structural form and the method, and extracts various typical features such as outer cylinder, plane, hole, end ring groove and taper thread. form. The expression of the feature is essentially a parameter table, which lists the reference orientation code of the feature and various parameters required for the process design, so as to provide a basis for the process design in detail and accurately.

2.3 supplemented by the description of the relationship between features

The relationship between the features is mainly to further determine the relationship between the processing features, and provide further basis for subsequent feature sequencing and reasonable process design, including: the associated size and shape tolerance between the same reference orientation features.

3 process creation method

Based on the feature analysis of parts, the process design can be divided into several stages of feature process chain generation, feature sorting, step sorting, and process route generation. The process design flow is shown in Figure 2.

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Figure 2 Process flow creation flowchart

3.1 Generation of characteristic process chains

Each feature surface needs to be processed through a series of processes. It corresponds to a set of processing chains, which we call the characteristic process chain. The characteristics of different processing environments correspond to different processing methods. When the manufacturing environment is constrained, the specific processing method is determined. A feature process chain consists of several processing steps in a certain order. For example, the characteristic process chain of an outer circular surface consists of roughing - semi-finishing - grinding. The principle of the characteristic process chain is: after the various methods are summarized and organized into a series of rules under certain conditions (such as feature type, size and precision, surface roughness and shape tolerance), the feature processing process is formed. The library, in actual operation, only needs to enter the library according to the corresponding parameters of each feature to call.

3.2 Determination of feature clamping scheme

The determination of the feature clamping scheme should be based on the premise of ensuring that the positioning reference of the fine reference positioning and clamping scheme can be processed, and the rough reference positioning scheme is decided. The coarse reference positioning scheme is actually the first positioning scheme in the routing, and the fine reference positioning scheme is its subsequent positioning scheme. According to the structural and technological characteristics of the jaw parts, the system summarizes several selection rules for positioning schemes.

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