# A Process Decision-Making Method for Planar Machining of Box-Type Components
## 3 Constructing a Hierarchical Information Model for Process Decision-Making
### Hierarchical Information Representation Model for Machining Process Decision-Making
#### 3.2.3 Processing Program Layer  
The \"Processing Program Layer\" constitutes the third tier of the hierarchical model for planar machining process decision-making of box-type parts. The primary function of this layer is to generate machining plans for each machinable surface of the box-type component and to establish the subordinate relationships between the design feature information and the corresponding machining plans. A planar machining plan consists of a chain of machining methods arranged in a specific sequence, following the \"roughing first, then finishing\" principle. The reasonable machining plan is derived through process knowledge based on the design features of the machinable surfaces, including precision  
Figure 5: Design features of box-type components and their machined surfaces.  
grade, design dimensions, geometric constraints, and surface roughness. Some machining plans for planar surfaces of box-type parts are summarized in the literature [32] and relevant empirical knowledge, as presented in Table 1. The relationship between certain machining plans for box-type components and their geometric tolerance constraints is shown in Tables 2 and 3.  
For example, if the accuracy class of the machined surface is IT10, the surface roughness is 6.3 \(\upmu\)m, and the surface has not undergone quenching, while it has a flatness geometrical tolerance constraint with a tolerance class of grade 11, then the appropriate machining scheme would be \"Rough milling--Semi-finish Milling\". This machining scheme is designated as CMP2, meaning that the first machining operation for this surface is rough milling, followed by semi-finish milling. These two operations together ensure that the required specifications are met.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Serial Number** & **Machining Program** & **Accuracy Grade** & **Surface Roughness** & **Applicable Range** \\ \hline CMP1 & Rough Milling & IT11–IT13 & 12.5–6.3 & & Flat surface \\  & Rough & & & & & machining without \\ CMP2 & Milling\(\rightarrow\)Semi-finish & IT8–IT11 & 12.5–3.2 & & & hardening \\  & Milling & & & & & & \\ CMP3 & Rough Milling\(\rightarrow\)Finish & IT7–IT9 & 6.3–1.6 & & & \\  & Milling & & & & & & \\ CMP4 & Milling\(\rightarrow\)Semi-finish & IT6–IT8 & 3.2–0.63 & & & \\  & Milling & & & & & & \\  & \(\rightarrow\)Finish Milling & & & & & & \\ \hline CMP5 & Rough Milling\(\rightarrow\)Finish & & & & & & Hardened or \\  & Milling & & & & & & unhardened ferrous \\  & Rough & & & & & & metal workpieces \\ CMP6 & Milling\(\rightarrow\)Semi-finish & IT5–IT6 & 0.4–0.2 & & & & \\  & Milling & & & & & & \\  & \(\rightarrow\)Finish Milling\(\rightarrow\)Griding & & & & & & \\ \hline CMP7 & Rough Milling\(\rightarrow\)Finish & & & IT5–IT6 & 0.8–0.1 & & \\  & Milling & & & & & & \\ CMP8 & Milling\(\rightarrow\)Semi-finish & IT5–IT6 & 0.8–0.04 & & & & \\  & Milling & & & & & & \\  & \(\rightarrow\)Finish Milling\(\rightarrow\)Scraping & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Selection of plane machining schemes.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Processing** & & & & & **Accuracy Class of Straightness and Flatness** & & & & & & \\
**Program** & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & **10** & **11** & **12** \\ \hline CMP1 & & & & & & & & & & & \(\bullet\) & \(\bullet\) \\ CMP2 & & & & & & & & & \(\bullet\) & \(\bullet\) & & \\ CMP3 & & & & & & & & \(\bullet\) & \(\bullet\) & & & \\ CMP4 & &