Trunk constraint matching method for process route

2022-08-12
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The backbone constraint matching method of part process route decision

the determination of process route (mainly process sequencing) is the key to the rationality of process design, and it is also one of the difficulties of process design. Process sequencing has strong pertinence, many factors need to be considered, and the treatment method is very flexible in production practice. Generative CAPP system, whether it is hierarchical, phased constraint driven sequencing, or Ang's method, divides sequencing constraints into static constraints and dynamic constraints, and sorts process routes at two levels; Or it can be transformed into the so-called topological sorting. Although there are some advantages, there are also some problems in the implementation of decision-making: it is difficult to express and extract process knowledge, the decision-making method is inconsistent with the thinking habits of process personnel, and there are many difficulties in the implementation of decision-making logic

the process route decision is generally considered from the whole part. The same large class of parts have their basically fixed process sequence, and have the inherent habits of the factory. There are few cases where the process sequence is completely created from scratch. The route trunk constraint matching method, which extracts the route decision-making knowledge and sets up the reasoning machine based on the part category, will better solve this problem

1 basic idea

the basic idea of trunk constraint matching method is: Based on the classification hierarchy of parts, summarize and summarize the commonness of various parts' process routes, and form a group or several groups of processing sequence rule sets, which is called process route trunk. The process route reasoning machine takes the process route trunk as the basis, considers the processing method, production batch, part geometry, manufacturing environment and other constraints, automatically matches the process trunk and makes appropriate corrections to deduce the process route of new parts. The trunk constraint matching method is based on group technology and expert system technology, which is different from the derived method, so it can better meet the needs of process decision automation. The basic process can be shown in Figure 1

Figure 1 process of trunk constraint matching method

2 extraction and expression of process trunk

1) part information description

because this is mostly a work that can be completed by men, the same type of parts have similarities in feature types, quantities and relationships, and some feature types, dimensions and accuracy of the same parts are the same or similar. Therefore, this paper establishes the corresponding process information description formats for several parts

for example, the "orientation feature method" is used to describe the process information of box parts:

a. the parts are divided into six orientations: front end face, rear end face, left side face, right side face, top face and bottom face, and each feature information is described in each orientation. It is numbered with three digits. For example, "102, hol" indicates the through-hole with serial number 2 on the front end face. Describe the positional accuracy between two feature numbers. Describe materials, blanks, batches, names and other data in the header information; The characteristics of inner cavity casting without machining have little to do with process design and will not be described. Code the parts with jlbm-1 system as required

b. set a unified coordinate system to determine the spatial position of each feature: take the axis line of the main support hole (such as the headstock spindle hole) as the z-axis, the direction pointing to the rear end is positive, the x-axis is horizontal to the right, and the coordinate origin is the hole center of the main support hole inlet. According to this method, the values of six azimuth coordinates can be determined. For example, the coordinate values of the front end feature are (± x, ± y, O)

c. introduce the concept of part information input template to minimize the workload of information input. A template is a template data file for the information description of similar parts, with many input references and default contents

for example, connecting rod parts can be described as: material, blank type, batch, code, big head aperture and deviation and roughness, small head aperture and deviation and roughness, big head end face distance and deviation and roughness, small head end face distance and deviation and roughness, hole center distance and symmetrical deviation, perpendicularity of hole center line to end face, parallelism of two hole center lines, auxiliary feature description

2) knowledge extraction and expression

the backbone of the process route is the global knowledge of part processing, which is based on the commonness (universality) of similar parts processing. Focus on the arrangement of processing procedures for the main features of parts. Only the commonness (processing method and processing object) of the processing sequence of various parts is extracted, and its individuality (process size, equipment, tooling, cutting amount, etc.) is discarded

only the representative features of the parts and the processing sequence of the main features are listed. The so-called representativeness refers to one of the same characteristics in a certain direction. For example, if there are several holes with the same accuracy on the side of a part, the processing order of only one hole is listed in the main route. The so-called main features generally refer to the functional features of parts or feature surfaces with high precision and difficult to machine. For example, the spindle hole and bottom surface of the headstock of a machine tool

in addition, the coarse datum and fine datum of similar parts are generally fixed on some important surfaces (such as the spindle hole and bottom surface of the spindle box part). These important surfaces are often the symbols to distinguish parts, which are directly given in the decision-making knowledge

organize inference engine and decision knowledge according to object-oriented method. Subclasses inherit or overload the decision knowledge and methods of the parent class. Due to the independent extraction of backbone knowledge, the relevant inference engine can be designed to be universal or at least universal in a large class of parts

the program internally uses a framework structure to create personalized products that customers need to express backbone knowledge, and externally stores them in the form of independent knowledge files. It consists of frame name, groove and constraint conditions. Each frame has several slots, and each slot has thousands of sides

frame name {ako slot: (part category); prop slot: (part description subframe);

locating slot: (Rough datum feature, fine datum feature);

rough machining: (each process in rough machining stage);

semi finish machining: (each process in semi finish machining stage);

finish machining: (each process in finish machining stage);}

3 constraint matching process

specific parts have their own personalities, so constraint matching must be carried out on the trunk of the process route. The process is as follows:

machining method and machining surface matching before the process route decision, the machining method chain of each machining surface of the part has been defined. Starting from the first record of the sorting rule, search for a processing method in the sorting rule in the part feature information Danieli group, which is the second largest metallurgical equipment production and R & D enterprise. Fortunately, it is the corresponding processing object feature, and then search for the corresponding processing method in the processing chain of this feature. If the processing method exists, the relevant information of the processing method and the corresponding features of the part is stored in the intermediate information file. Search repeatedly until all records of the collation end. The matching results of each search are recorded in turn, and finally the process route trunk of the corresponding parts is formed

there is a problem here, that is, how to match the machining object features in the sorting rules with the machining object features of the actual parts. In fact, the original information of the input part adopts the method of information template, and in the part information template, the feature numbers of the same orientation and the same function are the same, so searching by the part feature number can meet the requirements

process route trunk correction during the matching process, some corrections must be made to the process route trunk according to the specific conditions of the parts:

① soil addition method constraint correction. For example, for plane processing, precision milling and precision planing can generally achieve dimensional accuracy it7 and roughness ra5 O m; In the process route trunk, if only the finish milling process is set, but due to the limitations of machine tools and equipment, there is only the finish planing process in the plane processing method chain. At this time, it is necessary to replace the finish milling with the finish planing. For another example, if the actual processing chain of a hole is "drilling + expanding", and the processing chain of this kind of hole listed in the process trunk is "drilling + expanding + reaming", then the reaming process is deleted during matching

② there are two cases of feature correction. One is that the processing feature in the sorting rule has no corresponding feature matching it in the part information. At this time, the process corresponding to the processing feature should be eliminated; Another case is that there is a process feature (assumed to be a) that is not in the sorting rule in the part information. At this time, you must search the position of other features (assumed to be b) in the sorting rule in the part information with the same orientation as the feature, and then insert the processing method chain of a correspondingly

4 example

Figure 2 connecting rod parts figure

take Figure 2 parts as an example. There are many similarities in the function, structure and manufacturing process of this kind of parts. However, there are also some differences in the process due to the differences in batch, blank type (integral or separate forging of body cover), structure and accuracy, and the constraints of manufacturing equipment. Four kinds of process route trunks are set according to different batches and blank types. The following is one of them:

{ako slot: (medium batch connecting rods);

prop slot: (body cover separation, it_bighol>=6, ra_

bighol>=0.5, it_smallhol>=5, ra_

smallhol>=0.5, it_bigface

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