Error-proof process method for machining similar products


Aiming at the phenomenon that similar structural parts of aircraft are easy to produce wrong and mixed parts in the process of manufacturing and assembly, a complete set of error prevention process method is researched, and the design scheme of merging and feature differentiation is adopted in the product development stage, and the improvement measures of identifying similar and easily mixed products are adopted in the production and management stage, which effectively solves such problems.

At present, there are a large number of similar structural parts in aircraft products, which makes it very easy to have wrong and mixed parts in the manufacturing process, resulting in product scrap, which not only affects the delivery of products on schedule, but also increases the cost of products and brings great hidden danger to aircraft manufacturing. In view of the large number of easily mixed products in the development and batch production stages of each type of aircraft, a complete set of error-proof process method was finally arrived at through a lot of process research.

Method to prevent the occurrence of similar easily mixed products in the development stage

In the process of process review and approval at the development stage, in addition to the process review, we should avoid the appearance of similar products as much as possible and review whether the similar products are designed to prevent errors. If the structure allows, it should be recommended as a priority to merge similar and easily mixed products in the product design to reduce the product variety. When similar and confusing products are combined, there are still similar and confusing potential problems, the product design should be recommended for feature differentiation.

2.1 Merging method

In the process of process review and approval during the development stage, the process reviewer should sort out all the similar and confusing products and, without affecting the body structure and assembly, request the design to merge similar and confusing products and try to merge them into the minimum number of products. The following cases of products, the requirement to merge products, mutual borrowing.

(1) the same design structure, geometric tolerances, located in different parts of the same product.

(2) The design structure is consistent or basically consistent, and the geometric tolerance is ≤ 1/10 to 1/5 of the value specified in the general tolerance document of the model.

2.2 Feature differentiation method
When similar and easily mixed products still exist after the priority use of the merging method, they can be distinguished by the characteristics. For similar and easily confused products, obvious differences can be set on the shape contour (de-cornering, inner/outer rounding, vertical rib, tab, sag, cavity structure and hole position/spacing, etc.) for differentiation.

Production stage identification of similar and easily mixed products

In the production process, it is impossible to distinguish when similar structure and similar products are placed in a pile, and they are very easy to be confused. Since there are many types of products and complex management problems, measures need to be developed in the production stage.

3.1 Process hole identification method

Similar products in each type of aircraft have very high similarity between similar structures, which is very easy to cause mixed parts when processing. However, because some products have hole system structure in a structural area in the state of the part, while other products have hole system structure in the assembly state, so the process can be distinguished with the help of holes.

(1) process initial hole selection principles Process initial holes should be set in different positions for distinguishing similarity. If there are left and right symmetrical parts of similar and easy to mix products, the process hole of the product should have symmetry for error-proof marking. To make it easy to mix between symmetrical parts, we should make error-proof process holes on the left or right side of the easily mixed products, which will form symmetry by itself. If the symmetrical parts of similar easy-to-mix products are easy to mix with each other, the symmetrical parts should be regarded as independent individuals, and error-proof process holes should be made according to the principle of error-proof unity. Products with mounting hole structure can be identified by the method of prefabricated process holes to identify the similarity of the product; products with final holes in the finished state can be machined, before completing the final hole size required by the hole system structure, a special hole or a number of holes < final hole diameter of the process hole for error-proof management.

(2) Products with mounting hole structure identify similarity through prefabricated process primary holes Products with hole system structure in the part state can be error-proofed by making one or several process primary holes with hole diameter < final hole diameter before completing the final hole size during machining. The error-proof process holes of mixed products should be set in different locations.

For example, a batch of products with mounting holes, the final hole aperture is fa. n (1 ≤ n ≤ N, N is the number of product mounting holes) holes are selected on a single product set as error-proof process holes, the aperture is fb (b < a). The remaining (N-n) holes are made with hole diameter fa or fc (c < a and c ≠ b) as required. n error-proof process holes fb are made into final holes fa during assembly. the error-proof method for products with hole system is shown in Figure 1.

Figure 1: Error-proof method of structured products with holes

(3) No mounting hole structure products by prefabricated rivet initial hole to identify product similarity Only in the assembly state of the product exists in the hole system structure (i.e. rivet holes), in the state of the part can be prefabricated in one or several hole diameter < final hole diameter process hole to prevent errors management. The specific operations are as follows.

1) Extract the hole center coordinate value (of the prefabricated rivet initial hole).

(2) Using a medium (such as supply status) to transfer the hole center coordinate values and coordinate the work of each unit.

(3) Create a process numbering model (based on the hole center coordinates and product numbering model) as a basis for manufacturing similar products with rivet primary holes.

(4) the numbering principle of the process numbering model: product drawing number + product version + GS + process numbering model version. For example, a batch of products without mounting holes in the part state, similar structure, symmetrical parts mixed. In the part state for a single product selected n (1 ≤ n ≤ N, N is the number of mounting holes in the assembly state) holes set as error-proof process holes, the hole diameter is fd (d < e, e is the diameter of the mounting holes in the assembly state). The remaining (N - n) holes, made of hole diameter f e or as required hole diameter f f (f < e and f ≠ d). n holes fd in the assembly of the final hole fe. parts state without hole system structure of the error-proof method of products shown in Figure 2.

Figure 2: Error-proof method of the product without hole system in the part state  

3.2 Scheduling distinction method

The manufacturing unit makes a reasonable scheduling plan according to the list of similar/symmetrical parts, and puts them into production in time and batches for differentiation.

Various differentiation methods are used to identify similar and confusing products

4.1 Hardness point distinction method (only for metal products)

The hardness spot distinction method uses the location or area where indentation is produced during hardness testing of metal products (indentation is generally not covered by surface plating and coating) to distinguish between different hardness testing locations for similarly intermixed products, which can be clearly defined in the manufacturing instructions/procedures by the process personnel. The selection of hardness test locations must be in accordance with the hardness documentation requirements. Hardness testers and inspectors shall be implemented and monitored in strict accordance with the manufacturing instructions/procedures.

4.2 Permanent imprint mark differentiation method

(1) permanent imprint mark If the product allows for concave and convex imprint mark, the concave and convex imprint mark can be made in the designated area of the product immediately after machining, such as marking the vibratory pen mark, etching marks and metal hard marks and other concave and convex marks that cannot be covered or eliminated by subsequent processes.

(2) Removable permanent markings If permanent markings are not permitted, permanent markings can be made in the form of additional process tabs or process lugs, which are to be removed and repainted as required before final delivery of the part.

The form and location of the process tabs or process lugs will be determined by the shop, and each lot of parts may have all or one of the selected process tabs or process lugs added.