Difficult Machining Due to Wrong Blank Selection

In the field of machining, the selection of blanks is crucial to the production of parts. It not only affects the economy of blank manufacturing but also directly relates to the cost of machining. This article will discuss the common types of blanks, considerations for selection, and the determination of blank shapes and sizes.

Blanks are mainly divided into castings, forgings, profiles, and welded parts. Castings are suitable for complex shapes and are categorized into hand molding and machine molding, suitable for different production scales. Forgings are suitable for high-strength steel parts and are divided into free forging and die forging, with the latter offering higher precision but also higher costs. Profiles come in hot-rolled and cold-drawn varieties, with hot-rolled being less expensive and cold-drawn offering higher precision. Welded parts are simple to manufacture but require aging treatment.

When selecting blanks, considerations must be given to the material of the parts, structure, production type, existing conditions, and the application of new processes. Parts made of cast iron and bronze should choose castings, while steel parts can select profiles or forgings based on strength requirements. Blanks with complex shapes are usually cast, with large parts using sand casting and medium to small parts considering advanced casting methods. The production type influences the choice of blank manufacturing method, with high-volume production favoring methods with high precision and productivity.

The shape and size of the blank are based on the requirements of the part, plus machining allowances and tolerances. The machining allowance and tolerance of the blank affect the labor and material consumption of machining. The trend in modern mechanical manufacturing is to reduce machining through blank refinement. When determining the shape and size of the blank, it is also necessary to consider the setup of process tabs, the adoption of integral blanks, and the use of combined blanks, as well as the impact of blank manufacturing, processing, and heat treatment.

Finally, drawing a blank diagram is necessary. It is based on the part drawing with added blank allowances and considers manufacturing conditions. The blank diagram uses double-dashed lines to distinguish between machined and non-machined surfaces. In summary, the rational selection and refinement of blanks are key to improving production efficiency and reducing costs.