Usually when products just research or design, they need to do prototype. The prototype is the first step to verify the feasibility of the products, is the most direct and effective way to find out the defects and the lack of the design. Therefore, the defects can be improved on target. The design and completion of the product can not be perfect, or even can't be used. Once the product is defective, it will be completely discarded, and it is a great waste of manpower, material resources and time. But generally speaking the prototype is a few samples , with short period,less manpower and material resources, and quickly finding out the shortcomings of product design, so as to provide sufficient basis for product stereotype and mass production.   

Due to various conditions, the early prototype is completed by hand in most of its works, therefore, the prototype with a long period is too difficult to strictly meet the appearance and structure of the size of the drawings. so check the appearance or structure rational function is also compromised.

With the progress of science and technology, the rapid development of CAD and CAM technology provides better technical support for model manufacturing, making the precision of the model possible.