The quality of machine tool invest castings mainly includes appearance quality, internal quality and service quality. The internal quality of machine tool castings mainly refers to the chemical composition, physical properties, mechanical properties, metallographic structure, holes, cracks, inclusions, segregation and other conditions existing in the machine tool castings; the service quality of machine tool castings refers to the durability of machine tool castings under different conditions, including wear resistance, corrosion resistance, cold and heat resistance, fatigue, shock absorption and other properties, and Machinability, weldability and other process properties. The quality of machine tool casting has a great influence on the performance of mechanical products.
The primary quality index of casting parts is mechanical properties. There are two methods to test the mechanical properties of castings. One is tensile test, the other is hardness test. The tensile test tests the tensile strength, yield strength and elongation of the workpiece, while the hardness test reflects the comprehensive properties of various physical quantities, such as elasticity, plasticity, strength, toughness and wear resistance, under their respective specified conditions. Tensile test is specified in china casting standard for almost every product. Hardness tests are specified for most products.
Tensile test equipment is complex, high investment, need professional personnel, need to prepare samples, test efficiency is low, high cost. The hardness test equipment is simple, easy to master, the indentation is very small, can be regarded as non-destructive testing, can directly test finished or semi-finished cnc machining parts. The test efficiency is high, and it can be used to test the batch parts one by one. With the development of hardness tester manufacturing technology, various portable instruments, especially high-precision portable instruments, have emerged, which makes hardness testing simple, fast and accurate. It makes it possible to carry out on-site hardness testing, hardness control on production line and accurate hardness testing of large workpieces.