Investment casting also called lost wax casting is popular used for manufacturing precision metal casting and machining parts, every step in the process of metal casting, from pattern-making to heat treating, should be done carefully to avoid problems.
Chemical Composition Inspection
Chemical composition is the only feature that identifies the specification of material. Spectrum analysis is the most widely used method to do material chemical composition inspection. As you known, investment casting also called lost wax casting is pouring melted steel into shell pattern through the spure. Different steel has its own characteristics, so any composition error of elements might bring much trouble to customers. Before pouring, we must test the chemical composition of materials accordingly for each furnace of melted steel, with the help of spectrometer we can get accurate testing result shown the composition of each element contained. Also, with the testing result, we could ensure the test result meets the standard compositions of the specified steel grade, then this furnace of melted steel is accepted to use and make record for each batches.
Ningbo Investment Casting Co., Ltd has strictly quality control procedure in material. When ordering raw material from our audited suppliers, material certificate is requested and provided. We will randomly pick some samples to do the chemical composition in-house to have a second confirmation, and then make the labels for each batch. Finally, the labeled raw material will be delivered into our warehouse.
Before production, we will pick sample of raw material to compare the composition of each element by spectrograph. Before the melted steel pouring, we must test the chemical composition accordingly for each furnace of melted steel, with the help of spectrometer we can get accurate composition of each element contained. The furnace of melted steel is accepted to use only the test result meets the standard compositions of the specified steel grade, and our tester will make record for each result of furnace.
And after casting or heat treatment process, our testing equipment will help us to confirm if the material composition is changed during the production process. Our spectrometer is linked to a computer. The reports are stored on the system so that the information is always available. Proper archiving of each batch testing result ensures the traceability of your product. What’s more, we will keep test bars or coupons in-house for 2 years at least.
All the testing results will be shown in a material report. In the report, you can see the material specification, quantity of samples, part number, purchase order number, heat number, each element, defined limits, testing value of each element, tester, ect. As per our quality control process, we submit our material report to our customer for final judgment if our investment castings are qualified or not.
Mechanical Properties Testing
Mechanical testing is one of the most important parts of any materials testing program. For Tensile Testing and Impact Strength testing will destroy the test piece in the process. Our steel foundry will cast test coupons alongside the product casting. Quality test results from the test coupon in same heat treatment furnace are assumed to be true of the cast product as well. So usually, we’ll do mechanical properties testing both for machined test coupon and the test bar which is machined from casting body if the investment casting is available and suitable enough to machine a test bar.
It is measured by a tensile tester, by pushing materials to failure so we can collect data to determine ultimate tensile strength, yield strength, elongation and reduction area rate and more. The testing confirms the properties comply per the specified mechanical requirements. To confirm the properties of the investment cast part, Ningbo Investment Casting lab will perform below mechanical properties testing to confirm proper investment casting quality. Tests conform to ASTM E8/E8M, E18, E384 and B578.
Tensile Testing- A destructive test process that provides ultimate tensile strength, yield strength, elongation and reduction area rate of the products. Tensile tests are usually carded out on test bar, strip or machined coupon with either circular or rectangular cross section. Test pieces are screwed into or gripped in jaws and stretched by moving the grips apart at a constant rate while measuring the load and the grip separation. Our tensile tester is linked to a computer as well. The testing results are stored on the computer for future trace.
Universal Tensile Testing Machine
Impact Strength-Impact strength is measured by allowing a pendulum to strike a grooved machined test piece and measuring the energy absorbed in the break.
The test is at specified temperature while the temperature controlled. In Ningbo Investment Casting Co., Ltd., usually at least 3 charpy tests (V-notched) will be developed in the longitudinal direction in accordance with ASTM E23 or GB/T229-2007.The absorbed energy decreases at lower temperatures. We could handle the impact test Akv2(J) @+20°C, -20°C, - 40°C and -45°C depends on the requirement or castings’ service condition.
Hardness Testing-Is not an intrinsic property of a material. The values ascribed are due to a complex combination of deformation and elastic behavior. Hardness is the property that shows a materials ability to resist permanent deformation when it is under load. The greater the hardness of a material the greater the material will resist deformation. We will do hardness test when there is a hardness requirement on investment castings. For the acceptable investment castings, the tested casting hardness value must be within the given range, relevant hardness value will be listed on the MTR and submit to our customer for approval.
At Ningbo Investment Casting Co., Ltd, there are mainly three types of hardness testing, Brinell Hardness Testing, Rockwell Hardness Testing and Vickers Hardness Testing.
Corrosion Resistance Tests
Corrosion tests are not usually required unless the investment castings are to be used for the corrosive environments or corrosion resistant alloy such as casting stainless steel in which case tests may be carried out on body of investment casting parts and test bars (coupon). Our lab usually use various salt spray exposures of which the most frequent is the neutral salt spray.
If you have any steel investment castings with all of the needed material testing, pls feel free to contact us.