Investment casting is popular used for manufacturing precision metal parts, every step in the process of metal casting, from pattern-making to heat treating, should be done carefully to avoid problems with the soundness, surface finish, mechanical properties, and final dimensions of the finished casting. Yet even castings made with diligence should undergo inspection for quality control. Some problems can arise unexpectedly, so to guarantee the quality of products, it is necessary to do quality control before delivery. Inspection allows foundry and clients to feel confident they have a quality casting.
We offer a wide variety of in-house investment casting quality verification and product testing services to find casting defects through destructive and non-destructive testing design to provide our customers with the highest quality cast product. No matter where the product is applied, each precision investment castings is inspected and approved before delivery.
Visual Inspection uses the human eye to identify surface defects, cracks, air holes, pin holes, slag or sand inclusions, mis-runs, cold shuts, and shrinkage porosity. And all the inspection result must be documented and stored to record all the products made from our foundry.
Dimensional Inspection is undertaken to ensure a part meets dimensional requirements/tolerances. Although sometimes, the finished product looks perfect after visual inspection, it does not mean they can put into use without doubt. In this case, dimensional inspection is vital to guarantee. This can be done manually by using measuring tools for investment castings such as vernier caliper, depth indicator, dial indicator, ect., and designed testing gauge to do 100% testing for critical dimensions and with a coordinate measuring machine (CMM) that uses probes to get very precise measurements.
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. Before production, we will compare the composition of each element by spectrograph, and the recorded result will show if the material is within the range. 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. And each batch testing result will be recorded in our laboratory room for future trace. What’s more, we will keep test bars or coupons in-house for 2 years at least.
Mechanical Properties Testing
Mechanical testing is one of the most important parts of any materials testing program. By pushing materials to failure, we can collect data to determine ultimate tensile strength, yield strength, elongation and reduction area rate and hardness and more. To confirm the properties of the investment cast part, Ningbo Investment Casting lab will perform mechanical testing to approve the quality of products. The testing confirms the properties comply per the specified mechanical requirements. Our lab will do 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.
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.
Hardness Testing-Is not an intrinsic property of a material. The values ascribed are due to a complex combination of deformation and elastic behavior. We will do hardness test when there is a hardness requirement on investment castings. Hardness testing result is mostly shown in HB or HRC. Additionally macro and micro hardness testing is available.
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.
Non-destructive Testing (NDT)
Nondestructive Testing (NDT) is one of the main procedures of quality control in steel casting, and plays an important role in assuring that steel castings will perform well during service. Nondestructive Testing (NDT) technicians perform the necessary tests to locate the indicators and discontinuities that may cause failures or shut downs in such systems. These tests are performed in a manner that does not affect the future usefulness of steel castings. Non-destructive testing is done by our foundry QC person, customers’ QC engineers, and third-party NDT technicians to verify the internal and external soundness of a casting without damaging the casting itself.
Non-destructive Testing (NDT) Methods Performed on Steel Investment Casting
Visual and Optical Testing (VT)
Visual Examination can be an effective way to recognize surface imperfections that could adversely affect our steel castings. Visual Examiners use knowledge of how a steel cast part is manufactured, the function of the human eye, lighting requirements, and precise measuring tools to evaluate materials.
Liquid Dye Penetrant Inspection (LPI)
DPI is a testing method used for surface defects of all metal investment castings. In this inspection process, the tester first cleans the casting to remove any particles of grit or dust that may prevent the liquid dye from going into cracks in the metal. Once clean and dry, a dye solution with color is applied to the surface of the castings. The dye, which is suspended in penetrating oil, finds its way into the surface defects. When a special developer is applied, the casting defects become clearly visible. The solution is to detect any cracks or other surface defects due to porosity or gas that produced on the surface. Sometimes it is difficult to find the surface defects by naked eye, such as tiny cracks, pores or other surface defects.
Magnetic Particle Inspection (MPI)
MPI is similar to LPI in that it is used to find small cracks and holes on or near the surface or shallow subsurface of investment castings. It is accomplished by inducing a magnetic field into a ferromagnetic material and applying iron particles to the surface of the metal castings being examined. MPI testing is convenient and affordable. Cracks and defects have differing magnetic properties than those of the surrounding material. Their presence will interrupt the magnetic field, causing distortion, which indicates the shape and position of the crack or void.
Ultrasonic Testing (UT)
Ultrasonic Examination finds defects by using high frequency acoustic energy transmitted into a steel casting, to detect discontinuities or locate changes in material characteristics. Sound waves travel through a casting until they hit the opposite surface or an interface or defect. Any barrier reflects the sound waves, which bounce back and are recorded for an analyst to look at. Ultrasonic Testing (UT) in a technology similar to the ultrasounds used by medical technicians.
Radiographic Inspection (X-Ray)
Radiographic Examination involves using radioactive isotopes (gamma rays) or X-rays on steel casting create images or films. The ghostly images produced through casting X-Ray show dark spots where there are shrinkage cavities, the small breaks and crevices of heat cracking, or the pinhole dots of porosity. These images help an experienced metalworker decide if the casting’s mechanical properties are compromised by shrinkage, inclusions, or holes and whether they can be fixed before castings are shipped.
After all of the inspections are completed, we will submit all the reports with related photos for our customer approval. Then we’ll arrange the shipment once we got the approval from our customer. If you have any request for metal castings, please do not hesitate to email Ningbo Investment Casting Co., Ltd for price.