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​How to purchase investment castings?

Purchasing investment castings is a professional job.Purchasing manager is necessary to learn about related investment casting technical knowledge, and fully communicate with foundry engineers.

1.Choose investment casting foundry

It will need joint efforts of both sides to get high quality castings.Before purchasing,buyers need to spend a certain amount of time to develop suppliers.Except to choose a good supplier,before casting design,technical communication between the purchaser and foundry is very important, therefore purchasers and suppliers should focus on establishing long-term and mutually beneficial cooperation and good interactive relationship.

In China,there are two kinds of different production process in investment casting foundry,One is water glass lost wax casting process,the production cost of such process is low,but dimension accuracy and surface roughness is not good.It is mainly used to produce carbon steel and low alloy steel castings,whose quality requirement is not very high.And it is hard to make high level castings.Another is silica sol casting,this size accuracy and surface finish are all good.Investment casting purchaser first needs to understand production process of casting foundry and testing ways,thus to know whether the investment castings produced by one certain foundry is what you expected.Purchaser also need to know the production capacity and management level to see whether they could send qualified investment casting within shortest lead time.

2.Inquiry and offer

Buyers when send inquiry sheet to investment casting foundry, should try to accurately explain information in detail like casting material processing and technical quality requirements, such as the required machining parts,locating datum,heat treatment,surface treatment, packaging requirements,inspection and test items and the inspection report, etc.Should also provide casting demand for years and every single number, place of delivery,etc.It will be best to offer the volume and weight of the casting for foundry.Delivery period and terms of payment are also offer an important factor to consider, should make this clear when inquiry or quotation.Requirements about casting quality should be economic,applicable and reasonable, on the premise of meet the use function. Higher requirements will increase the difficulty of manufacturing, which may also affect the production cost and price, this is not good for both purchaser and foundry.

Ambiguous or misleading questions should to be clarified at inquiry and quotation stage. Especially material and tolerance.In general,to the same material specification,casting and steel rolling material profile have different standards and brand, its chemical composition and mechanical properties have subtle differences, we should try to adopt casting standard when you order it. For example,Responding casting material grade of American AISI304 is ASTM A743 CF-8.AISI316 corresponding casting standard grade is CF-8M. 

3.Drawing or sample offered

Part drawing is the main quotation and production basis, the more information in the drawing,the less misunderstanding will be. Detail drawings should clearly show casting name,material,tolerance,surface roughness,critical dimensions,permitting the residual gate height,processing base,processing surface and the machined surface,parts modified content,inspection requirements,heat treatment and surface treatment requirements,etc.We suggest casting purchasers offer casting drawing and machining drawing castings separately.For irregularly shape and complex investment casting,it is best for purchaser to also provide three-dimensional drawing,for foundry correctly understand drawings and made mold with machining center.

4.Mould and samples confirmed

Investment casting sample will start from the mold design and manufacturing.Investment casting mold production costs are generally in the quotation list alone, is a one-time cost, generally need to be payed by the purchaser in advance.Mould ownership generally belongs to the purchaser, can be preserved and used by tinvestment casting foundry, but firstly need to reach an agreement.

When foundries need to modify the original design of investment castings,they should map casting or separate write written amendments to ask for purchaser's confirmation and then start to open investment casting mold.

After the mould ready, foundry need to provide sample to purchaser,to check the size,assembly, or other necessary testings.Once after sample is approval,purchaser could only place mass porduction order to investment casting foundry. Due to the mould done,some sizes are not very convenient to be modified.If it will not affect use function,customers can directly use don't require to modify mould.When the mould from a foundry to another foundry, due to using of different wax material, shell material and technological conditions,it is necessary to reconfirm the samples.

5.Place mass production order

Purchaser before formal production orders should determine whether the following is implemented:

After mold is made,many dimensions of investment castings are guaranteed by mould,foundry just needs to contain a few important sizes. Purchaser needs to point out key control size,control requirements of important surface and acceptance criteria.Only key points are clear, could the production process control is more targeted.It will be beneficial to ensure quality, reduce unnecessary consumption and improve the production efficiency.Besides,purchaser should place order in advance to ensure enough production time.