Purchasing Guidelines

The ordering of stainless steel castings takes a certain amount of time and energy to qualify a potential supplier foundry. To get the best value from the stainless steel casting also requires a cooperative effort on the part of the customer and the supplier foundry from the early stages of the design through to the end manufacturing process. Good planning ahead of time will pay dividends for both you (the customer) and your supplier foundry.

The purpose of requesting a quotation for a stainless steel casting is basically to determine the lowest purchased casting cost. The customer then must weigh all of the provisions of the quotation including exceptions taken to drawings, specifications, and processing requirements, as well as supplier foundry experience, tooling requirements, tolerances, finish allowances, and delivery. Such factors as reduced machine work, better tolerances, improved delivery schedules and reliability are particularly important to determine the lowest end cost of the casting.

To avoid misunderstandings, reduce costs, and expedite the processing of quotations, all or some of the following information should be included in a request for a quotation:

  • Design – What is the part? See design below.
  • Quantity – What is the anticipated or required volume, both first order quantity and annual quantity?
  • Material and inspection requirements – what should the part be made of, and how should the part be tested before delivery?
  • Actual or estimated casting weight. Actual weight information is preferred. Estimates can be provided by the supplier foundry in the absence of actual weight information, but this may require offering prices that are subject to changes based on the actual weight of the casting(s) in question at the time of production.
  • Drawing – Machine drawings are preferred over casting drawings. Drawings or sketches are mandatory if samples are not available. Drawing should include dimensional tolerances, indications of critical areas and surfaces to be machined. See machining below.
  • Heat Treatment – Whether to use solution treatment after stainless steel casting?
  • Surface Finish – Any special surface finish requirement?

Design

To achieve the most efficient production and the highest quality product, the part should be designed to take advantage of the flexibility of the stainless steel casting process. The stainless steel foundry must have either the designer’s drawings and know the length of the run (number of parts to be made).

Stainless steel castings are generally finished with un-machined as-cast surfaces, unless otherwise specified. To take advantage of the stainless steel casting process, the supplier foundry should also know which surfaces are to be machined and where datum points are located. The acceptable dimensional tolerances must be indicated when a drawing is provided. Tolerances are normally decided by agreement between the supplier foundry and customer. Close cooperation between the customer’s design engineers and the supplier foundry is essential to optimize the stainless steel casting design.

Material

There are several stainless steel grades (304, 316, 304L, 316L, 17-4 ph, 2205, etc) available in stainless steel casting process. The purchaser should clearly know the differences of each grade and select the most suitable one to produce stainless steel castings. If you are not familar with the stainless steel material, just ask for the help of supplier foundry to determine the right one. Or, just ask the foundry to see if it is possible to cast in two or more grades for your testing, then decide the material based on the factors of low cost and best working performance.

Once starting the order, do not forget to ask for the material testing report from the foundry, and confirm the material compositions are all within the ranges. Any error on the material compositions may shorten serving life or bad working performance.

Machining

Tolerance refers to the dimensional accuracy achievable for a given production method. For the stainless steel process, mold expansion, solidification shrinkage, and thermal contraction all influence the tolerance of the finished part. Consequently, there are limits for tolerances in an as-cast part. Subsequent machining is commonly employed when a tighter tolerance is required.

In the final analysis the supplier foundry is responsible for giving the designer a cast stainless steel product that is capable of being transformed by machining to meet the specific requirements intended for the function of the part. To accomplish this goal a close relationship must be maintained between the customer’s engineering and purchasing staff and the stainless steel casting producer.

Heat Treatment

Heat treatment of stainless steel castings is normally operated before machining. And solution treatment is the only heat treatment method used after stainless steel casting, whose purpose is to improve the inner properties and make machining more easily. Customer should advise if the heat treatment is required when requesting a quotation from the stainless steel foundry.

Surface Finish

In terms of stainless steel castings, there are different surface finish ways, including shot blasting, sand blasting, electropolishing, mirror polishing, etc. Just point out which surface finish way is used for your stainless steel casting project.