Sand casting, gravity die casting or investment casting: how to help a buyer pick the process

The enquiry reads "need aluminium casting for motor end cover, best rate", with a sketch attached. The buyer has not named a process because the buyer does not know one. Quote only the process you run, and the buyer sets your number beside a foundry quoting another process and picks the lower, without seeing that one carries a die cost and the other carries extra machining. Reply with a short comparison: what each process costs once, what it costs per piece, the finish it gives, and the quantity at which the choice changes. Then recommend one.

Why a buyer who does not know the process picks on price

This enquiry often comes from someone who has never bought a casting: a design engineer at a small OEM replacing a fabricated bracket, or a purchase officer holding a drawing with "casting" written in the corner.

They look at the piece price. They do not see the pattern or the die as a one-time spend, nor the hours their own machine shop will spend on a rough casting. So a sand quote and a gravity die quote look like a cheap foundry and an expensive one, and nobody explains that they are different things.

The three processes, side by side

Many buyers read the "paid once" row and stop. Walk them to the machining row, because that is the cost the buyer will carry.

Three questions that settle it before price does

How many a year, and for how many years? Quantity decides whether a die pays for itself. Divide the extra cost of the die over the pattern by the saving per piece, counting the buyer's machining as well as your price. If the quantity the buyer will commit to in writing does not clear that number, stay with sand. Forecasts do not pay for dies. Setting both routes out as totals in the quotation is covered in pattern and die cost.

Which faces will the buyer machine, and what must the rest look like? A visible cover needs a cleaner skin than a hidden bracket. That can push a sand part towards a die even at modest quantities.

Which material, and what does the part do? Iron points to sand in most foundries. A small, intricate stainless part with costly machining points to investment casting. Aluminium can go either way, decided by the first question.

Skip all three when the drawing names the process or the part is already approved on another foundry's process, since reopening that delays approval. Skip them for a trader collecting rates, too; ask for the drawing and quantity first.

Sometimes the honest answer is another foundry: a thin-walled aluminium housing in large numbers belongs in a pressure die shop, and a two-tonne steel casting in a steel foundry. Say so. A buyer may well come back, when the next part fits your floor, to the foundry that told the truth.

A reply a buyer can read in two minutes

Send this as plain text, by email or typed into WhatsApp. Pick the two options that fit the part.

Thank you for the sketch of the end cover. Before we price it, three questions:
1. How many pieces a year, and for how long do you expect to buy this part?
2. Which faces will you machine, and does the outside need a clean finish?
3. Is the alloy fixed (for example LM6), or open to discussion?

A part like this can be made two ways:
A. Sand cast: a pattern once, a higher piece price, more machining at your end.
B. Gravity die cast: a die once, costing more than the pattern, then a lower piece price and less machining.
Below about (quantity) pieces in total, A works out cheaper for you. Above that, B does.
We suggest (A or B) because (reason). Prices for both follow once we have your answers.

For example: a Vatva foundry and a motor end shield

Imagine a foundry in GIDC Vatva, Ahmedabad, with a sand line for iron and aluminium and a small gravity die section. A motor maker in Vadodara sends a drawing of an aluminium end shield for a new motor range, marked "die cast, best rate". The details are illustrative.

The foundry took "die cast" at its word. It quoted a gravity die and a piece price. A rival quoted sand-cast pieces with only a pattern charge, and the purchase officer took the lower opening cost. The rival's route suited a design still changing, because a pattern is cheaper to alter than a die. Within two lots the buyer's machine shop was spending about 20 minutes more on each end shield than planned, and nobody had said that cost was theirs.

When the motor maker came back for a second frame size, the foundry answered differently. It sent both options. Beside them went the extra machining on the sand casting, in the buyer's own terms, and the break-even quantity. It recommended sand for the first lots while the design settled, and the die once the drawing froze. The buyer agreed to the sand lots first. The die followed only after a redesign delayed the frozen drawing by a quarter, so the foundry carried the sand route longer than it had hoped.

Put the comparison on your site

Many of these buyers search before they write. Give each process you run its own page on your website, with metals, weight range, finish and quantities; what that page should hold is set out in what a foundry should put on its site.

Answer the next vague enquiry with two options

Take the next enquiry that says "casting" without naming a process. Before you price it, send the three questions and the two options that fit. The rest of the foundry's selling job is on the casting and foundry page. If you want the table turned into website content and a sheet your buyers can forward inside their company, tell us what you need.