Best manufacturing method for this part?

[daniel_smith]

Hi folks,

I would like your advice on the what process(es) to use to manufacture the attached part. Attached is a 3D pdf file (open in Adobe 7 or later to spin the model around). We can either manufacture as one part (eg via investment casting) or split it into the two bodies and produce them separately. Click anywhere on the part to see the proposed split line which would enable a 2-piece tool to produce the bottom part. Draft and fillets have not been applied for modeling simplicity although we cannot have draft along the length of the internal walls.

Quantities:
year 1: ~5000
year 5: ~500000

Material:
Both parts have wear surfaces so we require hardness > Rc 50. At this stage, we're looking at 4340 steel although if we can achieve that hardness with SS, then that would be our preference for corrosion resistance.

So far we have considered:
Investment (lost wax) casting: Could manufacture as 1 complex part without draft along the length. Could also split and manufacture as two separate parts in order to simplify the tooling. This process involves a lot of manual work so we're concerned about how it will lend itself to large-scale production.
Die casting: Despite reading in several places that high carbon steel could be cold-chamber die-cast, I have had no manufacturers indicate they could make these parts. It seems they all limit die-casting to aluminium, zinc and magnesium. Can any speak to this?
Metal injection molding: The part is at the upper end of the size for this process, not an economical process for large scale production.

Thanks team! Look forward to hearing your ideas.

Cheers,
Daniel

[Kelly_Bramble]

What are the the critical surfaces and the required mechanical tolerances? WIll there be high loads applied?

Investment casting can make this part however it will be expensive and the tolerances will be loose by machining standards. Moreover, the grain structure will be iso-tropic and fatigue loading will be an enemy to this component.

From a cost to manufacture and mechanical tolerances point of view you will need to break this part up.

[daniel_smith]

Thanks for the feedback Kelly.

This part will not experience significant loads so fatigue isn't of concern here.

Critical surfaces are indicated in the attached image; the T profile acts as a sliding rail.

We had a quote come back at US$2.03/unit for investment casting based on 8000units/yr. Do you think that by splitting it up we would be able to reduce total cost beyond that? Or would the advantage of doing that be in reducing complexity and tightening tolerances?

[Kelly_Bramble]

Thanks for the feedback Kelly.

This part will not experience significant loads so fatigue isn't of concern here.

So, why Rc 50. and 4340 steel?

Critical surfaces are indicated in the attached image; the T profile acts as a sliding rail.

So, what are the tolerances of those surfaces

We had a quote come back at US$2.03/unit for investment casting based on 8000 units/yr.

$2.04 a unit? For an investment cast? - that seems impossible low, even for China or India. Are you sure?

[daniel_smith]

So, why Rc 50. and 4340 steel?

It is a hard wearing surface with a metal object repeatedly sliding along it but isn't subjected to considerable stresses or impact loads.

So, what are the tolerances of those surfaces

These surfaces should be alright at a 0.25mm (0.010in) tolerance and all other tolerances are likely to be OK at +/- 0.5mm (0.020in)

$2.04 a unit? For an investment cast? - that seems impossible low, even for China or India. Are you sure?

I too was surprise at the cost, especially given how manual the investment casting process is. We're based in New Zealand and manufacturing costs in China are generally 1/5 of the local cost. A local company estimated ~US$10/unit so China coming back with ~US$2 is pretty well aligned with that rule of thumb. I am waiting to hear back from other suppliers though because it does seem fairly light.

[JAlberts]

My experience with investment castings has been too long past for me to speak as to the quoted cost; but many years ago I was able to reduce the manufacturing cost of an ASME Section 8 pressure relief valve product by 50% using ASME Section 8 approved alloy materials and minimal post casting machining and found dimensional control and consistency to be very good. In service, there have never been any performance problems with material strength, porosity or endurance in spite of considerable impact forces on the components during opening and closing cycles. One caveat , the casting was done in the USA.