Cast Urethane Parts, No Steel Mold: A 250-Piece Case for an Automation Client

1. The Numbers on This Order

250 cast urethane parts. ABS-equivalent structural fittings for an industrial automation cell. $1,300 total. 10 calendar days from order confirmation to the shipping label.

No steel injection mold was cut. The client kept the geometry open for one more validation cycle. $2,600 that would have gone into a hard tooling deposit stayed in their engineering budget.

Below is what actually shipped, what the alternative route would have cost, and the exact volume where hard steel tooling becomes the cheaper answer.

2. Where This Client Stood on Their Product Timeline

The client makes industrial automation equipment. The part is an internal structural fitting inside a live automation cell. ABS material specified on the drawing. 250 pieces needed for first-round product validation.

The design was not frozen. Two mounting-hole positions and one slot depth were still open, and the client’s engineering team expected at least one revision after the first-article batch ran through the cell.

Two sourcing routes were on the RFQ. Cut a steel injection mold now at the current CAD, wait five weeks for T1 samples, and rework the mold at $420 to $2,100 per revision cycle. Or skip the mold, run the 250 pieces through vacuum casting, and keep the design open until the validation batch had actually seen shop-floor loads.

The engineering call: at 250 pieces with unfrozen geometry, committing to a hard steel mold is not a cost decision. It is a risk decision. The mold is money spent on a shape the product team has not yet confirmed.

3. The Vacuum Casting Route: What EPOC CRAFTER Actually Ran

A master pattern was cut first. A silicone mold was pulled from that pattern in 2 to 3 days. Then 250 cast urethane parts came out of that mold in staggered batches over the next week.

3.1 Resin: ABS-Equivalent Polyurethane

The casting resin was an ABS-equivalent polyurethane. Tensile strength lands in the 40 to 55 MPa range on the resin datasheet. Flexural modulus 2,000 to 2,500 MPa. For static-load internal fittings that do not see impact or fatigue cycling, this covers the mechanical envelope of GP-grade injection-molded ABS.

Where cast urethane parts do not substitute for ABS: UL94 flame rating, chemical resistance against specific hydrocarbons, and applications with cyclic mechanical loading above 10^4 cycles. Nothing on this drawing required those. The full comparison lives on the EPOC CRAFTER materials and properties page.

3.2 The Cost Line Items

Silicone soft mold: $0 in hard tooling amortization.

Per-piece unit cost: $5.30.

Total order cost, 250 pieces: $1,300.

Lead time, order confirmation to delivery: 10 calendar days.

Design change between runs: $0 in mold-modification fees. A revised master pattern can be cut for the next batch without carrying any sunk tooling cost.

4. What Steel Injection Molding Would Have Cost

EPOC CRAFTER ran the steel-mold numbers on this fitting geometry so the client’s procurement team could see both columns side by side before signing anything.

4.1 The Line Everyone Sees

Hard steel mold: $3,900.

Mold lead time: 5 weeks.

Mold cost amortized over 250 pieces: $15.60 per piece, before any per-shot injection cost is added.

At 250 pieces, the tooling amortization alone is roughly 3x the per-piece cost of the vacuum casting route. The mold arithmetic never closes at this volume.

4.2 The Lines Nobody Writes on the Quote

Mold modification after a design change: $420 to $2,100 per cycle. Parts in validation typically see one to three revisions before design freeze. Worst-case rework spend: $6,300 on top of the original $3,900 mold.

Schedule impact per rework cycle: 2 to 4 weeks. A two-cycle rework sequence adds 6 to 8 weeks to the timeline. That is not a cost line on a spreadsheet. That is the client’s development runway.

Compression of the validation window: five weeks of mold lead time pushes first-article review to Week 6. Vacuum casting puts first articles in hand on Day 10. On this product’s timeline, that 32-day gap gave the design team room for one extra iteration round before locking geometry.

5. Break-Even: When Steel Injection Tooling Becomes the Right Answer

The break-even was calculated before the order was placed. The client wanted to know exactly when the answer would flip.

At $5.30 per piece through vacuum casting, annual production of 3,000 pieces costs $15,900.

At the same 3,000-piece volume with a hard steel single-cavity production mold, tooling amortization drops below $1.40 per piece. Per-piece rapid injection molding cost for a standard ABS structural fitting sits at $2.10 to $3.50 depending on cycle time and cavity layout. Total per-piece cost through hard tooling at 3,000 annual pieces: $3.50 to $4.90. That reaches or drops below the cast rate.

The switch point in one line: annual demand stable above 3,000 pieces per year, design frozen, no further geometry revisions expected.

The rule the client left with. Below 3,000 pieces per year, or before design freeze, run prototype plastic parts through vacuum casting. After design freeze and above 3,000 pieces per year, cut the mold.

For this client, the first 250 pieces ran through casting. When the product validates and annual demand ramps past 3,000 units on a confirmed geometry, EPOC CRAFTER quotes the steel mold. By then the geometry the mold gets cut to is one the client has already tested in a real cell.

6. What Shipped with the 250 Pieces

Dimensional inspection covered slot width, mounting hole position, and part envelope against the approved drawing. A batch inspection record was produced for all 250 pieces, not a sample subset.

The shipment included the 250 cast urethane parts boxed for automation-cell installation, the full dimensional inspection record, and a resin material data sheet confirming mechanical properties.

Incoming inspection at the client site reported zero rejects. The parts went into the automation cell for validation on the same week they landed.

For context on how EPOC CRAFTER runs batch-level inspection discipline on other low-volume orders, see the 160-piece CNC aluminum case shipped from CAD to Europe in 9 days.

7. Where Cast Urethane Parts Fit, and Where They Do Not

Vacuum casting wins on this order because three conditions lined up:

1. Volume between roughly 20 and 500 pieces.

2. Design not yet frozen, revisions still expected.

3. Mechanical requirements inside the ABS-equivalent polyurethane envelope.

Change any of those three and the answer shifts. Volume above 3,000 pieces per year with frozen geometry, injection molding wins on unit cost. Parts that need UL94 flame rating, food-contact certification, or fatigue cycling beyond static load, the route moves to CNC-machined ABS or aluminum-tooled low volume production. Parts with wall thickness under 1.0 mm or undercuts the silicone mold cannot demold cleanly, the DFM review flags it before the pattern is cut.

The three conditions above are the actual test. Not the material name in isolation, not the piece count in isolation, not the delivery deadline in isolation. Send EPOC CRAFTER the CAD file and a note on where the design currently stands, and get a vacuum casting quote inside 12 hours with both routes priced and the break-even calculated to the annual demand on the drawing.

8.Frequently Asked Questions

How much do 250 cast urethane parts cost compared to injection molding the same part?

On this order, 250 ABS-equivalent cast urethane parts cost $5.30 per piece, $1,300 total, with zero tooling investment. A single-cavity steel injection mold for the same geometry would have cost $3,900 up front, adding $15.60 per piece in tooling amortization before any per-shot injection cost. At 250 pieces the steel route lands at approximately $18 to $19 per piece all-in. The casting route came in below one third of that.

How do cast urethane parts compare mechanically to injection-molded ABS?

ABS-equivalent polyurethane casting resin delivers tensile strength of 40 to 55 MPa and flexural modulus of 2,000 to 2,500 MPa on the resin datasheet. Injection-molded GP-grade ABS delivers tensile strength of 40 to 50 MPa and flexural modulus of 2,100 to 2,500 MPa. For static-load structural fittings, the cast parts are mechanically equivalent for validation-stage use. Parts that require UL94 flame rating, specific chemical resistance, or high-cycle fatigue performance need injection-molded ABS and cannot be substituted with standard cast urethane resin.

At what annual volume does injection molding become cheaper than vacuum casting for ABS-type parts?

For this fitting geometry the break-even sits at approximately 3,000 pieces per year after design freeze. Below that threshold, or before the design is confirmed, vacuum casting produces a lower total delivered cost once mold-modification risk is factored in. Above 3,000 pieces per year with frozen geometry, hard tooling amortization drops the per-piece cost to $3.50 to $4.90, matching or undercutting the casting rate. Break-even shifts with part size, cavity count, and cycle time, so the number should be recalculated per project.

How fast can cast urethane parts ship?

This 250-piece order shipped in 10 calendar days from order confirmation. Silicone mold cutting from a master pattern takes 2 to 3 days. Casting and post-processing run in staggered batches inside a working week. There is no 5-week steel mold lead time and no mold-debugging cycle. Design changes between orders do not trigger mold-modification fees, so the second batch can move on a revised master pattern without carrying any sunk tooling cost.