Calculate EPS shape molding machine capacity as: cavities per mold × 3,600 ÷ loaded cycle seconds × scheduled hours × OEE. Use the slowest saleable product, not the machine’s empty-cycle claim. Then divide required daily output by realistic daily capacity and round up; the result is the minimum machine count before allowances for mold changes or maintenance.
Start with pieces, not machine size
EPS molding machine capacity means the number of accepted parts a machine can produce in a stated period under a defined product, mold, utility supply, and operating schedule. A platen dimension alone cannot answer it. One 1,200 × 1,000 mm mold may carry one cooler-box cavity, four appliance-corner cavities, or dozens of small trays. The machine closes once in all three cases, but saleable pieces per cycle differ sharply.
Write the requirement in pieces per day for every SKU. If sales forecasts are in tonnes, convert them with verified part weight: pieces = required mass ÷ finished-part mass. At 0.32 kg per fish box, 3,200 kg/month equals 10,000 boxes; a 0.28 kg assumption would overstate demand by 14.3%. Weigh approved samples instead of using a drawing estimate.
The capacity formula buyers can audit
The base calculation has four inputs:
Good pieces per day = cavities × (3,600 ÷ loaded cycle seconds) × scheduled hours × OEE
OEE is availability × performance × quality. If availability is 90%, performance is 92%, and first-pass quality is 97%, OEE is 0.90 × 0.92 × 0.97 = 80.3%. For a new line with no measured history, use a transparent planning range such as 70%, 80%, and 85%, then test whether the purchase still works at the conservative case. Do not hide mold changes inside an optimistic 95% factor.
| Input | What to use | Common buying error |
|---|---|---|
| Cavities per mold | Approved mold layout after runner, vent, ejector, and edge clearances | Dividing platen area by product footprint with no clearance |
| Loaded cycle time | Trial result for the target density and thickest section | Using an empty-machine cycle |
| Scheduled hours | Net planned production time after breaks and planned cleaning | Calling an 8-hour shift eight productive hours |
| OEE | Measured history or a three-case planning range | Using 100% because the machine is automatic |
Need a blank input checklist for supplier comparisons? Request the capacity-input sheet through the engineering contact form; it keeps cavity count, loaded cycle, OEE, shifts, changeovers, and utility limits visible in every quotation.
Never use the empty-cycle number for output
The ChinaEps SM-1200 EPS shape molding machine has a 30–45 second empty-test timing baseline. Its loaded cycle is typically 60–90 seconds for fish-box or packaging parts at 14–25 kg/m³, and 120–150 seconds for thick, complex parts at 30–50 kg/m³. The difference is the time needed to fill, fuse, cool, stabilize, and eject the real product.
An empty-cycle calculation at 45 seconds and four cavities predicts 320 pieces/hour. The same mold at a measured 90-second loaded cycle produces 160 theoretical pieces/hour. Apply 80% OEE and the answer is 128 good pieces/hour. The sales plan would be overstated by 150% if the buyer used the empty figure and ignored OEE.
Wall thickness, density, bead grade, steam pressure at the mold, condensate removal, vacuum capacity, cooling-water temperature, and vent condition all move loaded cycle time. The shape molding cycle-time diagnosis explains how to separate those constraints on a running line.
Worked example: 6,000 fish boxes per day
Assume an approved four-cavity fish-box mold, an 82-second loaded cycle from a trial using the buyer’s density and wall section, two 8-hour shifts, 30 minutes of planned non-production time per shift, and 80% OEE. Net scheduled time is 15 hours per day.
- Theoretical cycles per hour = 3,600 ÷ 82 = 43.90.
- Theoretical pieces per hour = 43.90 × 4 = 175.6.
- Good pieces per hour = 175.6 × 0.80 = 140.5.
- Good pieces per day = 140.5 × 15 = 2,107.
- Machines required = 6,000 ÷ 2,107 = 2.85, rounded up to 3.
Three machines provide about 6,321 good pieces/day under those assumptions, only 5.4% above the target. If delivery contracts require 6,000 pieces even while one machine is down, three machines are insufficient: N+1 resilience requires a fourth machine or documented subcontract capacity. Capacity and redundancy are separate purchase decisions.
| Scenario | Loaded cycle | OEE | Good pieces/machine/day | Machines for 6,000/day |
|---|---|---|---|---|
| Conservative startup | 90 sec | 70% | 1,680 | 4 |
| Base case | 82 sec | 80% | 2,107 | 3 |
| Stable experienced crew | 75 sec | 85% | 2,448 | 3 |
Want this calculation checked before requesting quotes? Send product dimensions, weight, density, cavities, target pieces/day, shift pattern, and utility limits through the engineering inquiry form. The reply can state which assumption controls the answer instead of returning a generic machine count.
Calculate a mixed-product week, not a perfect single-SKU day
A factory selling five SKUs should calculate required machine-hours for each SKU, then add them. For SKU i:
Required machine-hoursi = required good piecesi ÷ good pieces per machine-houri
Add planned changeover hours separately. A same-format quick-insert change on the SM-1200 is about 45 minutes; a complete platen and steam-manifold reconfiguration can take 4–6 hours. Four full-format changes in a week therefore consume 16–24 machine-hours before one saleable part is produced. A weekly schedule that ignores that time may pass the daily formula and still miss customer orders.
| SKU | Weekly demand | Good pieces/hour | Run hours | Changeover hours |
|---|---|---|---|---|
| Fish box A | 18,000 | 140 | 128.6 | 0.75 |
| Appliance corner B | 24,000 | 310 | 77.4 | 0.75 |
| Thick insert C | 6,000 | 72 | 83.3 | 5.0 |
| Total | 48,000 | — | 289.3 | 6.5 |
If one machine offers 75 scheduled hours/week, this mix needs 295.8 ÷ 75 = 3.94 machines before maintenance reserve, so the answer is four machines. Averaging the three products into one invented cycle time would conceal the thick insert bottleneck.
Check whether the mold fits before counting cavities
The SM-1200 platen is 1,200 × 1,000 mm and its stated maximum product envelope is up to 1,150 × 950 × 350 mm, mold-dependent. That does not mean usable mold area equals 1.2 m². The layout needs margins for the mold frame, clamps, steam passages, vents, filling guns, ejectors, and safe wall thickness between cavities.
Ask the supplier for a signed cavity-layout drawing. It should show overall mold dimensions, cavity pitch, runner or fill-gun positions, venting, ejection, projected area, and expected part weight. For pressure-related design, the machinery should be assessed under the applicable market requirements; buyers can verify the current framework through the ISO standards catalogue and the EU’s official machinery legislation portal.
Utilities can cap capacity below the machine calculation
A machine-count formula assumes every machine can receive stable steam, cooling water, vacuum, and compressed air at the same time. The SM-1200 data source specifies 8–15 kg of steam per cycle depending on product mass and 0.4–0.8 MPa tank supply, regulated to 0.08–0.12 MPa at the mold chamber. Three machines peaking together can impose a short-duration steam load far above the hourly average.
Use the EPS boiler sizing method to calculate simultaneous demand, not the sum of daily averages. Also confirm cooling-water inlet temperature and flow during the hottest month, vacuum recovery between cycles, compressor free-air delivery, pipe diameter, and pressure loss. If pressure falls during simultaneous steaming, the loaded cycle used in the spreadsheet is no longer valid.
Upstream material flow matters too. The SPJY-1400 batch pre-expander, aging silos, and conveying system must supply enough conditioned beads for the molding schedule. A nominally fast molder waiting for aged beads has zero useful capacity during the wait. For short-cycle products, qualifying fast-cycling EPS beads with the actual mold can be more economical than buying another machine.
Apply a reject and rework rule that matches the product
OEE already includes the quality rate, so do not subtract rejects twice. If the capacity sheet uses availability and performance only, multiply by first-pass yield once. Separate cosmetic rejects that can be reprocessed from dimensional or fusion failures that miss the customer specification. A 97% first-pass yield means 3,000 rejected pieces for every 100,000 attempted; at 0.32 kg each, that is 960 kg of material tied up before any regrind recovery.
Food-contact boxes, certified helmet liners, and dimensional appliance packaging cannot share one generic reject assumption. Define the acceptance test, sampling frequency, and disposition rule before the production trial. ISO 9001 describes the quality-management framework, but the actual product specification and customer drawing decide whether a molded part is saleable; the ISO overview is a useful starting point for supplier-audit questions.
Use a supplier capacity trial as the purchase acceptance test
A defensible quote states its assumptions. Request a trial with the intended bead grade or an agreed equivalent, target density, representative wall thickness, planned cavity count, normal utility pressures, and at least 30 consecutive stable cycles. Record loaded cycle time, accepted pieces, rejects, steam pressure at the chamber, vacuum recovery, cooling-water temperature, and part weight.
Accept capacity against good pieces/hour, not the single fastest cycle. If the 30-cycle run averages 84 seconds but the quote uses 72 seconds, the quote overstates cycle-based capacity by 16.7%. Put the agreed test method, tolerance, and remedy in the technical annex to the purchase order.
| Supplier evidence | Minimum useful detail | Decision it supports |
|---|---|---|
| Mold layout | Dimensions, cavities, vents, fills, ejectors, projected area | Whether cavity count is physically credible |
| Cycle trial | 30 stable loaded cycles with product and utilities stated | Realistic cycle input |
| Quality record | Accepted count, rejection reason, part weight and dimensions | First-pass yield |
| Utility sheet | Peak steam, cooling water, vacuum, compressed air | Whether site utilities can sustain output |
| Changeover method | Same-format and full-format time demonstrated | Mixed-SKU weekly capacity |
A five-step buying rule
- Calculate each SKU with its approved cavity count and loaded cycle.
- Convert demand into machine-hours and add real changeover hours.
- Run conservative, base, and experienced-crew OEE cases.
- Verify peak utilities and upstream bead supply against simultaneous operation.
- Buy for the binding constraint, then decide separately whether uptime contracts require N+1 redundancy.
If the conservative case meets demand with one machine and the cavity layout is approved, one machine is defensible. If only the optimistic case meets demand, resize the mold, add cavities, improve utilities, or add a machine before ordering. For a wider specification review, compare the result with the EPS shape molding machine buyer’s guide.
Frequently Asked Questions
How do I calculate EPS molding machine capacity per hour?
Multiply mold cavities by 3,600, divide by the measured loaded cycle in seconds, and multiply by OEE. A four-cavity mold at 90 seconds and 80% OEE produces 4 × 3,600 ÷ 90 × 0.80 = 128 good pieces/hour.
What OEE should I use for a new EPS shape molding line?
Use a range instead of one promise: 70% for conservative startup, 80% as a base planning case, and 85% for a stable experienced crew, unless measured data supports another figure. Keep availability, performance, and first-pass quality visible so the supplier can challenge each assumption.
Does a larger platen always mean more capacity?
No. A larger platen increases the possible mold envelope, but capacity rises only if the approved layout carries more cavities without creating poor filling, venting, steam distribution, cooling, or ejection. A large single-cavity part can have lower pieces/hour than a smaller multi-cavity mold.
Should I use the fastest cycle shown in a quotation?
Use it only if it was measured with your representative product, density, wall thickness, cavity count, and normal utilities across a stable run. An empty-machine 30–45 second figure is a motion baseline, not a production-capacity guarantee.
How do mold changes affect daily capacity?
Subtract changeover time from scheduled production time or add it to required weekly machine-hours. A same-format insert swap may take about 45 minutes, while a full platen and manifold reconfiguration can take 4–6 hours.
How much spare capacity should an EPS factory buy?
Capacity margin and redundancy serve different risks. A 10–20% demand margin can absorb forecast error and normal variation, but it does not keep output whole during a machine outage. If contracts require full delivery with one machine unavailable, calculate N+1 capacity explicitly.
What information should I send for a capacity quotation?
Send product drawings, dimensions, verified weight, density, thickest and thinnest wall, daily demand by SKU, working days, shift pattern, proposed cavities, bead grade, mold-change frequency, and available steam, cooling water, vacuum, and compressed air.
Get a capacity sheet tied to your products
ChinaEps can return a product-by-product capacity sheet using your cavity layout, loaded cycle, shift calendar, OEE range, changeovers, and utility limits. Send the inputs through the capacity review form; the response will show the formula, assumptions, machine count, and limiting utility so the number can be checked before the purchase order. ChinaEps supplies CE-configured equipment, works under an ISO 9001 quality system, provides a five-year warranty, and supports commissioning for complete EPS lines.
