Cost per Part: Resin Dripping Economics Full Model
For a junior technician in a plating or surface-treatment factory, resin cost is not simply the price of one drum divided by the number of drops. The useful number is the total cost of producing one accepted part. Incorrect mixing, oversized batches, bubbles, overflow, delayed inspection, and damaged plated hardware can outweigh a small saving on resin.
This guide covers two-component epoxy dispensing into decorative recesses on rigid zinc-alloy bag hardware. Silicone, PVC plastisol, polyurethane, and UV-curable systems need separate recipes. Your responsibility is to measure consumption, follow the released work instruction, identify drift early, and give the supervisor reliable records.
1. Know Which Numbers Are Evidence
No authenticated QLQ resin-dripping batch report was available in the local knowledge base. The comparison below therefore separates published supplier data from an unperformed factory trial. It does not claim measured salt-spray performance for your plated hardware. All later prices, production counts, and control limits are explicitly illustrative planning assumptions, not quotations or universal processing specifications.
The local equipment catalogue, QLQ knowledge base: 03-Equipment Technology / Company Catalogue / Machine Catalogue / Page 25, identifies silicone mixing, vacuum, and dispensing equipment separately from PVC equipment. It provides no epoxy process capability. Never infer epoxy compatibility from a machine name.
2. Working Data: Published Tests and Batch Comparison
| Reference or trial | Mix ratio by mass | Hardness / exposure result | Thickness | Test condition | Use in costing |
|---|---|---|---|---|---|
| Feroca ClearWater rigid doming epoxy; supplier reference | 100 A : 30 B | Published Shore D 80 | Not reported | Supplier lists 24-hour cure and 48–72 hours for full mechanical cure; hardness specimen geometry and method not disclosed | Reference only; qualify on the actual finish |
| Fong Yong E-126 / H-100; supplier reference | 3 A : 1 B | Published Shore D 80; appearance unchanged after salt solution exposure | Not reported | Hardness at 25°C after seven-day room-temperature cure or 80°C for two hours; salt exposure: 5% NaCl, 24 hours, immersion, not salt spray | Reference for cure scheduling; not evidence of corrosion life |
| Factory control batch A: approved plated hardware | Released recipe | Pending measurement; record adhesion and defects | Pending; measure cured cross-section | Proposed: 30 parts, existing cure schedule, matched witness specimens; record temperature, batch mass, cure age | Measure resin input and accepted count |
| Factory trial batch B: smaller mix size | Same released recipe | Pending measurement; same inspection criteria as A | Pending; same measurement positions | Proposed: 30 matched parts; change mix size only; retain identical substrate, application, and cure conditions | Compare cup residue, labor time, and yield |
Sources: Feroca product instructions and Fong Yong published technical data. These are external resin references, not QLQ formulations. They use different hardeners and must not share a recipe.
For a customer requiring salt spray, obtain an agreed method, duration, edge treatment, and acceptance criterion before testing the complete plated assembly. Do not translate salt immersion into salt-spray hours. A thin dome on metal also cannot automatically provide a valid bulk Shore hardness reading; use a suitable witness specimen and the agreed test method.
3. Complete Application Formulation: Keep the Chemistry Fixed
The following clear application recipe uses the published Feroca 100:30 mass ratio. It is a complete two-component application mix, not a disclosure of proprietary raw ingredients. The supplier does not publish an allowable ratio tolerance: the nominal value is mandatory. For 130 g mixed material, weigh 100 g A and 30 g B. Approve adhesion to the actual plating or lacquer before release.
| Component | Range | Typical | Function | Replenishment |
|---|---|---|---|---|
| Matched epoxy resin A | Fixed at 100 mass parts; tolerance requires supplier confirmation | 100 g | Forms the decorative resin matrix | Prepare a fresh weighed batch; keep container closed |
| Matched hardener B | Fixed at 30 mass parts per 100 A; tolerance requires confirmation | 30 g | Cures the matched resin | Add only before initial mixing; never correct aging mixed resin |
| Compatible pigment | 0 for this clear recipe; any colored version requires separate approval | 0 g | Color when separately qualified | No addition to this released clear mix |
| Solvent / water / extra defoamer / filler | 0 added | 0 g | No approved role in this application recipe | Do not add; use the matched supplied components |
Replenishment here means making another fresh batch, not maintaining a reusable plating bath. Unused cured material, wash solvent, and rejected mixed resin belong in separate waste records. Follow the product safety data sheet, suitable gloves and eye protection, and the factory ventilation and waste procedure. Never use an open flame for bubble removal beside chemicals.
4. Build the Cost Model From Weighed Material
Choose one order, one part design, and one accounting period. Record dry cup tare, resin and hardener input, retained mixed residue, usable output, rejects, and rework. Do not estimate shot weight by counting drops: nozzle size, viscosity, and dispensing time change the mass. Weigh ten consecutive shots into a tared cup and divide by ten.
Purchased resin mass, kg = started parts × shot mass, g ÷ [1,000 × material utilization].
Blended price per kg = (100 × A price + 30 × B price) ÷ 130 for the example 100:30 system.
Accepted parts = first-pass accepted parts + successfully recovered rework parts.
Cost per accepted part = (material + labor + energy + consumables + equipment allocation + inspection + incremental rework + irrecoverable hardware loss) ÷ accepted parts.
Material utilization is deposited mass divided by purchased mix consumed, including cup and mixer waste. Yield is accepted pieces divided by started pieces. They are different denominators. If measured purchased consumption already includes waste, do not add another waste percentage. Likewise, rework resin and labor already in measured totals must not be counted twice.
5. A Fully Reconciled Worked Order
This training scenario uses USD solely as an accounting unit. Assume 10,000 started parts, 0.20 g deposited per part, 85% material utilization, and a hypothetical blended resin price of $12/kg. First-pass inspection accepts 9,400 parts. Rework recovers 200 of the remaining 600; 400 plated parts are irrecoverable. Final accepted quantity is 9,600.
| Cost category | Calculation / assumption | Order cost |
|---|---|---|
| Initial resin application | 10,000 × 0.20 / 1,000 / 0.85 × $12 | $28.24 |
| Direct labor | 8 paid operator-hours × $6/hour; hypothetical loaded rate | $48.00 |
| Measured energy | 10 kWh × assumed $0.15/kWh | $1.50 |
| Consumables | Cups, wipes, gloves, tips allocated to this order | $8.00 |
| Equipment allocation | Assumed $2/hour × 4 occupied equipment-hours | $8.00 |
| Inspection | Separate inspection labor; excluded from direct labor | $6.00 |
| Incremental rework | Additional resin and labor only; not included above | $10.00 |
| Lost plated hardware | 400 irrecoverable parts × assumed $0.08 incoming value | $32.00 |
| Total / accepted part | $141.74 / 9,600 | $0.01476 |
This is conversion cost plus hardware loss, not the complete selling cost. To include hardware in every accepted part, add its incoming value separately and reconcile any salvage credit. Packaging, freight, administration, and margin are outside this example. Record whether inspection is independent labor or already included in the operator rate.
Equipment allocation should use a consistent productive-hour basis: annual depreciation and maintenance divided by expected productive hours. Electricity is metered energy, not motor nameplate power multiplied blindly by shift duration. Cure occupancy can constrain output even when the dispenser is idle.
6. Trend Bands and Stop Limits
The limits below are proposed internal trial controls for the worked 0.20 g part, not resin-manufacturer guarantees. The engineer must validate and sign them before production. A tighter approved supplier instruction always overrides them. Epoxy mixing is not controlled by the pH bands used for plating baths.
| Parameter | Normal operating band | Danger / hold threshold | Technician response |
|---|---|---|---|
| A:B mass ratio | Nominal 100:30; example internal B check 29.7–30.3 per 100 A | Outside the approved tolerance; example outside 29.7–30.3 | Hold batch; do not assume this internal tolerance is supplier-approved |
| Room / material temperature | Proposed 20–25°C | Outside approved window; provisional hold below 18°C or above 30°C | Stabilize unopened materials; escalate cure or flow drift |
| Mixed batch age | Proposed dispensing within 0–10 minutes | 10–15 minutes: warning; at 15 minutes stop for this reference system | Start timer at first component contact; validate for actual batch mass |
| Ten-shot mean | Proposed 0.190–0.210 g/part | Outside this released trial band, or any visible overflow | Hold output since last good check; verify nozzle and settings |
| Material utilization | Planning target 85–90% | Below 80%: investigation trigger | Weigh residue; reduce unnecessary mix size |
| First-pass yield | Planning target 94–98% | Below 92% in a 100-part sample | Hold and separate bubbles, overflow, contamination, and cure defects |
| Unapproved additions | 0 g water or solvent | Any addition | Quarantine affected mix and parts |
A stable average can hide a single leaking valve. Record individual shot measurements during setup, not only the mean. Consecutive readings moving toward a limit warrant adjustment before rejects accumulate. Pot life must be verified at the actual cup mass and temperature; a supplier reference is not a timer guarantee for a larger batch.
7. Two Practical Troubleshooting Scenarios
Scenario A: Excess resin left in cups
This is a worked scenario, not a claimed customer result. If utilization rises from 85% to 92%, the example order needs 2.174 kg instead of 2.353 kg, saving only about $2.15 at $12/kg. If extra mixing adds half an operator-hour at $6/hour, labor rises $3. Smaller batches then increase total cost despite reducing waste. Trial two batch sizes and record mixing time, residue, accepted count, and bubble defects.
Scenario B: Cheaper resin but more damaged hardware
Again, this is a hypothetical decision example. A $2/kg reduction saves about $4.71 on the original resin quantity. If it produces 100 additional irrecoverable plated rejects at $0.08 each, hardware loss rises $8 and accepted output falls by 100. Reject the saving claim until the same substrate, cure conditions, and inspection criteria demonstrate equal performance. Check cleaner residue, wet parts, and lacquer compatibility before blaming resin price.
8. Engineer Notes
- Tare each clean cup and check the scale with an approved reference weight before weighing components.
- Separate the A and B transfer tools; label containers and record both lot numbers before mixing.
- Prepare clean, dry, level parts before combining components; start the batch timer immediately.
- Run a ten-shot weighing check after a tip change, stoppage, or recipe setup; retain the readings.
- Use approved mixing and degassing instructions; never dilute thickening mixed resin or add hardener to revive it.
- Label each cure tray with start time and recipe; prevent touching or stacking before approved handling release.
- Weigh waste separately and classify rejects by cause; preserve suspect samples for the engineer instead of discarding evidence.
9. Shift Checks
| Shift stage | Check item | Frequency | Acceptance criterion | Record |
|---|---|---|---|---|
| Before shift | Recipe, component identity, scale, environment, dry hardware | Every setup and material lot change | Released recipe; verified scale; approved conditions; no moisture or contamination | Setup sheet, lot IDs, temperature, reference-weight result |
| During shift | Weighing ratio and batch timer | Every mix | Approved ratio and usable time; no unauthorized additions | A/B masses, contact time, operator |
| During shift | Shot weight and visual defects | First ten shots; hourly and after intervention | Released weight band; correct fill, no bubbles or overflow under agreed inspection | Individual weights and defect counts |
| During shift | Cure trays and witness samples | Every tray; release check for every batch | Traceable cure schedule and agreed acceptance tests | Tray ID, cure times, inspection sign-off |
| After shift | Material and output reconciliation | Every order / shift close | Started count equals accepted, rejected, and remaining work-in-process; explain material differences | Waste masses, rework, accepted count, cost sheet |
Do not count uncured work-in-process as accepted output. Carry its quantity and cost forward. Keep cleaned hardware and mixed resin away from polishing dust, oil mist, and solvent work; layout discipline protects both quality and the accuracy of the cost model.
10. Questions a Technician Might Ask AI
These are example technician prompts, not authenticated customer quotations.
“AI, why is my cost per part rising when the resin price has not changed?”
Compare deposited shot weight, cup waste, paid hours, accepted count, and incoming hardware loss. Check the denominator first: fewer accepted parts spread the same setup and inspection costs over fewer units. Reconcile one complete order before comparing monthly averages with different product sizes.
“AI, can I add less hardener to make the resin last longer?”
No. Keep the matched supplier ratio. Change batch size, staging, or approved temperature control instead. Quarantine incorrectly mixed material. Ask the engineer to verify actual working time at your cup mass; changing hardener quantity is not an authorized cost-saving adjustment.
“AI, is Shore D 80 enough to prove my resin-coated hardware will pass salt spray?”
No. Hardness describes a polymer property, not the corrosion performance of the complete plated assembly. Qualify adhesion, edges, underlying finish, and cure using the customer's agreed tests. Published salt immersion results cannot substitute for your required salt-spray report.
11. What Would You Like to Solve?
Bring the problem down to one traceable order: part geometry, existing plating or lacquer, resin identity, shot weights, waste masses, cure records, and defect photographs. That information lets an engineer distinguish dispensing loss from substrate failure or incomplete cure.
For a process review, email [email protected] with your records and acceptance requirements. See surface-treatment line equipment, chemicals, and process support when upstream cleaning or finishing may be contributing to the issue. The objective is a verified lower cost per accepted part, without weakening the released recipe or quality standard.