A press can be waiting for material while the ERP shows plenty of resin in stock. Some may be reserved for another order. Another lot may be on quality hold, or the usable balance may still be sitting in a dryer. Resin inventory management improves when the system explains those differences.
The first question in an ERP setup should be simple: what does “available” mean for this job? A total in kilograms is useful only when the grade, approval, location, and timing make that material usable. Purchasing more resin before checking those details can increase stock without solving the shortage.
This guide explains the implementation decisions that connect stores, material handling, production, and purchasing. It also shows how to plan consumption and investigate a material variance. The aim is to give management a reliable stock position and give operators a workflow they can maintain.
What resin inventory management covers
Resin inventory management is the control of polymer stock from receipt through storage, preparation, production use, and recovery or disposal. It tracks the material grade, lot, quantity, location, and condition. In injection molding, it must also account for open bags, dryer and hopper balances, runners, purge, and approved regrind.
An enterprise resource planning system, or ERP, can connect those records with production orders and purchase requirements. The setup needs to match the physical movement of material. Otherwise, automation can post a consistent transaction that describes the wrong stock position.
Settle the material master before importing stock
Do not create one item called “nylon” and expect the operator to select the right bag later. Separate grades that have different specifications or approval requirements. Retain the manufacturer’s grade reference so purchasing and production identify the same material.
Likewise, define how the system distinguishes virgin resin, masterbatch, additives, and recovered material. A product family can group related items for reporting. It should not make them interchangeable for production.
The material master should give users enough detail to choose correctly:
- Polymer and exact manufacturer grade, including relevant reinforcement or additives.
- Color or masterbatch reference where it affects the approved recipe.
- Approved supplier and any customer or product restrictions.
- Inventory unit, purchase pack size, and conversion rules.
- Lot tracking, storage instructions, and required quality checks.
- Approved substitution and regrind rules, with revision control.
Two grades may look similar and still require separate approvals. Define who can authorize a substitution and how the production order records it. Purchasing should not treat a cheaper alternative as an equivalent item without that decision.
Use kilograms consistently and check pack conversions
Kilograms provide a practical inventory basis for resin, while the product drawing may state part weight in grams. Purchase orders may use bags or bulk deliveries. Test those conversions before loading opening balances.
For example, a 25 kg bag contains 25,000 g. A purchase of ten such bags adds 250 kg, while an open bag needs its actual remaining quantity. Counting every bag as full will overstate stock as soon as production starts taking partial quantities.
Odoo’s units of measure documentation describes purchasing in defined units. Verify the purchase, inventory, and manufacturing conversions in the proposed deployment. Keep the resin-to-part relationship in the bill of materials; a finished part is not a fixed packaging unit of resin.
Separate material location from material consumption
Moving a bag from stores to a dryer does not mean the resin has become finished parts. This is an important choice to settle before configuring production transactions. Decide where the system will keep material that has left stores but remains physically available.
Represent the relevant stores, preparation, and line locations at a level the team can count. Avoid creating a location for every piece of equipment unless the plant can maintain those records. The objective is a stock map that supports useful decisions.
Odoo documents inventory locations for organizing stock. The implementation must decide how transfers, material at the press, and consumption fit together. An internal transfer and a consumption posting serve different purposes.
Define how dryer and hopper stock appears
Choose a clear approach for material loaded at the line. The plant might transfer it to a line location, then record consumption and count the remaining balance. If it uses another posting method, define how unused material is represented and returned without double counting.
At shift handover, record the remaining grade, lot associations, and quantity using an agreed measurement method. Hopper estimates and bulk-bin measurements may carry uncertainty. Keep that uncertainty visible and investigate recurring differences rather than treating every estimate as an exact weight.
For shared dryers or conveying systems, confirm which equipment receives which lot. A scanned bag label needs a matching destination. The material handler should be able to complete that transaction without entering the same information in several screens.
Make quality status affect availability
On-hand stock includes material physically present. Job-ready stock must also be approved, uncommitted, and available at the required time. Display those distinctions when the planner checks a resin shortage.
Consider 900 kg of one grade in the plant. If 200 kg is on hold and 500 kg of the remaining approved stock is committed elsewhere, only 200 kg is uncommitted. In this example, those categories do not overlap, and no new receipt is due before the job starts.
Test whether material on hold can still be reserved or issued through another route. A location named “Quarantine” is not proof that every transaction prevents its use. The digital rule and the physical segregation need to agree.
Control open bags and material preparation
Keep an opened bag identifiable after the original packaging changes. Retain its grade, lot, remaining net weight, and relevant opening or preparation records. When returning material, check its identity and condition before making it available again.
Storage and drying requirements depend on the specific material. BASF’s Ultramid guidance, for example, describes moisture protection and points to grade-specific processing data. Follow the current supplier instructions for the grade being used; one generic drying setting cannot cover every resin.
ERP can retain the preparation record and prompt required checks. It cannot confirm actual moisture or dryer performance without the relevant measurements. Define which readings establish readiness and who can release material after a failed check.
Use a documented stock rotation policy within those approval rules. First in, first out can help rotate receipts. Where genuine expiry or retest dates apply, use those dates appropriately. An older lot should not take priority over a quality restriction.
Calculate resin demand from the molding process
A bill of materials based only on finished part weight can understate feed demand. Cold runners, rejected output, and purge can consume material beyond the weight of accepted parts. Their treatment needs to reflect the mold and approved production process.
Set the material requirement against the product, mold configuration, and approved blend. Keep startup or changeover losses separate from a steady production allowance where that improves planning. Check that the same loss does not enter both allowances.
A worked planning example
Assume a job requires 25,000 accepted parts. Each part weighs 18 g. A four-cavity mold has an 8 g cold runner per shot, equivalent to 2 g of runner per molded part with all cavities active.
The nominal feed is therefore 20 g per molded part. At perfect part yield, the job requires 500 kg. If the assumed part yield is 96%, the simplified estimate becomes about 520.8 kg before a separate purge allowance.
Add an illustrative 12 kg allowance for purge and changeover, and planned demand becomes about 532.8 kg. Round the issue plan as needed for whole shots and the plant’s dispensing method. These figures illustrate the calculation and are not recommended loss allowances for every mold.
The example assumes one resin with no additives or regrind. It applies the yield allowance to gross molding feed and treats the purge allowance separately. If rejected shots, cavity losses, or runner recovery behave differently, refine the model using recorded production data.
Also avoid subtracting future runner recovery from today’s requirement unless that recovered material will be approved and available when needed. A runner expected from this job cannot supply the beginning of the same job before it exists.
Reconcile actual use before changing the planning allowance
Resin inventory management needs a distinction between material transferred to a job and material actually processed. Begin with the issued amount, then account for unused returns and material still at the line. Compare the processed amount with measured outputs and recorded losses.
For example, issue 200 kg to a job, return 20 kg unused, and leave 10 kg unprocessed in the dryer or hopper. With no opening line stock or other movements in this example, the material processed is 170 kg.
Suppose the measured output record is as follows. The categories are separate, and runners have not yet been reused.
| Output or variance | Quantity in kg | Treatment in the review |
| Accepted molded parts | 140 | Recorded production output |
| Rejected molded parts | 8 | Recorded reject weight |
| Recoverable runners | 15 | Identified recovery stock |
| Purge for disposal | 5 | Recorded process loss |
| Unexplained difference | 2 | Investigate before adjustment |
| Material processed | 170 | Reconciliation basis |
The measured outputs total 168 kg, leaving a 2 kg difference against processed material. Check timing, weights, transactions, and omitted movements before deciding the cause. An inventory adjustment can correct a balance, but it does not explain why that balance became wrong.
Keep runners in an identifiable recovery record while they await the required processing and approval. Do not restore their weight to the virgin resin item as if it were an unopened bag. Likewise, avoid charging every kilogram issued as a final loss while unused stock remains at the line.
Manage regrind as a controlled input
Regrind needs its own material identity and stock record. Retain the contributing production sources, material grade, quantity, and quality status. Where the process requires generation tracking, record the known history and define how mixed sources affect that classification.
The allowable blend depends on the material and approved product requirements. BASF’s recovery guidance for Ultramid describes grade and application factors that affect reuse. Establish the permitted use through the required validation and approval rather than adopting a universal percentage.
Record the actual virgin resin, regrind, and masterbatch used in a blend. Clarify whether a percentage means a share of the total blend or an addition relative to another ingredient. That definition changes the quantities in the recipe.
Then preserve the link from the recovered batch to later production. If the original source becomes suspect, the team needs to identify the later output too. Our guide to ERP software for plastic injection molding covers the wider manufacturing requirements.
Replenish against dated demand and usable supply
Set purchase requirements using the production schedule, usable stock, and receipts expected before the job needs them. Include supplier lead time and any required inspection or preparation time. Material arriving tomorrow may be too late for a job starting today.
For stable demand, a reorder point can provide a starting rule. At 200 kg per working day and five working days from replenishment decision to usable receipt, expected lead-time demand is 1,000 kg. An illustrative 300 kg buffer gives a reorder point of 1,300 kg.
Review that buffer against demand changes and supply performance. For variable demand, use dated order requirements alongside the rule. Keep order multiples, minimum purchase quantities, and storage capacity visible before approving a suggestion.
Odoo’s reordering rules support minimum and maximum quantities and purchase multiples. Its replenishment report uses demand and lead-time information. Verify which locations and quality states contribute to the proposed forecast so held material does not conceal a shortage.
Review slow-moving grades separately. A large stock total can hide material that no approved product currently needs. Show the remaining kilograms, value, last use, and open customer demand before deciding whether to buy more.
What to verify before an ERP rollout
Odoo for manufacturing can connect purchasing, stock movements, bills of materials, and production records. The value of a Manufacturing ERP setup depends on how accurately those records describe the plant. Demonstrate resin inventory management with actual workflow variations before enabling broad automation.
Pilot one grade and one representative product. Receive a lot, issue a partial bag, transfer material to preparation, record use, and return the balance. Add a material top-up, a quality hold, and runner recovery.
The acceptance review should settle five practical questions:
- Can stores and production see where the remaining resin is?
- Does the system distinguish a transfer from consumption?
- Can the team retrieve every material lot used by the order?
- Do quality holds and prior commitments affect the shortage view correctly?
- Can users explain the difference between planned and actual use?
Agree on who records each event and who can correct it. Check the scale, scanner, and data-entry workload at the press. Confirm the Odoo version, edition, and installed applications, then identify any extra work for dryer readings, blend control, or machine integration.
For the wider scope, explore ERP for injection molding manufacturers. Run the pilot through a shift change before extending the process to other lines. That handover often exposes incomplete returns and material that belongs to an earlier job.
Frequently asked questions
Why does ERP show resin in stock when production says it is unavailable
On-hand resin may be on hold, committed to another order, in an unsuitable grade, or still awaiting preparation. It may also sit in a line location that the planner has overlooked. Review quantity by grade, lot, location, status, and need date rather than relying on the plant total.
Should we deduct resin when it moves from stores to a dryer
Record the movement, but distinguish it from material consumption. If the ERP treats the move as a final issue, define how unused stock and returns remain visible. Reconcile opening line stock, additions, processed material, and closing stock so the same resin is not counted twice or lost from the record.
How do we calculate resin requirements when the mold has cold runners
Include part and runner weight for the active mold configuration, then apply the appropriate production-loss model. For a four-cavity mold with an 8 g runner, the runner contributes 2 g per molded part. Record purge separately where appropriate, and avoid counting rejected output twice in the allowance.
Can we use one regrind percentage for every product
No universal percentage suits every resin and part. Use the approved material and customer requirements, supported by the required validation. Record the blend basis and the recovered material’s source history. Resin inventory management should distinguish available regrind from regrind approved for the particular order.
How should we track resin remaining in an open bag
Retain the material grade and lot, measure the remaining net quantity, and label the bag or replacement container. Record its location and relevant condition or preparation history. A partial bag should not appear as a full pack, and its return should not automatically make it ready for another job.
Can Odoo automate resin purchasing without ignoring quality holds
Odoo documents reordering and replenishment features, but the proposed configuration must handle usable stock correctly. Test a shortage with resin on hold, existing commitments, and a late supplier receipt. Check the forecast, purchase suggestion, and issue permissions in the exact deployment before relying on automation.
Which resin inventory measures should management review
Review job-ready stock, stock-related production stops, consumption variance, and slow-moving material value. Separate recoverable runners from disposal losses and unexplained differences. Use consistent units and periods. These measures help management distinguish a purchasing shortage from an approval, preparation, or recording problem.
Book a demo for your resin inventory workflow
Want a clearer view of usable resin and actual consumption? Book an Odoo manufacturing demo with Apagen. Bring a sample material list, one molding bill of materials, and a recent stock variance so we can discuss the workflow your plant needs.
Ask us to demonstrate resin inventory management from receipt to dryer stock, production use, returns, and regrind in the proposed solution. Email sales@apagen.com or call +91 9971800665 to request your demo.