Injection molding scrap management becomes difficult when the production report says “1,000 rejects” but the scrap bin contains parts, runners, and purge from several jobs. Finance wants a cost. Quality wants a cause. Stores needs to know what material can return to production.
An ERP system can connect those records. However, the result depends on how you define scrap, capture it at the press, and record its final use or disposal. A single scrap field rarely answers all three departments’ questions.
For an ERP implementation, the first task is to follow one rejected part from detection to final disposition. That exercise exposes missing records before they become dashboard problems. This guide explains the workflow, calculations, and controls an injection molding factory needs.
What is injection molding scrap management
Injection molding scrap management is the process of recording defective parts and material waste, tracing their production source, deciding their disposition, and using the data to prevent repeat losses. An ERP system links these events to production orders, quality records, inventory movements, and costs.
Track rejected parts in pieces and material in kilograms. Keep recoverable material visible until it is approved, reused, sold, or disposed of. Recovering resin can reduce material loss, but it does not remove the original quality failure or the machine time spent making that part.
Define the categories before building reports
During system design, ask production, quality, stores, and finance to agree on what each category means. Otherwise, one shift may report runner weight as scrap while another reports only rejected pieces. The combined percentage will be misleading.
Use separate records for these events:
- Rejected parts: pieces that fail the defined acceptance criteria.
- Startup rejects: rejected pieces produced before the approved production release.
- Runners and sprues: non-part material produced by the molding process.
- Purge and changeover waste: material used during cleaning or a material change.
- Material handling losses: measured spills, contamination, or other unusable resin.
- Quality hold: material or parts awaiting a decision, with quantity and location recorded.
Startup describes when a reject occurred. Flash or a short shot describes its defect. Store both fields on the same event so startup rejects remain a subset of total rejects, rather than an extra quantity added twice.
A quality hold is also different from a confirmed reject. Keep held stock out of approved availability through a tested workflow. Once quality decides, record whether the stock is released, reworked, recovered, or scrapped.
Capture the event while its production context is available
A bin weighed at the end of the day tells you how much material accumulated. It may tell you very little about where it came from. The ERP entry needs the job context while that information is still available.
Pre-fill the production order, part revision, machine, mold, shift, and operator from the active work order. Then ask the operator to enter the rejected quantity, observed defect, and cavity where identifiable. Link the material grade and resin lot to the actual feed records.
For weighed material, record the net kilograms, container identification, and collection period. Remove the container tare weight. Keep the source lots linked if material from several approved sources enters one recovery batch; avoid presenting a mixed batch as a single virgin lot.
Keep the defect and the root cause separate
“Flash” is an observation. “Damaged parting line” is a possible cause that needs confirmation. Operators should be able to report the defect without guessing which department caused it.
Start with a short reason list, clear definitions, and reference photographs. Include an “awaiting investigation” option. Later, quality or process engineering can add the confirmed cause, supporting evidence, action owner, and closure date.
Make entry practical at the press
Test the screen during an actual shift. Operators should not have to search for the mold number or type the resin grade each time. A well-designed entry can use a few taps, with a photo when it helps explain the defect.
Agree on when events must be recorded, such as at detection or within a defined collection interval. Label bins by job and material. At shift handover, review open holds and bins awaiting weighing so their source does not disappear with the departing team.
Calculate reject rate and material waste separately
For a closed production run with all molded pieces classified, the part reject rate is rejected pieces divided by total molded pieces, multiplied by 100. Total molded pieces includes accepted and rejected output within the same reporting scope.
Suppose a four-cavity mold produces 20,000 pieces over 5,000 shots. Inspection accepts 19,000 pieces and rejects 1,000. There are no unresolved holds or rework in this illustrative example.
The part reject rate is 1,000 ÷ 20,000 × 100 = 5%. First-pass accepted output is 95%. Counting the 5,000 shots as the denominator would mix shots with pieces and produce the wrong result.
A worked material reconciliation
Assume each accepted part weighs 18 grams. The combined runner and sprue weighs 8 grams per shot. The job also produces 8 kg of purge, recorded separately from molded pieces.
For this example, the weighed rejected parts total 18 kg. Actual reject weight matters: short shots, flash, and incomplete parts may differ from the approved part weight. Use measured weights when reliable material accounting is required.
| Recorded output | Weight in kg | Basis |
| Accepted parts | 342 | 19,000 × 18 g |
| Rejected parts | 18 | Net weighed quantity |
| Runners and sprues | 40 | 5,000 × 8 g |
| Purge | 8 | Net weighed quantity |
| Total material accounted for | 408 | Sum of recorded outputs |
Now check the feed side. With no opening line stock or other movements, assume stores issues 450 kg, receives 25 kg back, and records 17 kg of unprocessed material remaining at the line. Material processed is 450 − 25 − 17 = 408 kg.
Both sides reconcile. The material outside accepted parts is 18 + 40 + 8 = 66 kg, or about 16.2% of processed feed. That figure includes potentially recoverable material; it is not a disposal rate. It answers a different question from the 5% part reject rate.
If the feed balance were 410 kg, the 2 kg difference would need investigation. Check weighing, open hopper stock, missed returns, and posting times. Do not automatically turn an unexplained variance into a confirmed scrap event.
Design ERP postings so each loss is counted once
The most important system question is what each transaction does to stock. A defect entry, a quality alert, a scrap move, and a regrind receipt can refer to the same physical material. They should share a traceable reference, while each performs its own defined purpose.
Odoo’s manufacturing scrap documentation explains that scrapping removes items from physical inventory and records them in a virtual scrap location. That transaction serves a different purpose from transferring recoverable material to an internal location for inspection or grinding.
For Odoo for manufacturing, demonstrate both paths in the proposed database. Confirm where rejected output is recorded, which item is removed, and how approved recovered material becomes a separate stock item. Never assume a generic scrap button covers the complete recovery workflow.
Pay particular attention to resin consumption. If the job has already consumed the resin contained in a rejected part, an additional resin scrap transaction must not consume that same quantity again. Test the entire sequence through stock balances and job costing before rollout.
In a Manufacturing ERP project, also confirm who can release a hold, approve recovery, change a reason, or correct a posting. Record changes with their user and time. Corrections should preserve the connection to the original event.
Control regrind without hiding the original loss
Grinding a rejected part changes its material form. It does not make the rejected piece acceptable. Keep the original rejection against the job, then record recovery as a linked event with its own quantity and status.
For each recovery batch, capture material grade, color, source jobs or lots, net weight, contamination checks, and approval. Record processing history where it can be established. If batches are mixed, preserve their source links and any uncertainty about prior processing.
BASF’s Ultramid processing guidance says reuse depends on contamination, drying, processing history, and whether the application permits recovered material. These are material-specific considerations. A clean appearance alone does not establish suitability for reuse.
Define the approved blend by product and material. Specify whether the percentage means regrind divided by total feed or regrind divided by virgin feed. Those calculations differ. The ERP should record the actual approved blend and prevent unapproved material from appearing as usable supply.
Measure grinding input and output as well. A 50 kg input does not justify a 50 kg stock receipt if usable output weighs 47 kg. Record the remaining 3 kg according to its measured disposition or unresolved variance.
Use the records to reduce repeat scrap
ERP supports injection molding scrap management by making the pattern visible and assigning follow-up work. Process engineering still needs to investigate the physical cause. A dashboard cannot establish that a resin lot, operator, or machine caused a defect merely because they appear together.
Investigate the largest recurring loss
Build a Pareto report that ranks defects by rejected pieces, kilograms, or cost. Choose the measure explicitly. A high-count defect in a small part may have a different business impact from a lower-count defect in an expensive component.
Then compare the same part and process across molds, machines, cavities, lots, and shifts. In an illustrative case, most flash rejects might come from cavity three of one mold. That would justify a focused investigation of that cavity rather than a plant-wide parameter change.
Keep the evidence with the quality record: photographs, inspection readings, setup revision, maintenance history, and the time the pattern began. These details help the team test an explanation instead of relying on memory.
Connect changes to inspection and maintenance
Avient’s injection molding troubleshooting guide lists several possible contributors to shorts, flash, and surface defects. Its guidance reinforces the need for systematic investigation. Apply the relevant material guidance and approved process window when evaluating changes.
Set inspection requirements around events that matter to your plant, such as a startup, tool repair, or material change. Odoo’s quality checks documentation describes checks linked to manufacturing and inventory operations. Validate how your deployment handles event-based triggers and release controls.
Link recurring tool-related defects to maintenance work. After the repair, compare equivalent runs and confirm that output still meets specification. If a cavity is disabled temporarily, update the active cavity count used for planning and reporting.
Close actions only after checking the result
Give each investigation an owner, a due date, and a verification plan. Odoo’s quality alerts documentation describes records for root cause, responsibility, and corrective and preventive actions.
A reduction from 5% to 3% is two percentage points, or a 40% relative reduction in reject rate. However, compare equivalent products and conditions. A different product mix or longer production runs can change the result without fixing the original problem.
Give management a cost view with a clear basis
A resin-only calculation can show material exposure quickly. For example, 18 kg of rejected parts at an illustrative ₹200 per kg represents ₹3,600 of material content. It excludes the cost of processing those parts and any recovery value.
For a broader review, identify the costing basis and include the relevant machine time, labor, inspection, and handling. Avoid adding conversion costs twice if they are already included in the rejected product’s cost. Keep expected recovery value separate until the material is approved and its value can be supported.
Review reject rate by product, startup waste per changeover, recurring defect cost, recovered stock awaiting approval, and overdue corrective actions. Show the quantity and denominator behind each percentage. A plant average without product detail offers little direction for the next improvement.
Pilot the complete workflow before connecting every press
Start with a manageable group of machines, including a multi-cavity job and a job that produces recoverable runners. Follow normal production, shift handover, a quality hold, and a correction. Compare the physical bins and line stock with the ERP records.
Ask the team to demonstrate five acceptance scenarios:
- Record a reject with its job, defect, and cavity without duplicating production output.
- Hold material and release or reject it through the agreed approval process.
- Recover approved material into a separate item with source traceability.
- Reconcile issued resin, returns, line balances, and recorded outputs.
- Correct an entry while preserving the original reference and change history.
If machine or MES integration is in scope, define the meaning of each signal. A shot counter records cycles, not necessarily good parts. Validate active cavities, trial shots, counter resets, missing events, and repeated transmissions before using automatic counts in official reports.
Apagen’s ERP for injection molding manufacturers page provides the wider context for connecting this workflow with production, inventory, and tooling. Scrap records become more useful when they share those operational references.
Frequently asked questions
Should runners and purge be included in our reject rate
Keep them out of a part-based reject rate because they are material quantities, not rejected pieces. Report runners and purge in kilograms alongside the reject rate. If you publish a material waste percentage, define its categories and processed-feed denominator, and show how much material remains recoverable.
Does our scrap rate become zero when we reuse all rejected parts
No. The parts still failed acceptance, so their original rejection remains in the quality report. Approved reuse can reduce disposal and some material purchases. It does not recover the machine time, inspection effort, or other conversion costs already spent on those rejects.
How do we track scrap from just one cavity in a multi-cavity mold
Record the cavity against the reject event and capture the number of pieces produced by that cavity. Calculate its reject rate using its own output. If cavity identification is unavailable, mark it unknown. Revisit the count when cavities are disabled or when a family mold produces different parts.
Why does our scrap bin weight disagree with the ERP report
Check whether both records cover the same period, jobs, and material categories. Then check container tare, mixed bins, unrecorded purge, duplicate entries, and material moved for grinding. Also verify hopper balances and returns. Keep any remaining difference visible until the team resolves it.
Can Odoo track scrap and regrind without customization
Odoo provides manufacturing scrap transactions and quality capabilities in supported configurations. Your complete workflow may still need additional fields, controls, reports, or integration for cavities and recovery batches. Ask the implementation team to demonstrate your actual sequence in the proposed edition and version, including stock movements and costing.
Can we automate scrap entry from injection molding machines
Partly, depending on the machine, inspection system, interfaces, and integration. A press can supply cycle data, while reject confirmation may require inspection or operator input. Define which system owns each count and how the integration handles resets, missed events, and duplicate messages. Validate piece counts against physical output.
What scrap percentage should management target
Set targets using your validated process, customer requirements, material, product, and run conditions. There is no single target suitable for every molding job. Track startup and steady-production losses separately, compare equivalent runs, and reduce recurring defects while maintaining acceptance criteria. A lower number achieved by changing classifications is not an improvement.
Book a demo for your scrap management workflow
Want to see where your factory loses material and how the ERP records can guide action? Book an Odoo manufacturing demo with Apagen. Bring a sample production report, your scrap reason list, and one resin reconciliation so we can discuss the workflow your plant needs.
Ask us to demonstrate injection molding scrap management from reject entry and quality hold to approved recovery, stock reconciliation, and reporting in the proposed solution. Email sales@apagen.com or call +91 9971800665 to request your demo.