An injection molder sells parts for a few cents, yet makes them with a mold worth tens of thousands of euros, a press that runs around the clock, and a raw material whose price moves with oil and chemicals. The margin is decided in fractions of a cent per part: a cycle two seconds longer, one more point of scrap, or a material price clause missing from a contract is enough to wipe it out.
That is exactly where generic ERP systems fall short. They handle a production order, a bill of materials and a stock level well enough. They are far less comfortable with the fact that a mold is an asset that wears out shot by shot, that the same part can run on three different presses at three different cycle times, or that 15% of reground recycled material changes the traceability an automotive customer demands.
This guide is written for owners, operations directors and IT leaders at plastics processors with 50 to 500 employees. It describes what an ERP must really do on an injection molding floor, sets out a cost-per-part calculation, and then compares solution profiles by company size.
Industry Specifics That Break a Generic ERP
Four characteristics show up in every plastics project, and each one becomes a functional gap if it is not handled at scoping.
Customer-Owned or Own Tooling
The mold is the first friction point. Depending on the contract, it belongs to the customer (who paid for it and lends it to you), to the molder (who amortizes it in the part price) or to both (shared funding). That distinction decides who pays for maintenance, who can move the mold to another supplier, who insures it, and how it appears in the books: a fixed asset on your balance sheet, or simply an item held on behalf of a third party.
A generic ERP treats tooling as an item or a fixed asset. What you actually need is a dedicated mold record linked to an owner, a customer and one or more part numbers, with its own shot counter and intervention history.
Volatile Material Prices
Material is usually the first line of the cost build-up, and its price moves between quote and delivery. The molder buys pellets (polypropylene, polyamide, ABS and so on) at fluctuating prices while customers want stable part prices. Hence price adjustment clauses: the part price is revised according to a material index agreed in the contract. The ERP must carry that rule, not a parallel spreadsheet.
Long Runs and Changeovers
Unlike a job shop machining small batches, injection molding lives on long runs with dedicated molds, and changeovers are expensive: removing the mold, purging the material, setting up, and validating the first part. A schedule that ignores changeover times is wrong by Monday morning.
Scrap and Non-Conforming Parts
Every start-up, every purge and every rejected part consumes material and machine time. Some scrap can be reground and reused; the rest is lost. The ERP must separate these flows rather than burying them in a single consumption variance.
Mold Management: Ownership, Amortization, Maintenance, Shot Count
The tooling module is the most discriminating criterion in a plastics requirements specification. Its minimum functions:
- Mold record: number, cavity count, compatible press(es), dimensions and required clamping force, owner, customer, location (shop floor, tool crib, at the customer, in repair).
- Shot counter: incremented with each production run, either declared by the operator or fed automatically by the press. The counter drives both amortization and maintenance.
- Amortization per part: the mold cost is spread over a forecast volume of parts or shots. A 4-cavity mold produces 4 parts per shot, which changes the allocation base.
- Shot-triggered preventive maintenance: cleaning, lubrication, and inspection of ejectors and cooling channels every N shots, not every N months. A mold that sat idle for six months does not need the same service as one that ran without a break.
- Repair and modification history: essential when discussing a recurring defect with a customer, or to justify billing for tool rework.
The Link With CMMS
Molds and presses belong to industrial maintenance. There are two options: a maintenance module built into the ERP, or a dedicated CMMS interfaced with it. The deciding criterion is whether the shot counter and maintenance work orders live in the same reference data as scheduling. Otherwise the planner launches a mold whose preventive service is overdue, or needlessly takes a perfectly healthy mold out of service. Our guide to CMMS and industrial maintenance in the ERP covers the integration models.
Press Scheduling: Sequencing, Changeovers, Cycle Rates, OEE
Scheduling Under Multiple Constraints
Scheduling an injection shop means assigning molds to presses while respecting several constraints at once: press tonnage and platen dimensions, mold availability, material and colorant on hand, required auxiliaries (dryer, robot, temperature controller) and available crews. On top of that comes changeover optimization: running two same-color parts back to back avoids a long purge, while going from black to white is costly.
General-purpose ERP systems offer basic finite-capacity scheduling. Industry-specific ERPs or specialized APS modules model the changeover matrix by color, material and mold. That is often what makes the difference from a fleet of around twenty presses.
Cycle Times
The theoretical cycle time sits on the mold record, but it differs from the actual cycle time depending on the press, the material and the season. The ERP must manage a cycle rate per mold/press pair rather than a single rate per item; otherwise costs and promised lead times are wrong.
Machine Data and OEE
Overall equipment effectiveness (OEE) combines availability, performance and quality. Getting it without manual entry means connecting the presses to the information system: either through an MES or through a direct gateway (OPC UA is the most common protocol on recent presses; older equipment needs data-collection boxes). The data collected feeds three uses: actual progress of production orders, mold shot counters and downtime causes.
The architecture question to settle at scoping: does the ERP handle shop-floor tracking, or does a dedicated MES collect the data and pass on only summaries? In a plant with around ten presses, the ERP’s native shop-floor tracking is often enough. Beyond that, or where a customer requires traceability of process parameters, an MES is justified.
Materials and Blends: Pellets, Regrind, Colorants, Price Indexation
Lot Traceability
Every lot of pellets received must be identified (supplier, lot number, certificate), then linked to the production orders that consumed it, and therefore to the lots of parts shipped. When a nonconformity is found at a customer, the upstream trace (which material lot) and the downstream trace (which customers received parts from that lot) should take minutes, not days.
Blends and Percentage-Based Bills of Materials
An injected part is rarely made from a single component. A typical BOM includes virgin resin, a percentage of recycled regrind, a colorant masterbatch dosed as a percentage, and sometimes additives. A suitable ERP manages BOMs in proportions rather than fixed quantities, and calculates requirements per production order from the part weight, the runner weight and the expected scrap rate.
In-House Regrind
Sprues, rejected parts and purges can be ground and fed back into production. The ERP must treat regrind as an item in its own right, with its own stock, valuation and usage rules: a medical customer may forbid any regrind, while an automotive customer may allow a maximum percentage on certain parts. Without that rule coded into the BOM, compliance depends on the setter’s memory.
Material Price Adjustment Clauses
Plastics contracts often contain a formula: part price = base price + change in the material index, with a review frequency and sometimes a threshold. The ERP must store the formula per contract, capture the reference index and automatically recalculate the price to invoice. Its inventory valuation also matters: the choice between FIFO, weighted average cost or standard cost changes the apparent margin when prices move. Our article on inventory valuation in the ERP explains how to configure these methods.
Cost per Part: Material, Machine, Labor, Scrap, Tooling
The cost per part adds up five components. The table below is a purely illustrative example, built on invented assumptions for demonstration: it represents neither a market price nor an industry average.
Illustrative assumptions: 40 g part, 4-cavity mold, 30-second cycle (480 parts per hour), material at €2.20 per kilo, press hourly rate of €120, one operator at €40 per hour covering two presses, a €60,000 mold amortized over 4 million parts, 3% scrap.
| Component | Calculation | Cost per part (€) |
|---|---|---|
| Material | 0.040 kg x 2.20 | 0.088 |
| Machine time | 120 / 480 | 0.250 |
| Labor | 20 / 480 | 0.042 |
| Tooling | 60,000 / 4,000,000 | 0.015 |
| Subtotal | 0.395 | |
| Scrap (3%) | 0.395 / 0.97 - 0.395 | 0.012 |
| Total cost | 0.407 |
What the example shows, within the stated assumptions:
- Machine time weighs more than material. A 4-cavity mold that loses 10% of its rate pushes the machine line from 0.250 to about 0.278 euro, more than the effect of a 10% rise in material price (about 0.009 euro).
- Mold amortization is small per part on a long run, but becomes dominant on a short run.
- Scrap acts upstream: it flows through every component.
The lesson for the ERP: it must calculate this cost per mold/press pair, using actual cycle rates fed from the shop floor, and compare standard cost with actual cost per production order. Without that reconciliation, variances (cycle rate, scrap, material price) stay invisible until the annual close.
Recycled Plastics, REACH and Customer Requirements
Recycled Content and the Packaging Regulation
The EU Packaging and Packaging Waste Regulation (EU) 2025/40 (text on EUR-Lex) sets minimum shares of post-consumer recycled plastic in plastic packaging, with a first step in 2030 and a second in 2040, calculated by packaging type. The text exempts certain sensitive uses, such as direct packaging of medicines. If you produce packaging, the ERP must therefore distinguish post-consumer recycled material, in-house regrind and virgin material, with supplier evidence.
REACH: Knowing What Your Parts Contain
Article 33 of the REACH Regulation (EUR-Lex) requires a supplier of articles to inform the recipient when a Candidate List substance (SVHC) exceeds 0.1% by weight. For a molder, the sources of risk are additives, colorants and masterbatches. The ERP must link each material reference to supplier declarations and raise an alert when the Candidate List changes.
Automotive and Medical Requirements
Automotive customers ask for lot traceability, composition data (see our automotive ERP guide on IATF 16949 and IMDS) and a control plan per part. Medical customers add process validation, parameter freezing and a ban on changing material without approval. In both cases the ERP must lock the validated BOM: any change of material or colorant supplier goes through an approval workflow.
Which ERP by Company Size: Solution Profiles
Vendor names change quickly, so the right approach is to compare profiles before products. The table summarizes their strengths and limits for a plastics processor.
| Profile | Strengths | Limits | Best for |
|---|---|---|---|
| General-purpose manufacturing ERP (major vendors) | Finance, purchasing, multi-site, integrator ecosystem | Tooling and changeovers must be configured or developed, high project cost | Multi-site mid-size companies, groups |
| Plastics-specific ERP | Mold record, shot counter, proportion-based BOMs, native press scheduling | Smaller vendor, sometimes thinner finance, dependence on a niche player | Molders with 50 to 300 employees, one or two sites |
| Odoo (Community or Enterprise) | Controlled licence cost, modularity, modern interface | Tooling and material indexation to be developed by the partner, quality varies widely by integrator | SMEs with simple processes and a partner who knows injection molding |
| Cloud industry solutions | Fast deployment, updates included | Limited customization, depth on molds to be verified | Companies without an IT team, growing mid-size firms |
Recommendation by profile:
- Under 100 employees, about ten presses: a plastics-specific ERP or a well-integrated Odoo, with lightweight machine data collection.
- 100 to 300 employees, two sites, automotive or medical customers: a plastics-specific ERP with a quality module, or a general-purpose manufacturing ERP backed by an MES.
- Over 300 employees, several countries: a general-purpose manufacturing ERP, with custom development on tooling and a unified MES.
Whatever the profile, insist on a demonstration with your data: a 4-cavity mold owned by the customer, with material price indexation and regrind fed back in. A vendor who can do that live saves you months of development.
Implementation Roadmap and Pitfalls
The Steps
- Scoping: map molds, presses, materials, price adjustment contracts and customer requirements. Document the functional gaps.
- Master data: mold records (owner, cavities, cycles), mold/press pairs, proportion-based BOMs, routings. This is the longest workstream.
- Pilot on a limited scope: a few presses and one representative customer, with actual cost calculation.
- Machine connectivity: connect the most critical presses first, then extend.
- Rollout and cutover: outside production peaks, with a reliable material and mold inventory.
The Pitfalls
- Underestimating mold data migration: actual shot counts are often unknown or wrong. Plan a stocktake before cutover.
- Freezing a single cycle rate per item: the cost becomes wrong as soon as a mold moves to another press.
- Forgetting material indexation: price differences not passed on accumulate as silent losses.
- Connecting all presses at once: a mixed fleet needs boxes and adaptations machine by machine.
- Neglecting shop-floor change management: without reliable operator entry of scrap and downtime, OEE and actual cost stay theoretical.
Going Further
If your business also touches packaging, read our guide to ERP for printing and packaging, which covers neighboring issues (tiered quotes, consumables traceability, machine connectivity). To scope your plastics project, get in touch: we will prepare the requirements specification and the demonstration on your own data with you.
