Injection molding process: from customer order to dispatch

The stages below follow one typical part: a black ABS housing for an electrical switch, moulded in a four-cavity mould with masterbatch for colour, with brass inserts fitted in-house and a logo pad printed by a vendor. A plant moulding PP closures or PET preforms will have fewer steps after moulding, but the sequence of records is much the same.

At each stage, the useful question is not only what happens, but what record it leaves. Those records are what the plant needs when a customer calls about a bad batch.

The process at a glance

1. 1Customer orderPart, quantity and delivery date, with the mould and the machines it fits.
2. 2BOMABS grade by weight, black masterbatch, brass inserts and cartons, with the revision fixed.
3. 3Material planningResin, masterbatch and inserts checked against stock by lot and open purchase orders.
4. 4ProcurementResin and masterbatch received by supplier lot and checked on arrival.
5. 5Production orderThe job is placed on a machine, with the mould change before it, and material is issued by lot.
6. 6Mould change and mouldingMould loaded, first-off approved, then counts, scrap by cause and downtime per shift.
7. 7In-process inspectionWeight, key dimensions and visual checks at a set frequency.
8. 8Secondary operationsInserts fitted in-house, logo pad printed at a vendor against a challan.
9. 9Final QCSample check on the finished lot, then release, rework or reject.
10. 10Finished goods and dispatchPacked lots received into stock, then picked against the order and shipped.

What happens at each stage, and what it records

1. Customer order

The customer sends a purchase order or a monthly schedule for the housing. Each line becomes a sales order line with the part number, colour, quantity and delivery date. Because the part can only run in its own mould, the order also needs to know which mould it uses and which machines that mould fits by tonnage and platen size.

2. BOM

The BOM holds the ABS grade at the part weight plus its share of the runner, the black masterbatch at its let-down ratio, two brass inserts per part and the carton and polybag. If the customer allows regrind, the BOM says how much. The revision released to the job should be fixed on it. The guide to multi-level BOM management explains why.

3. Material planning

Requirements from all open jobs are compared with stock by lot and open purchase orders. Masterbatch is where moulders are most often caught out: the resin is in stores, but the colour needed is not, or it has been used on another job. A useful shortage report names the job it will stop and when.

4. Procurement and incoming checks

Resin arrives in bags or octabins with the supplier's lot number and a certificate. Masterbatch and inserts arrive by lot too. Incoming checks confirm the grade, the lot and the quantity, and inserts are sampled for size. A lot that fails is held. The record holds supplier, lot, quantity and result.

5. Production order

The job is placed on a machine for a set number of hours, worked out from the quantity, the cycle time and the four cavities. The mould change before it is planned as its own operation with its own time. Stores issues the ABS and masterbatch lots to the job. From this point, every count and check on the job links back to those lots.

6. Mould change and moulding

The setter removes the previous mould, loads the housing mould, connects water and heaters and sets the process. ABS takes up moisture, so the resin is dried before it reaches the hopper. The first shots are scrapped while the process settles, then the first-off parts are checked and approved. The actual time the change took is recorded, with a reason if it ran over.

During the run, the operator records the counter reading per shift, rejects by cause (short shots, flash, sink marks, silver streaks, burn marks) and any stop with its reason, such as a heater fault, mould water, waiting for material or a cavity blocked off. Runners and rejects are ground, and the regrind is recorded as its own lot before it goes back into a hopper. The record shows what the machine made, by shift and operator, against its target.

7. In-process inspection

QC weighs a shot and checks key dimensions, the insert bosses and the surface at the frequency the inspection plan sets. Part weight is often the earliest sign of a filling problem. If a housing fails, the batch is held and stays put until quality chooses rework, use as is, or reject. The article on reducing rejection by inspecting at the operation explains why catching it here matters.

8. Secondary operations

Brass inserts are fitted in-house, by heat staking or ultrasonic insertion, as the next operation on the routing, with its own counts and rejects. The housings then go to a pad printing vendor on a challan and come back against it. The record holds the quantity sent and returned, any short or vendor-rejected parts, and the vendor's charge for the order's cost.

9. Final QC

The finished lot is checked on a sample: print position and adhesion, insert pull-out, colour against the approved master, and visual defects. QC then records release, rework or reject, signed with a name. A held lot cannot move to finished goods until it is decided.

10. Finished goods and dispatch

Packed cartons are received into finished goods by lot against the order. Dispatch picks by lot against the customer's delivery date and ships with a delivery note and invoice. A complaint about the housings will start from this record of which lots went on which delivery.

What to record and control at each stage

Where the process usually breaks

• At the plan, when the mould change is treated as a gap and not given its own time.
• At material issue, when resin is tipped into the hopper from whichever bag is nearest, with no lot recorded.
• At the machine, when counts are written once at shift end and the slow hours are hidden in the total.
• At regrind, when ground runners go back into the hopper without a record, so consumption and trace both have a gap.
• At first-off, when the run starts before approval, so startup rejects are counted as production.
• At the vendor, when printed parts come back without being counted against the challan.

How is one batch traced back from dispatch?

Say a customer reports cracked housings from one delivery. The trace runs backwards: delivery note to finished lot, finished lot to the moulding batch, then to the machine, the shift and the operator, the in-process checks and rejects recorded, any regrind lot issued, and finally the ABS and masterbatch lots and their suppliers. When each stage left its record on the lot, that is a lookup. When the records are on bag tags and in registers, it is an investigation.

How FleekERP records each stage

In FleekERP the housing job carries every one of these stages on its work order. The order carries the part, mould and machine. Production planning places the job on the machine with the mould change as its own operation, against capacity and material readiness. Stores receives and issues resin, masterbatch and regrind by lot. Operators log counter readings, scrap by cause and downtime by reason on their phones, QC records first-off and in-process checks, the printing vendor sits on the routing with its challan, and dispatch picks by lot. The invoice syncs to Tally or Zoho. The plastics industry page shows the same flow from the plant's side.

How the process differs by plant type

• Custom moulders: many parts and moulds for many customers, so mould changes and planning by machine dominate the work.
• Closures and caps: high-cavity moulds on long runs, where a blocked cavity or a small cycle time drift costs the most output.
• Technical and engineering parts: tighter dimensions, more in-process checks, and inserts or assembly after moulding.
• Household and consumer products: frequent colour changes, so masterbatch planning and purging between colours matter.
• Blow moulding and extrusion: different machines, but the same need to record material lots, output against rate, scrap and stops.