In injection molding, most of the process lives in the machine settings and the mold, so the work instruction has two jobs: lock in the approved process so every setup reproduces it, and tell the operator what to look for at the press. A molder serving automotive, medical and consumer customers may have to meet three quality systems with one set of presses.
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Which standards apply to a molder
Most custom molders run an ISO 9001 system and add requirements by market. Automotive work brings IATF 16949 and the AIAG core tools: PPAP, control plans, setup verification and process capability. Medical work brings ISO 13485 and, in the United States, the FDA QMSR, with process validation and lot traceability. A captive molder inside an OEM follows whatever the parent system requires.
Across all of them, the auditor wants the same thing: the approved process is written down, setups reproduce it, changes go through review, and the parts you ship match the parts that were approved. The ISO 9001 vs IATF 16949 and ISO 9001 vs ISO 13485 comparisons help when one press serves several markets.
The documents a molding cell depends on
The process sheet records the approved setup for one mold on one press: temperatures, pressures, speeds, times, transfer position and cushion, usually with allowed windows. The work instruction then covers the human steps around it: mold change, material preparation, first-shot approval, part handling, inspection, and what to do when the press drifts.
Material handling is where many molding problems start. Drying time and temperature, regrind limits, colourant ratio and lot traceability all need to be in an instruction, not in someone’s memory. Mold maintenance and the mold’s own revision history belong in the same controlled set.
Tie each process sheet to a mold number, press number and revision.
State who may adjust settings and how far, and when a change needs engineering approval.
Keep boundary samples or photos of acceptable and rejectable cosmetic defects at the press.
The templates and tools that matter most
Coplain pages for plastics injection molding, in priority order
Cpk for critical dimensions during approval and production.
Example: Mold startup and first-shot approval
Example An excerpt from a work instruction at Lakeshore Molded Products, a fictional custom molder. Mold, press and settings are example values; use your own approved process sheet and customer requirements.
Startup of mold M-118 on press P-07 after a mold change
Critical characteristics
CC1 snap-fit width, CC2 no short shots on the latch
Approved by
Process engineer, quality engineer
Tools, materials and PPE
Process sheet PS-M118-P07
Dryer log for the resin lot
Caliper, ID on the setup record
Boundary sample board for M-118
Heat-resistant gloves, safety glasses
Steps
Confirm material is ready. Check the dryer log shows the resin lot has dried for the time and temperature on the process sheet, and record the lot number. Key point: Do not start with resin that has not completed its drying time. Reason: Wet resin causes splay and weak parts that may pass a visual check.
Load the approved process. Load the stored setup for M-118 and compare each setting on the screen with the process sheet. Key point: Settings outside the sheet’s window need process engineer approval. Reason: The approved process is what the parts were qualified with.
Purge and run to stable. Purge the barrel, then run shots until the cushion and cycle time are steady. Key point: Scrap the startup shots; never mix them with good parts. Reason: Parts made before the process is stable are not approved.Safety: Purge into the guarded purge pan; hot material can spatter.
Approve the first shot. Compare one full shot with the boundary samples and measure CC1 on each cavity. Key point: Record each cavity’s value with the caliper ID. Reason: Every cavity must be proven, not just one.
Release the cell. Sign the setup record and set the press to automatic. If any check fails, stop and call the process engineer. Key point: Do not adjust settings to chase a dimension without approval. Reason: Unapproved adjustments move the process away from its validated window.
Acceptance criteria
Material lot recorded with completed drying time
All settings within the process sheet window
CC1 within tolerance on every cavity; CC2 shows a full latch with no short shot
Common audit findings
These are the kinds of findings auditors and customers commonly write in this industry, with a way to prevent each one in the instruction itself.
Press settings in use do not match the approved process sheet, with no record of approval. Define adjustment limits on the sheet and require a signed record for anything outside them.
Process sheets are not tied to a specific mold and press revision. Put mold, press and revision in the sheet header and in the stored setup name.
Material drying or regrind use is not recorded. Add drying and regrind entries to the startup record, with the resin lot.
First-shot approval does not cover every cavity. List each cavity on the setup record, as in the Example above.
Cosmetic acceptance relies on operator judgement with no standard. Keep controlled boundary samples or photos at the press.
Mold repairs are not reviewed for their effect on approved parts. Route mold changes through the engineering change notice process and decide when re-approval is needed.
Frequently asked questions
What is the difference between a process sheet and a work instruction?
The process sheet records machine settings for one mold on one press. The work instruction covers the human steps: mold change, material, startup, inspection and reactions. Both are controlled documents.
Do we need a new PPAP after a mold repair?
It depends on the repair and your customer. Many automotive customers require notification, and sometimes resubmission, for tool changes that could affect the part. Check the customer’s requirements before running parts.
How much should an operator be allowed to adjust?
Set a written window for each setting on the process sheet. Inside it, the operator records the change; outside it, the process engineer approves first.
Should molding instructions include photos?
Yes. Photos of the part, boundary samples and the setup are often clearer than text, especially for cosmetic defects and gate trimming.
Sources
ISO 9001:2015 Quality management systems — Requirements, ISO
IATF 16949:2016 Quality management system requirements for automotive production and relevant service parts organizations, International Automotive Task Force
ISO 13485:2016 Medical devices — Quality management systems — Requirements for regulatory purposes, ISO
APQP, PPAP, FMEA, SPC and MSA reference manuals, AIAG
Turn your documents into audit-ready work instructions
Upload a process sheet or setup notes and Coplain’s Job Aid Builder drafts startup, first-shot and mold-change instructions with the approved windows and checks in each step.