Can the SOP absorb the inspection items?

A: Only where an operation has 3 items or fewer. Beyond that, the person doing the work and the person judging it wait on each other, and the two documents split again.

Which document changes first?

A: It depends on the trigger. A parameter change moves the SOP first, a decision rule change moves the SIP first, and the other follows inside 24 hours.

Can one SOP cover several operations?

A: No. One SOP and one SIP per operation, so 6 operations give 12 files. Merging only produces a document that operators read as far as page two.

What if old copies are not all returned?

A: Trace the photocopy, then reissue and log it. A return rate below 100% adds one document-control check to that quarter's audit.

Which file does a customer see?

A: The SIP first, because customers care how acceptance is decided. SOP parameters and tooling go out as an extract under confidentiality terms, and if both are released the version numbers must match.

Sop Sip: SOP vs SIP

Quick answer: A sop sip pair splits one operation in two: the SOP fixes sequence, parameters and tooling, the SIP fixes inspection, frequency and limits.

Two documents per operation, and why one will not do
Reading one injection step from both sides
Length, owner, and where each document stops
Three revision triggers and the A0 ladder
Controlled copies and the 24-hour swap
FAQ

1. Two documents per operation, and why one will not do

The usual failure is a merged file: page one explains how to start the machine, page two explains what counts as acceptable, and nobody can tell who is judging. Kept apart, the roles stay legible. The SOP answers sequence, parameters and tooling; the SIP answers inspection item, frequency, decision and record.

Document	Question it answers	Content	Owner	Length
SOP (moulding)	How is it done	Sequence, pressure, tooling	Process	3 pages
SIP (moulding)	How is it judged	9 items, every 2 hours, decisions	Quality	2 pages
SOP (packing)	How is it done	Bagging order, label position, stacking	Process	2 pages
SIP (packing)	How is it judged	3 label items, 5 cases, decisions	Quality	1 page

A standard case runs through 6 operations, so 2 documents each gives 12 files and about 30 pages. The risk is not file count but a mismatch inside one operation: the SOP sets hold pressure at 6.5 seconds, the SIP judges parts made at 8, and the batch is scrap either way.

Reading conditions differ too: the SOP stands at the machine and needs larger type, the SIP sits on the bench and needs tight rows.

2. Reading one injection step from both sides

Hold pressure is an action and belongs to the SOP. Weight and flash are results and belong to the SIP. The pair exists to connect them.

Sop sip cross-check on an open black case: egg-crate foam base holding long black parts, flat lid foam, two front latches and one pressure valve

For moulding, the SOP sets hold pressure 6.5 seconds, cooling 24 seconds and mould temperature 45 °C; the SIP checks single-part weight 2.45 kg within ±1.5%, flash at the parting line under 0.15 mm, and 5 cases every 2 hours. Lose hold pressure and weight drops first; cut cooling and flash appears first.

The mapping is not one to one. Half a second of hold pressure may cost only 8 g, well inside ±1.5%, while flash is already visible. That is why the SIP carries both weight and flash.

The reverse direction matters too: five consecutive over-weight parts send the engineer back to the SOP, to check hold pressure and back pressure.

Some items live only in the SIP: colour difference, latch force, label position. The SOP offers no action for them beyond a self-check note.

3. Length, owner, and where each document stops

An SOP that reads like a manual goes unread; an SIP that reads like a standard goes unfilled. A page ceiling beats a format rule: 2 to 4 pages for the SOP, 1 to 2 for the SIP. Over the ceiling means one file is covering two operations.

Ownership splits the same way: process writes the SOP and production signs, quality writes the SIP and process counter-signs. Whoever signs must recite the key parameters.

Keep the SIP to 9 items and 5 record columns: date, lot, measured value, decision, signature. Extra columns get filled with whatever is easy.

Write the boundary on the cover: an SOP containing "judged acceptable" has crossed it, and an SIP containing "hold pressure first, then cool" has crossed it the other way.

4. Three revision triggers and the A0 ladder

Revisions cannot travel by word of mouth. Three triggers cover most changes: a process parameter, a material grade, a machine or mould. All three use one change note; only the signatures differ.

Sop sip revision review: an olive green case open on a steel bench, kraft paper bags on black foam, orange warehouse racks behind

Trigger	File that moves first	Deadline	Sign-off
Process parameter	SOP first, SIP follows	24 hours	Process, quality
Material grade	Both together	24 hours	Process, quality, buying
Machine or mould	SIP decision item	72 hours	Quality, maintenance
Customer drawing	Both reissued	5 working days	Three parties

The change note carries 5 fields: line number, before and after values, originator, sample serial, effective date. A note missing a field goes back to be completed.

Version numbers start at A0, the first change makes A1, a correction inside one version is A1.1. Each revision is validated on 3 sample parts, and a change without a sample never reaches a version number.

5. Controlled copies and the 24-hour swap

A controlled copy has 3 homes: machine, inspection bench, file. The SOP lives at the machine, the SIP at the bench, both sit in the file, and 1 read-only PDF sits in the controlled folder.

Location	Document	Swap action
Machine board	Current SOP	Old sheet removed and returned
Inspection bench	Current SIP	Page swapped, new version stamped
File cabinet	One of each	Old version stamped void, kept 3 years
Controlled folder	Read-only PDF	Old file moved to archive

The swap has 24 hours and the return rate is measured at 100%. A shortfall means a photocopy is circulating, and the first question is where it came from, not who is to blame.

Sample the swap the same day: ask 3 operators for the version number, and anyone who cannot answer marks a machine that never received the sheet.

SIP sampling runs every 2 hours and SOP training runs 30 minutes per document. Both are kept 3 years and reviewed every 12 months, and the review answers one question: does this line still match the floor?

Conclusion

The value of the pair is alignment, not detail: the SOP governs sequence, parameters and tooling, the SIP governs inspection items, frequency, decisions and records, one of each per operation, 2 to 4 pages against 1 to 2, one change note per revision, 24 hours to swap and 100% return. Hold those numbers and the two documents interlock instead of drifting apart.

This article covers case-side specifications only and does not address any handling, loading or use of the contents.