Lean Manufacturing

5S in injection molding is the Japanese lean methodology — Seiri (Sort), Seiton (Set in order), Seiso (Shine), Seiketsu (Standardize), Shitsuke (Sustain) — applied to the press floor, the mold storage area, the resin room and the tool crib to cut waste, shorten changeovers and prevent contamination of plastic parts. The framework comes from the Toyota Production System and is the entry point to lean manufacturing in plastics processing. Adopted correctly, 5S typically reduces setup time by 20–50 %, drops scrap from contamination, and is often the prerequisite for advanced practices such as single minute exchange die (SMED) and rigorous preventive maintenance. ## The five S's translated to the mold shop | Pillar (JP) | English | What it means on an injection floor | |---|---|---| | Seiri | Sort | Remove obsolete tools, broken inserts, dead drums of resin, expired colorants. | | Seiton | Set in order | Shadow-boards at every press; one labeled home for each torque wrench, hose, drying hopper. | | Seiso | Shine | Daily wipe-down of platens, nozzle area, parting line; sweep regrind dust; clean dryer filters. | | Seiketsu | Standardize | One-page setup sheets, color-coded resin bins (e.g. red = ABS, blue = PC), photo-standards at each cell. | | Shitsuke | Sustain | Weekly 5S audits scored 1–5, posted KPI board, supervisor walk-throughs. | The original Japanese spelling matters: every term starts with "S" in romaji, which is why the method is universally known as 5S. ## Why 5S is critical specifically in injection molding A plastics plant is not a metal-cutting shop. Three molding-specific risks make 5S non-negotiable: 1. Contamination of melt. Even a single pellet of the wrong resin in the hopper can scrap a whole shot of a medical or optical part. Sort + Standardize keep resin streams separated by color-coded bins, dedicated scoops and labeled hopper loaders. 2. Mold damage during changeover. A misplaced eyebolt, missing clamp or hidden hand-tool causes dropped tools and parting-line dings. Set in order means every clamp, locating ring and water jumper has a marked slot on the changeover cart. 3. Process drift. Drips of oil on the platens, dirty thermolator hoses or clogged purge bins push cycle time up shot after shot. Daily Shine routines protect the stable process window the engineer validated. ## A practical 5S checklist for an injection cell - Sort: any tool not used in the last 90 days is red-tagged and moved out of the cell. - Set in order: shadow-board for wrenches, allen keys, brass picks; labeled hooks for water hoses; numbered storage for inserts. - Shine: end-of-shift 5-minute clean — platens wiped, ejector area cleared of flash, regrind bin emptied, dryer filter inspected. - Standardize: laminated setup sheet at the press with screw RPM, back pressure, barrel zones, mold open/close speeds and a part photo. - Sustain: weekly audit by a team leader using a 25-point checklist; score posted on the cell board; corrective actions in a Kaizen log. ## 5S applied to the mold storage area Mold storage is where most plants lose 5S discipline. A disciplined storage program includes: - Numbered racks with a unique location per mold and a database link. - Rust-preventive (VCI paper or oiling) before storage, recorded on the tool history card. - Maximum 3 molds high stacking and minimum 50 mm clearance for an overhead crane sling. - Pre-storage cleaning of cavities — no plastic residue allowed before the mold goes back. ## Common pitfalls - Treating 5S as a one-off "clean-up day" instead of a daily rhythm. - Buying expensive shadow-boards before the Sort step — you organize tools you should have thrown out. - Auditing without consequences — the score has to drive Kaizen actions, otherwise the system decays. - Forgetting the resin room and the regrind area — they are part of the value stream, not "support". ## Related terms See also: lean manufacturing, single minute exchange die, preventive maintenance, cycle time. ## FAQ ### What are the 5 S's of 5S? Sort (Seiri), Set in order (Seiton), Shine (Seiso), Standardize (Seiketsu) and Sustain (Shitsuke). In an injection-molding plant they translate to: discard obsolete tooling, give every tool and resin bin a marked home, keep platens and dryers clean, write one-page setup sheets, and audit the cell every week. ### How does 5S benefit injection molding specifically? It directly attacks the three biggest molding losses: resin contamination, changeover time and process drift. Plants that run 5S well typically report 20–50 % shorter changeovers, double-digit drops in contamination scrap, and far fewer near-misses around moving molds and platens. ### Is 5S the same as housekeeping? No. Housekeeping is just cleaning. 5S is a system: it includes cleaning (Shine), but also discarding unused items (Sort), engineering tool locations (Set in order), writing standards (Standardize) and auditing discipline (Sustain). 5S is also the foundation for single minute exchange die and Total Productive Maintenance. ### How often should a 5S audit be done on a molding floor? Most well-run plants audit every cell weekly with a 20–30-point checklist, plus a monthly cross-plant audit by a leadership team. Scores are posted publicly and Kaizen actions tracked to closure.

DFM (Design for Manufacturing) is the discipline of tailoring a part's design so it can be produced economically, repeatably and robustly by injection molding, avoiding geometries that drive scrap, long cycles or expensive tooling. ## Core DFM principles for injection - Uniform wall thickness: variation <25 % to avoid sinks and warpage - Draft angle: minimum 0.5° per side, 1 – 2° on textured surfaces - Corner radii: minimum 0.5 × wall thickness to reduce stress concentration - Ribs: height 2.5 – 3 × wall thickness, rib thickness 50 – 70 % of adjacent wall - Bosses: outer diameter 2 × screw diameter, no thick build-ups - No undercuts unless served by slides or special ejectors ## Recommended thickness by resin - PP, PE: 0.8 – 3.0 mm - ABS, PS: 1.0 – 4.0 mm - PA, PC: 0.8 – 3.5 mm - POM: 1.0 – 3.0 mm - Fiber-reinforced: up to 6 mm tolerable ## Benefits of DFM - 20 – 40 % lower mold cost by avoiding slides and complex ejectors - 10 – 25 % shorter cycle time from more uniform cooling - Sub-1 % scrap in stable production - Longer mold life from lower stress in critical areas ## Common pitfalls Importing sheet-metal or machined designs without adapting them to injection, thick walls "for strength" (creates sinks), deep textures without enough draft (scratches at ejection), and hollow bosses flush to the wall without root radius.

Preventive maintenance (PM) is the set of scheduled actions carried out on an injection molding machine and its auxiliaries to prevent breakdowns before they happen, instead of repairing after a failure. In an injection molding plant it is the single biggest lever on unplanned downtime and machine OEE. ## Why it matters An unplanned stop in the middle of a production run scraps parts, breaks the thermal steady state and can damage the mold. Planned maintenance is scheduled into low-demand windows, keeps the press repeatable, and extends the life of the screw, barrel and hydraulics. ## Preventive maintenance checklist for an injection molding machine | Frequency | Tasks | |-----------|-------| | Daily | Check oil level and temperature, water-circuit flow, hopper/dryer, safety gates and light curtains, clean the mold area | | Weekly | Grease tie-bars and toggle/clamp, inspect heater bands and thermocouples, check hoses and couplings for leaks | | Monthly | Hydraulic-oil analysis, clean oil cooler and filters, verify check-valve (non-return valve) seal, calibrate pressure and temperature sensors | | Annual | Inspect screw and barrel wear, replace seals, full hydraulic service, electrical-cabinet and PLC backup, geometry/parallelism check | ## Preventive vs. predictive vs. corrective maintenance - Corrective: repair after the failure — cheapest to plan, most expensive in lost production. - Preventive: fixed time- or cycle-based schedule — predictable, but can over-service parts that are still healthy. - Predictive (IIoT): sensors track vibration, oil condition and cycle data to service only when needed — the modern target for Industry 4.0 cells. ## What is preventive maintenance in injection molding? It is time- or cycle-based servicing of the molding machine, auxiliaries and molds — lubrication, inspection, calibration and part replacement — done on a schedule to stop failures before they cause unplanned downtime. ## What goes on a preventive maintenance checklist? Daily oil and water checks, weekly lubrication and heater-band inspection, monthly hydraulic and check-valve service, and an annual screw/barrel wear inspection with full seal replacement. ## What is the difference between preventive and predictive maintenance? Preventive follows a fixed schedule; predictive uses sensor data (vibration, oil, cycle counts) to service only when the data shows it is needed, avoiding both breakdowns and unnecessary work.

Scrap is any material or product that leaves the molding process without becoming a saleable part: defective mouldings plus non-part plastic such as runners, sprues, start-up shots and purgings. It is tracked as a scrap rate and is one of the largest hidden costs in an injection molding plant. ## Two kinds of scrap - Process scrap: runners, sprues, flash, start-up and changeover shots — usually clean and recyclable as regrind. - Reject scrap: parts that failed inspection — short shot, flash, sink marks, burns, splay, contamination or dimensional fails. ## Scrap rate Scrap rate = scrap ÷ total produced (by count or by mass). Example: 60 rejects in 2,000 shots = 3 %. It feeds the quality term of OEE; a 3 % scrap rate means 3 % of your machine time, resin and labor produced nothing to sell. ## Why it matters and how to reduce it Resin is usually the biggest cost in a molded part, so every scrapped gram is lost money plus the energy spent making it. Reduce it with a stable, documented process window (scientific molding), mold and dryer maintenance, and root-cause work on the dominant defect. Some process scrap returns as regrind, but regrind ratios are capped because reprocessing degrades the polymer. ## Related terms - See also: regrind, short shot, flash, runner, sprue ## What is scrap in injection molding? It is everything that does not ship: rejected parts plus runners, sprues, start-up shots and purge. It is measured as a scrap rate against total production. ## What is the difference between scrap and regrind? Scrap is the discarded material; regrind is scrap that has been ground up to be re-melted and reused. Clean process scrap becomes regrind, while contaminated or degraded scrap is waste. ## How do you reduce the scrap rate? Stabilize the process to a documented window, keep molds and dryers maintained, attack the top defect by root cause, and use a hot-runner or smaller-runner design to cut process scrap.

SMED (Single-Minute Exchange of Die) is a lean method for cutting the time it takes to change over an injection mold — ideally to "single minutes" (under ten). In molding, every minute a press spends swapping molds is a minute it is not making parts, so SMED directly attacks that downtime and is a core tool of lean manufacturing. ## The core idea: internal vs external setup SMED separates changeover work into two kinds: - Internal setup: steps that can only be done with the machine stopped (unbolting the mold, lifting it out, hanging the new one). - External setup: steps that can be done while the press is still running the previous job (pre-heating the next mold, staging the resin, color and hoses, kitting the tools). The method then (1) converts as much internal work to external as possible, and (2) streamlines what remains. ## How it is applied to mold changes - Pre-stage everything: next mold pre-heated, dried resin ready, paperwork and tools at the press before the run ends. - Quick-connect hardware: quick couplings for water and hydraulics, quick clamps and standardized mold heights so nothing is hand-threaded. - Standard work: a documented, practiced changeover sequence with two people in parallel. - No adjustment after: a good SMED changeover starts making good parts almost immediately, instead of a long tuning chase. ## Why it matters Faster changeovers turn a long scheduled stop into a short one, raising machine availability and OEE. They also make small lots economical — less inventory, faster response — and free capacity without buying more presses. SMED pairs with preventive maintenance, 5 s and a quality system as standard shop practice. ## Related terms - See also: lean manufacturing, quick couplings, scheduled stop, 5 s, preventive maintenance ## What is SMED in injection molding? A lean changeover method that cuts mold-change time toward single-digit minutes by separating internal setup (machine stopped) from external setup (done while running), converting internal to external work and streamlining the rest. ## What is the difference between internal and external setup in SMED? Internal setup must be done with the press stopped (removing and mounting the mold); external setup can be done while the press is still running the prior job (pre-heating the next mold, staging resin and tools). SMED moves as much as possible to external. ## How does SMED reduce downtime? By pre-staging the next mold and materials, using quick couplings and clamps, following a practiced standard sequence and eliminating post-change adjustment — shrinking the scheduled stop and raising machine availability.