Just In Time injection molding Just-in-Time sounds simple:
make only what you need, when you need it. But in practice, JIT in molding requires significant preparation and discipline. Here’s how to use JIT in injection molding.
Understanding JIT in Molding
JIT Principles
| Principle | Application |
|---|---|
| Eliminate waste | No excess inventory |
| Flow production | Single-piece flow |
| Pull system | Produce to demand |
| Perfect quality | Zero defects |
| Continuous improvement | Always getting better |
JIT Benefits
| Benefit | Impact |
|---|---|
| Inventory reduction | 50-80% lower WIP |
| Floor space | 30-50% reduction |
| Quality improvement | Faster feedback |
| Cash flow | Lower tied-up capital |
| Responsiveness | Faster to changes |
JIT Requirements
Prerequisites
| Requirement | Why It Matters | Implementation |
|---|---|---|
| Stable demand | Pull requires predictability | Forecasting, leveling |
| Reliable equipment | No machines = no JIT | TPM, preventive maintenance |
| Short changeovers | Frequent small lots | SMED implementation |
| Supplier reliability | Material on demand | Strong supplier relationships |
| Quality at source | No defects pass downstream | Poka-yoke, SPC |
Molding-Specific Requirements
| Requirement | Challenge | Solution |
|---|---|---|
| Machine availability | Shared resources | Dedicated cells |
| Changeovers | Time to switch | Quick changeover |
| Tool availability | Multiple tools | Tool management |
| Material supply | Bulk delivery | Kanban, JIT delivery |
Pull Systems
Kanban in Molding
| Kanban Type | Use | Information |
|---|---|---|
| Production kanban | Schedule production | Part number, quantity |
| Withdrawal kanban | Move parts | From where, to where |
| Supplier kanban | Order material | Material, quantity |
Kanban Calculation
| Parameter | Formula | Example |
|---|---|---|
| Daily demand | Parts/day | 1,000 parts |
| Container size | Parts/container | 100 parts |
| Lead time | Days to produce | 2 days |
| Safety stock | Days of buffer | 0.5 days |
| Kanban count | (Daily × Lead + Safety) / Container | (1,000 × 2.5) / 100 = 25 |
Container Systems
| Element | Specification |
|---|---|
| Container size | 1-2 hours of demand |
| Number of containers | Based on kanban calculation |
| Withdrawal frequency | 1-4 times per shift |
| Replenishment time | Based on distance |
Implementation Roadmap
Phase 1
Foundation (Months 1-3)
| Activity | Output |
|---|---|
| Current state analysis | Value stream map |
| Identify waste | Top 10 opportunities |
| Establish stability | TPM, quality focus |
| Supplier dialogue | JIT readiness assessment |
Phase 2
Quick Wins (Months 3-6)
| Activity | Target |
|---|---|
| Reduce changeover | 50% reduction |
| Container system | 1-2 part families |
| Visual management | Andon, boards |
| Material delivery | Daily instead of weekly |
Phase 3
Pull System (Months 6-12)
| Activity | Target |
|---|---|
| Kanban implemented | Key part families |
| Level production | Heijunka box |
| Supplier kanban | Key materials |
| Supermarket pull | Where appropriate |
Phase 4
Continuous Flow (Months 12-24)
| Activity | Target |
|---|---|
| Cell design | U-shaped cells |
| One-piece flow | Where possible |
| Takt time | Matched to demand |
| Full JIT | Standard work |
JIT Metrics
Key Performance Indicators
| Metric | Calculation | Target |
|---|---|---|
| Inventory turns | COGS / Average inventory | >10/year |
| WIP days | WIP / Daily COGS | <5 days |
| Lead time | Order to shipment | <1 week |
| Changeover time | Total / Number | <30 minutes |
| Schedule adherence | On-time schedule | >95% |
Measurement Frequency
| Metric | Frequency |
|---|---|
| Inventory turns | Monthly |
| WIP levels | Daily |
| Lead time | Per order |
| Changeover time | Per changeover |
| Schedule adherence | Daily |
JIT Challenges in Molding
Common Challenges
| Challenge | Root Cause | Solution |
|---|---|---|
| Machine sharing | Multiple products | Dedicated capacity |
| Long changeovers | Complex tools | SMED |
| Tool availability | Multiple programs | Tool management system |
| Material availability | Bulk delivery | JIT delivery agreements |
| Quality issues | Process instability | Quality at source |
Problem-Solving Approaches
| Problem | Method | Action |
|---|---|---|
| Missed delivery | Root cause analysis | Fix the problem |
| Quality issue | Poka-yoke | Prevent recurrence |
| Changeover delay | Time study | Reduce elements |
| Stockout | Pull system | Increase visibility |
JIT and Suppliers
Supplier Integration
| Level | Relationship | Information Sharing |
|---|---|---|
| Transactional | Arms-length | Orders |
| Cooperative | Partnership | Forecasts, plans |
| Collaborative | Strategic | Full integration |
| JIT/VMI | Partnership | Real-time data |
Supplier Performance
| Metric | Target | Monitoring |
|---|---|---|
| On-time delivery | >98% | Daily tracking |
| Quality | <0.5% PPM | Per lot |
| Lead time variability | <5% | Weekly review |
| Flexibility | 24-hour response | Emergency requests |
JIT Implementation Checklist
Preparation Value stream mapped Waste identified Stability achieved Supplier readiness assessed Investment approved
Quick Wins Changeovers reduced Containers implemented Visual management active Material delivery improved Operators trained
Pull System Kanban calculated Kanban implemented Supermarket established Level production started Daily management active
Continuous Flow Cells designed Flow established Takt time matched Full JIT operational Continuous improvement active
The Bottom Line JIT isn’t about doing without—it’s about eliminating waste.
Lower inventory. Faster response. Better quality. Happier customers. But JIT requires preparation. You need stable processes, reliable equipment, and capable suppliers. Without those, JIT just means running out of parts faster. Build the foundation. use incrementally. Stay disciplined. That’s how JIT provides value.