Custom injection molding is the right choice when you need more than 5,000 units per year, want your logo or part number moulded into the product, or need dimensions that off-the-shelf items cannot match. Tooling costs range from $2,000 for a simple single-cavity mould to $50,000+ for a multi-cavity hot-runner system, but the per-unit price often falls 30–60 % below catalogue equivalents at volume.
LSY Plastic has operated custom injection moulding for OEM clients since 1989. We run JSW, Mitsubishi and Nippon Steel presses from 180 T to 2,500 T, maintain an in-house mould workshop and serve buyers in logistics, hospitality, food service and electronics. This guide walks through the full OEM process from concept to mass production.
When Does Custom Injection Molding Make Financial Sense?
The break-even point between off-the-shelf and custom-moulded parts depends on volume, part complexity and branding requirements.
| Scenario | Off-the-Shelf | Custom Injection Molding |
|---|---|---|
| Annual volume under 3,000 | Cheaper (no tooling) | Tooling cost dominates |
| Annual volume 5,000–20,000 | Moderate | Break-even at 6–12 months |
| Annual volume over 20,000 | Expensive per unit | Strong savings (30–60 %) |
| Logo or text on product | Pad print label extra cost | Moulded-in, zero marginal cost |
| Non-standard size or feature | Often unavailable | Exact match to specification |
| Special colour for branding | Limited stock colours | Custom masterbatch per order |
| Material modification | Fixed resin grade | UV, flame retardant, ESD additive |
Stage 1: Design Review and DFM (1–2 Weeks)
DFM (Design for Manufacturability) is the first step. You send a 3D model, sketch or sample part. Our engineers check:
- Wall thickness: Uniform walls prevent sink marks and warping. Typical range is 2.0–4.0 mm for structural parts.
- Draft angles: 0.5–1.5 degrees per side ensures clean ejection from the mould.
- Rib design: Ribs should be 60 % of wall thickness to avoid thick sections that create voids.
- Undercuts: Side-action cores or lifters add 15–30 % to tooling cost. We flag these early.
- Gate location: Determines weld-line position and cosmetic finish. We simulate flow with Moldflow CAE.
Deliverable: DFM report with recommended design changes, material suggestion and preliminary tooling quote.
Stage 2: Mould Design and Steel Cutting (3–5 Weeks)
Once the design is frozen, mould design begins. Key decisions include:
- Cavity count: 1, 2, 4 or 8 cavities depending on annual volume and machine tonnage
- Steel grade: P20 for prototypes and short runs; H13 or S136 hardened steel for 500,000+ shots
- Hot runner vs cold runner: Hot runners eliminate sprue waste and cycle faster but add $3,000–10,000 to tooling
- Surface finish: SPI A-2 (gloss), SPI B-3 (semi-gloss) or textured VDI 30 for hiding flow lines
LSY Plastic’s mould workshop machines cores and cavities on CNC and EDM equipment. Typical mould lead time is 25–35 days for single-cavity tools and 40–55 days for multi-cavity production moulds.
Stage 3: Tool Trial and Sample Approval (1–2 Weeks)
The first mould trial (T0) produces 20–50 sample shots. We measure critical dimensions, check weight consistency and inspect for flash, sink marks or weld lines.
- T0 samples: Sent to you for fit and function testing
- T1 corrections: Adjustments to gate size, cooling channel flow or ejector pin positions
- Final approval (FA): You sign off dimensions, colour and surface finish
Most projects need two trial shots. Complex parts with metal inserts or over-moulding may need three.
Stage 4: Mass Production and Quality Control
After final approval, production moves to the scheduled press. LSY Plastic’s quality protocol includes:
- Incoming resin inspection: Melt flow index, moisture content and colour batch check
- In-process monitoring: Cavity pressure sensors and real-time temperature logging
- First-article inspection: Full dimensional report on the first shot of each shift
- Random sampling: AQL 1.0 for critical dimensions, AQL 2.5 for cosmetic defects
- Final inspection: 100 % check for functional features (threads, snaps, inserts)
Production rates depend on part size and machine. A 500 g hotel service cart component on a 650 T press cycles in 45–55 seconds, giving approximately 60–80 shots per hour per cavity.
Tooling Cost Breakdown by Part Complexity
| Part Type | Cavities | Steel Grade | Estimated Tooling Cost | Lifespan (shots) |
|---|---|---|---|---|
| Simple tray or basin | 1 | P20 | $2,000 – $4,000 | 100,000 |
| Medium crate with ribs | 1 | P20 / H13 | $4,000 – $8,000 | 300,000 |
| Complex pallet with steel tubes | 1 | H13 | $8,000 – $15,000 | 500,000 |
| Multi-cavity small part | 4 | H13 | $12,000 – $25,000 | 500,000 |
| Hot-runner precision part | 2–4 | S136 | $20,000 – $50,000 | 1,000,000 |
These costs include mould design, steel, machining, heat treatment, assembly and trial shots. They do not include shipping or customs duties.
Lead Time Summary: From Concept to Container
- DFM and quoting: 5–10 business days
- Mould design and steel cutting: 25–55 days (depending on cavity count)
- Tool trials and sample approval: 7–14 days
- First production run (pilot): 10–20 days
- Mass production (per container): 15–30 days
- Total new-product development: 9–14 weeks
Repeat orders using existing moulds reduce lead time to 3–5 weeks from PO to FCL shipment.
Material Options for Custom Moulding
LSY Plastic processes the following resins for custom orders:
- HDPE: General purpose, chemical resistant, cost-effective for pallets, crates and bins
- PP: Higher heat resistance, stiffer than HDPE, good for hot-fill and steam-cleaning applications
- ABS: Glossy surface, impact resistant, used for decorative hotel accessories and covers
- PC: Transparent, high impact, for inspection windows or LED covers
- Modified compounds: UV stabilised, flame retardant (UL94 V-0), conductive / ESD, glass-filled for stiffness
We source virgin resin from Sinopec, PetroChina and imported suppliers. Recycled-content blends up to 40 % are available for non-food applications.
Common Pitfalls and How to Avoid Them
- Underestimating wall thickness: Thin walls save material but warp and crack. Follow DFM guidance.
- Ignoring shrinkage: HDPE shrinks 1.5–3.0 % depending on wall thickness and cooling rate. Dimensions must be scaled in mould design.
- Skipping pilot runs: Always order 500–1,000 pilot units for field testing before committing to a 20,000-unit run.
- Poor gate placement: Aesthetic surfaces should be opposite the gate to hide flow lines.
Conclusion
Custom injection molding pays off at volumes above 5,000 units per year and is essential when off-the-shelf products do not match your specification. The upfront tooling cost is recovered through lower unit prices, brand differentiation and supply-chain control. With in-house mould design, steel cutting and 180 T–2,500 T production capacity, LSY Plastic delivers custom plastic parts from concept to container in 9–14 weeks.
Have a product idea or need a quote for custom moulding?
Send your drawing or sample to WhatsApp +86 19311059570 or email fstyx01@lsyplastic.com. We reply with a DFM report and tooling quote within 5–7 business days. Samples are available at cost price after mould completion.
Related reading: About LSY Plastic | Our Factory and Equipment | Customer Cases