How to Source Injection Molded Parts
Injection molding RFQ checklist: resin grade, volume and mold class, cavities, mold ownership, gate and ejector marks, texture, tolerances and sampling.
768 injection molding companies in the Noramark directory
Injection molding is a tooling purchase followed by a parts purchase. The mold, in aluminum or steel, can cost from a few thousand dollars for a simple aluminum tool to well over $100,000 for a large multi-cavity hardened tool, and it decides part cost, quality and lead time for its whole life. Parts then run in seconds each. Most of the sourcing decision is about the tool.
A good molding RFQ gives the resin by grade (not just "ABS"), the annual volume and expected program life, the tolerances and cosmetic requirements that matter, and who owns and stores the mold. Ask for mold and part prices separately, the mold class or guaranteed shot life, the number of cavities, and the design-for-molding review (draft, walls, gates) the molder will do before cutting steel.
RFQ checklist
16 things to settle on the drawing or in the request before you ask for injection molded part quotes. Print it and tick it off against the print, or copy it into the RFQ.
Resin
Resin by trade name and grade, or generic type with required properties, plus color and how it is colored (precolored or masterbatch)
Grades within one resin family differ in flow, shrink and strength. Shrink is cut into the mold, so changing grade later can change part size.
Special requirements: UL 94 flame rating, food contact, UV stability, medical or other certified grades
These narrow the resin choice and raise its price, and certified grades can carry minimum buys.
Fillers and reinforcement: glass or mineral content
Glass-filled resins wear molds faster and shrink differently along and across the flow, which affects mold steel choice and warp.
Mold
Annual volume and program life, for the mold class (SPI Class 101 to 105) or a guaranteed shot life
A prototype tool rated for a few hundred shots and a production tool rated for a million are different purchases. Aluminum tools commonly run into the tens of thousands of shots; hardened steel runs for hundreds of thousands to millions.
Number of cavities, or leave it to the molder to optimize
More cavities raise the mold price and lower the part price. A family mold (different parts in one tool) is cheaper but harder to balance.
Mold ownership, storage, maintenance and transfer terms
The buyer usually pays for and owns the mold while the molder keeps it. Put maintenance, insurance and the right to move it in writing.
Gate location, ejector pin marks and parting line restrictions
Gates and ejectors leave marks. If a surface is cosmetic or sealing, say so, or the molder decides where the marks go.
Undercuts, side actions and inserts the geometry needs
Every slide or lifter adds mold cost and maintenance. A small design change can often remove one.
Hot runner or cold runner, if you have a preference
Hot runners cost more up front and reduce scrap and cycle time at volume.
Part requirements
Critical dimensions with tolerances realistic for the resin and size
Plastics shrink and warp. ±0.05 mm (±0.002") across a 100 mm part is hard in most resins; ask for the molder's tolerance guide for the resin.
Draft on every surface in the pull direction, and a nominal wall thickness
Parts without draft stick in the mold, and uneven walls sink and warp. The molder will ask for changes if these are missing.
Surface finish or texture by SPI polish grade or VDI 3400 / texture supplier code, with draft for texture
Textured walls need extra draft, often about 1 degree per 0.025 mm (0.001") of texture depth, and high polish costs mold-making time.
Cosmetic acceptance: sink, flash, flow lines, weld lines and gate vestige limits by surface
Without a written cosmetic standard, disputes start at the first shipment.
Secondary operations: threaded inserts, ultrasonic welding, pad printing, assembly
Each is a station, a fixture and labor per part.
Approval and delivery
Sampling and approval: first shots (T1), dimensional report, capability study, or PPAP level
Sampling rounds take weeks and sometimes mold changes. Plan them and name the documents.
Packaging and labeling for production parts
Bulk boxes, layered trays and bagged counts cost different amounts per part, and cosmetic parts need protection.
What to send with the RFQ
- A STEP model of the part, with draft if it is designed in; the molder will propose changes.
- A drawing with critical dimensions, resin, color, texture and cosmetic requirements.
- Annual volume, program life and first order quantity.
- Details of the existing mold, if you are transferring a tool.
- A target part price, and whether you want a prototype mold first.
Lead times
| Prototype or first parts | Aluminum or prototype steel molds: about 2-6 weeks to first shots. |
|---|---|
| Production or repeat orders | Production steel molds: about 8-16 weeks to first shots, plus 2-6 weeks of sampling and adjustment before approval. Repeat orders from an approved mold: 2-4 weeks. |
Typical of U.S. job shops, from order or approved drawing to shipment; confirm with the shop for your part.
What drives the cost
- The mold: size, steel, cavities, side actions, hot runner and surface finish.
- Part size and wall thickness, which set press size and cycle time.
- Resin price, especially engineering and high-temperature resins such as PEEK and Ultem.
- Tolerances and cosmetic requirements that raise scrap or need tight process control.
- Secondary operations and assembly.
- Run size: press setup and material purge happen every run.
Common mistakes
- Designing without draft or with uneven walls, then paying for mold changes.
- Specifying "ABS" with no grade, then finding the next lot of resin shrinks differently.
- Machining tolerances on molded features.
- No written terms for mold ownership and transfer.
- Skipping a prototype mold while the design is still changing.
Questions to ask the shop
- Do you build molds in-house or source them, and where?
- What mold class and steel do you propose, and what shot life do you guarantee?
- Which press will run the part, and what cycle time do you expect?
- What does your design-for-molding review include?
- Who pays for mold maintenance and repairs?
Typical processes
Typical materials
Charts and calculators
Frequently asked questions
- How much does an injection mold cost?
- As rough ranges: simple single-cavity aluminum molds from the low thousands of dollars; production steel molds for mid-size parts often $15,000-60,000; large multi-cavity hardened molds with hot runners and slides above $100,000. Size, cavities, slides and finish move the number more than the part's shape alone.
- Aluminum or steel mold?
- Aluminum tools are cheaper and faster to build and cool quickly, and commonly run tens of thousands of shots in unfilled resins. Steel tools cost more and take longer but last for hundreds of thousands to millions of shots and stand up to glass-filled resins. Choose on the total shots over the life of the program.
- Who owns the mold?
- Usually the buyer who paid for it, while the molder holds it. Put ownership, storage, maintenance and transfer terms in writing, and ask for the mold to be marked as your property.
Build the RFQ: attach the print and this checklist
Attach the drawing (PDF) and the model (STEP), and put your answers to the checklist in the description. A Noramark sourcing specialist matches the request with U.S. shops that make injection molded parts and contacts you within 1 business day.
