Custom plastic injection molding for grilles, trim, bumper trim, lips, side skirts and large rear spoilers. Yirox runs 42 injection molding machines from 90 to 2,500 tons, three two-shot cells and an in-house mold shop at its IATF 16949 certified factory in Wuxi, China. Each program starts with a DFM review and ends with FAI, CMM data and PPAP up to Level 3.
| Item | Yirox capability |
|---|---|
| Machines | 42 injection molding machines, clamp force 90–2,500 t (largest are two-platen) |
| Two-shot (2K) molding | 3 machines: 280 t and 380 t rotary-table, 530 t rotary-core |
| Automation | Take-out robots on all 42 machines (30 three-axis, 12 five-axis); 6 with in-mold monitoring |
| Monthly capacity | About 1.5 million parts and 520 t of resin, two shifts of 16 hours |
| Materials | ABS, PP, modified PP, TPO, ASA, PC, PC/ABS; 2K combinations PC+PMMA, ABS+TPE, PC/ABS+TPU |
| Accuracy | ±1.0 mm general, ±0.5 mm on critical features, seams ±0.1 mm, part weight ±1 g |
| Mold shop | In-house, 6–8 molds per month, molds up to 25 t, P20/H13 steel |
| Finishing | In-house painting lines and chrome plating line |
| Quality | ISO 9001, IATF 16949, FAI, CMM, PPAP up to Level 3 |
| Order size | Low MOQ on selected items; confirmed in your quote |
Plastic injection molding is a manufacturing process that melts plastic pellets and injects the melt under high pressure into a closed steel mold. The plastic cools inside the cavity, the mold opens and a finished part is ejected.
The same mold then repeats the cycle, which is why injection molding is the standard process for plastic parts made in thousands or millions of identical pieces. Automotive injection molding adds tougher demands on fit, finish and weathering than most consumer parts.
For automotive exterior parts the process matters for more than cost. A front lip, grille or bumper trim must hold its shape on the vehicle, line up with body panels and keep a clean surface for paint or chrome.
Those results depend on how the part is designed, how the mold is built and how the molding process is controlled shot after shot. This page explains each step and shows the equipment Yirox uses to make it work.
If you want a longer guide to the process, defects and history of molding in the car industry, read our article on automotive injection molding. The rest of this page focuses on what you need to know as a buyer of molded exterior parts.
Every injection molded part goes through the same four stages. The settings for each stage are developed during mold trials and then locked into the production process sheet.
The two halves of the mold close and the machine holds them shut with clamp force. Large exterior parts need more tonnage because the projected area of the part is bigger.
Dried resin is melted in the heated barrel. The screw pushes the melt through the nozzle, runner and gates until the cavity is full.
Pressure is held while the plastic shrinks, then cooling water in the mold removes heat. Cooling is usually the longest part of the cycle.
The mold opens and ejector pins or a robot remove the part. Runners are separated and the part moves to trimming, inspection or finishing.
Before any of this happens, the resin must be dried. Materials such as ABS, PC and PC/ABS absorb moisture from the air, and wet resin causes silver streaks on the surface. Mold temperature also matters: a stable, correct mold temperature gives an even gloss and reduces warpage on long parts like side skirts.
One material, one cavity or family of cavities, one cycle. This covers most exterior parts: grilles, mirror housings, door handle covers, fender flares, side skirts and spoiler bodies.
Two materials are molded into one part in a single cycle. A rotary table or rotary core moves the first shot to a second cavity, where the second material is molded onto it. We use it for combinations such as PC+PMMA, ABS+TPE and PC/ABS+TPU, for example a hard part with a soft seal or grip.
Like two-shot molding, overmolding bonds a soft TPE or TPU layer to a rigid substrate. It adds sealing, grip or noise damping without a separate assembly step. The material pair must be chosen for chemical bonding.
Bumper trim and large rear spoilers need high clamp force and long mold openings. Our 1,300–2,500 t two-platen machines are used for these parts.
Injection molding is the right choice for most plastic exterior parts, but not for every quantity. Here is a fair summary.
| Advantages | Limitations |
|---|---|
| Low cost per part once the mold is made | The mold is an up-front investment |
| Repeatable dimensions and weight from shot to shot | Design changes after the mold is cut cost time and money |
| Molded-in texture, color and clip features with no extra steps | Wall thickness, draft and ribs must follow design rules |
| Wide choice of engineering plastics for weather and impact | Very low quantities may suit other processes better |
| Parts can go straight to painting, chrome plating or assembly | Large parts need high-tonnage machines and big molds |
For very small quantities or early design checks, other processes may be better. We have an SLA printer for quick form checks, and partner factories for vacuum casting and vacuum or thermoforming. When volumes are steady, injection molding gives the lowest cost and the most consistent parts.
Good design for manufacturing (DFM) is the cheapest way to avoid problems. These are general guidelines used across the injection molding industry. Our engineers check each one against your part in the DFM report.
Thick and thin areas cool at different speeds, which causes sink marks and warpage. Keep walls as even as possible and core out thick sections. Change thickness gradually rather than in a step.
Draft is a small taper that lets the part release from the mold. Smooth surfaces need less draft than textured surfaces, because texture grips the steel. Deep textures need extra draft, which we confirm against the texture you choose.
Ribs add stiffness without making walls thick. A rib that is too thick shows as a sink mark on the visible face. Clip towers and screw bosses should connect to walls with ribs rather than solid plastic.
Exterior trim often uses clips or tape. Clip features need room for slides or lifters in the mold. Deciding fixing points early avoids expensive mold changes.
The gate is where plastic enters the part. Gate marks and weld lines should sit on hidden faces, or where paint or texture can cover them. On painted or chrome plated parts this matters even more.
Every plastic shrinks as it cools, and long thin parts tend to bow. Mold flow analysis, rib layout and cooling design help keep a side skirt or spoiler straight enough to fit the car.
Mold flow analysis is a computer simulation of how molten plastic fills, packs and cools inside the mold. It is run during DFM, before the mold steel is cut, so problems are fixed on screen instead of in a hardened tool. For long exterior parts such as side skirts, spoilers and bumper trim, it is one of the most useful checks in the whole project.
Gate position decides how the part fills, where weld lines appear and how it warps. On a visible gloss black part, gates are placed on hidden faces or edges, and on long parts several gates or a hot runner with sequential valve gates may be compared in the simulation.
Want risks found before steel is cut?Send your 3D file and we will review gates, wall thickness and shrinkage with a DFM report before injection molding tooling starts.
The simulation flags the defects below before the mold exists, so the fix is a design change rather than a tool correction.
| Risk | What the analysis shows | Typical fix in design | |
|---|---|---|---|
| Weld lines | Where two flow fronts meet | Move the gate or add a flow leader so lines fall on hidden or painted faces | |
| Sink marks | Thick areas that shrink after the surface sets | Core out thick sections, thin ribs and bosses | |
| Warpage | Uneven shrinkage along the part | Change gate position, rib layout or cooling channels | |
| Air traps | Pockets the melt closes around | Add venting at the predicted spots | |
| Short shots | Areas that fill last at low pressure | Adjust wall thickness or add gates | |
| Gate blush and jetting | High shear near the gate | Change gate type or size |
Results from the analysis go straight into the mold design and are checked again on the first trial shots.
Wall thickness, draft and ribs are checked against the material.
Fill, pack, cool and warp are run with the planned gates.
Gates, ribs, venting and cooling are adjusted on the CAD and mold design.
The mold is built to the reviewed design.
First shots are compared with the predicted weld lines, sink and warpage.
Steel is adjusted where needed before the next trial and sample approval.
Simulation does not replace a mold trial, but it reduces the number of corrections after T1. Results and the agreed changes are shared with you in the DFM report.
The right resin depends on where the part sits on the vehicle, whether it will be painted or plated, and how much impact and sunlight it must handle. These are the materials we mold for exterior parts.
| Material | Typical exterior uses | Notes |
|---|---|---|
| ABS | Spoilers, grilles, mirror housings, trim | Rigid and easy to paint; plating-grade ABS is used for chrome plated parts |
| PP and modified PP | Bumper trim, fender flares, mud flaps | Tough and flexible; needs surface treatment and primer before painting |
| TPO | Flexible exterior trim | Good impact resistance in cold weather |
| ASA | Trim left in molded black | Better UV resistance than ABS for unpainted parts |
| PC | Clear or tough parts | High impact strength; often used in two-shot with PMMA |
| PC/ABS | Housings and structural trim | Balance of toughness and heat resistance; not suitable for chrome plating |
| TPE and TPU | Second shot in 2K or overmolding | Soft seals, grips and edges bonded to ABS, PC/ABS or PC |
If you are unsure which material to choose, send us the part function and the market it will be sold in. We will suggest a resin and finish in the DFM report.
Exterior parts must fit the vehicle and line up with nearby panels. These are the accuracy levels we work to on molded exterior parts.
| Feature | Tolerance |
|---|---|
| General dimensions | ±1.0 mm |
| Critical features (clip points, mating edges) | ±0.5 mm |
| Seams and gaps between mating parts | ±0.1 mm |
| Part weight | ±1 g, with unit-to-unit variation of 0.3% or less |
Critical features are agreed with you during DFM and marked on the inspection plan. They are checked by CMM at first article and by checking fixture during production. See our quality inspection and CMM page for how we measure.
Many exterior parts can be finished straight from the mold. Others need paint or chrome. Choosing early affects material, gate location and texture.
The part comes out of the mold in black or another color, often with a grained texture. This is common for trim and fender flares in ASA, PP or TPO. It is the lowest-cost finish.
Gloss black, body color or other colors are sprayed in our paint shop. Painted parts need clean, sink-free surfaces. Read more on our painting and surface finishing page.
Grille bars, badges and trim can be chrome plated on plating-grade ABS. The part design and material must suit plating from the start. See chrome plating on plastic.
Most defects come from part design, mold design or process settings. We review the risk in DFM and confirm the fix during mold trials.
| Defect | What it looks like | How we prevent it |
|---|---|---|
| Sink marks | Shallow dents over thick areas or ribs | Even wall thickness, correct rib ratio, adequate packing pressure |
| Warpage | Long parts bow or twist | Balanced cooling, rib layout, mold temperature control |
| Flash | Thin plastic film at the parting line | Correct clamp force, mold fit and maintenance |
| Weld lines | Visible line where melt fronts meet | Gate position, melt and mold temperature |
| Short shots | Part not fully filled | Gate size, venting, injection speed |
| Splay or silver streaks | Silver streaks on the surface | Resin drying with desiccant dryers |
| Gloss variation | Uneven shine across the part | Stable mold temperature and polish |
These are the exterior parts we mold most often, grouped by machine size.
Small parts that hold larger parts in place or finish an edge. They run on 90–250 t machines, often in multi-cavity molds.
Visible parts with fine detail and good surface quality. Many are painted gloss black or chrome plated after molding. They run on 250–450 t machines.
Small visible covers that are often painted or chrome plated. Surface quality and fit to the handle are checked closely.
Long parts where straightness and fit matter. They run on 450–800 t machines with careful cooling design to control warpage.
Styling parts with large visible surfaces, usually painted. Front lips run on 800–1,300 t machines.
The largest parts we mold, on 1,300–2,500 t two-platen machines.
We mold exterior parts for automotive brands, aftermarket brands and distributors. Some buyers bring a finished design; others need help from the first sketch.
Body kits, spoilers, lips and trim for vehicle-specific product lines, often combined with our vehicle-specific development service.
Molded parts built to your drawings and standards, with PPAP documents. See OEM and ODM auto parts.
Repeat supply of molded and finished parts under your brand, packed for retail or warehouse. See private label and packaging.
Comments on wall thickness, draft, gates, parting lines and texture before steel is cut.
Our mold shop builds and maintains the tool. See tooling and sampling.
T1 samples for fit and finish checks, with changes until approval.
First article inspection against your drawing before production.
When your program requires it.
Painting and chrome plating without shipping parts between suppliers.
You send 3D data or a sample. We sign an NDA if needed and quote the mold and part price.
Our engineers send a DFM report and agree material, finish and critical features with you.
The mold is built in our mold shop and checked before the first trial.
First trial parts are molded, measured and sent for your review and test fit.
After any changes, final samples are approved with FAI, CMM data and PPAP if required.
Process settings are locked and parts run with in-process checks, finishing and packing.
A complete request gets a faster and more accurate quote. If you do not have everything, send what you have and we will tell you what is missing.
Order quantity: we offer low MOQ on selected items. The exact quantity depends on the part, material and finish and is confirmed in your quote.
Have your injection molding files ready?Send them with the target quantity and we will quote plastic injection molding tooling and parts.
Buyers often ask why two similar-looking parts have different prices. These are the main cost drivers, in order of impact.
| Cost driver | Why it matters |
|---|---|
| Mold size and complexity | Slides, lifters and large steel blocks add machining time |
| Number of cavities | More cavities cost more up front but lower the part price |
| Part size and tonnage | Larger machines cost more per hour |
| Cycle time | Thick walls cool slowly, which lowers output per hour |
| Material | Engineering resins such as PC/ABS cost more than PP |
| Finish | Painting or chrome plating adds process steps and inspection |
| Quantity | Set-up and inspection costs are shared across more parts |
You can lower cost by keeping walls even, avoiding undercuts where possible and choosing molded-in finishes for hidden or textured parts. We point out these savings in the DFM report.
Many buyers search for an injection molding company in China because of cost and supply chain depth. Price is only part of the decision. These are the questions worth asking any supplier, including us.
At Yirox the answer to the first five is in-house: molding, mold shop, painting and chrome plating are all run in our own factory in Wuxi. Our quality system is certified to ISO 9001 and IATF 16949, and we supply FAI, CMM data and PPAP up to Level 3.
Processes we do not run ourselves, such as sheet metal and aluminum die casting, are handled by partner factories that we manage.
We run 42 injection molding machines with clamp force from 90 to 2,500 tons. Each tonnage group is matched to the size of the parts it molds.
| Clamp force | Machines | Typical parts |
|---|---|---|
| 90–250 t | 12 | Clips, brackets, small trim strips |
| 250–450 t | 11 | Grilles, mirror housings, door handle covers |
| 450–800 t | 10 | Fender flares, side skirts, spoiler bodies |
| 800–1,300 t | 5 | Front lips, large trim panels |
| 1,300–2,500 t (two-platen) | 4 | Bumper trim, large rear spoilers |
Consistent parts come from more than the molding machine. Robots, temperature control and dry resin all reduce variation.
| Equipment | Quantity and details |
|---|---|
| Two-shot machines | 280 t rotary-table, 380 t rotary-table, 530 t rotary-core |
| 2K material combinations | PC+PMMA, ABS+TPE, PC/ABS+TPU |
| Take-out robots | On all 42 machines: 30 three-axis, 12 five-axis |
| In-mold monitoring | 6 machines |
| Mold temperature controllers | 46 |
| Central chiller units | 8 |
| Desiccant dryers | 30 |
| Shifts | Two shifts, 16 hours per day |
| Monthly output | About 1.5 million parts, 520 t of resin |
Robots remove every part the same way, at the same time in the cycle, which keeps cooling and handling consistent. In-mold monitoring on selected machines watches each shot so a bad cycle is caught early.
Our mold shop is in the same factory as molding, so tool changes and repairs are fast. It builds 6–8 molds per month, handles molds up to 25 t and uses P20 and H13 steel, with mold life of 300,000–500,000 shots depending on the steel and part.
The mold shop is supported by four 3-axis machining centers (800×500×500 mm, ±0.01 mm), two CNC lathes, two engraving-milling machines, two wire EDM machines, two EDM machines and two surface grinders. Our fixture shop builds checking fixtures with MSA %GRR of 10% or less. See tooling and sampling for how molds are developed and approved.
Every molded program has an inspection plan agreed with you. First articles are measured on our CMMs, production parts are checked on checking fixtures, and appearance is checked against an approved sample.
Our quality system is certified to ISO 9001 and IATF 16949. See our certifications.
90 to 2,500 t covers small clips to bumper trim in one factory.
Painting and chrome plating are in-house.
Mold changes are handled by our own mold shop.
IATF 16949, FAI, CMM and PPAP up to Level 3.
About 20,000 m² factory and partner factories for other processes.
Packing and documents for overseas buyers.
DFM, mold build, trials and sample approval.
Explore automotive mold tooling →
3C2B paint lines, gloss black and color matching.
Explore automotive plastic painting →
Decorative chrome on plating-grade ABS.
Explore chrome plating on plastic →
FAI, CMM and PPAP for molded parts.
Explore CMM inspection and PPAP →
Scan a part or vehicle to build CAD.
Explore 3D scanning and reverse engineering →Every process in our Wuxi factory.
Explore our manufacturing capabilities →Molded parts that arrive mixed up, relabeled or off-color cost you margin after the invoice. Our automotive injection molding runs on 42 machines in our own IATF 16949 factory, and we pack to your channel so parts arrive ready to sell.
Worried a reorder won’t match? Your molds and colors are held to approved samples.
See the aftermarket brand program →
Too many suppliers to manage? Combine SKUs in one container from one factory.
See the auto parts importer program →
Parcels arriving damaged? We pack parcel-safe and print and apply your FBA labels.
See car accessories manufacturing for e-commerce →Buyers on the issues we flagged before tooling and how production held up.
“We started with one spoiler mould to test them. They flagged a weld line position in our drawing before quoting, which our previous supplier had missed. Three containers later, they are still quoting the same lead time they actually hold. Not the cheapest quote we received — the only one we stopped re-checking.”
“We had been through a frustrating mold project with another supplier, so we were cautious this time. Having the sample inspection records and dimensions available made a real difference. We could review the actual parts instead of relying on promises.”
Names and companies withheld at the customer’s request.
Cost has two parts: the mold and the price per part. The mold cost depends on part size, complexity, number of cavities and steel. The part price depends on material, cycle time, finish and quantity. Send us your CAD or a sample and we will quote both.
Custom injection molding makes a part to your own design, using a mold built for that part. Standard parts come from existing molds. Most of our work is custom molding of exterior parts.
Tonnage depends mainly on the projected area of the part and the material. Small clips run on 90–250 t machines, while bumper trim and large rear spoilers need 1,300–2,500 t two-platen machines. We choose the machine during DFM.
Yes. We have three two-shot machines (280 t, 380 t and 530 t) and mold combinations such as PC+PMMA, ABS+TPE and PC/ABS+TPU.
Our standard is ±1.0 mm, with ±0.5 mm on critical features and ±0.1 mm on seams. Part weight is held to ±1 g.
Mold ownership is agreed in the quote and contract for each project. See our tooling and sampling page for details.
We offer low MOQ on selected items. The quantity for your part is confirmed in your quote.
DFM means design for manufacturing. It is a review of your part design before the mold is built, checking wall thickness, draft, ribs, gates, parting lines and texture so the part molds cleanly and fits. Every Yirox mold starts with a DFM report.
Yes. We mold PC and PC/ABS as well as ABS, PP, modified PP, TPO and ASA. PC/ABS is not suitable for chrome plating; plated parts use plating-grade ABS.
Yes. We can sign an NDA before you share drawings or samples.
Send your CAD files, drawings or a sample part. We will reply with a DFM review and a quote for the mold and parts.
