Every plastic component you pick up — a connector cap, a bus bar shroud, a small bracket sitting inside a machine — started life as a mould. And most people, even folks working in procurement for OEMs, don't really know what goes into building one. It's not a quick job. A good mould can take weeks to design and build, and if it's rushed or done poorly, every single component that comes out of it inherits that mistake, thousands of times over.

We've been running an injection moulding operation at Manju Plastic in Faridabad for over 25 years now, working mainly with automotive, electrical, and renewable energy OEMs. Tooling and mould-making is a big part of what we do, so this is something we get asked about a lot — how does a mould actually come together? Here's the process, broken down the way we'd explain it to a customer walking through our facility.

It Starts With the Product Design

Before anyone touches a block of steel, there's a design phase. Our team works with the customer's product drawings — or sometimes just a concept — and figures out the exact shape, dimensions and tolerances the final plastic part needs to meet. This stage also decides things like wall thickness, draft angles, and where parting lines will sit, because all of that directly affects how the mould gets built later.

Then Comes the Tool Design

Once the product design is locked, our tool design team gets to work on the mould itself. This is where the cavity and core get planned out — basically the two halves that will shape the molten plastic into the final part. Cooling channels, ejector pin positions, gate locations, venting — all of it gets mapped out on the design before any machining starts. Get this stage wrong, and you'll end up with parts that warp, have sink marks, or just don't eject cleanly from the mould.

Machining the Mould

This is the part most people picture when they think of tool-making — actually cutting the steel. In our in-house tool room, this involves CNC machining, EDM (electrical discharge machining) for the finer details, and a fair bit of manual finishing work. Mould steel is hard stuff, so this stage takes precision and patience. Even a slight error at this point can throw off the entire dimensional accuracy of the final component.

Fitting and Assembly

Once the cavity and core sections are machined, they get assembled together as a complete mould. This includes fitting the ejector system, cooling lines, guide pins and bushings, and making sure everything aligns perfectly when the mould opens and closes. A mould that doesn't align properly will either damage itself over repeated cycles or produce inconsistent parts.

Trial Runs and Adjustments

Before a mould goes into full production, it gets mounted on an injection moulding machine and run through trial shots. This is where we check the actual moulded part against the design — dimensions, surface finish, whether the plastic is filling every part of the cavity properly, whether there's flash or warping. Almost every mould needs some fine-tuning at this stage, whether that's adjusting cooling time, tweaking a gate, or polishing a cavity surface.

Full Production

Once the trial samples pass inspection and match the customer's specifications, the mould is ready for full-scale production. At this point, it's mounted on one of our injection moulding machines and starts running the actual production cycle, whether that's for automotive plastic parts, electrical components, or industrial applications like joint shrouds and protective covers.

Material Selection Matters Too

A mould is only half the story — the plastic material used matters just as much. Depending on what the component is for, we work with materials like PP, PA6, PA66, ABS, POM, PBT, PC, HDPE, LLDPE, PMMA, PPS and PEEK, each chosen based on strength, heat resistance, flexibility or chemical resistance requirements. An automotive part sitting near an engine bay, for instance, needs a very different material than an indoor electrical cover.

Common Materials & Applications

Why the Manufacturing Process Matters So Much

A mould isn't a one-time cost you pay and forget — it's what determines the quality of every single part produced from it, sometimes across hundreds of thousands of cycles. A poorly built mould leads to defects, rejections, and eventually the cost of redoing the tool altogether. That's why the design, machining and trial stages need to be handled properly the first time, not rushed to save a week or two.

About Manju Plastic

At Manju Plastic, we've been in the plastic injection moulding business for more than 25 years, working out of our ISO 9001:2015 certified facility in Faridabad, Haryana. We handle the full process in-house — product design, prototyping, tool design, tool manufacturing, injection moulding, assembly, testing and inspection — for OEMs and Tier-1 suppliers across automotive, electrical, renewable energy and industrial sectors.

With 19 injection moulding machines, an in-house tool room, and over 300 components developed for 15+ OEM customers, we're set up to handle everything from prototype development to full production runs. We work with clients across Faridabad, Gurugram, Delhi NCR, Noida, and other parts of Haryana, Punjab, Rajasthan and beyond.

If you're developing a new plastic component and need support with mould design, tooling or production, feel free to get in touch with our team in Faridabad. We're happy to walk you through the process and figure out the right approach for your project.