Small Batch Of Table Connectors Producing by Insert Molding Process

Application Industry	Tools & Equipment
Tolerance(Accuracy)	Parts: ±0.03mm
Manufacturing Process	Insert Molding Service
Mold Type	Rapid Tooling
Parts Material	PA66+50%GF, Brass
Surface Treatment	None

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In early 2019, a modular workstation manufacturer came to KingStar Mold with a specific need: they needed table connectors—the parts that lock desk frames to tabletops—and they needed them in small, variable batches. Their line of compact office desks, popular with startups and co-working spaces, relied on these connectors to hold up under daily use, but their order volumes were small: 300 pieces per quarter, with occasional swings to 200 or 400 depending on how many desks they sold that month. They didn’t want small batches to mean loose fits, weak parts, or inflated costs.

What mattered most to them

These connectors weren’t just afterthoughts. The client’s desks sold on their “tool-free assembly” promise, so the parts had to work flawlessly:

They needed to hold 35kg without bending—that’s a laptop, monitor, and a stack of notebooks, the typical load their customers put on a desk.
After 800+ times being taken apart and reassembled (about how often a small office might rearrange furniture over 3 years), they still had to stay tight.
They had to line up with pre-drilled holes in the wooden tabletops within 0.03mm. Miss that mark, and assembling the desk would turn into a frustrating struggle for their customers.
And they needed to ship within 10 days of ordering. The client kept lean inventory, so delays here would stop their own production lines.

The tricky parts of small-batch work

We decided on insert molding for these connectors: a metal core for strength, wrapped in a tough plastic to avoid scratching the tabletops. But small runs threw up unique problems that don’t show up in big production:

Small batches make mistakes costly
In large runs, if 1 out of 100 parts is off, it’s no big deal. But with 300 pieces, 12 bad parts (4%) would mean the client didn’t have enough to finish their desk orders. When we ran our first 50 prototypes, 6 of them (12%) had metal cores that shifted during molding—so the plastic didn’t wrap evenly, and they wobbled when fitted into the desk holes.
Molds wear out faster with frequent use
We use rapid tooling for small batches—it’s more cost-effective than steel molds for low-volume production. But with quarterly runs, that mold gets loaded, used, and stored 4 times a year. After just 2 runs, we noticed tiny scratches on the mold’s surface. When we injected plastic, those scratches caused uneven flow, leaving some connectors 0.06mm thicker than others—too thick to fit the table holes.
Costs add up quickly in small runs
Tooling, setup time, and even scrap parts hit harder when you’re making 300 instead of 30,000. Early numbers showed each connector would cost $3.80 to make—way over the client’s $3 target. Most of that extra cost came from those 12% defective parts (wasting material) and the 3 hours it took to set up the mold each time (eating into labor efficiency).

How we fixed it

We focused on three things: making the parts more consistent, keeping the mold in shape longer, and cutting out waste—all without losing precision.

Getting the metal cores to stay put
The shifting cores were the biggest issue. Our engineers noticed the metal pieces were sliding in the mold because there was nothing to hold them. So we added two tiny pins (0.5mm thick) to the mold. These fit into pre-drilled holes in the metal cores, locking them in place. After that, only 1 or 2 out of 300 connectors had shifting issues—way better than 12%.
Fixing the uneven plastic flow
The thick/thin problem came from plastic rushing into one side of the mold faster than the other. Instead of one big opening (a “gate”) where plastic enters the mold, we added a second smaller gate, placed opposite the first. This split the flow evenly, so the plastic wrapped around the metal core at the same rate. Suddenly, the thickness variation dropped from 0.06mm to 0.01mm—well within the 0.03mm tolerance.
Making the mold last longer
The scratches on the mold were from repeated setup. We coated the mold with a thin layer of hard chrome (5 microns thick), which acts like a protective shield. That made the mold last twice as long—from 600 uses to 1,200—so we didn’t have to replace it mid-project. We also added quick-connects to the cooling lines, cutting setup time from 3 hours to 45 minutes.
Trimming costs
With fewer bad parts (1-2 per batch instead of 12) and faster setups, we used less material and labor. By the second quarter, each connector cost $2.70—under the client’s $3 cap.

What happened in the end

Over three years, we made 12 batches—3,600 connectors total. Here’s what worked:

Nearly every part (99.5%) fit the table holes within that 0.03mm tolerance. Only 18 needed minor sanding, and none held up the client’s production.
When we tested them, they held 35kg for 24 hours straight without bending, and after 800 assembly cycles, they still felt tight.
When the client suddenly needed 400 pieces one quarter, we adjusted the run in 3 days and shipped on time.

Small batches don’t have to mean compromises. By tweaking the mold to fix little problems, keeping the tooling tough, and cutting out waste, we made parts that worked as well as mass-produced ones—at a price that let the client grow their desk line by 20% over those three years.

Requirements

Requirement Category	Specific Data
Production Volume	– Base quantity: 300 units per quarter – Flexibility: Adjustable to 200–400 units with 2 weeks’ notice
Durability	– Static load resistance: Withstand 35kg (equivalent to typical desktop loads) without deformation – Assembly cycle endurance: Maintain integrity through 800+ assembly/disassembly cycles (matching 3–4 year workstation lifespan)
Dimensional Precision	– Alignment tolerance: ±0.03mm (to fit pre-drilled tabletop holes for seamless assembly)
Turnaround Time	– Batch delivery: Complete within 10 business days of order confirmation to avoid client production delays
Cost Parameters	– Per-unit production cost cap: Under $3 (to support mid-tier pricing competitive with mass-produced alternatives)

Frequently Asked Questions

What if my project involves a challenge I don’t see in any case study?webadmin2025-07-14T06:14:41+00:00

What if my project involves a challenge I don’t see in any case study?

No worries—our case studies focus on the usual kinds of problems, but we deal with unique or tricky challenges all the time. Even if your specific issue isn’t featured, the problem-solving approach and technical skills you see in the case studies still apply. Send us a note with what you’re up against, and we’ll walk through how we’d tackle it for you.

Are the techniques and methods shown in these case studies up to date?webadmin2025-07-14T06:14:02+00:00

Are the techniques and methods shown in these case studies up to date?

We keep our case studies fresh—they show the methods we actually use right now. When we start using new tools, materials, or process fixes (like better mold simulation software or greener plastics), we update the case studies to include those too. That way, what you’re seeing matches how we work in today’s manufacturing landscape.

How can I discuss applying similar approaches to my project?webadmin2025-07-14T06:08:51+00:00

How can I discuss applying similar approaches to my project?

If a case study clicks with what you’re working on, just get in touch with our team. Share the details of your project, and we’ll talk through how the strategies highlighted—like material pairing, mold tweaks, or process adjustments—might fit your goals. If needed, we can also craft custom solutions that match what you need.
Feel free to reach out at sales@kingstarmold.com to start the conversation.

Are these case studies based on real projects?webadmin2025-07-14T06:05:23+00:00

Are these case studies based on real projects?

Yes, all our case studies are based on real client collaborations. To protect our clients’ rights, we only share details that have been approved for disclosure—including specific timelines, challenges, solutions, and measurable outcomes, all backed by data from client production records or third-party testing.

How can these case studies help me understand if you’re a good fit for my project?webadmin2025-07-14T06:03:08+00:00

How can these case studies help me understand if you’re a good fit for my project?

Each case study delves deeply into specific issues, such as how to extend the lifespan of components or how to accelerate production speed, and shows you how we solved these problems. Even if your project is not exactly the same as them, these cases can help you clearly understand how we handled the issues: breaking down the problem, adjusting the method, and achieving results. This enables you not only to see the outcomes we have achieved, but also to understand how we think about solutions – so you can roughly judge whether we can meet the requirements of your project.

How does insert molding differ from over molding?webadmin2025-07-14T05:56:20+00:00

How does insert molding differ from over molding?

Let’s start by breaking down what each process actually does.

Insert molding is all about integrating a pre-made component—something like a small metal piece, a ceramic part, or even a rigid plastic piece—into a plastic part during manufacturing. Here’s how it works: you first place that pre-made “insert” into a mold, then inject molten plastic around it. As the plastic cools, it bonds tightly to the insert, creating a single part where the insert adds specific properties the plastic alone can’t provide. Think of something like a USB connector: the metal pins inside are inserts, and the plastic housing forms around them, holding them in place while letting electricity flow through the metal.

Over molding, on the other hand, is about layering materials. It starts with a base part—usually a rigid plastic, though sometimes metal—that’s already been formed. Then, a second material, often something softer like rubber or a flexible plastic, is injected over this base. The result is a part that combines the strength of the base with the properties of the overlaid material. A common example is a tool handle: the core might be a hard plastic for structure, and the outer layer is a soft, grippy material that makes it comfortable to hold.

Now, how do these two differ?

For one thing, the role of the added material is distinct. In insert molding, the insert is like a functional piece that the plastic wraps around—it might add strength (like a metal rod in a plastic bracket) or conductivity (like copper in an electronic part). The plastic here is mostly there to hold the insert in place and give the part its overall shape. In over molding, the base part is already a complete structure, and the overlaid material is there to add secondary traits: maybe flexibility, a better grip, or a seal. It’s less about adding a “working” component and more about blending textures or functions.

The process flow is different too. Insert molding requires careful placement of the insert before any plastic is injected—you need to make sure it stays put while the molten plastic flows around it, which is why molds often have little pins or slots to hold inserts in place. Over molding usually happens in two steps: first, the base part is made, then it’s moved to another mold (or the same mold shifts) to have the second material injected over it. It’s more about building up layers than encapsulating a pre-made piece.

Material compatibility also plays differently. Insert molding often pairs dissimilar materials—like metal and plastic—so you have to make sure the plastic can bond to the insert, maybe by roughing up the insert’s surface. Over molding typically uses materials that work well together, like a hard plastic base and a soft rubber that adheres to it without much extra work.

In the end, it comes down to what you need the part to do. If you need a piece that combines a specific functional component (like a metal pin for electricity) with plastic, insert molding is the way. If you want to blend a rigid structure with something soft or flexible, over molding makes more sense.

What are the common challenges in insert molding and how to solve them?webadmin2025-07-14T05:45:26+00:00

What are the common challenges in insert molding and how to solve them?

Common Problems You May Encounter

One frequent issue is inserts shifting out of place during injection. When this happens, parts often don’t work right—like connectors that fail to conduct electricity. The fix here is to tweak the mold’s positioning setup: adding tighter-fitting clamping slots or small locating pins that hold the insert steady, so it doesn’t move when plastic flows in.

Another problem is weak adhesion between the plastic and the insert. Over time, this can make the insert loosen or even fall out, especially under stress. To improve this, you can rough up the insert’s surface—sandblasting works well—or pick a plastic that bonds better with the insert material. It’s about making sure the two materials “grab” onto each other properly.

Inserts can also warp or crack if the injection pressure or temperature is too high. Sometimes the material just isn’t strong enough. In these cases, dialing back the pressure or heat often helps. If that’s not enough, switching to a tougher material—like using hardened steel instead of regular steel for metal inserts—usually does the trick.

Then there’s the issue of plastic cracking around the insert, mostly from uneven cooling and shrinkage. This tends to happen where the plastic meets the insert. Adjusting how long you hold pressure during cooling can ease the stress, as can softening the insert’s edges—rounding off sharp corners, for example, keeps the plastic from pulling too hard as it sets.

Two Problems We’ve Fixed

Case 1: Shifting pins in USB-C connectors

A client was making USB-C connectors, but 15% of them were faulty because the small metal pins inside kept moving during molding. This meant the connectors often didn’t charge or transfer data properly. We reworked the mold with two tiny locating pins (fitted to within 0.01mm of the pin’s size) and added a quick visual check before injection to make sure pins were seated right. After that, only 0.3% of parts had issues.

Case 2: Loose plastic on sensor housings

A car parts maker was having trouble with their sensor housings—plastic kept peeling away from the aluminum inserts, which risked sensor failure. We suggested sandblasting the aluminum to give it a rougher surface (measuring Ra 1.6μm, which gives the plastic more to grip) and switching to a PA66 plastic that expands and shrinks at a rate closer to aluminum. Tests afterward showed the bond was 40% stronger when we pulled on the inserts—no more peeling.

What should you keep in mind when designing inserts for insert molding?webadmin2025-07-14T05:37:13+00:00

What should you keep in mind when designing inserts for insert molding?

How you treat the insert’s surface matters. Things like sandblasting to create tiny grooves or adding coatings (zinc plating, for example) help the plastic grip better. This stops the insert from pulling away when the part is used.

The insert’s size has to fit snugly with the mold. Keeping dimensions tight makes sure it stays in place when plastic is injected—no shifting, which would mess up the part or even damage the mold.

Sharp edges and corners on the insert are best avoided. When plastic cools and shrinks, these sharp spots can concentrate stress, making the finished part more likely to crack.

The insert and plastic should expand and shrink at similar rates when heated or cooled. If they don’t align, it can create stress inside the part as it cools, leading to warps or cracks later on.

The insert’s shape needs to make it easy to put in the mold and keep it there. Small grooves or bumps, for example, can act like anchors, holding it steady while plastic is being injected.

We have a design team that has handled numerous insert molding projects before. Whether you need assistance in reviewing your existing design or require us to start the design from scratch for you, you can contact us.

What are the common insert materials used in insert molding?webadmin2025-07-14T05:31:35+00:00

What are the common insert materials used in insert molding?

Common insert materials include metals such as copper, steel, and aluminum. Copper inserts are widely used in electronic connectors—think the metal pins in USB ports, where they’re molded into plastic housings to ensure stable electrical conductivity. Steel inserts often find their place in automotive parts, like seat frames, where they reinforce plastic structures to handle repeated weight and stress. Aluminum, valued for its lightweight properties, is frequently embedded in laptop casings or car interior components to balance strength and reduced weight.

Ceramics are another key group, particularly useful in scenarios needing high-temperature resistance or insulation. For instance, ceramic inserts are often used in electrical insulators or small components within engine systems, where they protect plastic parts from heat damage while blocking unwanted electrical flow.

Pre-formed plastic parts also serve as inserts, enabling the creation of complex structures. A common example is tool handles: a rigid plastic core is molded into a softer, grippable outer layer to combine structural support with comfort, seen in items like screwdrivers or power tool grips.

Even fiber-reinforced composites are employed, typically to boost localized strength. They’re often found in industrial gear, such as plastic gears with composite inserts that enhance durability in high-wear areas, or in sports equipment like bicycle frames where they add rigidity without excessive weight.

What are the main differences between insert molding and traditional injection molding?webadmin2025-07-14T05:27:56+00:00

What are the main differences between insert molding and traditional injection molding?

Although both involve cooling the melted plastic into the desired shape, there are still differences between them.

Traditional injection molding produces parts using only plastic: molten plastic is injected into a mold, where it cools and solidifies into a single-material component. Insert molding, by contrast, begins with placing prefabricated inserts—such as small metal components or ceramic pieces—inside the mold cavity. Molten plastic is then injected around these inserts, bonding with them as it sets to form a part combining plastic and the inserted material. This requires careful attention to ensuring compatibility and secure bonding between inserts and plastic, with mold designs needing specific features to hold inserts in place reliably.

Traditional injection molding offers a simpler process with fewer steps, less complex tooling, and faster production cycles—factors that make it cost-effective for high-volume manufacturing. It accommodates a wide range of plastics and avoids issues like insert misalignment or poor bonding. However, it is limited to single-material parts, which may lack the structural reinforcement or functional attributes—such as conductivity or heat resistance—provided by multi-material designs. Additional assembly steps are often necessary to integrate components like fasteners or metal parts.

In contrast, insert molding eliminates the need for secondary assembly. It embeds the inserts (typically metal hardware) directly into the plastic, thereby reducing labor costs and improving the integrity of the components. It can combine the multi-functional properties of the plastic with the unique properties of the inserts – for example, using metal to enhance strength or using ceramics for insulation – making it easier to produce complex and high-performance components. Its disadvantages include the higher initial mold cost due to the need to design special mold features for placing the inserts, the longer production cycle caused by the need to position the inserts, and the risk of insufficient bonding or insert displacement if the material or process parameters do not match.

In terms of practical application, traditional injection molding is highly suitable for simple, single-material components, such as packaging, basic consumer goods (such as plastic containers) or non-structural parts, which are prioritized in terms of cost and production speed. Injection molding technology performs well in manufacturing components that require higher functionality, such as automotive components with metal contacts, electronic devices that need to have both insulation and conductivity functions, or industrial tools with reinforced parts – in these scenarios, the combination of materials can bring value beyond what a single plastic can provide.

What is insert molding?webadmin2025-07-14T05:16:28+00:00

What is insert molding?

Insert molding works by first putting pre-made parts—like small metal pieces or other materials—into a mold. Then you inject molten plastic into that mold. As the plastic cools and hardens, it bonds firmly to those pre-made parts, turning everything into a single solid piece. It’s similar to using hot plastic to “glue” components together, resulting in one strong part instead of having to put pieces together later.

Technically, this injection molding method embeds preformed inserts—usually metals, ceramics, polymers, or composites—into the final plastic part. The process starts with carefully positioning these inserts in the mold cavity before molten plastic is injected. As the plastic cools and sets, it wraps around the inserts, creating mechanical or chemical bonds that form a unified structure. This cuts out the need for extra assembly steps like screwing or gluing parts together, shortens production time, and makes the finished part sturdier. By combining the useful properties of the inserts—such as conductivity or strength—with the flexibility of plastic, it lets manufacturers make complex, multi-material parts designed for specific uses.

Note:
We maintain pre-market confidentiality agreements and sign NDA/NNN with all our customers. Every case you see has been shared with client approval. To protect sensitive information, some details have been blurred or modified. All photos were taken internally by KingStar Mold. Thank you for your support and cooperation.

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